| This dissertation is a theoretical study of energy absorption and the formation of large scale surface structures in laser-surface interaction, which are crucial to pulsed laser deposition. Studied in detail are the energy absorption at high photon flux for various wavelengths and pulse durations, including the effects of surface roughness and impurities. The stability of the laser-irradiated surface is studied.; A Kelvin-Helmholtz instability model is used to successfully explain, for the first time, the formation of large scale surface structures with a rather regular wave pattern. These large scale surface structures are observed on an aluminum target after it is ablated by multipulse (250 – 4200) KrF excimer laser irradiation (248 nm, 40 ns, 5 – 10 J/cm2). This wave pattern has a spacing of order 30 μm, which is much larger than laser wavelength. By using parameters inferred from measurements, the Kelvin-Helmholtz instability growth rate is calculated in terms of the thickness of molten layer, the spatial extent and the kinetic energy density of the surface plasma plume. The maximum growth rate is estimated to be about 0.66 μs -1 (per pulse), at the kinetic energy density of about 0.26 J/cm 3. The growth rate and the prevailing wavelengths are in qualitative agreement with the multipulse experiments.; The large scale surface roughness is important in short-wavelength multipulse laser ablation on a metallic target. The multiple reflections of laser light on the rough surface, whose roughness scale is much larger than laser wavelength, may increase the energy absorption over a flat surface by an order of magnitude. A scaling law for the enhanced absorption as a function of degree of roughness, laser wavelength and material properties is derived from a simple statistical model.; The resonant absorption of a short laser pulse in a doped dielectric slab is studied. The resonant absorption by the impurities is due to their finite linewidth at the transition frequency, which is taken to be close to the laser frequency. The model predicts that tens of percent of the laser energy could be absorbed with a modest amount of impurity over a wide range of parameters. It is found that the energy absorption efficiency is maximized for a certain degree of doping concentration (at a given laser pulselength) and also for a certain pulselength (at a given doping concentration). This study could also be of interest to the semiconductor industry, as it may be used to determine the proper amount of photochemicals in photoresists, when various lithography wavelengths (e.g., 436, 365, 248, 193 nm, etc.) are used. |
