183 research outputs found
Intertwined electron-nuclear motion in frustrated double ionization in driven heteronuclear molecules
We study frustrated double ionization in a strongly-driven heteronuclear
molecule HeH and compare with H. We compute the probability
distribution of the sum of the final kinetic energies of the nuclei for
strongly-driven HeH. We find that this distribution has more than one
peak for strongly-driven HeH, a feature we do not find to be present for
strongly-driven H. Moreover, we compute the probability distribution of
the n quantum number of frustrated double ionization. We find that this
distribution has several peaks for strongly-driven HeH, while the
respective distribution has one main peak and a "shoulder" at lower n quantum
numbers for strongly-driven H. Surprisingly, we find this feature to be a
clear signature of the intertwined electron-nuclear motion
t-SURFF: Fully Differential Two-Electron Photo-Emission Spectra
The time dependent surface flux (t-SURFF) method is extended to single and
double ionization of two electron systems. Fully differential double emission
spectra by strong pulses at extreme UV and infrared wave length are calculated
using simulation volumes that only accommodate the effective range of the
atomic binding potential and the quiver radius of free electrons in the
external field. For a model system we find pronounced dependence of shake-up
and non-sequential double ionization on phase and duration of the laser pulse.
Extension to fully three-dimensional calculations is discussed
Photo-electron momentum spectra from minimal volumes: the time-dependent surface flux method
The time-dependent surface flux (t-SURFF) method is introduced for computing
of strong-field infrared photo-ionization spectra of atoms by numerically
solving the time-dependent Schr\"odinger equation on minimal simulation
volumes. The volumes only need to accommodate the electron quiver motion and
the relevant range of the atomic binding potential. Spectra are computed from
the electron flux through a surface, beyond which the outgoing flux is absorbed
by infinite range exterior complex scaling (irECS). Highly accurate infrared
photo-electron spectra are calculated in single active electron approximation
and compared to literature results. Detailed numerical evidence for performance
and accuracy is given. Extensions to multi-electron systems and double
ionization are discussed.Comment: 18 pages, 5 figure
Two--Electron Atoms in Short Intense Laser Pulses
We discuss a method of solving the time dependent Schrodinger equation for
atoms with two active electrons in a strong laser field, which we used in a
previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to
calculate ionization, double excitation and harmonic generation in Helium by
short laser pulses. The method employs complex scaling and an expansion in an
explicitly correlated basis. Convergence of the calculations is documented and
error estimates are provided. The results for Helium at peak intensities up to
10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly
accurate calculations are presented for electron detachment and double
excitation of the negative hydrogen ion.Comment: 14 pages, including figure
Spectrum of Neutral Helium in Strong Magnetic Fields
We present extensive and accurate calculations for the excited state spectrum
of spin-polarized neutral helium in a range of magnetic field strengths up to
G. Of considerable interest to models of magnetic white dwarf stellar
atmospheres, we also present results for the dipole strengths of the low lying
transitions among these states. Our methods rely on a systematically saturated
basis set approach to solving the Hartree--Fock self-consistent field
equations, combined with an ``exact'' stochastic method to estimate the
residual basis set truncation error and electron correlation effects. We also
discuss the applicability of the adiabatic approximation to strongly magnetized
multi-electron atoms.Comment: 19 pages, 7 figures, 10 table
â'Subaltern Victimsâ or âUseful Resourcesâ? Migrant Women in the Lega Nord Ideology and Politics"
Since the mid-2000s we have witnessed the emergence of a new phenomenon in several European countries: the mobilisation of issues of womenâs rights and gender equality by populist radical right parties (PRR)1 in anti-immigration campaigns. Recent contributions have illustrated some aspects and contradictions of these phenomena, for instance in relation to the PRR partiesâ embrace not only of womenâs but also gay rights (Bracke 2011). Others have described the double standard applied to migrant men and women in the context of raising hostility towards the Muslim population, not only by PRR parties, but within the mainstream more generally; whereas Muslim men have been mostly described as representing a social and cultural danger to European societies as well as being inherently misogynist, Muslim women have been portrayed prevalently as victims to be rescued (Abu-Lughod 2013). Little however has been written on the gendered ideology and strategies of these parties, particularly when it comes to addressing the issue of migrant women. This chapter aims to address these gaps in the scholarly literature by focusing on the gendered dimensions of anti-immigration ideology, policy and politics in the case of the LN. In particular, we draw on the empirical findings of two research projects to analyse the instrumental mobilisation of womenâs rights by the LN to stigmatise migrant, particularly Muslim, communities
Atom interferometry with trapped Bose-Einstein condensates: Impact of atom-atom interactions
Interferometry with ultracold atoms promises the possibility of ultraprecise
and ultrasensitive measurements in many fields of physics, and is the basis of
our most precise atomic clocks. Key to a high sensitivity is the possibility to
achieve long measurement times and precise readout. Ultra cold atoms can be
precisely manipulated at the quantum level, held for very long times in traps,
and would therefore be an ideal setting for interferometry. In this paper we
discuss how the non-linearities from atom-atom interactions on one hand allow
to efficiently produce squeezed states for enhanced readout, but on the other
hand result in phase diffusion which limits the phase accumulation time. We
find that low dimensional geometries are favorable, with two-dimensional (2D)
settings giving the smallest contribution of phase diffusion caused by
atom-atom interactions. Even for time sequences generated by optimal control
the achievable minimal detectable interaction energy is on
the order of 0.001 times the chemical potential of the BEC in the trap. From
there we have to conclude that for more precise measurements with atom
interferometers more sophisticated strategies, or turning off the interaction
induced dephasing during the phase accumulation stage, will be necessary.Comment: 28 pages, 13 figures, extended and correcte
Interpreting Attoclock Measurements of Tunnelling Times
Resolving in time the dynamics of light absorption by atoms and molecules,
and the electronic rearrangement this induces, is among the most challenging
goals of attosecond spectroscopy. The attoclock is an elegant approach to this
problem, which encodes ionization times in the strong-field regime. However,
the accurate reconstruction of these times from experimental data presents a
formidable theoretical challenge. Here, we solve this problem by combining
analytical theory with ab-initio numerical simulations. We apply our theory to
numerical attoclock experiments on the hydrogen atom to extract ionization time
delays and analyse their nature. Strong field ionization is often viewed as
optical tunnelling through the barrier created by the field and the core
potential. We show that, in the hydrogen atom, optical tunnelling is
instantaneous. By calibrating the attoclock using the hydrogen atom, our method
opens the way to identify possible delays associated with multielectron
dynamics during strong-field ionization.Comment: 33 pages, 10 figures, 3 appendixe
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