Glasses for Seeing Beyond Visible

Conventional glasses based on oxides have a transparency limited by phonon absorption in the near IR region and have a limited interest for analyzing information located far beyond the visible. The IR spectral domain is nevertheless of prime interest, since it covers fundamental wavelength ranges used for thermal imaging as well as molecular vibrational signatures. Besides spectacular advances in the field of IR detectors, the main significant progresses are related to the development of IR glass optics, such as lenses or IR optical fibres. The field of IR glasses is almost totally dominated by glasses formed from heavy atoms such as the chalcogens S, Se and Te. Their transparency extends up to 12, 16 and 28 μm for sulfide‐, selenide‐ and the new generation of telluride‐based glasses, respectively. They cover the atmospheric transparency domains, 3–5 and 8–13 μm, respectively, at which the IR radiation can propagate allowing thermal imaging and night‐vision operations through thick layers of atmosphere. The development of new glass compositions will be discussed on the basis of structural consideration with the objective of moulding low‐cost lenses for IR cameras used, for instance, in car‐driving assistance. Additionally, multimode, single‐index, optical fibres operating in the 3 to 12 μm window developed for in situ remote evanescent‐wave IR spectroscopy will also be mentioned. The detection of molecular IR signatures is applied to environmental monitoring for investigating the pollution of underground water with toxic molecules. The extension of this technique to the investigation of biomolecules in three different studies devoted to liver tissues analysis, bio‐film formation, and cell metabolism will also be discussed. Finally we will mention the developments in the field of single‐mode fibres operating around 10 μm for the Darwin space mission, which is aiming at discovering, signs of biological life in telluric earth‐like exoplanets throughout the universe. Seeing red! Looking into the invisible is not a paradox any more thanks to technological advances that permit us to substitute our retina with matrices of IR detectors exhibiting a greater and greater number of pixels, while functioning at room temperature.