Globar source

Continuum microscope (Thermo Fischer) Source = synchrotron Spotlight microscope (Perkin Elmer) Source = 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 main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

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... 

One solution to this dilemma has been advanced by Hamaguchi and co-workers who have made use of a MoSi2 IR source newly developed by JASCO that provides approximately twice the emissive intensity of conventional globar sources. This probe source was incorporated into a dispersive TRIR spectrometer that allows access to the entire mid-IR spectrum with high sensitivity (A A < 10 ) and sufficient time (50 ns) and frequency (4-16 cm ) resolution to probe a wide range of transient intermediates in solution. 

Now that the parameters of typical prototype systems have been considered, it seems worthwhile to consider further variations that could be used to enhance the power and/or versatility of the basic apparatus. An obvious improvement would be to use a completely tunable IR probe source. As mentioned above, a globar source is completely tunable but with a lower than desired number of photons per unit bandwidth (60,73). There are a number of other means of producing completely tunable IR probe radiation with enough intensity to pull the detector out of the blackbody-noise regime. 

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). 

Evacuation is not necessary in this region and sources are much less of a problem than they are in the far-infrared. A heated black body emits strongly in the near- and mid-infrared and a Nemst filament, consisting of a mixture of rare earth oxides, or a silicon carbide Globar, emulate a black body quite well. 

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). 

Performing an FTIR experiment requires some specialized equipment. First, a broadband radiation source is needed. Typically a SiC globar is used that reaches temperatures of 1200-1500 K. When studying species that are weak absorbers or are in low concentration a brighter source is needed and high temperature sources (>2500 K) for such experiments have been developed [75]. These devices are nearly... 

The basic components of a dispersive infra-red spectrophotometer are shown in Fig. 1. The source of infra-red radiation is an electrically conducting element, such as a Globar or Opperman source, which is maintained at about 1000°. 

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... 

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