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Probing of laser-induced crack modulation by laser-monitored surface waves and surface skimming bulk waves J. Acoust. Soc. Am. 131, EL250 (2012); 10.1121/1.3684737 Impulsive fracture of fused quartz and silicon crystals by nonlinear surface acoustic waves Initiation of impulsive fracture near the source of a nonlinear surface acoustic wave ͑SAW͒ pulse, launched by laser-based transient pressure shocks, is investigated. A numerical method is developed that solves the problem of nonlinear SAW generation, the propagation of SAW pulses in nonlinear media, and the initiation and growth of cracks by such pulses. The characteristic features of SAW profiles in linear media, nonlinear media with quadratic nonlinearity, and nonlinear media with crack induction provide a tool to determine the critical stress of dynamic fracture. Former discrepancies between theoretical and experimental pulse shapes were eliminated by taking into account the effects of fracture. Good agreement was obtained with experiments in isotropic fused quartz. By calculating the stress field of the nonlinear SAW pulse modified by the interaction with a crack and by applying the condition of vanishing shear stress at the crack tip, the angle of crack penetration into the solid was estimated. At a depth of 7.1 m, for example, this angle was approximately 50°to the surface normal, in reasonable agreement with previous measurements in isotropic fused quartz.

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“…15. ͑1͒-͑4͒ the finitedifference time-domain ͑FDTD͒ method was used, which in many respects is analogous to that used in Ref.…”

Section: ͑3͒mentioning

confidence: 99%

Interrelation between nonlinear elastic surface pulses and dynamic fracture

Lomonosov

Hess

2005

Journal of Applied Physics

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“…2͑b͒ being detected. 13 The square feature in the center of Fig. 2͑a͒ arises from a LBW traveling in the near-surface region.…”

Section: ͑4͒mentioning

confidence: 99%

“…This corresponds to a constant frequency surface in wave vector space. Figure 2͑b͒ shows the corresponding result of theoretical calculations for surface acoustic waves ͑SAW͒, pseudosurface acoustic waves ͑PSAW͒ and quasi-longitudinal bulk waves ͑LBW͒ ͑traveling parallel to the surface͒ on the same scale, 1,13,20 that is the slowness surfaces for these modes with the conventional axes k x / and k y / multiplied by the constant value of to give k x and k y . 21 ͑We have ignored small film loading and piezoelectric effects in the calculation.͒ The lines traced out by the experimental ͉G(k, )͉ are reproduced well by the theory.…”

Section: ͑4͒mentioning

confidence: 99%

“…This crystal is strongly anisotropic in this cut and results in a complex phonon focusing pattern, ideal for evaluating techniques for acoustic mode analysis. 9, 13 We use an ultrafast optical pump and probe technique based on a common-path interferometer. 14 Acoustic waves are thermoelastically excited at a ϳ4 m Gaussian spot ͑full width at half maximum intensity͒ in the sample using optical pulses normally incident from the substrate side at wavelength 415 nm, repetition rate 80 MHz, duration ϳ1 ps, and optical fluence ϳ2 mJ cm Ϫ2 , producing an initial transient temperature change ϳ200 K. With this impulsive source, broadband acoustic excitation up to ϳ1 GHz is achieved in the lateral direction, with maximum efficiency in the 300-700 MHz range ͑or wavelength ϳ7 m͒.…”

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confidence: 99%

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Direct access to the dispersion relations of multiple anisotropic surface acoustic modes by Fourier image analysis

Sugawara

Wright

Matsuda

2003

Applied Physics Letters

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We present a method based on a combination of temporal and spatial Fourier image analysis, involving the incorporation of a time-reversed acoustic propagation component, that can be used to obtain the angular dispersion or general dispersion relations of multiple surface acoustic modes excited by a localized pulsed source. The method is applied to the study of acoustic propagation at the surface of the highly anisotropic single-crystal TeO 2 coated with a thin gold film. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1602151͔ Surface acoustic wave propagation on bulk materials and thin film structures has proved of fundamental and practical interest for studying anisotropy and measuring film thicknesses or elastic properties. 1-6 A common method for such investigations is to use plane acoustic wave fronts, and to repeat the experiment for each propagation direction sequentially. However, the imaging of acoustic waves emanating from a point source is very useful for materials characterization because phenomena dependent on propagation direction, such as surface phonon focusing, can be effectively and immediately recorded with an omnidirectional acoustic wave vector distribution. [7][8][9][10][11] For surface acoustic imaging with impulsive point sources, the group velocity is readily measured from the wave front shape. However, it is the phase velocity-or its reciprocal, the slowness-that is more directly related to material elastic properties. 12 Impulsive point-source acoustic excitation of anisotropic samples by nature involves the generation of several surface and bulk acoustic modes that can produce complex overlapping wave fronts; no general method for the direct and automatic extraction of the individual dispersion relations ͑and hence the phase velocities͒ from such experimental images involving multiple propagating modes traveling parallel to the surface has been proposed. Previous methods can only be applied to images where only one acoustic mode propagates in any particular direction. 9 In this letter we present a general technique for analysis in time-resolved acoustic imaging at surfaces in the two lateral spatial dimensions that allows the extraction of the full set of dispersion relations for all excited modes simultaneously.We demonstrate the method with experiments on the transparent tetragonal crystal TeO 2 cut in the ͑001͒ orientation and coated with a thin polycrystalline gold film of thickness ͑40 nm͒ small enough to avoid significant thin film dispersion here and thus simplify comparison with theory. This crystal is strongly anisotropic in this cut and results in a complex phonon focusing pattern, ideal for evaluating techniques for acoustic mode analysis. 9, 13 We use an ultrafast optical pump and probe technique based on a common-path interferometer. 14 Acoustic waves are thermoelastically excited at a ϳ4 m Gaussian spot ͑full width at half maximum intensity͒ in the sample using optical pulses normally incident from the substrate side at wavelength 415 nm, repetition rate 80 MHz, du...

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“…As a class of optical materials, tellurium oxide (TeO 2 ) commands interest in terms of fundamental theory and engineering applications [1][2][3][4][5], for example, TeO 2 -based glasses find application in laser devices and nonlinear optics [6][7][8][9][10][11]. The a-phase of tellurium dioxide exhibits excellent acousto-optical properties arising from its elastic behavior and high birefringence [12][13][14][15].…”

mentioning

confidence: 99%