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Physical Review A

Collisional redistribution of circularly polarized light in barium perturbed by argon

W. J. Alford, N. Andersen, Michael Scott Belsley, J. Cooper, D. M. Warrington, Keith R. Burnett

Published May 1, 1985• 30 citations
Publisher

Abstract

We have measured the orientation of the Ba 6p ${\mathrm{}}^{1}$P level produced by collision-induced excitation from the ground state by circularly polarized light. The detuning dependence of the far-wing excited-state orientation can be interpreted in terms of reorientation of molecular orbitals which occur during the collision. Effects due to rotational coupling are seen to occur at large blue-wing detunings. We have also determined the collisional rate for destruction of orientation by measuring the pressure dependence of the excited-state orientation.

DOI
10.1103/physreva.31.3012

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Two-Photon Polarization Spectroscopy of Atomic Cesium Using Circularly Polarized Light

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Measurements of collisional depolarization cross sections play an important role in gaining valuable information about the interaction between inert and rare-gas atoms.A key element in understanding collisional dynamics is the detailed analysis of the polarization of the emitted photons.In order to investigate the collisional cross section of the excited J=1/2 cesium atoms, by collisions with the ground level argon atoms, experimental measurements were made studying circular polarization spectra.Orientation in the J=1/2 level was optically induced by circularly polarized light with a positive helicity.A two-photon double-resonance (6s 2 S 1/2 →6p 2 P 1/2 → 10s 2 S 1/2 ) condition was achieved using nanosecond pulsed dye lasers, and the intensity of the cascade fluorescence was monitored in the presence of argon atoms ranging from 10 -4 torr to 100 torr.

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Collisional redistribution in Hg-Kr: Polarization spectrum of the redistributed light

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We have measured the alignment of Hg(6 $^{3}$${\mathit{P}}_{1}$) atoms following off-resonant excitation of the Hg 6 $^{1}\mathrm{S}_{0}$--6 $^{3}\mathrm{P}_{1}$ transition in the presence of Kr. We present a polarization spectrum for both red and blue wings out to detunings beyond 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This represents a considerable extension to the existing results, which has been made possible by the use of a pump-and-probe excitation scheme. In the experiment a pulsed laser, detuned from the resonance, creates an alignment in the upper state. This is probed by tuning a delayed second laser to a higher transition and monitoring laser-induced fluorescence from the two-step process. The alignment of the asymptotic Hg(6 $^{3}$${\mathit{P}}_{1}$) atoms is determined by comparison of the signals obtained for different relative polarizations of the lasers. We discuss the advantages of this method and the relation of the raw data to the polarizations presented. The results are discussed within the context of a simple quasiclassical model of the process.

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Manifestation of higher polarization moments in the dipole emission under conditions of stepwise excitation and anisotropic collisions

V. N. Rebane, T. K. Rebane

The induction of higher polarization moments-the octupole orientation and the hexadecapole alignment—in the case of two-step excitation of atoms through dipole transitions and their manifestation in the polarization of dipole emission under conditions of anisotropic collisions are studied. For all channels of the two-step excitation process J 0→J 1 J, the efficiencies of production of higher polarization moments with integer and half-integer angular momenta from J=2 to J=7 through the absorption of linearly or circularly polarized light are calculated. The rates of collisional relaxation and interconversion of higher polarization moments, for both orientation and alignment, as functions of frequency detuning of the laser line from the center of the Doppler profile are calculated. The theory is illustrated by an example of two channels of excitation of the atomic state J=2 by circularly polarized light: J 0=0→J 1=1J=2 and J 0=3→J 1=2 (or 3)→J=2. In the first case, the octupole orientation enhances or attenuates the signal of circular polarization depending on the laser frequency detuning. In the second case, it represents the only source producing orientation and circular polarization of the emitted light.

