628 research outputs found
Terrace-like structure in the above-threshold ionization spectrum of an atom in an IR+XUV two-color laser field
Based on the frequency-domain theory, we investigate the above-threshold
ionization (ATI) process of an atom in a two-color laser field with infrared
(IR) and extreme ultraviolet (XUV) frequencies, where the photon energy of the
XUV laser is close to or larger than the atomic ionization threshold. By using
the channel analysis, we find that the two laser fields play different roles in
an ionization process, where the XUV laser determines the ionization
probability by the photon number that the atom absorbs from it, while the IR
laser accelerates the ionized electron and hence widens the electron kinetic
energy spectrum. As a result, the ATI spectrum presents a terrace-like
structure. By using the saddle-point approximation, we obtain a classical
formula which can predict the cutoff of each plateau in the terrace-like ATI
spectrum. Furthermore, we find that the difference of the heights between two
neighboring plateaus in the terrace-like structure of the ATI spectrum
increases as the frequency of the XUV laser increases
Data-driven Approximation of Distributionally Robust Chance Constraints using Bayesian Credible Intervals
The non-convexity and intractability of distributionally robust chance
constraints make them challenging to cope with. From a data-driven perspective,
we propose formulating it as a robust optimization problem to ensure that the
distributionally robust chance constraint is satisfied with high probability.
To incorporate available data and prior distribution knowledge, we construct
ambiguity sets for the distributionally robust chance constraint using Bayesian
credible intervals. We establish the congruent relationship between the
ambiguity set in Bayesian distributionally robust chance constraints and the
uncertainty set in a specific robust optimization. In contrast to most existent
uncertainty set construction methods which are only applicable for particular
settings, our approach provides a unified framework for constructing
uncertainty sets under different marginal distribution assumptions, thus making
it more flexible and widely applicable. Additionally, under the concavity
assumption, our method provides strong finite sample probability guarantees for
optimal solutions. The practicality and effectiveness of our approach are
illustrated with numerical experiments on portfolio management and queuing
system problems. Overall, our approach offers a promising solution to
distributionally robust chance constrained problems and has potential
applications in other fields
Pulse-duration dependence of high-order harmonic generation with coherent superposition state
We make a systematic study of high-order harmonic generation (HHG) in a
He-like model ion when the initial states are prepared as a coherent
superposition of the ground state and an excited state. It is found that,
according to the degree of the ionization of the excited state, the laser
intensity can be divided into three regimes in which HHG spectra exhibit
different characteristics. The pulse-duration dependence of the HHG spectra in
these regimes is studied. We also demonstrate evident advantages of using
coherent superposition state to obtain high conversion efficiency. The
conversion efficiency can be increased further if ultrashort laser pulses are
employed
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