Refractive Index of Photo-thermo-refractive Glass

Photo-thermo-refractive (PTR) glass is used to fabricate volume Bragg gratings. The gratings are formed by exposing PTR glass to UV light interference patterns and then annealing the glass. This produces a grating by locally modulating the refractive index. The diffraction efficiency of these gratings is dependent on the refractive index modulation amplitude. We report the refractive indices of unprocessed and processed PTR glass at wavelengths from 0.4 to 4.6 microns and discuss their uses in specifying VBGs for laser beam combining