Abstract

Within three years local optoacoustic signal representation techniques used first for crack detection /1/ have become a convenient method for thermal structure imaging even on a microscopic scale /2,3/. It has been found that the phase angle is the quantity of more interest for imaging because the depth range is larger /4/ and the influence of optical surface absorption can be eliminated /3/. However, a disadvantage of the well established techniques based on gas microphone or piezoelectric detection is the need of physical contact with the sample.

© 1981 Optical Society of America