Section 6. Advances in IR materials Infrared transmitting glasses and glass-ceramics X.H. Zhang * , L. Calvez, V. Seznec, H.L. Ma, S. Danto, P. Houizot, C. Boussard-Ple ´del, J. Lucas Laboratoire des verres et ce ´ramiques, UMR CNRS 6512, campus de Beaulieu, Universite ´ de Rennes I, 35042 RENNES, France Available online 15 May 2006 Abstract The demand for infrared materials which exhibit higher performance is still growing; both on the thermal and mechanical side as well as on the width of the optical window, with an extension of the transparency towards the long wavelength region to satisfy the require- ments of space applications. Glasses as well as glass-based ceramics offer the advantage of unique rheological properties allowing mold- ing and fiber drawing. In controlling the nucleation/growth process in a chalcogenide glass modified by an alkali halide, it has been possible to develop a new generation of glass ceramics containing nanosize grains and transparent in the mid infrared. For the optical exploration of the universe, new low phonon glasses transparent in the 20 lm region and beyond are needed and to reach this goal a new family of telluride glasses was developed in combining Te with Ge with the addition of Gallium or Iodine for stabilization. These new optical glasses are transparent from 2 to 20 lm and can be drawn into fiber. Ó 2006 Elsevier B.V. All rights reserved. PACS: 42.70.C; 42.70.K; 81.05.P Keywords: Glass-ceramics; Infra-red fibers; Chalcogenides; Chalcohalides; Optical properties 1. Introduction Due to recent advances in design of optics as well as of detectors, the thermal imaging technologies are no more strictly restricted to military applications. Infrared cameras for surveillance, driving assistance have to be more afford- able and one of the key issues lies on the fabrication of low cost reliable optics. Transparent materials in the 8–12 lm atmospheric window are needed and they must be also shaped in complex forms such as aspheric and diffractive lenses, at the lowest cost. To satisfy these requirements, chalcogenides glasses offer the best alternative. Indeed a vast family of Se based glasses has their IR cut-off located beyond 12 lm and are very stable in normal air conditions. Due to a high flexibility in their chemical compositions, it is possible to adjust their rheological properties in order to benefit from their plasticity. Consequently, in using a strict control of the temperature as well as of the chemical nature of the mold, successful operations of lenses molding have been conducted, leading to the preparation of aspheric and diffractive lenses without going through the expensive procedure of polishing or diamond turning [1,2]. Also due to the continuum of the chemical bond, a glass is intrinsically sensitive to fracture propagation rending these materials sensitive to shocks and to fracture propaga- tion. It is also well established that a glass is by nature a meta-stable solid and tends to come back to equilibrium by crystallization. This apparent disadvantage can be transformed into a positive point as long as the nucleation and growth of the crystalline species can be controlled, leading then to a new class of composite materials; the glass ceramics. During the last decades, progress in the develop- ment of oxide based glass ceramics has been spectacular and several products having outstanding mechanical and thermal properties are on the market. As far as optical properties are concerned it is clear that the formation of grains inside a glass matrix can be a 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.03.029 * Corresponding author. Tel.: +33 2 2323 6937; fax: +33 2 2323 5611. E-mail address: xzhang@univ-rennes1.fr (X.H. Zhang). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 2411–2415