New speckle velocimeter using two self-mixing laser diodes

We propose a novel laser speckle velocimeter using two self-mixing laser diodes (SM-LDs). It has been observed that the speckle signal measured by the measurement system has a strong dependence on the path illuminated by an SM-LD. When a thin surface with a different surface characteristic attached to a moving plane is illuminated, the frequency of the intensity changes of the waveform changes. Finding the time instant when this target surface is illuminated gives the opportunity to find the velocity of the moving plane. In this study we propose a method to find the time at which the surface is started to be illuminated and exploit this change in the waveform of the speckle signal to detect the velocity of the target transversely translating across the laser beam.