Frequency response of optical beam deflection by ultrasound in water

Acoustic waveforms create fluctuations in the index of refraction of the medium. An optical beam passing through the disturbance will be deflected or displaced from the original path. The acoustic wave can be detected by sending a laser through the disturbance and sensing the path changes of the beam with a position-sensitive photodetector. This paper presents a model of this interaction in water to predict the sensitivity and frequency response. The model demonstrates that the frequency response of the system is broadband, allowing detection from a few hundred hertz to 20 MHz. This technique has potential use for underwater acoustic sensing and ultrasonic inspection of materials.