Transformation of laser-induced broadband pulses of longitudinal ultrasonic waves into pulses of shear waves in an isotropic solid plate immersed in a liquid

Abstract

Transformation of laser-induced broadband pulses of longitudinal ultrasonic waves into pulses of shear waves and back into pulses of longitudinal waves (further called as the “double” transformation) in an isotropic solid plate immersed in a liquid is theoretically studied. It is shown that the time profile of the pulse of shear waves strongly depends on the angle of incidence and only at a certain value of this angle the time profiles of the incident longitudinal-wave pulse and induced shear-wave pulse coincide. For various angles of incidence, the broadband pulses of longitudinal waves experimentally obtained after the double transformation in an aluminum and fused silica plane-parallel plates immersed in distilled water correspond to the theoretically calculated profiles except for the increased duration of experimental pulses. Based on the double transformation scheme, the method of broadband acoustic spectroscopy of longitudinal and shear waves for isotropic solid plates in the spectral range of the blue-green glass laser source of ultrasound (1–40 MHz) was proposed and experimentally realized for the first time. The obtained frequency dependences of the attenuation coefficients of longitudinal and shear ultrasonic waves in stainless steel, cast babbit, and brass can be used for appropriate choice of an operating frequency range by ultrasonic nondestructive testing of these materials.