Nonstationary plasma-thermo-fluid dynamics and transition in processes of deep penetration laser beam-matter interaction

摘要

A qualitative analysis of the role of some hydrodynamic flows and instabilities by the process of laser beam-metal sample deep penetration interaction is presented. The forces of vapor pressure, melt surface tension and thermocapillary forces can determined a number of oscillatory and nonstationary phenomena in keyhole and weld pool. Dynamics of keyhole formation in metal plates has been studied under laser beam pulse effect ($lambda $EQ 1.06 $mu@m). Velocities of the keyhole bottom motion have been determined at 0.5 $MUL 10$+5$/ - 10$+6$/ W/cm$+2$/ laser power densities. Oscillatory regime of plate break- down has been found out. Small-dimensional structures with d-$lambda period was found on the frozen cavity walls, which, in our opinion, can contribute significantly to laser beam absorption. A new form of periodic structure on the frozen pattern being a helix-shaped modulation of the keyhole walls and bottom relief has been revealed. Temperature oscillations related to capillary oscillations in the melt layer were discovered in the cavity. Interaction of the CW CO$-2$/ laser beam and the matter by beam penetration into a moving metal sample has been studied. The pulsed and thermodynamic parameters of the surface plasma were investigated by optical and spectroscopic methods. The frequencies of plasma jets pulsations (in 10 - 10$+5$/ Hz range) are related to possible melt surface instabilities of the keyhole.