Linear photodiode detector array

Rothwell, Martinson and Gorman have studied the formation of stress induced crazes in polymethyl methacrylate. The sample was initially stressed and held at a strain of 3.5 %. Upon relaxation, SAXS-patterns of 1.5 s were recorded using a linear photodiode detector array. A sequence of selected curves recorded in a plane parallel to the strain direction is shown in Fig. 49. The peak at h = 0.014 is probably due to an... 

Sihcon charge coupled devices (CCDs), commonly used in soHd-state video cameras and in research appHcations, are being appHed to low light level spectroscopy appHcations. The main advantage of area array CCDs over linear photodiode detectors is the two-dimensional format, which provides simultaneous measurements of spatial and spectral data. 

The use of a linear detector array in the image plane of a polychromator in place of the fluorescence monochromator in Figure 12.1 enables the parallel data accumulation of complete fluorescence spectra. Silicon photodiode arrays, operated in a CCD mode(34) are the most widely used detector elements. The spectral response of the diodes enables fluorescence to be detected from the near-UV up to ca. 1100 nm with a peak response in the near-IR. Up to 8192 elements are now available commercially in a single linear array at low cost. However, the small length of each element (ca. 10 [im) presently limits sensitivity and hence cylindrical lens demagnification is often necessary. 

Also, to facilitate the use of this detector an extensive computer software system has been written which allows the user almost unlimited freedom in the way that the data taken over the bandwidth of the detector may be plotted or displayed for visual examination. The linear photodiode arrays used as detectors have been shown to have a significant response in the ultraviolet region of the spectrum. 

The scope of ultraviolet and visible spectrophotometry can be further extended when combined with a chromatographic separation step such as HPLC. The development of rapid-scanning detectors based on the linear photodiode array permits spectra to be acquired during the elution of peaks. Computer-aided manipulation of these spectra has led to new strategies for the examination of chromatographic peak homogeneity, based on classical techniques in spectroscopy. The use of microcomputers enables the development of archive retrieval methods for spectral characterisation (A. F. Fell etal, J. Chromat., 1984, 316, 423-440). 

Rapid-scanning Spectrophotometers. These en loy multi-channel detectors. The most commonly encountered detector of diis t e is tlie linear photodiode array. The reversed-optics mode is employed, so that radiation is passed throu tiie sample or reference cell, tiien dispersed by a dif action grating polychiomator integrated intensity of radiation incident on it which is determined by tiie spectial dispersion photo ode ratio. If, for example, a 200-nm txmdwidtii of radiation were dispersed across 256 photodiodes, tiie nominal resolution per photodiode woitid be 0.78 nm. 

The use of a commercially available diode array multichannel detector is also described. The advantage of using such a detector is the ability to immediately record a complete spectrum from near UV to IR with one measurement. The detector is a linear photodiode array consisting of 1024 diodes. It takes 25 ms to record the full spectrum, making the apparatus suitable for applications which start in the millisecond time domain. The experiment, i.e. the arbitrary recording of the spectra as well as the irradiation of the sample, is controlled by a computer program according to a timetable which is preset individually. 

While the SIT vidicon detection system provides unique and exciting spectroscopic detection capabilities, inherent limitations of vidicon detection prevent it from replacing other detectors such as photographic emulsions, photomultiplier tubes, or linear photodiode arrays. Rather, the SIT vidicon is complementary to the more traditional spectroscopic detectors. 

The diffraction equipment used for the study of conducting polymers in no way differs fi-om that used for the study of conventional polymers. This short section does not cover the experimental methods in any technical detail, however, but merely presents some considerations about their applicability. Details can be found in the standard books on this topic [3-5]. Admittedly, these books are somewhat dated they do not, for instance, reflect the impact of computers on both automation of equipment and data evaluation. Another result of the ever-accelerating progress in microelectronics (still based on metals and inorganic semiconductors instead of polymers), is to be found in the field of x-ray detector systems linear photodiode array detectors, Charge-Coupled-Device area detectors and Image Plate detectors have all become available recently. 

PMTs and linear photodiode array detectors are discussed in detail in Chapter 5. This section will cover the 2D array detectors used in arc/spark and plasma emission spectrometers. In order to take advantage of the 2D dispersion of wavelengths from an Echelle spectrometer, a 2D detector is required. The detector should consist of multiple... 

Reduction of "non-optlcal noise sources below the shot noise limit of the detector is thus critical in extending the performance of HPLC optical detectors. One must understand these noise sources prior to optimizing the design of a detector, and prior to applying new technology such as that of the linear photodiode array to HPLC detection. 

Figure 1 Schematic of a fiber-optic-based multichannel fluoro-meter I DA=512-element intensified linear photodiode array detector L is the lens and OF 1 and OF 2 are the excitation and emission fibers, respectively.

Milano et al. [153, 154] and Cook [34] introduced an approach to derivative spectra by substituting electronic wavelength modulation for the mechanical systems used in derivative spectrometers. This effect is achieved by superimposing a low-amplitude, periodic wave form on the horizontal sweep signal. In this way spectra were generated. Warner et al. [155] applied a vidicon detector for fast detection of fluorescence spectra and obtained derivatives of the stored data by digital computation. Cook et al. [156] also made use of a silicon vidicon detector for multichannel operations in rapid UV-VIS spectrophotometers with the possibility of first-order differentiation. For the same purpose Milano et al. [93, 157] used a multichannel linear photodiode array for detection of spectra in polychromator optics and stored data manipulations (d ). Technical explanations of the principles of diode array and vidicon devices cem be found in [158-161]. 

With multiplex detectors, the radiation of the various wavelengths no longer need to be measured sequentially (one after the other). Instead, by parallel imaging of many wavelengths on a spatially resolving detector they can be measured simultaneously so that a complete spectrum is recorded. This can be done by using linear photodiode arrays or, more recently, so-called charge-coupled devices (CCDs) [2], [3], 147], [48). 

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