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

摘要

Abstract: A 2D directional laser Doppler velocimeter (LDV), whichis based on the generation of heterodyne signals ofdifferent carrier frequencies, so that differentvelocity components can be detected simultaneously willbe presented. The carrier frequencies are generated bya chirp frequency modulation of a diode-pumpedmonolithic Nd:YAG miniature ring laser in combinationwith fiber delay lines of a few 100 m lengths. Sincethis heterodyne technique is based on a completespliced fiber optic unit without additional frequencyshift elements, a simple alignment-insensitiveheterodyne LDV system can be realized. Together withthe Nd:YAG laser, emitting about 1 W single-frequencypower, a portable powerful LDV was realized. Thegenerated LDV signals are evaluated by the quadraturedemodulation signal processing technique, which allowsthe measurement of the Doppler frequency with a hightime resolution. As a result, frequency modulated LDVsignals, e.g. from sound waves or turbulent flows, canbe evaluated.!2