IR interferometer

On metals in particular, the dependence of the radiation absorption by surface species on the orientation of the electrical vector can be fiilly exploited by using one of the several polarization techniques developed over the past few decades [27, 28, 29 and 30], The idea behind all those approaches is to acquire the p-to-s polarized light intensity ratio during each single IR interferometer scan since the adsorbate only absorbs the p-polarized component, that spectral ratio provides absorbance infonnation for the surface species exclusively. Polarization-modulation mediods provide the added advantage of being able to discriminate between the signals due to adsorbates and those from gas or liquid molecules. Thanks to this, RAIRS data on species chemisorbed on metals have been successfidly acquired in situ under catalytic conditions [31], and even in electrochemical cells [32]. 

Of course, even in low temperature solutions, unstable compounds may not be very long-lived. Modern fast-scanning FT-IR interferometers can produce high signal-to-noise spectra in a single scan. This means that metal carbonyl compounds with half-lives as short as 2 seconds can be easily detected using an unmodified interferometer (28,29). With improved interferometers, we anticipate that such studies will soon be extended to compounds with lifetimes —100 mseconds. However, detection of shorter lived species, such as reaction intermediates, requires much faster and more sensitive techniques. 

FIGURE 16-4 inierferometers in an FTIR spectrometer. Subscript 1 defines the radiation path in the IR interferometer, Subscripts 2 and 3 refer to the laser and white-light interferometers, respectively. (Courtesy of Thermo Electron Corp., Franklin. MA.)... 

More research is needed with both spectroscopic tools, especially with the recent advances in the field of Fourier transform Raman spectroscopy and the tremendously improved sensitivity and stability of the IR interferometers. In addition, the availability of new algorithms such as the ratio method (32), factor analysis (20, 33), and recently developed nonlinear techniques (34), coupled with an easy access to fast computers, will advance spectral analysis tremendously and make it more precise and reliable. 

WIIT is a 1 150 functional scale model of the space far-IR interferometer SPIRIT, and is designed to observe complex scenes representative of far-IR astronomical fields. It provides full Mv-plane coverage and a wide FOV, operating at visible rather than far-IR wavelengths for several practical reasons (Leisawitz et al. 2012) (a) the optical apertures and the delay line are scaled down from those intended for a far-IR instrument in proportion to the wavelength (b) a CCD detector with sensitivity... 

The main goals of WIIT are to observe astronomically representative test scenes with a Double Fourier interferometer that is equivalent in functionality and performance to a space far-IR interferometer, and compare observed interferograms with those predicted by a high-fidelity computer model of the testbed in which error terms associated with individual hardware components are modelled and can be switched on or off. This comparison can be performed by visibility analysis. 

Figure 7.57. In situ ATR spectra of P. putida adsorbed at Ge IRE (50 x 20 x 3 mm, with 19 active reflections inside) after lOOh of adsorption (1) biofilm without toluene (2) 5 ppm toluene (3) 15 ppm toluene. Arrows increase of polysaccharide peaks at 5 ppm toluene and of carboxylic group peak at 15 ppm toluene. Spectra were obtained with multichannel ATR/FTIR spectrometer constructed on basis of RFX-30 FT IR interferometer (Laser Precision Analytical). Reprinted, by permission, from J. Schmitt, D. E. Nivens, D. C. White, and H.-C. Flemming, Water Sci. Tech. 32, 149 (1995), p. 154, Fig. 5. Copyright 1996 International Association on Water Quality (lAWQ).

In the last decade we have witnessed impressive progress in the applications of infrared (IR) microspectroscopy, especially in the field of life sciences and more specifically for medical diagnosis. Different initiatives, meetings and conferences have been dedicated to the study of IR spectroscopy applied to investigate or to classify single cells or tissue sections. The key tools for such research are the IR microscope used for imaging and Fourier transform IR interferometer (FTIR) for spectral analysis. 

The optical systems of modern FT-IR interferometers are interfaced to modern computers that have high-speed computing and data-processing capabilities, and which contain a large amount of memory and an operating system with a convenient Windows function, as well as a wide variety of application-specific software. 

Because the lower wavenumber limit covered by a conventional FT-IR spectrometer operating in the mid-infrared region is typically 400 cm it is necessary, in order to measure far-infrared spectra, to exchange a few of the main optical components of an FT-IR interferometer these are described here ... 

IR interferometers seem first to have been tried out for examining the very low signal levels of IR emission from astronomical sources. They were shortly... 

A multiplex/multichannel microimaging FTIR system has been developed. The strategy is to combine an IR focal plane array detector with a step-scan interferometer. A InSb focal array detector was used with a 128 x 128 pixel distribution. The detector was interfaced with a with a commercially available step-scan FT-IR interferometer. 

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