Photoacoustic depth profiling by cross-correlation using a GaAs light emitting diode

We present a new approach to depth profiling optically opaque multilayered samples. The presence of interfaces in a sample is revealed by cross-correlating a randomly generated optical probe beam from a GaAs light emitting diode and its generated photoacoustic signal. The technique attains a throughput advantage over previous profiling methods since it operates without an external optical modulator. Random intensity modulation of the light source is achieved by direct current modulation of the diode. We show the effectiveness of our technique by establishing the double-layer structure of a magnetic tape.