Multichannel charge injection device

Optical spectroscopy ranging from Raman through Atomic is under considerable pressure to replace the "tried and true" photomultiplier tube (PMT) with multichannel devices. Two classes of solid state devices, the Charge Coupled Device (CCD) and the Charge Injection Device (CID), hold great promise for meeting this need. Operating modes of these devices are reviewed. Characteristics pertinent to analytical spectroscopy are presented. 

A Charge-Injection Device Instrument. A number of companies offer multichannel simultaneous spec-ironielcrs based on echellc spectrometers aiid two-dimensional array devices. This type of instrument has replaced other types of multichannel emission spectro-melers in many applicaiions. 

There are a number of different types of photon detectors, including the photomultiplier tube, the silicon photodiode, the photovoltaic cell, and a class of multichannel detectors called charge transfer devices. Charge transfer detectors include photodiode arrays, charge-coupled devices (CCDs), and charge-injection devices (ClDs). These detectors are used in the UV/VIS and IR regions for both atomic and molecular spectroscopy. 

Simultaneous multichannel instruments are of two general tfp s polychromators and spectrographs. Poly-chromators contain a series of photomultiplier tubes for detection, but spectrographs use two-dimensional charge-injection devices (CIDs) or charge-coupled devices (CCDs) as transducers. Older instruments used photographic emulsions as transducers. 

More recently, charge-transfer devices, such as charge-coupled devices (CCDs) and charge-injection devices (ClDs), have been employed in Raman spectrometers. Figure 18-11 shows a fiber-optic Raman spectrometer that uses a CCD as a multichannel detector. Here, high-quality bandpass and band-rejection (notch) filters provide good stray light rejection. The CCD array can be a two-dimensional array or in some cases a linear array. 

The main detectors used in AES today are photomultiplier tubes (PMTs), photodiode arrays (PDAs), charge-coupled devices (CCDs), and vidicons, image dissectors, and charge-injection detectors (CIDs). An innovative CCD detector for AES has been described [147]. New developments are the array detector AES. With modem multichannel echelle spectral analysers it is possible to analyse any luminous event (flash, spark, laser-induced plasma, discharge) instantly. Considering the complexity of emission spectra, the importance of spectral resolution cannot be overemphasised. Table 8.25 shows some typical spectral emission lines of some common elements. Atomic plasma emission sources can act as chromatographic detectors, e.g. GC-AED (see Chapter 4). 

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