A pulsed photoacoustic investigation of ultrasonic mode conversion

Abstract

Experiments have been undertaken into the generation and detection of ultrasonic transients in metals over a 40-MHz bandwidth, using pulsed-laser generation and interferometric detection. Longitudinal, shear, and surface waves have been investigated, and their form compared favorably to theory. The techique has been used to study the interactionof surfaceand bulk waves with slots in the surface of aplate. It has been shown that significant mode conversion occurred from surface to bulk waves and vice versa. The significance of this result to nondestructive testing is discussed.On a entrepris des experiences sur la generation et la detection de transients ultrasoniques dans les metaux, dans une bande de 40MHz de largeur, en utilisant la generation par laser pulse et la detection interf6romCtrique. On a Ctudit les ondes longitudinales, les ondes de cisaillement et les ondes de surface; la forme de ces ondes se compare favorablement A la forme thtorique. La technique a CtC utilisie pour etudier I'interaction d'ondes de surfaces et de volume avec des fentes dans la surface d'une plaque. On a montre qu'il se produit un conversion de mode importante, des ondes de surface aux ondes de volume et rkciproquement. L'importance de ce rtsultat pour les tests non destructifs sera discutie.[Traduit par la revue]Can. J. Phys. 64. 1334 (1986)

Mechanisms of pulsed photoacoustic generation

“…such as capacitance transducers (9,46,47) or interferometers (48)(49)(50), although polyvinylidene difluoride (PVDF) detectors may be of use (51). he thermoelastic wave form presented in Fig.…”

Probing of laser-induced crack modulation by laser-monitored surface waves and surface skimming bulk waves

“…[1][2][3][4] In particular, all-optical generation and detection of various acoustic modes of the sample, including Rayleigh surface acoustic waves, surface skimming bulk waves, and various mixed modes, due to conversion of bulk elastic excitations into the surface ones and vice versa, and monitoring their propagation times between the points of their generation and detection was proved to be a reliable method for the gauging of artificially created surface irregularities such as slots, notches, surface-breaking flaws, etc. [5][6][7][8][9][10][11] However, the experimental results obtained until now on all-optical diagnosis of real cracks are rare 7,12-14 and much less impressive than those on the artificial cracks. This indicates the necessity to improve the sensitivity of laser-based techniques for real crack localization and characterization.…”

Laser removal of oxide films: laser ultrasonics diagnostic

“…At the same time, numerous papers described the application oflaser interferometry to the detection ofultrasonic waves 8,9,10,11 The laser ultrasonic technique, also defined as "laser ultrasonics" (contactiess non-destructive testing method) can provide important information on materials characterization 1213 e.g. microstructural characteristics 14 This technique may be also used to measure acoustic velocities, in ceramic-metal composites 15 in metals at elevated temperatures 16 whilst their greatest shortcoming is their poor sensitivity compared to conventional contact systems.…”