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Physical Review

Hanle Effect in 2P1 Helium

Edward S. Fry, W. Williams

Published Jul 5, 1969• 14 citations
Publisher

Abstract

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.

DOI
10.1103/physrev.183.81

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

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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.

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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.

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Radiative Lifetime of the 2 S01 Metastable State of Helium

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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.

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Lifetime of the First Excited Atomic States of Rb87

J. D. Feichtner, Joe H. Gallagher, Masataka Mizushima

The Hanle effect on the resonance lines of the ${\mathrm{Rb}}^{87}$ atom has been observed. The line shape of the signal for the $5^{2}S_{\frac{1}{2}}\ensuremath{\leftrightarrow}5^{2}P_{\frac{3}{2}}$ is found to be Lorentzian, while that for the $5^{2}S_{\frac{1}{2}}\ensuremath{\leftrightarrow}5^{2}P_{\frac{1}{2}}$ is dispersion-type. The half-width of these lines was observed to be 3.146\ifmmode\pm\else\textpm\fi{}0.13 G and 23.0 G\ifmmode\pm\else\textpm\fi{}5%, respectively. These values yield the lifetime of (2.71\ifmmode\pm\else\textpm\fi{}0.14) \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$sec and (3.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$sec for the $5^{2}P_{\frac{3}{2}}$ and $5^{2}P_{\frac{1}{2}}$ states, respectively. The oscillator strengths for the corresponding transitions are found to be 0.673\ifmmode\pm\else\textpm\fi{}0.03 and 0.32\ifmmode\pm\else\textpm\fi{}0.03, respectively. When the temperature of the scattering cell was changed from 0 to 36\ifmmode^\circ\else\textdegree\fi{}C, an apparent increase of the linewidth at higher temperature was observed. This effect has been explained as a magnetic-field-dependent radiative transfer effect at optical depth of the order of the scattering cell dimensions. When the data were analyzed with such an effect included, the reduced Hanle signal showed no temperature dependence of the half-width.

Physical Review•Dec 5, 1967•17 citations
The oscillator strength for the resonance (11S\ensuremath−21P1^{1}S\ensuremath{-}2^{1}P11S\ensuremath−21P) transition in atomic helium has been determined from a measurement of the lifetime of the 21P2^{1}P21P state. This lifetime was obtained using a modified zero-field level crossing (Hanle) method. The scattering sample was a thermal velocity beam of 21S2^{1}S21S metastable atoms. Resonant 2-\ensuremath{\mu} (21S\ensuremath−21P2^{1}S\ensuremath{-}2^{1}P21S\ensuremath−21P) radiation is absorbed by the 21S2^{1}S21S atoms, which are excited to the 21P2^{1}P21P state. This state then primarily decays to the ground 11S1^{1}S11S state with the emission of resonance (584 \AA{}) radiation. The lifetime of the 21P2^{1}P21P 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 \ensuremathτ(21P)\ensuremath{\tau} (2^{1}P)\ensuremathτ(21P) is (5.63 \ifmmode\pm\else\textpm\fi{} 0.22) \ifmmode\times\else\texttimes\fi{} 10\ensuremath−10{10}^{\ensuremath{-}10}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 (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.
The radiative lifetime of the 21P12^{1}P_{1}21P1​ and 31P13^{1}P_{1}31P1​ state of atomic helium has been measured by the level-crossing technique. In the experiment, a beam of 21S02^{1}S_{0}21S0​ metastable atoms was first produced and then excited to the 21P12^{1}P_{1}21P1​ or 31P13^{1}P_{1}31P1​ 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 1P1^{1}P_{1}1P1​ states decayed to the 11S01^{1}S_{0}11S0​ 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 21S02 ^{1}S_{0}21S0​ 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 23S12 ^{3}S_{1}23S1​ and the 21S02 ^{1}S_{0}21S0​ 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 21S02 ^{1}S_{0}21S0​ state is separated from that of the 23S12 ^{3}S_{1}23S1​ state by illuminating the beam with an rf-discharge helium lamp. The 21S02 ^{1}S_{0}21S0​ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the 21P12 ^{1}P_{1}21P1​ state, which then decays preferentially to the 1S0^{1}S_{0}1S0​ ground state; the 23S12 ^{3}S_{1}23S1​ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the 21S02 ^{1}S_{0}21S0​ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of 21S02 ^{1}S_{0}21S0​ 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 He3{\mathrm{He}}^{3}He3 and He4{\mathrm{He}}^{4}He4 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 23S1{2}^{3}{S}_{1}23S1​ level of He4{\mathrm{He}}^{4}He4 have been investigated using transverse optical pumping. A steady-state technique based on the n=0n=0n=0, p=0p=0p=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=0n=0n=0, p=1p=1p=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.
The Hanle effect on the resonance lines of the Rb87{\mathrm{Rb}}^{87}Rb87 atom has been observed. The line shape of the signal for the $5^{2}S_{\frac{1}{2}}\ensuremath{\leftrightarrow}5^{2}P_{\frac{3}{2}}$ is found to be Lorentzian, while that for the $5^{2}S_{\frac{1}{2}}\ensuremath{\leftrightarrow}5^{2}P_{\frac{1}{2}}$ is dispersion-type. The half-width of these lines was observed to be 3.146\ifmmode\pm\else\textpm\fi{}0.13 G and 23.0 G\ifmmode\pm\else\textpm\fi{}5%, respectively. These values yield the lifetime of (2.71\ifmmode\pm\else\textpm\fi{}0.14) \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$sec and (3.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$sec for the 52P325^{2}P_{\frac{3}{2}}52P23​​ and 52P125^{2}P_{\frac{1}{2}}52P21​​ states, respectively. The oscillator strengths for the corresponding transitions are found to be 0.673\ifmmode\pm\else\textpm\fi{}0.03 and 0.32\ifmmode\pm\else\textpm\fi{}0.03, respectively. When the temperature of the scattering cell was changed from 0 to 36\ifmmode^\circ\else\textdegree\fi{}C, an apparent increase of the linewidth at higher temperature was observed. This effect has been explained as a magnetic-field-dependent radiative transfer effect at optical depth of the order of the scattering cell dimensions. When the data were analyzed with such an effect included, the reduced Hanle signal showed no temperature dependence of the half-width.