Closed-loop power control of lasers

[heroic]

In the end, it's still a good project and a useful tool, especially for getting accurate greys.

I am specifically closing the optical/modulation loop. I'm having some problems tuning the PID filter but I think I can get it close enough to work... maybe next week I'll be able to try some slow scans and if I tighten up the code enough it should work out. The sensor is fast enough to detect > 100 kHz and the modulation input is rolled off at about 15 kHz on my lasers, so I should be able to get a really tight light mode loop.

[FourDee]

Why do you insist on implementing this crcuit in a digital way, while this could easily be solved in an all-analog way?

[heroic]

Why do you insist on implementing this crcuit in a digital way, while this could easily be solved in an all-analog way?

Because a microcontroller costs $1, a photosensor costs twenty cents, and the DAC I am using costs 75 cents. It's cheaper than the alternative, and it always has perfect linearity. Plus, there's enough power left over in the microcontroller to do thermal control.

[Pangolin]

Still, is promising, no?

Yes, I am sure for stable lasers, such as normal laser diodes, and even some well-behaved DPSS this can be made to work. There is already a product that does the very thing you are doing called "Iris color". It was mentioned in a previous post. He does it digitally as well.

Bill

[DZ]

Heroic, how are you progressing on this? I've been thinking of working on an analog loop for solid state lasers, but I'd like to see how you've been progressing with the digital solution. I think this would be the final key to having a solid state laser projector equal or exceed the output quality of a pcaom/gas system.

[heroic]

Hey DZ,

I got the hardware mostly working, but then reality intruded and I had to work on stuff I actually get paid to do, so I didn't progress from there. It's still on my bench now, though, and I have some pretty cool scope trace files showing what I'm contending with.

I hope to make a little more progress in a week or two but right now I am afraid I have to oil the wheels in the biggest machine a little. :-/

[DZ]

Ah, I do know the feeling. Well keep up posted, I'm very interested. I'm probably going to tinker around with an analog version to see what I can come up with. Thanks!

[dsli_jon]

Hey heroic -

you might be interested to know that Eye Magic also sell a system to accomplish this. I believe it uses a PID loop, similar to galvo feedback.

http://www.eyemagic.gr/laser-iris-colorsafe.html

As Biil B and others have mentioned, from-what I hear, the 'Iris' works pretty-well... I have-been trying to think of a reason to justify buying one just to check it out, for awhile - you up for a mini 'R-E project'?

I fund it, you test it (I'm too stinkin busy... ) and report to PL, et al / perhaps learn something different / validate your own ideas / approach, etc.. We would just have-to do it on a 'You fry-it, You buy-it' basis, whattaya think?

PM-me or just post your thoughts... if not interested, that's cool, too I'll get one of those 'Round Tuits' one of these days...

peace..
j

[heroic]

Hey heroic -



http://www.eyemagic.gr/laser-iris-colorsafe.html

As Biil B and others have mentioned, from-what I hear, the 'Iris' works pretty-well... I have-been trying to think of a reason to justify buying one just to check it out, for awhile - you up for a mini 'R-E project'?

I fund it, you test it (I'm too stinkin busy... ) and report to PL, et al / perhaps learn something different / validate your own ideas / approach, etc.. We would just have-to do it on a 'You fry-it, You buy-it' basis, whattaya think?

PM-me or just post your thoughts... if not interested, that's cool, too I'll get one of those 'Round Tuits' one of these days...

peace..
j

Hmmm... that sounds like it might be fun. The only question is whether it fits in my enclosure It's pretty compact in there.

I'm definitely interested, how much do they cost? (Don't worry, I won't fry it...)

[drlava]

You might be able to reverse and learn something from the circuits but the code in that atmel is probably locked down. Your time might be better spent testing and improving your own version, but at least you'll be able to compare the two and help improve yours in the process.