Physical Review A

Alignment of Cd atoms by photoionization

C. Denise Caldwell, Richard N. Zare

Published Jul 1, 1977• 68 citations

Abstract

The $^{2}D_{\frac{3}{2}}$ and $^{2}D_{\frac{5}{2}}$ excited states of the cadmium ion are produced through photoionization of cadmium atoms by a beam of Hei 584-\AA{} radiation. The presence of alignment in the ions is detected by measuring the degree of linear polarization $P$ of the resulting emission. It is found that $P(^{2}D_{\frac{5}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=\ensuremath{-}0.052\ifmmode\pm\else\textpm\fi{}0.005$ for the 4416-\AA{} transition, and $P(^{2}D_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=+0.12\ifmmode\pm\else\textpm\fi{}0.04$ for the 3536-\AA{} transition, demonstrating that both $^{2}D$ fine-structure components are aligned. A simple calculation is presented which ignores anisotropic final-state interactions. This calculation correctly predicts the sign of the degree of polarization, but fails to reproduce the experimental results.

DOI: 10.1103/physreva.16.255

Related papers

Magneto-optical trapping of cadmium

Kathy-Anne Brickman, M.-S. Chang, M. Acton +5 more

arXiv:0706.1608Physical Review AOct 11, 200751 citations

Alignment of ions in Penning collisions

David W. Fahey, L. D. Schearer, W. F. Parks

Physical Review AOct 1, 19793 citations

Polarization-dependent Mg(3p^{1}P_{1}→5s^{1}S_{0}, 4d ^{1}D_{2})–rare-gas-atom excited-state optical collisions: Experiment and theory

Rosemary A. Lasell, Burcin Bayram, Mark D. Havey +2 more

Physical Review ASep 1, 199710 citations

Alignment in two-step pulsed laser excitation of Rydberg levels in light atoms: The example of sodium

Keith B. MacAdam, Michael A. Morrison

Physical Review AAug 1, 19939 citations

Étude du transfert d'excitation et de cohérence dans la fluorescence sensibilisée mercure-cadmium : I. — Étude théorique

Bernard Cheron

Journal de physiqueJan 1, 197516 citations

Observation of interference between quadrupole and dipole transitions in low-energy (2-eV) photoionization from a sodium Rydberg state

Gerd Leuchs, Stephen J. Smith, S. N. Dixit +1 more

Physical Review LettersFeb 17, 198614 citations

Physical Review A

Alignment of Cd atoms by photoionization

C. Denise Caldwell, Richard N. Zare

Published Jul 1, 1977• 68 citations

Publisher

Abstract

The

^{2}D_{\frac{3}{2}}

and

^{2}D_{\frac{5}{2}}

excited states of the cadmium ion are produced through photoionization of cadmium atoms by a beam of Hei 584-\AA{} radiation. The presence of alignment in the ions is detected by measuring the degree of linear polarization

P

of the resulting emission. It is found that

P(^{2}D_{\frac{5}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=\ensuremath{-}0.052\ifmmode\pm\else\textpm\fi{}0.005

for the 4416-\AA{} transition, and

P(^{2}D_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=+0.12\ifmmode\pm\else\textpm\fi{}0.04

for the 3536-\AA{} transition, demonstrating that both

^{2}D

fine-structure components are aligned. A simple calculation is presented which ignores anisotropic final-state interactions. This calculation correctly predicts the sign of the degree of polarization, but fails to reproduce the experimental results.

