Advances in optics over the last two decades have led to the development of optical processing mechanisms in photorefractive materials that provide unique capabilities for intelligent sensing applications. These capabilities include adaptability to environmental effects, image correlation, and optical computing. This paper describes the utilization of photorefractivity for performing noncontacting optical vibration detection that is most useful for small peak amplitudes less than #lambda#/4#pi#. Multi-wave mixing with synchronous detection allows measurement of both the vibration amplitude and phase of a vibrating surface directly as a function of the excitation frequency. Narrow bandwidth detection with flat frequency response can be achieved at frequencies above the photorefractive response (approx 100 Hz). A minimum detectable displacement amplitude of a few picometers has been demonstrated for a point measurement, with the possibility of further improvement. Full-field imaging of vibrating surfaces is performed in a manner that employs the adaptive properties of the photorefractive effect for real-time processing. The result is an output image intensity directly proportional to the vibration amplitude for small amplitudes, making this approach complementary to other electronic speckle interferometry methods. An all optical vibration measurement technique is demonstrated by employing laser thermoelastic heating for excitation. Measurements of a vibrating stainless steel plate are presented showing the capabilities of the photorefractive approach for vibrational spectral analysis.
展开▼
