We present linear and circular polarization measurements of $3^{1}P\ensuremath{-}2^{1}S$ (501.6 nm) photons detected in delayed coincidence with electrons inelastically scattered from the $3^{1}P$ level of helium. Vector polarization and coherence parameters of the coincident radiation provide direct experimental evidence of the coherent nature of the excitation process. Atomic orientation is obtained directly from the circular polarization measurements. Analysis of the data also yields $\ensuremath{\lambda}$ and $\ensuremath{\chi}$ parameters for $3^{1}P$ excitations, which are compared with previous data and theory.We present linear and circular polarization measurements of $3^{1}P\ensuremath{-}2^{1}S$ (501.6 nm) photons detected in delayed coincidence with electrons inelastically scattered from the $3^{1}P$ level of helium. Vector polarization and coherence parameters of the coincident radiation provide direct experimental evidence of the coherent nature of the excitation process. Atomic orientation is obtained directly from the circular polarization measurements. Analysis of the data also yields $\ensuremath{\lambda}$ and $\ensuremath{\chi}$ parameters for $3^{1}P$ excitations, which are compared with previous data and theory.

Physical Review LettersMar 15, 1976144 citations

Distribution of Excitation Transfer in Helium

John D. Jobe, Robert M. St. John

Physical Review AMay 1, 19720 citations

Coherence transfer between the 2P1/2 and 2P3/2 states in sodium, induced in collisions with helium atoms

M. Elbel, B. Niewitecka, L. Krause

The Hanle effect, which is commonly exhibited by atoms that emit resonance fluorescence while in a magnetic field, has been observed in sensitized fluorescence of sodium vapor. The sodium atoms were excited by σ+ polarized D1 radiation which produced a vector polarization in the 32P1/2 state, and were then transferred to the 32P3/2 state by collisions with helium atoms. The fluorescence was observed at an angle of 325° to the direction of excitation, and the magnetic field was perpendicular to the directions of the exciting and fluorescent light beams. The addition of helium resulted in the appearance of a circularly polarized D2 component in the fluorescent light. The polarization of the sensitized fluorescence decreased with increasing field as in the ordinary Hanle effect but the width of the Hanle signal was smaller than that observed in resonance fluorescence. The observed narrowing effect is in good agreement with theoretical predictions.The Hanle effect, which is commonly exhibited by atoms that emit resonance fluorescence while in a magnetic field, has been observed in sensitized fluorescence of sodium vapor. The sodium atoms were excited by σ+ polarized D1 radiation which produced a vector polarization in the 32P1/2 state, and were then transferred to the 32P3/2 state by collisions with helium atoms. The fluorescence was observed at an angle of 325° to the direction of excitation, and the magnetic field was perpendicular to the directions of the exciting and fluorescent light beams. The addition of helium resulted in the appearance of a circularly polarized D2 component in the fluorescent light. The polarization of the sensitized fluorescence decreased with increasing field as in the ordinary Hanle effect but the width of the Hanle signal was smaller than that observed in resonance fluorescence. The observed narrowing effect is in good agreement with theoretical predictions.

Canadian Journal of PhysicsDec 15, 197011 citations

Spin-polarized helium

Glen McHale

WORLD SCIENTIFIC eBooksJan 1, 19890 citations

Coherent Excitation of the 4F1 State of Helium by Electron Impact

D Cvejanović, Albert Crowe

The Stokes parameters ${P}_{1}$ , ${P}_{2}$ , ${P}_{3}$ , and ${P}_{4}$ have been measured in a scattered electron-polarized cascade photon correlation study of the $4^{1}F$ state of helium excited by 29.6 eV electron impact. This is the first detailed experimental study of electron impact excitation leading to the transfer of three units of angular momentum. The data are expected to be influenced by the breakdown of $\mathrm{LS}$ coupling for $L\ensuremath{\ge}3$ states, even in a simple system like helium, providing a further challenge for theory.The Stokes parameters ${P}_{1}$, ${P}_{2}$, ${P}_{3}$, and ${P}_{4}$ have been measured in a scattered electron-polarized cascade photon correlation study of the $4^{1}F$ state of helium excited by 29.6 eV electron impact. This is the first detailed experimental study of electron impact excitation leading to the transfer of three units of angular momentum. The data are expected to be influenced by the breakdown of $\mathrm{LS}$ coupling for $L\ensuremath{\ge}3$ states, even in a simple system like helium, providing a further challenge for theory.

Physical Review LettersApr 6, 199812 citations

We present linear and circular polarization measurements of $3^{1}P\ensuremath{-}2^{1}S$ (501.6 nm) photons detected in delayed coincidence with electrons inelastically scattered from the

3^{1}P

level of helium. Vector polarization and coherence parameters of the coincident radiation provide direct experimental evidence of the coherent nature of the excitation process. Atomic orientation is obtained directly from the circular polarization measurements. Analysis of the data also yields $\ensuremath{\lambda}$ and $\ensuremath{\chi}$ parameters for

3^{1}P

excitations, which are compared with previous data and theory.

The Stokes parameters

{P}_{1}

{P}_{2}

{P}_{3}

, and

{P}_{4}

have been measured in a scattered electron-polarized cascade photon correlation study of the

4^{1}F

state of helium excited by 29.6 eV electron impact. This is the first detailed experimental study of electron impact excitation leading to the transfer of three units of angular momentum. The data are expected to be influenced by the breakdown of

\mathrm{LS}

coupling for $L\ensuremath{\ge}3$ states, even in a simple system like helium, providing a further challenge for theory.