Silicon vidicon detectors

Figure 1. Diode structure and principles of operation of the silicon vidicon detector...

A vidicon detector is a photosensitive device composed of a two-dimensional array of several thousand very small detectors, each capable of responding to incident radiant energy. The most useful vidicon detector for analytical spectroscopy is the silicon vidicon detector. 

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]. 

Two-dimensional (2D) spectroscopy The silicon vidicon is a two-dimensional OID with an area-array target comprising a few hundred thousands dicrete photodiodes. Since these diodes can be randomly read out by the scanning beam, the detector is capable of performing some very useful spectrometric tasks ... 

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

While these data show that the image dissector is superior to the silicon target vidicon in several respects for atomic spectroscopy, the silicon vidicon and other integrating detectors retain significant advantages for molecular absorption (39) and fluorescence spectroscopy (40) where resolution requirements are not so demanding, available radiant fluxes are higher, and a... 

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. 

OLESIK AND WALTERS Silicon-Intensified Target Vidicon Detector... 

Busch et al used a silicon diode vidicon detector with an 0.5-m monochromator. They reported spectral lines 1.4 A apart to be resolvable and obtained data on eight elements (Mo, Fe, Ca, Al, Ti, W, Mn, and K) simultaneously. A spectral range of 200 A was possible with a single setting of the grating. Figure 9-14 is a multielement flame emission spectrum in the region 3886-4086 A obtained with this technique. 

As an attractive alternative to the vidicon the array of elements can be connected directly to individual voltage detectors on a silicon integrated circuit (usually referred to as a ROIC read-out integrated circuit ) via solder bumps . The resulting signals can then be electronically processed to yield a picture in the standard way. Fig. 7.13 shows a section through part of such an imaging array. 

---