GLASSES AND GLASS-CERAMICS TRANSPARENT IN THE INFRARED RANGE TO BE USED AS OPTICAL SENSORS

Abstract

The present work deals with the study of infrared transparent glasses and their applications for sensor use. Their behavior under LASER irradiation, as well as the possibility to modify the surface, and the exploration of new glass compositions has been studied. Four tasks were completed with the main goal of designing infrared optical sensors. In a first task, the deposition of various thin films at the surface of a chalcogenide glass has been investigated in order to produce nano porous surfaces. Films were produced by vapor deposition and cathodic sputtering. Vapor deposition did not produce homogeneous films while cathodic sputtering lead to layers of controlled thickness which could produce a porous surface by selective etching. In a second task, the possibility of writing waveguide with femtosecond laser was investigated in Ge-Ga-S/Se-CsCl glasses. It was shown that high power leads to negative index changes unfit for light guiding, while low power lead to small positive index change. It was also shown that the filamentation method lead to homogeneous waveguide with large positive index changes. In a third task, photo-induced phenomena were investigated, especially photo-induced fluidity, on the binary system Ge-Se. The study initiated with the work on relaxation of fiber optics of composition Ge-Se₃ Ge-Se₄ and Ge-Se₉ and their response to shear stress under LASER irradiation in the Urbach region. This leads to the determination of their viscosity under irradiation as a function of the power and wavelength used. This preliminary study enabled using this technique for optical tapering of chalcogenide fibers. A tapered fiber was obtained with good control over the diameter, and length of the sensor and improved sensing sensitivity was demonstrated. Finally, exploration of new glassy systems containing no chalcogenide elements but only heavy halide compounds (PbI₂, PbBr₂, CsI…) were investigated. These amorphous ionic compounds lead to infrared window transmitting from 500 nm up to 26 μm, unfortunately their moisture sensitivity as well as poor mechanical and thermal properties did not make them good candidate for sensor applications.