Physical Review A

Quenching of the 2pnd Po1 doubly excited states of helium by a dc electric field

K. Bučar, M. Žitnik, A. Mihelič, Francis Jean Penent, P. Lablanquie, J. Palaudoux, L. Andrić, Markus Braune, R. Püttner

Published Jul 11, 2014• 1 citation

Abstract

The fluorescence yield quenching of low-lying doubly excited $2pnd$ $^{1}{P}^{o}$ states is observed to depend strongly on a dc electric field strength and its orientation with respect to the polarization of the incoming photon beam. The reduction of the yield accompanied by the lifetime shortening is attributed to the Stark mixing with the neighboring $2sns$ $^{1}{S}^{e}$ states, which redirects the $2pnd$ $^{1}{P}^{o}$ decay to the prompt autoionization channel. For $n\ensuremath{\ge}4$, the lifetimes decrease from several hundred picoseconds down to several tens of picoseconds when an electric field in the kV/cm range is applied parallel to the photon probe polarization. Practically no lifetime change is observed for polarization perpendicular to the electric field direction. The results of the complex-scaling calculations are in a good agreement with the experimental data.

DOI: 10.1103/physreva.90.013412

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Effect of electric fields on the decay branching ratio of Pe1 doubly excited states in helium measured by time-resolved fluorescence

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Physical Review A

Quenching of the 2pnd Po1 doubly excited states of helium by a dc electric field

K. Bučar, M. Žitnik, A. Mihelič, Francis Jean Penent, P. Lablanquie, J. Palaudoux, L. Andrić, Markus Braune, R. Püttner

Published Jul 11, 2014• 1 citation

Publisher

Abstract

The fluorescence yield quenching of low-lying doubly excited

2pnd

^{1}{P}^{o}

states is observed to depend strongly on a dc electric field strength and its orientation with respect to the polarization of the incoming photon beam. The reduction of the yield accompanied by the lifetime shortening is attributed to the Stark mixing with the neighboring

2sns

^{1}{S}^{e}

states, which redirects the

2pnd

^{1}{P}^{o}

decay to the prompt autoionization channel. For

n\ensuremath{\ge}4

, the lifetimes decrease from several hundred picoseconds down to several tens of picoseconds when an electric field in the kV/cm range is applied parallel to the photon probe polarization. Practically no lifetime change is observed for polarization perpendicular to the electric field direction. The results of the complex-scaling calculations are in a good agreement with the experimental data.

DOI: 10.1103/physreva.90.013412

Related papers

Effect of electric fields on the decay branching ratio of Pe1 doubly excited states in helium measured by time-resolved fluorescence

M. Žitnik, Francis Jean Penent, P. Lablanquie +5 more

We have measured the lifetimes of $^{1}P^{e}$ $(n=9--12)$ doubly excited states in static electric fields $(1--6\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm})$ by observing the decay of the fluorescence signal as a function of time. The effects of the field on these helium states below the second ionization threshold are twofold: their excitation becomes possible due to the Stark mixing with the optically allowed $^{1}P^{o}$ series, and their lifetime is strongly modified by the opening of the autoionization channel, not accessible in zero field. Although the electric field represents only a tiny perturbation of the atomic potential, a substantial shortening of the lifetimes below $100\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ is observed. This is the simplest quantum system where the ratio of autoionization to fluorescence decay probability can be effectively controlled by an electric field of moderate strength.We have measured the lifetimes of $^{1}P^{e}$ $(n=9--12)$ doubly excited states in static electric fields $(1--6\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm})$ by observing the decay of the fluorescence signal as a function of time. The effects of the field on these helium states below the second ionization threshold are twofold: their excitation becomes possible due to the Stark mixing with the optically allowed $^{1}P^{o}$ series, and their lifetime is strongly modified by the opening of the autoionization channel, not accessible in zero field. Although the electric field represents only a tiny perturbation of the atomic potential, a substantial shortening of the lifetimes below $100\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ is observed. This is the simplest quantum system where the ratio of autoionization to fluorescence decay probability can be effectively controlled by an electric field of moderate strength.

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We present a theoretical framework for the calculation of photon-yield spectra from radiative-cascade decays of photoexcited helium atoms in a static electric field for incident photon energies below the first ( $N=1$ ) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the $1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P$ states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.We present a theoretical framework for the calculation of photon-yield spectra from radiative-cascade decays of photoexcited helium atoms in a static electric field for incident photon energies below the first ($N=1$) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the $1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P$ states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.

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Measurement of the fluorescence decay rate of 2 P J 3 positronium

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Electric Field Quenching of Metastable 2S01 Helium

Richard D. Petrasso, A.T. Ramsey

We have measured the transition rate of the normally metastable helium $2^{1}S_{0}$ state in the presence of a uniform electric field by observing the attenuation of a metastable beam of helium passing between parallel electric field plates. This attenuation, when combined with our measurement of the velocity distribution of the beam, yields a transition rate of $(0.926\ifmmode\pm\else\textpm\fi{}0.020){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, where $F$ is the field strength in kV/cm. This agrees well with our calculated value of $(0.920\ifmmode\pm\else\textpm\fi{}0.030){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ which is derived from a sum of oscillator strengths published by various workers.We have measured the transition rate of the normally metastable helium $2^{1}S_{0}$ state in the presence of a uniform electric field by observing the attenuation of a metastable beam of helium passing between parallel electric field plates. This attenuation, when combined with our measurement of the velocity distribution of the beam, yields a transition rate of $(0.926\ifmmode\pm\else\textpm\fi{}0.020){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, where $F$ is the field strength in kV/cm. This agrees well with our calculated value of $(0.920\ifmmode\pm\else\textpm\fi{}0.030){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ which is derived from a sum of oscillator strengths published by various workers.

