Physical Review

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

L. D. Schearer

Published Feb 5, 1968• 8 citations

Abstract

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.

DOI: 10.1103/physrev.166.30

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Optical Pumping of Helium in the S13 Metastable State

F. D. Colegrove, P. A. Franken

Physical ReviewJul 15, 1960118 citations

Collision-Induced Mixing in the 2P3 Levels of Helium

L. D. Schearer

Physical ReviewAug 5, 196729 citations

Theory of double refraction in a gas due to spin alignment: Observations of birefringence in optically pumped helium

S Pancharatnam

Journal of Physics B Atomic and Molecular PhysicsMar 1, 19684 citations

Alignment of Metastable Helium Atoms by Unpolarized Resonance Radiation

P. A. Franken, F. D. Colegrove

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.)

Physical Review LettersNov 1, 195832 citations

Lifetime of the 2P11 and 3P11 States of Atomic Helium

James M. Burger, Allen Lurio

Physical Review AJan 1, 197121 citations

Radiative Lifetime of the 2 S01 Metastable State of Helium

Robert S. Van Dyck, C. E. Johnson, Howard A. Shugart

Physical Review AOct 1, 197199 citations

Physical Review

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

L. D. Schearer

Published Feb 5, 1968• 8 citations

Publisher

Abstract

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.

DOI: 10.1103/physrev.166.30

Related papers

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

Collision-Induced Mixing in the 2P3 Levels of Helium

L. D. Schearer

The cross section for the transfer of excitation from the $2^{3}P_{0}$ level of helium to the $2^{3}P_{1}$ and $2^{3}P_{2}$ levels as a result of collisions with the ground-state helium atom ( $1^{1}S_{0}$ ) has been measured with a conventional resonance-fluorescence technique. A ${\mathrm{He}}^{4}$ source excited the $2^{3}S_{1}\ensuremath{-}2^{3}P_{0}$ transition in a ${\mathrm{He}}^{3}$ absorption cell. The scattered light was examined with a high-resolution grating spectrometer and the ratio of the $2^{3}P_{0}\ensuremath{\rightarrow}2^{3}S_{1}$ to the $2^{3}P_{1,2}\ensuremath{\rightarrow}2^{3}S_{1}$ intensities was measured as a function of cell pressure from 0.05 to 10 Torr. The cross section for collision-induced transitions out of the $2^{3}P_{0}$ level is found to be (68\ifmmode\pm\else\textpm\fi{}3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at room temperature.The cross section for the transfer of excitation from the $2^{3}P_{0}$ level of helium to the $2^{3}P_{1}$ and $2^{3}P_{2}$ levels as a result of collisions with the ground-state helium atom ($1^{1}S_{0}$) has been measured with a conventional resonance-fluorescence technique. A ${\mathrm{He}}^{4}$ source excited the $2^{3}S_{1}\ensuremath{-}2^{3}P_{0}$ transition in a ${\mathrm{He}}^{3}$ absorption cell. The scattered light was examined with a high-resolution grating spectrometer and the ratio of the $2^{3}P_{0}\ensuremath{\rightarrow}2^{3}S_{1}$ to the $2^{3}P_{1,2}\ensuremath{\rightarrow}2^{3}S_{1}$ intensities was measured as a function of cell pressure from 0.05 to 10 Torr. The cross section for collision-induced transitions out of the $2^{3}P_{0}$ level is found to be (68\ifmmode\pm\else\textpm\fi{}3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at room temperature.

Physical ReviewAug 5, 196729 citations

Theory of double refraction in a gas due to spin alignment: Observations of birefringence in optically pumped helium

S Pancharatnam

Transverse birefringence has been observed in an aligned spin assembly consisting of helium 4 atoms in the metastable state 2 3 S 1 . The alignment of the spins was produced by optical pumping with unpolarized light. Using a cross-beam of off-resonant radiation, for example from a helium 3 lamp, together with a suitable combination of polarizer and analyser, birefringence signals could be displayed analogous to the absorption signals conventionally used for the optical monitoring of magnetic resonance. An analysis of the phenomenon is given, showing quite generally that birefringence monitors separately the degree of alignment of the spin assembly, even when orientation is also present; the latter can be monitored by the magnetic rotation of the plane of polarization for axial light. The analysis also includes the effect of the spectral characteristics of the monitoring lamp, i.e. the central frequencies of emission and the Doppler width, on the strengths of absorption and birefringence signals displayed by optically thin samples.Transverse birefringence has been observed in an aligned spin assembly consisting of helium 4 atoms in the metastable state 2 3 S 1 . The alignment of the spins was produced by optical pumping with unpolarized light. Using a cross-beam of off-resonant radiation, for example from a helium 3 lamp, together with a suitable combination of polarizer and analyser, birefringence signals could be displayed analogous to the absorption signals conventionally used for the optical monitoring of magnetic resonance. An analysis of the phenomenon is given, showing quite generally that birefringence monitors separately the degree of alignment of the spin assembly, even when orientation is also present; the latter can be monitored by the magnetic rotation of the plane of polarization for axial light. The analysis also includes the effect of the spectral characteristics of the monitoring lamp, i.e. the central frequencies of emission and the Doppler width, on the strengths of absorption and birefringence signals displayed by optically thin samples.

