Abstract:

Intense laser radiation was used to generate a Rayleigh wave pulse of finite amplitude in fused quartz [A. Lomonosov and P. Hess, Proc. 14th ISNA, edited by R. J. Wei (Nanjing, 1996), pp. 106--111]. The laser beam was focused with a cylindrical lens to form a strip having dimensions 6 mmx50 (mu)m on the solid. Measurements of the vertical (normal) component of the particle velocity at the surface were made with a second laser beam at distances 2.3 and 18.3 mm away from the irradiated strip. The horizontal (in-plane) component is related through the Hilbert transform. A Rayleigh wave pulse of duration 50 ns, velocity amplitude 30 m/s, was measured at 2.3 mm and used as the initial condition for numerical calculations based on a theoretical model for nonlinear Rayleigh waves in isotropic solids [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569(A) (1992)]. Numerical predictions for the waveform at 18.3 mm are in close quantitative agreement with the measurement. Nonlinear propagation effects produced well-defined shocks with cusped spikes in the horizontal velocity waveform, and a nearly doubling of the pulse duration due to the different propagation speeds of the head and tail shocks. [Work supported by Volkswagen, ISF, NSF, and ONR.]