Self-mixing feedback Doppler vibrometry

Laser Doppler velocimetry uses the Doppler shift of light scattered from moving particles. In self-mixing laser Doppler velocimetry some of the scattered light is allowed to re-enter the laser cavity and here it is mixed with the originally generated cavity mode. This interference results in a fluctuation of the laser intensity with a frequency equal to the Doppler shift (self-mixing interference or back-scattered modulation), according to ?f=2nv(cos?? )/?. Here ?f , n , v, ? and ? stand for the Doppler frequency shift, the refractive index of the medium, the velocity of the scatterer, the angle between the velocity vector and the optical symmetry axis, and the wavelength of the laser light in vacuum. The laser Doppler self-mixing velocimeter has been statically calibrated, using a rotating disk covered with white paper. Authors report about the Doppler signal amplitude of the velocimeter as function of the characteristics and colour of the target surface. Dependence of the Doppler peak amplitude from the target distance and the angle between target and optical axis of the sensor are also reported. Results regarding dynamic characteristics of the sensor are reported and it is shown its capability to be used as a laser Doppler vibrometer.