Self-assembled three-dimensional periodic micro-nano structures in bulk quartz crystal induced by femtosecond laser pulses.

In-volume, self-assembled, three-dimensional, periodic micro-nano structures are induced in quartz crystal by tightly focused, 500-kHz femtosecond laser pulses. With suitable pulse energy, three different types of periodic structures can be observed in modified regions using scanning electron microscopy. The first one with period (ΛE ) of ~400 nm in the direction of the laser polarization, i.e. nanograting, shows indicative features similar to that in fused silica. The second one with period (ΛS ) in the scan direction and the third one with period (Λk ) in the laser propagation direction are both equally spaced by ~1 μm, which is close to the laser wavelength. Moreover, the structure with period (Λk ) covers almost the whole cross-section of modified regions, which is distinctive to that observed in fused silica. Through the comparison of the structures induced by 1-kHz pluses and those by 500-kHz pluses, we deduce that the heat accumulation effect may have a positive influence on the formation of nanogratings in quartz crystal.