Adaptation of polytec laser interferometer to ultrasonic NDE applications
Lisa M. Adler, Péter B. Nagy, Gabor Blaho · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1991
Ultrasonic methods have a very important role in the nondestructive evaluation (NDE) of materials. Conventional ultrasonic techniques are based either on direct contact between the ultrasonic sensor (transducer) and the work piece to be inspected or on liquid coupling when both the ultrasonic and the work piece are submerged in water. In many applications such as process monitoring, it would be desirable to use remote, non contact ultrasonic sensors. One of the most promising non contact methods to couple waves without actual mechanical contact is a combination of pulsed laser generation with laser interferometric detection. The main advantage of these optical remote sensing techniques is their ability to work in high-temperature or otherwise hostile environments and on rough surfaces, awkward shapes, and moving objects, aswell. As a result of the recent development of inexpensive. rugged, portable Q-switched neodymium-doped yttrium aluminum garnet (nd:YAG) solid-state lasers, generation of ultrasonic waves by pulsed infrared laser irradiation has become a fairly simple technique which can be easily adapted to most applications, even hostile environments. Laser detection, on the other hand, turned out to be much less feasible in such applications, mainly because of its inherent sensitivity to external mechanical vibrations. We have developed anmore » ultrasonic detector which can be used as an instrument which is unconditionally stable and can be used in Industrial environment. The instrument is a modified version of the Polytec Laser Vibrometer to work in the MHz region. The principal applications of this instrument are continuous monitoring of material parameters such as elastic moduli, internal temperature, phase transition, grain growing, etc., as well as flaw detection in demanding industrial application requiring remote sensing techniques. The enclosed report includes a detailed description and operation of the Laser Ultrasonic Detector.« less