MECHANISM OF LASER WELDING
Laser welding of metals is performed with beams focused to irradiate levels in the range of 106 to 107 W / cm2. At such power densities, melting occurs in less than a millisecond. First, the radiation pressure becomes appreciable capable of supporting 0.5 mm liquid steel column. Next, the molten liquid has an appreciable vapour pressure. The metal vapour, now interacts with light through the process of inverse population, where electrons in the field of an ion may be accelerated by electromagnetic radiation. This heats the vapour, increasing the number of ions and hence the absorption. Now the plasma, which is a highly ionised gas that absorbs laser light and emits back body radiation. As long as power density is sufficient to sustain it the plasma will act as an efficient absorber.