Optical method for two-dimensional ultrasonic detection

Two-dimensional detection of ultrasonic waves is based on pressure-induced changes of optical reflectance at a glass-liquid interface, imaged with a t ime-gated video camera. The method is used to record optoacoustic waves gen erated after irradiation of optically absorbing targets with 6 ns long lase r pulses. Measurements of absolute pressure values with high temporal and s patial resolution (in the range of 10 ns and 10 mu m, respectively) is demo nstrated. The sensitivity is varied between 0.19% and 0.81% gray level modu lation per bar. The detector plane is optically transparent, making it poss ible to irradiate the sample through the detector without disturbing the ac oustic measurement. Two-dimensional recording of ultrasonic waves is ideall y suited for the analysis of acoustic emission from small sources and for o ptoacoustic imaging of optical absorption differences in an opaque material . (C) 1999 American Institute of Physics. [S0003-6951(99)03834-6].