Femtosecond-laser-assisted fabrication of double-layer diffraction gratings inside fused silica glass

Abstract

We have fabricated double-layer diffraction gratings with a zigzag shape inside fused silica glass by using a femtosecond laser, the intention of which is to overcome the hindrance of shortening grating's period. Our primary focus is to utilize double-layer gratings to achieve a diffraction pattern similar to that from a single-layer diffraction grating with the same period as the double-layer grating. We fabricated two kinds of double-layer gratings, where the grating's period was either 6 mu m or 2 mu m for both layers. The first set of diffraction gratings was printed 70 mu m inside the glass substrates. This layer was followed by the second layer grating engraved just below the first layer grating (The shifted grating's position was shifted to the right by 3 mu m for the 6-mu m-period grating and by 1 mu m for the 2-mu m-period grating). By varying the layer gap, we have found the optimal position (layer gap: 500 nm) to achieve a diffraction pattern similar to that of a single-layer diffraction grating with half the grating's period of the double-layer gratings.