Laser-delayed double shock-wave generation in water-confinement regime

Abstract

This paper investigates the different physical processes involved during laser-delayed double shock-wave generation in water-confined geometry. With this technique, two laser pulses, separated by a Δt duration, irradiate a target immersed in water at an intensity of a few GW/cm2 and form a high pressure plasma which results in a double shock-wave generation. This 2 pulses configuration is currently being investigated as an attractive method for improving the LASer Adhesion Test (LASAT) [L. M. Barker and R. E. Hollenbach, J. Appl. Phys. 43, 4669–4674 (1972)] technique by adapting the time delay Δt to the position of interfaces. The LASAT technique is a noncontact adhesion test allowing to generate a high-level tensile stress near interfaces with the use of laser-driven shock wave. The generation of two delayed high-intensity shock waves by laser plasma in the water-confinement regime has been investigated at 10ns@532 nm with the new Nd:YAG laser GAIA from Thales Laser company in the new facility HEPHAISTOS. For each incident Gaussian laser impulsion, the characterization of the high-amplitude laser-plasma-generated shock wave and its propagation through the target has been performed using a velocity interferometer system for any reflector [L. Berthe et al., “State-of-the-art laser adhesion test (LASAT),” Nondestr. Test. Eval. 26(3–4), 303–317 (2011)]. The new laser facility allows us a nanosecond-control of the time delay between the two laser pulses and a precise control of each laser maximum-intensity. Therefore, the influence of the first laser-induced plasma, on the second shock-wave generation has been studied by modifying different parameters such as the delay Δt and the intensity I1 and 12 of each pulse and different aluminum plate thicknesses from 0.2 to 1.5 mm. Preliminary tests show that the maximum pressure level of the second generated shock wave is sensitive to the time delay between the two impulsions and influenced by the plasma generated by the first laser pulse.