Fig. 2. Point spread function for optical transducer.
The response signal from a point source of acoustic energy generated by the pulsed laser. The site of laser irradiation was a bed of collagen and India ink located 18 mm below the water/air surface. The beam was directed by mirror to various sites perpendicular to the midplane of null response between the two HeNe laser beams. As the irradiation site was moved about the response was measured. The signal falls off as 1/r where r is the distance between the site of sound generation and the nearest HeNe laser beam.