Two complementary ways of thin-metal-film patterning using laser beam interference and direct ablation

Abstract

Interference of several identical laser beams allows for the fabrication of periodical structures over large areas. We present two complementary techniques for the patterning of thin films using the laser beam interference and direct ablation of material. The first one is based on precise control of the laser fluence relative to the ablation threshold of the film. Additional means for pattern management are provided by separate control of the intensity and phase of the interfering laser beams. Interference of four or six laser beams permits fabrication of periodical arrays of circular holes. Flexibility and sensitivity to the process parameters of the method beyond of simple hole arrays are shown for the thin Cr film ablation. Another versatile means for pattern generation in the films is the scanning of the periodic laser beam distribution over a workpiece in a sub-period area. By translation of the sample in small steps between laser shots, the structures with their shape independent of the interfering beam intensity distribution can be fabricated by overlapping the ablated holes. Slit- and cross-shaped periodical structures were fabricated using direct structuring with interfering nanosecond and femtosecond pulses. The thin-film structures fabricated by both techniques can be used as spectrally-selective elements for terahertz and infrared radiation.