  Acousto-optics imaging (AOI) is a hybrid imaging modality that is capable of
mapping the light fluence rate in deep tissue by local ultrasound modulation of
the diffused photons. Since the intensity of the modulated photons is
relatively low, AOI systems often rely on high-gain photodetectors, e.g.
photomultiplier tubes (PMTs), which limit scalability due to size and cost and
may significantly increase the relative shot-noise in the detected signal due
to low quantum yields or gain noise. In this Letter, we have developed a
homodyne AOI scheme in which the modulated photons are amplified by
interference with a reference beam, enabling their detection with low-gain
photodetectors. We experimentally demonstrate our approach with a silicon
photodiode, achieving over a 4-fold improvement in SNR in comparison to a
PMT-based setup.
