The Resonant Faraday Effect

Abstract

The resonant Faraday effect occurs for radiation at frequencies close to the absorption lines of a magnetoactive material. In the paper we present a theory for isolated absorption lines with Voigt profiles. The background source is also assumed to have a Voigt profile. The theory shows how the resonant Faraday effect can be used to determine relative transition probabilities, as well as the magnitude of the Lorentzian component of the line profiles.Experimental results for an argon plasma are presented and show that the relative transition probabilities of atomic transitions with a common lower level can be measured to an accuracy of 1%. For strong absorption lines, the Voigt "a" parameter can also be determined to an accuracy of lo%, even when the Doppler width is 14 times larger than the Lorentzian width.La resonance de I'effet Faraday se presente a des frequences voisines des raies d'absorption dans un milieu magneto-actif. On presente dans cet article une theorie de cette resonance pour des lignes d'absorption isolees ayant un profil de Voigt. Cette theorie montre comment la resonance de I'effet Faraday peut Ctre utilisee pour determiner des valeurs relatives des probabilites de transition, ainsi que la grandeur de la composante lorentzienne des profils de ligne.Les resultatsexperimentaux qui sont present& pour le cas d'un plasma d'argon montrent que les probabilites relatives peuvent Ctre dtterminees avec une precision de 1% dans le cas de transitions atomiques vers un mCme niveau inferieur. Pour des lignes d'absorption fortes, le parametre "a" de Voigt peut Ctre obtenu avec une precision de lo%, mCme lorsque la largeur Doppler est 14 fois plus grande que la largeur lorentzienne.

The measurement of oscillator strengths

“…With these refinements, Camm and Curzon (1972) obtained excellent agreement between the computed and experimental irradiance as a function of B and achieved as low as 1% uncertainty for relative transition probabilities. In addition these authors were able to determine the value of a to 10%.…”

“…They used a neon Geissler tube for the source and found that the experimental and theoretical irradiance distributions did not always agree to within the experimental uncertainties. Subsequently Camm and Curzon (1972) in an elegant and productive investigation of Ar I used identical discharge tubes for both the source and the absorbing atoms (S and the test cell shown in figure 4). In addition, they removed the effects of radial density gradients in the test cell by restricting the aperture of the source beam to the centre of the cell.…”

“…t It was noticed by both Seka and Curzon (1968) and Camm and Curzon (1972) that k,l depended slightly on the magnetic field strength. They concluded that the population of the lower state depended on the magnetic field.…”

Pressure broadening of 772.376 and 772.421 nm argon lines and kinetics of argon metastable atoms

“…In 1960-1970s, motivated by the determination of the oscillator strength of resonance lines of rare-gas atoms, but also for testing the applicability of different collision broadening theories, several groups have measured the pressure broadening coefficients of different argon lines. The resonance Faraday effect on some argon lines absorbed by metastable atoms has been used in 24,25 , but most of the line profiles were obtained from the analysis of the profile of plasma induced emission, by scanning Fabry-Perot interferometer 26,27,28 or with a spectrometer 29,30,31,32 . However, the necessary correction for the apparatus function of the experimentally recorded spectral profiles of the lines introduced large uncertainty on deduced broadening coefficients.…”

Transmission characteristics of an excited-state Faraday optical filter at 532 nm

“…A filter based on the anomalous dispersion of the Faraday rotation in the resonance lines of certain atomic gases was first described and demonstrated by Ohman (1956). The theoretical framework for the resonant Faraday effects has been established (Camm et al 1972, Roberts et al 1980, Yeh 1982, Chen et al 1987. Yin and Shay (1991) developed the theoretical framework for FADOF based on ground-state transitions by using a quantum-mechanical treatment of the resonant Faraday effect.…”