Information on stabilized HeNe lasers (which includes those used for both scientific and metrology applications) has been moved to a new chapter: Commercial Stabilized HeNe Lasers.
For current production lasers, the manufacturers' Web sites often provide basic specifications. A Google search is usually the easiest way to find them, but most are also linked from the chapter: Laser and Parts Sources. For older lasers, it's often difficult to obtain detailed specs so estimates based on physical size, and then testing may be the only option.
The sections in this chapter are arranged approximately in alphabetical order by manufacturer.
Red (632.8 nm):
Rated Melles Griot Coherent Model Power Length Model Number ------------------------------------------------ 31-2017-000 0.8 mW 7.00" 05-LHR-601 31-2016-000 0.8 mW 7.00" 05-LHP-601 31-2033-000 2 mW 12.40" 05-LHR-321 31-2025-000 2 mW 12.40" 05-LHP-321 31-2058-000 4 mW 15.50" 05-LHR-141 31-2041-000 4 mW 15.50" 05-LHP-141 31-2074-000 7 mW 18.00" 05-LHR-171 31-2066-000 7 mW 18.00" 05-LHP-171 31-2090-000 10 mW 19.05" 05-LHR-991 31-2082-000 10 mW 19.05" 05-LHP-991 31-2108-000 17 mW 25.07" 05-LHP-925 31-2196-000 17 mW 25.07" 05-LHR-925 31-2140-000 35 mW 40.60" 05-LHP-928 *
* Cylindrical head in rectangular case.
Green (543.5 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2264-000 0.3 mW 12.40" 05-LGR-321 31-2298-000 1.0 mW 20.09" 05-LGP-293? 31-2772-000 2.0 mW 20.09" 05-LGR-393
Yellow (594.1 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2230-000 2.0 mW 17.95" 05-LYR-173
Orange (611.9 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2207-000 2.0 mW 15.60" 05-LOR-151
Some examples for three specific Coherent models:
Rated CDRH New Melles Griot Coherent Model Wavelength Power Power Power Length Model Number ------------------------------------------------------------------------------- 21-2090-000 632.8 nm (Red) 10 mW 30 mW 17 mW 19.05" 05-LHR-991 31-2772-000 543.5 nm (Green) 2 mW 5 mW 2.7 mW 20.09" 05-LGR-393 31-2230-000 594.1 nm (Yellow) 2 mW 10 mW 4.8 mW 17.95" 05-LYR-173
The "CDRH Power" is what is listed on the safety sticker. The "New Power" was the average power measured on several samples of these laser heads I tested that appear to have never been used, or have seen very little use.
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Plasma Laser Power Power Diam gence Spacing Voltage Current Tube Head Supply ------------------------------------------------------------------------------- * 1? mW 0.89 mm 0.91 mR 781 MHz 1.00 kV 5.0 mA 3121/P 3221/P 5??? 1? mW 0.64 mm 1.30 mR 685 MHz 1.74 kV 6.5 mA 3120/P 3220/P 5020 1 mW 0.64 mm 1.30 mR 685 MHz 1.74 kV 6.5 mA 3121/P 3221/P 5020 1.5 mW 0.49 mm 1.70 mR 635 MHz 1.77 kV 4.5 mA 3102P 3203P 5000 2 mW 0.83 mm 1.00 mR 575 MHz 1.90 kV 6.0 mA 3136 2 mW 0.64 mm 1.30 mR 685 MHz 1.74 kV 6.5 mA 3122/P 3222/P 5020 3 mW 0.64 mm 1.30 mR 685 MHz 1.74 kV 6.5 mA 3123/P 3223/P 5020 2 mW 0.49 mm 1.70 mR 635 MHz 1.77 kV 4.5 mA 3102 3203 5000 4 mW 0.83 mm 1.00 mR 435 MHz 2.30 kV 6.5 mA 3124/P 3224/P 5020 5 mW 0.83 mm 1.00 mR 435 MHz 2.30 kV 6.5 mA 3125/P 3225/P 5020 7 mW 0.82 mm 1.10 mR 410 MHz 2.50 kV 7.0 mA 3227/P 5040 10 mW 0.68 mm 1.20 mR 350 MHz 2.80 kV 7.0 mA 3230/P
Note: "/P" indicates that both a random and linearly polarized version was available. "*" appears to be a special version of the 3121.
Suffixes: H = random polarized with flying leads, H-P = linear polarized with flying leads, H-C = random polarized with Alden connector, H-PC linearly polarized with Alden connector. So a 5 mW linearly polarized cylindrical head with Alden would be 3225H-PC. All have the "H" which I presume means "HeNe". :)
Melles Griot is probably the largest manufacturer of HeNe lasers still in existence (as of 2013). They have also taken over the HeNe product lines of competitors like Aerotech and Hughes, and still manufacture some lasers based on those companies' designs, though that represents only a small fraction of their production. See An Assortment of Melles Griot HeNe Laser Tubes and Laser Heads for some typical examples. (Photo courtesy of Meredith Instruments.) These are probably from the mid-1980s - the glasswork of newer lasers differs subtly and the laser head color scheme is now black with the yellow/black on white label. ;-) But otherwise, the latest models are similar.
All Melles Griot HeNe laser tubes are now hard-sealed with essentially unlimited shelf life - 12 years is quoted but for all practical purposes, it is infinite. (Only some very early and/or "other color" laser tubes may have had any soft-seals.) Most standard tubes have a planar HR mirror and a concave OC mirror with its curvature selected for maximum stability. This long radius near hemispherical cavity configuration puts the beam waist at the HR with a slightly diverging beam from the OC. But a compensating curvature on the outer surface of the OC mirror of most laser tubes that are sold as or in standard products results in a positive lens and the beam that exits the laser is quite well collimated. (Specific applications like barcode scanning may call for a divergence other than the minimum possible to avoid the need for an additional external lens.)
And in the "I always wondered about that" department, the correct way to pronouce Melles Griot is
MEL-liss (emphasis on the first syllable).
GREE-o (emphasis on the first syllable).
This was confirmed both by someone who knew Jan Melles and Richard Griot personally, and from a VP at Melles Griot. But apparently, some of their employees don't even get it right. :)
The following data came from a variety of sources including an old Melles Griot brochure, the 1999 catalog, and the Melles Griot Web site. Go to "Product Info", "Lasers", "HeNe".
This is not a complete list but probably includes most of those you're likely to come across.
Red (632.8 nm):
Minimum e/2 c/2L Supply Nominal (1) Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LHR/P- ------------------------------------------------------------------------------ 0.5 mW 0.46 mm 1.70 mR 1271 MHz 1.15/5 kV 3.2 mA 15/125 mm 001 (2) 0.4 mW 0.34 mm 2.40 mR 1360 MHz 1.22/5 kV 3.2 mA 23/118 mm 007 0.5 mW 0.46 mm 1.70 mR 1271 MHz 1.15/8 kV 3.2 mA 16/127 mm 625 (3) 0.5 mW 0.46 mm 1.70 mR 1272 MHz 1.18/8 kV 4.5 mA 25/127 mm 640 0.5 mW 0.46 mm 1.77 mR 1063 MHz 1.32/5 kV 4.0 mA 25/150 mm 213 0.4-1 mW 0.46 mm 1.77 mR 1063 MHz 1.32/5 kV 4.0 mA 25/150 mm 214 (7) 0.5 mW 0.47 mm 1.70 mR 1200 MHz 1.29/5 kV 3.3 mA 19/135 mm 002 (4) 0.5 mW 0.48 mm 3.20 mR 1078 MHz 1.30/8 kV 3.7 mA 25/145 mm 017 0.5 mW 0.49 mm 1.70 mR 1040 MHz 1.25/5 kV 4.5 mA 29/152 mm 700 0.5 mW 0.50 mm 1.61 mR 1039 MHz 1.29/5 kV 4.5 mA 25/152 mm 601 0.5 mW 0.50 mm 1.61 mR 1039 MHz 1.29/5 kV 4.5 mA 37/152 mm 604 0.6 mW 0.47 mm 1.70 mR 1078 MHz 1.43/5 kV 4.0 mA 25/146 mm 004 0.6 mW 0.85 mm 0.95 mR 787 MHz 1.29/5 kV 4.5 mA 37/200 mm 410 0.8 mW 0.47 mm 1.70 mR 1078 MHz 1.33/5 kV 3.0 mA 25/149 mm 006 0.8 mW 0.46 mm 1.77 mR 1063 MHz 1.32/5 kV 4.0 mA 25/150 mm 211 0.85 mW 0.76 mm 2.70 mR 638 MHz 1.13/5 kV 3.7 mA 28/243 mm 099 0.9 mW 0.47 mm 1.70 mR 1078 MHz 1.38/5 kV 3.3 mA 25/147 mm 049 0.9 mW 0.48 mm 1.70 mR 1100 MHz 1.20/5 kV 4.0 mA 25/146 mm 704 0.9 mW 0.48 mm 8.00 mR 1078 MHz 1.31/5 kV 3.5 mA 25/145 mm 041 0.9 mW 0.65 mm 1.24 mR 862 MHz 1.05/5 kV 4.0 mA 28/183 mm 491 1.0 mW 0.53 mm 1.50 mR 883 MHz 1.47/8 kV 4.5 mA 29/178 mm 900 1.0 mW 0.59 mm 1.35 mR 687 MHz 1.79/8 kV 6.5 mA 37/226 mm 011 1.0 mW 0.59 mm 1.35 mR 687 MHz 1.79/8 kV 6.5 mA 37/226 mm 110 1.0 mW 0.66 mm 1.25 mR 683 MHz 1.10/8 kV 3.5 mA 28/227 mm 101 1.5 mW 0.53 mm 1.50 mR 889 MHz 1.71/8 kV 4.5 mA 25/178 mm 008 1.5 mW 0.58 mm 1.39 mR 793 MHz 1.66/8 kV 5.0 mA 37/228 mm 130 1.6 mW 0.76 mm 1.06 mR 636 MHz 1.67/8 kV 5.0 mA 29/244 mm 070 2.0 mW 0.49 mm 1.65 mR 638 MHz 1.45/10 kV 3.7 mA 29/243 mm 038 2.0 mW 0.55 mm 1.47 mR 822 MHz 1.94/10 kV 4.5 mA 25/191 mm 009 2.0 mW 0.59 mm 1.35 mR 687 MHz 1.77/10 kV 6.5 mA 37/226 mm 219 2.0 mW 0.59 mm 1.35 mR 687 MHz 1.79/10 kV 6.5 mA 37/228 mm 021 2.0 mW 0.59 mm 1.35 mR 687 MHz 1.79/10 kV 6.5 mA 37/228 mm 120 2.0 mW 0.63 mm 1.40 mR 641 MHz 1.82/10 kV 4.5 mA 29/241 mm 088 2.0 mW 0.72 mm 1.10 mR 612 MHz 1.85/10 kV 6.5 mA 29/255 mm 080 2.0 mW 0.76 mm 1.06 mR 638 MHz 1.57/10 kV 4.5 mA 29/243 mm 097 2.0 mW 0.76 mm 1.06 mR 636 MHz 1.71/10 kV 5.0 mA 30/250 mm 073 2.0 mW 0.79 mm 1.00 mR 574 MHz 1.81/10 kV 6.5 mA 37/270 mm 320 2.5 mW 0.52 mm 1.53 mR 822 MHz 1.77/10 kV 4.5 mA 25/198 mm 690 2.7 mW 0.58 mm 1.41 mR 694 MHz 1.81/10 kV 4.5 mA 28/226 mm 082 4.0 mW 0.80 mm 1.00 mR 438 MHz 2.29/10 kV 6.5 mA 37/353 mm 140 5.0 mW 0.80 mm 1.00 mR 438 MHz 2.29/10 kV 6.5 mA 37/353 mm 164 5.0 mW 0.80 mm 1.00 mR 438 MHz 2.29/10 kV 6.5 mA 37/353 mm 150 5.0 mW 0.80 mm 1.00 mR 438 MHz 2.31/10 kV 6.5 mA 37/353 mm 200 7.0 mW 0.75 mm 2.05 mR NA-MM 1.90/10 kV 6.5 mA 37/353 mm 160 (5) 7.0 mW 1.02 mm 0.79 mR 373 MHz 2.65/10 kV 7.0 mA 37/410 mm 170 10 mW 0.65 mm 1.24 mR 341 MHz 2.64/10 kV 6.5 mA 37/450 mm 991 12 mW 1.20 mm 3.40 mR NA-MM 2.09/10 kV 6.5 mA 37/350 mm 185 (5) 16 mW 1.47 mm 1.40 mR NA-MM 2.48/10 kV 7.0 mA 37/464 mm 981 (5) 17 mW 0.96 mm 0.83 mR 267 MHz 3.70/12 kV 7.0 mA 37/571 mm 825 17 mW 0.96 mm 0.83 mR 267 MHz 3.70/12 kV 7.0 mA 37/571 mm 925 17 mW 0.70 mm 1.16 mR 257 MHz 3.87/12 kV 7.0 mA 37/594 mm 871 20 mW 0.70 mm 1.16 mR 257 MHz 3.87/12 kV 7.0 mA 37/594 mm 847 25 mW 1.23 mm 0.66 mR 165 MHz 5.10/15 kV 8.0 mA 42/920 mm 827 25 mW 1.42 mm 2.40 mR NA-MM 3.20/10 kV 7.0 mA 42/590 mm 831 (5) 30 mW 1.48 mm 2.50 mR NA-MM 3.20/10 kV 7.0 mA 42/590 mm 931 (5) 35 mW 1.23 mm 0.66 mR 165 MHz 5.10/15 kV 8.0 mA 42/920 mm 927 35 mW 1.23 mm 0.66 mR 165 MHz 5.10/15 kV 8.0 mA 42/920 mm 928 (6)
LHR models are random polarized; LHP models are linearly polarized. Not all model numbers have both versions. Nearly all barcode scanning tubes are only available random polarized.
For lower power lasers, models ending in an even number are often (but not always) a bare tube, with the corresponding head being the same number incremented by (or ORed with) 1. For high power lasers, the laser head number is listed. Low power is defined as less than 10 mW in chart, above.
