Optimization of the ultraviolet nanosecond laser materials processing based on an analytical model

The Project is devoted to an optimization of the main effects of ultraviolet laser ablation based on a mathematical analytical model. The main goal of the project is to improve excimer laser ablation technology of materials processing - by obtaining an enhanced energetic efficiency of material removal and increased quality of processed structures (i.e. obtaining of laser spots having sharp clean boundaries with minimized melt dross, higher uniformity of material removal across the spot, greater spatial resolution, and with greater aspect ratio of obtained deep keyholes). Methods to achieve this goal include: 1) Development of an analytical thermal model of ultraviolet (UV) ablation of metals (aluminum, copper, steel), polymers (PE, PTFE), and oxides (Fe 2 O3 , ZrO2 ) by pulse nanosecond excimer laser radiation (wavelengths 193 and 248 nm, pulse duration 20-40 ns) with taking into account heat conduction, melting, evaporation and ablation plume shielding. 2) Optimization of a number of main effects in W laser ablation on the basis of the model developed. These main ablation effects to be optimized are following: a) Resolidified melt dross on the boundaries of laser spot. A search for ways to reduce or avoid it and thus to obtain high quality laser spots with accurate clean boundaries. b) Melt expulsion by vapour (plasma) on metals during nanosecond W laser ablation. A search for irradiation and material parameters giving an enhanced material removal efficiency, important for laser drilling. c) Droplets in laser ablation plume. A search for ways to eliminate them (important for improvement of quality in pulsed laser ablation deposition of thin films). d) "Dog ears"- an effect visualized for ``top-hat" (rectangular) spatial laser intensity distribution as a narrow region of increased material removal on the bottom of the spot, immediately adjacent to the side walls of the keyhole and looking like dog ears. A search for ways to obtain more uniform material removal across the spot. e) Effect of an external gas cross jet on a plasma plume behavior, material removal rate and prevention of oxidation, if mert gas is used. f) Saturation of plasma plume shielding in W laser ablation. Its dependence on metal reflectivity. g) Self-stopping ablation in multipulse excimer laser drilling of deep keyholes. A search for ways to obtain greater depth of "saturated" keyholes, with much smaller tapering angles and practically cylindrical straight side walls. The results of the proposed project besides of their fundamental significance (in mathematical modeling of high intensity laser-matter interaction, plasma physics) can have possible practical applications in industry, such as elaboration of new improved technologies of laser materials processing, fabrication of innovative devices.