Fabrication of Internal Diffraction Gratings in Planar Fluoride Glass Using Low-density Plasma Formation Induced by a Femtosecond Laser

Abstract

The fabrication of internal diffraction gratings with photo-induced refractive index modification in planar fluoride plates was demonstrated using low-density plasma formation excited by a high-intensity femtosecond (130 fs) Ti:sapphire laser (λ p = 790 nm). The refractive index modifications with diameters ranging from 350 nm to 5 μm were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than 1 × 10 12 W/cm 2 . The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred. The maximum refractive index change (Δn) was estimated to be 1.3 × 10 -2 . The low-density plasma formation (n c < 1.79 × 10 27 m -3 ]) causes the increase of the refractive index modification with fluoride glass. © 2008 Elsevier B.V. All rights reserved.