Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Dynamics and Structure of Negative Ions - Photoinduced double detachment on nano- and femtosecond time scales

Hannes Hultgren

Published May 5, 2020• 0 citations
OpenAlex

Abstract

The goal of the presented work is to investigate double detachment of\nnegative ions on nano- and femtosecond time scales. I have performed\nthree types of experiments.\nFemtosecond time resolved pump-probe experiments have been performed\non electron dynamics in the valence shell of carbon, silicon\nand germanium atoms. The atom under investigation was prepared\nby strong field photodetachment of its parent negative ion in a linearly\npolarized femtosecond laser pulse. The detachment process coherently\npopulates the fine structure levels of the atomic ground state\ngiving rise to an electronic wave packet moving in the valence shell\nof the atom. The wave packet is probed by strong field ionization at a\ntime delay controlled on a femtosecond time scale. The ionized electrons\nare detected in an electron imaging spectrometer. The energy\nand angular distribution of the ionized electrons provide information\non the phase of the wave packet. The results reveal a periodic spatial\nrearrangement of the electron cloud in the atom. The experimental\nprocedure and detection scheme developed provide the first direct visualization\nof an electronic wave packet moving in the ground state of\nan atom.\nThe process of rescattering in strong field detachment has also been\ninvestigated. The detached electron is accelerated in the laser field.\nWhen the E-field changes its direction the electron follows and may\nreturn and collide with the core. I have investigated the rescattering\neffect in negative fluorine ions and compared with previous results on\nbromine ions. Furthermore, strong field detachment experiments of\nF \n2 were conducted and the results from molecular fluorine ions are\ncompared to results from atomic fluorine ions.\nPhotodetachment cross sections and doubly excited states in K and\nCs have been investigated through double detachment. A resonant\nionization scheme was used where the ion beam and laser beams were\nin a collinear configuration allowing for measurements of partial cross\nsection channels individually with nearly 100% detection efficiency.\nA new threshold behavior has been found in photodetachment into\natomic states having a large and negative polarizability. A new model\nwas developed to explain the observed phenomena. Furthermore, two\nnew resonances stemming from doubly excited states were found below\nthe K(7 2P) channel opening in K and a set of new resonances\nwas observed in Cs below the Cs(10 2P) channel.

Related papers

Strong-Field Photodetachment of Negative Ions – Orbital Alignment Effects and Tomographic Imaging of Photoelectrons

Mikael Eklund

Photoelectron imaging techniques are used to experimentally investigate photodetachment of negative ions in a strong laser-field as well as the orbital alignment dynamics in the residual neutral.\n\nStrong-field photodetachment in a linearly polarized pulsed laser with 100 fs pulse length is used to create a wave packet in the neutral atoms of carbon, germanium and silicon. The negative ions of these three atomic species are isoelectronic with a half-filled $p$-shell. The photodetachment rate is highly dependent on the magnetic quantum number $m_\\ell$ with the orbital with $m_\\ell = 0$ having a detachment rate of an order of magnitude larger than orbitals with $m_\\ell$ non-zero, with the polarization axis acting as a quantization axis. The residual neutral is thus left in an aligned state after photodetachment. The aligned state constitutes of a coherent superposition of fine-structure states and the population in the different orbitals will accordingly display a time-dependent spatial oscillation. The created wave packet is subsequently probed through photoionization by a second strong-field laser pulse.\n\nSecondly, a tomographic method is implemented to observe the three-dimensional distribution of photoelectrons produced in strong-field photodetachment processes. The method makes no assumptions of the existence of any symmetry axes in the photoelectron distribution and is thus applicable to any laser polarization ellipticity. Traditional imaging methods are dependent on the photoelectron distribution to be cylindrically symmetric by using either linearly or circularly polarized light, a requirement which can be lifted by using a tomographic technique. The method is applied to multiphoton detachment of the negative ion of silver.\n\nFinally, strong-field photodetachment of homonuclear diatomic negative ions is performed. The possibility of the additional electron being ejected from either of the two atomic centers can significantly alter the photoelectron distribution compared to an atomic negative ion with the same detachment energy. Experiments are performed on C$_2^-$, Si$_2^-$ and Ag$_2^-$ and compared to theoretical models.

•Sep 7, 2015•0 citations

s-wave photodetachment in a static electric field

N. D. Gibson, B. J. Davies, Daniel J. Larson

Photodetachment from negative ions in a static electric field has been studied using ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$. These experiments were done with greater precision than previous studies and allow a quantitative comparison of data with theory. A 10-keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam velocity. A pulsed dye-laser beam, perpendicular to the ion beam, photoneutralized the ions. The relative cross sections were measured by detecting the resulting fast neutral atoms. Detachment below threshold and oscillations on the cross section above threshold were observed near the ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$ threshold at 16 269.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and near the ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ threshold at 29 138.3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The phase of the oscillations in the data is in good agreement with predictions for s-wave photodetachment in a static electric field, but the amplitude of the oscillations is found to be slightly reduced.

