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ArcticMyst Security by Avery

RGB laser DIY help

Joined
Mar 5, 2012
Messages
942
Points
28
Hello all.

So I want to start a new project, a RGB laser, in a lab style host.
I'm going to be using Dichros, and 50mw Green, a 40mw 445nm blue, and a 180mw red.

Now, I see 2 major problems;
One, is the different beam diameters. I'v never had a 445nm before, so I cant say how big it is, but a green will definitely be the thinnest, and the red will be quite big, this will create beams that have a messed up outer edge, so say for example I make a yellow, the green will be tiny and the red will create a red outer layer, instead of all yellow. How can I fix this? I had the idea of putting there red laser through a hole, so only a small portion of the laser gets through, but this will (apperantly) give me horrible divergence, so I dunno.

And second, the power supply to the 3 laser modules. Each laser will need different volts, the green about 3, the red about 5, and the blue, well, I dont know that one, so will I need to use seperate power supplies to power each laser?

If I only need one power supply for all 3 lasers, then when I switch just one laser on, will the extra power kill the lasers? so say the power supply puts out 18v and I switch on a green laser which needs 3v, will the cicuit compensate for the extra 15v, or will the green get all 18v?

I know these are noobish questions, but I just want to clarify before I drop money into this project, better safe than sorry :beer:

Thank you

P.S: Sorry if in wrong section.
 





ARG

0
Joined
Feb 27, 2011
Messages
6,772
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Get single mode diodes for the red (638 or 660) & blue, the beam specs will be so much better and will align a lot better as well. What you are describing with the overlapping is called fringing. So far as I know there isn't a way to correct that, just get the beams to match up as best you can.

You will need separate drivers, but you can use one power supply.

The driver will regulate the current, it wont fry the lasers using one at a time. IMO the best way to do this is to use 12V 1A PSU and get 3 x-drives. (Not sure if they can handle 18V)
 
Joined
Oct 26, 2007
Messages
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ARGLaser is right: the best place to start is with lasers that already have good beamspecs. Some lasers just aren't going to combine very well, such as green lasers and diode lasers, because the green lasers are DPSS and have smaller beams. Likewise, the multimode laser diodes like the higher powered 638nm and 445nm lasers have terrible beamspecs (especially the 638nm) and need extra optics to correct them.

If you're making a projector, sometimes you can adjust the focus according to the distance to the target surface to make the dot somewhat better aligned, but even that may not work well.
 
Joined
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Thanks for the suggestions guys. I did consider single mode diodes at one point, but they would increase the cost of the whole project, as the cheapest I could find were like $50 each. Dave offered me a $20 decanned blue, so I was going to get that, a LPC-815 and a 50mw green from somewhere. Is the beam specs for the 815 really that bad?
 
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No, the LPC-815 actually has relatively good beamspecs. The red-laser diodes with poor beamspecs are those Mitsubishi 638nm laser diodes that have different divergences in each of their axises that give the beam a bar-shape.

The problem with the LPC-815, or really any of the 655nm/660nm laser diodes is that they're just not that bright compared to ~635nm laser diodes. They also have an upper limit in their output power, so you can't just throw more power at the problem without also adding more laser diodes and doing some beam combining.

That's why you'll see some of the pre-made projectors, like the Reke500, use two 660nm laser diodes combined using a polarized beam-combing cube. Other projector makers have taken a different route and use the Mitsubishi diodes, which produce a brighter beam with less power, but with a bar-shaped beam/spot.

Personally, I've been trying to get those Mitsubishi 638nm lasers to work for the red channel instead of working with 660nm lasers, which just aren't bright enough for color mix I'd like. The problem with those lasers is, of course, that the beam needs to be corrected or else it looks terrible.

If you want to go with 638nm diodes, you can try some of the long-focal-length lenses that Lazeeer sells. They produce better beams by essentially chopping off the sides of the beam. While this sound bad, those laser diode produce so much light that it is still quite usable. The "correction" isn't perfect, but it's usable for shorter distances.
 
Joined
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I don't think brightness will be much of a problem, I'm not trying to create a projector or anything, more of a lab laser which can have 7 colours of laser beams, so the beam diameters are quite important as otherwise it will look like a weird beam, I have seen setups on YouTube with 2 reds, combined using a PBS cube. I need about 180mw of red light (according to dave) , and the LPC-815 is capable of around 300mw, so it should be fine, my only problem would be the beam diameter of the red and blue compared to the green, so how do I compensate for that?
 
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Joined
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At those power levels you're dealing with it probably won't matter. Still, brightness matters if you want a proper mix of colors, and even with experimental lasers it's nice to be able to get that right color mix so your beam doesn't look too blue or green. 638nm is about 5-10x the brightness of 660nm depending on your dark adapted vision and gives you quite a bit of room to play with. To get a proper mix you'll need to drop the power of the other channels.

For correcting the beam diameter, you'll probably have to live with what you have or purchase some specialized beam-correcting optics. I'm not even sure what would be required for green or how much they'd cost. You'll soon discover just how expensive all these optics are and what a pain they are to align, etc.
 




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