Physical Review A

Scheme for multistep resonance photoionization of atoms

Bo Liu, Xi‐Jing Ning

Published May 30, 2001• 6 citations

Abstract

Traditional schemes for multistep resonance photoionization of atoms let every employed laser beam interact with the atoms simultaneously. In such a situation, analyses via time-dependent Schr\"odinger equation show that high ionization probability requires all the laser beams must be intense enough. In order to decrease laser intensity, we proposed a scheme that the laser beam used to pump the excited atoms (in a higher bound state) into an autoionization state does not interact with the atoms until all the population is transferred by the other lasers from a ground state to the bound state. As an interesting example, we examined three-step photoionization of ${}^{235}\mathrm{U}$ with our scheme, showing that the intensity of two laser beams can be lowered by two orders of magnitude without losing high ionization probability.

DOI: 10.1103/physreva.64.013401

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Physical Review A

Scheme for multistep resonance photoionization of atoms

Bo Liu, Xi‐Jing Ning

Published May 30, 2001• 6 citations

Publisher

Abstract

Traditional schemes for multistep resonance photoionization of atoms let every employed laser beam interact with the atoms simultaneously. In such a situation, analyses via time-dependent Schr"odinger equation show that high ionization probability requires all the laser beams must be intense enough. In order to decrease laser intensity, we proposed a scheme that the laser beam used to pump the excited atoms (in a higher bound state) into an autoionization state does not interact with the atoms until all the population is transferred by the other lasers from a ground state to the bound state. As an interesting example, we examined three-step photoionization of

{}^{235}\mathrm{U}

with our scheme, showing that the intensity of two laser beams can be lowered by two orders of magnitude without losing high ionization probability.

DOI: 10.1103/physreva.64.013401

Related papers

Multimode and level-degeneracy effects in two-step resonant photoionization processes

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A theoretical model of two-step resonant ionization which includes an autoionizing state is developed. The effects examined include interactions with a multimode laser and Zeeman and hyperfine multiplets. We approach this problem starting from first principles by treating the atom-radiation system as a unit. Theoretical analysis and numerical calculations of ionization probabilities are given. The intermode scattering is investigated in detail, and a simple physical interpretation of the dynamical effect is given. Comparisons of ionization probabilities for two-step processes with first-step excitations by single-mode or two-mode lasers are made. It is found that, if the mode spacing in a multimode-laser beam is less than the Doppler width of the atom, the multimode laser can more effectively produce ions than a single-mode laser does. This leads to the conclusion that the resonance effect is more important than the power-broadening effect. This is shown to be also true when Zeeman and hyperfine multiplets are included.A theoretical model of two-step resonant ionization which includes an autoionizing state is developed. The effects examined include interactions with a multimode laser and Zeeman and hyperfine multiplets. We approach this problem starting from first principles by treating the atom-radiation system as a unit. Theoretical analysis and numerical calculations of ionization probabilities are given. The intermode scattering is investigated in detail, and a simple physical interpretation of the dynamical effect is given. Comparisons of ionization probabilities for two-step processes with first-step excitations by single-mode or two-mode lasers are made. It is found that, if the mode spacing in a multimode-laser beam is less than the Doppler width of the atom, the multimode laser can more effectively produce ions than a single-mode laser does. This leads to the conclusion that the resonance effect is more important than the power-broadening effect. This is shown to be also true when Zeeman and hyperfine multiplets are included.

