Study on Fabrication of the Nano-sized Periodic Structure by Femtosecond Laser Irradiation. -Mechanism of the Nano-sized Periodic Structure by Thin Cu Film on the Surface of Fused Silica-

Abstract

Femtosecond lasers can be used for forming the nano-sized periodic structure on the surface of fused silica. However, the processing control range is narrow and unstable due to the nonlinearity of the multiphoton absorption process. By coating the surface with a thin metallic film, we found that the periodic structure can be formed easily below the ordinary ablation threshold for fused silica. But, the periodic structure processing mechanism was not understood. We proved the thing that the thin metallic film on the fused silica contributed to a nano-sized periodic structure formation. When fused silica coated copper was irradiated with femtosecond laser, micro-sized Copper particles were formed on the surface of fused silica and the priodic structure of 800nm size was formed around micro-sized Copper particles. 800nm periodic structure formed around there by interference of the diffraction light of laser. Copper remains convex section of the 800nm periodic structure, and that is localized surface plasmon polariton (SPP). The nano-sized periodic structures is formed by SPP around nano-sized copper particles. We found the processing condition to determine nano-sized periodic structure. The pitch length of nano-periodic structure is determined by the volume of copper and the laser energy density. The depth of the structure is determined by the number of pulses of laser irradiation.