Evaluation of acousto-optic effect in liquid using high-frequency and high-intensity ultrasound

Abstract

Piezoelectric thin film transducers that can receive and transmit high-frequency and high-intensity ultrasound are powerful tools for future medical and industrial applications. Our group has developed acousto-optic devices where the refractive index can be controlled at high speed and high precision using ultrasound, but there are few reports on the interaction between high-frequency (tens to hundreds MHz) and high-intensity (MPa) ultrasound and visible light in liquids. In this study, we evaluated the acousto-optic interaction using polarized CW laser (532 nm) and a piezoelectric KNbO3 thin film transducer formed by hydrothermal method. The transducer was driven continuously at the fundamental or higher resonance frequencies (32, 96, 160, or 210 MHz) in a water cell, and the projection light of a laser beam penetrating perpendicularly to the sound axis was observed. The length of the projection light was elongated in the sound axis on the screen as the driving frequency increased. These results implies that the relationship between the wavelength of ultrasound and the laser beam width is the critical parameter for the acousto-optic phenomenon; the profile of the projection light is dependent on a ratio of the wavelength of ultrasound and the beam width of the laser beam.