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].