Optics and Spectroscopy•Jan 1, 2001•2 citations
We have measured the orientation of the Ba 6p 1{\mathrm{}}^{1}1P level produced by collision-induced excitation from the ground state by circularly polarized light. The detuning dependence of the far-wing excited-state orientation can be interpreted in terms of reorientation of molecular orbitals which occur during the collision. Effects due to rotational coupling are seen to occur at large blue-wing detunings. We have also determined the collisional rate for destruction of orientation by measuring the pressure dependence of the excited-state orientation.
We have measured the far-wing collisional redistribution line shape, the redistributed fluorescence polarization, and the collisional alignment decay rates for barium perturbed by argon and xenon. The experiment was performed with a heated gas cell ($T\ensuremath{\sim}900$ K) with perturber-gas densities in the 1---30-Torr range and laser light detuned \ifmmode\pm\else\textpm\fi{} 3--- 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ from the 5535-\AA{} Ba I $6^{1}S\ensuremath{-}6^{1}P$ resonance line. Metal-vapor densities were determined by a Rayleigh scattering technique, which is outlined in detail. By correlating structure in the line shape with that of the polarization, we are able to make definitive statements about the interatomic potentials. The Ba data show strong similarities with previous experimental results for similar two-electron atoms, namely Ca, Sr, and Hg, and so our conclusions are of relevance to these systems as well.
We have measured the polarization of collisionally redistributed light as a function of detuning from line center for the Hg3P1–1S0 transition in the presence of Ar. We present a polarization profile for the red wing between 5 and 18 cm−1 and polarizations for two detunings in the blue wing. We compare this type of experiment to the complementary method of photodissociation and discuss the issue of coherence between excitation path-ways. The data are analyzed using a simple molecular reorientation model suggested by others which includes coherent excitation. The model is shown to be unable to completely account for the high polarizations measured in this experiment. We suggest reasons for the failure of this model.
We have made systematic measurements of the polarization of fluorescence from Sr-rare-gas systems excited off resonance by linearly polarized light. Measurements of this type give information about the evolution during a collision after the absorption of a photon. This information is important in obtaining and verifying aspects of the interaction potential that cannot be studied using conventional line-broadening experiments. We have also measured the collisional-alignment decay rates for Sr-rare-gas systems by observing the perturber-pressure dependence of the polarization of the fluorescence. To the best of our knowledge this is a new technique for measuring these decay rates.
Measurements of collisional depolarization cross sections play an important role in gaining valuable information about the interaction between inert and rare-gas atoms.A key element in understanding collisional dynamics is the detailed analysis of the polarization of the emitted photons.In order to investigate the collisional cross section of the excited J=1/2 cesium atoms, by collisions with the ground level argon atoms, experimental measurements were made studying circular polarization spectra.Orientation in the J=1/2 level was optically induced by circularly polarized light with a positive helicity.A two-photon double-resonance (6s 2 S 1/2 →6p 2 P 1/2 → 10s 2 S 1/2 ) condition was achieved using nanosecond pulsed dye lasers, and the intensity of the cascade fluorescence was monitored in the presence of argon atoms ranging from 10 -4 torr to 100 torr.
We have measured the alignment of Hg(6 3^{3}3P1{\mathit{P}}_{1}P1​) atoms following off-resonant excitation of the Hg 6 1S0^{1}\mathrm{S}_{0}1S0​--6 3P1^{3}\mathrm{P}_{1}3P1​ transition in the presence of Kr. We present a polarization spectrum for both red and blue wings out to detunings beyond 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This represents a considerable extension to the existing results, which has been made possible by the use of a pump-and-probe excitation scheme. In the experiment a pulsed laser, detuned from the resonance, creates an alignment in the upper state. This is probed by tuning a delayed second laser to a higher transition and monitoring laser-induced fluorescence from the two-step process. The alignment of the asymptotic Hg(6 3^{3}3P1{\mathit{P}}_{1}P1​) atoms is determined by comparison of the signals obtained for different relative polarizations of the lasers. We discuss the advantages of this method and the relation of the raw data to the polarizations presented. The results are discussed within the context of a simple quasiclassical model of the process.
The induction of higher polarization moments-the octupole orientation and the hexadecapole alignment—in the case of two-step excitation of atoms through dipole transitions and their manifestation in the polarization of dipole emission under conditions of anisotropic collisions are studied. For all channels of the two-step excitation process J 0→J 1 J, the efficiencies of production of higher polarization moments with integer and half-integer angular momenta from J=2 to J=7 through the absorption of linearly or circularly polarized light are calculated. The rates of collisional relaxation and interconversion of higher polarization moments, for both orientation and alignment, as functions of frequency detuning of the laser line from the center of the Doppler profile are calculated. The theory is illustrated by an example of two channels of excitation of the atomic state J=2 by circularly polarized light: J 0=0→J 1=1J=2 and J 0=3→J 1=2 (or 3)→J=2. In the first case, the octupole orientation enhances or attenuates the signal of circular polarization depending on the laser frequency detuning. In the second case, it represents the only source producing orientation and circular polarization of the emitted light.