Modification of thin metallic films using ultrashort laser pulses involves interplay of numerous physical processes. Finding a right combination of laser parameters is essential for achieving the desired modification of a thin film deposited on a substrate. Numerical modeling is a convenient tool for gaining insights into ultrafast evolution of material properties and to predict an optimal range of irradiation parameters. In this work, a mathematical model is presented that describes the ultrafast laser heating and temperature relaxation in a thin molybdenum film deposited on a glass substrate. The laser energy absorption by molybdenum is described using a two-temperature model. The model takes into account the heat exchange between the film and the substrate through a boundary condition applied on the lattice temperature. The implicit numerical scheme employed for simulations was verified in respect of energy conservation. The model has been validated by comparison with experimental data on melting threshold fluences. ultrashort laser pulses, thin film, melting threshold, twotemperature model, energy conservation
A systematic experimental study was performed to determine laser irradiation conditions for the large-area fabrication of highly regular laser-induced periodic surface structures (HR-LIPSS) on a 220 nm thick Mo film deposited on fused silica. The LIPSS were fabricated by scanning a linearly polarized, spatially Gaussian laser beam at 1030 nm wavelength and 1.4 ps pulse duration over the sample surface at 1 kHz repetition rate. Scanning electron microscope images of the produced structures were analyzed using the criterion of the dispersion of the LIPSS orientation angle (DLOA). Favorable conditions, in terms of laser fluence and beam scanning overlaps, were identified for achieving DLOA values <10∘. To gain insight into the material behavior under these irradiation conditions, a theoretical analysis of the film heating was performed, and surface plasmon polariton excitation is discussed. A possible effect of the film dewetting from the dielectric substrate is deliberated.
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