Ultrasound-modulated optical tomography using four-wave mixing in photorefractive polymers

Ultrasound-modulated optical tomography uses a well focused ultrasound beam to modulate diffuse light inside soft biological tissues. This modality combines the advantages of ultrasound resolution with optical contrast. However, because of the low ultrasound modulation efficiency, the large background of un-modulated photons gives a low signal-to-noise ratio. Here we report a technique for detection of ultrasound-modulated light using a phase conjugated signal generated by four-wave mixing in a photorefractive polymer. The experimental results demonstrate the potential of this method to detect ultrasound-modulated optical signals in a highly scattering media with an excellent signal-to-noise ratio.