<title>Spatial modulation characteristics of scattered laser radiation and acousto-optical imaging of weak scattering media</title>

Abstract

Ultrasound modulation of scattered laser light was studied to develop the technique of acoustooptical visualization of the objects imbedded in scattering media. The focused ultrasound wave intersected the laser radiation in a medium. They passed through the medium laser light was collected by a photo-detector. The ac current characterized the optical properties of the zone of intersection of laser and sound beams. On the basis of the suggested model of coherent- optical interaction of laser radiation with ultrasonic wave, the expression for ac current was derived taking account of finite size of the laser beam diameter and the Gaussian distribution of the laser beam intensity, when the Bragg angle was much less than 1. The influence of medium scattering properties and geometry of experiment on the ac photo-detector current and signal to noise ratio was analyzed. With a use of theoretically predicted and experimentally confirmed results, the images of the absorbing half-plane using distributions of the ac amplitude of the current at 3 MHz ultrasound frequency and dc signal were reconstructed in weak scattering media. The possibilities of the acoustooptical imaging were discussed on the basis of the results obtained after comparison with traditional measurements of dc photocurrent distributions.