Fourier transform infrared radiation source

The heart of a Fourier transform infrared spectrophotometer is the interferometer in Figure 20-26. Radiation from the source at the left strikes a beamsplitter, which transmits some light and reflects some light. For the sake of this discussion, consider a beam of monochromatic radiation. (In fact, the Fourier transform spectrophotometer uses a continuum source of infrared radiation, not a monochromatic source.) For simplicity, suppose that the beamsplitter reflects half of the light and transmits half. When light strikes the beamsplitter at point O, some is reflected to a stationary mirror at a distance OS and some is transmitted to a movable mirror at a distance OM. The rays reflected by the mirrors travel back to the beamsplitter, where half of each ray is transmitted and half is reflected. One recombined ray travels in the direction of the detector, and another heads back to the source. 

Fourier transform infrared (FTIR) spectroscopy has been extensively developed over the past decade and provides a number of advantages. The main part of FTIR spectrophotometer is the Michelson interferometer. Radiation containing all IR wavelengths (e.g., 4000-400 cm 1) is emitted by source of infrared radiation (Globar) and is split into two beams. One beam is of fixed length, and the other is of variable length (movable mirror). 

The samples were characterized by means of X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), electron diffraction (ED), and Mossbauer spectroscopy. XRD analysis was carried out on a HZG-4A diffractometer by using Ni-filtered Co Ka radiation. IR-spectra were recorded on an AVATAR FTIR-330 spectrometer. TEM/ED examinations were performed with a LEO 906E and a JEOL 4000 EX transmission electron microscopes. The resonance spectra were recorded in air at 298 K and processed by using a commercial SM2201 MSssbauer spectrometer equipped with a 15 mCi Co (Rh) source. 

There was also described and discussed the relatively new Fourier transform infrared emission spectroscopy (IRES), its principle, an appropriate FT-IRES setup and applications. FT-IRES is unique in that it does not require an external radiation source, because the sample itself is the source. The radiation emitted from the sample is collected and sent to the detector. The ratio of the sample signal to that from a black body source represents the spectrum. However, appli-... 

Four different methods used for integrated-path remote gas sensing are discussed here. One of these (tunable diode laser absorption spectroscopy, TOLAS) uses a narrow linewidth source of radiation (usually a laser diode) and the other three methods use broadband sources of radiation. These three analyze the spectrum of the radiation after it has traversed the atmospheric path in different ways both differential optical absorption spectroscopy (DOAS) and Fourier transform infrared (FTIR) spectroscopy analyze the entire spectrum over the spectral region of interest, whilst absorption correlation methods record the spectrum after it has been filtered optically with either an optical filter or a sample of the target gas itself. These four methods use an active source of radiation. It is also possible to carry out integrated-path remote gas sensing using a passive source. 

The former in situ approach may involve the measurement of a static orientation, or some real-time effect. Where short measurement times are of the essence, it is sometimes possible to achieve reliable measurements either by increasing the sensitivity, as in Fourier transform infrared spectroscopy, or by using sources of much more intense radiation such as synchrotron-generated X-rays. 

Figure 2.10 A diagram of a Fourier transform infrared (FTIR) spectrometer. FTIR spectrometers employ a Michelson interferometer, which splits the radiation beam from the IR source so that it reflects simultaneously from a moving mirror and a fixed mirror, leading to interference. After the beams recombine, they pass through the sample to the detector and are recorded as a plot of time versus signal intensity, called an interferogram. The overlapping wavelengths and the intensities of their respective absorptions are then converted to a spectrum by applying a mathematical operation called a Fourier transform.

The principle of a Michelson interferometer which is used in a Fourier transform infrared (FT-IR) spectrometer is illustrated in Fig. 2.4. As seen in Fig. 2.4(a) the device consists of two plane mirrors, one fixed and one moveable, and a beam splitter. One type of beam splitter is a thin layer of germanium on an IR-transmitting support. The radiation from the source is made parallel and as seen in Fig. 2.4(b), strikes the beam splitter at 45. The beam splitter has the characteristic that it transmits half of the radiation and reflects the other half. The transmitted and reflected beams from the beam splitter strike two mirrors oriented perpendicular to each beam, and are reflected back to the beam splitter. 

Fourier transform infrared spec-trochemical imaging review of design and applications with a focal plane array and multiple beam synchrotron radiation source. Appl. Spectrosc., 66 (5),... 

Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy were used to study the photo-oxidation of both poly(alpha-methylstyrene) (PMS) and polystyrene (PS) films which had been irradiated at different temperatures and with different radiation sources under an oxygen atmosphere. The oxidised films were treated with ammonia or sulphur tetrafluoride and photolysis carried out under vacuum. Photoproducts from both polymers were broadly similar, but aromatic ketone concentration was higher from the PMS and a new ketone was also identified from this source. Routes for formation of identified photoproducts are proposed. 13 refs. 

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