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Thread: Time to Blank

  1. #1
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    Default Time to Blank

    Hey all,

    Last year I finally installed some DT40s on my laser and I'm very happy with the results so far. My next step, besides tuning my collimator on my DPSS is achieving adequate blanking. My laser (Melles Griot GSD-series) only has 40Hz TTL, so that's out the window.

    Assuming I can fit a third galvo in the path of the beam, (which I can -one way or another), what would you recommend as far as hardware to do this?

    I have a pair of GM20s, but I have a feeling one of those won't cut it. Additionally, I 'd need to get or build something to control one of those. Should I opt for another DT40 and amp?

    My DAC is an FB3 and I'm using a 3 watt, 532nm laser. The GM20s have mirrors on them and were originally installed on my laser system.

    -Jonathan

  2. #2
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    Quote Originally Posted by platinum View Post
    Hey all,

    Last year I finally installed some DT40s on my laser and I'm very happy with the results so far. My next step, besides tuning my collimator on my DPSS is achieving adequate blanking. My laser (Melles Griot GSD-series) only has 40Hz TTL, so that's out the window.

    Assuming I can fit a third galvo in the path of the beam, (which I can -one way or another), what would you recommend as far as hardware to do this?

    I have a pair of GM20s, but I have a feeling one of those won't cut it. Additionally, I 'd need to get or build something to control one of those. Should I opt for another DT40 and amp?

    My DAC is an FB3 and I'm using a 3 watt, 532nm laser. The GM20s have mirrors on them and were originally installed on my laser system.

    -Jonathan
    Well, you have several options to choose from. You can use flag blanking, which is very easy to implement, however, it is your slowest option. The second option, is optical leverage blanking. Sorta hard to explain in text, see photo below. It is about as fast as you can get without going AOM. Which is your last option. If you can find a nice AOM, then you can get full analog blanking, which is by far the best way to go. The downside to the AOM is that you can expect to loose a significant percentage of that 3W. The upside, is you can use the waiste beam for other effects such as diffraction and lumia.

    Flag Blanking-------Very Slow----0% light loss
    Optical Leverage---some loss of light, challenging to align----Very fast
    AOM---Difficult to align, substantial loss of light---Very fast, capable of analog
    Attached Thumbnails Attached Thumbnails scanhead.jpg  

    Cap0053.JPG  


  3. #3
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    AOM!
    min. power loss fast blanking for graphics

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    I got real lucky and got a nice bunch of laser gear all at once. I did have to figure out how to align it by myself, but that was a lot of fun! I have always wondered what is really going on inside the PCAOM crystal. How does it really work to fade the beam?

    James.

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    To fade the beam that is done by the intensity of the soundwave

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    Lightbulb

    David,
    I got a nice AOM out of a grocery store scanner that I need your help in hooking up. If it won't work on the blue, it should on the 130mW ttl maxyz I got. Maybe a quick project at SELEM.

    To be honest, I am about ready to go all AOM or PCAOM on the DPSS just so everything will blank togther. F the loss...
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  7. #7
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    The AOM option will probably have to wait for now. I feel that would be considerably pricey compared to the other two options. As far as flag blanking and optical leverage.. the keep-it-simple side of me says go with flag blanking. I have limited space to work with as I am working with a Mobolazer platform. The DT40s are mounted (rather extravagantly) over one of the 10 apertures on the unit.

    I decided to keep the Mobo option for mirror effects and wide-coverage capability. There's not too much room in between the aperture and the scanners, but I figure I could mount something the size of a GM20 in the path of the beam. I suppose if I was really crazy I might be able to blank the master beam before it goes into the servo array. This might make for interesting effects with the stationary beams somehow.

    Anyway, I'm unclear as yet, whether a GM20 could cut it as a blanking device. Am I right to assume it's too slow? Or am I not giving the old things enough credit?

    Attached are two pictures for illustration of what I have to work with:
    Attached Thumbnails Attached Thumbnails DT40Mobo.JPG  

    DT40Mobo2.jpg  


  8. #8
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    Quote Originally Posted by James Lehman View Post
    I got real lucky and got a nice bunch of laser gear all at once. I did have to figure out how to align it by myself, but that was a lot of fun! I have always wondered what is really going on inside the PCAOM crystal. How does it really work to fade the beam?

    James.
    Acousto Optic. Piezoelectric element that sends acoustic waves trough the crystal.

    An acousto-optic modulator consists of a piezoelectric transducer which creates sound waves in a material like glass or quartz. A light beam is diffracted into several orders. By vibrating the material with a pure sinusoid and tilting the AOM so the light is reflected from the flat sound waves into the first diffraction order, up to 90% deflection efficiency can be achieved.
    http://en.wikipedia.org/wiki/Acousto-optic_modulator
    I hired an Italian guy to do my wires. Now they look like spaghetti!

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    Quote Originally Posted by allthatwhichis View Post
    David,
    I got a nice AOM out of a grocery store scanner that I need your help in hooking up. If it won't work on the blue, it should on the 130mW ttl maxyz I got. Maybe a quick project at SELEM.

    To be honest, I am about ready to go all AOM or PCAOM on the DPSS just so everything will blank togther. F the loss...
    Hey Aaron, I'd be glad to help get the AOM going at SELEM, though I probably wont have all the tools I may need. If you like, you can still send your stuff to me and I can fix it up here in Jax before SELEM. Either way, its up to you.

    Anyway, I'm unclear as yet, whether a GM20 could cut it as a blanking device. Am I right to assume it's too slow? Or am I not giving the old things enough credit?
    I'm not sure how well a GM20 would work for flag blanking, I think it would be very slow. I've never tried flag blanking with a dt-40, but that may be the best bet. Just rip the mirror off and replace it with a thin piece of metal, I use to cut apart the metal piece on diskettes to use for flag blanking. One other thought, what ever piece of metal you use, you may want to leave it shiny, if you paint it black, it will try to absorb alot of that 3W and may quickly overheat the scanner.

  10. #10
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    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    check the polarization of your laser, if it is random, use a galvo and flag or figure 4 leverage
    like in that posted photo. If it is polarized, use a AOM. AOMs are not the difficult witchs they are made out to be. Most modern chinese stuff is polarized as they use YVo4 and not yag.

    Steve Roberts

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