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Thread: Light Feedback for Blue and Green.

  1. #1
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    Default Light Feedback for Blue and Green.

    Ok, I own red diode and green dpss, (oh hell, I have 800 mW or so, 500 of it red)
    But mine are fast.I was just watching 300EVILs video of SELEM and it dawned on me, blue is very, very, bad when your watching 6 RGB systems running at once. If I made up a simple light feedback board and sensor pickoff, would somebody or somebodies test it? The idea being it will somewhat linearize the blue response and possibly speed it up. This is a standard thing in the scientific laser world, I'm suprised it never made to to the low cost DPSS market.

    Input voltage would be 0-5 and output would be 0-5, and I'd make sure a protection zener diode clamp circuit was installed so your laser never saw more then 5V. A small second order 65 khz filter low pass would stop any possible oscillations and protect the driver from too sharp a pulse.

    Any takers? I cant afford SS blue for a long time, and have argons, but it might make things better for the rest of you.

    You would be using your existing driver, just adding the light loop to your normal input.
    Its gonna slam 5V into the blue until it comes to the right power level, the magic of negitive feedback!

    It should improve linarity and speed. Normally I would do (and have done this in the past) with 6x oversampling PWM, but most blue drivers are not that fast. The PWM technique results in steps of equal lumenosity, which is beautiful, but if the driver cant do on/off at 350 kilohertz, its a waste of time unless you put a AOM in front of your blue. Past tests in the mid 90s with a input ADC sampling at 500 kilohertz, running into a digital 8 bit PWM system using counters and comparitors, which then modulated a TTL input AOM. I couldnt afford a analog AOM at the time and printer AOMs were 50$ used with driver. This resulted in ultra smooth fades as we could change color 6x per point or more. But I digress.


    I will of course test it on my DPSS greenie b4 I send it 2 U

    Steve Roberts
    Last edited by mixedgas; 09-12-2008 at 12:02.

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    eyemagic have a board that does just this

    Go for it Steve, we would be more than happy to test it, or even help build it
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    Sign me up!
    I can also help with electronics if needed

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    I've been thinking of making something along these lines, mainly to get rid of the lumps and kinks in the voltage to intencity curves for both DPSS and direct diodes, particularly when TEC cooling hasn't started working after lasers have been on standby for a while.
    Avago make an interesting RGB sensor that might work well:
    ADJD-E622-QR999
    http://www.avagotech.com/docs/AV02-0826EN

    B.

  5. #5
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    OK, I'm out of town for 5 days, but coming soon, light feedback, based on a proven lexel design. We'll build two or three of them in parallel.

    Steve

  6. #6
    mixedgas's Avatar
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    Quote Originally Posted by fuzcub View Post
    I've been thinking of making something along these lines, mainly to get rid of the lumps and kinks in the voltage to intencity curves for both DPSS and direct diodes, particularly when TEC cooling hasn't started working after lasers have been on standby for a while.
    Avago make an interesting RGB sensor that might work well:
    ADJD-E622-QR999
    http://www.avagotech.com/docs/AV02-0826EN

    B.
    take a look at the crossover between the blue and green curves at 532 nm :-(

    nice try, other companies make one, find one that doesnt cross over at 532, that is your mission, should you decide to accept it :-)

    Steve

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    Absoultely. In fact, I just made a modulation test setup that measures linear response to command signal, to get at this very issue.

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