IR-REGION DEVICES

For purposes of discussion, we denote IR-region devices as including those operating in broader spectral regions. These include, e.g. Visible-IR or IR-Microwave regions, 

20-9 (a,b) Specular Reflectance FTIR electrochromic data, in 2nd Ashwin configuration for solid-state, thin film, flexible devices of  

Diffuse Reflectance FTIR eleetrochromic data, with emittance computations shown, for optimized P(AAl) system in CONI device configuration. For the emittance computation, 8 points are taken from these spectra, and 2 points beyond the ca 25 iim limit shown, are extrapolated. After Chandrasekhar [919]. 

Comparative Specular Reflectance FTIR electrochromic data, using CON2 Ashwin device configuration but with common CP systems, as indicated. Tliese data show that choice of the CP system is critical for IR-region electrochromism. After Chandrasekhar. 

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There are other light detectors of interest in luminescence measurements such as photodiodes and other solid-state devices. Their sensitivity is very low compared with PM tubes, and there is a requirement for considerable amplification of the photocurrents. The solid-state photodetectors have the advantage of broad wavelength response in the IR region, beyond the range of PM tubes. 

Tunable filters in the form of AOTF devices, liquid crystal tunable filter (LCTF) and also tunable cavity Fabry-Perot etalon (FPE) devices have been considered in non-moving part instrument designs for many years. Today, the AOTF and the LCTF devices are used in the NIR spectral region.9,10 Originally, designs were also proposed for mid-IR AOTF devices, but these have not become available, mainly because of fabrication issues (cost and material purity). Tunable FPE devices, which are really just variable cavity interference filters, have been developed for the telecommunications industry. While these have been primarily used in the NIR, in most cases they can be fabricated to work also in the mid-IR, the latter being only an issue of material/substrate selection. 

Lanthanides activated luminescent materials are widely used for solid-state lasers, luminescent lamps, flat displays, optical fiber communication systems, and other photonic devices. It is because of the unique solid-state electronic properties that enable lanthanide ions in solids to emit photons efficiently in visible and near IR region. Due to the pioneer work by Dieke, Judd, Wyboume, and others in theoretical and experimental studies of the... 

Figure 19.9 illustrates the principle of surface modification of oxide nanoparticles with dyes. Dyes that absorb in the visible and/or IR region become colorless (or change to another color) upon undergoing reduction (or oxidation) under the influence of an electrochemical bias. The feasibility of this concept has already been demonstrated in our laboratory by binding a thiazine dye to nanostructured Sn02 film [156]. Reverse electrochromism obtained using such dye systems provides an alternate approach to conventional oxide-based electrochromic devices. 

Because many atmospheric constituents absorb efficiently in the infrared spectral region, the development of an IR multichannel spectrometer was important to complement our near IR spectrometers. Originally, the pyroelectric vidicon (16) was selected as the IR image devices. This imager is a thermal rather than photon detector, and as such detects only variations... 

A thermopile is a thermal detector capable of measuring the total incident radiant flux (in W/m2) in the UV, visible, and IR regions of the spectrum, with a response that is essentially independent of wavelength. It is the reference against which the other devices can be calibrated, but is not recommended for direct use because it is expensive and not a straightforward instrument to use correctly (Jagger, 1985). 

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