Fabrication and stitching of embedded multi-layer micro-gratings in fused silica glass by fs laser pulses

Fabrication and stitching of internal 2D, 1D and multi-layer micro-gratings in fused silica glass using amplified Ti:sapphire femtosecond laser were reported. These gratings have the pitch of 4 mu m and the size of 400 mu m x 400 mu m. For a two-layer 1D micro-grating where a second-layer grating was overwritten on a first-layer grating at the exact X,Y position and the different Z depth, the diffraction efficiency can reach more than 25% due to the grating thickness increase. If a second-layer grating was stitched with a first-layer by the shift of 2 mu m in the X direction and at the different Z depth, the diffraction angle was doubled but the diffraction efficiency was about 9%. The last result has the potential application for fabricating high-density micro-/nano-structures beyond the diffraction limit through 3D stitching.