mqdtfit: A collection of Python functions for empirical multichannel quantum defect calculations

The Python functions distributed with this article can be used for calculating the parameters of multichannel quantum defect theory models describing excited bound states of complex atoms. These parameters are obtained by fitting a model to experimental data provided by the user. The two main formulations of the theory are supported, namely the one in which the parameters of the model are a set of eigen channel quantum defects and a transformation matrix, and the one where these parameters are the elements of a reactance matrix. The distribution includes programs for calculating theoretical energy levels, calculating mixing coefficients and channel fractions and producing Lu-Fano plots

Atoms interacting with intense, high-frequency laser pulses: Effect of the magnetic-field component on atomic stabilization

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The structure of the Glauber third-order optical potential

The author considers the second-order and third-order contributions, V 2 and V3, to a local optical potential for the scattering of electrons by an S-state atom, which is constructed so that the corresponding scattering amplitude reproduces the three first terms of the Born series in lowest order. It is shown that the structure of the third-order Glauber optical potential, introduced by Byron and Joachain (1981) to represent V3, reflects the local nature of V2.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

High-order above-threshold ionization of argon: plateau resonances and the Floquet quasienergy spectrum

The Floquet quasienergy spectrum of argon in a strong laser field of 800 nm wavelength is calculated for intensities up to 7×1013 W cm–2, and beyond for some states, using a discrete complex basis set. Many of the dressed excited states of interest shift nonponderomotively in complicated ways but keep an ionization width narrow enough to produce sharp enhancements of above-threshold ionization (ATI) through Stark-shift-induced resonances. The quasienergy map is compared to high-resolution ATI spectra for 120 fs Ti:sapphire pulses [Nandor et al., Phys. Rev. A 60, R1771 (1999)]. The plateau enhancements happen at intensities where the dressed ground state is in resonance or in the wing of resonances with dressed excited states. The resonant dressed states are identified. In many cases, the same state is responsible for an enhancement of ATI in the low as well as the high orders. No evidence is found for enhancements that are not concomitant with any curve crossing and could thereby be interpreted as channel-closing enhancement

Differential cross sections for positron-atomic-hydrogen inelastic scattering at intermediate energies

We present differential cross sections for the excitation of atomic hydrogen to the 2s and 2p states, for incident positron (and electron) energies ranging from 100 to 400 eV, obtained by using the unitarized eikonal-Born-series method. © 1988 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

State multipoles for the excitation of the n=2 manifold of atomic hydrogen by fast electrons and positrons

Using the unitarised eikonal Born series (UEBS) method, the authors have calculated the values of the state multipoles describing coherence effects between amplitudes for the excitation of the n=2 states of atomic hydrogen by electron and positron impact, in the energy range between 100 and 400 eV. They also present UEBS results for various alignment and orientation parameters and for the position of the centre of charge of the excited atom, for both electron and positron impact. © 1990 IOP Publishing Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe