Atomic fluorescence lasers

The laser atomic fluorescence excitation and emission spectra of sodium in an air-acetylene flame are shown below. In the excitation spectrum, the laser (bandwidth = 0.03 nm) was scanned through various wavelengths while the detector monochromator (bandwidth = 1.6 nm) was held fixed near 589 nm. In the emission spectrum, the laser was fixed at 589.0 nm, and the detector monochromator wavelength was varied. Explain why the emission spectrum gives one broad band, whereas the excitation spectrum gives two sharp lines. How can the excitation linewidths be much narrower than the detector monochromator bandwidth ... 

M. A. Bolshov, C. F. Boutron, F. M. Ducroz, U. Gorlach, O. M. Kompanetz, S. M. Rudniev, B, Hutch, Direct ultratrace determination of cadmium in Antarctic and Greenland snow and ice by laser atomic fluorescence spectrometry. Anal. Chim. Acta, 251 (1991), 169-175. 

M. A. Bolshov, C. F. Boutron, A. V. Zybin, Determination of lead in Antarctic ice at the picogram-per-gram level by Laser Atomic Fluorescence Spectroscopy, Anal. Chem., 61 (1989), 1758-1762. 

M. A. Bolshov, S. N. Rudniev, J. P. Candelone, C. F. Boutron, S. Hong, Ultratrace determination of Bi in Greenland snow by laser atomic fluorescence spectrometry, Spectrochim. Acta, 49B (1994), 1445-1452. 

Laser-excited atomic fluorescence spectrometry is capable of extremely low detection limits, particularly when combined with electrothermal atomization. Detection limits in the femtogram (10 g) to attogram (10 g) range have been shown for many elements. Commercial instrumentation has not been developed for laser-based AFS, probably because of its expense and the nonroutine nature of high-powered lasers. Atomic fluorescence has the disadvantage of being a singleelement method unless tunable lasers with their inherent complexities are used. 

Tab. 18. Detection limits in laser atomic fluorescence spectrometry.

Grazhulene S., Khvostikov V. and Sorokin M. (1991) The possibilities of glow discharge cathode sputtering for laser atomic-fluorescence analysis of microelectronics materials, Spedrochim Acta, Part B 46 459-465. 

Method Performance General Broekaert (1994) provides a good comparison of the figures of merit power of detection, matrix effects and cost, for many atomic spectrometric elemental determination methods including atomic absorption, atomic emission, laser atomic fluorescence. 

FIGURE 14 Laser atomic fluorescence in flame atomizers. The photomultiplier tube (PMT) is equipped with a band-pass filter. 

The atom probe field-ion microscope (APFIM) and its subsequent developments, the position-sensitive atom probe (POSAP) and the pulsed laser atom probe (PLAP), have the ultimate sensitivity in compositional analysis (i.e. single atoms). FIM is purely an imaging technique in which the specimen in the form of a needle with a very fine point (radius 10-100 nm) is at low temperature (liquid nitrogen or helium) and surrounded by a noble gas (He, Ne, or Ar) at 10 -10 Pa. A fluorescent screen or a... 

There is little evidence for 1 1 compounds between elements in this group under normal conditions. The diatomic van der Waals molecules, CaMg, SrMg and SrCa, however, have been synthesized by codepositing the atoms from separate sources with argon or krypton into solid matrices at 12 K. These low-T species are identified from their laser-induced fluorescence spectra. The ground-state spectroscopic data for these alkaline-earth dimers form a sensible series between the parent molecules Mg2, Caj and Sr2. ... 

Electron diffraction spectroscopy ETA LEAFS Electrothermal atomisation laser-excited atomic fluorescence... 

LEAFS Laser-excited atomic fluorescence scattering... 

Several characteristics of the metal beam have been studied in detail. It is well known that metal clusters and metal oxides are formed as a result of the ablation process. However, these potentially interfering species have been studied in detail130 and it has been concluded that they do not introduce any doubt as to the validity of the experimental results. Much more important than cluster or oxide formation are the atomic electronic state populations of the metal beams. For each metal reactant, these have been characterized using laser-induced fluorescence (LIF) excitation spectroscopy. For Y, only the two spin-orbit states of the ground electronic state (a Dz/2 and a D-3,/2) were observed.123... 

Yuzefovsky et al. [241] used Cis resin to preconcentrate cobalt from seawater prior to determination at the ppt level by laser-excited atomic fluorescence spectrometry with graphite electrothermal atomiser. 

Laser-excited atomic fluorescence spectrometry has been used to determine down to 1 ng/1 of lead in seawater [359]. 

Cobalt Co(III) adsorbed on C18 bonded silica Laser excited atomic fluorescence spectrometry - [241]... 

In order to record excitation spectra, the radical ions must first be thermalized to the electronic ground state, which happens automatically if they are created in condensed phase (e.g. in noble-gas matrices, see below). In the gas-phase experiments where ionization is effected by collision with excited argon atoms (Penning ionization), the unexcited argon atoms serve as a heat bath which may even be cooled to 77 K if desired. After thermalization, excitation spectra may be obtained by laser-induced fluorescence. 

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