Physical Review Letters

Determination of gJ(He4, 2S13)gJ(H1, 1S122) : Resolution of a Discrepancy

George M. Keiser, H. G. Robinson, C. E. Johnson

Published Nov 3, 1975• 14 citations

Abstract

A new measurement of the ${g}_{J}$ factor in the $2^{3}S_{1}$ metastable state of $^{4}\mathrm{He}$ has been made using an optical-pumping technique. Our result is $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.15(10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This value agrees with theory and provides confirmation of a recent atomic-beam measurement. Further doubt is cast on an earlier optical-pumping determination, thereby resolving a possible discrepancy between theory and experiment.

DOI: 10.1103/physrevlett.35.1223

Related papers

An experimental determination of gJ(He4, 2S13)gJ(H1, 1S122)

George M. Keiser, H. G. Robinson, C. E. Johnson

Physical Review ASep 1, 197722 citations

gJ factor of metastable S25 atomic oxygen using a time-of-flight, atomic-beam magnetic-resonance method

Tuncay Incesu, Ahsanul Huq, Howard A. Shugart

Physical Review ASep 1, 19781 citation

Dipole polarizability of 2S13 and 2S01 metastable helium measured by the electric deflection time-of-flight method

David A. Crosby, Jens C. Zorn

Physical Review AAug 1, 197725 citations

The First Measurement of the $2^{3\!}S_1 - 2^{3\!}P / 3^{3\!}P$ Tune-Out Wavelength in He*

B. M. Henson

arXiv:1708.08200Aug 28, 20170 citations

The First Measurement of the $2^{3}S_{1} \rightarrow 3^{3}P - 2^{3}P$ Tune-Out Wavelength in He*

B. M. Henson

Aug 28, 20170 citations

Optical Pumping of Helium in the S13 Metastable State

F. D. Colegrove, P. A. Franken

Physical ReviewJul 15, 1960118 citations

Physical Review Letters

Determination of gJ(He4, 2S13)gJ(H1, 1S122) : Resolution of a Discrepancy

George M. Keiser, H. G. Robinson, C. E. Johnson

Published Nov 3, 1975• 14 citations

Publisher

Abstract

A new measurement of the

{g}_{J}

factor in the

2^{3}S_{1}

metastable state of

^{4}\mathrm{He}

has been made using an optical-pumping technique. Our result is

\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.15(10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}

. This value agrees with theory and provides confirmation of a recent atomic-beam measurement. Further doubt is cast on an earlier optical-pumping determination, thereby resolving a possible discrepancy between theory and experiment.

DOI: 10.1103/physrevlett.35.1223

Related papers

An experimental determination of gJ(He4, 2S13)gJ(H1, 1S122)

George M. Keiser, H. G. Robinson, C. E. Johnson

The ratio of the ${g}_{J}$ factor of $^{4}\mathrm{He}(2^{3}S_{1})$ to that of $^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})$ has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He ${g}_{J}$ factor that depended upon the intensity of the discharge used to excite the He atoms to the $2^{3}S_{1}$ state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the ${g}_{J}$ factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.The ratio of the ${g}_{J}$ factor of $^{4}\mathrm{He}(2^{3}S_{1})$ to that of $^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})$ has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He ${g}_{J}$ factor that depended upon the intensity of the discharge used to excite the He atoms to the $2^{3}S_{1}$ state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the ${g}_{J}$ factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.

Physical Review ASep 1, 197722 citations

gJ factor of metastable S25 atomic oxygen using a time-of-flight, atomic-beam magnetic-resonance method

