Physical Review A

Enhanced polarization of electron spins in He4 by simultaneous optical pumping with circularly and linearly polarized resonance radiation

L. D. Schearer, Padetha Tin

Published Oct 1, 1990• 5 citations

Abstract

The polarization of helium (2 $^{3}$${\mathit{S}}_{1}$) metastable atoms saturates at 50% when the ensemble is optically pumped with the ${\mathit{D}}_{0}$ (2 $^{3}$${\mathit{S}}_{1--}$2 $^{3}$${\mathit{P}}_{0}$) transition. We have obtained polarizations approaching 100% with a simple, straightforward modification to the conventional experimental arrangement. The addition of a small amount of \ensuremath{\pi}-polarized ${\mathit{D}}_{0}$ light incident on the cell perpendicular to the defining field direction doubles the polarization produced by circularly polarized ${\mathrm{\ensuremath{\sigma}}}^{+}$ light along the field direction. A simple rate-equation model illustrates the enhancement.

DOI: 10.1103/physreva.42.4028

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The modulated absorption of light in an optical pumping experiment on4He

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Physical Review A

Enhanced polarization of electron spins in He4 by simultaneous optical pumping with circularly and linearly polarized resonance radiation

L. D. Schearer, Padetha Tin

Published Oct 1, 1990• 5 citations

Publisher

Abstract

The polarization of helium (2

^{3}$${\mathit{S}}_{1}

) metastable atoms saturates at 50% when the ensemble is optically pumped with the

{\mathit{D}}_{0}

^{3}$${\mathit{S}}_{1--}

^{3}$${\mathit{P}}_{0}

) transition. We have obtained polarizations approaching 100% with a simple, straightforward modification to the conventional experimental arrangement. The addition of a small amount of \ensuremath{\pi}-polarized

{\mathit{D}}_{0}

light incident on the cell perpendicular to the defining field direction doubles the polarization produced by circularly polarized

{\mathrm{\ensuremath{\sigma}}}^{+}

light along the field direction. A simple rate-equation model illustrates the enhancement.

DOI: 10.1103/physreva.42.4028

Related papers

Simple and efficient method of spin-polarizing a metastable helium beam by diode laser optical pumping

Bernd Granitza, M. Salvietti, Eugenia Torello +2 more

Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 23 S→23 P0,1,2 (D0, D1, and D2) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D2 line.Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 23 S→23 P0,1,2 (D0, D1, and D2) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D2 line.

Review of Scientific InstrumentsAug 1, 199514 citations

The modulated absorption of light in an optical pumping experiment on4He

Robert B. Partridge, George William Series

Optical pumping experiments have been performed on helium 4 atoms in the metastable level 2 3 S 1 with the object of studying the modulation of light in absorption in the longitudinal and transverse beams. Magnetic resonance curves were obtained similar to those found in emission in double-resonance experiments. With a particular geometrical arrangement employing circular polarizers, the Bloch magnetic resonance curves were obtained. Modulation at four times the applied frequency was obtained with a linear polarizer in the pumping beam. This modulation is ascribed to the circulation of coherence in the optical pumping cycle. From the behaviour of the resonance signals as a function of the frequency and amplitude of the stimulating field, it is inferred that a substantial part of the signal arises from coherence which has survived two complete cycles. The observations are satisfactorily explained by the theory developed in the previous paper.Optical pumping experiments have been performed on helium 4 atoms in the metastable level 2 3 S 1 with the object of studying the modulation of light in absorption in the longitudinal and transverse beams. Magnetic resonance curves were obtained similar to those found in emission in double-resonance experiments. With a particular geometrical arrangement employing circular polarizers, the Bloch magnetic resonance curves were obtained. Modulation at four times the applied frequency was obtained with a linear polarizer in the pumping beam. This modulation is ascribed to the circulation of coherence in the optical pumping cycle. From the behaviour of the resonance signals as a function of the frequency and amplitude of the stimulating field, it is inferred that a substantial part of the signal arises from coherence which has survived two complete cycles. The observations are satisfactorily explained by the theory developed in the previous paper.

Proceedings of the Physical SocietyAug 1, 196612 citations

Optical Pumping of Helium in the S13 Metastable State

F. D. Colegrove, P. A. Franken

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 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.

Physical ReviewJul 15, 1960118 citations

Observation of oriented 23 S 1 helium atoms in a sodium-helium plasma irradiated by polarization-modulated laser radiation

Sergei P. Dmitriev, N. A. Dovator, R. A. Zhitnikov +2 more

Journal of Experimental and Theoretical Physics LettersMar 1, 19970 citations

Measurement of the spin polarization of an optically pumped ensemble of He (23S) atoms

Chu Cheng, Karl Giberson, Allen Ray Harrison +3 more

Review of Scientific InstrumentsSep 1, 19828 citations

Depolarization of Light Scattered by Aligned 2S3 and 2P3 Helium Atoms at Resonance

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.

Physical ReviewFeb 5, 19688 citations

The polarization of helium (2

^{3}$${\mathit{S}}_{1}

) metastable atoms saturates at 50% when the ensemble is optically pumped with the

{\mathit{D}}_{0}

^{3}$${\mathit{S}}_{1--}

^{3}$${\mathit{P}}_{0}

{\mathit{D}}_{0}

light incident on the cell perpendicular to the defining field direction doubles the polarization produced by circularly polarized

{\mathrm{\ensuremath{\sigma}}}^{+}

light along the field direction. A simple rate-equation model illustrates the enhancement.

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

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.