Main Question or Discussion Point
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?