Light Globar

Light sources can either be broadband, such as a Globar, a Nemst glower, an incandescent wire or mercury arc lamp or they can be tunable, such as a laser or optical parametric oscillator (OPO). In the fomier case, a monocln-omator is needed to achieve spectral resolution. In the case of a tunable light source, the spectral resolution is detemiined by the linewidth of the source itself In either case, the spectral coverage of the light source imposes limits on the vibrational frequencies that can be measured. Of course, limitations on the dispersing element and detector also affect the overall spectral response of the spectrometer. 

The pump source in the dispersive experiment is typically a nanosecond laser the probe source can be broadband IR light from a globar or tunable IR light from a CO laser or a semiconductor diode laser. Although CO and diode lasers can produce... 

A Globar is a SiC infrared light source A rod of diameter 5 to 10 mm and length 20 to 50 mm, when heated to between 1000°C and 1700°C, emits infrared radiation with wavelengths between 4 and 15 /tm (overall wave-number range 6000 to 100 cm-1). 

In principle, an FTIR instrument consists of a Michelson interferometric arrangement (see Fig. 6.6-3) with a light source G (globar), a beam splitter BS, a fixed mirror FM, a movable mirror MM, and a detector (MCT). The very sensitive MCT detectors... 

The infrared light source generates wideband radiation by heating solid materials to incandescence using electric power. There are two commonly used IR sources the Nernst glower, which is composed of mainly oxides of rare-earth elements and the Globar, which is... 

In an FT-IRM experiment, as the aperture size is decreased, so does the IR flux that reaches the detector, and hence the signal-to-noise ratio (SNR) decreases. A conventional globar source iUuminates light into a -100 pm area consequently the typical aperture settings are 20 to 100 pm. 

Fig. 46. Optical diagram of the Polytec MIR 160 Fourier spectrometer (No. 5b in Tables 2, 3, 4). M 1, M 2, M 5, M 6, M 7 plane mirrors M 3, M 4 paraboloid mirrors MS spherical mirror MT toroid mirrors G Globar source S high pressure Hg-lamp L He-Ne-laser IS Interferometer scanner BS beampslitter PC photo-cell D pyroelectric detector WL white light source...

IRS Infrared Spectroscopy Thin crystal, glass, liquid I.R. light (W-filament, globar, Hg-arc) I.R. spectrum Electronic transitions (mainly in semiconductors and superconductors) vibrational modes (in crystals and molecules) 12,13,14... 

A source with somewhat lower intensity hut with longer life than the Globar or Nernst glower is a lightly wound spiral of nichrome wire heated to about 1100 K by an electrical current. A rhodium wire healer sealed in a ceramic cylinder has simil.ir properties, although it is more expensive. Nichrome wire stturees ire less... 

Transmitted IR spectra for rocks and minerals are generally measured by making thin sections of samples with thicknesses of from 20 to 200 pm, which depend on concentrations and absorption coefficients based on Beer-Lambert law. A Fourier Transform IR microsjjectrometer totally used in this study is equipped with a silicon carbide (globar) IR source and a Ge-coated KBr beamsplitter. IR light through a sample is measured using a mercury-cadmium-telluride detector. 

Infrared radiation from an incandescent source, such as an SiC Globar, is collimated and passed through a rapid-scanning interferometer so that each wavelength in the spectrum is modulated at a different frequency. The beam of radiation is then focused onto the first window of the light-pipe and the infrared beam emerging from the second window is refocused onto a sensitive detector (typically a liquid-nitrogen-cooled mercury cadmium telluride (MCT) photoconductive detector). A typical system is... 

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