Physical Review A•Mar 1, 1993•40 citations

Autoionizing states of negative ions in strong resonant laser fields: The negative rubidium ion

Henrik Stapelfeldt, Philip Trøst Kristensen, Ulric B. Ljungblad +2 more

We have performed an experimental study of the atomic system ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$, for which the ground state 5${\mathit{s}}^{2}$ is coupled to the autoionizing state 5${\mathit{p}}_{1/2}$6s by means of a strong resonant laser field. The investigations are based on irradiation of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ with intense (I\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}${10}^{10}$ W/${\mathrm{cm}}^{2}$) laser pulses of duration \ensuremath{\sim}1 ns. Single-photon detachment of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ is suppressed due to the Fano interference between transitions directly to the continuum and transitions via the autoionizing state. In contrast, two-photon absorption is at the same time resonantly enhanced since no such destructive interference is present in this process. These observations constitute experimental evidence of general features predicted from theoretical considerations of autoionizing states in strong laser fields. Furthermore, we discuss the role of autoionizing states in multiphoton double-ionization processes. Electron spectroscopy has been used to show that double ionization of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ primarily is the result of a sequential removal of the two electrons via an excited Rb state. The perspectives for direct two-electron ionization in negative ions are briefly discussed.

Physical Review A•Aug 1, 1994•17 citations

Orbital alignment in atoms generated by photodetachment in a strong laser field

Mikael Eklund, Hannes Hultgren, D. Hanstorp +1 more

A pump-probe laser scheme is employed to investigate orbital alignment and its dynamics in the ground state of laser-generated neutral atoms. The alignment is initiated by electron photodetachment of an atomic negative ion in a strong laser pulse. The electron density distribution in the ground state of the residual atom is probed by means of strong-field ionization in a second laser pulse at a delayed time. The principle of the probe method relies on the fact that the portion of the electron density distribution oriented along the laser polarization axis constitutes the ionization yield in the high-energy jets of emitted electrons. A systematic study is carried out on C, Si, and Ge atoms, which possess two electrons in an open $p$ shell. A pronounced temporal modulation in the yield of high-energy electrons is observed for C and Si, revealing a periodic spatial rearrangement of the electron density distribution in these atoms. Its period is defined by the beat between the $J=1$ and $J=2$ spin-orbit components of the ground state.

Physical Review A•Aug 26, 2013•5 citations

The Dipole Response of an Ionization Threshold within Ultrashort and Strong Fields

Paul Birk

In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold.

•Jan 1, 2021•0 citations

Dynamics of photoinduced collisions of cold atoms probed with picosecond laser pulses

Fredrik K. Fatemi, K. M. Jones, He Wang +2 more

Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form ${\mathrm{Na}}_{2}$ molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.

