Laser thermo‐optical source of sound at a fractal surface in a liquid.

Abstract

Surfaces of real bodies are rough, uneven, or porous as a rule and are characterized by fractal properties. Surfaces may be fractal up to the molecular‐level scale. Rough oceanic surface is also fractal. Laser photo‐ acoustic diagnostics of various media have been developing in recent years. It is based on laser excitation of sound (ultrasound or hypersound). Special features of laser sound excitation in a liquid half‐space with the rough statistical fractal surface are investigated. It is assumed that an harmonically modulated laser beam is incident on the liquid surface. The height (amplitude) of surface waves is greater than the sound wavelength and the absorption length of light in the liquid. Fractal properties of the surface are characterized by the Weierstrass function and connected with it by a structural function. The Kirchhoff approximation is used to solve the boundary problem. The influence of fractal properties of the surface and parameters of laser radiation and liquid on the amplitude and s...