Vaporization of Metal Absorbing Laser Radiation

Abstract

The problem of vaporization of a light-absorbing metal into vacuum is considered. It is assumed that the density of the light energy flux is not excessively large so that there is no significant absorption of light by the vapor. The expansion of the vapor thus occurs in a centered rarefaction wave. The obtained boundary conditions relate the values of the hydrodynamic variables in the rarefaction wave with the surface temperature of the metal. This is accomplished by an approximate solution of the gaskinetic problem of vapor motion within a thin film directly adjacent to the phase interface. The velocity of the vaporization front, the surface temperature of the metal, the temperature and velocity of the vapor, and the recoil momentum are calculated.

Nanosecond Laser Ablation: Mathematical Models, Computational Algorithms, Modeling

“…Taking into account strong spatiotemporal diversity of processes in the nonequilibrium layer and continual media, KL is usually represented as a strong discontinuity in the gas-dynamic parameters. In such case, the kinetic processes in KL are not explicitly considered, and various phenomenological approaches [65][66][67][68][69][70][71][72] were used to determine boundary conditions on the outer side of the KL, which makes it possible without solving the kinetic problem, to determine the joining conditions under certain assumptions about the type of the nonequilibrium distribution function inside the discontinuity. One of the first works in which intensive evaporation was analyzed on the basis of phenomenological model is the work of Crout [65].…”

“…Later papers used Mott-Smith approach [66], which was applied to the structure of the shock waves. With the help of this approach [67,68] expressions for gas-dynamic parameters at M = 1 were obtained. Later in [69], this approach was extended to the entire range of evaporation 0 ≤ M ≤ 1.…”

Thermoelastic and Ablative Generation of Ultrasound: Source Effects

“…This is achieved within a few mean free paths by collisions between particles in a Knudsen layer region. The Knudsen layer is analyzed by treating this region as a gas dynamic discontinuity across which conservation of mass, momentum, and energy are applied [12,13]. This process has previously been modeled for the vacuum case [12], as well as for cases when the surface is surrounded by air at various pressures [13].…”

“…The Knudsen layer is analyzed by treating this region as a gas dynamic discontinuity across which conservation of mass, momentum, and energy are applied [12,13]. This process has previously been modeled for the vacuum case [12], as well as for cases when the surface is surrounded by air at various pressures [13]. For the present analysis, in order to calculate the pressure applied to the sample surface, it is only necessary to know the pressure jump across the Knudsen layer under vacuum conditions.…”

Ultrashort Laser Pulses Machining

“…Just a few years after the laser invention, it was already being used as a tool to ablate [14] and machine [15] a wide variety of materials, including metals [16], dielectrics [17], semiconductors [18], composites [19] and biological tissues [20]. At that time, the machining was based on thermal processes arising from the material heating by the laser [21], and the ablation occurred as a consequence of melting and vaporization resulting from phase transitions due to the heat deposited into the material being processed [22,23].…”