Multiple-component laser Doppler velocimeter using achirp-frequency-modulated Nd:YAG ring laser and fiber delay lines,

摘要

Abstract: A 2D directional laser Doppler velocimeter (LDV), which is based on the generation of heterodyne signals of different carrier frequencies, so that different velocity components can be detected simultaneously will be presented. The carrier frequencies are generated by a chirp frequency modulation of a diode-pumped monolithic Nd:YAG miniature ring laser in combination with fiber delay lines of a few 100 m lengths. Since this heterodyne technique is based on a complete spliced fiber optic unit without additional frequency shift elements, a simple alignment-insensitive heterodyne LDV system can be realized. Together with the Nd:YAG laser, emitting about 1 W single-frequency power, a portable powerful LDV was realized. The generated LDV signals are evaluated by the quadrature demodulation signal processing technique, which allows the measurement of the Doppler frequency with a high time resolution. As a result, frequency modulated LDV signals, e.g. from sound waves or turbulent flows, can be evaluated.!2