The operating voltage across the tube itself can be found by subtracting the voltage drop across the ballast resistor (I*Rb), from the value listed in the table. Actual starting voltages are typically 3 to 5 times the tube operating voltage (though the specifications may be higher). Note that I've assumed a 75K ballast resistance for all tubes. The actual manufacturer recomendation may differ slightly but 75K should be acceptable for most.
Both random (LHR) and linearly polarized (LHP) models are available for most of the lasers listed above. The only other difference in specifications for red HeNe lasers between these is their price - about 10 to 15 percent higher for a complete polarized laser. So you can imagine the difference in the tube cost alone since everything else is identical. (The output power of "other-color" linearly polarized HeNe lasers compared to similar size random polarized models, particularly for yellow and green which have very low gain, tends to be much less since the losses through the internal Brewster plate become more significant.)
And speaking of prices, if you have to ask, you can't afford a new HeNe laser! But since you asked, prices (Summer 2002) from Melles Griot vary from around $300 for a 0.5 mW laser head to over $4,000 for one rated at 35 mW (power supply sold separately)! Prices in Summer 2005 haven't changed that much but only complete systems can be ordered on-line. Prices: $587.83 (0.5 mW) to $4,532.88 (35 mW). Fortunately, surplus prices tend to be much more reasonable - typically between 5 and 20 percent of these depending on actual age and condition as well as many other factors including your luck in finding a good deal. And yes, in 2012, they are higher. :-)
One for the trivial triviality department: If the random polarized model required for an order isn't available, the equivalent linear polarized laser may be substituted, but it will have an LHR label. I'm kind of inferring the cause from testing many Melles Griot lasers, but it has occurred too often to simply be due to labeling "accidents". Most applications would not be hurt by the "upgrade" unless intended to demonstrate the mode sweep characteristics of a random-polarized laser. (Adjacent longitudinal modes are usually orthogonally polarized.) Trying to locate a suitable head for this purpose was how I discovered one of these Melles Griot "goofs". ;-)
Green (543.5 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LGR- ---------------------------------------------------------------------------- 0.08 mW 0.88 mm 2.35 mR NA-MM 0.88/8 kV 3.7 mA 25/149 mm 004 0.2 mW 0.63 mm 1.26 mR 732 MHz 1.56/8 kV 4.5 mA 29/215 mm 025 0.2 mW 0.75 mm 0.92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 171 0.3 mW 0.81 mm 0.99 mR 574 MHz 2.20/10 kV 6.5 mA 37/269 mm 321 0.5 mW 0.80 mm 1.01 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 141 0.5 mW 0.80 mm 1.01 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 151 0.5 mW 1.35 mm 1.10 mR NA-MM 1.94/10 kV 6.5 mA 37/351 mm 252 0.8 mW 0.89 mm 0.92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 173 1.0 mW 1.30 mm 1.00 mR NA-MM 1.87/10 kV 6.5 mA 37/351 mm 161 1.0 mW 0.80 mm 0.86 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 293 1.5 mW 0.86 mm 0.81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 193 2.0 mW 0.86 mm 0.81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 393
Green (543.5 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LGP- ----------------------------------------------------------------------------- 0.2 mW 0.75 mm 0.92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 171 0.2 mW 0.77 mm 0.90 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 141 0.3 mW 0.77 mm 0.90 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 151 0.3 mW 0.86 mm 0.89 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 173 1.0 mW 0.86 mm 0.81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 193 1.0 mW 0.86 mm 0.81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 293
Yellow (594.1 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LYR- ----------------------------------------------------------------------------- 0.?? mW ??? mm ?.?? mR NA-MM 0.??/5 kV 3.? mA 25/149 mm 006 0.35 mW 0.63 mm 1.26 mR 732 MHz 1.62/8 kV 4.5 mA 29/215 mm 025 0.35 mW 0.69 mm 1.09 mR 574 MHz 1.95/10 kV 6.5 mA 37/269 mm 320 0.75 mW 0.80 mm 1.01 mR 438 MHz 2.43/10 kV 6.5 mA 37/351 mm 151 1.0 mW 0.75 mm 0.92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 171 2.0 mW 0.75 mm 0.92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 173 2.0 mW 1.17 mm 1.00 mR NA-MM 2.09/10 kV 6.5 mA 37/351 mm 161
Yellow (594.1 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LYP- ---------------------------------------------------------------------------- 1.0 mW 0.75 mm 0.92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 173
Orange (611.9 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LOR- ---------------------------------------------------------------------------- 0.?? mW ??? mm ?.?? mR NA-MM 0.??/5 kV 3.? mA 25/149 mm 006 0.5 mW 0.63 mm 1.26 mR 732 MHz 1.66/8 kV 4.5 mA 29/215 mm 025 2.0 mW 0.80 mm 1.01 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 4.0 mW 1.17 mm 1.00 mR NA-MM 2.07/10 kV 6.5 mA 37/351 mm 161
Infra-Red (1,523 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LIR- ---------------------------------------------------------------------------- 0.5 mW 1.26 mm 1.59 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 1.0 mW 1.33 mm 1.48 mR 373 MHz 2.97/10 kV 6.0 mA 37/410 mm 171
Infra-Red (1,523 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LIP- ---------------------------------------------------------------------------- 0.4 mW 1.26 mm 1.59 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 0.8 mW 1.33 mm 1.48 mR 373 MHz 2.97/10 kV 6.0 mA 37/410 mm 171
Infra-Red (3,391 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LFR- ---------------------------------------------------------------------------- 1.0 mW 0.83 mm 1.60 mR 438 MHz 2.50/10 kV 6.0 mA 37/351 mm 151
Infra-Red (3,391 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LFP- ---------------------------------------------------------------------------- 1.0 mW 0.83 mm 1.60 mR 438 MHz 2.50/10 kV 6.0 mA 37/351 mm 151
Note: Some of the listed values for divergence in particular appear to be questionable. For example, for the same beam diameter, diffraction limited divergence should be proportional to wavelength. The discrepency for the 3,391 nm IR tube is particularly striking. Either the divergence or beam diameter are almost certainly incorrect. It probably doesn't matter much though because the 3,391 nm model is no longer manufactured. I also suspect the output power rating for the 05-LGR-171 may be a bit higher than listed in the source for this information.
Brewster angle window HeNe tubes (red, 633 nm):
Minimum Supply Supply Nominal Number Output Voltage Voltage Tube Tube Size Model of Power Tube Only Rb=68K Current Diam/Lgth 05-LHB- Windows ------------------------------------------------------------------- ??? mW ????? V ????? V ??? mA 30/178 mm* 190 2 1.0 mW 1,430 V 1,870 V 6.5 mA 37/222 mm 270 1 1.0 mW 1,460 V 1,900 V 6.5 mA 37/253 mm 290 2 3.5 mW 1,080 V 1,520 V 6.5 mA 37/265 mm 370 1 4.0 mW 1,030 V 1,470 V 6.5 mA 37/265 mm 570 1 5.0 mW? 1,340 V* 1,780 V* 6.5 mA 37/310 mm 379 1 6.0 mW 1,430 V 1,870 V 6.5 mA 37/351 mm 670 1
The following are high-Q optically contacted one-Brewster laser tubes or heads. (Usually, these model numbers apply to the heads, but it seems the tube inside is likely to have the exact same model number.) All except the 05-LHB-562 are probably intended for applications like particle counters or Raman gas analyzers where maximum intra-cavity power is required. The 05-LHB-562/563 is strange since these have an internal OC, which makes no sense for a high-Q tube. :) The "Minimum Output Power" is estimated since there are no official specifications. Except for the LHB-564 which I haven't tested, the internal mirror probably has an RoC of 60 cm. (This based on the dissection of a previously smashed LHB-568 or LHB-580.)
Minimum Intra- Supply Supply Nominal Number Output Cavity Voltage Voltage Tube Tube Size Model of Power Power Tube Only Rb=70K Current Diam/Lgth 05-LHB- Windows ------------------------------------------------------------------------------- 2.0 mW (1) -- 1,060 V 1,500 V 6.5 mA 37/267 mm 562/563 1 1.0 mW 10 W 520 V 1,000 V (2) 3.0 mA 37/150 mm 564 1 5.0 mW 30 W 1,060 V 1,500 V 6.5 mA 37/267 mm 568 1 5.0 mW 30 W 1,060 V 1,500 V 6.5 mA 37/267 mm 580 1 5.0 mW 35 W 1,060 V 1,500 V 6.5 mA 37/267 mm 569 1 5.0 mW 60 W 1,060 V 1,500 V 6.5 mA 37/267 mm 569-510 1
The output power assumes is based on measurements for the 05-LHB-568/9 (with a 99%@633 nm OC) and guesses for the 05-LHB-580, not any actual specifications. The LHB-564 may not lase with a 99% OC; the recommended one is 99.7%. A new LHB-568 or 05-LHB-569 may be capable of 6 or 7 mW of output power based on my tests. But these lasers are typically used with matching ultra-high reflectance low loss HRs to achieve maximum intra-cavity power of 10s of WATTs as listed above. And that's the minimum specification! :) Even the cute short LHB-564 may actually do more than 35 WATTs with its matching external HR mirror! For normal use with a 98-99% OC mirror, healthy tubes of a given model seem to have a similar output power with little correlation to the intra-cavity power printed on the tube: 5 to 6 mW for all except the LHB-564, which is 1 to 2 mW.
Brewster angle window HeNe tubes (green, 543.5 nm):
These are extremely unusual due to the low gain of the HeNe green (543.5 nm) lasing line. For the most part, they may be considered curiosities. And I've yet to see any real specifications.
Minimum Intra- Supply Supply Nominal Number Output Cavity Voltage Voltage Tube Tube Size Model of Power Power Tube Only Rb=70K Current Diam/Lgth 05-LGB- Windows ----------------------------------------------------------------------------- ??? mW ??? W ????? V ????? V 5.5 mA? 37/265 mm 580 1 0.5 mW? 1.0 W? ????? V ????? V 5.5 mA 37/??? mm 563 1
The 05-LGB-563 is a high-Q optically contacted one-Brewster laser head with an internal OC mirror for 543.5 nm. It may be used with an external HR or OC, with a total output power of 0.5 to 1 mW, and an intra-cavity power of up to around 1 W with an external HR. However, since the internal OC is relatively highly transmitting at 633 nm, it could also be used for single-pass gain tests, and with difficulty will even lase at 633 nm with a pair of external mirrors. However, since the AR coating at 543.5 nm is not that good at 633 nm, the achievable output power at 633 nm is quite low and it isn't very stable. However, getting any 633 nm coherent photons could be a double extra credit challenge for the motivated student! ;-)
So far, Melles Griot disavows any knowledge of the existence of the 05-LGB-563, though they have Melles Griot stickers with manufacturing dates of May 2012. Perhaps the heads were a test run or for a project that was cancelled. I do have an 05-LGB-580 tube, given to me by Melles Griot. See the section: A Green One-Brewster HeNe Laser.
The most common application for one-Brewster HeNe tubes was probably for particle counting since by using an external high quality HR mirror, the intracavity flux can be several watts which makes a speck of anything stand out! (Some larger one-Brewster HeNe tubes can do as much as 100 W intracavity!) Passing the air/gas/whatever flow through the cavity of a one-Brewster HeNe laser is similar to passing it through the output beam of a high power laser - at a fraction of the cost (and it's much safer as well since if anything macroscopic in size (like an eyeball or piece of paper) were to block the intracavity beam, lasing simply stops with no damage to vision and no risk of fire!
Most of the LHB models have HR mirrors that are probably optimal for 632.8 nm (red) though newer versions, at least, may be quite broadband and better than 99.9 percent from 590 to 680 nm so operation at some of the non-632.8 nm wavelengths may be possible. However, older versions may not have such nice HRs. The LGB models are really only good at 543.5 nm.
Other variations on these tubes are also produced (though they may be special order). I was given an 05-LGB-580 which has an HR optimized for 543.5 nm (green). With an external green HR, the behavior is very similar to the red version but with loads of circulating green photons instead of red ones. :) I was told that this tube may have been made for the sole purpose of confirming the quality of the mirrors to be used in normal internal mirror HeNe laser tubes. So, I doubt you could buy 1. Maybe 1,000, but not just 1! Applications for such a tube would be very limited due to the low gain as it stops lasing entirely in a few minutes after cleaning the optics just due to dust settling on the B-window.
The 05-LHB-370, 05-LHB-570, 05-LHB-670, and 05-LHB-580 have wide bores and generally operate with multiple transverse modes to achieve maximum intracavity power in particle counting applications. The 05-LHB-270 and 05-LHB-290 have narrow bores like most conventional HeNe tubes. (The 05-LHB-270 appears physically similar to an 05-LHR-120 except for the Brewster window at one end.) The model 05-LHB-570 is the one-Brewster HeNe tube used in the CLIMET 9048 one-Brewster laser head described in the section: A One-Brewster HeNe Laser Tube. You can't tell from the model numbers but both Melles Griot and Hughes style designs may be used. For example, the 05-LHB-570 looks like a normal Melles Griot tube but with a Brewster angle window frit sealed to the metal end-cap instead of an OC mirror. The 05-LHB-580 looks like a Hughes style tube, but with an optically contacted Brewster window instead of an OC mirror (though some Hughes style polarized HeNe tubes are just one-Brewster tubes with an OC mirror attached to a glass tube that slips over the Brewster stem and is itself glued in place). Thus, the 05-LHB-580 is actually a much higher quality (and more expensive) tube than the 05-LHB-570 but you can't tell this from the catalog listing! Here are diagrams of each type:
One possible explanation of why the Hughes style design is used for the high quality tubes with optically contacted Brewster windows is that since Hughes already produced HeNe tubes with a glass Brewster stem (as noted above), when Melles Griot took over the Hughes HeNe laser product line, making the modifications for the graded seal to accommodate the fused silica Brewster stem (needed to match the expansion coefficient of the fused silica window) was probably easier than starting with a metal end-cap.
Zero degree (perpendicular) AR coated window HeNe tubes:
Minimum Supply Supply Nominal Number Output Voltage Voltage Tube Tube Size Model of Power Tube Only Rb=68K Current Diam/Lgth 05-WHR- Windows ------------------------------------------------------------------- 4.0 mW 1,030 V 1,470 V 6.5 mA 37/269 mm 570 1 6.0 mW 1,670 V 2,110 V 6.5 mA 37/351 mm 252 2* 8.0 mW 1,670 V 2,110 V 6.5 mA 37/351 mm 183 1
*: 05-WPR-252 is the same tube as the 05-WHR-252 and was part of an educational kit (now defunct).
