Scheme of the experimental setup. The pump laser illuminates the spherical mirror, launching the focused ultrasound beam. The plane of incidence of the optical probe beam is perpendicular to the plane of incidence of the ultrasound beam.
(a) Transient profile of surface slope induced by focused shear waves in silica. (b) The frequency spectra illustrate the intensity envelope of the laser pulse, the attenuation in water, and the spectrum of the PBD signal shown in (a).
Detailed spectra of transient profiles induced by the focused shear beam. Vertical lines represent the positions of critical frequencies, solid for symmetrical modes, and dashed for antisymmetrical modes.
Distribution of the maximum amplitude of the transient profiles at the free glass surface for the case of an angle of incidence of (a) and an angle of incidence of (b) .
(a) Faster arrival and nonlinear increase of the transient profile amplitudes for increasing laser pulse power density in the case of efficient Rayleigh wave excitation. (b) Nonlinear growth and widening of the spectra of the respective transient profiles.
Variation of the transient profile observed when the edge of the silicon wafer is approached by the probe spot. The “sharply focused” series is plotted as solid lines. In (a) the thick black line shows in addition the profile obtained far from the edge . “Weakly focused” transient profiles come early and are represented by dashed lines. The transient profiles in plot (b) were obtained at from the edge and those in (c) at .
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