Formation of Microstructure in SiO2 Thin Film by a Femtosecond Laser Pulse

Abstract

Non-erasable micro grating structures were successfully encoded in 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; λ=800 nm, pulse duration; 100 fs, pulse energy; ∼ 3 mJ/pulse). The encoded periodic spacing varied with the angle, θ, between the two crossed pulses according to d=λ/(2sin (θ/2)). A minimum periodic spacing of ∼ 430 nm was achieved for a laser wavelength of 800 nm. Volume compaction resulting from structural alterations of the silica network in amorphous SiO2 induced by intense femtosecond laser irradiations was responsible for the formation of these grating structures. Further, an array of dot structures was fabricated in amorphous SiO2 thin films by a encoding two perpendicular gratings.