5,417 research outputs found
Manipulating the torsion of molecules by strong laser pulses
A proof-of-principle experiment is reported, where torsional motion of a
molecule, consisting of a pair of phenyl rings, is induced by strong laser
pulses. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis,
connecting the two phenyl rings, allowing a perpendicularly polarized, intense
femtosecond pulse to initiate torsional motion accompanied by an overall
rotation about the fixed axis. The induced motion is monitored by femtosecond
time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for
and generalizes the experimental findings.Comment: 4 pages, 4 figures, submitted to PRL; Major revision of the
presentation of the material; Correction of ion labels in Fig. 2(a
Solving the m-mixing problem for the three-dimensional time-dependent Schr\"{o}dinger equation by rotations: application to strong-field ionization of H2+
We present a very efficient technique for solving the three-dimensional
time-dependent Schrodinger equation. Our method is applicable to a wide range
of problems where a fullly three-dimensional solution is required, i.e., to
cases where no symmetries exist that reduce the dimensionally of the problem.
Examples include arbitrarily oriented molecules in external fields and atoms
interacting with elliptically polarized light. We demonstrate that even in such
cases, the three-dimensional problem can be decomposed exactly into two
two-dimensional problems at the cost of introducing a trivial rotation
transformation. We supplement the theoretical framework with numerical results
on strong-field ionization of arbitrarily oriented H2+ molecules.Comment: 5 pages, 4 figure
Simulation of transition dynamics to high confinement in fusion plasmas
The transition dynamics from the low (L) to the high (H) confinement mode in
magnetically confined plasmas is investigated using a first-principles
four-field fluid model. Numerical results are in close agreement with
measurements from the Experimental Advanced Superconducting Tokamak - EAST.
Particularly, the slow transition with an intermediate dithering phase is well
reproduced by the numerical solutions. Additionally, the model reproduces the
experimentally determined L-H transition power threshold scaling that the ion
power threshold increases with increasing particle density. The results hold
promise for developing predictive models of the transition, essential for
understanding and optimizing future fusion power reactors
Thermodynamics, strange quark matter, and strange stars
Because of the mass density-dependence, an extra term should be added to the
expression of pressure. However, it should not appear in that of energy
according to both the general ensemble theory and basic thermodynamic
principle. We give a detail derivation of the thermodynamics with
density-dependent particle masses. With our recently determined quark mass
scaling, we study strange quark matter in this new thermodynamic treatment,
which still indicates a possible absolute stability as previously found.
However, the density behavior of the sound velocity is opposite to the previous
finding, but consistent with one of our recent publication. We have also
studied the structure of strange stars using the obtained equation of state.Comment: 6 pages, 6 PS figures, REVTeX styl
Ionization of oriented targets by intense circularly polarized laser pulses: Imprints of orbital angular nodes in the 2D momentum distribution
We solve the three-dimensional time-dependent Schr\"{o}dinger equation for a
few-cycle circularly polarized femtosecond laser pulse interacting with an
oriented target exemplified by an Argon atom, initially in a or
state. The photoelectron momentum distributions show distinct
signatures of the orbital structure of the initial state as well as the
carrier-envelope phase of the applied pulse. Our \textit{ab initio} results are
compared with results obtained using the length-gauge strong-field
approximation, which allows for a clear interpretation of the results in terms
of classical physics. Furthermore, we show that ionization by a circularly
polarized pulse completely maps out the angular nodal structure of the initial
state, thus providing a potential tool for studying orbital symmetry in
individual systems or during chemical reactions
BeeFarm – mapping resources for pollinators at the farm
The aim of the BeeFarm project is to develop a farmer’s tool for assessing resources for bees at the farm. The tool includes a guided tour through the fields and semi-natural habitats of a farm, in order for the farmer to systematically assess the bee resources on the farm. The tool will make it possible for the farmers to identify resources, which are potentially limiting wild pollinator populations
Differential atom interferometry beyond the standard quantum limit
We analyze methods to go beyond the standard quantum limit for a class of
atomic interferometers, where the quantity of interest is the difference of
phase shifts obtained by two independent atomic ensembles. An example is given
by an atomic Sagnac interferometer, where for two ensembles propagating in
opposite directions in the interferometer this phase difference encodes the
angular velocity of the experimental setup. We discuss methods of squeezing
separately or jointly observables of the two atomic ensembles, and compare in
detail advantages and drawbacks of such schemes. In particular we show that the
method of joint squeezing may improve the variance by up to a factor of 2. We
take into account fluctuations of the number of atoms in both the preparation
and the measurement stage, and obtain bounds on the difference of the numbers
of atoms in the two ensembles, as well as on the detection efficiency, which
have to be fulfilled in order to surpass the standard quantum limit. Under
realistic conditions, the performance of both schemes can be improved
significantly by reading out the phase difference via a quantum non-demolition
(QND) measurement. Finally, we discuss a scheme using macroscopically entangled
ensembles.Comment: 10 pages, 5 figures; eq. (3) corrected and other minor change
Influence of molecular symmetry on strong-field ionization: Studies on ethylene, benzene, fluorobenzene, and chlorofluorobenzene
Using the molecular strong-field approximation we consider the effects of
molecular symmetry on the ionization of molecules by a strong, linearly
polarized laser pulse. Electron angular distributions and total ionization
yields are calculated as a function of the relative orientation between the
molecule and the laser polarization. Our studies focus on ethylene
(CH), benzene (CH), fluorobenzene (CHF), and ortho
chlorofluorobenzene (1,2 CHClF), the molecules representing four
different point groups. The results are compared with experiments, when
available, and with the molecular tunneling theory appropriately extended to
non-linear polyatomic molecules. Our investigations show that the orientational
dependence of ionization yields is primarily determined by the nodal surface
structure of the molecular orbitals.Comment: 13 pages, 10 figures. Submitted to Physical Review
Photon emission from bare quark stars
We investigate the photon emission from the electrosphere of a quark star. It
is shown that at temperatures T\sim 0.1-1 MeV the dominating mechanism is the
bremsstrahlung due to bending of electron trajectories in the mean Coulomb
field of the electrosphere. The radiated energy for this mechanism is much
larger than that for the Bethe-Heitler bremsstrahlung. The energy flux from the
mean field bremsstrahlung exceeds the one from the tunnel e^{+}e^{-} pair
creation as well. We demonstrate that the LPM suppression of the photon
emission is negligible.Comment: 35 pages, 5 figure
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