Nitrogen laser beam interaction with titanium surface

Solid titanium target was irradiated with a N_2 laser beam of a maximal energy density of 1.1 J/cm^2 per pulse and of a duration of 6 ns. The plasma, formed near the titanium surface, was analyzed by emission spectroscopy, and the irradiated Ti surface was studied by a metallographic microscope. The results of both investigations reveal the influence of resonant absorption of the laser radiation by the generated plasma. The plasma is dense and strongly ionized, with an electron density of 1.5×10^18 cm^-3 and electron temperature of 2.7 eV. The surface heating was found to be several times more efficient than in the cases when resonant absorption is absent. Most of the observed surface patterns appear to be caused by nonuniform surface heating and a very rapid cooling. The other features are interpreted as a possible consequence of plasma-hot surface interactions