Nanostructure covered micro holes fabrication by femtosecond laser on fused silica glass surface

We report on the fabrication of nanostructure covered micro holes on the surface of fused silica glass by irradiation with single-beam direct femtosecond laser pulses. Nano-bumps or nano-pillars were formed on the side wall near the surface as well as near the bottom of the micro holes with a diameter down to 100nm. On the top of the nano-bumps, grouped and spherical shaped nanostructures down to 10 nm were observed. Nano-gratings with an average period of 175 nm-200 nm were found at the bottom of the holes, which is less than λ
_i
/2η period (η is the refractive index of the material).