Hanle Effect In The Singlet-2p State Of Helium.

Edward S. Fry

Published Jan 1, 1969• 0 citations

Abstract

The oscillator strength for the resonance (11S-21P) transition in atomic helium has been determined from a measurement of the lifetime of the 2^ state.This life time was obtained using a modified zero field level crossing (Hanle) method.The scattering sample was a thermal velocity beam of 2^8 metastable atoms.Resonant 2 micron (218-2^2) radiation is absorbed by the 21S atoms, which are excited to the 2^P state.This state then primarily decays to the ground 1^8 state with the emission of resonance ($84A) radiation.The lifetime of the 21P state was determined from measurements of the magnetic field dependence of the 584Â intensity.This new technique eliminates the problem of constructing a vacuum ultra violet resonance lamp.The measured lifetime t(2 P) is (5.69 ±0.23) x Id"10 sec.The resulting absorption oscillator strength for the resonance transition is 0.270 ±0.011.This oscillator strength agrees with tie theoretical value.

DOI: 10.7302/18357

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Lifetime of the 6s6p1P1 level of barium

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The lifetime of the first excited singlet P level of barium, 6s6p1P1, has been determined from the width of the zero field level crossing, i.e. the Hanle effect, of the 6s6p1P1 –6s21S0, 5535 Å resonance line. The resonance radiation was produced in a hollow cathode lamp and the scattering atoms by an atomic beam. After taking account of coherence narrowing, the lifetime is determined to be 8.37 ± 0.14 × 10−9 s, in good agreement with other recent work.

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

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The density dependence of the Hanle effect in the resonance line of atomic barium

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Zero-Field Level-Crossing Resonances in Optically Pumped 23S1 He4

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Physical Review LettersDec 18, 197215 citations

Hanle Effect In The Singlet-2p State Of Helium.

Edward S. Fry

Published Jan 1, 1969• 0 citations

Publisher

Abstract

DOI: 10.7302/18357

Related papers

Hanle Effect in 2P1 Helium

Edward S. Fry, W. Williams

The oscillator strength for the resonance ($1^{1}S\ensuremath{-}2^{1}P$) transition in atomic helium has been determined from a measurement of the lifetime of the $2^{1}P$ state. This lifetime was obtained using a modified zero-field level crossing (Hanle) method. The scattering sample was a thermal velocity beam of $2^{1}S$ metastable atoms. Resonant 2-\ensuremath{\mu} ($2^{1}S\ensuremath{-}2^{1}P$) radiation is absorbed by the $2^{1}S$ atoms, which are excited to the $2^{1}P$ state. This state then primarily decays to the ground $1^{1}S$ state with the emission of resonance (584 \AA{}) radiation. The lifetime of the $2^{1}P$ state was determined from measurements of the magnetic-field dependence of the angular distribution of the 584 \AA{} intensity. This new technique eliminates the problem of constructing a vacuum ultraviolet resonance lamp. The measured lifetime $\ensuremath{\tau} (2^{1}P)$ is (5.63 \ifmmode\pm\else\textpm\fi{} 0.22) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ sec. The resulting absorption oscillator strength for the resonance transition is 0.273 \ifmmode\pm\else\textpm\fi{} 0.011. This oscillator strength agrees with the theoretical value.The oscillator strength for the resonance ($1^{1}S\ensuremath{-}2^{1}P$) transition in atomic helium has been determined from a measurement of the lifetime of the $2^{1}P$ state. This lifetime was obtained using a modified zero-field level crossing (Hanle) method. The scattering sample was a thermal velocity beam of $2^{1}S$ metastable atoms. Resonant 2-\ensuremath{\mu} ($2^{1}S\ensuremath{-}2^{1}P$) radiation is absorbed by the $2^{1}S$ atoms, which are excited to the $2^{1}P$ state. This state then primarily decays to the ground $1^{1}S$ state with the emission of resonance (584 \AA{}) radiation. The lifetime of the $2^{1}P$ state was determined from measurements of the magnetic-field dependence of the angular distribution of the 584 \AA{} intensity. This new technique eliminates the problem of constructing a vacuum ultraviolet resonance lamp. The measured lifetime $\ensuremath{\tau} (2^{1}P)$ is (5.63 \ifmmode\pm\else\textpm\fi{} 0.22) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ sec. The resulting absorption oscillator strength for the resonance transition is 0.273 \ifmmode\pm\else\textpm\fi{} 0.011. This oscillator strength agrees with the theoretical value.

