Slow "analog" attenuation methods

Hey guys, I have a couple of 591nm laser modules that I would like to put into my lumia projector. I like to fade in/out my lumia effects and also control the brightness. These summation lasers don't work well, or at all, at low power levels so fading/attenuating via modulation is out. Since we're talking gradual fades over the course of a half second of more, I don't need fast "blanking". What's a good way to mechanically attenuate a beam? I know in the good old days it was either a galvo/retro reflector or an AOM. I have some of the old Stocker Yale GM20 knock-offs. I was thinking of just using a flag on one of those guys. Since the beam is going into lumia glass, I don't think I need to worry about aberrations from the edge of the flag, right? If anyone has a better idea, please let me know.

If you are OK with slower response, you can get completely adjustable attenuation using a pair of polarizing filters. Mount the first one in a fixed mount, and the other one in a rotating mount such that you can rotate it up to 90 degrees. Start out with both filters aligned in the same direction (both horizontal or both vertical). Then, as you rotate the second filter, the beam will slowly fade to zero as the second filter approaches 90 degrees. Speed limit is based on how fast you can rotate that second polarizing filter.

Flag blanking is much quicker, of course, but it won't give you smooth fading.

The other option would be to use an AOM; you can find cheap surplus units on Ebay from time to time.

Adam

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Originally Posted by buffo

If you are OK with slower response, you can get completely adjustable attenuation using a pair of polarizing filters. Mount the first one in a fixed mount, and the other one in a rotating mount such that you can rotate it up to 90 degrees. Start out with both filters aligned in the same direction (both horizontal or both vertical). Then, as you rotate the second filter, the beam will slowly fade to zero as the second filter approaches 90 degrees. Speed limit is based on how fast you can rotate that second polarizing filter.

Flag blanking is much quicker, of course, but it won't give you smooth fading.

The other option would be to use an AOM; you can find cheap surplus units on Ebay from time to time.

Adam

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Thanks, Adam. I didn't even think about using polarizing filters. I'll most likely go down this route.

Thinking about this a bit more - you don't really need to secure the second filter in a mount... You could stick it on the end of a short servo arm and just let it rotate through 90 degrees that way. (Assuming your filter was large enough, that is.)

Adam

The flag will work just fine, and without the losses involved with 2 polarizers. Can the lasers handle pwm? A reasonably fast strobe won't hurt low speed lumia.

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Originally Posted by laserist

The flag will work just fine, and without the losses involved with 2 polarizers. Can the lasers handle pwm? A reasonably fast strobe won't hurt low speed lumia.

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I was thinking about that, they might be able to. Summation lasers are pretty far outside of my knowledge as far as theory of operation. I know they are power/temperature sensitive so, it's possible that it will work. I'll see how the flag method works. I would like to preserve as much power as possible since these are only 30mw and I need every precious mw! Thanks again!

Surprised nobody has mentioned ND wheels/variable beam splitters. Bonus: you get a waste beam to do "whatever" with.

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Originally Posted by CountFunkula

Surprised nobody has mentioned ND wheels/variable beam splitters. Bonus: you get a waste beam to do "whatever" with.

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i put it in my pocket for later.

How about an open "V" slot cut into a metal rectangle and painted w/flat black Krylon based on something like this:

Attachment 61079

Although this shows an early, rotating beam chopper wheel of mine that was moved into and out of beam path with a motor driven lead screw, it worked great as a beam attenuator at high rotational speeds as the beam diameter entered the very narrow tip of the "V". This disk was made of 1/16th inch flat cardboard, painted flat black, hot glued onto a 12v motor shaft hub and used with a 1 watt mixed-gas ion laser. (Metal would be better, but I never had a blade catch fire in the two years of use in planetarium laser shows. A/O's eventually replaced this.

For a simple analog attenuator for one beam only one "V" is needed. The hard part is coming up with a way to move the open "V" slot in and out of the beam path.

hint: DC motor driven lead screw.

For attenuation the "V" would only need to be an inch long, with it's widest part just a bit larger than the beam diameter.

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Originally Posted by lasermaster1977

For a simple analog attenuator for one beam only one "V" is needed. The hard part is coming up with a way to move the open "V" slot in and out of the beam path.

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I plan on using a Stocker Yale actuator (a poor man's GM20). I should be able to gradually apply voltage in small increments, inducing very minute deflection. This should give me decent control of the flag. I'm curious now about the shape of the edge of the flag. Perhaps I'm overthinking this for attenuating a beam that's only diffusing through lumia glass. Outside of modulation, I haven't had to mess around with the "old school" tech before!

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Originally Posted by absolom7691

I plan on using a Stocker Yale actuator (a poor man's GM20). I should be able to gradually apply voltage in small increments, inducing very minute deflection. This should give me decent control of the flag. I'm curious now about the shape of the edge of the flag. Perhaps I'm overthinking this for attenuating a beam that's only diffusing through lumia glass. Outside of modulation, I haven't had to mess around with the "old school" tech before!

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I'd like to see what your Stocker Yale actuator looks like. I found one of their linear actuators on line but not much else.

We just used thin aluminum strips cut from a soda cans with General Scanning servos for image blanking or beam flags. I posted photos of this on PLF somewhere. On the old school tech methods I found the edge shape or thickness didn't make much difference as long it was flat black. .o62 aluminum sheet stock worked great. Neither of these methods caused beam flares as they went from open to close.

This is the guy, R4-077. They look similar to the beefy GS open loop galvos.

Attachment 61081

I actually found a datasheet that I had posted here a few years ago in this thread: https://www.photonlexicon.com/forums...Loop-Amplifier

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Originally Posted by absolom7691

This is the guy, R4-077. They look similar to the beefy GS open loop galvos.

Attachment 61081

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Awesome and BEEFY! I was unfamiliar with these.

Thanks

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Originally Posted by lasermaster1977

Awesome and BEEFY! I was unfamiliar with these.

Thanks

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In the past, I found that they performed about a 1/4 as well as the g-124s, even as big as they are!! (Of course, that's as-is not comparing to g-124s with the accelerator cards). They are tanks, though!

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Originally Posted by absolom7691

I actually found a datasheet that I had posted here a few years ago in this thread: https://www.photonlexicon.com/forums...Loop-Amplifier

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Oh yeah, like those sold by Laser FX, Laser Show Systems. I'd forgotten our PLF info exchange in that thread. (I just found Laser FX's weblink on the R4-077).
Who else sells them?

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Originally Posted by lasermaster1977

Oh yeah, like those sold by Laser FX, Laser Show Systems. I'd forgotten our PLF info exchange in that thread. (I just found Laser FX's weblink on the R4-077).
Who else sells them?

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At this stage in the game, I have only found NOS. Kevin (Junktronix) is who I bought mine from. https://www.photonlexicon.com/forums...344-Junktronix

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Originally Posted by absolom7691

At this stage in the game, I have only found NOS. Kevin (Junktronix) is who I bought mine from. https://www.photonlexicon.com/forums...344-Junktronix

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Thanks. I guess they are a pretty old item now.