Which red to use?

[Doc]

473 then

[FourDee]

Ah, but 445 has better modulation characteristics

[buffo]

I think the optimal solution would be to have a little of both.

I've seen a few projectors that have had only 445 nm diodes in them for blue, and I can tell you that I immediately missed the brighter blue that you get with a 473 nm DPSS unit. Sure, that deep 445 nm blue is pretty, but you ALSO need the brighter blue in my opinion.

The only way I'd ever put a 445 nm blue in a projector is if it already had a 473 nm blue in it.

Adam

[heroic]

I've been playing with diodes and DPSSes at a few different frequencies for a while now. This is my take:


405nm - violet. Makes things fluoresce nicely- almost like a blacklight laser, but doesn't make people's teeth glow (they hate that). Photometrically, not very bright per watt of output. Needs a LOT of fog to make a good beam effect (short wavelengths scattering). Diodes have small emitters so you can get good beam specs. Diodes are used in Blu-ray burners so they are cheap. Good modulation is available. These diodes are unbelievably sensitive to static discharge so be careful. The fluorescence from hitting day-glow or phosphorescent material will be several times brighter to the eye than the spot from the beam itself; haven't quite worked out how to use this to my advantage yet. Even 'broadband' dichro mirrors don't reflect it very well (it approaches the bandgap of TiO2) so you probably want aluminized galvo mirrors if you are going to be using a lot of this.

440nm - deep royal blue. Beautiful colour but the diodes are expensive. Beam specs available are not as good as 405 but still pretty good. Diodes are used in photostereolitho machines and dental epoxy curing devices, so not as cheap as the 405nm diodes, but they tend to come in higher powers. Modulation is good, like all direct injection diodes. Beams are not as visible as 473. Will make things fluoresce but not as good as 405.

473nm - bright blue with just a hint of greeniness. DPSS so lasers are large and annoying to modulate. Noisy at the lower end. The most visible blue, you get more bang for what is often a very large amount of bucks. Lots of speckle and sparkle; lasers are temperature sensitive in the extreme, taking a long time to warm up. Expect to burn a lot of power to get a couple hundred milliwatts of light. Used in some lab applications. 473 will charge phosphorescent materials but the reflected spot is far brighter than the fluorescence and so you won't be able to see the effect til the laser turns off.

532nm - good ol' YAG green with just a hint of yellowiness. Visible in the extreme, you need maybe 1/2 as much of this as you have 473nm blue... everyone knows what this is like. DPSS is horrible for modulation. Much more efficient than 473nm SHG DPSSes but still not as good as the diode lasers.

Nobody seems to be making green direct injection diodes yet so DPSS is your only option unless you like argon.

635nm - orangey red. The most visible red diode colour, but the beam specs are somewhere between 'diabolical' and 'awful'. Expect modehopping at low powers. These diodes are big fat multimode diodes used for medical sensing applications and I'm not sure what else. Expect also to lose most of the beam off the edges of your galvo mirrors. Noticably orangey, restricts gamut somewhat.

640nm - still orangey but less so, highly visible and now available with really good beam specs. These diodes are used in DVD-RW drives, so they are small emitter types and pretty cheap. Probably the best of the red diodes, but again, gamut will be restricted because they're not so deep red.

650nm - like the red of oxygenated blood, these diodes are used in pointers (low powers) and in DVD drives (higher powers) so they're extremely cheap and have pretty good beam specs available. Work well with glass optics. Good modulation is available and the diodes are well characterized since they've been around so long.

660nm - intense ruby red, diodes are used in DVD-R drives, pretty good beam spec, deep red, not so visible as 640 or 635 (on the order of 1.6:1 I guess) but diodes are cheap and available in high powers. Emitters are small and diodes are not multimode so they modulate well and you can get good results. Dichros are available to mix 660 with 635 so that may work in your application if you can't use a lot of power but need high visibility.

671nm - DPSS red, great beam quality but not very visible at all, horrible power consumption compared to diodes, DPSS modulation as usual sucks, not as noisy as the blue or green DPSSes but still pretty noisy. Long coherence lengths are available if holography is your thing, but generally to be avoided since these lasers are expensive. Used in some forms of microscopy and spectroscopy. Deepest visible red, but you lose brightness of course.

[Pitts]

Hi some of these issues I have struggled with over the last few years..

This showthread.php?t=5492&highlight=445 does show why the 445 certainly helps, however I have both 445 and 473 and there is no doubt that the 473 is "brighter" side by side corrected for mw. There is however an argument that 445 makes a nice white. There is further argument that mixing some 445 with 473 and may be even some green may give a better result. I am doing this right now but the dichroic glass filter is a bank buster.(for its size).
[IMG]file:///C:/DOCUME%7E1/user/LOCALS%7E1/Temp/moz-screenshot.jpg[/IMG]
Also on the subject of red be careful here... although I have no doubt that the 640 diodes are nice you do have to ask what happens when they get "combined" into one beam, which is in reality a collection of closely spaced beams appearing as one (or close to) it has no choice but to get "fatter"..
This seems to vary from manufacturer to manufacturer. Probably at lower powers this is not such a problem.(using less diodes)..

Plenty of good threads here on this subject try some searches you will probablly dig up what you need.

Cheers

Ray
NZ

[gamble901]

Wow thanks guys that really helps out a lot! A big question though, what is modulation? I see that word being used a lot here and I can't say I know what it means.

[heroic]

Wow thanks guys that really helps out a lot! A big question though, what is modulation? I see that word being used a lot here and I can't say I know what it means.

Modulation means intensity control. It comes in two kinds- analogue, which is continuously variable between off and full brightness, and digital, also known as TTL, which is either on or off.

[p1t8ull]

640nm - still orangey but less so, highly visible and now available with really good beam specs. These diodes are used in DVD-RW drives, so they are small emitter types and pretty cheap.

Thats interesting.. I didn't know 640's were used in RW drives.. I wonder which ones they use? any more info?
Unless they have improved the spec the Mitsubishi ML520G51's have awful divergence - not much good for lightshow use, the Opnext/Hitachi HL6385DG's are the ones to get

[heroic]

Thats interesting.. I didn't know 640's were used in RW drives.. I wonder which ones they use? any more info?

They seem to show up in the drives that support DVD-RAM, but asides from frequency I don't know what type; the two examples I've seen weren't marked and I at first thought they were 635 (from the colour) until I checked them on a spectro and they turned out to be right around 640 nm.