Glasses for Seeing Beyond Visible

Abstract

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 microm for sulfide-, selenide- and the new generation of telluride-based glasses, respectively. They cover the atmospheric transparency domains, 3-5 and 8-13 microm, 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 microm 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 mum for the Darwin space mission, which is aiming at discovering, signs of biological life in telluric earth-like exoplanets throughout the universe.

The Development of Advanced Optical Fibers for Long-Wave Infrared Transmission

“…In contrast to selenium, tellurium does not vitrify in the elemental form but instead crystallizes into a semimetallic solid with hexagonal structure [25,26]. The metallic character of tellurium results from significant p-orbital overlap [27] which promotes the formation of periodic helicoidal chains and prevents the structural disorder required for glass formation.…”

Glassy Materials and Light: Part 1

“…62 Dentre os sistemas vítreos mais explorados e conhecidos, podemos citar o sulfeto de arsênio, As-S, largamente usado para fabricação de fibras óticas para transmissão de luz no infravermelho próximo e médio (0,7 a 14 mm) 63 e o vidro ternário Ga-La-S, que permitiu a fabricação das primeiras fibras laser de calcogenetos. 64 Vidros e vitrocerâmicas à base de calcogenetos também podem ser usados para aplicações como lentes, objetivas ou janelas transparentes no IV.…”

Sub-Tg viscoelastic behaviour of chalcogenide glasses, anomalous viscous flow and stress relaxation

“…Theoretically, if a strain is instantly imposed, the relaxation modulus at t = 0 is equal to the elastic modulus G(0) = G0. So, one can write: (1) where ϕ (t) is a dimensionless function called "relaxation function". 7) Similarly, creep test consists in imposing a constant stress (σ 0) and monitoring the evolution of strain (ε(t)).…”

“…Due to this ability, they have been used in infrared cameras optics and optical fiber in order to carry signals emitted by thermal sources or by a laser source such as CO2 laser. 1) Chalcogenide glasses, in particular TAS glass (ternary system Te2As3Se5), are used in evanescent wave spectroscopy of biomolecules in human lung cells, 2),3) IR signatures being recorded in order to mesure the impact of toxic agents on cell health for example. But most of chalcogenide glasses such as GexSe1-x or Te-As-Se exhibit poor mechanical properties.…”