Abstract

We have measured the dependence of the modulation of the light field transmitted through a scattering medium by a quasi-cw ultrasound beam upon sample thickness and parameters of the optical and acoustic excitation. A modulation signal is obtained using heterodyne detection for samples with anisotropy parameter g = 0.85 which are thicker than 100 scattering mean free paths. Tomographic imaging with diffuse light is demonstrated in a sample which is about 40 scattering mean free paths thick and contains an absorbing sphere. The results are in accord with a prediction that the modulation signal is proportional to the volume integral of the product of the optical intensity, the probability that a photon will arrive at the detector from this point and the acoustic intensity. Some factors that determine the signal-to-noise ratio for this imaging modality are discussed.

© 1996 Optical Society of America