Tuncay Incesu, Ahsanul Huq, Howard A. Shugart

A time-of-flight, atomic-beam magnetic-resonance method was used to compare the ${g}_{J}$ factor of $2{p}^{3}3s^{5}S_{2}$ atomic oxygen with the ${g}_{J}$ factor of metastable $2^{3}S_{1}$ atomic helium in magnetic fields of 3209 and 4228 G. The metastable oxygen and helium atoms were produced in a pulsed radio-frequency discharge source and after traversing the apparatus were detected by electron emission from a tungsten surface. By collecting data only in a given interval of the time-of-flight distribution the $\mathrm{O}(^{5}S)$ and $\mathrm{He}(^{3}S)$ states were isolated from other discharge products. From 158 pairs of resonances taken with four relative field and hairpin orientations the atomic magnetic $g$ factor is ${g}_{J}(^{5}S_{2}, ^{16}\mathrm{O})=\frac{{\ensuremath{\mu}}_{J}}{J}=\ensuremath{-}2.0020910(10)$.A time-of-flight, atomic-beam magnetic-resonance method was used to compare the ${g}_{J}$ factor of $2{p}^{3}3s^{5}S_{2}$ atomic oxygen with the ${g}_{J}$ factor of metastable $2^{3}S_{1}$ atomic helium in magnetic fields of 3209 and 4228 G. The metastable oxygen and helium atoms were produced in a pulsed radio-frequency discharge source and after traversing the apparatus were detected by electron emission from a tungsten surface. By collecting data only in a given interval of the time-of-flight distribution the $\mathrm{O}(^{5}S)$ and $\mathrm{He}(^{3}S)$ states were isolated from other discharge products. From 158 pairs of resonances taken with four relative field and hairpin orientations the atomic magnetic $g$ factor is ${g}_{J}(^{5}S_{2}, ^{16}\mathrm{O})=\frac{{\ensuremath{\mu}}_{J}}{J}=\ensuremath{-}2.0020910(10)$.

Physical Review ASep 1, 19781 citation

Dipole polarizability of 2S13 and 2S01 metastable helium measured by the electric deflection time-of-flight method

David A. Crosby, Jens C. Zorn

The static dipole polarizability of helium atoms in the metastable $2^{3}S_{1}$ and $2^{1}S_{0}$ states has been determined by measuring the deflection of a beam of excited helium atoms that is caused by an inhomogeneous electric field of known properties. The necessary velocity distribution information is obtained from time-of-flight measurements, and a resonance quenching technique made it possible to distinguish the singlet and triplet components of the beam. The results, $\ensuremath{\alpha}(2^{3}S_{1})=(44.6\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{3}$ and $\ensuremath{\alpha}(2^{1}S_{0})=(108\ifmmode\pm\else\textpm\fi{}13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{3}$ , agree with the theoretical value that has been used to calibrate earlier polarizability measurements of the alkali metals and the heavier noble gases.The static dipole polarizability of helium atoms in the metastable $2^{3}S_{1}$ and $2^{1}S_{0}$ states has been determined by measuring the deflection of a beam of excited helium atoms that is caused by an inhomogeneous electric field of known properties. The necessary velocity distribution information is obtained from time-of-flight measurements, and a resonance quenching technique made it possible to distinguish the singlet and triplet components of the beam. The results, $\ensuremath{\alpha}(2^{3}S_{1})=(44.6\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{3}$ and $\ensuremath{\alpha}(2^{1}S_{0})=(108\ifmmode\pm\else\textpm\fi{}13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{3}$, agree with the theoretical value that has been used to calibrate earlier polarizability measurements of the alkali metals and the heavier noble gases.

Physical Review AAug 1, 197725 citations

The First Measurement of the $2^{3\!}S_1 - 2^{3\!}P / 3^{3\!}P$ Tune-Out Wavelength in He*The First Measurement of the $2^{3\!}S_1 - 2^{3\!}P / 3^{3\!}P$ Tune-Out Wavelength in He*

B. M. Henson

The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength' which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted value [PhysRevA.88.052515] of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength' which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted value [PhysRevA.88.052515] of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.

arXiv:1708.08200Aug 28, 20170 citations

The First Measurement of the $2^{3}S_{1} \rightarrow 3^{3}P - 2^{3}P$ Tune-Out Wavelength in He*The First Measurement of the $2^{3}S_{1} \rightarrow 3^{3}P - 2^{3}P$ Tune-Out Wavelength in He*

