Physical Review Letters

Alignment of Metastable Helium Atoms by Unpolarized Resonance Radiation

P. A. Franken, F. D. Colegrove

Published Nov 1, 1958• 32 citations

Abstract

Experiments in which helium atoms in the /sup 3/S/sub 1/ metastable state were aligned by the action of unpolarized optical resonance radiation are reported. The alignment was detected by resonance methods; the observed line widths are of the order of a milligauss with a raw signal-to-noise ratio of approximates 1OO: 1. The simplest experimental arrangement is described and the theory outlined. (W.D.M.)

DOI: 10.1103/physrevlett.1.316

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Physical Review Letters

Alignment of Metastable Helium Atoms by Unpolarized Resonance Radiation

P. A. Franken, F. D. Colegrove

Published Nov 1, 1958• 32 citations

Publisher

Abstract

DOI: 10.1103/physrevlett.1.316

Related papers

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L. D. Schearer

The $2^{3}S_{1}$ (metastable) and $2^{3}P_{1,2}$ excited-state atoms of ${\mathrm{He}}^{4}$ are aligned by an unpolarized beam of resonance radiation. The alignment is detected by the depolarization of the resonance fluorescence at 1\ensuremath{\mu}, which occurs when either the $2^{3}S_{1}$ level or the $2^{2}P_{1,2}$ levels are saturated by a rf magnetic field at the Zeeman frequency. The observed signals are several orders of magnitude larger than the corresponding signals observed by monitoring intensity changes in the transmitted beam. Considerably smaller signals are observed even in the absence of the pumping beam. Expressions for the intensity of the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ components of the scattered radiation are derived in terms of the alignment and density of the metastable atoms. The alignment of the $2^{3}S_{1} (F=\frac{3}{2})$ and the $2^{3}P_{2} (F=\frac{5}{2})$ levels of ${\mathrm{He}}^{3}$ is also observed. The excited-state linewidth as a function of pressure leads to a radiative decay time of $\ensuremath{\tau}\ensuremath{\approx}0.96\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ sec and a mixing cross section of 53\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ . The alignment of the $3^{3}P$ level of ${\mathrm{He}}^{4}$ is also observed by monitoring polarization changes of the 3889 \AA{} line.The $2^{3}S_{1}$ (metastable) and $2^{3}P_{1,2}$ excited-state atoms of ${\mathrm{He}}^{4}$ are aligned by an unpolarized beam of resonance radiation. The alignment is detected by the depolarization of the resonance fluorescence at 1\ensuremath{\mu}, which occurs when either the $2^{3}S_{1}$ level or the $2^{2}P_{1,2}$ levels are saturated by a rf magnetic field at the Zeeman frequency. The observed signals are several orders of magnitude larger than the corresponding signals observed by monitoring intensity changes in the transmitted beam. Considerably smaller signals are observed even in the absence of the pumping beam. Expressions for the intensity of the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ components of the scattered radiation are derived in terms of the alignment and density of the metastable atoms. The alignment of the $2^{3}S_{1} (F=\frac{3}{2})$ and the $2^{3}P_{2} (F=\frac{5}{2})$ levels of ${\mathrm{He}}^{3}$ is also observed. The excited-state linewidth as a function of pressure leads to a radiative decay time of $\ensuremath{\tau}\ensuremath{\approx}0.96\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ sec and a mixing cross section of 53\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. The alignment of the $3^{3}P$ level of ${\mathrm{He}}^{4}$ is also observed by monitoring polarization changes of the 3889 \AA{} line.

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Sergei P. Dmitriev, N. A. Dovator, Victor A. Kartoshkin

We have experimentally detected a signal of magnetic resonance (MR) from 85Rb atoms in the 52 S 1/2 state by measuring the absorption of light from a helium lamp producing optical orientation of metastable 23 S 1 4He atoms in a cell containing alkali metal vapor and gaseous helium at a pressure of 1 Torr. The ratio of MR signal amplitudes in Rb and He atoms did not exceed 10–2. Peculiarities of the formation and observation of the collisional polarization of Rb atoms in alkali–helium plasma are discussed.We have experimentally detected a signal of magnetic resonance (MR) from 85Rb atoms in the 52 S 1/2 state by measuring the absorption of light from a helium lamp producing optical orientation of metastable 23 S 1 4He atoms in a cell containing alkali metal vapor and gaseous helium at a pressure of 1 Torr. The ratio of MR signal amplitudes in Rb and He atoms did not exceed 10–2. Peculiarities of the formation and observation of the collisional polarization of Rb atoms in alkali–helium plasma are discussed.

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The

2^{3}S_{1}

(metastable) and

2^{3}P_{1,2}

excited-state atoms of

{\mathrm{He}}^{4}

are aligned by an unpolarized beam of resonance radiation. The alignment is detected by the depolarization of the resonance fluorescence at 1\ensuremath{\mu}, which occurs when either the

2^{3}S_{1}

level or the

2^{2}P_{1,2}

levels are saturated by a rf magnetic field at the Zeeman frequency. The observed signals are several orders of magnitude larger than the corresponding signals observed by monitoring intensity changes in the transmitted beam. Considerably smaller signals are observed even in the absence of the pumping beam. Expressions for the intensity of the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ components of the scattered radiation are derived in terms of the alignment and density of the metastable atoms. The alignment of the

2^{3}S_{1} (F=\frac{3}{2})

and the

2^{3}P_{2} (F=\frac{5}{2})

levels of

{\mathrm{He}}^{3}

is also observed. The excited-state linewidth as a function of pressure leads to a radiative decay time of $\ensuremath{\tau}\ensuremath{\approx}0.96\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ sec and a mixing cross section of 53\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$

{\mathrm{cm}}^{2}

. The alignment of the

3^{3}P

level of

{\mathrm{He}}^{4}

is also observed by monitoring polarization changes of the 3889 \AA{} line.

The alignment of

{\mathrm{He}}^{4}

atoms in the (

n=2

, metastable)

^{3}S_{1}

state is described. Metastable atoms are produced by an rf discharge in a glass tube containing a few mm of pure helium, and the one micron pumping light ($2^{3}P\ensuremath{-}2^{3}S$) is provided by a helium lamp. A resonance signal is obtained from radio frequency disorientation by monitoring the transmitted pumping light. The double maximum line shape of this signal for strong rf magnetic fields is discussed. Included also is a discussion of the angular dependence of the signal when unpolarized light is used and an explanation of the inversion of the resonance signal for certain densities of the metastable helium atoms.The measured relaxation time of the oriented metastable atoms in the discharge is about 2.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ second and the pumping time is about a millisecond. A method is proposed and initial measurements are given for the cross section for destruction of metastable helium atoms by collision with foreign gas atoms. The application of optical pumping in helium to the measurement of weak magnetic fields is also discussed.

The authors have observed the alignment of the

5p^{2}P_{\frac{3}{2}}

state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.