Laser Doppler velocimeter with optical frequency shifting

A bi-directional laser Doppler velocimeter utilizing optical frequency shifting has been developed. Optical frequency shifting is achieved by using a rotating radial grating. A high diffraction efficiency permits the system to be used in the fringe mode. The zero velocity frequency shift can be varied from 0.1 to 2.5 MHz with a stability better than 0.2%. Important applications are velocity measurements in reversing flows, highly turbulent flows, two-phase flows, and boundary layers. The system described may also be used for vibration analysis. Experimental results are presented.