Material property measurement in hostile environments using laser acoustics

Well known acoustic methods have been used to measure various intrinsic and extrinsic material properties. Laser acoustics, employing optical generation and detection of elastic waves, has a unique advantage over other acoustic methods, it is noncontacting. In addition, optical generation and detection probe beams can be focused to the micron scale and/or shaped to alter the transduction process with a degree of control not possible using contact transduction methods. Laser methods are amenable to both continuous wave and pulse-echo measurements and have been used from Hz to 100s of GHz (time scales from sec to psec) and with amplitudes sufficient to fracture materials. The paper reviews recent applications of laser acoustic methods for determining material properties in hostile environments that preclude the use of contacting transduction techniques. Recent technological advances in solid-state lasers and telecommunications have greatly aided the development and implementation of laser acoustic methods, particularly at ultra high frequencies. Consequently, laser acoustic material property measurements exhibit high precision and reproducibility. Optical acoustic imaging is both quantitative and rapid.