SYNTHESIS OF AN ULTRASONIC ARRAY USING LASER-BASED TECHNIQUES.

The extension of the techniques of thermoelastic generation of ultrasound using a laser and the interferometric detection of ultrasound to the formation of arrays of sources and receivers is described. These techniques are of interest for the rapid inspection of materials without the need for contact or immersion of the material. Results of experiments to study the ultrasonic source characteristics as a function of laser spot size and shape, and as a function of the surface boundary constraints, are reported. The requirements of the detector such as the sensitivity, bandwidth, acceptance angle, and suitability for use in an array are described. Results of an analysis of the suitability of different interferometers are presented.