ABSORPTION OF THE LASER-BEAM BY THE PLASMA IN DEEP LASER-BEAM WELDINGOF METALS

We present a simple model for the keyhole plasma in deep penetration w elding with a laser beam. Simplifying the complete set of transport eq uations investigated by C. Tix and G. Simon [Phys. Rev. E 50, 453 (199 4)] for high laser powers yields an energy balance for the plasma, whi ch can be treated analytically. The mean plasma temperature is calcula ted accounting for higher charge states of the ions. For high laser in tensities double and higher charged ions dominate in the plasma bulk i n the case of iron. The degree of absorption remains approximately con stant for increasing laser power. The critical Peclet number for which the absorbed laser energy is able to maintain a keyhole increases str ongly with increasing laser power. The energy absorption by the plasma is enhanced for higher modes of the laser intensity distribution. (C) 1995 American Institute of Physics.