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