FTIR interferometer

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

Er is becoming very small. Here, however, the effect will be masked by other effects contained in the data, such as the effect of small changes in source intensity, external interference or, in the case of FTIR, interferometer misalignment, or any of several other effects that change the actual values of reference and sample energy at the limits of the spectral range. 

More recently, Weiller (39) has extended this work by performing a detailed rapid-scan FTIR study of M(CO)e (M = Cr or W) in liquid Xe and liquid Kr. A pulsed UV laser source, synchronized to the moving mirror of the FTIR interferometer, was used to photolyze the hexacarbonyls. MCCOsKr was characterized in liquid Kr, Cr(CO)gXe in liquid Xe, and W(CO)sXe in liquid Xe and liquid Kr doped with 5% Xe. M(CO)gKr has... 

Interferometer An optical device that takes one beam of light and splits it into two beams of light. The two light beams travel different paths, are recombined, and then leave the interferometer. There is an interferometer at the heart of every FTIR. Interferometers measure interferograms. 

For radiofrequency and microwave radiation there are detectors which can respond sufficiently quickly to the low frequencies (<100 GHz) involved and record the time domain specttum directly. For infrared, visible and ultraviolet radiation the frequencies involved are so high (>600 GHz) that this is no longer possible. Instead, an interferometer is used and the specttum is recorded in the length domain rather than the frequency domain. Because the technique has been used mostly in the far-, mid- and near-infrared regions of the spectmm the instmment used is usually called a Fourier transform infrared (FTIR) spectrometer although it can be modified to operate in the visible and ultraviolet regions. 

The most important component of an FTIR spectrometer is an interferometer based on the original design by Michelson in 1891, as shown in Figure 3.11. 

One of the main design problems in an FTIR spectrometer is to obtain accurate, uniform translation of Mj over distances 6 which may be as large as 1 m in a high-resolution interferometer. 

If was nof until fhe developmenf of Fourier fransform infrared (FTIR) specfromefers (see Section 3.3.3.2) fhaf fhe possibilify of using an infrared laser routinely was opened up. The intensify advanfage of an infrared interferometer, wifh which a single specfrum can be obfained very rapidly and fhen many specfra co-added, coupled wifh fhe developmenf of more sensitive Ge and InGaAs semiconductor infrared defectors, more fhan compensate for fhe loss of scatfering intensify in fhe infrared region. 

In the infrared spectral range in general Fourier transform (FT) interferometers are used. In comparison with dispersive spectrometers FTIR enables higher optical throughput and the multiplex advantage at equivalent high spectral resolution. In... 

In an FTIR spectrometer, a source (usually a resistively heated ceramic rod) emits infrared radiation that is focused onto an interferometer whose main components consist of a beamsplitter, fixed mirror, movable mirror, and detector. The beamsplitter divides the beam into two beams. One beam is reflected off the beamsplitter toward the fixed mirror and is then reflected back through the beamsplitter to the detector. The other beam is transmitted through the beamsplitter toward the movable mirror and is then reflected off of the beamsplitter and to the detector [1],... 

In an industrial-design FTIR spectrometer, a modified form of the G enzel interferometer is utilized.A geometric displacement of the moving mirrors by one unit produces four units of optical path difference (compared with two units of optical difference for a Michelson type interferometer). The modified Genzel design reduces the time required to scan a spectrum and further reduces the noise effects asstxiated with the longer mirror translation of most interferometers. 

Figure 4.5 Schematic diagram of a Fourier transform infrared (FTIR) spectrometer. Infrared radiation enters from the left and strikes a beam-splitting mirror (BS) angled such that half of the beam is directed towards a fixed mirror (Mi) and half towards a moveable mirror (M2). On reflection the beam is recombined and directed through the sample towards the detector. M2 is moved in and out by fractions of a wavelength creating a phase difference between the two beam paths. This type of device is called a Michelson interferometer.

Figure 6. Schematic diagram of an interferometer as used in FTIR instruments.

The methodology that involves instruments that utilize the interferometer and Fourier transformation mentioned in Section 8.6 has come to be known as Fourier transform infrared spectrometry (FTIR). 

FIGURE 8.15 An illustration of an FTIR instrument showing the light source, the interferometer, the sample compartment, and detector. 

What is an interferometer and what is its function in an FTIR instrument ... 

Figure 5. Schematic drawing of a high throughput pulsed slit jet FTIR setup involving a 600 mm nozzle that is synchronized to the interferometer scans [154],...

The basic configuration of an FTIR spectrometer is schematically shown in Figure 1.17. The essential instrument of this spectrometer is a Michelson interferometer... 

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