B. M. Henson

The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength' which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted value\cite{Mitroy2013} of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.The workhorse of atomic physics, quantum electrodynamics, is one of the best-tested theories in physics. However recent discrepancies have shed doubt on its accuracy for complex atomic systems. To facilitate the development of the theory further we aim to measure transition dipole matrix elements of metastable helium (He*) (the ideal 3 body test-bed) to the highest accuracy thus far. We have undertaken a measurement of the `tune-out wavelength' which occurs when the contributions to the dynamic polarizability from all atomic transitions sum to zero; thus illuminating an atom with this wavelength of light then produces no net energy shift. This provides a strict constraint on the transition dipole matrix elements without the complication and inaccuracy of other methods. Using a novel atom-laser based technique we have made the first measurement of the tune-out wavelength in metastable helium between the $3^{3}P_{1,2,3}$ and $2^{3}P_{1,2,3}$ states at 413.07(2) nm which compares well with the predicted value\cite{Mitroy2013} of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.

Aug 28, 20170 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

A new measurement of the

{g}_{J}

factor in the

2^{3}S_{1}

metastable state of

^{4}\mathrm{He}

has been made using an optical-pumping technique. Our result is

\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.15(10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}

The ratio of the

{g}_{J}

factor of

^{4}\mathrm{He}(2^{3}S_{1})

to that of

^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})

has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the

^{4}\mathrm{He}(2^{3}S_{1})

Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the

^{4}\mathrm{He}(2^{3}S_{1})

Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He

{g}_{J}

factor that depended upon the intensity of the discharge used to excite the He atoms to the

2^{3}S_{1}

state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the

{g}_{J}

factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.

A time-of-flight, atomic-beam magnetic-resonance method was used to compare the

{g}_{J}

factor of

2{p}^{3}3s^{5}S_{2}

atomic oxygen with the

{g}_{J}

factor of metastable

2^{3}S_{1}

atomic helium in magnetic fields of 3209 and 4228 G. The metastable oxygen and helium atoms were produced in a pulsed radio-frequency discharge source and after traversing the apparatus were detected by electron emission from a tungsten surface. By collecting data only in a given interval of the time-of-flight distribution the

\mathrm{O}(^{5}S)

and

\mathrm{He}(^{3}S)

states were isolated from other discharge products. From 158 pairs of resonances taken with four relative field and hairpin orientations the atomic magnetic

g

factor is ${g}_{J}(^{5}S_{2}, ^{16}\mathrm{O})=\frac{{\ensuremath{\mu}}_{J}}{J}=\ensuremath{-}2.0020910(10)$.

The static dipole polarizability of helium atoms in the metastable

2^{3}S_{1}

and

2^{1}S_{0}

states has been determined by measuring the deflection of a beam of excited helium atoms that is caused by an inhomogeneous electric field of known properties. The necessary velocity distribution information is obtained from time-of-flight measurements, and a resonance quenching technique made it possible to distinguish the singlet and triplet components of the beam. The results, $\ensuremath{\alpha}(2^{3}S_{1})=(44.6\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$

{\mathrm{cm}}^{3}

and $\ensuremath{\alpha}(2^{1}S_{0})=(108\ifmmode\pm\else\textpm\fi{}13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$

{\mathrm{cm}}^{3}

, agree with the theoretical value that has been used to calibrate earlier polarizability measurements of the alkali metals and the heavier noble gases.

The First Measurement of the

2^{3\!}S_1 - 2^{3\!}P / 3^{3\!}P

Tune-Out Wavelength in He*

3^{3}P_{1,2,3}

and

2^{3}P_{1,2,3}

states at 413.07(2) nm which compares well with the predicted value [PhysRevA.88.052515] of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.

The First Measurement of the

2^{3}S_{1} \rightarrow 3^{3}P - 2^{3}P

Tune-Out Wavelength in He*

3^{3}P_{1,2,3}

and

2^{3}P_{1,2,3}

states at 413.07(2) nm which compares well with the predicted value\cite{Mitroy2013} of 413.02(9) nm. We have additionally developed many of the methods necessary to improve this measurement to the 100 fm level of accuracy where it will form the most accurate determination of transition rate information ever made in He* and provide a stringent test for atomic QED simulations. We believe this measurement to be one of the most sensitive ever made of an optical dipole potential, able to detect changes in potentials of $\sim$200 pK and is widely applicable to other species and areas of atom optics.

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.