Photo-emf detector enables laser ultrasonic receiver

摘要

Conventional photodetectors typically are used to provide a signal proportional to the power of an incident beam of light. In recent years, a new photoeletector has been developed based on the nonsteady-state photoelectromotive force (photo-emf). Exciting advances in the field and a real-time demonstration of the detector technology as applied to laser ultrasonic inspection, were offered as part of CLEO 2000 (San Francisco, CA) last May (see frontis). This new detector produces an output signal proportional to the transient lateral motion of an incident optical pattern on its surface. When the pattern is stationary, no output signal is produced, regardless of the location or amount of incident power. This detector can be incorporated into an optical interferometer that can measure ultrasonic waves in materials, just as a conventional contact PZT ultrasonic transducer does, but without contacting the sample under inspection. The special properties of this detector permit in-process ultrasonic inspection in industrial environments where background vibrations, rough surfaces, high temperatures, and rapid process motions would foil both contact PZT transducers and traditional laser interferometers.