Abstract: An acousto-optical method and device for measuring the radiation produced by a transducer is described wherein such radiation is in the range of about 500 KHz to 10 MHz. The method consists of propagating ultrasound frequencies from the transducer through a transparent liquid medium in a cell, said cell having a transparent window or suitable device to provide a clear path for the radiation waves and passing a light through said cell at about a right angle to the direction of said ultrasound wherein the light is modulated in phase with the frequency of the ultrasound. The modulation of the light corresponding to the frequency of the ultrasound can be detected by a photo-cell measured and displayed on various devices. Further, a transducer can be calibrated absolutely using this method and apparatus from known constants and easily measured quantities. Moreover, it is readily adapted to measure the radiation of an unknown source to a known absolute source.