Raman–Nath diffraction caused at the focal point of a concave type transducer

Abstract

To estimate the intensity of sound pressure in the vicinity of the focal point of a concave type transducer, Raman–Nath diffraction caused at the focal point of a concave type transducer is theoretically and experimen- tally discussed. Sound field, near the focal point, including the acoustic nonlinearity, is theoretically calculated by using the KZK equation. Light intensity of zeroth order Raman–Nath diffraction is also calculated as a function of the sound pressure at the focal point. In the high intensive sound region, it is found that the acoustic nonlinearity makes the light intensity curve disappear at the local peaks. The He–Ne laser whose beam spot diameter is 1.2 mm is supplied as a light source. Light intensities of the zeroth-order Raman–Nath diffraction caused at the focal point are observed by changing the driving voltage of the transducer. The experimentally obtained graph shows the relatively same pattern compared with the theoretically calculated one. The sound pressure at the focal point is estimated by fitting those two results. It is confirmed that the sound pressure estimated by the optical method shows good agreements with the estimated one by the hydrophone measurements.