Analysis of Ultrasonic Waves Excited in a Metal Plate by Nanosecond Laser Pulses

摘要

Laser excitation of ultrasonic waves in ferromagnetic plates has been experimentally stud-ied. The obtained results can be recommended for use in the development of methods and equipment for testing thin-walled metal articles. Generation of ultrasonic waves in metals by use of laser pulses of nanosecond duration has a number of substantial advantages over conventional techniques. First, it becomes unnecessary to use piezoelectric (PE) transducers (PETs) and contact media because, in this case, the irradiated surface of an article itself serves as an ultrasound source. The dimensions and shape of such a thermoacoustic source can be easily controlled with lenses, and the laser itself can be placed at a large distance from the tested object. Second, the duration of acoustic pulses generated by a laser beam in a metal is as long as several tenths of a microsecond; i.e., the frequency spectrum of excited vibrations is much wider than that of resonance PETs. This makes it pos-sible to increase the body of information on the physicocomechanical properties of the tested object, its microstructure, and the shape and nature of flaws revealed in it; to reduce the dead zone; etc.