Encoding of holographic grating and periodic nano-structure by femtosecond laser pulse

Abstract

By fully utilizing distinct features of femtosecond (FS) pulses such as ultra-short time domain and good coherence, we have successfully encoded micro-gratings and multi-dimensional periodic nano-structures either on or beneath surfaces of versatile materials including dielectrics, semiconductors, metals and plastics. In the setup for the encoding, a regenerative amplified pulse from a mode locked Ti:sapphire laser was split into two beams, then overlapped on the top surface or in the interior of the materials to give a ∼50 μm spot. The optical paths of the two beams should be adjusted precisely within ∼30 μm to induce the interference. Use of the third harmonic generation (THG) from air made the adjustment possible not restricted from colliding angles. Surface relief type gratings due to laser ablation and refractive index type gratings resulted from structural changes in silica glasses, embedded gratings in diamond, gratings capable of light coupling and decoupling to a LiNbO 3 wave guide, and two-dimensional nano-structures in silica glass are demonstrated as examples. We expect the present technique to open up a frontier of diffractive optics with the formation of periodic nano-structures applicable to emerging devices such as planar wave guides, quantum dots and photonic crystals.