Study of Vibration Measurement by Laser Methods
SYLVANIA ELECTRONIC SYSTEMS-WEST MOUNTAIN VIEW CA
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This report describes results of the second phase of a study of techniques for using laser radiation to detect and measure vibration of mechanical structures. During the first study phase, a number of methods were suggested and demonstrated two of these were selected as sufficiently promising to merit further investigation. One of these methods is the intermediate frequency optical heterodyne system, which provides quantitative data about the motion of a particular very small area on the mechanical structure. The other method is a qualitative interference technique for observing the vibrational mode patterns, so that the number of points to be measured by other methods can be reduced. During the second study phase, these two methods have been developed analytically and experimentally. A breadboard optical heterodyne system was built, and detection of audio frequency vibrations at levels from one centimeter to less than 0.1 micron peak-to-peak has been achieved with a variety of surface materials. The performance of this system using two different types of demodulation circuits was investigated in detail. A model structure was fabricated for tests involving comparisons of the qualitative and quantitative methods. It has been shown that a very good knowledge of the vibrational modes can be obtained using the two methods in combination. The qualitative interference method also has been extended to include the measurement of axes of rotation.
- Lasers and Masers