Pulse time profile influence on laser processing

M. G. Lobok ; V. I. Mazhukin

Matematičeskoe modelirovanie, Tome 19 (2007) no. 9, pp. 54-78

Résumé

Theoretical analysis of laser pulse time shape influence on speed of heating process, phase transformations and material removal, was made based on multi-front Stefan problem. Modeling revealed that quantitative and qualitative characteristics of the processes, that take place in radiated surface, depending on whether the system switches to quasi-steady or steady state during the pulse duration. In steady state material removal is controlled by specific heat of evaporation, in the same time, for highly non steady states leading role has thermal conductivity and capacity. For that reason during short pulse interactions ($\tau_L\le 10^{-6}$s) thermal mechanism leads to intensive removal of metals with low thermal conductivity (titan). During long interactions ($\tau_L\approx10^{-4}-10^{-3}$s), when the system goes to steady (or quasi-steady) state, the amount of removed media depends on the specific heat of evaporation and does not depend on thermal conductivity of the material. Copper, that has high thermal conductivity metal, and with specific heat of evaporation lesser than titan's, mass removal during quasi-steady processes is higher.