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Coherent control of atomic photoionization

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Laser probe of the atomic ionization continuum: Stimulated recombination into an excited state

Burke Ritchie

A two-laser theory is formulated for the photoionization of Li atoms. The first laser is tuned above the ionization threshold of $\mathrm{Li}(2s)$ . The second laser probes the ionized target. Stimulated recombination into $\mathrm{Li}(\mathrm{ns})$ occurs near the Raman-type resonance point ${\ensuremath{\epsilon}}_{\mathrm{ns}}\ensuremath{-}{\ensuremath{\epsilon}}_{2s}\ensuremath{-}{\ensuremath{\epsilon}}_{1}+{\ensuremath{\epsilon}}_{2}=0$ (where $n>2$ and ${\ensuremath{\epsilon}}_{q}$ is a photon energy). Near the resonance point the ionization probability is characterized by a line profile which resembles that for an autoionizing resonance.A two-laser theory is formulated for the photoionization of Li atoms. The first laser is tuned above the ionization threshold of $\mathrm{Li}(2s)$. The second laser probes the ionized target. Stimulated recombination into $\mathrm{Li}(\mathrm{ns})$ occurs near the Raman-type resonance point ${\ensuremath{\epsilon}}_{\mathrm{ns}}\ensuremath{-}{\ensuremath{\epsilon}}_{2s}\ensuremath{-}{\ensuremath{\epsilon}}_{1}+{\ensuremath{\epsilon}}_{2}=0$ (where $n>2$ and ${\ensuremath{\epsilon}}_{q}$ is a photon energy). Near the resonance point the ionization probability is characterized by a line profile which resembles that for an autoionizing resonance.

Physical Review AOct 1, 198415 citations

Resonant photoionization of Ni I into autoionizing states

Peter Lievens, Erno Vandeweert, Peter Thoen +1 more

Two-step resonant photoionization of free Ni atoms is studied by one-color and two-color processes, using pulsed lasers with photon energies around half the ground-state ionization energy. Two-color two-step resonance ionization from the ground state a ${\mathrm{}}^{3}$ ${\mathit{F}}_{4}$ and the first metastable state a ${\mathrm{}}^{3}$ ${\mathit{D}}_{3}$ via the triplet states z ${\mathrm{}}^{3}$ ${\mathit{G}}_{3,4,5}^{0}$ was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.Two-step resonant photoionization of free Ni atoms is studied by one-color and two-color processes, using pulsed lasers with photon energies around half the ground-state ionization energy. Two-color two-step resonance ionization from the ground state a${\mathrm{}}^{3}$${\mathit{F}}_{4}$ and the first metastable state a${\mathrm{}}^{3}$${\mathit{D}}_{3}$ via the triplet states z${\mathrm{}}^{3}$${\mathit{G}}_{3,4,5}^{0}$ was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.

Physical Review ASep 1, 199626 citations

Traditional schemes for multistep resonance photoionization of atoms let every employed laser beam interact with the atoms simultaneously. In such a situation, analyses via time-dependent Schr"odinger equation show that high ionization probability requires all the laser beams must be intense enough. In order to decrease laser intensity, we proposed a scheme that the laser beam used to pump the excited atoms (in a higher bound state) into an autoionization state does not interact with the atoms until all the population is transferred by the other lasers from a ground state to the bound state. As an interesting example, we examined three-step photoionization of

{}^{235}\mathrm{U}

with our scheme, showing that the intensity of two laser beams can be lowered by two orders of magnitude without losing high ionization probability.

A two-laser theory is formulated for the photoionization of Li atoms. The first laser is tuned above the ionization threshold of

\mathrm{Li}(2s)

. The second laser probes the ionized target. Stimulated recombination into

\mathrm{Li}(\mathrm{ns})

occurs near the Raman-type resonance point ${\ensuremath{\epsilon}}_{\mathrm{ns}}\ensuremath{-}{\ensuremath{\epsilon}}_{2s}\ensuremath{-}{\ensuremath{\epsilon}}_{1}+{\ensuremath{\epsilon}}_{2}=0$ (where

n>2

and ${\ensuremath{\epsilon}}_{q}$ is a photon energy). Near the resonance point the ionization probability is characterized by a line profile which resembles that for an autoionizing resonance.

{\mathrm{}}^{3}

{\mathit{F}}_{4}

and the first metastable state a

{\mathrm{}}^{3}

{\mathit{D}}_{3}

via the triplet states z

{\mathrm{}}^{3}

{\mathit{G}}_{3,4,5}^{0}

was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.