Opto-Acoustics:Old Idea with New Applications

Abstract

The opto-acoustic (OA) or photo-acoustic (PA) effect is the generation of acoustic waves by electromagnetic waves or other types of radiation incident on a sample. This effect was discovered by A. G. Bell in 1880, who observed that audible sound is produced when chopped sunlight is absorbed by a sample. Although the OA effect is very old, there is a great resurgence of interest in it in the past several years, both theoretically and experimentally. This appears to be due to the following reasons:

• 1) Intense light sources (various lasers and arc lamps) have become more readily available in recent years.

• 2) Highly-sensitive acoustic detectors (microphones, hydrophones, thin-film piezoelectric detectors, etc) have been developed.

• 3) OA technique has been shown to be one of the most sensitive spectroscopic technique for gases as well as for condensed samples.

• 4) OA methods have many unique applications, e.g. spectroscopic studies of opaque or powdered materials, studies of energy conversion processes, and imaging of invisible or subsruface features in solids; furthermore, future “exotic” applications like air-to-ocean communications or cosmic ray detections appear possible.