Self-mixing laser Doppler vibrometer

In this paper, an extremely small, simple and economic laser Doppler sensor is presented. It simply consists of a laser diode and of an optical system composed by two lenses in order to focus the laser light. The sensor is able to measure velocity and it is based on the self-mixing effect that occurs in a semiconductor laser diode when the emitted radiation is back reflected toward the cavity and then re- introduced inside. The velocity is calculated measuring the position of the frequency peak on the frequency spectrum of the intensity signal generated by the photodiode present inside the laser diode when modulated by feedback light coming from the moving scattering particles. The laser Doppler self-mixing velocimeter has been statically calibrated, using a rotating disk covered with white paper. The sensor has then been dynamically characterized using an electro-magnetic shaker and a Laser Doppler Vibrometer as reference.