Physical ReviewJul 5, 196914 citations

Lifetime of the 6s6p1P1 level of barium

L. O. Dickie, F. M. Kelly

Canadian Journal of PhysicsApr 1, 197019 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 density dependence of the Hanle effect in the resonance line of atomic barium

F. M. Kelly, M. S. Mathur

The change in the Hanle effect of the singlet resonance line of neutral barium has been studied over a wide range of density. The low density region has been used to confirm a lifetime of 8.37 ± 0.08 ns for the 6s6p1P1 level. We have determined the cross sections for the relaxation of the multipole moment of order 2 for collisions of the excited level with the ground level and with the metastable 6s5d1D2 level, and comparisons are made with the measured value of [Formula: see text] for the ground level with theoretical predictions.The change in the Hanle effect of the singlet resonance line of neutral barium has been studied over a wide range of density. The low density region has been used to confirm a lifetime of 8.37 ± 0.08 ns for the 6s6p1P1 level. We have determined the cross sections for the relaxation of the multipole moment of order 2 for collisions of the excited level with the ground level and with the metastable 6s5d1D2 level, and comparisons are made with the measured value of [Formula: see text] for the ground level with theoretical predictions.

Canadian Journal of PhysicsJan 1, 197740 citations

Zero-Field Level-Crossing Resonances in Optically Pumped 23S1 He4

Robert E. Slocum

Parametric resonances associated with zero-field level crossings of the ${2}^{3}{S}_{1}$ level of ${\mathrm{He}}^{4}$ have been investigated using transverse optical pumping. A steady-state technique based on the $n=0$ , $p=0$ resonance (Hanle effect) is used to measure spin-state lifetimes and determine the dependence of the thermal relaxation time on the state of the active helium discharge. The $n=0$ , $p=1$ resonance is quite strong and suitable for measuring weak magnetic fields. A sensitivity of 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ G is demonstrated for this measurement technique.Parametric resonances associated with zero-field level crossings of the ${2}^{3}{S}_{1}$ level of ${\mathrm{He}}^{4}$ have been investigated using transverse optical pumping. A steady-state technique based on the $n=0$, $p=0$ resonance (Hanle effect) is used to measure spin-state lifetimes and determine the dependence of the thermal relaxation time on the state of the active helium discharge. The $n=0$, $p=1$ resonance is quite strong and suitable for measuring weak magnetic fields. A sensitivity of 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ G is demonstrated for this measurement technique.

Physical Review LettersDec 18, 197215 citations

The oscillator strength for the resonance ($1^{1}S\ensuremath{-}2^{1}P$) transition in atomic helium has been determined from a measurement of the lifetime of the

2^{1}P

state. This lifetime was obtained using a modified zero-field level crossing (Hanle) method. The scattering sample was a thermal velocity beam of

2^{1}S

metastable atoms. Resonant 2-\ensuremath{\mu} ($2^{1}S\ensuremath{-}2^{1}P$) radiation is absorbed by the

2^{1}S

atoms, which are excited to the

2^{1}P

state. This state then primarily decays to the ground

1^{1}S

state with the emission of resonance (584 \AA{}) radiation. The lifetime of the

2^{1}P

state was determined from measurements of the magnetic-field dependence of the angular distribution of the 584 \AA{} intensity. This new technique eliminates the problem of constructing a vacuum ultraviolet resonance lamp. The measured lifetime $\ensuremath{\tau} (2^{1}P)$ is (5.63 \ifmmode\pm\else\textpm\fi{} 0.22) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ sec. The resulting absorption oscillator strength for the resonance transition is 0.273 \ifmmode\pm\else\textpm\fi{} 0.011. This oscillator strength agrees with the theoretical value.

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.

Parametric resonances associated with zero-field level crossings of the

{2}^{3}{S}_{1}

level of

{\mathrm{He}}^{4}

have been investigated using transverse optical pumping. A steady-state technique based on the

n=0

p=0

resonance (Hanle effect) is used to measure spin-state lifetimes and determine the dependence of the thermal relaxation time on the state of the active helium discharge. The

n=0

p=1

resonance is quite strong and suitable for measuring weak magnetic fields. A sensitivity of 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ G is demonstrated for this measurement technique.