Omnichrome 532/150T

[mixedgas]

Based on years of looking at such spots, my bet is you have one very dirty optic in the system somewhere. Hence the horizontal ellipsis in the beam.

You might want to walk the mirrors before changing optics.

I see a lot of gain based on the flash, and your tube voltage is not typical of a low pressure error. Hence don't panic yet.

The camera does exaggerate the flash a bit. The AGC / Gamma Correction simply doesn't know how to deal with that bright spot.

I'll see what I have in parts and get back to you.

UHP grade in my case comes from a carefully developed relationship with a chemical supplier who can drop ship gallons. I pay the Hazmat when I can afford it.

The copper "hot dogs" are filled with silica gel. Yours do not look like the older shape which was spun, not soldered/brazed. . So before I reassemble I remove them. I first heat them with a moving torch to outgas, then oven bake out according to Silica Gel procedures. In your case you can just bake, rather then risk opening the solder with a torch.

Usual culprit on the head light card is the 2n2222A emitter follower following the light opamp. OK to replace with a Plastic Package if you can't get a "A" model. The metal case is preferable, but not so available. Its not worth an extra 20$ to obtain one. 2n3904 is a reasonable sub. Any small signal NPN @ 125/250 mW capability with a good Beta will do.



Steve

[Xenonion]

Okay, there is a large amount of specular reflections around the central laser spot. The search for suitable solvent continues.

The system seems to be performing very well for it's age. The tube has cut out a few times when running at idle, but restarts without issue. The tube has run for maybe 2 hours tops at this point.

Replaced the 2N3019 with a 2N3904 this evening. Turns out it's a user error and not the light board. The connector was setup for the head potentiometer (connector pins 3-4) instead of the power supply potentiometer at full power. Changed the jumper to pins 2-3, and the light response works fine. Between "2 mW-25 mW" output, at between 4-9 amps, of course the light output is only relative since no calibration has probably lasted. This is consistent with the part number 532-BS-(A03?), single line 25 mW output.

The other laser head taken apart is an older version, but designated only 532. The optics look cleaner, might try switching the optics over though the reflectivity/transmission look very similar to the functioning head and I suspect they are also 488 nm optics. Do you know the diameter of these optics off hand?

The silica gel chambers are like you say assembled instead of spun cylinders. Not convinced that they are actually soldered, they have a harder silicon sealant around the joints. My suspicion is that they are actually plumbing fittings. I'll bake them out when I reassemble after cleaning the optics. These are definitely the budget lasers, any idea what typical application these got put into? Most I've seen are for confocal or other microscopy.

Take Care,
Mark

[macona]

Get yourself a battery powered scope for working on these. I have an Owon HDS242S handheld scope/dmm and it's great. Rated to 40MHz but will go faster. Decent battery life too.

For cleaning optics I have been using the firstcontact polymer cleaning kit. It's not cheap (~$100) but it will last you a long time. Ive used it on everything from CO2 laser optics to gratings. We use it at work too. (we design and build laser micromachining systems)

[Xenonion]

Macona, thank you for the suggestions. I should have gone for the battery powered scope instead of the isolation transformer.

The first contact website doesn't have the small kits, but looks like Edmunds does. Still ~$100 after shipping, but is far better than trying to source the solvents.

Installed the new parts in the broken power supply, see picture.
Mosfets: IXFH26N50P3 (to replace the IXFH24N50)
D20 (MUR1560G), C35 (220µF, 250V)

Everything looked good from the checkout standpoint. Rails were: ± 15.2 volts, IC2 pin 7 14.673v, IC2 pin 1 14.343v, TP2 ~94khz at 72% duty cycle. Gate drive signal looked okay, captured a screenshot. Powersupply was in current limit mode.
Turned key, system powered on and laser started normally. As I'm adjusting the current (no meter connected), within 30 seconds of power on BOOM! Q8 let all of it's smoke out at once. Powered the system down and called it a night.

Couple of things to chase, I didn't actually look at the drive waveform or duty cycle to see if it was at voltage. Just used the multimeter functions, to get frequency and duty cycle at the tap point. Along the same lines, the checkout says this frequency should be between 100-110khz so technically low.

Q8 was initially blown in the powersupply, so this might be a deeper problem and I'll have to do more exploring and parts testing to determine where the fault is.

As a side project, having two laser heads one with a low pressure tube. Took the optics from the non-working tube and put them on the working tube and aligned them with a small hope that the other optics were multi-line. After alignment, they are not but the alignment experience was good to have.

Mark

P.S. mixedgas I'm still interested in anything ya want to part with.

[macona]

These old air cooled ions are fun. I have an ILT 5500A that I have used occasionally as a space heater in the garage. It does have the multiline mirror set. I used to have an old spectra physics that had the line selecting prism on the rear mirror which was pretty cool. Argons have some of the prettiest colors.

[Xenonion]

These old air cooled ions are fun. I have an ILT 5500A that I have used occasionally as a space heater in the garage. It does have the multiline mirror set. I used to have an old spectra physics that had the line selecting prism on the rear mirror which was pretty cool. Argons have some of the prettiest colors.

You are absolutely correct. The mixture of high voltage start, high power running, and wonderful variety of colors makes them a joy to mess around with. Like you I used to have several other lasers which for various reasons and situations had to go. Used to have a Innova 90, as a college kid, of course no way to power it no remote or frankly place to keep it, picked it up from university surplus.

[Xenonion]

Following the pyrotechnics show from the FETs, that power supply was shelved. Only have one functioning head, if I get another potentially running, I’ll attempt to repair the blown power supply. The other low hour tube I have (~200 hours) still doesn’t strike, have been running the filament for hours in a vain hope to get it to strike.

The next step for the functional head, was to put multi-line optics in place. Found some on ebay and after the USPS wandered around with them for awhile finally got them installed. Admittedly, the alignment is bad, quick and dirty (still need to get cleaning materials) but it does lase. The optics specifics are: 514-457 nm 60 cm RoC HR+OC, HR-99.5-99.8%R, OC-97.2-97.8%R, I did not grab a picture but they are dark optics. I’ve included a picture of the single line 488 nm optics I took out where the OC is almost completely transparent. There’s also a picture of the laser with the single line optics running and static.

After installation, I was so bummed the tube was running at idle ~4amps and only 488 nm was visible so more power. At 10 amps the tube gives 5 lines after warmup! As a curiosity, what is a crude relationship between lines and current on this old tube.

<7 Amps – 488 nm
7.3 A – 488/477 nm
8.1 A – 477/488/497/515 nm
10.7A - 458/477/488/497/515 nm

After doing that, I adjusted the optics with a significant power increase, so this really isn’t relevant just curious.

The laser is in current mode now, which really demonstrates how unstable the plasma is visibly changing as the laser runs. The tube is still low hours (1994 manufacture), at 473 hours and I have only put ~10 hours of operation on the head since I got it. I’ll need to run it a lot longer to get the pressure under control in the tube. A couple of questions.

Does the tube need to have the end caps and desiccator tubes installed? I presume these are for harsh environment operation? Or are the tube seals susceptible to humidity and fail without containment? I’d rather not put the covers back on, to avoid any possibility of breaking the Brewster stems.

Now that I have new optics, and lots more output than the 25 mw spec, the optical feedback system is going to be overwhelmed. Has anyone either reduced the signal from the sensor or changed the feedback board potentiometer settings?

A minor aside, as the head heats up the fan blades thermally expand and start rubbing on the housing. I’ll need to modify it but might be reason for the laser to be low hours and in relatively good condition, because it is loud.

Thanks again to everyone for the suggestions!