Rather than mirrors, one or both ends of these HeNe tubes have optical flats with very high quality AR coatings to permit the use of external mirrors. One advantage of this arrangement is that external optics can be used to control polarization (the output beam of Brewster tubes is always linearly polarized and can't be changed). However, note that residual stresses in the windows and asymmetries in the tube construction will still generally result in some polarization preference, but it will be similar to that of a common random polarized HeNe laser tube. External polarization optics will generally be sufficient to override this.
The 05-WHR-252 and 05-WHR-183 appear to be identical except for the number of windows - and the loss of 2 mW with the two window version!
Red (632.8 nm):
Output Size Model Power (LxWxH) Applications Price -------------------------------------------------------------------------- ML800 0.8 239x72x74 Student use demonstrations $389.00 ML810 0.8 239x72x74 Student use demonstrations $399.00 ML811 0.5 181x33x47 Pointer, CE approved $399.00 ML855 5.0 540x72x74 Lecture demos, research, holography $899.00 ML868 0.8 328x72x74 Modulated, lecture demos, communication $489.00 ML869 1.5 328x72x74 Modulated, lecture demos, communication $499.00
Green (543.5 nm):
Output Size Model Power (LxWxH) Applications Price ------------------------------------------------------------------------- ML815 0.08 181x33x47 Pointer, CE approved $719.00
Information on older Metrologic lasers may be found in Vintage Lasers and Accessories Brochures and Manuals.
Here are photos of some typical samples of Metrologic steel-ceramic hard-seal tubes:
The bore is ceramic and the outer casing is all metal with the mirror mounts of a modern design allowing for mirror alignment. It is assumed that the mirrors are attached using glass frit to preserve the hard-seal claim, though the appearance is more like that of Epoxy. However, it does not scratch easily. All of the tubes in the photos are in good health despite their age. So, the Metrologic hard-seal approach does work.
My tests of two samples show that longitudinal mode characteristics are that of a flipper or worse. The behavior of the short tube wasn't too bad but is was a consistent flipper as shown in Mode Sweep of Short Metrologic Metal-Ceramic Hard-Seal HeNe Laser Tube. I won't torture you with plots of the long one. It's ugly. However, this is too small a sample to draw any firm conclusions.
Note that later Metrologic HeNe lasers continued to be advertised as "hard-seal" but use modern Melles Griot (glass) tubes.
METROLOGIC INSTRUMENTS, INC. DAAA09-86-C-0834 PN 11746797-2 TUBE,LASER,PLASMA,HELIUM-NEON NSN 6920-01-148-4713 WARRANTY FOR 24 MONTHS WARRANTY EXPIRES: FEBRUARY 1989 SERIAL NUMBER: 703-045
There is no doubt this is a military laser. It is a nicely machined stainless steel cylinder about 1.75 inches in diameter by 14 inches in length, with a precision welded flange at the connector-end. It weighs in at over 3 pounds! The tube is potted in a rubbery material at both ends with the HV connections via a pair of female contacts. There is no physical difference between the anode and cathode terminals but they are labeled "P1+" and "P2", respectively.
So, you'd think that this laser has to be at least 5 mW, right? Wrong! What's inside appears to be a 9 or 10 inch tube rated at about 1 mW with a TEM00, random polarized beam. The tube is long enough that polarization variations due to mode cycling are relatively small. The sample I have produces about 1.4 mW. It runs best on about 5 mA at 1,250 V, but remains stable down to about 2 mA. At 3.0 mA, the output power is around 1.1 mW. The internal ballast resistor is at least 90K ohms (might be a bit larger). So, almost any HeNe laser power supply designed for a 1 to 2 mW laser should be suitable. H&R recomends their model G7-001 but their much cheaper TM91LSR1495 works fine, and the typical barcode scanner brick would probably be adequate as well even though the current is generally lower (3 to 3.5 mA). It indeed runs happily on the small copper-covered barcode scanner bricks at 3.0 mA (with the 91K ohm ballast resistor removed to reduce stress on the supply).
For the longest time, I didn't know whether this was simply a common barcode scanner tube in a fancy expensive package, or one of the Metrologic Hard-Seal Steel-Ceramic tubes. (See the previous section.) The high cost might only be justified in, well, military applications. :) If they could charge $400 for a toilet seat or *real* hammer, just think of what a laser would go for. :-) Someone I know tried a medical X-ray machine on the head cylinder without success. I was resisting the temptation to gouge out all the potting material and ruin the magnificent packaging, then only to find a common barcode scanner tube inside! With the laser powered (to provide internal illumination), I tried looking in the output-end through a dielectric filter that blocked 633 nm and I think there was glass visible inside but it was hard to tell. The side of the mirror looks somewhat strange but maybe that's just because it is coated with the rubber potting compound.
On the H&R Web site, this laser is listed as a "Ruggedized HeNe Laser Head" used for some sort of weapons training/sighting application. It would also make a decent hammer. :) If there was a steel-ceramic Metrologic tube inside, hammering nails probably wouldn't affect its lasing performance at all. I'd love to know how much one of these beauties cost the American taxpayer. :-)
But I couldn't resist the temptation any longer. I finally dug out the potting at the output end of the head only to discover that it contains a boring glass laser tube, probably NEC based on the appearance of the metal mirror mount stems, but I can't rule out a Metrologic frit-sealed glass tube. The rubbery potting material is only about 1/2" deep. The tube itself is nestled in several layers of foam padding so it probably wouldn't be very difficult to remove the tube entirely, but that would be so BORING! The rubbery potting could be easily replaced if I had nothing better to do.
I wonder if the U.S. Government knew they were paying a zillion dollars for a laser using a common barcode scanner tube, and possibly made in Japan! :) Perhaps the original contract was based on a steel-ceramic tube and the version sent for inspection and testing did indeed have the good stuff inside. But later, it was cost reduced. Who would know? ;-)
Their HeNe laser tubes are unique is being constructed mostly of a metal cylinder into which the cathode can is inserted, with glass only at the anode-end. Conventional internal mirror tubes and perpendicular window tubes use frit seals while most of the one-Brewster tubes apparently use soft seals as they do tend to degrade when not used for a long time.
The current offerings may be found at their Web site but the selection has been steadily declining over the years.
Here are some specifications for four REO tunable lasers. All of these models were listed in their 1989 price list though only the LSTP-1010 shows up in a recent catalog. As expected, all are linearly polarized (500:1) since they use a Littrow tuning prism external to the laser tube. Originally, there were both versions in a rectangular case, as well as a cylindrical laser head with separate power supply. The latter (denoted with a "C" following the model number) must never have been produced in any quantity as I've yet to see one!
|<---------------- Output Power ---------------->| Model Price 543.5 nm 594.1 nm 604.6 nm 611.9 nm 632.8 nm -------------------------------------------------------------------------- LSTP-0010 $3,200 0.1 mW 0.3 mW 0.5 mW 0.5 mW 0.5 mW LSTP-0020 $2,200 -- 0.2 mW 0.2 mW 0.5 mW 2.0 mW LSTP-0050 $2,860 -- 0.5 mW 0.5 mW 1.0 mW 3.5 mW LSTP-1010 $4,050 0.3 mW 0.6 mW 0.5 mW 2.5 mW 4.0 mW
Note the line at 604.6 nm (orange/yellow) which is almost never seen in other other-color HeNe lasers (at least it isn't supposed to be there). :) A new LSTP-1010 with careful cleaning and alignment may actually produce more than 3 times the spec'd power for 543.5 nm, 594.1 nm, and 604.6 nm.
One or more of the other visible HeNe wavelengths may also be present in some samples. I've seen one with a small amount of 629.4 nm and heard of another that produces almost 1 mW or 640.1 nm. These are just not guaranteed in the specifications but may result from subtle variations in the mirror coating wavelength reflectivity functions for the Littrow prism and OC.
And for only $5,195.00 (in 2014) plus shipping and handling, you can now buy your very own LSTP-1010 through REO (if they'll pay attention), Newport, and elsewhere. :) (Edmund Optics and Thorlabs used to carry them also but no longer do.)
These lasers show up on eBay from time-to-time but are almost invariably dead or dying, though I know of one instance where such a laser turned out to work on all lines at near rated power after some tender loving care. (Apparently, its power supply had died so the laser was put on the shelf for who knows how long, but the tube recovered after being run for many hours.) A PMS tunable laser from 1984 is physically similar to the REO version sold today (2007). However, the Littrow prism has been improved and the heater on the OC mirror has been eliminated. Installing a new tube in an old case is possible but will probably not result in quite the same performance as a new laser. The output power for all lines will not be as high as with a new prism and the green line in particular could be down right whimpy. :) Even so, the laser may still exceed the LSTP-1010 specifications (at least initially), though possibly just barely for the green line. However, there may be surprises like some 640.1 nm or 629.4 nm due to differences in the coatings. Of course, since it's likely that a new tube will likely be almost as expensive as a new laser, a tube swap is not going to be cost effective.
Some photos (from Dave):
Since the case is used as the laser resonator frame, thermal stability of these lasers is rather poor. It may require several hours in a reasonable constant temperature environment for the output power to settle down. And if set for maximum output power even at 633 nm (the strongest wavelength) when fully warmed up, there may be no output at all when restarted cold. Thus, unless one is familiar with the laser, the first reaction may be to start turning the two knobs at random, resulting in it becoming hopelessly misaligned. In that case, see the next section. :) But first check the shutter as there is no positive detent to keep it in the open position so it can easily slide closed by accident.
Lasers from pre-1984 (PMS) to the present (REO) are physically similar and most parts are interchangeable. However, older lasers will include a small heater coil that slips onto the OC mirror of the tube, powered by a transformer glued to the bottom of the case. The heater was supposed to eliminate "color centers" in the mirror coating. However, I've yet to be convinced this made the slightest difference with any of the tunable or "other color" HeNe lasers on which it was present. It's gone on newer lasers, replaced by an AC line filter in some. And newer lasers use a rectangular tuning prism which is not interchangeable with the older cylindrical one as the mounts differ.
I've also seen an LSTP laser with fiber-coupled output. The stability for this setup is even worse especially if using a single mode fiber since the case also serves to maintain fiber alignment. Low output power or a total lack of output could then be due to a problem with the laser or the fiber alignment being wrong. But check the shutter. ;-)
There is a special fiber coupler and mating patch cord with adjustable focus to optimize coupling for each wavelength, though in my experience, this isn't really necessary for the relatively narrow 544 to 633 nm wavelength range.
A modest redesign to improve stability and usability would consist of:
(From: Lynn Strickland (firstname.lastname@example.org).)
The five lines are 543.5, 594.1, 604.6, 611.9, and the common (red) 632.8 nm. You might see a flash at 629.4 nm and at 640.1 nm, but nothing to write home about. The 629 and 640 nm lines are so weak, and so close to 633 that they're sometimes hard to distinguish. There should be nothing at the IR lines (1,153, 1,523 or 3,391 nm).
As originally designed, these lasers used a Brewster window tube with a Littrow prism as the wavelength selection mechanism. The tube's internal mirror was a broad band output coupler. Don't know if it's changed, but I doubt it.
(Same in 2007. --- Sam.)
The fundamental design issue is that the optimum Bore-to-Mode Ratio (BMR) for green is much higher than for red. (BMR is the ratio of limiting aperture size to mode radius. To get TEM00 operation for green, the optimal number is about 4.2, for red it's about 3.5.) If you know the wavelength, mirror curvature, and spacing, you can calculate the mode radius at any point in the cavity. The capillary bore serves as the limiting aperture, so adjusting bore length and bore diameter sets the BMR, which in turn determines transverse mode purity.
Thus, if you optimize the BMR for green power (which you have to do), the red is under-apertured, and has something like 50% off-axis modes. It's getting close to a doughnut-mode.
REO builds some of the highest 'Q' Brewster tubes in the world (probably THE highest), exclusively for the company, Particle Measuring Systems (PMS). REO and PMS used to be one in the same, but the owner sold off the particle counter biz a few years back, for something like $75 million. They now have some sort of supply agreement. The REO tubes aren't the most robust or mechanically stable, but if you get them packaged right, probably some of the highest power you can get from a given tube length. This is mostly due to coatings (all Ion Beam Sputtered), and a super-polishing process they have for substrates. As they say, it's all done with mirrors. ;)
A green Brewster tube IS a bitch! The original REO (PMS) tube was a 5 mW size - about 15" long. They did a soft-seal on the B-window because it's fused silica. Don't know if they've gone to optical contacting/graded seal now - I'd hope so.
I think REO added a 7 mW, maybe even a 10 mW size for power. I recall seeing some longer ones at a trade show. As for cavity power, I've seen a REO B-tube with 2 HRs do almost 45 Watts of intra-cavity circulating power. They're probably higher than that now. These puppies are like $1,700 each in volume and only sold to PMS - pretty hard to come by.
There is a weak line at 635.2 nm which could also show up as its gain is higher than that of the 594.1 nm and 604.6 nm lines. 640.1 nm is actually quite strong - next in line after 632.8 nm. See the section: Instant HeNe Laser Theory for a listing. But it's probably killed by the mirror coating selectivity.
Here is a photo of the PMS One-Brewster HeNe Laser Tube and a closeup of the Littrow Prism Tuning Assembly from PMS Tunable HeNe Laser showing its proximity to the one-Brewster tube's Brewster window. There are adjustments for wavelength and transverse (alignment). The Littrow prism is the shiny thing at the far left. The Brewster window is next to it. There is normally a tight fitting metal cover to keep out dust which has been removed to take the photo. Except for the high quality internal OC mirror and window, the HeNe tube itself isn't that much different from the common variety, though the metal envelope - typical of PMS/REO tubes - may help stability. It does have a heater coil on the OC mirror mount. According to a PMS patent (4,740,988: Laser Device Having Mirror Heating), this is to eliminate color centers that may develop in the mirror coatings from exposure to UV in the bore light. (These heaters are on some but not all older PMS HeNe laser tubes.) The resistance is around 31 ohms and it runs on 9 VAC from a small transformer. I've never really seen any definitive improvement in anything when running the heater. New tubes don't need it. The rest of this laser is unremarkable - a brick power supply and case. :)
To restore alignment using the knobs, it's usually not necessary to go inside, but read through the following just in case since it's easy to miss important precautions in the excitement of the adventure. :-)
CAUTION: To remove the cover, take out the screws ONLY at the top of the end-plates and lift the cover straight up. DO NOT remove or even loosen the screws at the bottom of the rear end-plate since it could tilt forward and smash the prism into the Brewster window. :( Note that since the resonator is formed by all parts of the laser case, removing the lid will likely change alignment enough to matter and lasing will probably be lost entirely. Thus, it is best done with the laser lasing red so the Transverse and Color adjustments can be made incrementally as the screws are loosened. Of course, if the laser doesn't work, the alignment won't matter much.
