A contribution to the understanding of the plasma ignition mechanism above a metal target under UV laser irradiation

Abstract

In this paper, the plasma ignition process above a metallic surface submitted to UV laser irradiation is studied. An easy model based on the hypothesis of thermal equilibrium between ejected vapour and heated surface, and of a local thermodynamic equilibrium state of the vapour, is used to characterize the metallic vapour at the end of the laser pulse. Then the efficiency of the different elementary mechanisms liable to sustain or to prevent the ionization process in this medium is discussed depending on the laser power density. In this work, the calculations are applied to the case of the interaction between an excimer XeCl laser beam (λ = 308 nm, τ 1 = 28 ns) and titanium target. It is shown that the thermal heated metallic vapour is partially ionized and contains excited and singly ionized species at high densities (10 19 -10 20 atoms cm −2 ). The electron temperature in this medium is found to be around 1 eV. The study of the ionization rise in the vapour evidences the important role played by the single-photon ionization process and the electron/ion inverse bremsstrahlung effect. For laser power densities above 100 MW cm −2 (laser fluence of 2 J cm −2 ), the ionization level is found to increase before the laser pulse end, and a thermal evaporation regime is reached. As the laser power density exceeds 500 MW cm −2 (fluence of 10 J cm −2 ), an avalanche breakdown is liable to occur in the vapour before the pulse end and the plasma governs the evaporation mode. The results presented here are in good agreement with experimental observations and with results from more complex models reported in the literature.

Conformity of Aluminum Thin Films Deposited onto Micro‐Patterned Silicon Wafers by Pulsed Laser Deposition, Magnetron Sputtering, and CVD

“…The high density and featureless structure of the PLD films is typical of a high energy deposition process (zone II according to the literature9) and is due to the large kinetic energy carried by the Al atoms in the plasma plume expending in vacuum. The mean Al atom energy is of the order of tenths of eV, against several eV in MS 9, 23. In the latter case, the structure shown by SEM (see Fig.…”

Dynamics of UV short pulse laser-induced plasmas from a ceramic material “titanium carbide”: a hydrodynamical out of equilibrium investigation

“…Ti * + 5 eV→ Ti + +e − C * + 5 eV → C + +e − 4-The inverse Inverse Bremsstrahlung absorption: which considers the electron-neutral (Zel'dovitch, 1966) and electron-ion absorptions (Thomann et al 1997…”

Modeling and numerical simulation of laser matter interaction and ablation with a 193 nanometer laser for nanosecond pulse

“…Gremi (Thomann et al , 1997): Equation 50 Equation 51 e Si + is the ionization potential of the silicon from its fundamental level 8.1 eV (Zeldovitch and Raizer, 1966).…”