High-efficiency Bragg gratings in photothermorefractive glass

Photosensitive silicate glasses doped with silver, cerium, fluorine, and br omine were fabricated at the Center for Research and Education in Optics an d Lasers. Bragg diffractive gratings were recorded in the volume of these g lasses with a photothermorefractive process (exposure to UV radiation of a He-Cd laser at 325 nm is followed by thermal development at 520 degrees C). Absolute diffraction efficiency of as much as 93% was observed for l-mm-th ick gratings with spatial frequencies up to 2500 mm(-1). No decreasing of d iffraction efficiency was detected at low spatial frequencies. Original gla sses were transparent (absorption coefficient less than I cm(-1)) from 350 to 4100 nm. Induced losses in exposed and developed glass decreased from 0. 3 to 0.03 cm(-1) between 400 and 700 nm, respectively, and did not exceed 0 .01-0.02 cm(-1) in the IR region from 700 to 2500 nm. Additional losses cau sed by parasitic structures recorded in the photosensitive medium were stud ied. (C) 1999 Optical Society of America OCIS codes: 050.7330, 090.2900, 16 0.2750.