Quantitative assessment of laser-induced stress waves

Reproduced with permission from B.P. Fairand, A.H. Clauer, R.G. Jung, and B.A. Wilcox, “Quantitative assessment of laser-induced stress waves generated at confined surfaces,” Applied Physics Letters, 25 (8), 431-433, (1974). Copyright 1974 by American Institute of Physics.

B. P. Fairand, A. H. Clauer, R. G. Jung, and B. A. Wilcox Battelle Columbus Laboratories, Columbus, Ohio 43201. Received 22 April 1974; in final form 15 July 1974)
Laser-induced stress waves in iron samples were analyzed by measuring the pressure environment at the back surface of various sample thicknesses. These results were compared with numerical calculations obtained from a one-dimensiona1 radiation hydrodynamics computer code.  The experiments were conducted in an air environment under ambient conditions and the metal surfaces were confined by transparent overlays. Peak pressures exceeding 50 kbar were measured with quartz pressure transducers at a laser power density of about 109 W/cm2. Computer predictions agreed favorably with the experimental results and indicated that peak pressures exceeding 100 kbar could be generated by appropriate modifications in the laser environment and target overlay configuration.

Generation of stress waves in solids using high-power pulsed lasers has been pursued for some time. 1-6 Over the past four years various methods to enhance the magnitude of these stress waves by modifications in the target surface conditions have received considerable attention. 7-13 In an earlier study it was established that the in-depth microstructural and mechanical properties of aluminum alloys covered with transparent overlays were significantly altered when they were irradiated in air by a highpower Q-switched laser. 14 The laser-induced pressure environment was not monitored in those experiments. However, the high dislocation densities observed from transmission electron micrographs strongly suggested that high-amplitude stress waves, i.e., well above the dynamic yield strength of the material, were being propagated in depth. This paper reports on experiments with iron-base alloys where quartz piezoelectric transducers were used to dynamically measure the pressure environment as a function of sample thickness. The measured shape of the pressure pulse and its magnitude were compared to theoretical calculations performed by a one-dimensional radiation hydrodynamics computer code. Additional computer studies were made to assess the effect of different sample surface configurations on stress wave production. These studies confirmed that peak pressures exceeding 100 kbar can be generated with a high-power Q-switched laser.

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