Etude des plasmas générés par interaction laser-matière en régime confiné (application au traitement des matériaux par choc laser)

Abstract

In this work, we study the plasmas generated by laser-matter interaction in a water confinement regime, and more particularly, their application to laser-shock processing of materials. With the aim to get a better understanding of the physical processes involved in this particular interaction regime, an original modeling has been developed. First, a numerical code describing the breakdown process in water allows us to compute the characteristics (peak intensity and full width at half maximum pulse duration) of the laser pulse which is transmitted through the confinement window. These parameters are then used in an auto-consistent hydrodynamic model describing the confined plasmas (dense cold correlated and partially degenerated plasmas), in order to compute the thermal and mechanical loadings induced at the surface of the processed sample. Last, these loadings are used as input parameters in the FEM code ABAQUS to simulate the thermal and mechanical residual stresses induced by the process.The results of the simulations have been validated by comparison with various experimental measurements carried out with laser irradiation conditions (1064 nm and 532 nm wavelengths, 3 ns and 10 ns pulse durations) similar to those used for the industrial application of the process. These results show that small focal spot sizes allow to greatly reduce the heating of the target by the confined plasma, and thus to avoid the thermal effects induced by the process. This highlights the fact that such reduced focal spot sizes could be used in order to realize laser shock processing without any thermal rotective coating. Furthermore, they allow to explain recent results obtained with the process configuration eveloped by Toshiba (very small focal spot diameter, high repetition rate, no protective coating), which were not clearly understood until now.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF