Plasma Formation During Pulse-Periodical Laser Treating of Metals

Development of laser torch forming near the irradiated surface was investigated by means of fast holographic filming. It is shown that the density of plasma formation on the border of irradiated spot and in the centre are different. This effect is connected with different conditions of energy dissipation from the plasma connected with lateral unloading. The difference of concentration maximums on different regimes of laser treating is also observed. For instance, during mono-pulse action maximum is disposed in the centre of irradiated spot, during two-pulse action two maximums symmetrically removed from the centre are observed. This effect can be connected with the refraction of laser radiation in the already existing plasma. It is also shown that each laser pulse brings separate contribution in laser plasma formation on the surface of irradiated sample. For plasma plumes forming by the second and by next laser pulses presence of several plasma fronts supported by laser radiation and spreading along the laser beam in the already existing plasma is characteristic.