Pulse duration dependence of femtosecond-laser-fabricated nanogratings in fused silica

Femtosecond laser radiation tightly focused in bulk fused silica is used to generate self-ordered nanogratings when the sample is translated under the lens at constant speed. The nanogratings are preserved over a length scale of millimeters. We demonstrate that nanogratings are formed for all pulse durations tested, ranging from 40to500fs, and that the pulse energy threshold for this phenomenon increases with decreasing pulse duration. We use high spatial resolution diagnostics based upon selective chemical etching followed by atomic force microscopy and scanning electron microscopy to reveal the morphology of the nanogratings.