Physical Review AJan 1, 197210 citations

Branching ratios in the radiative decay of helium doubly excited states

Marcello Coreno, Kevin Charles Prince, Robert Richter +3 more

The doubly excited singlet states of He below the $N=2$ threshold may decay by autoionization or fluorescence. In the fluorescence decay channel, most decay cascades consist of emission of three photons, of which the first is a VUV photon, the second is in or near the visible range, and the last is another VUV photon. We have studied the fluorescence channel decay dynamics of the $(2,{0}_{\mathrm{n}})$ , $(2,{1}_{\mathrm{n}})$ and $(2,\ensuremath{-}{1}_{\mathrm{n}})$ $^{1}\mathrm{P}$ , $n=3--7$ , states by wavelength dispersed photon-induced fluorescence spectroscopy. We have detected the photons in the second step of the cascade and determined the branching ratios for the strongest lines in this step. From these data we are able to calculate the branching ratios of the first step in the cascade. The results are in good agreement with calculations of the main decay channels of the higher resonances, but about 20--30 % lower, and so we are able to describe quantitatively the whole fluorescence cascade of the above-mentioned doubly excited states.The doubly excited singlet states of He below the $N=2$ threshold may decay by autoionization or fluorescence. In the fluorescence decay channel, most decay cascades consist of emission of three photons, of which the first is a VUV photon, the second is in or near the visible range, and the last is another VUV photon. We have studied the fluorescence channel decay dynamics of the $(2,{0}_{\mathrm{n}})$, $(2,{1}_{\mathrm{n}})$ and $(2,\ensuremath{-}{1}_{\mathrm{n}})$ $^{1}\mathrm{P}$, $n=3--7$, states by wavelength dispersed photon-induced fluorescence spectroscopy. We have detected the photons in the second step of the cascade and determined the branching ratios for the strongest lines in this step. From these data we are able to calculate the branching ratios of the first step in the cascade. The results are in good agreement with calculations of the main decay channels of the higher resonances, but about 20--30 % lower, and so we are able to describe quantitatively the whole fluorescence cascade of the above-mentioned doubly excited states.

Physical Review ANov 23, 200518 citations

The fluorescence yield quenching of low-lying doubly excited

2pnd

^{1}{P}^{o}

2sns

^{1}{S}^{e}

states, which redirects the

2pnd

^{1}{P}^{o}

decay to the prompt autoionization channel. For

n\ensuremath{\ge}4

We have measured the lifetimes of

^{1}P^{e}

(n=9--12)

doubly excited states in static electric fields

(1--6\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm})

by observing the decay of the fluorescence signal as a function of time. The effects of the field on these helium states below the second ionization threshold are twofold: their excitation becomes possible due to the Stark mixing with the optically allowed

^{1}P^{o}

series, and their lifetime is strongly modified by the opening of the autoionization channel, not accessible in zero field. Although the electric field represents only a tiny perturbation of the atomic potential, a substantial shortening of the lifetimes below

100\phantom{\rule{0.3em}{0ex}}\mathrm{ps}

is observed. This is the simplest quantum system where the ratio of autoionization to fluorescence decay probability can be effectively controlled by an electric field of moderate strength.

N=1

) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the

1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P

states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.

We have measured the transition rate of the normally metastable helium

2^{1}S_{0}

state in the presence of a uniform electric field by observing the attenuation of a metastable beam of helium passing between parallel electric field plates. This attenuation, when combined with our measurement of the velocity distribution of the beam, yields a transition rate of $(0.926\ifmmode\pm\else\textpm\fi{}0.020){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, where

F

is the field strength in kV/cm. This agrees well with our calculated value of $(0.920\ifmmode\pm\else\textpm\fi{}0.030){F}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ which is derived from a sum of oscillator strengths published by various workers.

The doubly excited singlet states of He below the

N=2

threshold may decay by autoionization or fluorescence. In the fluorescence decay channel, most decay cascades consist of emission of three photons, of which the first is a VUV photon, the second is in or near the visible range, and the last is another VUV photon. We have studied the fluorescence channel decay dynamics of the

(2,{0}_{\mathrm{n}})

(2,{1}_{\mathrm{n}})

and $(2,\ensuremath{-}{1}_{\mathrm{n}})$

^{1}\mathrm{P}

n=3--7

, states by wavelength dispersed photon-induced fluorescence spectroscopy. We have detected the photons in the second step of the cascade and determined the branching ratios for the strongest lines in this step. From these data we are able to calculate the branching ratios of the first step in the cascade. The results are in good agreement with calculations of the main decay channels of the higher resonances, but about 20--30 % lower, and so we are able to describe quantitatively the whole fluorescence cascade of the above-mentioned doubly excited states.