Wavelength dependent of laser shock-wave generation in the water-confinement regime

The generation of high-intensity shock waves by laser plasma in the water-c onfinement regime has been investigated at 1.064, 0.532, and 0.355 mu m las er wavelengths. Experimental characterizations of pressures induced by lase r plasma have been performed with a velocimetry interferometer for any refl ector. For each incident laser wavelength, above a laser power density thre shold, maximum pressure levels saturate and the pressure durations are redu ced due to parasitic plasma occurring in water. However, it is shown that t his threshold is lower at the 0.532 and 0.355 mu m wavelengths than at the 1.064 mu m wavelength. The generation of the parasitic plasma in water is e asier with a short wavelength because it would be dominated by multiphotoio nization mechanisms. Below the saturation pressure threshold, the pressure levels are significantly higher at the 0.532 and 0.355 mu m wavelengths tha n at the 1.064 mu m wavelength. Unlike the detrimental effect of short lase r wavelengths on water breakdown plasma, the confined laser interaction is shown to be more efficient in ultraviolet than in infrared laser irradiatio n. (C) 1999 American Institute of Physics. [S0021-8979(99)03811-6].