Generation of ultrasound by repetitively Q-switching a pulsed Nd:YAG laser

Abstract

Repetitively Q-switching a Nd:YAG laser during a single flashlamp pulse has been used successfully to generate a train of acoustic pulses with a repetition rate as high as 53 kHz. The spectral content of this multiple-pulse ultrasonic signal is significantly narrower in bandwidth than that of a single pulse. A corresponding reduction in the detection system bandwidth results in a marked improvement in detection sensitivity.

A Model of Temporal Intensity Modulation for Laser Generated Ultrasound

“…But it would be desirable in some NDE applications to narrow the signal bandwidth to improve the signal to noise ration (SNR), and also to have direct control over the center frequency of the generated ultrasound. In principle, this may be achieved by temporal [3,4] or spatial modulation [5,6] of the Iaser pulse, or both [7]. The purpose of this work was to develop a numerical model of a single, tem porally modulated Iaser source of ultrasound in the thermoelastic regime, for isotropic metals.…”

Pseudo-random modulation of a laser diode for generating ultrasonic longitudinal waves

“…Pulse modulation techniques can spread the laser energy over time or space, thus reducing laser power densities and minimizing damage. Previous experiments by various organizations using spatial or temporal pulse modulation [3][4][5][6][7][8][9] have been shown to generate detectable surface, plate, and bulk ultrasonic waves with narrow frequency bandwidths . Using narrow frequency bandwidths improved signal detectability, but required the use of expensive and powerful lasers and opto-electronic systems.…”

Pulse compression techniques for laser generated ultrasound

“…It also significantly limits the signal-to-noise achievable with laser generated ultrasound. Some methods for improving the effective signal-to-noise are based on modulating the laser source, either temporally or spatially, [3][4][5][6][7][8][9]. Previous reports on temporal modulations of a laser source to produce longitudinal waves produced narrow band ultrasonic waves having improved signal-to-noise but sacrificed temporal resolution, [7][8][9].…”