Two-electron excitations in atomic calcium. I

Greene, Chris H.; Kim, Longhuan

doi:10.1103/physreva.36.2706

Cited by 124 publications

(69 citation statements)

References 57 publications

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“…The photoionization of the outer shell of neutral calcium has been studied using different methods in the past [6][7][8], and experimental data exist [9][10][11]. Three-state R-matrix calculations were found to be quite successful in describing the complex resonance structure endemic in outer-shell photoionization of free Ca [6]; thus, the R-matrix method was selected to perform the calculations.…”

Section: Introductionmentioning

confidence: 99%

Photoionization of confined Ca in a spherical potential well

Hasoğlu

Zhou

Gorczyca³

et al. 2013

Phys. Rev. A

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The photoionization cross section of the Ca atom, confined by a spherical annular potential, has been calculated using a modification to the Belfast R-matrix code for a variety of depths of the confining potential. The results show that the external potential affects the cross section, which is dominated by doubly excited autoionizing states, quite significantly, causing much of the oscillator strength to move into the discrete region of the spectrum. In addition, increasing well depth causes a level crossing between the first two excited states of Ca + , thereby changing the ordering of resonances dramatically. The calculation for free Ca shows excellent agreement with experiment.

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Section: Introductionmentioning

confidence: 99%

Photoionization of confined Ca in a spherical potential well

Hasoğlu

Zhou

Gorczyca³

et al. 2013

Phys. Rev. A

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“…By employing intermediate resonances, such as the 4s4p 1 P o state, experimentalists control the Ca · ion isotopes that are trapped [22,23,18]. We have recently demonstrated that the use of model potentials gives photoionization cross sections [20] in very good agreement with experiment [24] and the best other theoretical calculations [25]. In figure 3, we build on this work by presenting photoionization cross sections for the m 0 level of the 4s4p 1 P o state, which is used as an intermediate state in the trap loading experiments.…”

Section: Extension To Other Two-electron Systemsmentioning

confidence: 89%

Two-photon double ionization of helium

Hart¹,

Liang²,

McKenna³

2003

AIP Conference Proceedings

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The combination of B-spline basis sets with R-matrix theory has provided a powerful tool for the description of double ionization processes. We demonstrate this first by investigating electron-impact ionization of Li 2· . By applying the Floquet Ansatz, the same techniques can be employed to describe multiphoton double ionization processes through the R-matrix Floquet approach. Results for two-photon double ionization of He confirm the lower values of time-dependent closecoupling calculations compared to perturbation theory. The approach can be extended to quasi-twoelectron systems through the use of model potentials. This is demonstrated by calculating photoionization cross sections near threshold for the m 0 level of the 4s4p 1 P o state of calcium.

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“…Besides the older version of this theory [5], which relied on a semi-empirical fitting procedure to obtain the parameters needed for the description of the spectrum and which has been recently extended [6] to the calculation of multiphoton cross-sections and angular distributions, there has also been much progress in combining MQDT with ab-initio R-matrix calculations [7,8] that offer a unique (within a certain energy range) interpretation of AI series and their interactions in alkaline earth atoms (Sr, Ca). Although all such calculations are tacitly assuming weak-field conditions, where the field is used as a probe of the atomic structure, they offer, nevertheless, a very important initial step towards a realistic strong-field calculation.…”

Section: Introductionmentioning

confidence: 99%

Rydberg series of autoionizing states in strong laser fields

Lyras

1990

Z Phys D - Atoms, Molecules and Clusters

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We study the behavior of Rydberg series of resonances excited by intense laser fields. Our approach is based on a semiclassicat formalism for the evolution in time of the atomic states coupled by the laser. The atomic system is described by a two-channel model in a Multichannel Quantum Defect Theory approach. We calculate the total ionization and the photoelectron spectrum after a certain interaction time. We present results both for on-resonance and off-resonance excitation of the series. We employ a more or less realistic pulse shape that corresponds to a narrow Fourier bandwidth. We show that the effects of the non-resonant members of the series on the photoelectron spectra can be important and we study it both as a function of laser intensity and as a function of the interaction time. We also show that our model correctly describes the RaN oscillations between the ground state and the excited AI state when the field is sufficiently strong. PACS: 32.80.Dz L IntroductionIn the last 10 years the problem of excitation of autoionizing (AI) states by strong laser radiation has received considerable attention by both theorists and experimentalists. The first problem to be dealt with [1] was that of an isolated AI state (represented by a discrete state coupled to a structureless continuum through configuration interaction) excited by single photon absorption from a field that was strong, in the sense that the radiative couplings in the process were comparable to or stronger than the ones responsible for autoionization. Following this, the problem of excitation of a number of AI states [2] (also described as discrete states coupled to one or more smooth continua) by multiphoton processes under the same strong-field conditions, was formulated and solved, with emphasis on the application to certain alkaline earth atoms. Other variations of such processes, for example radiative coupling of groups of AI states [3], also applied to alkaline earth atoms, * Presently at Physics Department, University of Southern California, Los Angeles, CA 90089-0484, USA have appeared in the literature. As a result of this activity (which we do not intend to review in the present paper), one can say that the theoretical problem of strong field excitation of A! resonances is understood, as long as these states can be described in terms of a finite number of bound states coupled to a few continua.It is known, however, that in almost all realistic situations (which are directly relevant to experimental studies), the proper description of an AI state must include its coupling to a whole series of bound states and their adjacent continuum. This is quite often called a whole channel. It is the purpose of this paper to offer a generalization of the earlier treatments to the case of AI states described by the interaction of complete channels.A convenient and flexible way of formulating and handling the problem of channel coupling and its application to the description of complex atomic spectra is offered by the Multichannel Quantum Defect Theory (M...

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Two-electron excitations in atomic calcium. I

Cited by 124 publications

References 57 publications

Photoionization of confined Ca in a spherical potential well

Photoionization of confined Ca in a spherical potential well

Two-photon double ionization of helium

Rydberg series of autoionizing states in strong laser fields

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