Saturation gain-length product during short-wavelength plasma lasing Appl. Phys. Lett. 101, 081105 (2012) Laser induced avalanche ionization in gases or gas mixtures with resonantly enhanced multiphoton ionization or femtosecond laser pulse pre-ionization Phys. Plasmas 19, 083508 (2012) A new scheme for stigmatic x-ray imaging with large magnification Rev. Sci. Instrum. 83, 10E527 (2012) Additional information on J. Appl. Phys.Generation of a high amplitude shock wave by laser plasma in a water confinement regime has been investigated for an incident 25-30 ns/40 J/ϭ1.064 m pulsed laser beam. Experimental measurements of temporal and spatial profiles of induced shock waves for this regime of laser shock processing of materials were performed using a velocimetry interferometer system for any reflector system. Above a 10 GW/cm 2 laser intensity threshold, a saturation of the peak pressure is shown to occur while the pressure pulse duration is reduced by parasitic plasma occurring in the confining water. The observation of the interaction zone with a fast camera system shows that this breakdown plasma, which mainly occurs at the very surface of the water rather than within the water volume, limits the efficiency of the process. This plasma absorbs the incident laser energy, and the power density reaching the target gradually decreases with increasing power densities while the shock-wave duration is correspondingly reduced. Both pressure measurements and plasma observations allow explaining the current limit of high amplitude shock-waves generation by laser plasma in the water-confinement mode and open new research areas for the understanding of breakdown plasma effects at the surface of the confining water. © 1997 American Institute of Physics. ͓S0021-8979͑97͒03618-9͔

The generation of high-intensity shock waves by laser plasma in the water-confinement regime has been investigated at 1.064, 0.532, and 0.355 μm laser wavelengths. Experimental characterizations of pressures induced by laser plasma have been performed with a velocimetry interferometer for any reflector. For each incident laser wavelength, above a laser power density threshold, maximum pressure levels saturate and the pressure durations are reduced due to parasitic plasma occurring in water. However, it is shown that this threshold is lower at the 0.532 and 0.355 μm wavelengths than at the 1.064 μm wavelength. The generation of the parasitic plasma in water is easier with a short wavelength because it would be dominated by multiphotoionization mechanisms. Below the saturation pressure threshold, the pressure levels are significantly higher at the 0.532 and 0.355 μm wavelengths than at the 1.064 μm wavelength. Unlike the detrimental effect of short laser wavelengths on water breakdown plasma, the confined laser interaction is shown to be more efficient in ultraviolet than in infrared laser irradiation.

Confined plasmas induced by neodynium glass laser at 1.06 μm and pulse width of 3 and 30 ns are studied. The metallic target is covered with a dielectric layer, glass or water, transparent to the laser radiation. Experimental measurements of the pressure induced by the plasma have been performed. For a certain range of laser power density these measurements agree particularly well with an analytical model. At high power densities (10 GW/cm2), the dielectric breakdown appears to be the main limiting process of the confining method. It is observed that this breakdown induces a saturation of the pressure. It is shown that the use of a short-rise-time laser pulse is the only way to reduce the effects of the breakdown and to obtain much higher-pressure shock waves. This is due to the dependence of the dielectric breakdown threshold on the laser pulse rise time.

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