Analytical model for modulation of diffuse light by pulsed ultrasonic waves

摘要

We present an analytical solution for the acousto-optical modulation of multiply scattered light in a mediumirradiated with a train of ultrasound pulses. Previous theory is extended to cases where the ultrasound inducedoptical phase increments between the different scattering events are strongly correlated. The relation between theultrasound induced motions of the fluid and the optical scatterers is generalized, and it is shown that correlationexists between the optical phase increments that are due to the scatterer movement and to the modulation ofthe 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 higherultrasound frequencies.