Keywords: infrared transmission, glass ceramics, chalcogenide, halide, mechanical properties, night vision, nanotechnology, oxyfluorides, transparency, microcrystals, nucleation, crystallisation
Glass and glass-ceramics transparent from the visible range to the mid-infrared for night vision
Many papers report studies on oxyfluorides glass-ceramics combining the optical advantage of fluoride environment for rare earth with the thermal and chemical advantages of oxide glasses [1?7], or on oxide-based glass-ceramics exhibiting exceptional thermo-mechanical properties such as zero thermal expansion coefficient. The transparency of these glass-ceramics is limited in the infrared region up to 4 ?m [8?12]. In this paper, we report the last results on totally new infrared transmitting chalcogenide glass-ceramics which are transparent up to 11 ?m for sulphur based glass or up to 16 ?m for selenium based glass. By selecting appropriate glass composition in several Ge-(Sb/Ga)-(S/Se)-MX (MX: alkali halide) systems, glass-ceramics with different microcrystals volume fraction can be reproducibly obtained by controlling nucleation and crystallisation annealing time and temperatures. It has been demonstrated that crystals smaller than 200 nm induce some additional losses only in the short wavelength region. The glass ceramics keep the same transmission as the original glass from 1 ?m up to 11 ?m or 16 ?m. Sulphur based glass-ceramics are still transparent in the second for glass and selenium based glass-ceramics keep an excellent transmission in the second and third atmospheric window. The obtained glass-ceramics exhibit much better resistance to cracks propagation than the corresponding pure glass matrix. Observations under electronic microscopy as well as X-ray diffraction have been used to determinate crystals size, density and crystalline phase. The possibility of combining the ceramisation process and the shaping by moulding has also been demonstrated.