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Physical Review A

Single- and multiphoton detachment from stored F− ions

Namic Kwon, Peter S. Armstrong, T. Olsson, Rusty P. Trainham, Daniel J. Larson

Published Jul 1, 1989• 32 citations
Publisher

Abstract

The cross sections for one-, two-, and three-photon detachment from fluorine negative ions have been measured using light at the fundamental and harmonic frequencies of a 1064-nm pulsed neodymium-doped yttrium aluminum garnet laser. The ions were stored in a Penning ion trap, the depletion due to illumination was measured, and the data were fitted to a model for stored ions illuminated by pulsed light. The values obtained for the detachment cross sections are ${\ensuremath{\sigma}}^{(1)}$=2.8(5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$, ${\ensuremath{\sigma}}^{(2)}$=2.0(7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}50}$ ${\mathrm{cm}}^{4}$ sec, and ${\ensuremath{\sigma}}^{(3)}$ ${=7.9}_{\mathrm{\ensuremath{-}}3.6}^{+6.6}$\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}83}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{2}$. These values are compared with theoretical calculations and other experimental results.

DOI
10.1103/physreva.40.676

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Journal of Physics B Atomic and Molecular Physics•Dec 1, 1972•7 citations
The cross sections for one-, two-, and three-photon detachment from fluorine negative ions have been measured using light at the fundamental and harmonic frequencies of a 1064-nm pulsed neodymium-doped yttrium aluminum garnet laser. The ions were stored in a Penning ion trap, the depletion due to illumination was measured, and the data were fitted to a model for stored ions illuminated by pulsed light. The values obtained for the detachment cross sections are \ensuremathσ(1){\ensuremath{\sigma}}^{(1)}\ensuremathσ(1)=2.8(5)\ifmmode\times\else\texttimes\fi{}10\ensuremath−18{10}^{\mathrm{\ensuremath{-}}18}10\ensuremath−18 cm2{\mathrm{cm}}^{2}cm2, \ensuremathσ(2){\ensuremath{\sigma}}^{(2)}\ensuremathσ(2)=2.0(7)\ifmmode\times\else\texttimes\fi{}10\ensuremath−50{10}^{\mathrm{\ensuremath{-}}50}10\ensuremath−50 cm4{\mathrm{cm}}^{4}cm4 sec, and \ensuremathσ(3){\ensuremath{\sigma}}^{(3)}\ensuremathσ(3) =7.9\ensuremath−3.6+6.6{=7.9}_{\mathrm{\ensuremath{-}}3.6}^{+6.6}=7.9\ensuremath−3.6+6.6​\ifmmode\times\else\texttimes\fi{}10\ensuremath−83{10}^{\mathrm{\ensuremath{-}}83}10\ensuremath−83 cm6{\mathrm{cm}}^{6}cm6 sec2{\mathrm{sec}}^{2}sec2. These values are compared with theoretical calculations and other experimental results.
The R-matrix Floquet approach is applied to study the negative and ions in a light field. Detachment rates are obtained for detachment processes involving up to three photons. The results obtained in the present approach are compared to other experimental and theoretical results. For two- and three-photon processes reasonable agreement with other calculations has been found, while for two-photon detachment the results agree with the experimental cross sections. The three-photon results are in less good agreement with experiment although the larger error bars make accurate comparisons more difficult. The changes in the detachment behaviour for these ions are compared to each other as well as to the detachment behaviour of .
Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can be reached by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the whole set of data with an analytic formula. We give here the appropriate formula, valid for any number N of exciting photons, with the assumptions of (1) an initially even and momentumless (J equals 0) atom or ion and (2) that after excitation of an electron, the residual core be left in an odd state. These are the conditions met by multiphoton detachment from halogen negative ions. With elliptically polarized light of (lambda) equals 1064.2 nm, we have measured the angular distributions of three-photon detached electrons from the ion I-, and four-photon detached electrons from Cl- and F-. The experimental results are quantitatively analyzed and commented on.
An accelerated beam of Cl− ions is photodetached by a single-mode Nd:YAG laser, and the resulting neutrals are detected. By measuring the saturation intensity of this process, one derives the cross section for four-photon detachment. This cross section is smaller by a factor of 6 than a recently calculated value. Comparison of the photodetachment saturation intensity of Cl− with those of other halogen negative ions shows that this corresponds to regular behavior among the halogen elements, suggesting limitations in the theoretical models.
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.