Detection of the nonballistic component of scattered light in the process of acousto-optic visualization

For determining the optimum conditions of detecting the signal during acousto-optic visualization, the modulation characteristics of radiation of a laser beam crossed by a focused acoustic beam in a medium and scattered by this medium were studied. The characteristics were obtained by measuring the amplitude of the alternating-photocurrent component at the ultrasonic frequency as a function of the geometry of the experiment, the parameters of the scattering medium, and the laser radiation power. Special attention was given to the magnitude of the signal-to-noise ratio. A photodetector recording the field of the nonballistic component of the scattered radiation was positioned outside the geometrical sizes of the laser beam. The photocurrent component corresponding to this radiation at the ultrasonic frequency was used as a parameter of the acousto-optic visualization. Images of optically opaque objects immersed into a medium whose scattering parameters corresponded to the transition from the regime without scattering to the multiple-scattering regime were obtained.