Multielement detectors

The first detectors to be used in OMA systems were standard TV image tubes. These were silicon vidicons or the more sensitive Silicon Intensified Target (SIT) detectors, which both employed silicon targets to convert optical information into electronic form. More recently, the use of solid state detectors in the form of a diode array (Reticon) has been found to have some advantages over the vidicons and SIT tubes. Current developments in the field of charge coupled devices (CCD) will probably soon provide an even better multielement detector for use in OMA systems. 

The sensitivity of both vidicons and diode arrays can be enhanced using a microchannel plate image intensifier. For example, Tracor Northern in their IDARSS system have used a Genii microchannel plate inverter intensifier, fiber-optically coupled to a Reticon diode array. With such a system, single photoelectron sensitivity, i.e. one count per photon, can be 

In order to actually carry out time resolved spectroscopy, the gating process must be synchronized to both the experiment and the reading and digitizing processes. This is not trivial but can be done using additional logic and timing circuits (see, for example, ref. 107). 

The study of the dynamics of excited states is still a rapidly expanding field. If, for example, Table 1 had been prepared even just two or three 

An example of a solid state detector is the Reticon self-scanning photodiode array, which was specifically designed for spectroscopic applications [104]. These diode arrays contain 512 or 1024 silicon diode sensor elements on 25 jum centers corresponding to a density of 40 diodes mm . Each diode is 2.5 mm high giving each element a slit-like geometry with a 100 1 aspect ratio. Beam registration problems do not apply to the diode array since the channel dimensions are defined by a photomask and hence the detector element size and position are completely reproducible. Solid state detectors do not suffer from lag [105] and althou they will bloom, the effect is much less severe than in a vidicon. 

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Solid-state metal-matrix composite processing, 16 169-173 Solid-state multielement detector arrays, 23 141... 

Recent developments in light detectors over the entire region from UV-Vis to near-IR have been of significant benefit to electronic spectroscopy. There have been improvements and enhancements of more traditional single element detectors such as photodiodes and photomultiphers as well as more dramatic advances in multielement detectors snch as CCDs. 

An AED detector is a multielement detector capable of detecting elements with atomic emission lines in the vacuum UV, UV-VIS, and near IR portions of the electromagnetic spectrum. 

A laser beam is passed through the measurement cell and brought to a waist of focus at the plane of the multielement detector. This is the reverse Fourier optical setup. Conventional Fourier optics arrangements are also used. 

Most modern laboratory Raman instruments use spectrographs with multielement detectors. Figures 3 and 4 show optical diagrams of the more important spectrographs used for Raman spectroscopy. The Czerny-Turner spectrograph and its many variants are the most popular. Concave grating spectrographs... 

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