Multiplexed two-wave mixing interferometry.

摘要

This dissertation outlines the development of photo-acoustic detection arrays using multiplexed two-wave mixing in photorefractive media. Photo-acoustic phased arrays are useful because they provide non-contact measurements at multiple positions simultaneously, a small footprint, and they can be used on awkward geometries and at high-temperature or hostile environments. The photo-acoustic phased array system described in this dissertation consists of a point or line laser-generated ultrasonic source and a multiplexed two-wave mixing (MTWM) interferometer for ultrasound detection.; The multiplexed two-wave mixing interferometer system enables detection of ultrasonic signals from an array of focused points on the sample surface simultaneously. The advantage that this system has over single point detection scheme is that multiple signals can be collected at the same time which allows for true optical phased array detection. The element size of the array in this system can be precisely controlled down to the micrometer range using a focusing lens. Furthermore, the element spacing, the number of elements in the array, as well as the shape of the receive array can be easily controlled, allowing for dynamic changes in imaging resolution and range.; The basic theory of the photo-acoustic phased array system is presented in this dissertation. Applications of this system for surface acoustic waves and bulk waves imaging are demonstrated. It is also shown that this multiplexed two-wave mixing interferometer system can be used to characterize material anisotropy and fast recovery of lamb wave dispersion curves. An infrared version of this system with a long pulse laser system as the source is also described and discussed. Imaging applications of this infrared system using surface acoustic waves and bulk waves are also presented.