A finite element model to predict the ablation depth in pulsed laser ablation

Effect of surface roughness on the ultrashort pulsed laser ablation fluence threshold of zinc and steel

Here, we employ theory and experiments to investigate the laser ablation process of a metal (Al) using nanosecond laser-pulses at 532 nm wavelength in atmospheric air. We analyze experimentally the dependence of the ablation rate of Al on laser fluence which is varied over a wide range (from ∼4 to 500 J/cm2) by changing the laser pulses energy. The experimental data indicate that the ablation rate increases approximately linearly to ∼1.5 μm/pulse when increasing the fluence to ∼50 J/cm2, whereas further increase of the laser fluence leads to a much slower, non-linear increase of the ablation rate. By extrapolating towards zero the linear fitting curve, we find the ablation threshold fluence of Al to be ∼1.9 J/cm2. To understand and control the underlying phenomena involved in laser ablation, we propose a robust and efficient theoretical model for reliable yet fast calculation of the ablation rate of metals. We use a one-dimensional photo-thermo-hydrodynamic model that accounts for the material heating, melting, evaporation, melt ejection, and ablation plasma shielding during nanosecond laser irradiation. The model considers that the reflectivity of the target surface, the heat capacity, thermal conductivity, and the mass density of the metallic material depend on the aggregation state. The non-linear heat equation of the model is solved numerically in a multi-step iterative method. The solution of the heat equation gives the time evolution of the temperature within the target, leading further to the evaporation and melt ejection velocities, and to the ablation rate. There is a good agreement between the numerical and the experimental results on the ablation rate for a very wide fluence range, i.e., up to 150 J/cm2 when phase separation occurs in the ablating layer whose average temperature during the laser pulse reaches the Al critical temperature. The validity fluence range of the present model is approximately one order of magnitude wider than in previous theoretical works on nanosecond laser ablation of metals.

Theoretical photo-thermo-hydrodynamic approach to the laser ablation of metals

Fabrication of laser deposited high-quality multilayer zone plates for hard X-ray nanofocusing

Tin oxide (SnO 2 ) thin films were grown on Si (1 0 0) substrates using pulsed laser deposition (PLD) in O 2 gas ambient (10 Pa) and at different substrate temperatures (RT, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). XRD measurements showed that the almost amorphous microstructure transformed into a polycrystalline SnO 2 phase. The film deposited at 400 °C has the best crystalline properties, i.e. optimum growth conditions. However, the film grown at 300 °C has minimum average root mean square (RMS) roughness of 3.1 nm with average grain size of 6.958 nm. The thickness of the thin films determined by the ellipsometer data is also presented and discussed.

Effects of deposition temperature on the structural and morphological properties of SnO2 films fabricated by pulsed laser deposition

Finite element analysis of the initial stages of the laser ablation process

The ablation process induced by excimer lasers is a collective phenomenon that basically involves two phenomena: the laser radiation–matter interaction and the dynamic of the ablation plume. The laser parameters, the thermal and optical properties of the material, and the surface morphology are critical factors in the ablation mechanisms affecting the direction of the ablation plume expansion. In this study, the role of the surface roughness and the evolution of its morphology under the laser irradiation were investigated. Assuming a thermal ablation model, a theoretical study of the initial steps of the laser ablation process by a finite element method using ANSYS (6.1) was performed. Different ablation experiments were carried out on silicon and copper targets using a XeCl laser. The target surface morphology changes were observed by SEM and the plume deflection was recorded by a digital camera. An acceptable agreement between the experimental and simulated results was found. This study contributes to a better understanding of the physical processes involved in the laser ablation and the relations between the plume deflection angle and the surface roughness.

Laser ablation of silicon and copper targets. Experimental and finite elements studies

The conventional configuration (substrate parallel and frontal to the target surface) of the pulsed laser ablation deposition technique has been modified for improving the film uniformity with acceptable deposition rates, leading to the ‘dynamic deposition configuration’. The novelty of this arrangement is the ability to place by computer-control the substrate synchronously in front of the plume axis compensating the plume deflection effect. The new geometrical configuration was used to deposit films of Ti, Al and Cu. All the deposited films exhibited both high thickness uniformity and remarkable deposition rates. Initial results of the experiments are explained and compared with the results obtained in the conventional configuration, in otherwise similar experimental conditions.

The pulsed laser ablation deposition technique: a new deposition configuration for the synthesis of uniform films

Detailed studies of the plume deflection effect during long laser irradiation of solid targets

The results of a new geometrical configuration of pulsed laser ablation deposition technique that uses a hemi-cylindrical transparent plastic substrate are presented and discussed With the new arrangement, two distinct components with different material compositions have been clearly observed While the first component comprises atoms, ions and molecules and constitutes visible or the so-called “luminous” plume, the second component is formed of fragments, clusters and liquid droplets and is invisible to the naked eye The latter component constitutes a major part of the ablated material The luminous plume symmetry axis does not coincide with the mass distribution symmetry axis In the case of Si ablation and 45° incident beam angle, the maximum deflection angle of the luminous plume reaches 30° with respect to the normal to the target surface, while the deflection angle of the second component is higher than 40° The change in the target morphology and the dependence of the composition of the ablated material on local fluence, along with the hydrodynamic effects, is sought to explain this previously unexpected and unreported phenomenon

Plume separation effect in pulsed laser ablation deposition

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