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Journal of Physics B Atomic and Molecular Physics

Pressure broadening of the Hanle effect in a neon discharge

C. Gerald Carrington, Alan Corney

Published Jun 1, 1971• 41 citations
Publisher

Abstract

Investigates the levels of the 2p 5 3p configuration of neon by studying the polarization of the light emitted by a dc neon discharge. The pressure broadening of the Hanle signals was studied and cross sections were obtained for the destruction of alignment for collisions with both helium and neon ground state atoms. The measurements have been made at 315 K and 85 K. The cross sections for the 2p 2 and 2p 6 levels (Paschen notation) change considerably with temperature, while the cross sections for other levels are almost independent of temperature.

DOI
10.1088/0022-3700/4/6/015

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Messung der Relaxation der Ausrichtung elektronenstoßangeregter Heliumzustände unter dem Einfluß von Eigenstößen und Kaskaden / Influence of Collisions and Cascades on the Measurement of Alignment Relaxation of Helium States Excited by Electron Impact

W. Schöck

Abstract Influence Using impact excitation, the measurement of alignment relaxation rates of atomic states is influenced by cascading transitions. The two methods for measuring the collisional depolarization, the Hanle-effect and the direct measurement of the polarization of the emitted radiation, were investigated theoretically and compared. The results were checked by measuring the depolarization of helium states excited by electron impact. The depolarization cross sections of the 3,4,5 3P-states were determined from Hanle-effect measurements as 1.8(4), 3.9(5), and 5.6(6) · 10-14 cm2 respectively.

Zeitschrift für Naturforschung A•Dec 1, 1972•3 citations
Investigates the levels of the 2p 5 3p configuration of neon by studying the polarization of the light emitted by a dc neon discharge. The pressure broadening of the Hanle signals was studied and cross sections were obtained for the destruction of alignment for collisions with both helium and neon ground state atoms. The measurements have been made at 315 K and 85 K. The cross sections for the 2p 2 and 2p 6 levels (Paschen notation) change considerably with temperature, while the cross sections for other levels are almost independent of temperature.
Alignment cascade phenomena have been studied in the neon 2p levels (Paschen notation) Hanle effect and double resonance techniques in a mild discharge. The levels are aligned directly by an optical excitation mechanism. Most 2p levels show evidence of alignment cascade from the 2s 4 , 3s 1 or 3d levels below 0.1 Torr; addition of argon impurities greatly enhances the cascade signal relative to the direct alignment signal. Data used previously in pressure broadening studies are shown to be free of cascade errors and are used to establish upper limits for the 2p level life times. A correction for coherence narrowing is estimated; this gives natural life times systematically less than those obtained by methods in which cascade effects are not carefully eliminated. In common with other Hanle effect measurements for these levels the values are marginally smaller than the threshold life times of Bennett and Kindlmann (1966).
In a temperature-controlled neon discharge cell under a magnetic field up to 7 T, a linearly polarized laser pulse has produced polarized neon atoms (atomic alignment) on the 2p 2 (in the Paschen notation) level from the 1s 3 level. The subsequent fluorescence to the 1s 2 level was observed with its polarized components being resolved. The disalignment rate coefficients of the 2p 2 atom due to neon atom collisions were determined at the temperature of 77 and 300 K. At each temperature, the rate coefficient shows no dependence on the magnetic field within the experimental accuracy.
In a positive column of a glow discharge, a linearly polarized laser pulse produces aligned neon atoms in the 2p 2 (Paschen notation) level, and the subsequent fluorescence is observed with its polarized components resolved. The relaxation rate of the alignment, or the disalignment rate, is thus determined. The populations of the 1s 2 – 1s 5 levels are found to be strongly dependent on the discharge current, and so are the degrees of radiation re-absorption of the transition lines from 2p 2 to these levels. A Monte Carlo simulation is performed by which the disalignment rate by radiation re-absorption for these transitions is determined, where the isotope splitting of the transition lines is taken into account. This rate is subtracted from the observed disalignment rate, resulting in the rate being independent of the degree of radiation re-absorption. Thus, disalignment due to atom collisions and that due to radiation re-absorption are separated. For the latter disalignment the disalignment rate deduced by the simulation, treating the four transitions simultaneously, is found to be virtually equal to the sum of the disalignment rates for each of the transitions. The approximate expression for the disalignment rate given by D’Yakonov and Perel’ (1965 Sov. Phys.–JETP 20 997) is quantified, so that it can be applied to estimating the disalignment rate of an upper level having several transition lines with finite optical thickness.
Abstract The linewidth of the Hanle effect signal of the orientation and alignment of the resonance level 5 1P1 of the cadmium isotop Cd114 is measured as a function of the pressure of various noble gases, of hydrogen and deuterium. The cross sections for broadening of the orientation and alignment signals due to atomic collisions are derived from the pressure dependence of the linewidth. The multipole depolarization-cross sections were found to be In order to separate the depolarization effects from quenching effects in the case of hydrogen and deuterium polarization measurements of the resonance radiation were also undertaken. The alignment depolarization- and the quenching cross sections were found to
The interaction of an intense optical-maser field with excited atoms in a gas discharge leads to a considerable change in the population of those levels which are resonant at the maser frequency. This will cause a change in the population of other levels that are connected to the maser levels through collision-induced nonradiative as well as radiative transitions. Using the 1.15-\ensuremath{\mu} optical maser, these effects have been studied in detail for the 2s2s2s levels of neon where the changes are completely due to collisions. By analyzing the intensity changes in spontaneous emission originating from a gas-discharge cell placed within the maser resonator, we have observed the approach to a partial thermalization of two closely spaced levels. In this way we have been able to obtain the atomic-collision cross section for excitation transfer between the 2s22{s}_{2}2s2​ and 2s32{s}_{3}2s3​ levels. In pure neon this has been found to be ${\ensuremath{\sigma}}_{23}=(2.3\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2. For a helium-neon mixture the measured cross section is ${\ensuremath{\sigma}}_{23}=(1.8\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2. The experimental method used to determine these cross sections eliminates the uncertainties caused by the effects of electron-atom collisions and radiative cascade. These techniques also yield the ratio of the Einstein coefficients for the transitions $2{s}_{2}\ensuremath{\rightarrow}2{p}_{10}$ and $2{s}_{3}\ensuremath{\rightarrow}2{p}_{10}$. The measured ratio is $\frac{{A}_{2}}{{A}_{3}}=3.0\ifmmode\pm\else\textpm\fi{}0.4$.
Abstract Influence Using impact excitation, the measurement of alignment relaxation rates of atomic states is influenced by cascading transitions. The two methods for measuring the collisional depolarization, the Hanle-effect and the direct measurement of the polarization of the emitted radiation, were investigated theoretically and compared. The results were checked by measuring the depolarization of helium states excited by electron impact. The depolarization cross sections of the 3,4,5 3P-states were determined from Hanle-effect measurements as 1.8(4), 3.9(5), and 5.6(6) · 10-14 cm2 respectively.