Optical Measurement of Ultrasonic Nanometer Motion of Rough Surface by Two-Wave Mixing in Bi₁₂SiO₂₀

Abstract

Motion of a rough surface of an ultrasonic transducer was measured using an optical interferometer based on photorefractive two-wave mixing in a Bi 12 SiO 20 crystal. The displacement equivalent to noise was 0.10 nm in a band-width of 8.0 MHz. The low-frequency noise was automatically compensated by an adaptive property of the photorefractive grating without an electric feedback loop.