COMPUTATIONAL STUDY OF HEAT-TRANSFER AND GAS-DYNAMICS IN THE PULSED-LASER EVAPORATION OF METALS

Pulsed laser irradiation of nanosecond duration is used in a variety o f applications, including laser deposition of thin films and micromach ining. Of fundamental interest is the prediction of the evaporative ma terial removal rates, as well as the velocity, density, and temperatur e distributions of the ejected particles as functions of the laser-bea m pulse energy, temporal distribution, and irradiance density on the t arget material surface. In order to address these issues, the present work establishes a new computational approach for the thorough treatme nt of the heat transfer and fluid flow phenomena in pulsed laser proce ssing of metals. The heat conduction in the solid substrate and the li quid melt is solved by a one-dimensional transient heat transfer model . The ejected high-pressure vapor generates shock waves against the am bient background pressure. The compressible gas dynamics is computed n umerically by solving the system of Euler equations for mass, momentum , and energy, supplemented by an isentropic gas equation of state. The aluminum, copper, and gold targets considered were subjected to pulse d ultraviolet excimer laser irradiation of nanosecond duration. Result s are given for the temperature distribution, evaporation rate, and me lting depth in the target, as well as the pressure, velocity, and temp erature distributions in the vapor phase. (C) 1995 American Institute of Physics.