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Interim Report

Responses to Summary Questionnaire. Trapped Ion Research at Harvard University and Proposed Research at the University of Virginia.

Norman F. Ramsey, Daniel J. Larson

Published Nov 2, 1978• 0 citations
OpenAlex

Abstract

The trapped ion apparatus has been assembled during the past year and successfully used to study the photodetachment of S(-) ions. A periodic dependence of the photodetachment cross section on the light frequency was observed for the first time in any atom. The oscillatory structure could be attributed to the excitation of the detached electrons to discrete cyclotron levels in the magnetic field. The experiments so far also indicate that state dependent photodetachment should provide an effective means for producing and detecting population differences in certain stored ionic species. Plans are now in preparation for studying the microwave spectrum of S(-) with this technique. (Author)

Related papers

Trapped Ion Research.

Norman F. Ramsey, Daniel J. Larson

The trapped ion apparatus has been assembled during the past year and successfully used to study the photodetachment of S(-) ions. A periodic dependence of the photodetachment cross section on the light frequency was observed for the first time in any atom. The oscillatory structure could be attributed to the excitation of the detached electrons to discrete cyclotron levels in the magnetic field. The experiments so far also indicate that state dependent photodetachment should provide an effective means for producing and detecting population differences in trapped ions. (Author)

•Apr 3, 1979•0 citations

Theory of the photodetachment of negative ions in a magnetic field

William A. M. Blumberg, Wayne M. Itano, Daniel J. Larson

The behavior of the photodetachment cross section of the ${S}^{\ensuremath{-}}$ ion near thresholds in a magnetic field is derived. This cross section is shown to have an oscillatory dependence on photon energy. The calculation is based on first-order time-dependent perturbation theory, and final-state interactions are ignored. The weights of individual transitions between the various Zeeman sublevels for different light polarizations are given in terms of the appropriate angular momentum coupling coefficients. Broadening of the features of the cross section due to the motion of the ions is included in the calculation. The Wigner-law behavior known to be valid for zero magnetic field is shown to result from the magnetic field dependent cross section in the limit of low magnetic field. The theory is shown to be in good agreement with experimental results. The extension of the theory to other atomic negative ions is discussed.

Physical Review A•Jan 1, 1979•84 citations

Photodetachment of trapped negative gold ions: II. Observation of window resonances

R.-J. Champeau, A. Crubellier, Dan Marescaux +2 more

We present measurements of photodetachment cross sections of negative gold ions stored in a RF trap, in the energy range from about to above threshold. A number of different laser devices have been used. The results complement those described in a previous paper. The photodetachment spectrum exhibits a strong resonance, located at above ground level and a much fainter one at . These resonances can be represented as Fano profiles and reveal the presence of autodetaching excited levels of (most probably and ). Furthermore, the opening of a new photodetachment channel near 360 nm (corresponding to the first excited level of neutral Au) is accompanied by an increase of the photodetachment yield.

Journal of Physics B Atomic Molecular and Optical Physics•Feb 28, 1998•5 citations

Photodetachment of atomic negative ions near threshold in a magnetic field

Daniel J. Larson, R. C. Stoneman

The effect of final-state interactions on the photodetachment cross section of negative ions in a magnetic field is discussed. Experiments on the location of the $^{2}P_{\frac{3}{2}}$ threshold in ${\mathbf{S}}^{\ensuremath{-}}$ as a function of magnetic field show clearly the effect of the zero-point energy of an electron in a magnetic field. The experiments also give a precise value for the electron affinity and provide information about the interaction between the atom and the detached electron.

Physical Review A•Apr 1, 1985•33 citations

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

Hannes Hultgren

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.

•May 5, 2020•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
The trapped ion apparatus has been assembled during the past year and successfully used to study the photodetachment of S(-) ions. A periodic dependence of the photodetachment cross section on the light frequency was observed for the first time in any atom. The oscillatory structure could be attributed to the excitation of the detached electrons to discrete cyclotron levels in the magnetic field. The experiments so far also indicate that state dependent photodetachment should provide an effective means for producing and detecting population differences in certain stored ionic species. Plans are now in preparation for studying the microwave spectrum of S(-) with this technique. (Author)
The trapped ion apparatus has been assembled during the past year and successfully used to study the photodetachment of S(-) ions. A periodic dependence of the photodetachment cross section on the light frequency was observed for the first time in any atom. The oscillatory structure could be attributed to the excitation of the detached electrons to discrete cyclotron levels in the magnetic field. The experiments so far also indicate that state dependent photodetachment should provide an effective means for producing and detecting population differences in trapped ions. (Author)
The behavior of the photodetachment cross section of the ${S}^{\ensuremath{-}}$ ion near thresholds in a magnetic field is derived. This cross section is shown to have an oscillatory dependence on photon energy. The calculation is based on first-order time-dependent perturbation theory, and final-state interactions are ignored. The weights of individual transitions between the various Zeeman sublevels for different light polarizations are given in terms of the appropriate angular momentum coupling coefficients. Broadening of the features of the cross section due to the motion of the ions is included in the calculation. The Wigner-law behavior known to be valid for zero magnetic field is shown to result from the magnetic field dependent cross section in the limit of low magnetic field. The theory is shown to be in good agreement with experimental results. The extension of the theory to other atomic negative ions is discussed.
We present measurements of photodetachment cross sections of negative gold ions stored in a RF trap, in the energy range from about to above threshold. A number of different laser devices have been used. The results complement those described in a previous paper. The photodetachment spectrum exhibits a strong resonance, located at above ground level and a much fainter one at . These resonances can be represented as Fano profiles and reveal the presence of autodetaching excited levels of (most probably and ). Furthermore, the opening of a new photodetachment channel near 360 nm (corresponding to the first excited level of neutral Au) is accompanied by an increase of the photodetachment yield.
The effect of final-state interactions on the photodetachment cross section of negative ions in a magnetic field is discussed. Experiments on the location of the 2P32^{2}P_{\frac{3}{2}}2P23​​ threshold in ${\mathbf{S}}^{\ensuremath{-}}$ as a function of magnetic field show clearly the effect of the zero-point energy of an electron in a magnetic field. The experiments also give a precise value for the electron affinity and provide information about the interaction between the atom and the detached electron.
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.
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.