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 μm or 2 μm for both layers. The first set of diffraction gratings was printed 70 μm 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 μm for the 6-μm-period grating and by 1 μm for the 2-μm-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.