Laser ablation of Cu and plume expansion into 1atm ambient gas

Abstract

A one-dimensional gas-dynamic model is presented for the laser ablation of Cu and the expansion of the Cu vapor in a background gas ͑He͒ at 1 atm. The ionization of Cu and He, the inverse bremsstrahlung absorption processes and photoionization process, and the back flux onto the target are considered simultaneously. The binary diffusion, the viscosity, and the thermal conduction including the electron thermal conduction are considered as well. Numerical results show that the consideration of ionization and laser absorption in the plume greatly influences the gas dynamics. The ionization of Cu enables the recondensation at the target surface to happen even during the laser pulse. The ionization degree of Cu and He may change greatly with the location in the plume. For laser irradiances ranging from 2 to 9 ϫ 10 12 W/m 2 , the simulations show that the second-order ionization of Cu competes with the first-order ionization. In the region close to the target surface, the first-order ionization of Cu dominates. In the core of the plasma, the second-order ionization of Cu may dominate over the first-order ionization at laser irradiances higher than 7 ϫ 10 12 W/m 2 . In the mixing layer, the first-order ionization of Cu is always more important than the second-order ionization although the latter increases monotonously with laser irradiance. The ionization of He is only important in the mixing layer. The plume expansion velocity is much larger than that without ionization and laser absorption by the plume. The relative importance of different laser absorption mechanisms may change with time. Close to the surface photoionization and electron-neutral inverse bremsstrahlung are always important. Once the ionization in the plume starts, at later time, electron-ion inverse bremsstrahlung can become more important than photoionization in the plume core until the shock wave front. Unlike in the vacuum case, electron-neutral inverse bremsstrahlung is very strong due to the relatively high number density of neutral atoms in the plume in the presence of a dense ambient gas. A similar laser irradiance threshold is found for the ablation rate and the plasma formation in the plume, which agrees well with the case of nanosecond laser ablation of metals in vacuum.

Plasma enhancement of femtosecond laser-induced electromagnetic pulses at metal and dielectric surfaces

“…26 examined similar experimental parameters with a 1-atm Helium gas background 27 and found qualitatively similar results, albeit without the sharp, 1 to 2-ns scale laser reflection/absorption feature. We infer from this simulations that the nanosecond pulse-generated plasma density in our experiment can be near the critical density for absorption of the femtosecond laser wavelength, and that the plasma density may encourage efficient transmission and eventual absorption of the femtosecond laser pulse, when the femtosecond pulse is incident on the target sometime within the duration of the nanosecond laser pulse.…”

Morphology of ejected particles and impact sites on intercepting substrates following exit-surface laser damage with nanosecond pulses in silica

“…Measurements of dynamic parameters of these explosive processes (such as the generation and propagation of the shock wave and the ionized gas, and kinetics and distribution of ejected and redeposited particles as a function of laser parameters and energy deposited) have provided insight into the dynamics of the generated ejection plume. [1][2][3][4][5][6][7][8] Experimental evidence and modeling suggest that the material is exposed to pressures of the order of 10 GPa and temperatures of the order of 1 eV. [9][10][11][12] Considerably less information exists on the relaxation of the metastable superheated material and the surrounding "cold" material that was exposed to high pressures and stresses generated during the process.…”

Modeling of Plasma Expansion during Pulsed Electron Beam Ablation of Graphite

“…, , and are the temperature, density, and pressure at the target surface, respectively, and is the specific heat ratio of vapor. The boundary conditions are, Plasma properties have been calculated from relationships and expressions given in Chen and Bogaerts [13]. Equations (1-10) have been set up and solved using COMSOL Multiphysics ® .…”