Signal/noise ratio in laser Doppler systems

A comprehensive analysis is presented of the signal/noise ratio of laser Doppler systems. Three parameters have been introduced:an easily measurable generalised system parameter is used to account for the noise performance of the system. The signal is determined by the coherent-reflectivity loss factor of the target, and the overall signal/noise ratio is specified by a noise figure. As defined, the noise figure is almost independent of signal strength and can be used as a unique specification of the optical receiver. It is shown that the system can easily be optimised using these parameters and its performance predicted. Three types of photodetector (photomultipliers, p-i-n photodiodes and avalanche phqtodiodes) have been considered and it is shown that a confident choice can be made for a specified set of operating conditions.