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Thread: material that has light-sensitive transparency?

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    Default material that has light-sensitive transparency?

    is there any material that if illuminated from one side by IR beam or visible light beam or beam of specific polarization will become transparent or opaque in that spot and the opposite when not?

    Thinking of something like a beamsplitter where one beam can be used to selectively block or show areas of another, fatter beam.

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    ... AOM (Acusto-Optical-Modulators) use crystals, which can "switch" the output angle of the laser beam by applying a high voltage.

    AFAIK there are some "light-switches" assembled of two fibers with a narrow gap of some hundred nanometers between them, where the transmission is modulated by light from the side ... but don't know, if there is some material in the gap or only air ...

    Viktor

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    is that an optical kerr effect crystal by any chance?

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    No. Closer to a sonar transducer, actually.

    The AOM works by applying an RF signal from a separate driver module to the crystal. This sets up a standing compression (sound) wave in the crystal. The areas of higher (node) and lower (anti-node) density formed by the standing wave act as a diffraction grating to deflect the incoming beam off-axis slightly (~ 1 degree) so it misses the aperture hole in the crystal housing and is thus blocked (or blanked).

    You could use an AOM to switch the beam, and you could trigger the AOM driver by connecting an IR sensor to the signal input on the driver, but that doesn't sound like the device you want...

    Adam

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    There are laser addressed liquid crystals and ferroelectric crystals that are also laser addressed. You as a mere civilian will not be getting your hands on them any time soon, sorry. Both are Wassenaar and ITAR controlled technologies. There are also dyes that photobleach temporarily, but those are recovering too fast for what you want to do. Addressible Light valves and eidophore went out of style decades ago. I've actually had my hands on a working light valve, but that was a one time gift from a special friend. You could try DMDs...

    Steve
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    Quote Originally Posted by mixedgas View Post
    There are also dyes that photobleach temporarily, but those are recovering too fast for what you want to do.
    Recovering? Please tell me more.

    You could try DMDs...
    resolution of DMD is poor for this

    Steve[/QUOTE]

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    Elmers makes a washable kids glue that's water clear that has nonlinear optical properties. It reacts very slowly though. I happened to notice the effect when I pointed my ~250mW 520 pointer through a bottle of the stuff. It slowly started to defocus the beam and after I turned the pointer off I could see...not sure what to call it...kind of like a little shock front in the liquid that slowly dissipated. Almost certainly useless for anything but playing around with but it's kind of interesting for a half hour or so.

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    There are two broad classes of optically active dyes. Those that photo bleach and decompose, and those that bleach for a few hundred nanoseconds to a few microseconds. The later are used in q-switched and mode locked lasers.

    Steve
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    Thanks!

    Quote Originally Posted by mixedgas View Post
    Those that photo bleach and decompose, and those that bleach for a few hundred nanoseconds to a few microseconds.
    This actually sounds very promising unless I misunderstand. Will a constant infrared or UV beam keep the spot bleached until it is turned off or moved from that spot?
    What do we mean by bleaching in this context btw?

    Depending on whether I understood properly what these materials can do I can give a more detailed usage for my project to determine if this is in my budget level and appropriate for the sizes and conditions I need them used in.

    By the way someone mentioned polarizers combined with "saturating absorbers" as possible option but didn't get into detail and disappeared. Any ideas what he had in mind?
    Photochromic materials were also mentioned but shown to have too slow of response time.

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    Saturated absorber's are dyes, ceramics, glasses that bleach when a high illumination threshold is reached. Mainly used in pulsed lasers for mode locking or q-switching at enormous energies.

    A crude example is eyeglasses that turn into sunglasses when UV moves /changes charge on a silver ion implanted in the glass. In fact that is probably the only example I can think of that has a decay time longer then a millisecond or so.

    With the exception of the photochromic sunglasses, and the electrochromic window glass in development, everything else needs such high energy density to impractical to bleach with a mere diode laser.

    Steve
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