<title>Laser-based ultrasound detection through turbid media</title>

Abstract

Adaptive laser-based ultrasound detection uses laser homodyne detection in an adaptive interferometer to detect ultrasound displacements. This technique has been applied to non-destructive evaluation for detection of surface displacements. However, in biomedical ultrasound applications, ultrasound displacements of interest may be inside tissue and the detection light beam may need to propagate through turbid media. Here we report laser-based adaptive ultrasonic detection that can detect ultrasound displacements inside or through turbid media using a fsec-laser as the light source in an adaptive optical coherence detection scheme. The use of an interferometer and a femtosecond laser gates out the unwanted scatter while still allowing homodyne detection. In our laser-based ultrasound system, an adaptive Mach-Zehnder interferometer is based upon two-wave mixing in semiconductor quantum-well films. It provides depth information inside the sample by adjusting the optical delay in the reference beam arm. Homodyne detection was experimentally studied for low intensity and highly wavefront distortion caused by turbid media. Using this system, ultrasonic homodyne signals through 11 MFP turbid media have been successfully detected.