Detector multichannel

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

No account of UV detectors would be complete without mention of the diode array (multichannel) detector, in which polychromatic light is passed through the flow cell. The emerging radiation is diffracted by a grating and then falls on to an array of photodiodes, each photodiode receiving a different narrow-wavelength band. A microprocessor scans the array of diodes many times a... 

Topics which will be presented in this chapter include the hardware, software, automation, valve and column configurations, and integration used in comprehensive 2DLC. Aspects of the 2DLC experiment in conjunction with multichannel detectors such as UV diode array optical detectors and mass spectrometers are discussed along with the handling of the data, which is expected to expand in scope in the future as chemometric methods are more widely used for data analysis. 

The advantages of imaging (using multichannel detectors or global imaging methods) over conventional mapping experiments are obvious, whenever multicomponent samples have to be investigated ... 

R. Bhargava and I.W. Levin, Spectrochemical Analysis using Infrared Multichannel Detectors, Blackwell Publishing, 2005. 

Other detection modes in bright CL or BL reactions are multichannel detectors, which provide simultaneous detection of the dispersed radiation and produce a permanent image of a wide area. Photographic films or plates are emulsions that contain silver halide crystals in which incident photons produce stable clusters of silver atoms within the crystals. Internal amplification is provided in the development process by an electron donor that reduces the remaining silver ions to silver atoms within the exposed crystals. A complexing agent is used to remove the... 

DNA samples are introduced into the 96-capillary array. When the samples are separated through the capillaries, the fragments are irradiated with laser hght. A charge coupled device measures the fluorescence and acts as a multichannel detector. The bases are identifled in order in accordance to the time required for them to reach the laser-detector region. 

Spectrochemical analysis using infrared multichannel detectors... 

By far the most common lamps used in AAS emit narrow-line spectra of the element of interest. They are the hollow-cathode lamp (HCL) and the electrodeless discharge lamp (EDL). The HCL is a bright and stable line emission source commercially available for most elements. However, for some volatile elements such as As, Hg and Se, where low emission intensity and short lamp lifetimes are commonplace, EDLs are used. Boosted HCLs aimed at increasing the output from the HCL are also commercially available. Emerging alternative sources, such as diode lasers [1] or the combination of a high-intensity source emitting a continuum (a xenon short-arc lamp) and a high-resolution spectrometer with a multichannel detector [2], are also of interest. 

The availability of solid-state detectors (such as the charge-coupled detector, CCD) makes it possible to acquire simultaneously significant portions of the spectra or even the entire rich spectra obtained by ICP-OES in the UV-Vis region, thus providing a large amount of data. The commercial availability of ICP-OES instruments with these multichannel detectors has significantly renewed interest in this technique. However, some limitations, such as the degradation of the spectral resolution compared with photomultiplier-based dispersive systems, still remain. 

There are several advantages to a tunable filter system. First, it is unnecessary to have a multichannel detector (for single-point measurements), since only one wavelength is being selected at a time. The size of the detector is also much more flexible, since spectral resolution of the system is not a function of the detector and input aperture as it is in a classical monochromotor, but rather limited only by the functional characteristics of the filter. Second, since focusing and dispersive elements are minimized the spectrometer could be made very small. Third, the entire spectrum does not need to be obtained the random access nature of the filter allows only the spectral features required for a measurement to be made. This can be a significant advantage for routine measurements. 

Figure 1.4 Layout and principle of operation of IR microscopes when single-channel detectors are employed (top) and when multichannel detectors are employed (bottom). Single-channel detection requires the use of apertures. Multichannel detectors typically range from a linear 16-element detector to large 65 536-element (256 x 256) detectors.

Near-infrared chemical imaging using multichannel detectors inherits many of the attributes of conventional NIR spectroscopy using a single-channel detector. In addition to its well-documented capabilities as a spectroscopic technique, in comparison to other vibrational imaging approaches, it has unparalleled flexibility in terms of managing widely varying sample size, placement, shape and color. As has been shown with the three examples presented in this chapter, the technique easily... 

Let us assume that, in all cases, the optical arrangement is properly optimized, for bringing IR flux both from the source to the sample and from the sample to the detector, with all necessary matching. To estimate the spectral flux on the detector, one needs, first of all, to know the flux emitted by the source. If the spectral flux of the source Fsrc is known, then the average spectral flux reaching one pixel of a multichannel detector can be estimated as... 

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