Research on Quantity Measurement with a Laser Doppler Velocity Meter . Onderzoek Aan Meetvolume van een Laser Doppler Snelheidsmeter.

摘要

The use of a laser-Doppler velocity meter (LDV) to measure velocities of fluids and gases without disturbing the moving medium is discussed. The principle of the LDV is based on the scattering of light by flowing particles. The dual-scatter method is used to describe the LDV. By focusing two coherent laser beams by means of a positive lens, an interference pattern arises. The accuracy of velocity measurements is affected by the change in the distance between the interference fringes in the probe volume. Analytical and numerical calculations concerning the shape of the interference fringes are presented. The results show that the divergence of the laserbeam has an important influence upon the change of the distance between the fringes. The influence upon the interference pattern by changing the following parameters is verified. (Author)