Journal of Physics B Atomic and Molecular PhysicsMar 1, 19684 citations

Alignment of Metastable Helium Atoms by Unpolarized Resonance Radiation

P. A. Franken, F. D. Colegrove

Physical Review LettersNov 1, 195832 citations

Lifetime of the 2P11 and 3P11 States of Atomic Helium

James M. Burger, Allen Lurio

The radiative lifetime of the $2^{1}P_{1}$ and $3^{1}P_{1}$ state of atomic helium has been measured by the level-crossing technique. In the experiment, a beam of $2^{1}S_{0}$ metastable atoms was first produced and then excited to the $2^{1}P_{1}$ or $3^{1}P_{1}$ state with resonance radiation. The lifetimes were measured by observing the zero-field level-crossing signals in the detected 584- or 537-\AA{} fluorescent radiation when these $^{1}P_{1}$ states decayed to the $1^{1}S_{0}$ ground state. The results are $\ensuremath{\tau} (2^{1}P_{1})=(5.57\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec and $\ensuremath{\tau} (3^{1}P_{1})=(1.73\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec. These values are in excellent agreement with theory.The radiative lifetime of the $2^{1}P_{1}$ and $3^{1}P_{1}$ state of atomic helium has been measured by the level-crossing technique. In the experiment, a beam of $2^{1}S_{0}$ metastable atoms was first produced and then excited to the $2^{1}P_{1}$ or $3^{1}P_{1}$ state with resonance radiation. The lifetimes were measured by observing the zero-field level-crossing signals in the detected 584- or 537-\AA{} fluorescent radiation when these $^{1}P_{1}$ states decayed to the $1^{1}S_{0}$ ground state. The results are $\ensuremath{\tau} (2^{1}P_{1})=(5.57\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec and $\ensuremath{\tau} (3^{1}P_{1})=(1.73\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec. These values are in excellent agreement with theory.

Physical Review AJan 1, 197121 citations

Radiative Lifetime of the 2 S01 Metastable State of Helium

Robert S. Van Dyck, C. E. Johnson, Howard A. Shugart

A time-of-flight technique has been used to measure the radiative lifetime of the $2 ^{1}S_{0}$ state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the $2 ^{3}S_{1}$ and the $2 ^{1}S_{0}$ states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable $2 ^{1}S_{0}$ state is separated from that of the $2 ^{3}S_{1}$ state by illuminating the beam with an rf-discharge helium lamp. The $2 ^{1}S_{0}$ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the $2 ^{1}P_{1}$ state, which then decays preferentially to the $^{1}S_{0}$ ground state; the $2 ^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the $2 ^{1}S_{0}$ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of $2 ^{1}S_{0}$ metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.A time-of-flight technique has been used to measure the radiative lifetime of the $2 ^{1}S_{0}$ state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the $2 ^{3}S_{1}$ and the $2 ^{1}S_{0}$ states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable $2 ^{1}S_{0}$ state is separated from that of the $2 ^{3}S_{1}$ state by illuminating the beam with an rf-discharge helium lamp. The $2 ^{1}S_{0}$ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the $2 ^{1}P_{1}$ state, which then decays preferentially to the $^{1}S_{0}$ ground state; the $2 ^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the $2 ^{1}S_{0}$ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of $2 ^{1}S_{0}$ metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.

Physical Review AOct 1, 197199 citations

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}

\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 cross section for the transfer of excitation from the

2^{3}P_{0}

level of helium to the

2^{3}P_{1}

and

2^{3}P_{2}

levels as a result of collisions with the ground-state helium atom (

1^{1}S_{0}

) has been measured with a conventional resonance-fluorescence technique. A

{\mathrm{He}}^{4}

source excited the $2^{3}S_{1}\ensuremath{-}2^{3}P_{0}$ transition in a

{\mathrm{He}}^{3}

absorption cell. The scattered light was examined with a high-resolution grating spectrometer and the ratio of the $2^{3}P_{0}\ensuremath{\rightarrow}2^{3}S_{1}$ to the $2^{3}P_{1,2}\ensuremath{\rightarrow}2^{3}S_{1}$ intensities was measured as a function of cell pressure from 0.05 to 10 Torr. The cross section for collision-induced transitions out of the

2^{3}P_{0}

level is found to be (68\ifmmode\pm\else\textpm\fi{}3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$

{\mathrm{cm}}^{2}

at room temperature.

The radiative lifetime of the

2^{1}P_{1}

and

3^{1}P_{1}

state of atomic helium has been measured by the level-crossing technique. In the experiment, a beam of

2^{1}S_{0}

metastable atoms was first produced and then excited to the

2^{1}P_{1}

3^{1}P_{1}

state with resonance radiation. The lifetimes were measured by observing the zero-field level-crossing signals in the detected 584- or 537-\AA{} fluorescent radiation when these

^{1}P_{1}

states decayed to the

1^{1}S_{0}

ground state. The results are $\ensuremath{\tau} (2^{1}P_{1})=(5.57\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec and $\ensuremath{\tau} (3^{1}P_{1})=(1.73\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec. These values are in excellent agreement with theory.

A time-of-flight technique has been used to measure the radiative lifetime of the

2 ^{1}S_{0}

state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the

2 ^{3}S_{1}

and the

2 ^{1}S_{0}

states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable

2 ^{1}S_{0}

state is separated from that of the

2 ^{3}S_{1}

state by illuminating the beam with an rf-discharge helium lamp. The

2 ^{1}S_{0}

state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the

2 ^{1}P_{1}

state, which then decays preferentially to the

^{1}S_{0}

ground state; the

2 ^{3}S_{1}

state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the

2 ^{1}S_{0}

atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of

2 ^{1}S_{0}

metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both

{\mathrm{He}}^{3}

and

{\mathrm{He}}^{4}

is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.