Coherent forward scattering

Coherent forward scattering Intensity of scattered radiation 

In a system for coherent forward scattering, the radiation of a primary source is led through the atom reservoir (a flame or a furnace), across which a magnetic field is applied. When the atom reservoir is placed between crossed polarizers scattered signals for the atomic species occur on a zero-background. When a line source such as a hollow cathode lamp or a laser is used, determinations of the respective elements can be performed. In the case of a continuous source, such as a xenon lamp, and a multichannel spectrometer simultaneous multielement determinations can also be performed. The method is known as coherent forward scattering atomic spectrometry [309, 310]. This approach has become particularly interesting since flexible multichannel diode array spectrometers have became available. 

These can be calculated both for the case of the Voigt and the Faraday effect [310]. 

In the case of the Faraday effect (with the field parallel to the observation direction), there are two waves which are polarized parallel to the magnetic field. When n+ and n are the refractive indices, nm = ( + + n )/2 and An = (n+ — n )/2 the intensity lp(k) at the wavenumber k is given by  

Io(k) is the intensity of a line of the primary radiation with wavenumber k and I is the length of the atom reservoir. The sinusoidal term relates to the rotation of the polarization plane and the exponential term to the atomic absorption. As both nm and An are a function of the density of the scattering atoms, lp(k) will be proportional to the square of the density of scattering atoms (N), according to  

For the Voigt effect, the scattered radiation has two components. One is polarized 

Scattering of radiation is a one-step process in which two photons are involved, one being absorbed by the atom and one being emitted. The intensity of scattered radiation is particularly high because when monochromatic radiation is used as the 

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When, however, phonons of appropriate energy are available, transitions between the various electronic states are induced (spin-lattice relaxation). If the relaxation rate is of the same order of magnitude as the magnetic hyperfine frequency, dephasing of the original coherently forward-scattered waves occurs and a breakdown of the quantum-beat pattern is observed in the NFS spectrum. 

Coherent forward scattering (CFS) atomic spectrometry is a multielement method. The instrumentation required is simple and consists of the same components as a Zeeman AAS system. As the spectra contain only some resonance lines, a spectrometer with just a low spectral resolution is required. The detection limits depend considerably on the primary source and on the atom reservoir used. When using a xenon lamp as the primary source, multielement determinations can be performed but the power of detection will be low as the spectral radiances are low as compared with those of a hollow cathode lamp. By using high-intensity laser sources the intensities of the signals and accordingly the power of detection can be considerably improved. Indeed, both Ip(k) and Iy(k) are proportional to Io(k). When furnaces are used as the atomizers typical detection limits in the case of a xenon arc are Cd 4, Pb 0.9, T11.5, Fe 2.5 and Zn 50 ng [309]. They are considerably higher than in furnace AAS. 

Yamamoto M., Murayama S., Ito M. and Yasuda M. (1980) Theoretical basis for multielement analysis by coherent forward scattering atomic spectroscopy Spectrochim Acta, Part B 35 43-50. 

ESCA electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy) ESI electrospray ionization ET-AAS (Also denoted GFAAS, EAAS, EA-AAS, ETAAS, ETA-AAS) electrothermal atomization atomic absorption spectrometry ETA-CFS electrothermal atomization -coherent forward scattering (atomic magneto-optic rotation) spectrometry ETAES electrothermal atomization atomic emission spectrometry ETAES electrothermal atomization atomic fluorescence spectrometry ETA-LEI electrothermal atomization -laser enhanced ionization spectrometry... 

Deak L, Bottyan L, Nagy DL and Spiering H (1996) Coherent forward-scattering amplitude in transmission and grazing incidence Mossbauer spectroscopy. Physical Reviews B Condensed Matter 53 6158-6164. 

Coherent forward scattering (CFS) atomic spectrometry is a multi-element method. The instrumentation required is simple and consists of the same components as a... 

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