Fig. 3A. Irradiation of absorbing object from below.

Experimental setup irradiated the absorbing object from below and detected sound at air/water surface. The absorbing object was a gel with India ink (20 mm long x 10 mm wide x 2 mm thick) located 11 mm below the air/water surface which is seen in figure as the black absorber at bottom of phantom. The phantom was translated while the laser source and HeNe beam detector remained fixed.

Fig. 3B. Edge detection of absorbing object.

The edge of the absorbing object was clearly sensed by the photoacoustic imaging with sub-mm resolution of the edge. The transduction of surface movement by the HeNe laser interferometer was not adversely affected by addition of optical scatterer to the water and the signal and image resolution did not degrade.