693 research outputs found
Efficient evaluation of accuracy of molecular quantum dynamics using dephasing representation
Ab initio methods for electronic structure of molecules have reached a
satisfactory accuracy for calculation of static properties, but remain too
expensive for quantum dynamical calculations. We propose an efficient
semiclassical method for evaluating the accuracy of a lower level quantum
dynamics, as compared to a higher level quantum dynamics, without having to
perform any quantum dynamics. The method is based on dephasing representation
of quantum fidelity and its feasibility is demonstrated on the
photodissociation dynamics of CO2. We suggest how to implement the method in
existing molecular dynamics codes and describe a simple test of its
applicability.Comment: 5 pages, 2 figure
Selective amplification of scars in a chaotic optical fiber
In this letter we propose an original mechanism to select scar modes through
coherent gain amplification in a multimode D-shaped fiber. More precisely, we
numerically demonstrate how scar modes can be amplified by positioning a gain
region in the vicinity of specific points of a short periodic orbit known to
give rise to scar modes
Ultrahigh harmonics from laser-assisted ion-atom collisions
We present a theoretical analysis of high-order harmonic generation from
ion-atom collisions in the presence of linearly polarized intense laser pulses.
Photons with frequencies significantly higher than in standard atomic
high-harmonic generation are emitted. These harmonics are due to two different
mechanisms: (i) collisional electron capture and subsequent laser-driven
transfer of an electron between projectile and target atom; (ii) reflection of
a laser-driven electron from the projectile leading to recombination at the
parent atom.Comment: 5 pages, 4 figure
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Effect of Random Clustering on Surface Damage Density Estimates
Identification and spatial registration of laser-induced damage relative to incident fluence profiles is often required to characterize the damage properties of laser optics near damage threshold. Of particular interest in inertial confinement laser systems are large aperture beam damage tests (>1cm{sup 2}) where the number of initiated damage sites for {phi}>14J/cm{sup 2} can approach 10{sup 5}-10{sup 6}, requiring automatic microscopy counting to locate and register individual damage sites. However, as was shown for the case of bacteria counting in biology decades ago, random overlapping or 'clumping' prevents accurate counting of Poisson-distributed objects at high densities, and must be accounted for if the underlying statistics are to be understood. In this work we analyze the effect of random clumping on damage initiation density estimates at fluences above damage threshold. The parameter {psi} = a{rho} = {rho}/{rho}{sub 0}, where a = 1/{rho}{sub 0} is the mean damage site area and {rho} is the mean number density, is used to characterize the onset of clumping, and approximations based on a simple model are used to derive an expression for clumped damage density vs. fluence and damage site size. The influence of the uncorrected {rho} vs. {phi} curve on damage initiation probability predictions is also discussed
Approximate Analytic Solution for the Spatiotemporal Evolution of Wave Packets undergoing Arbitrary Dispersion
We apply expansion methods to obtain an approximate expression in terms of
elementary functions for the space and time dependence of wave packets in a
dispersive medium. The specific application to pulses in a cold plasma is
considered in detail, and the explicit analytic formula that results is
provided. When certain general initial conditions are satisfied, these
expressions describe the packet evolution quite well. We conclude by employing
the method to exhibit aspects of dispersive pulse propagation in a cold plasma,
and suggest how predicted and experimental effects may be compared to improve
the theoretical description of a medium's dispersive properties.Comment: 17 pages, 4 figures, RevTe
Time-dependent unitary perturbation theory for intense laser driven molecular orientation
We apply a time-dependent perturbation theory based on unitary
transformations combined with averaging techniques, on molecular orientation
dynamics by ultrashort pulses. We test the validity and the accuracy of this
approach on LiCl described within a rigid-rotor model and find that it is more
accurate than other approximations. Furthermore, it is shown that a noticeable
orientation can be achieved for experimentally standard short laser pulses of
zero time average. In this case, we determine the dynamically relevant
parameters by using the perturbative propagator, that is derived from this
scheme, and we investigate the temperature effects on the molecular orientation
dynamics.Comment: 16 pages, 6 figure
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Reaction rate calculations via transmission coefficients
The transmission coefficient of a wavepacket traversing a potential barrier can be determined by steady state calculations carried out in imaginary time instead of by real time dynamical calculations. The general argument is verified for the Eckart barrier potential by a comparison of transmission coefficients calculated from real and imaginary time solutions of the Schroedinger equation. The correspondence demonstrated here allows a formulation for the reaction rate that avoids difficulties due to both rare events and explicitly time dependent calculations. 5 refs., 2 figs
Classical chaos with Bose-Einstein condensates in tilted optical lattices
A widely accepted definition of ``quantum chaos'' is ``the behavior of a
quantum system whose \emph{classical} \emph{limit is chaotic}''. The dynamics
of quantum-chaotic systems is nevertheless very different from that of their
classical counterparts. A fundamental reason for that is the linearity of
Schr{\"o}dinger equation. In this paper, we study the quantum dynamics of an
ultra-cold quantum degenerate gas in a tilted optical lattice and show that it
displays features very close to \emph{classical} chaos. We show that its phase
space is organized according to the Kolmogorov-Arnold-Moser theorem.Comment: 4 pages, 3 figure
Multi-filament structures in relativistic self-focusing
A simple model is derived to prove the multi-filament structure of
relativistic self-focusing with ultra-intense lasers. Exact analytical
solutions describing the transverse structure of waveguide channels with
electron cavitation, for which both the relativistic and ponderomotive
nonlinearities are taken into account, are presented.Comment: 21 pages, 12 figures, submitted to Physical Review
Optimal use of time dependent probability density data to extract potential energy surfaces
A novel algorithm was recently presented to utilize emerging time dependent
probability density data to extract molecular potential energy surfaces. This
paper builds on the previous work and seeks to enhance the capabilities of the
extraction algorithm: An improved method of removing the generally ill-posed
nature of the inverse problem is introduced via an extended Tikhonov
regularization and methods for choosing the optimal regularization parameters
are discussed. Several ways to incorporate multiple data sets are investigated,
including the means to optimally combine data from many experiments exploring
different portions of the potential. Results are presented on the stability of
the inversion procedure, including the optimal combination scheme, under the
influence of data noise. The method is applied to the simulated inversion of a
double well system.Comment: 34 pages, 5 figures, LaTeX with REVTeX and Graphicx-Package;
submitted to PhysRevA; several descriptions and explanations extended in Sec.
I
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