Analytical model for modulation of diffuse light by pulsed ultrasonic waves

Abstract

We present an analytical solution for the acousto-optical modulation of multiply scattered light in a medium irradiated with a train of ultrasound pulses. Previous theory is extended to cases where the ultrasound induced optical phase increments between the different scattering events are strongly correlated. The relation between the ultrasound induced motions of the fluid and the optical scatterers is generalized, and it is shown that correlation exists between the optical phase increments that are due to the scatterer movement and to the modulation of the optical index of refraction. Finally, it is shown that compared with the spectrum of the ultrasound pulses, the power spectral density of the acousto-optically modulated light is strongly attenuated toward the higher ultrasound frequencies.