Abstract: Ultrasonic transducers comprising an ultrasonic transducer element, a pair of electrodes provided on opposite sides of the element, and an acoustic impedance-matching layer formed on an ultrasonic wave-radiating surface of the element through one electrode. The acoustic impedance-matching layer is made of a porous polymer film or a composite material comprising thermally expanded resin microspheres dispersed in a cured product of thermosetting resin and has an acoustic impedance not larger than 0.6.times.10.sup.6 Ns/m.sup.3. Two-layer constructions may also be used as the acoustic impedance-matching layer.

Abstract: A light deflector utilizing the anisotropic Bragg diffraction in an anisotropic medium in which the directions of the wave front normal and the energy propagation of ultrasonic waves are arranged to be different and the frequency range of the ultrasonic wave for causing re-diffraction of light diffracted once by said ultrasonic wave is set outside the driving frequency range. The diffraction efficiency does not fall near the central frequency of the driving ultrasonic frequency range due to the prevention of rediffraction. Further, the driving frequency can be selected over a remarkably wide range compared to that of the conventional light deflector.

Abstract: An acousto-optic filter utilizing the far-off-axis anisotropic Bragg diffraction comprising an optically anisotropic crystal in which a light beam of incidence travels in a direction making a large angle with the crystalline axis and an ultrasonic wave travels in a predetermined direction. In the acousto-optic filter using a paratellurite crystal, the wavelength of the visible light is tuned by changing the frequency of the ultrasonic wave in a low frequency range below 100 MHz. The ultrasonic power required for driving the acousto-optic filter is about 1/500 that of the so far known acousto-optic filters. The bandwidth of the transmitted light can be changed from several angstroms to several hundred angstroms by selecting the incident angle of the light.

Abstract: An acousto-optic filter utilizing the far-off-axis anisotropic Bragg diffraction comprising an optically anisotropic acousto-optic medium embodied by a paratellurite crystal. An ultrasonic wave generated by a transducer is propagated in a direction different from that of the wave front normal to make the light-sound interaction length in the medium elongate by slanting the bonding surface of the transducer to the crystal medium.