CAUTION: DO NOT attempt to remove or even loosen the screws at the bottom of the rear plate. (Didn't I say that already???) The adjustable prism mount is directly attached to the rear plate and this is joined to the Brewster stem of the tube via an O-ring-sealed box with a removable cover. Removing the rear plate without observing exactly how this affects the relationship of the Littrow prism mount to the tube's Brewster stem and taking appropriate precautions may also break the tube.
CAUTION: The Brewster-end of the tube is all glass and fragile. The high voltage is also exposed in that area. So, if you have removed the cover of the laser, take care. It would be a darn shame if a reflex response to contact with the HV resulted in broken glass. :(
The sliding shutter has no positive detent to lock its position and it can change almost on its own, or at least by accidentally brushing it practically without feeling anything. Thus, if there is suddenly no output, check the shutter! ;-)
Then do a search in the vicinity, after having noted the exact original knob orientation. What is meant by "search" is to very slowly rotate the Color knob over a range of around 1/2 turn which includes the original setting, while moving the Transverse knobe back and forth by around 1/2 turn. Usually, this will get it back. The same also applies if there is no output after applying power. If optimized when warm, it's possible for there to be nothing when restarted cold. Grasp one knob in each hand and perform the local search without letting go - the entire required range will likely be less than 1/4 turn for either one, 1/2 turn at the most unless one of those monkeys that occupy the lab at night decided to play. :)
CAUTION: DO NOT turn the micrometer adjustments further than necessary, especially in the tighten direction. I believe there should be enough clearance between the Littrow prism and Brewster window such that contact is not possible, but you really don't want to find out this isn't the case. The total useful range is less than 1/2 turn for the Color knob and less than 1/4 turn for the Transverse knob. You won't find a blue line by turning the Color knob past green! :)
If it is still not possible to achieve lasing (or are unable to use the long procedure due to the lack of a suitable power meter), remove the cover, and adjust the rear prism mount as perpendicular to the optical axis as possible by eye, then search for lasing 1 or 2 turns in that vicinity. This is generally the "sweet spot". See below for precautions.
But if the cover over the tuning prism and Brewster window (not just the laser cover) has been removed previously, a blob of dust or Q-tip fuzz may have fallen onto one or both surfaces from just moving the laser around or just a random event and they will have to be cleaned properly. It is best to use the "drop-and-drag technique for cleaning delicate optics, but this can be difficult due to the cramped location, expecially if you aren't proficient at it. I've used isopropyl and Q-tips - way to many Q-tips, but acetone or methanol may work better. Keep the liquid off the adhesive as I'm convinced that it out-gases after sealing the cover. Do the cleaning powered, first with red, then with green. Looking at the scatter while monitoring the output with a laser power meter is the only way to really know when you've got it.
Of course, if the laser was obtained on eBay, then the non-lasing state is normal. :) :)
This proposal boosts the efficiency of the basic PMS/REO tunable HeNe laser design allowing for higher output power (particularly on the weak 543.5 and 594.1 nm lines), eliminates the need for optics cleaning - ever, and provides for nearly infinite shelf life without the need to be run periodically.
One problem that limits power in the REO tunable HeNe laser are losses through the Brewster window of the 1-B tube. The Brewster angle is only correct at a single wavelength so there will still be some Fresnel (reflection) at all the others. And, even super polished fused silica isn't perfect so there will still be some scatter. In addition, matching the orientation of the prism and the Brewster window of the tube is also critical to maximize power. If these issues could be eliminated, the available power at all wavelengths would increase, but this would be especially dramatic for the very weak 543.5 nm (green) and 594.1 (yellow). So, what I suggest is to place the tuning prism inside the tube via a flexible metal bellows. The adjustable external mount can be similar to the one in the present LSTP tuanble laser, so minimal changes to the mechanical design would be needed. With this approach, 2 of 3 Brewster surfaces are eliminated from the intracavity beam path. The 3rd one is for the Littrow prism which unfortunately cannot be eliminated unless a high efficiency grating could substitute for the prism. Dust collecting on the optics is also, of course, no longer a problem. :) A glass-to-metal or frit seal (both hard seals) could be used in place of the soft seal presently used to minimize stresses in the Brewster window, thus eliminating the need to be run periodically to maintain tube health. And in addition to the complete laser, a self-contained tunable laser "module" would also be a practical product offering. ;-)
These tubes are physically similar to the one in the tunable laser, but a bit shorter. Almost all are soft-sealed at the Brewster window. Samples from the early 1990s tend to have leaked, though in some cases running for a few days or months will restore them to full power. With some combinations of mirrors and tuning prism (including the original configuration with its external HR), it may be possible to obtain significant output power at 604.6 nm and/or 611.9 nm (orange, 2 mW or more), and trace amounts with only an external HR.
(However, not all particle counters, even PMS particles counters, used one-Brewster lasers. Some had a novel dual cavity configuration with a 5 mW internal mirror red HeNe laser tube and a separate resonant cavity comprising the outer side of the OC mirror coating and an external HR mirror. See the section: The PMS/REO External Resonator Particle Counter HeNe Laser.)
An older Siemens HeNe laser catalog may be found at Vintage Lasers and Accessories Brochures and Manuals.
Legend for Type: SM=Single transverse mode (TEM000; MM=Multimode, P=Linearly polarized.
Red (632.8 nm):
Model Number Power Type Head Tube ------------------------------------------------ 0.5 mW SM LGR-7656 (1) 0.5 mW SM P LGK-7650 LGR-7650 (1) 0.5 mW SM LGR-7651 0.5 mW SM LGR-7651A 0.6 mW SM LGK-7655 LGR-7655 0.75 mW SM LGK-7639 0.75-1.0 mW SM LGK-7657 0.8-1.4 mW SM LGR-7655-N 1.0 mW SM LGK-7655-S LGR-7655-S 1.0 mW SM LGK-7641-S LGR-7641-S 1.2 mW SM LGK-7632 LGR-7632 1.5 mW SM LGR-7608 LGR-7608 1.5 mW SM LGR-7649 2.0 mW SM LGR-7621S 2.0 mW SM LGR-7610 LGR-7610 2.0 mW SM LGR-7610H (2) LGR-7610H (2) 2.0 mW SM LGK-7672 2.0 mW SM P LGK-7634 LGR-7634 2.2-3.2 mW SM P LGK-7634 4.0 mw SM LGK-7630 LGR-7630 5.0 mW SM LGK-7627 LGR-7627 (1)(3) 5.0 mW SM P LGK-7628 LGR-7628 5.0 mW MM LGK-7621-MM LGR-7621-MM 5.2 mW SM P LGK-7628-1 LGR-7628-1 5.5-7.5 mW SM P LGK-7628-L 7.0 mW SM LGK-7627-M 10.0 mW SM LGK-7653-8 10.0 mW SM P LGK-7654-8 (45x505mm) 10.0 mW SM P LGK-7654-13 (44.25x490mm) 10.0 mW MM LGK-7627-MM LGR-7627-MM 12.0 mW? SM LGK-7637 12.0 mW? SM LGK-7638 15.0 mW? ?? ? LGK-7654-15 15.0 mW SM LGK-7665 15.0 mW SM P LGK-7665-P 18.0 mW SM LGK-7665-18 18.0 mW SM P LGK-7665-P18 20.0 mW SM LGK-7665-20 20.0 mW MM LGK-7658-7 25.0 mW SM P LGK-7626-L 25.0 mW SM P LGK-7626 25.0 mW SM P LGK-7676-L 28.0 mW SM P LGK-7676 30.0 mW SM P LGK-7626-S 30.0 mW SM P LGK-7676-S
Model Number Power Type Head Tube --------------------------------------------------- 0.5 mW SM LGK-7770 LGR-7770 0.5 mW SM P LGK-7774 0.5 mW SM P LGK-7786-P50 0.75 mW SM P LGK-7786-P75 1.0 mW SM LGK-7770-S 1.0 mW SM LGK-7785-P100 1.0 mW SM P LGK-7786-P100 1.05 mW SM P LGK-7786-P 1.2 mW SM LGK-7785-P120 1.5 mW SM LGK-7785-P150 1.5 mW SM P LGK-7786-P150 2.0 mW SM LGK-7785-P200 2.5 mW SM LGK-7785-P250 (on request)
Yellow (594.1 nm):
Power Type Model ------------------------------------- 1.5 mW SM LGK-7511 2.0 mW SM LGK-7512 P
Orange (611.9 nm):
Power Type Model ------------------------------------ 2.0 mW SM LGK-7411
SM: Single transverse mode, TEM00; P: Linearly polarized.
For models that are in current production, more complete specifications are available on the LASOS Web site.
This recently appeared on the LASOS Web site. It appears to be a general purpose HeNe plasma tube with two Brewster windows and may be the same tube used in the Spindler and Hoyer ML-500 tunable HeNe laser, as well as the tube used in the MEOS (and other) educational laser kits. The total length tip-tip is 398 mm with an operating voltage of 1,800 V at 6.5 mA. Having a relatively wide bore, single or multi-spatial mode operation is possible depending on the cavity geometry and additional intra-cavity mode selection devices like apertures.
Model Number Power Type Head Tube --------------------------------------------------- 5.0 mW 2-B LGR-7627 BK
The LGR-7638 laser tube is generally unremarkable except for the reasonably precise three-screw mirror adjuster at the cathode end. There is enough range that as long as you don't lose the beam entirely, it should be low risk to tweak mirror alignment on this laser. In all other respects, the tube looks like a stretch version of shorter Siemens/LASOS bare tubes with two spider bore supports and one square getter.
The following are based on physical measurements of an intact LGK-7638 laser head and my tests of a two samples of somewhat less than pristine samples of the LGR-7638 tube alone. Only one of these came close to new specs with a maximum output power of about 13 mW. Thus the electrical measurements are not likely to be exact, as operating voltage and optimal current may change with use.
The measurements and healthier of the tube samples were provided by Alan Scrimgeour in response to a posting on alt.lasers.
The LGK-7676 resonator consists of 4 full length 5/8 inch diameter rods joined by 10 thick plates. The tube is secured to these plates using sets of 4 screws with padded tips going in from all four sides at most locations. Some sets are adjustable for bore centering and optimizing straightness. The end-plates hold the mirror mounts. Coarse mirror adjustment is via some thinner rods attached to the ends of the main support rods, with pairs of nuts but no springs. This should permit the mirror mounts to be removed and replaced for cleaning of the optics without requiring coarse realignment. Fine mirror alignment uses Allen's head screws to press on rods which slightly warp the aluminum to which the actual mirror cell is attached. Viewed end-on, there are a pair of large hex nuts above the laser apertures. The entire affair looks sort of like a face with two eyes and a nose or mouth. :) Adjacent to the "eyes" on the rectangular plate are the pair of recessed 3/32" set screws for fine mirror alignment. This scheme works reasonably well with good sensitivity and repeatability except that the two adjustments at each end aren't quite independent. Note that with this scheme, walking of the mirrors requires turning the screws at the two ends in opposite directions. The fine adjustments are similar to those in the SP-907 but the coarse adjustments for that laser are three spring loaded nuts which means that removing the mirror mounts requires complete realignment (unless you are *really* good at counting turns!).
The entire resonator assembly is mounted on a thick piece of machined L-shaped aluminum fastened with screws at only two locations. However, under about half the thick plates (see above) on both sides of the "L" are adjustment screws to provide some sort of additional support.
The LGK-7676 uses a coaxial tube with about half of its bore exposed (as opposed to the side-arm tube with totally exposed bore used in Spectra-Physics lasers). While this does result in a more compact package (overall dimensions under 3"x3"x39"), there is less space for IR suppression magnets. In fact, the LGK-7676 only has two sets of magnets (in proximity to less than 25 percent of the bore) for this purpose but could definitely use more. Adding moderate strength magnets (greater than refrigerator strength but much less than rare-earth disk drive strength) almost anywhere along the bore - even outside the large gas reservoir - resulted in a noticeable increase in output power - about 1 percent for a single magnet. I would guess that with enough magnets, a 10 to 20 percent boost would be possible.
There are both anode and cathode ballast resistors of 81K and 27K, respectively. The power supply connector has 3 pins - anode, cathode, and Earth ground. But note that this pinout is not the same as on the physically similar connector on Spectra-Physics lasers. Thus, a Spectra-Physics power supply cannot be used on a Siemens/LASOS laser or vice-versa without modification or bad things will happen to the laser head and/or power supply. Check the power supply and laser head wiring to be sure they are compatible if not originally mated!
The sample I tested is an LGK-7676S with a spec'd output power of at least 30 mW. Of course, since I like to spend as little as possible to acquire these things, mine is a high mileage tube which apparently served hard duty in some sort of high speed printer since there was toner all over it. These are turning up on eBay (and possibly from surplus outfits directly), probably being replaced when their output power drops below a certain value by tiny diode lasers. :)
I was able to run it on my SP-255 exciter only by reducing the anode ballast resistor to 60K and removing the cathode ballast resistor entirely. Prior to this surgery, even with the input voltage to the SP-255 at 140 VAC (the upper limit of my Variac), it would only run for a minute or two (and only if it felt like it) and then cut out, not to restart for several minutes. With the modifications, it will now run all day at 120 VAC input, though restarting was sometimes still a bit of a problem until I added circuitry in an external pod to the SP-255 to boost its starting voltage. (Note that this may not be needed for LGK-7676, SP-907/107/127, and similar size lasers with lower mileage tubes.) See the section: Enhancements to SP-255.) The SP-207 is able to drive this laser without problems but I didn't happen to have one of those at the time.
