1 to 10 Kilohertz optical interferometry for hydrophone calibration

Optical methods for hydrophone calibration make use of a laser interferometer and a pellicle as an acousto-optical sensor. Such methods can give higher accuracy than the usual reciprocity-based method, since the acoustic pressure is measured directly and not through the response of a reference hydrophone. So far the method has been evaluated only above 10 kHz due to limitations imposed by the optical path length in water. The first results are given of tests performed in a water tank that allows to use frequencies starting from about 1 kHz, and a comparison with existing calibration data shows an agreement to within 1 dB.