Nobuhiko Sarukura

Fabrication of nonerasable gratings in SiO 2 glasses by a two-beam holographic method using infrared femtosecond laser pulses

Non-erasable fine pitched grating structures were successfully encoded in amorphous SiO2 glasses and amorphous SiO2 thin films on silicon wafers by colliding a pair of focused pulses split from a single femtosecond pulse from a 10 Hz mode-locked Ti:sapphire laser with a regenerative amplifier (wavelength: 800 nm; pulse duration: 100 fs; pulse energy: approximately 3 mJ/pulse). 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 approximately 430 nm was achieved for a laser wavelength of 800 nm. Structural alternations of silica network induced by intense fs-laser irradiations were observed. Laser ablation processes and volume compaction in amorphous SiO2 are origin of the formation of grating structures.