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Bulletin of the American Physical Society

Use of a diode laser to measure the spin polarization of an optically-pumped ensemble of He(2{sup 3}S) atoms

David Bixler, Christopher D. Wallace, Dongmei Huang, Adam Henry Wagman, F. B. Dunning, G. K. Walters

Published May 1, 1996• 0 citations

Abstract

A polarized He{sup +} ion source based on spin conservation in Penning ionization reactions involving polarized He(2{sup 3}S) atoms contained in an optically-pumped, rf-excited helium discharge is being developed for surface studies. To optimize source performance, the He(2{sup 3}S) polarization must be determined. The authors have devised a technique for doing this that involves measuring the attenuation of a circularly-polarized probe beam provided by a 1.083 {mu}m DBR diode laser whose output frequency is scanned by varying the drive current to allow separate measurements on the 2{sup 3}S{sub 1}-2{sup 3}P{sub 0}, 2{sup 3}P{sub 1} and 2{sup 3}P{sub 2} transitions. As will be discussed, several independent expressions for the polarization (and alignment) can be derived from the experimental data thus providing valuable internal consistency checks. The technique is simple to implement and reliable in operation.

Related papers

Optical manipulation of helium(2(3)S) atoms with a diode laser

David Bixler

A commercial Spectra Diode Laboratories, 1.083 $\mu$m diode laser has been used to efficiently spin polarize an atomic beam of He(2$\sp3$S) metastable atoms by optical pumping on the $\rm 2\sp3S\sb1\rightarrow2\sp3P\sb1$ (D1) transition. The diode laser is an InGaAs/GaAs strained multiquantum well with a distributed Bragg reflector to insure single longitudinal mode operation. The laser has been frequency stabilized to less than 1 MHz/hr drift. The helium metastable atom beam is produced by electron impact and the polarization is measured using a Stern-Gerlach analyzer. Atomic polarizations exceeding 97% have been obtained with $\sim$25 mW of power from the diode laser. A number of experiments currently under construction may also make use of the diode laser. These include the production of a spin polarized helium ion beam by optically pumping the metastable atoms in an rf discharge, and the trapping of helium metastable atoms in a magneto-optical trap (MOT).

•Jan 1, 1995•0 citations

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

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

A technique is described that enables simple, direct determination of the spin polarization of an optically pumped ensemble of He (23S) atoms. The polarization is obtained from measurements of the attenuation of the circularly polarized output of a color-center laser tuned to the 1.08 μm He (23S1→23P0) transition.

Review of Scientific Instruments•Sep 1, 1982•8 citations

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.

Review of Scientific Instruments•Aug 1, 1995•14 citations

Intense source of spin-polarized electrons using laser-induced optical pumping

L. G. Gray, Karl Giberson, Chu Cheng +3 more

A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (23S→23P) radiation provided by a NaF (F2+)* color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO2 produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 μA. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date.

Review of Scientific Instruments•Mar 1, 1983•32 citations

Record nuclear polarization in optically pumped 3He gas using a high power LNA laser

N. P. Bigelow, Christian Larat, Pierre-Jean Nacher +1 more

Optical pumping is an efficient method for creating nuclear polarization M in a gas of 3He. M is first achieved in the metastable 23S state and then transfered to the ground state. Polarized 3He has numerous applications: quantum fluids, precision magnetometry, nuclear targets, etc. Much progress in achieving high values of M has resulted from the development of efficient IR lasers capable of exciting the 23S–23P3He transition at 1.08 μm. Using a novel lamp pumped LNA laser delivering 5 W cw, we have achieved M >85% for samples in the torr pressure range. To measure M we have developed an accurate technique based on the change as a function of M of the ratio between σ and π polarized light absorbed from a weak; probe beam by the 23S metastable atoms. The probe was delivered by a single mode tunable diode pumped LNA laser that was frequency modulated by using an étalon mounted on a galvoplate. M was also measured by monitoring the circular polarization of the 668 nm line emitted by the dis charge. Experimental and theoretical results on the optimization of the pumping will be presented, and the laser systems will be discussed.

Annual Meeting Optical Society of America•Jan 1, 1992•0 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

An experiment on the observation of spin polarization of metastable helium atoms interacting with optically oriented sodium atoms under continuous rf discharge conditions is described. Laser radiation with alternating-sign circular polarization, tuned to the resonance excitation of the 3 2 S 1/2 –3 2 P 1/2 transition in Na atoms, is used as the source for optical pumping of ground-state sodium atoms.

Journal of Experimental and Theoretical Physics Letters•Mar 1, 1997•0 citations

A polarized He{sup +} ion source based on spin conservation in Penning ionization reactions involving polarized He(2{sup 3}S) atoms contained in an optically-pumped, rf-excited helium discharge is being developed for surface studies. To optimize source performance, the He(2{sup 3}S) polarization must be determined. The authors have devised a technique for doing this that involves measuring the attenuation of a circularly-polarized probe beam provided by a 1.083 {mu}m DBR diode laser whose output frequency is scanned by varying the drive current to allow separate measurements on the 2{sup 3}S{sub 1}-2{sup 3}P{sub 0}, 2{sup 3}P{sub 1} and 2{sup 3}P{sub 2} transitions. As will be discussed, several independent expressions for the polarization (and alignment) can be derived from the experimental data thus providing valuable internal consistency checks. The technique is simple to implement and reliable in operation.

A commercial Spectra Diode Laboratories, 1.083

\mu

m diode laser has been used to efficiently spin polarize an atomic beam of He(2$\sp3$S) metastable atoms by optical pumping on the $\rm 2\sp3S\sb1\rightarrow2\sp3P\sb1$ (D1) transition. The diode laser is an InGaAs/GaAs strained multiquantum well with a distributed Bragg reflector to insure single longitudinal mode operation. The laser has been frequency stabilized to less than 1 MHz/hr drift. The helium metastable atom beam is produced by electron impact and the polarization is measured using a Stern-Gerlach analyzer. Atomic polarizations exceeding 97% have been obtained with $\sim$25 mW of power from the diode laser. A number of experiments currently under construction may also make use of the diode laser. These include the production of a spin polarized helium ion beam by optically pumping the metastable atoms in an rf discharge, and the trapping of helium metastable atoms in a magneto-optical trap (MOT).

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.

A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (23S→23P) radiation provided by a NaF (F2+)* color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO2 produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 μA. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date.

Optical pumping is an efficient method for creating nuclear polarization M in a gas of 3He. M is first achieved in the metastable 23S state and then transfered to the ground state. Polarized 3He has numerous applications: quantum fluids, precision magnetometry, nuclear targets, etc. Much progress in achieving high values of M has resulted from the development of efficient IR lasers capable of exciting the 23S–23P3He transition at 1.08 μm. Using a novel lamp pumped LNA laser delivering 5 W cw, we have achieved M >85% for samples in the torr pressure range. To measure M we have developed an accurate technique based on the change as a function of M of the ratio between σ and π polarized light absorbed from a weak; probe beam by the 23S metastable atoms. The probe was delivered by a single mode tunable diode pumped LNA laser that was frequency modulated by using an étalon mounted on a galvoplate. M was also measured by monitoring the circular polarization of the 668 nm line emitted by the dis charge. Experimental and theoretical results on the optimization of the pumping will be presented, and the laser systems will be discussed.