25 research outputs found
Nonperturbative resonant strong field ionization of atomic hydrogen
We investigate resonant strong field ionization of atomic hydrogen with
respect to the 1s-2p-transition. By "strong" we understand that Rabi-periods
are executed on a femtosecond time scale. Ionization and AC Stark shifts modify
the bound state dynamics severely, leading to nonperturbative signatures in the
photoelectron spectra. We introduce an analytical model, capable of predicting
qualitative features in the photoelectron spectra such as the positions of the
Autler-Townes peaks for modest field strengths. Ab initio solutions of the
time-dependent Schroedinger equation show a pronounced shift and broadening of
the left Autler-Townes peak as the field strength is increased. The right peak
remains rather narrow and shifts less. This result is analyzed and explained
with the help of exact AC Stark shifts and ionization rates obtained from
Floquet theory. Finally, it is demonstrated that in the case of finite pulses
as short as 20fs the Autler-Townes duplet can still be resolved. The fourth
generation light sources under construction worldwide will provide bright,
coherent radiation with photon energies ranging from a tenth of a meV up to
tens of keV, hence covering the regime studied in the paper so that
measurements of nonperturbative, relative AC Stark shifts should become
feasible with these new light sources.Comment: 16 pages, 11 figures, IOP styl
Exact solutions for semirelativistic problems with non-local potentials
It is shown that exact solutions may be found for the energy eigenvalue
problem generated by the class of semirelativistic Hamiltonians of the form H =
sqrt{m^2+p^2} + hat{V}, where hat{V} is a non-local potential with a separable
kernel of the form V(r,r') = - sum_{i=1}^n v_i f_i(r)g_i(r'). Explicit examples
in one and three dimensions are discussed, including the Yamaguchi and Gauss
potentials. The results are used to obtain lower bounds for the energy of the
corresponding N-boson problem, with upper bounds provided by the use of a
Gaussian trial function.Comment: 13 pages, 3 figure
Hybridization-related correction to the jellium model for fullerenes
We introduce a new type of correction for a more accurate description of
fullerenes within the spherically symmetric jellium model. This correction
represents a pseudopotential which originates from the comparison between an
accurate ab initio calculation and the jellium model calculation. It is shown
that such a correction to the jellium model allows one to account, at least
partly, for the sp2-hybridization of carbon atomic orbitals. Therefore, it may
be considered as a more physically meaningful correction as compared with a
structureless square-well pseudopotential which has been widely used earlier.Comment: 16 pages, 10 figure
On Born approximation in black hole scattering
A massless field propagating on spherically symmetric black hole metrics such
as the Schwarzschild, Reissner-Nordstr\"{o}m and Reissner-Nordstr\"{o}m-de
Sitter backgrounds is considered. In particular, explicit formulae in terms of
transcendental functions for the scattering of massless scalar particles off
black holes are derived within a Born approximation. It is shown that the
conditions on the existence of the Born integral forbid a straightforward
extraction of the quasi normal modes using the Born approximation for the
scattering amplitude. Such a method has been used in literature. We suggest a
novel, well defined method, to extract the large imaginary part of quasinormal
modes via the Coulomb-like phase shift. Furthermore, we compare the numerically
evaluated exact scattering amplitude with the Born one to find that the
approximation is not very useful for the scattering of massless scalar,
electromagnetic as well as gravitational waves from black holes
Harmonium in intense laser fields: excitation, absorption, and transparency
Abstract. It is known that the dynamics of two (Coulomb-interacting) nonrelativistic electrons confined by a parabolic potential and driven by a classical, intense lase