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Thread: Noise from scanned object?

  1. #11
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    I have had this happen too. Especially with lasers that are pulsed. I have heard it many times on sensors and black anodized objects.
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  2. #12
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    http://img62.imageshack.us/img62/3985/laser.gif

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  3. #13
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    Doc,
    I had the exact same thing a few months back when setting up zones on my RGB.
    It threw me a first, as I couldn't work out what was making that noise. Turned out it was part of my duvet (had a dark brown suede-ish stripe to it).
    If I put my hand in the scan, it stopped, take it out and it'd make that cricket noise again.
    Very odd...

    Another odd "laser noise"
    Q-switched YAG focused onto copper: the material whistles at 13kHz (the exact q-switch freq!)
    Must be some percussive effect...
    Also very odd...
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  4. #14
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    In the case of your copper dealy, I would guess that the surface is getting hot and causing the air near it to expand, then cooling off when the pulse ends.

  5. #15
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    In fact most things sing when hit with a butch Q switched beam.
    Part of it is the surface ablating and part of it is just bulk thermal effects.

    Regards, Dan.

  6. #16
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    Its actually used for diagnostics in the lab with small, scanning, focused spots. Laser Acoustic Microscopy. There are quite a few variations in how they pick off the data, ie microphone, shockwave in the material, thermal camera, interferometry etc.

    Pulse mode Co2 cutting a thin tin can or sheet of brass sometimes just screams....

    A typical quote:
    Scanning Laser Acoustic Microscope Facility (SLAM)


    A scanning laser acoustic microscope (Sonomicroscope 100) is available for examining on the micron scale the elastic properties of materials. For biological materials, the microscope's resolution is around 20 micrometers and is able to provide quantitative data in the form of ultrasonic attenuation and speed. The microscope is interfaced to a custom Z-80 based microcomputer such that images can be quantitatively analyzed and processed on a 486-based PC to yield the spatial distribution of the attenuation coefficient and speed of sound. The microscope computer system is able to digitize the microscope images with a 768 x 255 resolution. The 195,840 pixel image can be frame averaged up to 256 times with the 512 Kbytes of memory on the image digitizing system.



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  7. #17
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    Sounds like someone out of a scifi film.

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