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Bragg cell in laser doppler vibrometer

  1. May 28, 2008 #1
    I know that Bragg cell used in laser doppler vibrometer (LDV) is used to give information about the direction of the velocity of the object that we measure. I also know that Bragg cell will shift the frequency of the laser beam(modulation frequency is reduced) when the object is moving towards the interferometer. But the problem is I want to know how Bragg cell can reduced the modulated frequency and next increased the frequency so that we know the velocity direction of the object. Can anybody explain?
  2. jcsd
  3. May 28, 2008 #2


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    I think the vibration frequency your are trying to measure is what is used to do the modulation?

    http://en.wikipedia.org/wiki/Acousto-optic_modulator" [Broken]

    Welcome to PF zaimir83
    Last edited by a moderator: May 3, 2017
  4. May 28, 2008 #3
    Thank you dlgoff.

    I still could not comprehend the statement well. For example, if I have a laser beam entering the bragg cell at 40MHz and the beam coming out of the cell have a frequency of 50MHz. Is the frequency coming out of the cell always has a fixed value? Or it will shift up and down over time?
  5. May 29, 2008 #4


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    If you have this situation, then you would be able to see in which direction you accelerate the device. You would get frequencies shifted up in one direction, and frequencies shifited down in the other direction. I think.
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