Remote laser generation of narrow-band surface waves throughoptical fibers

摘要

This paper demonstrates the use of a fiberoptic bundle fornflexible, compact, remote, and noncontact laser generation of surfacenultrasonic waves in materials. The bundle is able to deliver Nd:YAGnpulsed light with a 60% delivery efficiency up to an average energy ofn55 mJ/pulse for a pulse duration on the order of 10 ns and a pulsenrepetition rate of 20 Hz without signs of fiber damage. Details of thenbundle construction and surface preparation are given, and pulsed lightndelivery tests performed with single tapered fibers are discussed. Thenhigh-power light delivery capabilities of the bundle are demonstratednfor the generation of narrow-band surface waves in a Carbon/PEEKncomposite laminate by a spatial modulation technique that employs anperiodic transmission mask. Single laser pulse ultrasonic tonebursts arenclearly detectable using a small aperture piezoelectric transducer whilenensuring thermoelastic generation conditions. The theory of narrow-bandngeneration of surface acoustic waves is improved by accounting for thenstrength nonuniformity of the illumination sources. In addition, theneffect of the number of illumination sources on the bandwidth of thengenerated surface wave is assessed experimentally, and excellentnagreement is shown with the theoretical results predicted by thenimproved model