We demonstrate laser-based adaptive ultrasonic detection through turbid media using a photorefractive quantum well as a receiver, and a fsec-laser as a light source. An adaptive Mach-Zehnder interferometer is based upon two-wave mixing for homodyne detection. When the fsec-laser propagates through the turbid media, the transmitted light shows the first arrived unscattered signals and the delayed scattered background. Two laser pulses from a signal arm and a reference arm in the interferometer are combined at the adaptive holographic quantum well film. By choice of center wavelength, the two pulses are phase-locked for compensation of wavefront phase distortions. In addition, the scattered background is eliminated by adjusting the optical delay of the reference arm. Using this system, ultrasonic homodyne signals through 11 mean-free paths (mfp) turbid media are successfully detected.
© 2001 Optical Society of AmericaPDF Article