After bore straightening and mirror adjustments, I was able to squeeze more than 19 mW out of the laser at a somewhat reduced operating current (10 mA instead of the spec'd 11.5 +/- 0.5 mA). (I'm using the lower current only so I can look forward to increased power by a simple tweak in the future.) It would exceed 20 mW if when fully warmed up, the laser was shut off for 30 seconds and then restarted. But the output power would drop back to its previous level over the course of a minute or so once the "good" gas had time to migrate back out of the bore or something. :)
Now, 5 to 10 years later (who's counting?), the power has dropped to about 15 mW using the proper (11.5 mA) power supply. This is a soft-seal tube, so leakage is to be expected. Running it may recover at least some of the lost power as the bad gas gets cleaned up. Stay tuned.
Regrettably, Spectra-Physics no longer manufactures any HeNe laser tubes. They appear to sell selected complete HeNe laser systems from Research Electro-Optics, Inc. (REO) including a REO stabilized HeNe laser! tube!
Here is a chart of some older Spectra-Physics HeNe lasers. Most of these are from a 1988 catalog (along with 1988 prices). Not all information was available, thus the "???" in places. You can go to the Spectra-Physics (now Newport) Web site for current models (which are now quite limited, possibly to the SP-117A frequency/intensity stabilized laser only). But the hobbyist and experimenter is much more likely to acquire the classic ones below (unless very well endowed!). Typical output power when new may have been 50 percent or more greater than the value listed.
Scans of original Spectra-Physics brochures and catalogs which include some of these lasers can be found at Vintage Lasers and Accessories Brochures and Manuals.
Minimum Laser Wave- Mirrors Output Exciter Original Model length Int/Ext Power Model Price Description/Comments ------------------------------------------------------------------------------- 102R 632.8 nm I 2 mW 212 $ 610 Cyl. head, rand. pol. 102P 632.8 nm I 1.5 mW " $ ??? Cyl. head, lin. pol. 105R 632.8 nm I 5 mW 215 $ ??? Cyl. head, rand. pol. 105P 632.8 nm I 5 mW " $ ??? Cyl. head, lin. pol. 107 632.8 nm E 30 mW? 207 $ ?,??? Similar to 127 (1) 112 632.8 nm E 10-30 mW 200 $ 6,000 RF excited 115 632.8 nm E 3-6 mW 200 $ 4,650 RF excited, 24" resntr. 116 632.8 nm E 25 mW 250 $ 13,250 " " tuning prism 120 632.8 nm E 6 mW 256 $ 1,980 Small lab laser (2) -01 1,152 nm E 1 mW " $ 2,800 " " -02 3,391 nm E 1.25 mW " $ 2,800 " " 117 632.8 nm I 1 mW ???? $ ?,??? Stabilized (7) 117A 632.8 nm I 1 mW 217A $ 3,500 " " " 117B 632.8 nm I 1 mW I $ ?,??? " " " 117C 632.8 nm I 1 mW I $ ?,??? " " " 118A 632.8 nm I 1 mW 218A $ ?,??? " " " 119 632.8 nm I 0.07 mW 259 $ 5,775 " " " 122 632.8 nm E 5 mW? 253A $ ?,??? Short version of 124 (3) 123 632.8 nm E 10 mW? I $ ?,??? Between 120 and 124 124B 632.8 nm E 15 mW 255 $ 4,900 Popular lab laser (3) -01 1,152 nm E 2 mW " $ 5,500 " " -02 3,391 nm E 5 mW " $ 5,500 " " 125A 632.8 nm E 50 mW 261A $ 16,000 Huge-head >125 lbs. (4) -01 1,152 nm E 10 mW " $ 17,500 more than 6 feet long. -02 3,391 nm E 10 mW " $ 17,500 " " 127 632.8 nm E 35 mW I $ ??,??? 39 inch resonator (1) 130 632.8 nm E 0.6 mW I $ 1,525 Self contained (5) 130B 632.8 nm E 1.5 mW I $ 1,225 " " 130C 632.8 nm E 1.5 mW I $ ?,??? " " 131 632.8 nm E 1.0 mW 251 $ 2,350 632.8 nm E 1.0 mW 252 $ 2,825 132 632.8 nm I 2 mW I $ ??? Self contained (6) 132P 632.8 nm I 1.8 mW I $ ??? Self contained (6) 132M 632.8 nm I 3.5 mW I $ ??? " " 133 632.8 nm I 2 mW 233 $ ??? Separate rect. head (5) 133M 632.8 nm I 3.5 mW 233 $ ??? " " 133P 632.8 nm I 1.8 mW 233 $ ??? " " 134 632.8 nm I 3-5 mW I $ ??? Self contained 135 632.8 nm I 3-5 mW 235 $ ??? Separate rect. head (5) 136 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 136P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 137 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 137P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 138 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 138P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 142 632.8 nm I 2 mW 248 $ ??? Separate rect. head (5) 142P 632.8 nm I 1.5 mW 248 $ ??? " " 143 632.8 nm I 4 mW 247 $ ??? " " 143P 632.8 nm I 3.5 mW 247 $ ??? " " 144 632.8 nm I 5 mW 247 $ ??? " " 144P 632.8 nm I 4.5 mW 247 $ ??? " " 145 632.8 nm I 2 mW 248 $ ??? Separate cyl. head 145P 632.8 nm I 1.5 mW 248 $ ??? " " 146 632.8 nm I 4 mW 247 $ ??? " " 146P 632.8 nm I 3.5 mW 247 $ ??? " " 147 632.8 nm I 5 mW 247 $ ??? " " 147P 632.8 nm I 4.5 mW 247 $ ??? " " 155 632.8 nm I 0.5 mW I $ 310 Educational laser (6) 156 632.8 nm I 0.5 mW I $ ??? " " 157 632.8 nm I 3 mW I $ 525 Self contained 159 632.8 nm I 5 mW I $ 630 " "
For more details on the popular large-frame Spectra-Physics HeNe lasers, see the next section.
It should be possible to possible to obtain orange (611.9 nm), yellow (593.9 nm), and green (543.5 nm) output with similar modifications (at least for the longer lasers), though the gain of these lines is only a fraction of that for the red or IR lines (1152.3 nm and 3391.3 nm) so output power will be lower.
Some photos of these lasers can be found in the Laser Equipment Gallery under "Spectra-Physics Helium-Neon Lasers". Old brochures can be found at Vintage Lasers and Accessories Brochures and Manuals.
Spectra-Physics Laser: SP-120 (1) SP-124B (2) SP-125A ------------------------------------------------------------------------------- OUTPUT Wavelength (nm): 632.8 632.8 1152.3 3391.3 632.8 1152.3 3391.3 Minimum Power (mW): 5.0 15 2.5 5.0 50 10 10 BEAM CHARACTERISTICS Beam Diameter (mm): 0.65 1.1 1.4 2.5 1.8 2.4 4.1 Beam divergence (mR): 1.7 0.75 1.0 1.8 0.6 0.8 1.4 RESONATOR CHARACTERISTICS Transverse Mode: TEM00 Degree of Polarization: 1000:1 Angle of Polarization: Vertical (+/-5 Degrees except SP-120, +/-20 Deg.) Resonator Configuration: Long Radius Resonator Length (cm): 39 70.1 177.0 Longitudinal Mode Spacing: 385 MHz 214 MHz 85 MHz PLASMA TUBE Plasma Excitation: +3.7 kV, 6 mA +5 kV, 11 mA -6 kV at 30 to 35 mA (RF Opt: 15 W at 46 MHz) Starting Method: ~8 kV ~12 kV Trigger pulse on isolated (Direct from Exciter) bar adjacent to tube. AMPLITUDE STABILITY Beam Amplitude Noise: <.3% RMS <.3% RMS <2% RMS (RF: <.5%) Beam Amplitude Ripple: <.5% RMS <.2% RMS <.5% RMS (RF: <.6%) Long Term Power Drift: <5% over 8 hours and 10 °C Warmup Time: 30 Minutes 30 Minutes 1 Hour ENVIRONMENTAL CAPABILITY Operating Temperature: 10 to 40 °C Operating Altitude: Sea Level to 3,000 m (10,000 ft.) Operating Humidity: Below Dew Point POWER REQUIREMENTS Power Supply: 115/230 VAC, 50/60 Hz, +/-10% Exciter Model (DC): SP-256 (1) SP-255 (2) SP-261A Input Power: 50 W 125 W 456 W PHYSICAL CHARACTERISTICS Laser Head Size: 3.26" (W) x 3.26" (W) x ??? (W) x 3.66" (H) x 3.66" (H) x ??? (H) x 18.48" (L) 32.00" (L) ??? (L) Laser Head Weight: 7.5 lb 25 lb 100 lb Power Supply Size: 7.25" (W) x 7.25" (W) x 13" (W) x 3.72" (H) x 3.72" (H) x 6" (H) x 9.88" (D) 9.88" (D) 18" (D) Power Supply Weight: 7.5 lb 7.5 lb 30 lb
The 1974 brochure for the SP-124A lists 611.8 nm (orange) as an optional wavelength, power not specificed. The 594.1 nm (yellow, 11 mW) and 543.5 nm (green, 5 mW) wavelengths were also mentioned in a paper but although mirror sets for yellow at least were available, it's not known if they were from SP or an official SP product. The green may have required changes to gas pressure/fill ratio and operating current as well.
Actual power from these lasers may be much more than their ratings would indicate, especially when new: greater than 35 mW for the SP-124B and up to 200 mW (!!) for the SP-125A with optimal mirrors, 150 mW with a tuning prism. (However, I don't know how likely such 'hot' samples, especially of the SP-125A, really were.)
There is also a model 127 (OEM versions: SP-107 and SP-907) with the following partial specifications (632.8 nm). Beam diameter: 1.25 mm, divergence 0.66 mrad, length 38.75", height and width: about 4", power requirements: 5 kV, 11.5 mA, starting voltage: 12 kV + 6 kV pulse. This appears to be the only large-frame Spectra-Physics HeNe laser in current production. See the next section.
Mirror sets for green (543.5 nm), yellow (594.1 nm), and orange (611.9 nm) were available for the longer lasers. (The SP-120 and SP-122 may be too short for the low gain green line.) There were also tunable versions of the SP-125 and possibly others. The SP-116 was a tunable version of the RF excited SP-115. These used a Littrow prism in place of the HR mirror.
See the following sections for more information on these Spectra-Physics lasers.
Even without powering up the laser there are two things that can be inspected to get a rough idea of the tube's health (beyond the overall condition and that it isn't in a million pieces):
The actual plasma tube in these is the SP-082 with various -dash numbers after probably related to the actual output power. I believe higher -dash numbers mean a higher output power tube (at least when new). These laser heads may sometimes be listed based on the tube number but they are the same thing since you really can't buy a tube by itself unless someone was bored and decided to totally disassemble one!
The SP-107/907 resonator is over 38 inches long and of the "Stabilite" design similar to that of the SP-122 and SP-124 but the mirror mounts differ. There is an internal L-shaped structure and outer thinner metal skin. There are two versions, differing the design of their mirror mounts:
In addition to mirror alignment, there are a pair of bore centering brackets about 1/2 and 3/4 of the way relative to the cathode-end of the laser. These have an effect on both output power and beam shape. Carefully tweaking for maximum output power should done in conjunction with mirror alignment.
The bare resonators have no *beam* centering adjustments though the brackets securing the tube at each end can be shifted slightly along one axis by loosening their fastening screws. However, doing this after alignment will mess up everything else.
The tube has a side-mounted cathode chamber like other SP lasers but it is quite oversize - about twice the typical diameter. The ballast resistors (2 at the anode-end, 1 at the cathode-end, all 27K ohms) are mounted externally in glass tubes sealed with rubber and heat-shrink tubing. The power supply connector has 3 pins - cathode, anode, and Earth ground. But note that this pinout is not the same as on the physically similar connector on Siemens/LASOS lasers. Thus, a Spectra-Physics power supply cannot be used on a Siemens/LASOS laser or vice-versa without modification or bad things will happen to the laser head and/or power supply. Check the power supply and laser head wiring to be sure they are compatible if not originally mated!
IR suppression magnets are placed at every available location on two sides of the bore. Thin rubber boots seal the space between the Brewster windows and mirrors but these can be pushed back to permit cleaning of the windows and mirrors in-place (barely and not recommended unless the resonator has been previously disassembled as the optics stay quite clean). CAUTION: The part of the rubber boots surrounding the tube are easily torn if the boots are removed since they tend to stick to the tube. Some of these lasers include a metal cover and electrical heaters to decrease the warmup time required to achieve rated power and stability.
Depending on specific model, the SP-107/127/907 has a minimum output power of 25 or 35 mW but may do much more when new. The following is from a Spectra-Physics datasheet. Only the specs for the red version are shown but any of the other HeNe lasing wavelengths (except possibly 3.391 nm which may require a wider bore tube and removal of the IR suppression magnets) should be possible by substituting appropriate optics. A yellow or green version would be nice. :)
Spectra-Physics Laser: SP-107B ----------------------------------------------------------------- OUTPUT Wavelength (nm): 632.8 Minimum Power (mW): 25 or 35 BEAM CHARACTERISTICS Beam Diameter (mm): 1.25 Beam divergence (mR): 0.66 RESONATOR CHARACTERISTICS Transverse Mode: TEM00 Degree of Polarization: 500:1 Angle of Polarization: Horizontal (+/-5 Degrees) Resonator Configuration: Long Radius Beam Waist Location: Outer surface of output mirror Resonator Length: 93 cm Longitudinal Mode Spacing: 161 MHz PLASMA TUBE Type: Hard-seal (later versions), cathode in side-arm Operating Voltage: 5 (+/- 0.4) kV, 11.5 (+/- 0.5) mA Starting Voltage: ~15 kV Lifetime: Greater than 20,000 hours AMPLITUDE STABILITY Beam Amplitude Noise: <1% RMS Beam Amplitude Ripple: <1% RMS Warmup Time: 20 Minutes (95% power) ENVIRONMENTAL CAPABILITY Operating Temperature: 10 to 50 °C Operating Humidity: 5-90% non-condensing POWER REQUIREMENTS Power Supply: SP-207A (110/220 VAC +/- 10%) SP-207A-1 (100/200 VAC +/- 10%) SP-207B (90-130 VAC or 180-260 VAC) PHYSICAL CHARACTERISTICS Laser Head Size: 3.7" (W) x 3.7" (H) x 38.75" (L) Laser Head Weight: 23 lb Power Supply Size: 2.4" (W) x 1.4" (H) x 10" (L) Power Supply Weight: 3 lb
Complete specifications for the SP-107B can be found at Vintage Lasers and Accessories Brochures and Manuals.
