Overview of laser imprinted refractive index changes and related thermal stability in mid-infrared optical glasses

Various glass compositions adapted to mid-infrared (heavy metal oxide, fluoride and chalcogenide glasses) were irradiated by femtosecond laser and their refractive index variations characterized as a function of laser pulse energy. Their thermal stability was studied through isochronal annealing conditions in order to determine their erasure temperatures. The measured index variations were compared to values collected from literature for a broad range of glass candidates. Additional chalcogenide glasses studied in this article (e.g. GeSbS and 75GeS 2 -15In 2 S 3 –10CsCl) present very high refractive index variations (up to 5.5·10 −2 ), almost 3 times the maximum value reported in heavy metal oxide glasses (2·10 −2 , Corning 9754) or SiO 2 , bringing interest for the development of mid-infrared optical devices. Nevertheless, they can be limited by their relatively low thermal stability, since the refractive index variations fully erase around their glass transition temperatures (typ. 200–300 °C for chalcogenide glasses studied herein). • Fs laser direct writing creates index changes in mid-IR glasses, being useful for optical devices and sensors. • Chalcogenide glasses offer the highest refractive index contrast compared to heavy metal oxide and fluoride glasses. • In chalcogenides, these changes disappear at 200–300 °C during isochronal annealing, due to structural relaxation.