Spatial resolving laser Doppler velocity profile sensor using slightly tilted fringe systemsand phase evaluation

Abstract

In this paper we report on a differential laser Doppler velocimeter which offersspatially resolved measurements in the probe volume. For the first time, twolaser wavelengths are employed to generate two interference fringe systems withidentical fringe spacing which are slightly tilted towards each other. The relativephase shift varies linearly with the position along the optical axis, thus allowingspatially resolved measurements. In the centre of the measurement volume a spatialresolution in the nanometre range is achieved. The sensor was applied in a windtunnel for the determination of the wall shear stress of a laminar flat-plate flowwithout mechanical traversing. Spatially resolved measurements of the Blasiusvelocity profile are presented. All results agree well with the theoretical prediction.