Photoacoustic Doppler effect

Description

The photoacoustic Doppler effect is one specific kind of Doppler effect, which occurs when an intensity modulated light wave induces a photoacoustic wave on moving particles with a specific frequency. The observed frequency shift is a good indicator of the velocity of the illuminated moving particles. When a medium contains small optical absorbers and they are irradiated by a laser with intensity modulated at specific frequency, then an acoustic wave with the same frequency as the light intensity wave is induced. If the absorbers are moving, then there is a frequency shift in the induced acoustic wave. The magnitude of the frequency shift depends on the relative velocity and the photon density wave propagation direction, and the angle between the velocity and the ultrasonic wave propagation direction.