Intrinsic Sensitivity Limitations in Classical Interferometry

Abstract

Optical Interferometry has long been seen as the technology with the greatest promise for providing noncontact detection for ultrasonic and acoustic emission testing. Such techniques, once fully developed, would provide couplant-free operation using only a light beam which could be scanned easily over the surface of the specimen under test. Unfortunately, there is considerable development which must take place before optical transducers can replace contact transducers for a number of testing applications. While interferometers perform quite well in the laboratory, such systems are designed usually for a specific experimental task and are not suited for general testing applications. Many of the limitations on the application of interferometric detectors are practical ones imposed, for example, by the need for surface preparation or the nature of the acoustic signal being detected. Underlying such practical limitations, there exist certain intrinsic limits to performance set by the physical properties which govern the operation of the various interferometer systems. Indeed, these intrinsic performance limits vary for the several system designs and must be understood before efforts to develop practical systems can be successful.