DIRECT OPTICAL CHARACTERIZATION OF ULTRASONIC-WAVES USING RAMAN-NATH DIFFRACTION OF CONVERGENT LIGHT

An acousto-optic method for visualizing ultrasonic pulses based on Raman-Nath diffraction of a convergent light beam is presented and its basic features are experimentally confirmed. The laser light intensity of the far field diffraction orders becomes dependent on time, with a period of 1/fp* (where fp* denotes the repetition frequency or fundamental tone of the diffracting pulse). The spectrum of the modulated light measured by a photodetector in one specific direction behind the acousto-optic cell contains all the relevant information about the ultrasonic wave. Experimental verification has been obtained for continuous and pulsed ultrasound in a TeO2 crystal.