Acoustic and ultrasound sensor with optical amplification

Abstract

An optical lever acoustic and ultrasound sensor with increased sensitivity using an optical amplification means to amplify the motion of an incident acoustic wave and convert it to an electric signal for image processing. Three approaches to the optical amplification are disclosed. In the first approach, the vibrating mirror is part of a cantilever that increases the angular deflection of the incident light beam. In the second approach, a second, stationary mirror is positioned approximately parallel to the vibrating mirror surface. The reflected light beam is reflected back onto the vibrating mirror, and picks up a another increment of the acoustic signal with each reflection. In the third approach, the effective moment of the optical lever is increased within a small volume by the use of two stationary mirrors to increase the path length from the vibrating mirror to the position-sensitive detector. This increases the relative movement of the light beam on the surface of the position-sensitive detector and, therefore, the overall sensitivity of the sensor. The incident beam of light is focused by a lens between the light source and the vibrating mirror, so that the focal point is in the plane of the position-sensitive detector. The smaller spot size and greater intensity of the incident light allows greater detector sensitivity. Two or more chopped light beams may be directed at a single vibrating surface, and phase-locked loop circuitry used to reduce the signal-to-noise ratio.