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AIP conference proceedings

Can we rotate an atom?

J. P. Woerdman, M. Kristensen, Martijn A. van Eijkelenborg, Gerard Nienhuis

Published Jan 1, 1993• 0 citations
Publisher

Abstract

When we rotate matter the nuclei follow the macroscopic motion. One may ask whether the atomic electrons also follow the rotation microscopically. If they do, a mechanical Faraday effect arises. We discuss the connection between the mechanical Faraday effect and the usual (i.e., magnetic) Faraday effect. As material medium we consider resonant atoms immersed in a high‐density buffer gas. The electronic wave functions of the resonant atoms are predicted to be rotationally coupled to the buffer gas as soon as nonimpact broadening becomes appreciable at line center. Preliminary experimental results for the case Rb+Xe indicate that this occurs for Xe pressures of a few atmospheres.

DOI
10.1063/1.45033

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Faraday effect as a probe of hindered electronic precession in atoms

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Onset of a collisional modification of the Faraday effect in a high-density atomic gas

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We investigate, theoretically and experimentally, the onset of modified electronic precession due to quasimolecular behavior in dense atomic gases. The close connection between the angular coupling of collision pairs and a modification of the Faraday effect is pointed out. We have observed the onset of this quasimolecular modification of the atomic Faraday effect with high-resolution laser measurements of the absorption and Faraday spectra near the ${\mathit{D}}_{2}$ line of Rb atoms immersed in high-density buffer gases. The atomic Faraday effect itself is also affected by the presence of nuclear spin; this modifies the electronic precession through angular-momentum coupling. We describe how to separate the effect of nuclear spin from the effects due to quasimolecular behavior. In this way we establish the existence of angular coupling of the Rb valence electrons to neighboring buffer-gas atoms at densities above \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ in Xe buffer gas. In He buffer gas, quasimolecular modifications of the Faraday effect are approximately two times smaller than for Xe.

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Mechanical Faraday effect induced by binary collisions

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Theory and observation of Faraday rotation obtained with strong light fields

I O G Davies, P. E. G. Baird, J L Nicol

The authors have observed dramatic changes in both the magnitude and the lineshape of Faraday rotation on an allowed E1 transition in Sm I (4f 6 6s 2 7 F 0 -4f 6 6s6p 7 G 1 ) as a function of laser intensity and buffer-gas pressure. The effect is ascribed to the development of optical and Zeeman coherences and a theoretical treatment, based on the solution of steady-state density matrix equations is given. Effects of optical pumping on the odd isotopes 147 Sm and 149 Sm, both with I=7/2, are also considered.

Journal of Physics B Atomic and Molecular Physics•Oct 28, 1987•30 citations
When we rotate matter the nuclei follow the macroscopic motion. One may ask whether the atomic electrons also follow the rotation microscopically. If they do, a mechanical Faraday effect arises. We discuss the connection between the mechanical Faraday effect and the usual (i.e., magnetic) Faraday effect. As material medium we consider resonant atoms immersed in a high‐density buffer gas. The electronic wave functions of the resonant atoms are predicted to be rotationally coupled to the buffer gas as soon as nonimpact broadening becomes appreciable at line center. Preliminary experimental results for the case Rb+Xe indicate that this occurs for Xe pressures of a few atmospheres.
We compare the Faraday spectrum with the dispersion spectrum near the D2{\mathit{D}}_{2}D2​ line of Rb atoms immersed in a high density Xe buffer gas. We observe deviations from the standard Becquerel relation, which relates the Faraday effect of an atomic gas to its dispersion. The deviations are due to coupling of the Rb valence electron to the Xe environment. The Rb D2{\mathit{D}}_{2}D2​ transition dipole moment becomes rotationally locked to the instantaneous collision axes at Xe densities of \ensuremath{\sim}1020{10}^{20}1020 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.
We investigate, theoretically and experimentally, the onset of modified electronic precession due to quasimolecular behavior in dense atomic gases. The close connection between the angular coupling of collision pairs and a modification of the Faraday effect is pointed out. We have observed the onset of this quasimolecular modification of the atomic Faraday effect with high-resolution laser measurements of the absorption and Faraday spectra near the D2{\mathit{D}}_{2}D2​ line of Rb atoms immersed in high-density buffer gases. The atomic Faraday effect itself is also affected by the presence of nuclear spin; this modifies the electronic precession through angular-momentum coupling. We describe how to separate the effect of nuclear spin from the effects due to quasimolecular behavior. In this way we establish the existence of angular coupling of the Rb valence electrons to neighboring buffer-gas atoms at densities above \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}1019{10}^{19}1019 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ in Xe buffer gas. In He buffer gas, quasimolecular modifications of the Faraday effect are approximately two times smaller than for Xe.
Whereas mechanical rotation of a transparent solid induces rotation of the plane of linear polarization of a light beam, for a dilute vapor this mechanical Faraday effect must disappear. By studying the structure of the collision operator that is familiar in the unified theory of spectral line broadening, we demonstrate that a nonzero effect arises for a vapor of absorbing atoms embedded in a buffer gas. The size of the effect is easily compared with the magnetic Faraday effect, when the angular velocity is replaced with the Larmor precession frequency. Then, the mechanical effect is smaller by a factor of the order of the collision frequency multiplied with the duration of a collision. Furthermore, the mechanical effect is a linear combination of the frequency derivative of a (collision-broadened) dispersion curve and the derivative of an absorption curve.
Large Faraday rotations can be generated by circular birefringence of atomic samples in an axial magnetic field in the vicinity of atomic resonance lines. More generally, magneto-optical effects in atomic samples include circular dichroism in addition to birefringence, resulting in a modification of the ellipticity as well as the polarization alignment. Usually such effects are investigated for homogeneous linear polarizations, but the mechanisms apply also to polarization structures such as vector vortices. We investigate the effect of optical activity of a rubidium vapor in the hyperfine Paschen–Back regime along the D2 line, for the example of azimuthally polarized input light. We show that for low atomic densities, circular birefringence dominates over dichroism, and azimuthal polarization is rotated toward radial polarization. The rotation angle increases with increasing optical densities. At high vapor temperatures, dichroism becomes more and more relevant, leading to intricate variations of both alignment and ellipticity. Our results shine new light on the interplay between different magneto-optic effects at strong magnetic fields. Their highly sensitive response to detuning may find applications in spectroscopy and quantum sensing.
The authors have observed dramatic changes in both the magnitude and the lineshape of Faraday rotation on an allowed E1 transition in Sm I (4f 6 6s 2 7 F 0 -4f 6 6s6p 7 G 1 ) as a function of laser intensity and buffer-gas pressure. The effect is ascribed to the development of optical and Zeeman coherences and a theoretical treatment, based on the solution of steady-state density matrix equations is given. Effects of optical pumping on the odd isotopes 147 Sm and 149 Sm, both with I=7/2, are also considered.