It is possible to run these lasers on the smaller linear SP-255 exciter but starting may be erratic or not work at all (at least for non-pristine tubes) unless the AC line voltage is increased to 125 VAC for starting (it can then be backed off somewhat while operating). A bleeder resistor of 200M ohms or so rated for 15 kV can be installed to discharge the power supply capacitors after shutdown as starting of the longer SP-107/127/907 tube apparently requires the voltage to rise from close to 0 V to start reliably on the SP-255's whimpy starter. An alternative and better solution is to add a passive boost circuit to the starting multiplier of the SP-255. This can be in an external pod requiring no modifications to the exciter itself. Note that the added starting voltage may not be needed for LGK-7676, SP-907/107/127, and similar size lasers with lower mileage tubes. If your laser starts reliably, don't worry about it. Otherwise, see the section: Enhancements to SP-255.) Make sure the laser head frame is securely connected to the power supply (and earth) ground. Since the operating voltage and current are well within the capabilities of the SP-255, the laser and power supply should both be happy once started (though the AC line voltage may still need to be slightly above 115 VAC to minimize drop out/restarts if there are line dips, expecially for a high mileage tube which may have increased operating voltage). Changing the jumpers to use one of the lower line voltage taps on the SP-255's power transformer would probably help in a marginal case (low line voltage, or a laser with a higher HeNe tube voltage or higher ballast resistance) where regulation can't be maintained with adequate current without using a Variac to boost line voltage.
The laser tube is about 20 inches long with separate bore and gas chambers side-by-side. The bore uses rather thin glass tubing and is a very large diameter for a HeNe laser - about 3 to 4 mm ID - consistent with early HeNe laser technology. The laser head is nicely mounted with lots of fine machined hardware. It has no IR suppression magnets. There are two RF connectors on the side for the Spectra-Physics model 200 RF-type power supply. One of the connectors is for the actual RF signal; the other is for starting. There is an impedance matching network located under the "tube deck". This consists of a series LC circuit (C is adjustable for peaking the tuning) between the RF input and case with the output taken from the junction of the L and C. The RF drives a dozen or so electrodes with alternating polarities in close proximity to the tube bore. The start connection goes to the input of a potted transformer which produces a several kV pulse when the "Start button" on the exciter is pressed. The starting pulse goes to a separate small electrode clamped near the center of the tube bore.
The laser has external adjustable mirrors mounted on the very solid precision milled black anodized aluminum box support structure. Both mirrors have screw adjustments for coarse alignment not accessible from outside the case without removing the end-plates. The front mirror also has external fine adjustments in X and Y via two precision Lufkin micrometers and the rear mirror is mounted on a precision slide with an external micrometer adjustment for mirror separation (try to find that on any modern laser!). I don't know if the intent of this axial adjustment (over 1/2" of travel) was to fine tune the longitudinal or transverse modes or both. Since the resonator frame would experience little if any heating (and expansion), the micrometer could be used to center a longitudinal mode and maximize output for this low gain laser. In addition, the larger movement could possibly be used to select a particular transverse mode pattern, though actually achieving TEM00 operation in such a wide bore laser might not be possible.
The power supply for the SP-115 is a high quality 15 to 25 watt 40.68 MHz RF source consisting of a crystal controlled oscillator and a power amplifier using a 4x150 tube. All active elements are tubes, of course, but out of character for the era, the oscillator and driver are built on a printed circuit board. Overall, the system looks like something straight out of the ARRL Handbook (which is probably where the design came from!).
Not surprisingly, on the sample I have, the tube has leaked and only produces a weak purple glow when the RF is turned on. The getter has the "white cloud of death" syndrome and without an aluminum can cathode, there is no possibility of getter action anywhere else. (Not that a tube this far gone would have any chance of revival in any case. The tube would make an ideal candidate for refilling since the vacuum could be breeched by cutting the exhaust nipples at either end of the gas ballast without contaminating the Brewster windows.) The SP-200 does do a nice job of lighting 20 W fluorescent lamps and most likely screwing up radio reception in the neighborhood. :)
There was also a Spectra-Physics model 116 laser which appears similar but has a tuning prism to enable wavelength selection. It goes without saying that a working sample of an SP-116 would be a real prize. :)
Photos of a SP-120 laser head and the SP-120 resonator and tube can be found in the Laser Equipment Gallery (version 1.85 or higher) under "Spectra-Physics Helium-Neon Lasers". One thing the photos don't show because it had probably been removed, is the "starter helper" electrode, clamped to the bore near the side-arm. This is connected to the positive (anode) supply via a 100 pF HV capacitor. So, the initial rise in voltage produces a pulse on that electrode which helps to ionize the gas. Given the whimpy starter of the SP-256, it probably is worthwhile insurance. But I can understand why it was removed - getting the tube out for replacement or Brewster window cleaning is very difficult with that assembly in place.
The complete user manual for the SP-120 laser with SP-256 exciter can be found at Spectra-Physics Model 120 Laser with 256 Exciter Operation Manual. On the one sample of the SP-256 exciter that I've seen, the current was set for 7.2 mA. However, I don't know if this is the default optimum setting for the SP-120 laser or whether it had been tweaked. (The specs list 7 mA at 3.7 kV. But less than 6 mA will work on a healthy tube.)
There is also an SP-120S. The "S" stands for "Shutter" and indeed, these have a plastic shutter lever to block the beam. They also have really cheapo plastic end-covers which block access to the screws and thus make it impossible to do any adjustment without removing them entirely. Perhaps that's a good thing. :)
There are also IR versions indicated by additional numbers after the model: A 120-1 is 1,152 nm and a 120-2 is 1,523 nm, output power not known but probably not much. So, if you obtained an SP-120 on eBay that has a tube with a nice shiny getter and good discharge color but no beam, check the dash number! Some versions might have a black VIS-blocking filter in front of the output mirror, so that would be another clue. It's hard to pass red light through a black filter. :)
The resonator uses three-screw adjustable mirror mounts for coarse alignment (tweaking these is a true pain!). Fine alignment is done via a pair of recessed hex screw adjustments at each end which actually shifts the tube position at each end without affecting the mirror alignment. Each screw moves the end of the tube diagonally ( \ , / ) along a line intersecting the center of the mirror. So, use opposing pairs to walk the alignment. The adjustment screws are accessible via a pair of holes visible once the circular bezel/optics mount is unscrewed. It is possible to replace the tube in about 5 minutes without requiring major mirror re-alignment (no need to touch the coarse adjustments, only the tube centering).
The resonator is constructed from 3 pieces of thick very nicely machined aluminum stock - an L-channel and 2 end-plates bolted together to form a very rigid structure. It is supported at only three points and essentially floats inside the outer case (the "Stabilite" name as discussed for the SP-124 laser, below) which isolates the resonator from external stress (or so it is claimed). So, the clunking you hear when changing the position of the laser head is normal.
CAUTION: Unless the tube has been removed, there should be no need to clean the optics. Since there is no way to clean the Brewster windows with the tube in place and no way to clean the mirrors without removing them, it is a royal pain to be avoided. Remove, clean, install, test and tweak, repeat until output power comes back to what it was before attempting this stunt. :)
The one I obtained also used the strange SP-253A exciter - a switchmode power supply which sends medium voltage AC to a voltage multiplier/boost module in the laser head. See the end of the next section for more on this. There is also an SP-123 which appears similar but with an internal power supply. (Not sure why the large difrerence in output power in the table, above, though. Another reference to these lasers also shows a large difference of 3 and 7 mW for the SP-122 and SP-123, respectively.)
Really old SP-122s may have used a hot filament tube as I've acquired two "new" samples labeled "122T" and about the right dimensions. Spectra-Physics 122T HeNe Laser Tube with Hot Filament shows a pair of views of one of these. It was in a sealed plastic envelope with a punch card (!!) indicating that it was from SP stock in 1968! Closeup of SP-122T Filament/Getter Assembly shows the filament with the getter ring attached to one of the mounting posts. The filament requires several amps at 1 or 2 V. Both these tubes had leaked and the discharge color with the filament powered orange-hot was pink/purple. Interestingly, if the filament current was turned off, the discharge became a much more normal salmon color, but the dropout current rose so high that it would not stay lit at any reasonable current. If the current was simply reduced to the point where the filament was barely warm, the discharge could be maintained at 5 or 6 mA and the color wasn't too bad. Interestingly, the sustaining voltage actually was lower with reduced filament power! I can only guess that the hot filament was releasing gas contaminants that changed the discharge color and raised the discharge voltage. In fact, the discharge seemed to not be going to the filament at all, but to the getter and support posts as a noticeable silvery coating due to sputtering started appearing on the glass surrounding them. After this, the discharge color even with the filament running hot seemed to be a bit closer to normal, but was tending more toward orange with low filament power. This might mean that helium was being trapped faster than neon. Unfortunately, none of this is likely to help cure these tubes.
The SP-124 laser head is a box about 76 mm (H) x 76 mm (W) x 813 mm (L) (3" x 3" x 32"), nicely massive for its size. There are threaded beam apertures at both ends though the HR is backed by a solid aluminum plate so I don't think much light would ever get through that even if there was leakage through the mirror!
This is one of SP's "Stabilite" series lasers. This approach to frequency stabilization is based on a mounting system that employs optimally located pivots in an attempt to minimize the coupling of gravitational and vibrational torques and other distorting forces to the resonator cavity itself. In the SP-124, most of the mass of the laser head is in such an optimally mounted heavy solid frame with roughly an L cross section that runs nearly the full distance between the mirror mounts and attached to each of them at three points.
Adjustments accessible externally at each end of the laser allow the beam alignment (X and Y) to be tweaked very accurately by moving the entire optics chassis relative to the head mounting studs (which accept 6-32 screws or rubber feet). The adjustment scheme is sort of interesting (to me, at least): A V-shaped block (bolted to the rosonator and case) sits between a pair of wedges (part of the mounting stud assembly) that can be moved up and down via a pair of screws (call them A and B) and retained in position by a stiff spring. Rotating both A and B equally in the same direction moves the beam in Y; rotating A and B equally in opposite directions moves it in X. The setting may then be locked.
The external mirror HeNe tube is clamped in rubber mounts at its ends and also stabilized at the 1/3 and 2/3 (approximately) positions. Metal bellows join the tube mount brackets to the mirror mounts and, in conjunction with the rubber seals, prevent dust and dirt from getting on the inside surfaces of the mirrors and on the Brewster windows. The mirror mounts have hex head bolts for adjustments with set screws to prevent their settings from changing over time. An additional metal bellows joins the OC to the treaded output aperture.
The HeNe tube itself is a bare capillary about 7 mm OD with a 1.1 mm ID (no, I didn't measure it - just trust the specs!). The cathode, getter assembly, and HeNe gas reservoir is in a side-arm at the output-end of the laser bent to run parallel to the bore. It is about 32 mm x 178 mm (1-1/4" x 7") with the 'can' electrode nearly filling the glass envelope. The anode is (naturally) at the other end of the bore along with the three 9.8K ohm (5 W at least) ballast resistors also in a parallel side-arm inside the gas envelope as apparently is the case with other Spectra-Physics lasers of this era. Interesting, they are just ordinary Ohmite power resistors. I guess this approach does reduce problems with high voltage insulation breakdown but it would be a shame if the laser went bad because a $.50 resistor failed and could not be easily replaced! The total value of about 30K ohms would seem to be rather low but might have been selected to match the needs of the SP-253A exciter (see below) or additional external ballast resistors may be required. The SP-124B version of this laser may use a more normal 81K ballast resistance.
A series of relatively weak (e.g., refrigerator note holder strength) ceramic magnets 14 mm (W) x 22 mm (L) x 6 mm (H) (9/16" x 7/8" x 5/16") are mounted in close proximity under (15 magnets) and on one side (24 magnets) all along the length of the bore wherever they fit. (See the section: Magnets in High Power or Precision HeNe Laser Heads for an explanation of their purpose.) The approximate arrangement is shown below. I may have the poles backwards (which is of course irrelevant). A cheap pocket compass came in handy to determine the pole configuration!: The magnets were positioned with their broad faces about 2 mm from the bore.
Magnets N_S_N_S_N_S_N_S_N_S S_N_S_N_S_N_S_N N_S_N_S_N_S_N_S_N on side |_|_|_|_|_|_|_|_|_| |_|_|_|_|_|_|_| |_|_|_|_|_|_|_|_| (24) ------------------------------------------------------------- HR end ============================================================= OC end of bore ------------------------------------------------------------- of bore Magnets N_S_N S_N_S N_S N_S S_N S_N S_N S_N S_N S_N_S N_S_N below |_|_| |_|_| |_| |_| |_| |_| |_| |_| |_| |_|_| |_|_| (15) N_S_N +-----+-----+ Where: |_|_| = 2 adjacent ceramic magnets: |N S|S N| +-----+-----+I assume that the only reason there aren't 24 magnets below the tube is that the holes in the Stabilite frame got in the way.
Apparently, there must have been a couple of power supply options for the SP-124. Most of these lasers appear to use the Spectra-Physics Model 255 Exciter (SP-255). This is a traditional HeNe power supply providing operating and start voltage through a high voltage BNC connector. However, the laser I have apparently is supposed to use an SP-253A Exciter, a model for which no one (including Spectra-Physics) seems to have any information or even acknowledge exists though I have since found out that the SP-122 laser, a model slightly shorter than the SP-120 but built more along the lines of an SP-124, may have also used the SP-253A (possibly a slightly different version or at least different jumper options). For more information on what I have found out so far about the exciter, see the section: Spectra-Physics Model 253A Exciter (SP-253A).
Unfortunately, on the system I obtained, the boost/start module (which is what I assume was supposed to be inside the head to attach to the exciter) had been ripped out with the cable just chopped off and thus I can't even determine what was there originally. So, I removed the multiconductor cable and replaced it with a HV coax (terminated with a standard Alden connector) and wired it directly to the tube anode terminal and chassis ground (recall that the ballast resistors are inside the tube. Yes, I know, the 30K ballast resistance may be too low for use with the SP-255!)
