Infrared Femtosecond Laser Direct-Writing Digital Volume Gratings in Fused Silica

We demonstrate that digital volume gratings can be fabricated in fused silica glass conveniently by direct femtosecond laser writing. The diffraction efficiencies of volume gratings can be essentially modulated by simply stacking and offsetting the unit structure. A series of volume gratings, which have the pitches of 5 mu m and the size of 1 mm x 1 mm, have been fabricated with the writing speed of 500 mu m/s, with which the processing period of each grating layer could be reduced to several minutes with a 1-kHz femtosecond laser system. Results show that the power spectrum of the diffracted waves of the volume gratings are dependent on the layer gap and layer offsetting.