DOI: 10.1103/physreva.16.255

Related papers

Magneto-optical trapping of cadmium

Kathy-Anne Brickman, M.-S. Chang, M. Acton +5 more

We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the $^{1}S_{0}\ensuremath{\rightarrow}^{1}P_{1}$ transition at $229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in this two-electron atom and also photoionizes atoms directly from the $^{1}P_{1}$ state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be $2(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ from the $^{1}P_{1}$ state. When combined with nearby laser-cooled and trapped ${\mathrm{Cd}}^{+}$ ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the $^{1}S_{0}\ensuremath{\rightarrow}^{1}P_{1}$ transition at $229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in this two-electron atom and also photoionizes atoms directly from the $^{1}P_{1}$ state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be $2(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ from the $^{1}P_{1}$ state. When combined with nearby laser-cooled and trapped ${\mathrm{Cd}}^{+}$ ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.

arXiv:0706.1608Physical Review AOct 11, 200751 citations

Alignment of ions in Penning collisions

David W. Fahey, L. D. Schearer, W. F. Parks

The authors have observed the alignment of the $5p^{2}P_{\frac{3}{2}}$ state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.The authors have observed the alignment of the $5p^{2}P_{\frac{3}{2}}$ state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.

Physical Review AOct 1, 19793 citations

Polarization-dependent Mg(3p^{1}P_{1}→5s^{1}S_{0}, 4d ^{1}D_{2})–rare-gas-atom excited-state optical collisions: Experiment and theory

Rosemary A. Lasell, Burcin Bayram, Mark D. Havey +2 more

Experimental spectra for excited-state optical collisions between $\mathrm{Mg}(3p{}^{1}{P}_{1})$ atoms and rare-gas atoms are presented. Aligned Mg atoms are produced in the $3p{}^{1}{P}_{1}$ level by excitation with linearly polarized light. Collisions between the excited metal atoms and Ne or Ar rare-gas atoms are probed in a $1000\ensuremath{-}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range in the vicinity of the Mg $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}5s{}^{1}{S}_{0}$ and $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}4d{}^{1}{D}_{2}$ transitions. The probe radiation is linearly polarized either along or perpendicular to the alignment axis, leading to a linear polarization for the optical collision process as a function of detuning of the probe from the atomic resonances. Substantial spectral variation of the linear polarization reflects the different molecular transitions responsible for the excitation process, and the evolution of the atomic alignment into the molecular regime. In the present case, the transitions correspond to excitation from the Mg--rare-gas $3p{}^{1}{\ensuremath{\Pi}}_{1}$ and $3p{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ molecular terms to the $5s{}^{1}{\ensuremath{\Sigma}}_{0}^{+},$ $4d{}^{1}{\ensuremath{\Delta}}_{2},$ $4d{}^{1}{\ensuremath{\Pi}}_{1},$ and $4d{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ terms. Experimental details of the approach, and the results obtained, will be described. Discussion of the polarization spectra is made through theoretical modeling focusing on the effects of the symmetry of the molecular states involved in the process. The modeling employs the semiclassical theory developed earlier. For a range of qualitatively correct interaction potentials and corresponding Condon points for the photo-excitation channels, good agreement between experiment and theoretical estimates is obtained.Experimental spectra for excited-state optical collisions between $\mathrm{Mg}(3p{}^{1}{P}_{1})$ atoms and rare-gas atoms are presented. Aligned Mg atoms are produced in the $3p{}^{1}{P}_{1}$ level by excitation with linearly polarized light. Collisions between the excited metal atoms and Ne or Ar rare-gas atoms are probed in a $1000\ensuremath{-}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range in the vicinity of the Mg $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}5s{}^{1}{S}_{0}$ and $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}4d{}^{1}{D}_{2}$ transitions. The probe radiation is linearly polarized either along or perpendicular to the alignment axis, leading to a linear polarization for the optical collision process as a function of detuning of the probe from the atomic resonances. Substantial spectral variation of the linear polarization reflects the different molecular transitions responsible for the excitation process, and the evolution of the atomic alignment into the molecular regime. In the present case, the transitions correspond to excitation from the Mg--rare-gas $3p{}^{1}{\ensuremath{\Pi}}_{1}$ and $3p{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ molecular terms to the $5s{}^{1}{\ensuremath{\Sigma}}_{0}^{+},$ $4d{}^{1}{\ensuremath{\Delta}}_{2},$ $4d{}^{1}{\ensuremath{\Pi}}_{1},$ and $4d{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ terms. Experimental details of the approach, and the results obtained, will be described. Discussion of the polarization spectra is made through theoretical modeling focusing on the effects of the symmetry of the molecular states involved in the process. The modeling employs the semiclassical theory developed earlier. For a range of qualitatively correct interaction potentials and corresponding Condon points for the photo-excitation channels, good agreement between experiment and theoretical estimates is obtained.

