239 research outputs found
Photoelectron signature of dressed-atom stabilization in intense XUV field
Non-perturbative resonant multiphoton ionization is studied using the
resolvent operator technique. Scaling parameters for effective two-level
Hamiltonians are computed for hydrogen and helium atoms to provide a
quantitative description of Rabi oscillations at XUV wavelengths, which were
recently observed using a seeded Free-Electron Laser [S. Nandi et al., Nature
608, 488-493 (2022)]. The resulting photoelectron spectra exhibit a range of
Autler-Townes doublets, which are studied for different intensities, detunings
and interaction times. We identify a photoelectron signature that originates
from stabilization against ionization of helium atoms interacting with intense
circularly polarized XUV light. Thus, our work shows how it is possible to test
the prediction of dressed-atom stabilization by Beers and Armstrong [B. L.
Beers and L. Armstrong, Phys. Rev. A 12, 2447 (1975)], without the demanding
requirement of atomic saturation in the time domain.Comment: 14 pages, 6 figures, 3 tables; accepted versio
Frustrated tunneling dynamics in ultrashort laser pulses
We study a model for frustrated tunneling ionization using ultrashort laser
pulses. The model is based on the strong field approximation and it employs the
saddle point approximation to predict quasiclassical trajectories that are
captured on Rydberg states. We present a classification of the saddle-point
solutions and explore their behavior as functions of angular momentum of the
final state, as well as the carrier--envelope phase (CEP) of the laser pulse.
We compare the final state population computed by the model to results obtained
by numerical propagation of the time-dependent Schr\"odinger equation (TDSE)
for the hydrogen atom. While we find qualitative agreement in the CEP
dependence of the populations in principal quantum numbers, , the
populations to individual angular momentum channels, , are found to be
inconsistent between model and TDSE. Thus, our results show that improvements
of the quasiclassical trajectories are in order for a quantitative model of
frustrated tunneling ionizaiton
The maximality principle in singular control with absorption and its applications to the dividend problem
Motivated by a formulation of the classical dividend problem, we develop the
maximality principle for singular stochastic control problems with
2-dimensional degenerate dynamics and absorption along the diagonal of the
state space. This result is new in the theory of singular control and it
unveils deep connections to Peskir's maximality principle in optimal stopping
(Ann. Probab. 26, no. 4, 1998). We construct an optimal control as a Skorokhod
reflection along a moving barrier. The barrier can be computed analytically as
the smallest solution to a certain non-linear ordinary differential equation.
Contrarily to the classical 1-dimensional formulation of the dividend problem
our framework produces a non-trivial solution when the firm's capital evolves
as a geometric Brownian motion. Such solution is also qualitatively different
from the one traditionally obtained for the arithmetic Brownian motion.Comment: 23 pages, 3 figures, revised presentation, new section numbering,
updated figures, added reference
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