Fast optical LDA burst analyzer

A novel method for processing laser Doppler anemometer (LDA) signals is proposed. The basic idea is to process the signal trace obtained by a transient recorder not numerically but optically, storing it as an image in a spatial light modulator and obtaining the Fourier transform with the speed of light by the use of coherent laser light. Due to the finite resolutions of the transient recorder and the light modulator, the image consists of rows of equally spaced bars. As a result of the Fourier transformation, equally spaced dots are obtained. The distance between corresponding dots is proportional to the Doppler frequency to be determined. An experimental setup is described to perform tests using this principle. Simulated real Doppler bursts are treated. When the signal-to-noise ratio is very poor the new concept is found to be a powerful tool for Doppler burst processing. A simple algorithm is found to increase the confidence level in correct data collection