Diode atomic spectroscopy

Valuable information on the kinetics and mechanism of CF3 + N02 comes from the experimental and theoretical study by Pagsberg et al,226 The experiments, performed using time-resolved infrared diode laser spectroscopy, were supported by ab initio calculations to provide insight into the potential energy surface of the reaction system. The reaction was initiated by pulse radiolysis of Ar/SF6/CF3I mixtures. The abstraction reaction of the iodine atom from CF3I by fluorine atoms leads to the formation of CF3 radicals. The reactions... 

Ludin AI, Lehmann BE (1995) High-resolution diode-laser spectroscopy on a fast beam of metastable atoms for detecting very rare krypton isotopes. Appl Phys B61 461-465 Maloszewski P, Zuber A (1982) Determining the turnover time of ground water systems with the aid of environmental tracers, I. Models and their apphcability. J Hydrol 57 207-231... 

The most important applications for diode array systems are in molecular spectroscopy, since in general they do not have the resolution necessary for atomic spectroscopy. In molecular spectroscopy the most useful areas of application are for (1) scanning fast reactions to determine kinetics, (2) applications involving low light levels because spectra can be stored and added to each other, increasing the intensity, and (3) detectors for HPLC and capillary electrophoresis (CE). HPLC and CE are discussed in Chapter 13. 

U. Gustafsson, J. Alnis, S. Svanberg Atomic spectroscopy with violet laser diodes. Am. J. Phys. 68, 660 (2000)... 

In Florence, we have chosen an approach that combines laser spectroscopy with the direct frequency measures of the microwave experiments [4]. We take advantage of the obvious consideration that to obtain the FS separations there s no need to precisely know the optical transitions frequencies but just their differences. Thus, if we have two laser frequencies whose difference can be accurately controlled, we may use one as a fixed reference and tune the second across the atomic resonances, as illustrated by Fig. 1. In fact, our approach reverts to an heterodyne technique, where all the transitions are measured with respect to the same reference frequency, that can take any arbitrary but stable value. In the experimental realisation we obtain the two frequencies by phase-locking two diode lasers (master and slave), i.e. phase-locking their beat note to a microwave oscillator [14]. We show in Fig 2 a full-view of the experimental set-up. 

Vacancy-related complexes which were generated in silicon p -n diodes by irradiation with 6 MeV electrons in the temperature range of 350-800 K have been studied by means of deep level transient spectroscopy. Such defects are of interest because of their possible application in controlling the carrier lifetime in silicon power devices. Electronic parameters of defects incorporating up to three vacancies and an oxygen atom have been detemiined. Total introduction rate of radiation-induced defects increased about twice upon raising the irradiation temperature from 350 to 675 K. 

When using two lasers and applying two-photon spectroscopy, only those atoms that do not have a velocity component in the observation direction will undergo LEI. Then the absorption signals become very narrow (Doppler-free spectroscopy). This enhances the selectivity and the power of detection, however, it also makes isotope detection possible. Uranium isotopic ratios can thus be detected, similarly to with atomic fluorescence [673] or diode laser AAS. Thus for dedicated applications a real alternative to isotope ratio measurements with mass spectrometry is available. 

Ng K. C., Ali A. H., Barber T. E. and Winefordner J. D. (1988) Multiple mode semiconductor diode laser as a spectral line source for graphite furnace atomic absorption spectroscopy, Anal Chem 62 1893-1895. 

Fig. 2.7. Very high Rydberg states of the Ba atom recorded by laser spectroscopy using thermionic diode detection (after J.-P. Connerade et at. [27]).

Instead of measuring the attenuation of a beam, one may also count the ions produced with very high efficiency by the use of channelplates or a hot-wire detector [387], an approach which has mainly been applied in laser spectroscopy, where high sensitivity can be achieved by space charge amplification. The principle of the thermionic diode is that the atomic vapour under study is formed within the detector, and a current limited by the space charge is obtained by appropriately biasing a diode, consisting of an external anode (often the outer wall of the vacuum system, formed by a metal tube) and a heated cathode made of a suitable material to emit many electrons (thoriated W is suitable in many cases). A sketch of... 

Although most suitable for use with lasers, Thermionic diodes have also been successfully applied to synchrotron radiation studies by using wiggler magnets to enhance the intensity of the beam [390]. Last but not least, one should mention the important category of atomic beam experiments, complemented by the techniques of photoelectron and photoion spectroscopy. All these techniques are suitable for the experimental study of interacting resonances. We turn now to their theoretical description, which will be illustrated by experimental examples. 

Turning initially to multidetection, and here first to simultaneous usage, an obvious application is to combine the gradient FIA techniques with the use of detectors that provide several signals at several values of the instrumental variables, which indeed gives FIA a doubly dynamic character. In these techniques, which have already been mentioned in Section 2.4, advantage can be taken by multidetectors, such as the fast-scan vol-tammetric detectors [288] or by inductively coupled plasma atomic emission spectroscopy [808] or by diode array detectors [1017, 1075, 1382]. Combined with the advantages offered by chemometrics, these multidetection procedures may in fact be extended to multideterminations. 

In order to obtain conclusive results one normally focuses on a single transition and detects the emitted fluorescence photons bearing the fine structure information. This is achievable by dye lasers or tunable laser diodes. In some setups the light travels collinearly to fast atomic beams which has some advantages with respect to spectral resolution [44]. The technique of fast ion beam spectroscopy has been applied to numerous measurements on rare earth ions, e.g. [45-49]). Some more recent high-resolution optical hfs measurements include Ta [50], [51] and the noble gas Xe [52] illustrate these advanced... 

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