Analysis of signal-to-noise ratio and heterodyne efficiency for reference-beam laser Doppler velocimeter

Abstract

Heterodyne efficiency is a very important factor in a laser Doppler velocimeter (LDV). Gaussian-Airy mode is put forward to analyze the heterodyne efficiency. By studying the distribution of the optical field, the mathematic expression and simulation results of heterodyne efficiency are given under the conditions of both exact match and mismatch. The results of numerical analysis show that heterodyne efficiency of LDV depends on Gaussian beam's parameter Q, detector's parameter X 0, angle of collimation mismatching θ a , parameter of offset mismatching X a and the radius of curvature of the reference beam on the detector R( z). Heterodyne efficiency can reach 83.39% when Q=4.15×10 −7, X 0=6.1×10 −7, θ a = X a =0, R( z)=∞. But it declines to 0.5 when Fθ a enhances to 0.28. It decreases with the increment of the offset X a and the diminishment of the radius of curvature R( z). Results of experiment are in good accordance with the theoretical analysis.