35 research outputs found
Two-color polarization control on angularly resolved attosecond time delays
Measured photoionization time delays may exhibit large variations as a
function of the emission angles, even for spherically symmetric targets, as
shown in recent RABBITT (reconstruction of attosecond beating by interference
of two-photon transitions) experiments. The contributions from different
pathways to the two-photon quantum channels can already explain the observed
phase jumps that shape those angular distributions. Here, we propose a simple
analytical model to describe angularly-resolved RABBITT spectra as a function
of the relative polarization angle between the ionizing attosecond pulse train
and the assisting IR field. We demonstrate that the angular dependencies of the
measured delays can be analytically predicted and the position of the phase
jumps reduced to the analysis of a few relevant parameters.Comment: 10 pages, 4 figure
A Self-Consistent Model for Positronium Formation from Helium Atoms
The differential and total cross sections for electron capture by positrons
from helium atoms are calculated using a first-order distorted wave theory
satisfying the Coulomb boundary conditions. In this formalism a parametric
potential is used to describe the electron screening in a consistent and
realistic manner. The present procedure is self consistent because (i) it
satisfies the correct boundary conditions and post-prior symmetry, and (ii) the
potential and the electron binding energies appearing in the transition
amplitude are consistent with the wave functions describing the collision
system. The results are compared with the other theories and with the available
experimental measurements. At the considered range of collision energies, the
results agree reasonably well with recent experiments and theories.
[Note: This paper will be published on volume 42 of the Brazilian Journal of
Physics
Infinite square-well, trigonometric P\"oschl-Teller and other potential wells with a moving barrier
Using mainly two techniques, a point transformation and a time dependent
supersymmetry, we construct in sequence several quantum infinite potential
wells with a moving barrier. We depart from the well known system of a
one-dimensional particle in a box. With a point transformation, an infinite
square-well potential with a moving barrier is generated. Using time dependent
supersymmetry, the latter leads to a trigonometric P\"oschl-Teller potential
with a moving barrier. Finally, a confluent time dependent supersymmetry
transformation is implemented to generate new infinite potential wells, all of
them with a moving barrier. For all systems, solutions of the corresponding
time dependent Schr\"odinger equation fulfilling boundary conditions are
presented in a closed form
Analytical model for attosecond time delays and Fano's propensity rules in the continuum
Extracting single photoionization time delays associated with atomic (or
molecular) species from attosecond time scale two-photon experiments usually
relies on the theoretical description of continuum-continuum transitions. The
available models for those processes predict a universal phase contribution,
independent of the angular quantum numbers of final states. However, a recent
experimental-theoretical study [Fuchs, et al. Optica 7, 154 (2020)] determined
a sizable time delay dependence on the angular momentum of near-threshold
photoelectrons. In this study, we present an analytical model for the
two-photon two-color transition matrix amplitudes that reproduces the phase
dependence on the angular quantum number of final states. Finally, we show that
our analytical model can also describe the generalized Fano's propensity rules
[Busto, et al. Phys. Rev. Lett. 123, 133201 (2019)] for laser-assisted
photoionization.Comment: 7 pages, 4 figure
Double differential cross sections for liquid water ionization by impact of fast electrons
International audienceA theoretical study for the single ionization of water molecules in liquid phase by electron impact at high energies is presented. Through a first order model, we compute multiple differential cross sections considering an asymmetric coplanar geometry. The wavefunctions for a single liquid water molecule are obtained in a realistic way by using a Wannier orbital formalism. We compare our results with experiments for the vapor phase and previous theoretical results obtaining a good qualitative agreement
Model potentials in liquid water ionization by fast electron impact
International audienceWe study the ionization of water molecules in liquid phase by fast electron impact. We use our previous first-order model within an independent electron approximation that allows the reduction of the multielectronic problem into a monoelectronic one. The initial molecular states of the liquid water are represented in a realistic way through a Wannier orbital formalism. We complete our previous study by taking into account approximately the influence of the passive electrons of the target by means of different model potentials. We compute multiple differential cross sections for the most external orbital 1B1 and compare them with other results