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Thread: Fading Lasers without modulation, optically

  1. #1
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    Default Fading Lasers without modulation, optically

    I want to be able to fade in and out my lumia effects, but don't want to get into analog modulation. I have them TTL control currently. Does anyone make a wheel that is coated to increase reflectance and minimize transmission as spun? Looking at just putting it in the beam path and then using a stepper motor control to effectively fade the effect out or in.

    Thoughts? How else can this be done.

    Better yet tell me you have such a wheel and want to sell it to me, cause it is useless in the analog age
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    You could make your own "variable beam splitter".
    Laser + 1/2 wave plate in a rotation mount (driven by a stepper perhaps) + PBS cube.

    As the 1/2 wave plate is rotated, the ratio of the power from each of the output beams from the cube will vary sinusoidally.
    - There is no such word as "can't" -
    - 60% of the time it works every time -

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    very cool idea do you know does a BB 1/2 plate exist? seems there always individual colors.
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  4. #4
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    I have a few broadband quartz plates but they only cover about 50 nm in the blue-green. Mine cover 488 to 532 very well. Very expensive to have made. I had the honor of scrapping about 20 of them, with the cubes, from semiconductor inspection gear. I have a few left in the rotating mounts.

    For low energies good old crossed Polaroid polarizer works just fine, if it gets burned and starts doing a lumia you use two lenses to up-expand and then down collimate the beam.

    I can order full spectrum polymer plates, but the cost is probably more then you want to spend. They can handle 10 watts in some cases. I used to work for the professor who invented them. The polymer plate covers 485 to 630, it works OK out to 647.

    Steve
    Last edited by mixedgas; 09-25-2013 at 08:15.
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    Sorry, I didn't realise it was a polychromatic source.

    Daft idea of the day: Would stacking 1/2 wp's work? Say all three zero-order plates 445nm/532nm/638nm "sandwiched together" in the same mount, all properly aligned?
    - There is no such word as "can't" -
    - 60% of the time it works every time -

  6. #6
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    Dan,

    You could converge them at one and only one set point. Otherwise they would be known as a "Quartz Optical Depolarizer"
    Or "Hybrid polarization Shifter"

    Happy sticker shock, and note these don't span down to 445:

    http://www.meadowlark.com/store/Spec...achromatic.pdf

    I'm aware of a case where they were used to combine two big white light Ion systems. If one laser went down, the show stayed up.

    Steve
    Last edited by mixedgas; 09-25-2013 at 08:26.
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    how about a variable neutral density filter wheel?
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

  8. #8
    mixedgas's Avatar
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    Those variable wheels are not cheap, about 800$ new. I've got two of them and they are precious.

    Thorlabs has a linear strip variable density for 75$ to 96$ depending on model. Which, adding a surplus linear bearing off ebay, might be the way to go.

    You can also use a galvo with a flag on it, and a pair of lenses. This is tricky to set up and needs a lot of optics mounts.

    Steve
    Last edited by mixedgas; 09-25-2013 at 08:37.
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    How about a galvo with a wide mirror and a retro-reflector like in the old XY+blanking scanners?

  10. #10
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    Also, I have a linear variable ND filter here. Smaller and cheaper than the circular ones. If I can find it, I'll get you the specs.

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