Depth profiling of absorbing soft materials using photoacoustic methods

A Q-switched, frequency doubled, Nd:YAG laser coupled to an optical parametric oscillator generated 4.75-ns laser pulses at 726 nm to create subsurface acoustic waves in India ink solutions, India ink acrylamide gels, and in flat segments of elastin biomaterial stained with India ink. The acoustic waves traveled through the target and were detected by a piezoelectric transducer. The waveforms were converted to measurements of initial laser induced pressure and temperature as functions of depth in the material. An algorithm based on Beer's Law was developed and applied to the acoustic signals to extract information about the absorption coefficient as a function of depth in the samples.