High-efficiency Bragg gratings in photothermorefractive glass

TLDR

Photosensitive silicate glasses doped with silver, cerium, fluorine, and bromine were fabricated and Bragg gratings recorded by exposing them to 325 nm He–Cd UV light followed by thermal development at 520 °C. The gratings achieved up to 93 % diffraction efficiency in 1‑mm‑thick samples with spatial frequencies up to 2500 mm⁻¹, maintained performance at low frequencies, and exhibited low induced losses (≤0.02 cm⁻¹ in the IR) while the base glass remained transparent from 350 to 4100 nm.

Abstract

Photosensitive silicate glasses doped with silver, cerium, fluorine, and bromine were fabricated at the Center for Research and Education in Optics and Lasers. Bragg diffractive gratings were recorded in the volume of these glasses with a photothermorefractive process (exposure to UV radiation of a He–Cd laser at 325 nm is followed by thermal development at 520 °C). Absolute diffraction efficiency of as much as 93% was observed for 1-mm-thick gratings with spatial frequencies up to 2500 mm-1. No decreasing of diffraction efficiency was detected at low spatial frequencies. Original glasses were transparent (absorption coefficient less than 1 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 caused by parasitic structures recorded in the photosensitive medium were studied.