Method and apparatus for detecting surface wave vector dynamics using three beams of coherent light

Abstract

A method of detecting and measuring separately the components of vector dynamics on the surface of a vibrating object comprises directing three beams of coherent light onto a common spot on the surface. Each of these beams has a known optical frequency. Two are arranged symmetrically about a normal to the surface at the point of incidence and the third is arranged asymmetrically about the normal with respect to both the first and second beams. Superposition of each beam with the others on the surface produces scattered light embodying characteristic beat or carrier signals equal to the difference in frequencies between the beams. Vector dynamics including velocity and displacement of the vibrating surface induces Doppler shifts in the beams, which, in turn results in a modulation of the carrier frequencies resulting from the superposition of the beams. Each carrier frequency is then isolated and demodulated to produce a signal corresponding to various components of the vector dynamics on the surface that cause the modulation. Further analysis extracts information about the frequency and magnitude of resolved vector dynamics on the surface. The method can be applied at several locations on the object's surface to determine vector dynamics at several points simultaneously.