Optical fibre chalcogenide

Alternatively, it is possible to install fibre optic probes directly in the main stream in-line while the IR spectrophotometer remains remotely in a low vibration laboratory environment. In-line analysers, which do not remove any sample from the line, have the minimum possible lag time and do not change the sample physically or chemically from its nature in the process. Recently, bundles of 500 /xm optic fibres have been developed for the 5000-900 cm (2000-11,000 nm region), which permit transmission of IR energy over distances of several metres. Lowry et al. [76] have evaluated fibre-optic cables that might prove useful in FTIR remote sampling applications. The various optical fibres (chalcogenide, silver halide, heavy metal fluoride or sapphire) differ in their spectral window [77]. Due to the thermal stability and the spectral window, sapphire fibres are considered suitable for in-line characterisation of polymer melts in a production line (e.g. in an extruder head) as an alternative to discontinu-ously operating conventional off-line transmission IR spectroscopy of polymer films [78]. 

IR-transmitting optical fibres are evanescent wave sensors using a mathematical deconvolution technique to extract the absorbances and follow the concentrations of the components as they occur in both laboratory scale and process production. The fibre-optic probe used can be placed at specific locations within the samples or at the surface. The specificity of the technique, the speed of data acquisition and the portability of equipment make this method ideal as a tool to fundamentally probe polymer reactions and processes. Chalcogenide optical fibres are used to direct IR radiation from an FUR spectrometer through an attenuated total reflection (ATR) probe immersed in a reactor and back to the spectrometer. 

Fig. 3. Composite loss spectra for some common IR fibre optics ZBLAN fluoride glass SC sapphire, chalcogenide glass, PC AgBrCl, and hollow glass waveguide plot reproduced from Harrington, 2010.

Chalcogenide glasses from the Ge-Se system exhibit relatively low glass transition temperatures (from 41 (Se) to 340°C (Ge4oSe6o) and low activation enthalpy for flow (from 285 to 592 kJ/mol). As a consequence, they experience a time or rate dependent hardness at room temperature, especially for chalcogen-rich compositions (Fig. 3). Therefore, on one hand, these glasses offer a unique opportunity to study viscoelasticity at room-temperature, as was already mentioned earlier, but on the other hand, structural parts such as lens or fibres for applications in night visibility optical devices or in thermometry, are likely to suffer from creep deform-... 

Asobe M., Ohara T., Yokohama I., and Kaino T., Low power all-optical switching in a nonlinear optical loop mirror using chalcogenide glass fibre. Electron. Lett, 32,1396-1397 (1996). 

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