Precise knowledge of the acoustic field in biological tissue after pulsed laser irradiation is necessary in order to perform medical imaging. Often, the photoacoustic pulse is delivered as a circular, stress confined laser spot incident upon a planar surface, such as skin. The resulting photoacoustic wave propagates in the tissue and may be detected by a detector or array of detectors. The detected signals can then be used to reconstruct the optical properties and, perhaps, the structure of the tissue. In this paper, we study the beam profile of a circular laser spot incident upon tissue
phantoms and propose a paradigm for further investigations, comparing the photoacoustic source as a baffled acoustic piston. Two phantom geometries were studied, a hemisperical acrylamide gel and a dyed water solution. An acoustic transducer with an active area of 200 μm was scanned about the circumference of the hemisphere. The laser spot was incident on the face. For the dye solution, the transducer was submerged and rotated about the laser spot on the water
surface. The beam profile of the gel showed some diffractive lobes while the profile from the dyed solution did not, though the main lobe was more robust.