Physical Review ASep 1, 199710 citations

Alignment in two-step pulsed laser excitation of Rydberg levels in light atoms: The example of sodium

Keith B. MacAdam, Michael A. Morrison

Aligned atomic Rydberg states of sodium can be prepared using two-step excitation from the ground state by linearly polarized pulsed lasers. Information that is normally inaccessible, e.g., sublevel partial cross sections in charge-transfer experiments, can be obtained when aligned targets are used. The calculations of orbital alignment must carefully allow for fine and hyperfine structure, laser linewidths, pulse widths and delays, sublevel coherences, and other factors. In this paper we derive the orbital alignments and time-averaged d-state sublevel populations for 3 $^{2}$ ${\mathit{S}}_{1/2}$ \ensuremath{\rightarrow}3 $^{2}$ ${\mathit{P}}_{\mathit{J}1}$ \ensuremath{\rightarrow}n $^{2}$ D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment ${\mathit{A}}^{(2)}$ and hexadecapole alignment ${\mathit{A}}^{(4)}$ , with excitation through either ${\mathit{J}}_{1}$ =1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for \ensuremath{\Vert} ${\mathit{M}}_{\mathit{L}}$ \ensuremath{\Vert}=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.Aligned atomic Rydberg states of sodium can be prepared using two-step excitation from the ground state by linearly polarized pulsed lasers. Information that is normally inaccessible, e.g., sublevel partial cross sections in charge-transfer experiments, can be obtained when aligned targets are used. The calculations of orbital alignment must carefully allow for fine and hyperfine structure, laser linewidths, pulse widths and delays, sublevel coherences, and other factors. In this paper we derive the orbital alignments and time-averaged d-state sublevel populations for 3 $^{2}$${\mathit{S}}_{1/2}$\ensuremath{\rightarrow}3 $^{2}$${\mathit{P}}_{\mathit{J}1}$\ensuremath{\rightarrow}n $^{2}$D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment ${\mathit{A}}^{(2)}$ and hexadecapole alignment ${\mathit{A}}^{(4)}$, with excitation through either ${\mathit{J}}_{1}$=1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for \ensuremath{\Vert}${\mathit{M}}_{\mathit{L}}$\ensuremath{\Vert}=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.

Physical Review AAug 1, 19939 citations

Étude du transfert d'excitation et de cohérence dans la fluorescence sensibilisée mercure-cadmium : I. — Étude théorique

Bernard Cheron

L'auteur étudie le transfert d'excitation et de cohérence lors de collisions de seconde espèce non résonnantes entre un atome de mercure excité optiquement et un atome de cadmium dans l'état fondamental : Hg(6 3P 1) + Cd(5 1S0) → Hg(6 1S 0) + Cd(5 3P1) + 1,08 eV. Un modèle de collision dans lequel les collisions frontales jouent un rôle prépondérant est présenté et les taux de transfert d'orientation et d'alignement sont calculés. Dans ce modèle, le degré d'orientation ou d'alignement des atomes de cadmium dépend de la direction de la vitesse de ces atomes après le transfert d'excitation. L'influence du spin nucléaire est étudiée.L'auteur étudie le transfert d'excitation et de cohérence lors de collisions de seconde espèce non résonnantes entre un atome de mercure excité optiquement et un atome de cadmium dans l'état fondamental : Hg(6 3P 1) + Cd(5 1S0) → Hg(6 1S 0) + Cd(5 3P1) + 1,08 eV. Un modèle de collision dans lequel les collisions frontales jouent un rôle prépondérant est présenté et les taux de transfert d'orientation et d'alignement sont calculés. Dans ce modèle, le degré d'orientation ou d'alignement des atomes de cadmium dépend de la direction de la vitesse de ces atomes après le transfert d'excitation. L'influence du spin nucléaire est étudiée.

