Fluorinated silicate glass for conventional and holographic optical elements

This presentation is a survey of results of a long-term research at the laboratory of photoinduced processes at CREOL/UCF. A highly homogeneous and transparent sodium-zinc-aluminum-silicate glass doped with fluorine and bromine was developed. Glass is transparent from 220 to 2700 nm. It is a crown-type optical glass having refractive index at 587.5 rim n(d)=1.4959 and Abbe number v(d)=59.2. This glass shows low dependence of refractive index on temperature dn/dt < 10(-7) 1 /deg. Absorption coefficient in the near IR region is about 10(-4) cm(-1). Glass can withstand multi-kilowatt laser beams. Nonlinear refractive index is the same as for fused silica. Laser damage threshold for 8 ns is about 40/cm(2). This glass becomes a photosensitive one by doping with silver and cerium. It demonstrates refractive index decrement after exposure to UV radiation followed by thermal development and therefore is used for phase volume hologram recording. Spatial modulation of refractive index resulted from precipitation of nano-crystalline phase of sodium fluoride. The main mechanism of refractive index decrement is a photoelastic effect resulted from strong tensions generated in both crystalline and vitreous phases because of difference in their coefficients of thermal expansion. Volume Bragg gratings recorded in this glass, show extremely narrow spectral and angular selectivity and have low losses combined with high tolerance to laser radiation. These gratings possess a unique ability to produce laser beam transformations directly in angular space. This feature paves a way to creation of high power lasers with. stable narrow emission spectra and diffraction limited divergence.