A laseroptic hydrophone for high energy ultrasound

To know more precisely how pulsed high energy ultrasound (PHEUS) interacts with tissues one must define the acoustical dose. Establishing such an acoustical dose requires exact measurement of the ultrasonic wave with amplitudes up to 100 MPa and its associated phenomena like acoustic cavitation. Therefore a laseroptic hydrophone has been designed and built. The principle of the design is to couple the light of a laser diode into a fiber of quartz glass and to detect the wave induced variation of the refractive index in the medium at the end of the fiber. The sensitivity of the pressure gauge is 1.1 mV/MPa with a bandwidth of 10 MHz. Moreover, the rise and duration of cavitation bubbles which are dependent on the energy of the ultrasonic wave can be detected with the 50/125 mu m fiber.<>