<title>Direction sensitive laser Doppler velocimeter using the optical frequency shift of two stabilized laser diodes</title>

Abstract

The commonly used techniques for directional discrimination in velocity measurements involve a frequency shift of the LDA light beams which are focussed into the measuring volume. The paper presents a new technique for the generation of a frequency shift be using the optical frequency difference of two current and temperature stabilized monomode laser diodes. By focussing the output beams of the two frequency stabilized laser diodes into the measuring volume it is possible (1) to save the commonly required components for the beam splitting and frequency shifting and (2) to double the light intensity in the measuring volume. It will be shown that using conventional laser diodes, the influence of frequency shift fluctuations and large band widths on the measuring information in the carrier frequency signal can be eliminated by appropriate heterodyne signal processing techniques. The concept of the described new frequency shift technique will be discussed critically and first experimental results will be presented.