Multichannel imaging spectrometer

Application of laser Raman multichannel spectroscopy to a kinetic investigation in the liquid phase has been reported by Crunelle-Cras and Merlin (1977). A multichannel spectrometer with photoelectric image devices, interfaced with a data aquisition and handling system, permits the study of fast processes, exemplified by the fast oxidation of the sulfite ion by the bromate ion in an acidic medium. 

It should also be noted at this point that a multichannel detector can have multiple detector elements along two axes, one parallel to the direction of wavelength dispersion, and one perpendicular. The latter is parallel to the entrance slit in most dispersive instruments. For example, a CCD may have 1024 pixels along the wavelength axis and 256 along the vertical axis, for a total of 262,144 independent elements. This second dimension of the detector may be used in a variety of applications involving Raman imaging, multiple detection tracks, or echelle spectrometers. 

The spectrophotometer shown in Figure 25-21 can be controlled by most personal computers. The instrument (without the computer) can be purchased for about 10,000. Several instrument companies are combining aixay detector systems with fiber-optic probes that transport the light to and from the sample. These instruments allow measurements in convenient locations that are remote to the spectrometer. We are beginning to see more CCD and CID detectors used in multichannel systems, particularly when advantage can be taken of the two-dimensional nature of these detectors for imaging purposes (see color plate 14). 

A notable multichannel spectrometer which does not use an IPDA is the SIDS (Spatial Imaging Detector System) spectrometer... 

Table I, shows the spectrometers recently developed by the authors. All are based on the principle of multichannel spectroscopy utilizing image devices as sensors (1). In these spectrometers, a spectrum is scanned rapidly electronically, typically in 10 ms. Spectral data can be readily available ina digitized form, the sensitivity of these image devices is generally better than...

Spectrometer 1 is based on a linear self-scanned image sensor, capable of providing a 10 ms per spectrum, scan time. This spectrometer was borne by the S-310-8 rocket, which was launched from Kagoshima Space Center (131°04 45"E, 31°15 00"N) at 17 47 JST (Japan Standard time, 135°E) on February 2, 1980. The spectrometer, that measured the NIR absorption of atmospheric constituents such as and H 0, was according to our knowledge the first rocket-borne multichannel spectrometer capable of measuring spectra with an altitude resolution better than 2 km. 

Because many atmospheric constituents absorb efficiently in the infrared spectral region, the development of an IR multichannel spectrometer was important to complement our near IR spectrometers. Originally, the pyroelectric vidicon (16) was selected as the IR image devices. This imager is a thermal rather than photon detector, and as such detects only variations... 

A multichannel plate (MCP) is a type of CDEM in which a series of microchannels on a disk-shaped device are coated with an electron-emissive material to generate 10 to 10" amplification as the electrons cascade through the microchannels. MCPs can be stacked to increase amplification or focused onto a fluorescent surface for ion-beam imaging. Because of the short electron pulse widths ( 1 ns) obtained with MCPs, they are the ion detector of choice for time-of-flight mass spectrometers. 

In order to be able to measure many electron lines simultaneously a multichannel detector is frequently placed in the detector plane instead of using a detector behind an exit slit. The electrons then impinge on a micro-channel plate (see also Fig.6.38), in which electron multiplication occurs due to secondary emission by the inner wall material in the densely packed tubes in the plate. The original electron line image in the focal plane of the spectrometer is amplified and, by using two channel plates in series an electron multiplication of 10 can be obtained. The electron showers are converted into optical signals on a phosphor screen which is viewed by a diode array or vidicon (TV camera) (Fig.6.38). 

Figure 40 CCD detector image for a four-channel multichannel Raman analyzer based on an axial transmissive spectrometer with a multiplex grating. The eight stripes relating to the four lower-wavenumber ranges and four high-wavenumber ranges can be clearly observed. (Reproduced with permission from Kaiser Optical Systems, Inc.)...

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