Silicon-on-insulator photoconductors for ultrasonic vibration detection with laser speckle

Speckle-sized photoconductive silicon-on-insulator mesas have been designed to optically detect surface vibrations at frequencies extending into the megahertz range. When a single diode laser beam reflects off a vibrating surface as a moving speckle pattern, the photoconductive mesas can detect lateral speckle motion. The capability of noncontact, nondestructive testing via laser-induced ultrasonic vibrations was demonstrated using these photoconductive silicon mesas in a simple and rugged single-monitoring-beam configuration.