Non-erasable fine-pitched grating structures were successfully encoded in SiO 2 glasses and amorphous SiO 2 thin films on silicon wafers by colliding a pair of focused pulses split from a single femtosecond (fs) pulse from a 10 Hz mode-locked Ti:sapphire laser with a regenerative amplifier (wavelength; 800 nm, pulse duration; 100 fs). This pattern was not observed for cases in which the relative time delay of the two pulses was over 0.2 ps. The encoded periodic spacing was changed by varying the angle between the two crossed pulses. A minimum periodic spacing of ∼430 nm was achieved for a laser wavelength of 800 nm. Frenkel defect formation (oxygen vacancy + oxygen interstitial) and structural alternations of silica network induced by fs-laser irradiations were observed. Laser ablation processes and volume compaction in amorphous SiO 2 are origin of the formation of grating structures. Two-dimensional arrays of nanometer-sized holes or islands were successfully formed by two cross-superimposed holographic gratings.