Laser Doppler signal for high amplitude sound wave

Abstract

Laser Doppler velocimetry (LDV) is now recognized as a very useful technique for estimating acoustic velocity with a good time resolution in many applications. Previous research showed that the most important parameter in LDV for acoustics is the particle displacement and particularly its magnitude compared with the size of the probe volume formed by the crossing of the laser beams. Specific techniques were developed to estimate the acoustic wave when the displacement is of the same order of magnitude as the probe diameter and when it is much smaller. In this study, we investigate situations where the displacement is much higher than the probe volume. The measuring process has been simulated numerically and it appears that the process leads to an under-estimation of the velocity around zero. This under-estimation is due to the processing of the laser Doppler signal in the case of high displacements. The associated signal is a non poissonnian randomly sampled signal to which classical processing methods are not adapted. It is compared to experimental signals obtained in the context of a study of non linear effects in an acoustic wave guide. To this end, different processing of both simulated and experimental signals are presented and compared.