THERMOOPTICAL EXCITATION OF SOUND IN LIQUIDS BY MODULATED RADIATION OF AN UNSTABLE-CAVITY LASER

The thermooptical excitation of sound in a liquid by harmonically intensity-modulated laser radiation with a random distribution of intensity over the laser beam cross-section is considered. Processes are considered which are statistically homogeneous. It is assumed that the spatial spectrum of intensity fluctuations in a laser beam is described by a power (fractal) law. Expressions for the mean-square sound pressure in the acoustic field in a liquid, which is excited by unstable radiation of lasers with apertures shaped as narrow slots and circles, are obtained. It is demonstrated that the fractal structure of unstable chaotic laser radiation affects the structure of the acoustic field in a liquid in the high-frequency range of modulation of radiation intensity when the sound wavelength in a liquid is small as against the correlation length of fluctuations of radiation intensity and the dimensions of the laser beam at the liquid surface. An opportunity for photoacoustic diagnostics of the fractal structure of radiation of an unstable-cavity laser is noted.