Directional Laser Generation and Detection of Ultrasound with Arrays of Optical Fibers

Abstract

The generation and detection of ultrasound with laser beams has become a viable technique in nondestructive testing of materials [1,2]. The main advantage of the technique is its intrinsic non-contact nature. Its main limitation seems to be its fairly low efficiency as compared with that of other standard NDE techniques. An interesting recent development [3–5] consists in using optical fibers to guide the laser light and illuminate the sample under investigation in virtually any desired source configuration. Another inherent advantage of the use of optical fibers is that the optical bench is completely decoupled from the sample under investigation, thus rendering the technique practical for in-situ measurements. The objective of the present study is (1) to present some preliminary experimental results complementary of those of Vogel [4] on the generation of ultrasound with an array of optical fibers; (2) to discuss the possibility of generating directional surface waves in a very narrow frequency band, thus increasing the signal-to-noise ratio; and (3), to discuss the feasibility of the directional detection of ultrasound by using an array of optical fibers as a receiver, also with the goal of increasing the signal-to-noise ratio.