Multiple-pass laser beam deflection probe for detection of acoustic and weak shock waves in fluids

Abstract

We examine a novel laser beam deflection arrangement for detection of acoustic and weak shock waves in fluids. Novelty of the arrangement is folding of the probe beam by two parallel plane mirrors in such a way that the probe beam passes the wave propagation region several times before it reaches the deflection-detecting photodetector. In this way the probed wave interacts with several segments of the probing beam in sequence. A single oscilloscope trace of the photodetector output thus gives us the possibility to study the evolution of the probed wave at several distances from the source. To demonstrate the potentials of the arrangement we present wave forms of spherical blast waves detected in air during laser ablation of solid samples. We also discuss a simple theoretical model that qualitatively explains the most characteristic features of this arrangement.