Physical Review A•Aug 17, 2001•35 citations
The goal of the presented work is to investigate double detachment of\nnegative ions on nano- and femtosecond time scales. I have performed\nthree types of experiments.\nFemtosecond time resolved pump-probe experiments have been performed\non electron dynamics in the valence shell of carbon, silicon\nand germanium atoms. The atom under investigation was prepared\nby strong field photodetachment of its parent negative ion in a linearly\npolarized femtosecond laser pulse. The detachment process coherently\npopulates the fine structure levels of the atomic ground state\ngiving rise to an electronic wave packet moving in the valence shell\nof the atom. The wave packet is probed by strong field ionization at a\ntime delay controlled on a femtosecond time scale. The ionized electrons\nare detected in an electron imaging spectrometer. The energy\nand angular distribution of the ionized electrons provide information\non the phase of the wave packet. The results reveal a periodic spatial\nrearrangement of the electron cloud in the atom. The experimental\nprocedure and detection scheme developed provide the first direct visualization\nof an electronic wave packet moving in the ground state of\nan atom.\nThe process of rescattering in strong field detachment has also been\ninvestigated. The detached electron is accelerated in the laser field.\nWhen the E-field changes its direction the electron follows and may\nreturn and collide with the core. I have investigated the rescattering\neffect in negative fluorine ions and compared with previous results on\nbromine ions. Furthermore, strong field detachment experiments of\nF \n2 were conducted and the results from molecular fluorine ions are\ncompared to results from atomic fluorine ions.\nPhotodetachment cross sections and doubly excited states in K and\nCs have been investigated through double detachment. A resonant\nionization scheme was used where the ion beam and laser beams were\nin a collinear configuration allowing for measurements of partial cross\nsection channels individually with nearly 100% detection efficiency.\nA new threshold behavior has been found in photodetachment into\natomic states having a large and negative polarizability. A new model\nwas developed to explain the observed phenomena. Furthermore, two\nnew resonances stemming from doubly excited states were found below\nthe K(7 2P) channel opening in K and a set of new resonances\nwas observed in Cs below the Cs(10 2P) channel.
Photoelectron imaging techniques are used to experimentally investigate photodetachment of negative ions in a strong laser-field as well as the orbital alignment dynamics in the residual neutral.\n\nStrong-field photodetachment in a linearly polarized pulsed laser with 100 fs pulse length is used to create a wave packet in the neutral atoms of carbon, germanium and silicon. The negative ions of these three atomic species are isoelectronic with a half-filled ppp-shell. The photodetachment rate is highly dependent on the magnetic quantum number $m_\\ell$ with the orbital with $m_\\ell = 0$ having a detachment rate of an order of magnitude larger than orbitals with $m_\\ell$ non-zero, with the polarization axis acting as a quantization axis. The residual neutral is thus left in an aligned state after photodetachment. The aligned state constitutes of a coherent superposition of fine-structure states and the population in the different orbitals will accordingly display a time-dependent spatial oscillation. The created wave packet is subsequently probed through photoionization by a second strong-field laser pulse.\n\nSecondly, a tomographic method is implemented to observe the three-dimensional distribution of photoelectrons produced in strong-field photodetachment processes. The method makes no assumptions of the existence of any symmetry axes in the photoelectron distribution and is thus applicable to any laser polarization ellipticity. Traditional imaging methods are dependent on the photoelectron distribution to be cylindrically symmetric by using either linearly or circularly polarized light, a requirement which can be lifted by using a tomographic technique. The method is applied to multiphoton detachment of the negative ion of silver.\n\nFinally, strong-field photodetachment of homonuclear diatomic negative ions is performed. The possibility of the additional electron being ejected from either of the two atomic centers can significantly alter the photoelectron distribution compared to an atomic negative ion with the same detachment energy. Experiments are performed on C2−_2^-2−​, Si2−_2^-2−​ and Ag2−_2^-2−​ and compared to theoretical models.
Photodetachment from negative ions in a static electric field has been studied using ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$. These experiments were done with greater precision than previous studies and allow a quantitative comparison of data with theory. A 10-keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam velocity. A pulsed dye-laser beam, perpendicular to the ion beam, photoneutralized the ions. The relative cross sections were measured by detecting the resulting fast neutral atoms. Detachment below threshold and oscillations on the cross section above threshold were observed near the ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$ threshold at 16 269.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and near the ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ threshold at 29 138.3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The phase of the oscillations in the data is in good agreement with predictions for s-wave photodetachment in a static electric field, but the amplitude of the oscillations is found to be slightly reduced.
We have performed an experimental study of the atomic system ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$, for which the ground state 5s2{\mathit{s}}^{2}s2 is coupled to the autoionizing state 5${\mathit{p}}_{1/2}$6s by means of a strong resonant laser field. The investigations are based on irradiation of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ with intense (I\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}1010{10}^{10}1010 W/cm2{\mathrm{cm}}^{2}cm2) laser pulses of duration \ensuremath{\sim}1 ns. Single-photon detachment of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ is suppressed due to the Fano interference between transitions directly to the continuum and transitions via the autoionizing state. In contrast, two-photon absorption is at the same time resonantly enhanced since no such destructive interference is present in this process. These observations constitute experimental evidence of general features predicted from theoretical considerations of autoionizing states in strong laser fields. Furthermore, we discuss the role of autoionizing states in multiphoton double-ionization processes. Electron spectroscopy has been used to show that double ionization of ${\mathrm{Rb}}^{\mathrm{\ensuremath{-}}}$ primarily is the result of a sequential removal of the two electrons via an excited Rb state. The perspectives for direct two-electron ionization in negative ions are briefly discussed.
A pump-probe laser scheme is employed to investigate orbital alignment and its dynamics in the ground state of laser-generated neutral atoms. The alignment is initiated by electron photodetachment of an atomic negative ion in a strong laser pulse. The electron density distribution in the ground state of the residual atom is probed by means of strong-field ionization in a second laser pulse at a delayed time. The principle of the probe method relies on the fact that the portion of the electron density distribution oriented along the laser polarization axis constitutes the ionization yield in the high-energy jets of emitted electrons. A systematic study is carried out on C, Si, and Ge atoms, which possess two electrons in an open ppp shell. A pronounced temporal modulation in the yield of high-energy electrons is observed for C and Si, revealing a periodic spatial rearrangement of the electron density distribution in these atoms. Its period is defined by the beat between the J=1J=1J=1 and J=2J=2J=2 spin-orbit components of the ground state.
In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold.
Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form Na2{\mathrm{Na}}_{2}Na2​ molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.