초정밀 레이저 3D 가공 기법을 이용한 회절광학소자 제작

Abstract

A femtosecond laser has been used to fabricate Fresnel zone plates (FZPs) on the surface and inside of the fused silica plate. The radii of the annuli of the Fresnel zone plates are designed such that the phases of an input laser beam alternatively with respect to the increases of the annuli are changed byl/2 to have a specific focal point from the FZP. The beam transmittance of FZPs depending on the fabrication depths due to the filament effects due to strong powers of a femtosecond laser are measured. There are two types of fabricated FZPs with a single layer and multiple layers. A FZP with the multiple layers is fabricated to enhance the diffraction efficiency compared to FZP with a single layer. In addition to this method, a method of melting silica glass with different mesh sizes and with high melting point and damage threshold have been implemented to make 3-D shapes of FZPs using femtosecond and CO2lasers. In this way 3-D shapes of the FZPs with variable thickness of the FZP can be obtained instead of fabrications of FZPs due to small ablation or small changes of index of refraction of the fused silica crystal implemented above. Specific shapes with same lattice structures on a fused silica plate having the same lattice structure fabricated using a CO2laser can be obtained similarly as those using a high-temperature chamber.