Using my SP-255 to power the head, I get a nice pink glow in the bore (more red than orange indicating a rise in pressure from slow leakage over the years) but as expected, no coherent light. The low ballast resistance is fine as far as maintaining a stable discharge (I don't know if this would still be the case if the gas pressure in the tube were correct). Maybe someday in the far distant future after that hot place freezes over AND those pigs start flying, I will get around to regassing the tube! :)
This is definitely a LARGE-frame HeNe laser by weight alone: roughly 45 kg (100 pounds) for the head alone! And, it is around 2 meters (over 6 feet) long! Like its smaller cousin, the SP-124, there are models for normal red (632.8 nm) and two IR lines (1152.3 nm and 3391.3 nm). NEC made one almost as large (GLG5800, over 5-1/2 feet long) and Jodon has high power HeNe lasers but the SP-125 is still the largest production HeNe laser I've found.
The SP-125A tube has a common cathode in the middle of the tube with two anodes, one at each end. The dual discharges are driven from its SP-261A Exciter which provides 6 kV at up to 35 mA. The SP-250 Exciter is also compatible with this laser.
With a bit of rewiring of the laser head, one could feed the anodes separately reducing the individual current requirements so that a pair of power supplies similar to the SP-255 could be used. With this sort of scheme, it should also be possible to selectively power only one of the discharge paths for reduced beam output if desired. Yes, I know, why would you ever want *less* power? :)
Two sets of ballast resistors in the laser head totaling 87K ohms (75K+12K) provide the operating voltage to each of the anodes of the dual discharge tube. They are located between the anodes and chassis ground (The SP-261A's output is negative with respect to ground. Thus, ground is the positive supply voltage). The HeNe tube's single cathode is attached directly to the negative output of the SP-261A.
The starter operates in a manner similar to that of the method of triggering the xenon flashlamp in a typical electronic flash unit or solid state laser power supply - by pulsing an external electrode in close proximity to the HeNe tube bore. The whole tube is supported by metal rods which are insulated from the cavity structure by nylon disks. One of the rods is the trigger electrode. The starter runs off a voltage from the 75K/12K ohm taps of both ballast resistors ORed together so that it repeatedly generates a trigger pulse until BOTH discharges have been successfully initiated.
The SP-261A also has a low power RF output (this isn't the same as the RF power supply option mentioned below) which drives a pair of plates in proximity to the HeNe tube. The RF is supposed to stabilize the laser power (presumably by some sort of discharge dithering process). However, the RF apparently also results in interference with local radio stations. :(
An RF power supply option is/was also available. (Possibly some version of the SP-200 though the specs don't quite match for the one I have. See the section: Spectra-Physics Model 200 Exciter (SP-200).) This would replace theSP-261A and starter entirely by driving the tube directly with radio frequency energy - 15 W at 46 MHz. Note the greatly reduced power to the tube compared to the 150 to 210 W for the DC discharge! The drive is applied via coax from a BNC connector on the back of the laser to a resonant circuit about midway in the laser head. The two phases of the output of the resonant circuit connect to a pair of 0.1 inch diameter bars running the length of the tube about 0.6 inches from the centerline suspended from insulators.
Unfortunately, many SP-125s that appear as surplus are not good for more than long boat anchors (or as a parts unit for salvage of the optics and frame). Unless the tube has been replaced relatively recently, being soft-seal, it has likely leaked to the point at which the getter can no longer clean up the contamination. Refilling is the only option and that cost would make what you paid for the laser look like pocket change. And, refilling a HeNe tube is generally not a realistic basement activity. So, if you come across an SP-125 at a low price, unless it is guaranteed to lase, buyer beware. An SP-125 sold "as-is" almost certainly means the seller couldn't get it to work (not that everything possible wasn't tried) since they likely know it is worth 10 times as much in operating condition!
Also see the section: SP-120, 124, and 125 HeNe Laser Specifications and Spectra-Physics Model 261A Exciter (SP-261A).
(From: Marco Lauschmann (email@example.com).)
The SP125A is absolutely beautiful with much chrome and a metallic blue cover! It is nearly 2 meters long and looks like an older large-frame argon ion laser. A Spectra-Physica scientist noticed that this device will deliver twice the rated power with no problems. Others have claimed as much as 200 mW for the red (632.8 nm) model!
(Portions from: Phil Bergeron.)
In the trivia department, though perhaps useful if you're going back in time to play with one of these, the single pass gain has been measured to be at least 15 percent on a healthy SP-125A tube. But the 125A lasers were a pain. If the window was not perfectly clean, the power in the cavity was still high enough to make any dust, debris, or other contamination cook on and become tough to remove. Acetone, methanol, over and over, cleaning the windows was no fun. That is why the SP service guys were happy with say 65 mW. It might take a day to get 95 mW.
The tube assembly used in the SP-127 is the same as the SP-107B described above, with the side-arm plasma tube itself typically labelled "082-2 (25 mW), 082-3 (35 mW), or 082- (either). It has optically contacted Brewster windows rather than Epoxy seals, so it should have essentially unlimited shelf life. A brick power supply provides the required 11 to 12 mA at 5 kV, switchable between 115/230 VAC. The case is similar to those used for SP's ion lasers except that the SP-127 has slots on top to view the cheery glow of the bore discharge. :) Mirrors are relatively easily removable and replaceable without requiring major realignment, and swappable to change wavelengths. I'm not sure of all the wavelengths besides red (632.8 nm) that were supported by Spectra-Physics, but orange (604.6 nm and 611.9 nm), yellow (594.1 nm), and the near-IR lines (1,152 nm and 1,523 nm) would likely be possible without also replacing the tube. However, green (543.5 nm) might require a different gas-fill and the mid-IR line (3,391 nm) might require a larger bore to get any sort of reasonable power.
Unfortunately, SP has stopped manufacturing the SP-127 and sold off their parts inventory to Cambridge Lasers Laboratories, Inc., who will still rebuild these (and other SP HeNe lasers) - for a price. :)
The only readily available HeNe lasers with similar output power now are the internal mirror Melles Griot 05-LHR/P-927/928. The newer versions of these are traditional HeNe cylindrical laser heads mounted in a rectangular case, presumably for added thermal stability - or so they look simlar to the SP-127!
The tube inside the lasers in the photos is the typical small Spectra-Physics side-arm type (like those in the SP-155 and other similar lasers also shown on the Web page above) but with Brewster windows instead of mirrors. However, earlier versions may look a bit different with a side-arm for the anode as well and really early versions (SP-130, no B) actually used a heated filament for the cathode (though for some reason, the schematic of the SP130 with the heated filament is dated slightly later than the schematic of the SP130B with the cold cathode design).
Based on the length of the tube, I would have expected its output power to be in the 2 to 5 mW range. However, from the specifications in the manual, it turns out to be only 0.75 mW when used with the hemispherical mirror configuration (planar and 30 cm radius of curvature), but capable of a TEM00 beam despite its wide bore (2.5 mm). With a confocal configuration using a pair of 30 cm mirrors, the beam is multimode (non-TEM00) and output power may be as much as 1.5 mW.
When I obtained the first of these lasers (the one in the top two photos), the tube actually still lit up but there was no output beam. At first I thought it might even have a chance of working since the discharge color looked sort of reasonable, though somewhat less intense than I would have expected. Fiddling with the optics didn't yield any positive results. And then, when I wasn't looking, the discharge went out! As best I can tell, a crack must have opened somewhere in the tube and it is now at much higher pressure or up to air - bummer! I can find no visible damage or any evidence of this except that it won't start even on a much larger HeNe power supply and shows no signs of a glow from an RF source. So far, the getter hasn't changed color.
I don't think this laser was ever really alive - the tube was probably gasy or helium deficient or something but I still can't explain what happened. The only place it could have leaked that I can't see is under the anode connection which is kind of potted but there shouldn't have been any heat there to cause such a problem.
And to compound my disappointment, I dinged the OC removing the tube. Enough of it may be left to still work but the optics appear to be soft-coated as the AR coating came off totally by just barely touching it. However, that still hurts. Sometimes, you just have one of those days. :(
As it turned out, nothing I had done affected the tube. The gas fill was messed up and It was simply very hard to start. A few years later, a major laser service company regased the tube in exchange for a dead large frame argon ion laser (or maybe two of them). After swapping in good mirrors from another SP-130, as of 2010, it is happily lasing at about 0.5 mW. I sent it to my friend in Florida who provided the trade lasers, where it can bask in the Sunshine and will be and well cared for. :) This output power is slightly below spec but it was a chop and pump job so not only was the getter not replaced, but the interior of the tube was not even cleaned. So, 0.5 mW is quite respectable. And, it's even possible that cleaning of the mirrors and better cleaning of the Brewster windows would result in significantly more power. But my motto for lasers such as these is "do no harm". :)
The laser in the third photo was DOA with an up-to-air tube, seriously damaged mirrors (coatings mostly gone), and evidence of prior dissection attempts (cut wires, etc.). The tube in that one is probably one of the earliest non-heated filament types with a small cathode and separate side-arm for the anode.
However, I have since obtained a third SP-130B which originally had a red/blue discharge. But while running for a few hours, the color gradually changed to a mostly correct white-ish red-orange. And, with an optics cleaning and alignment, this SP-130B actually lases. The output power is not up to spec - about 0.25 mW at maximum current (it's rated at 0.75 mW) - but that's still a bit amazing considering its age. See the section: Reviving a Spectra-Physics Model 130B Antique Laser for details. I've had it for over 5 years now (since 2000) and it's output hasn't changed noticeably. I run it for a few seconds almost daily just to let it know that it's loved and that seems to keep it happy.
The internal power supply accounts for much of the weight and most of the height of the box and consists of:
There is no actual starter - the open circuit voltage of the power supply is about 5,000 VDC but drops to around 1,500 VDC under load.
For more info and schematics, see the section: Spectra-Physics Model 130 HeNe Laser Power Supply (SP-130).
Now, the question becomes: Do I leave the dead ones intact as examples of antique lasers or replace their tube and optics with modern 3 mW barcode scanner tubes (about the largest that would fit height-wise, a 1 inch diameter tube) to have working lasers? I guess there's nothing special about 3 mW HeNe lasers so leaving them intact would be the best option. And, it would be a shame to only have 3 mW when the power supply is easily capable of driving at least a 5 mW tube. In order to do a test with an SP098-2 barcode scanner tube (actual output: 2.8 mW), I had to add 500K ohms of ballast resistance in addition to what is built into the power supply to get the current low enough so the adjustment would include the optimum current setting. (I can hear the antique connoisseurs breathing a collective sigh of relief!) Who knows, maybe someone will drop replacement tubes and mirrors in my lap someday! Hint, hint. :)
There is also an SP-130C laser which is virtually identical in construction and function, except for the lack of an external current adjust pot and a row of magnets glued to the bottom of the cover over the bore to minimize losses from the IR lines.
I acquired a few old Spectra-Physics tubes in various stages of assembly (none work). Spectra-Physics 131 HeNe Laser Tube using Neon Sign Electrode Cathode shows one mostly complete sample. (It's missing the Brewster windows though that's hard to see.) I don't know if the SP-131 tube or a similar SP-130 tube were ever put into production. This is the first time I've seen SP tubes with neon sign electrodes rather than hot filaments or aluminum cathodes.
Photos of a typical SP-155 can be found in the Laser Equipment Gallery under "Spectra-Physics Helium-Neon Lasers".
The HeNe laser tube is the classic Spectra-Physics side-arm design but with the anode electrode mounted less than halfway along the length of the bore. The same tube with the anode mounted at the end would produce around 4 to 5 mW. In fact, the Spectra-Physics 157 (3 mW) and 159 (4 mW) lasers are virtually identical except for the tube's anode location and the use of a larger power supply. (The SP-156 is likely similar as well but I haven't seen one to confirm.) This also means that the longitudinal mode structure and thus mode sweep will be similar for all these lasers.
The power supply for the SP-155 is a basic transformer/doubler/multiplier design with a single transistor current regulator. The power supply on later versions of the SP-157 and SP-159 lasers may be a potted brick instead of a discrete PCB but all of the SP-155 lasers appear to retain the older quaint power supply design. :)
Note that other manufacturers sell (or have sold) lasers identical in appearance to the SP-155. For example, there is a Uniphase model 115ASL-1 and a Liconix L-388 (even though it is made by Uniphase). However, these use a hard-seal Uniphase barcode scanner HeNe tube (similar to a model 098 with a tiny collimating lens attached to its OC to reduce divergence) rather than the fancy Spectra-Physics side-arm tube we know and love. But their power supplies are similar or identical to that used in the SP-155. (There is also a Spectra-Physics model 155ASL which is physically identical to the Uniphase and Liconix lasers except for the name on the front. I assume it has the same construction though I haven't seen the insides of one up close and personal.)
Also see the section: Spectra-Physics Model 155 HeNe Laser Power Supply (SP-155).
