The onset and absorption of ionisation in the vapour for laser keyhole welding

The question of the transfer of energy from the laser beam to the work piece by inverse bremsstrahlung is considered in the case of laser keyhole welding and an equation is established for the conduction of this energy to the walls of the keyhole. From this the rate of transfer of power from the beam to the vapour by inverse bremsstrahlung and by conduction to the walls of the keyhole can be deduced, as well as the temperature distribution in the vapour in terms of the power of the laser and ambient conditions. It is found that there is a threshold below which no power is transferred by this mechanism, but that above this threshold there is a simple approximate relation between the incident power of the laser at a given cross section of the keyhole and the power absorbed by this mechanism at the keyhole wall. From these relations a simple model of the power absorbed by the work piece is constructed.