High-resolution velocity profile estimation with the scanning laser acoustic microscope

The authors introduce a technique for high-resolution velocity profile estimation with the scanning laser acoustic microscope (SLAM). In the past, the resolution of microscopic velocity profile was limited because the estimation process was based, in general, on interferometric data. Owing to a recent modification, the SLAM system is now equipped with a quadrature detector and is capable of holographic data acquisition. As a result, it is possible to measure quantitatively the two-dimensional phase distribution, which can be converted into the velocity profile. This technique consists of three major components. First, a phase error correction algorithm is used to remove the relative phase error from the holographic data samples. Subsequently, two-dimensional phase unwrapping on the corrected phase data is performed to obtain the exact phase distribution. Then the unwrapped phase variation can be converted into a quantitative profile of the propagation velocity. In addition to the detailed description of the algorithm, the authors demonstrate the accuracy and resolving capability of this velocity profile estimation technique with both test specimen and biological tissues samples