Optoacoustic sensor head for depth profiling

An optoacoustic sensor head for the time-resolved detection of laser-induced stress transits was developed. To allow the indirect detection of plane acoustic waves, the sensor is based on a prism with a PVDF film as pressure-sensitive element. This wideband piezoelectric transducer allows temporal resolutions of nanoseconds (7.5 ns) resulting in an estimated depth resolution of about 25 μm for aqueous samples with absorption coefficients over the range 5-125 cm^-1 (for 0.25 mJ/cm²). The response function of the total experimental setup is derived from the optoacoustic signal of a black absorber, which is necessary to correct theoretical calculations with regard to the finite time response of the detection system. In the case of homogeneous samples, the theory of optoacoustic signal generation is verified, qualitative results are achieved with layered samples.