V.I. Mazhukin

Overheated metastable states in pulsed laser action on ceramics

Volume overheating of solid and liquid phases in pulsed laser evaporation of superconducting ceramics is analyzed by numerical simulation. The mathematical model includes the processes of heating (with a volume energy release), melting‐solidification, and evaporation. It is shown that the maximum values of overheating of the solid phase (with respect to its melting point) exceed 100 degrees and those of the liquid phase exceed several hundred degrees (with respect to the surface temperature). The times of existence of these metastable states are tens and hundreds of nanoseconds, respectively. The dynamics of the processes are analyzed in a wide range of variation of the absorption coefficient (i.e., laser wavelength). It is shown that the probability of explosive decay of the metastable states in the solid phase increases with laser wavelength, whereas for the metastable states in the liquid phase the overheating parameters exhibit a maximum versus laser wavelength.

2D-simulation of the system : laser beam + laser plasma + target

The simulation is based on a set of two-dimensional transient equations of gas dynamics with two-dimensional radiation transfer equation completed by heat transfer equation for condensed phase. The influence of the laser radiation wavelength and the choice of the diameter of the initial high-temperature region in the gas phase (i.e. the region of optical breakdown) on the laser plasma dynamics and the transfer of the laser and plasma radiation energy to the target are analyzed.

Influence of temperature gradient to solidification velocity ratio on the structure transformation in pulsed- and CW-laser surface treatment

Abstract The temperature gradient G, the solidification velocity R, and the G/R ratio are used in solid-liquid interface analysis. The critical G/R values characterizing the transitions from a planar front to a cellular structure, and from a cellular to cellular-dendritic structure during solidification are determined. The regularities of the rapid solidification process are shown on the example of the titanium alloy subjected to boriding with a CW-laser. The G/R ratio and cooling rate values versus molted zone depth are analyzed. The dependence of the relative transition depth from cellular to cellular-dendritic structure on laser beam velocity is determined.

SIMULATION OF LASER MELTING AND EVAPORATION OF SUPERCONDUCTING CERAMICS

The peculiarities of pulsed laser melting and evaporation of the superconducting ceramics are analyzed by means of numerical simulation. The appearance of the overheated metastable states in solid and liquid phases is shown as a result of the phase front dynamics and volume nature of laser energy release. A method of dynamic adaptation for the multifront Stefan problem is proposed.

Peculiarities of laser melting and evaporation of superconducting ceramics

Abstract Pulse laser melting and evaporation of superconducting ceramics is simulated numerically. The dynamics of both phase fronts (evaporation and melting/solidification) are analysed during the whole thermal cycle. The appearance of overheated metastable states in the solid and liquid phases as a result of the phase front dynamics and the volume nature of laser energy release is shown. The influence of the volume absorption coefficient (or wavelength of laser radiation) on heat phenomena is analysed.

The influence of the electron structure of atoms shells on characteristics of optical breakdown in metal vapour

By making use of the collision-radiative model that describes the phenomenon of optical breakdown in a metal vapour, the influence of the electron structure of atoms shells on the threshold intensity and breakdown period is analyzed. Two metals to be examined, aluminium and copper, are close in their thermo-physical properties but differ in the configuration of the electron shells of their atoms. General characteristics of optical breakdown, the influence of excitation energies of the neutral atom electron shells, as well as the ionisation potential, and the influence of higher excited states on threshold intensity and breakdown period are analyzed.