Calibration of ultrasonic sensors using optoacoustics

Ultrasonic detectors are commonly calibrated by finding their response to incident plane waves. However, in optoacoustics, the response to broadband point sources is required. To induce such sources using the optoacoustic effect, the illuminated object's dimensions must be smaller than the resolution achievable by the optoacoustic system. The main difficulty in such measurements is that the magnitude of the field emitted by such sources is proportional to their dimensions, and thus may be weak compared to parasitic sources in the setup. In this work we experimentally demonstrate two methods for calibrating acoustic detectors. In both methods, acoustic sources are optoacoustically induced in large optically absorbing slabs. Despite the large dimensions of the illuminated objects, the geometry used yields wide-band acoustic fields, which are perceived by the detectors as originating from point sources.