The RMM355 is multi-transverse mode laser, which in itself is a novelty. This sample has an output power of about 40 mW 8.3 mA. (Yes, that's 40 mW.) The beam is generally circular with what is basically a top-hat profile (more or less flat with ripples), has a divergence of about 2.7 mR, and is random polarized. The model number does include "R" and "MM". :) The RMM355 (which is an earlier model, not listed on the Spectral Web site) is rated at 35 mW minimum output power and typically does 40 to 44 mW after warmup. The current version is the RMM355L which is rated at 42 mW minimum at 10 mA, and typically does 48 mW after warmup. Spectral actually has an even larger model which has a minimum output power of 60 mW!!. Wow, darn, I want one! :)
The laser head is a rectangular aluminum extrusion, capped at both ends with what look like black Plexiglas plates apparently attached with adhesive which has so far resisted my best efforts to remove them. The head is about 2-3/16x2-3/16x34-3/4 inches but the actual tube length is not known. There are no screws or mounting holes anywhere. However, based on the spec'd longitudinal mode spacing of 175 MHz, the tube in the RMM355L has a mirror spacing of about 33 inches - nearly the length of the laser head. I measured the operating voltage on the RMM355 and it is about 3,380 VDC, within the tolerance limits of the spec'd value for the RMM355L of 3,300 V, so the tube length is probably the same. The HeNe laser tube has internal mirrors and is probably of relatively conventional design, but with a wide bore. There is a simple hole in the output cap for the beam to pass (no shutter) and a hole in the rear plate for the Alden cable. I'm sure I could get more power by aligning the mirrors but it doesn't look like there is any easy non-destructive way of getting inside at either end. They seem to be glued all too well. What's the fun without tweakability! :)
Thankfully, regardless of the looks of the power supply box, the actual power supply is a Laser Drive brick, 2900 V at 7.8 to 8.3 mA, adjustable. It was set all the way up on my sample. 40 mW at 8.3 mA isn't too shabby but I tested the laser head using an SP-255 on a Variac and the it produces about 43 mW at 10 mA and 44 mW at 10.5 mA. I have since acquired a power supply that is adjustable via an external pot and goes up to 12 mA (which is apparently acceptable for this laser, at least for a short while). With that, I can get 48 mW at 12 mA. :)
The ML-500 consists of a Siemens two-Brewster (2-B) HeNe plasma tube mounted in a 4-bar resonator frame with adjustable mirror mounts at each end. Tunable or fixed wavelength mirror sets may be easily replaced without requiring significant adjustments. The wavelength selection mechanism uses a BiRefringent Filter (BRF) rather than a Brewster prism as with the more common PMS/REO tunable HeNe laser. The BRF is a quartz waveplate set at the Brewster angle that can be rotated by a precision micrometer. Only when a round trip through the BRF results in the same linear polarization as the plasma tube will there be low enough losses for lasing to occur. Since this is a strong function of wavelength, the orientation of the BRF provides a very precise wavelength selection mechanism with no mixing of adjacent wavelengths as may be present in the PMS/REO tunable lasers) and it eliminates the additional "Transverse" adjustment. However, the 2-B tube and BRF do add 2 additional optics surfaces that need to be kept clean. And the laser case is not very well sealed!!!
Note that the BRF plate is not keyed in its mount. It's just held in plate by a locking ring. If removed, it must be installed in close to the same orientation it was in originally for line selection to be effective since the range of adjustment is quite limited. The orientation is approximately at a 45 degree angle with respect to the baseplate, NOT aligned with it. Getting it close enough is somewhat hit or miss. If aligned with the baseplate, rotating the line selection knob has virtually no effect. The BRF plate is also thin and somewhat fragile. Take care in cleaning.
There's probably no fundamental reason that yellow (594.1 nm) could not be supported with appropriate mirrors and possibly extending the range of the BRF. But green (543.5 nm) generally requires a different gas-fill. Another issue with going to shorter wavelengths it maintaining the TEM00 spatial mode, as they will tend to run multimode give the same cavity geometry. But if PMS/REO could do it, why not S&H?? :)
There are some deficiencies in the design besides the lack of yellow and green. While very solidly constructed, the mirror mounts have rather wimpy springs so it's very easy for the movable plates to not seat properly due to a physical bump. This can happen in shipping so that a laser was working perfectly might appear to be damaged. Just touching the mount will general reseat it. The case seals are also mediocre. While the HR and the Brewster window near it have some additional protection, it's far from perfect. And the OC-end Brewster window, BRF, and OC mirror are totally exposed inside the case and particularly susceptible to contamination. This can also result in a failure to lase after shipping or just sitting.
Since the ML-500 has a hard-sealed 2-B plasma tube, the setup can be used with or without the BRF for general laser lab experiments. In fact, this is the same plasma tube available for such purposes from Siemens (now LASOS), costing around $1,500 new. It should be capable of well over 5 mW at 633 nm with optimal mirrors, though I've never seen that much power at 633 nm from the normal VIS mirror set, probably due to compromises in the broadband mirror coatings and cavity geometry.
My ML-500 has both the visible tunable mirror set and and the IR tunable OC with a fixed 1,152 nm HR. While the brochure simply shows the BRF mounted in a disk calibrated around its perimeter, this laser (and another one I know of) has a micrometer adjustment accessible through the top cover. That makes a lot more sense, except for the lack of sealing of the hole!
While the discharge color of the plasma tube appears perfect by eye, it may be slightly weak due to excessive scatter on the *inside* of both B-windows, cause unknown. Or the scatter may simply be more visible since it may run with higher intra-cavity power (higher reflectance OC). The output power with the red (tunable) mirrors but no BRF installed peaked at just above 2 mW. With the BRF installed, at first all I was able to get were the 3 red lines - 629.4 nm, 632.8 nm, and 640.1 nm with a maximum power at 632.8 nm of around 1.70 mW. The spec calls for 2.5 mW minimum at 632.8 nm, so this isn't that far below it, though I'm, sure a new laser does much better. With more care in cleaning and alignment, the output power at 632.8 nm increased to 1.85 mW with the BRF, and it was then possible to convince a few photons at 611.9 nm to make an appearance. But I have seen no sign of 635.2 nm. It's still possible that better cleaning of all the optical surfaces would result in spec power on all wavelengths.
I know it lases without the BRF with the IR mirror set, and S&H's claim about not requiring alignment when swapping mirrors sets is correct, but that's as far as I've gone. IR is SO boring. :)
A few months after first getting the laser to work with the BRF, I was able to obtain a new 750 mm RoC broadband HR mirror. With this mirror and the original OC, the output power at 632.8 nm using the BRF now exceeds 2.76 mW. (The output power without the BRF is now over 3.3 mW.) (There was a bit of mirror walking thrown in but its contribution was small.) And, a wee bit of the elusive 635.2 nm line appeared! So, I have at least seen all 5 lines, though I don't think any ones other than 632.8 nm are anywhere near spec power. Most of the improvement is probably due to using a curved HR, rather than that the mirror has a better coating or that the original is dirty. And with the two curved mirrors, the spatial mode is no longer pure TEM00 (for at least some wavelengths). So, boosting the power in this way may be cheating. :) The optics remained remarkably clean since the last time I had run the laser despite the relatively non-existent case seals. Simply cleaning the BRF resulted in getting back to the previous best power, and cleaning the front B-window added another 5 percent or so.
Installing the original HR mirror now results in the following:
Output Power Wavelength Measured Spec --------------------------------- 611.9 nm 0.22 mW 0.40 mW 629.4 nm 0.32 mW 0.70 mW 632.8 nm 2.19 mW 2.50 mW 635.2 nm -- 0.10 mW 640.0 nm 0.55 mW 0.70 mW
Initial alignment is best done with the BRF removed. This eliminates the uncertainty of the BRF setting, as well as the additional two optical surfaces that need to be very clean. An external alignment HeNe should be used, first for the HR (with the OC removed), and then for the OC. Both mirror mounts have calibrated (or at least labeled) adjustment knobs. However, I doubt there is any consistency from one unit to the next. Strangely, one knob is for the common screw (not X or Y), presumably to make it readily accessible from the top of the case. However, this could be confusing. On mine, the OC mirror X adjustment is optimal at 9.6 without the BRF and around 9.2 with it installed. If aligned without the BRF, that shift of -0.4 should get close enough to lase at appropriate settings of the BRF. Record the settings for future reference. The adjustments don't keep track of integer turns, but there should never be a need to rotate any of them by more than a fraction of a turn. Needless to say, all the external optical surfaces (plasma tube B-windows and BRF) must be *very* clean. The mirrors don't tend to collect crud like the windows and BRF do, so it's better to leave them alone unless known to be dirty.
Before installing the BRF, place it at the normal (Brewster) orientation between the output of the laser running at 633 nm and a linear polarizer oriented horizontally. Use the BRF micrometer to adjust for minimum transmission. This will set the BRF approximately for 633 nm so when it is installed and the X mirror adjustment is shifted by -0.4, there should be some lasing. Then peak the power. The sensitivity of BRF tuning is around 3.9 nm/turn. So, while the PMS/REO tunable has all the wavelengths (including green) compressed into less than 1 turn, going from 611.9 nm to 640.1 nm requires 6 or 7 turns of the BRF micrometer!
For the record, the mirror alignment settings for this laser are now 6.8 (rear left), 3.9 (rear right), 3.3 (front left), and 9.5 (front right). This probably has no relevance to any other laser in the explored Universe but I won't forget these values if they are here! ;-)
My overall opinion is that while the ML-500 is an elegant laser, for strictly VIS applications requiring multiple wavelengths, the PMS/REO LSTP tunable laser is a better choice with both yellow and green, and higher power for reds and oranges. However, it must be run periodically since the tube is soft-sealed and most will decay on the shelf after a few years.
Except as noted, these are all cylindrical laser heads with lab-style power supplies. Bare tubes are available from JDSU as well. Note that the divergence values for multimode (non-TEM00) lasers, and even whether some are TEM00 or multimode, may not be correct due to errors in both the on-line and printed datasheets I've seen.
Red (632.8 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------ 0.5 mW 0.48 mm 1.70 mR 1090 MHz 1.35 kV 4.0 mA 1108/P 1205 1308/P 0.8 mW 0.48 mm 1.70 mR 1090 MHz 1.35 kV 4.0 mA 1107/P 1205 1307/P 1.5 mW 0.63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1101/P 1201 1301/P 2.0 mW 0.63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1103/P 1201 1303/P 2.0 mW 0.63 mm 1.30 mR 730 MHz 1.80 kV 6.5 mA 1122/P 1206 1322/P 5.0 mW 0.81 mm 1.00 mR 435 MHz 2.35 kV 6-6.5 mA 1125/P 1202 1325/P 7.0 mW 0.81 mm 1.00 mR 435 MHz 2.45 kV 6-6.5 mA 1137/P 1202 1337/P 10.0 mW 0.68 mm 1.30 mR 320 MHz 3.10 kV 6.5 mA 1135/P 1216 1335/P *15.0 mW 0.70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1144/P 1218 1344/P *21.0 mW 0.70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1145P 1218 1345P *22.5 mW 0.70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1145 1218 1345
The models 1508/P and 1507/P are self-contained "Novette" lasers that run from DC wall adapters but have identical specifications to the 1308/P and 1307/P, respectively.
The lasers denoted with "*" used to have slightly higher power ratings but have been downgraded. I guess too many were failing within warranty.
There is also an 1103H laser head. A note says the 1103H is recommended for stabilized HeNe lasers. It is filled with isotopically pure neon and has an internal heater for cavity length control. (Internal to the cylinder, not the laser tube.) But the specs on the heater don't make sense: 15 VDC/3.5 A (52.5 W, standard) and 47 VDC/7.5 A (352.5 W, maximum). That's 5 to 50 times the heater power typically used for a stabilized laser! For this laser, a typical power when locked would be between 3 and 10 W, though it would be higher during warmup. And the standard and maximum values do not exhibit a linear relationship, though that't perhaps due to the increase in resistance of the heater when hot.
The next set is what were found in the PDF on the JDSU Web site in 2011. Most of the specifications are the same except for operating voltage (maybe JDSU calibrated their HV probes!) but a few models are no longer present:
Red (632.8 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------ 0.5 mW 0.48 mm 1.80 mR 1090 MHz 1.25 kV 4.0 mA 1108/P 1205 1308/P 0.8 mW 0.48 mm 1.70 mR 1090 MHz 1.25 kV 4.0 mA 1107/P 1205 1307/P 1.5 mW 0.63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1101/P 1201 1301/P 2.0 mW 0.63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1103/P 1201 1303/P 2.0 mW 0.63 mm 1.30 mR 730 MHz 1.80 kV 6.5 mA 1122/P 1206 1322/P 5.0 mW 0.81 mm 1.00 mR 435 MHz 2.30 kV 6.0 mA 1125/P 1202 1325/P 7.0 mW 0.81 mm 1.00 mR 435 MHz 2.30 kV 6.0 mA 1137/P 1202 1337/P 10.0 mW 0.68 mm 1.30 mR 320 MHz 3.10 kV 6.5 mA 1135/P 1216 1335/P 17.0 mW 0.70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1144/P 1218 1344/P 21.0 mW 0.70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1145P 1218 1345P 22.5 mW 0.70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1145 1218 1345The models 1508/P and 1507/P are self-contained "Novette" lasers that run from DC wall adapters but have identical specifications to the 1308/P and 1307/P, respectively.
Green (543.5 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 0.25 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1652/P 1207 1352/P 0.50 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1653 1207 1353 0.50 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1673P 1208 1373P 0.75 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1654 1207 1354 1.00 mW 2.50 mm ?.?? mR NA-MM 2.25 kV 5.5 mA 1654M 1207 1354M 0.75 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1674/P 1208 1374/P 1.00 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1675 1208 1375 1.50 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1676 1208 1376 1.60 mW 2.70 mm ?.?? mR 325 MHz 2.70 kV 5.0 mA 1676M 1208 1376M
Yellow (594.1 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 1.00 mW 0.73 mm 1.00 mR ?? MHz 2.25 kV 5.5 mA 1677 1207 1377 1.50 mW 2.50 mm 1.00 mR NA-MM 2.25 kV 5.5 mA 1678 1207 1378
Orange (611.9 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 3.00 mW 0.74 mm 1.10 mR ?? MHz 2.25 kV 5.5 mA 1679 1207 1379
The "M" versions for the above lasers are apparently multimode but with incomplete specifications. (The "M" here is apparently not the same as for the ones listed below.)
The next set is what are currently found in the .pdf on the JDSU Web site in 2011. Most of the specifications are the same except for operating voltage (maybe JDSU calibrated their HV probes!) but a few models are no longer present:
Green (543.5 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 0.25 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1652/P 1207 1352/P 0.50 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1653 1207 1353 0.50 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1673P 1208 1373P 0.75 mW 0.70 mm 0.98 mR 441 MHz 2.25 kV 5.5 mA 1654 1207 1354 0.75 mW 0.80 mm 0.86 mR 325 MHz 2.70 kV 5.0 mA 1674/P 1208 1374/P
Yellow (594.1 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 1.00 mW 0.73 mm 1.00 mR ?? MHz 2.25 kV 5.5 mA 1677 1207 1377
Orange (611.9 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 3.00 mW 0.74 mm 1.10 mR ?? MHz 2.25 kV 5.5 mA 1679 1207 1379
Some of these laser heads have an "M" version (or only come in an "M" version) which have 2 inch diameter mounting rings permanently attached.