Journal de physiqueJan 1, 197516 citations

Observation of interference between quadrupole and dipole transitions in low-energy (2-eV) photoionization from a sodium Rydberg state

Gerd Leuchs, Stephen J. Smith, S. N. Dixit +1 more

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from ${13}^{3}$ ${\mathrm{D}}_{3/2}$ -state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.A measurement of the azimuthal dependence of the angular distribution of photoelectrons from ${13}^{3}$${\mathrm{D}}_{3/2}$-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.

Physical Review LettersFeb 17, 198614 citations

The

^{2}D_{\frac{3}{2}}

and

^{2}D_{\frac{5}{2}}

P

of the resulting emission. It is found that

P(^{2}D_{\frac{5}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=\ensuremath{-}0.052\ifmmode\pm\else\textpm\fi{}0.005

for the 4416-\AA{} transition, and

P(^{2}D_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=+0.12\ifmmode\pm\else\textpm\fi{}0.04

for the 3536-\AA{} transition, demonstrating that both

^{2}D

229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

in this two-electron atom and also photoionizes atoms directly from the

^{1}P_{1}

state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be $2(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ from the

^{1}P_{1}

state. When combined with nearby laser-cooled and trapped

{\mathrm{Cd}}^{+}

ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.

The authors have observed the alignment of the

5p^{2}P_{\frac{3}{2}}

state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.

Experimental spectra for excited-state optical collisions between

\mathrm{Mg}(3p{}^{1}{P}_{1})

atoms and rare-gas atoms are presented. Aligned Mg atoms are produced in the

3p{}^{1}{P}_{1}

level by excitation with linearly polarized light. Collisions between the excited metal atoms and Ne or Ar rare-gas atoms are probed in a $1000\ensuremath{-}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ range in the vicinity of the Mg $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}5s{}^{1}{S}_{0}$ and $3p{}^{1}{P}_{1}\ensuremath{\rightarrow}4d{}^{1}{D}_{2}$ transitions. The probe radiation is linearly polarized either along or perpendicular to the alignment axis, leading to a linear polarization for the optical collision process as a function of detuning of the probe from the atomic resonances. Substantial spectral variation of the linear polarization reflects the different molecular transitions responsible for the excitation process, and the evolution of the atomic alignment into the molecular regime. In the present case, the transitions correspond to excitation from the Mg--rare-gas $3p{}^{1}{\ensuremath{\Pi}}_{1}$ and $3p{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ molecular terms to the $5s{}^{1}{\ensuremath{\Sigma}}_{0}^{+},$ $4d{}^{1}{\ensuremath{\Delta}}_{2},$ $4d{}^{1}{\ensuremath{\Pi}}_{1},$ and $4d{}^{1}{\ensuremath{\Sigma}}_{0}^{+}$ terms. Experimental details of the approach, and the results obtained, will be described. Discussion of the polarization spectra is made through theoretical modeling focusing on the effects of the symmetry of the molecular states involved in the process. The modeling employs the semiclassical theory developed earlier. For a range of qualitatively correct interaction potentials and corresponding Condon points for the photo-excitation channels, good agreement between experiment and theoretical estimates is obtained.

^{2}

{\mathit{S}}_{1/2}

\ensuremath{\rightarrow}3

^{2}

{\mathit{P}}_{\mathit{J}1}

\ensuremath{\rightarrow}n

^{2}

D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment

{\mathit{A}}^{(2)}

and hexadecapole alignment

{\mathit{A}}^{(4)}

, with excitation through either

{\mathit{J}}_{1}

=1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for \ensuremath{\Vert}

{\mathit{M}}_{\mathit{L}}

\ensuremath{\Vert}=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from

{13}^{3}

{\mathrm{D}}_{3/2}

-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.