Fabrication of sine-top broadband gold-coated gratings

Abstract

Broadband gold-coated grating (BGCG) is one of the key elements of large pulse compression systems. Compared with other pulse compression grating (PCG), BGCG have the advantages of simple structure and low cost etc. More importantly, this kind of grating can get high diffraction efficiency within a broadband range (usually 200 nm or more). In this paper the authors report a process for fabrication of sine-top BGCG. When gratings are intended for use with high-power lasers, their laser-damage threshold has an importance equal to that of the diffraction efficiency. These gratings fabricated by this method differ from conventional metal-on-photoresist PCGs in that the gratings patterns are generated by etching the fused silica substrate directly. This can improve the laser damage threshold. The groove depth and duty cycle of the photoresist mask were controlled by changing photoresist thickness and adjusting exposure and development time. The duty cycle of the fused silica grating was further corrected by oxygen plasma etching. Using this method, high efficiency sine-top BGCGs with line densities of 1740 lines /mm have been achieved, this paper has a good reference value to the further fabrication of larger aperture gold-coated PCG.