Effective Time of Nanogratings Formation on Sol-Gel Films by Two-Beam Laser Interference

The paper discusses the analytical modelling of periodic nanostructure formation on thin sol-gel films (SiO2 and AlZnO) by picosecond laser pulses utilizing a two-beam interference technique. The results obtained are in good correspondence with data of direct laser interference patterning of AlZnO films. The effective time, which includes the pulse duration, material heating, and cooling, is estimated for both cases. The heating time for films is determined by the thermodynamic equilibrium between the electron gas and atomic lattice. Heat outflow from the irradiation region results in cooling the films. As the first approximation, the effective time of nanograting formation is determined by thermal properties of a film, as well as by the period of the interference pattern and temperature distribution of a heat source. The nanogratings formation finishes during the film cooling and takes less than 5 ns from the start of irradiation. The formation time also depends on the interference pattern period and can be reduced by its decrease.