352 research outputs found
Dissociation spectrum of H from a short, intense infrared laser pulse: vibration structure and focal volume effects
The dissociation spectrum of the hydrogen molecular ion by short intense
pulses of infrared light is calculated. The time-dependent Schr\"odinger
equation is discretized and integrated in position and momentum space. For
few-cycle pulses one can resolve vibrational structure that commonly arises in
the experimental preparation of the molecular ion from the neutral molecule. We
calculate the corresponding energy spectrum and analyze the dependence on the
pulse time-delay, pulse length, and intensity of the laser for nm. We conclude that the proton spectrum is a both a sensitive probe of the
vibrational dynamics and the laser pulse. Finally we compare our results with
recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire
laser (nm). Integrating over the laser focal volume, for the
intensity W cm, we find our results are in
excellent agreement with these experiments.Comment: 17 pages, 8 figures, preprin
Semiclassical ionization dynamics of the hydrogen molecular ion in an electric field of arbitrary orientation
Quasi-static models of barrier suppression have played a major role in our
understanding of the ionization of atoms and molecules in strong laser fields.
Despite their success, in the case of diatomic molecules these studies have so
far been restricted to fields aligned with the molecular axis. In this paper we
investigate the locations and heights of the potential barriers in the hydrogen
molecular ion in an electric field of arbitrary orientation. We find that the
barriers undergo bifurcations as the external field strength and direction are
varied. This phenomenon represents an unexpected level of intricacy even on
this most elementary level of the dynamics. We describe the dynamics of
tunnelling ionization through the barriers semiclassically and use our results
to shed new light on the success of a recent theory of molecular tunnelling
ionization as well as earlier theories that restrict the electric field to be
aligned with the molecular axis
The propensity of molecules to spatially align in intense light fields
The propensity of molecules to spatially align along the polarization vector
of intense, pulsed light fields is related to readily-accessible parameters
(molecular polarizabilities, moment of inertia, peak intensity of the light and
its pulse duration). Predictions can now be made of which molecules can be
spatially aligned, and under what circumstances, upon irradiation by intense
light. Accounting for both enhanced ionization and hyperpolarizability, it is
shown that {\it all} molecules can be aligned, even those with the smallest
static polarizability, when subjected to the shortest available laser pulses
(of sufficient intensity).Comment: 8 pages, 4 figures, to be submitted to PR
Enhanced ionization in small rare gas clusters
A detailed theoretical investigation of rare gas atom clusters under intense
short laser pulses reveals that the mechanism of energy absorption is akin to
{\it enhanced ionization} first discovered for diatomic molecules. The
phenomenon is robust under changes of the atomic element (neon, argon, krypton,
xenon), the number of atoms in the cluster (16 to 30 atoms have been studied)
and the fluency of the laser pulse. In contrast to molecules it does not
dissappear for circular polarization. We develop an analytical model relating
the pulse length for maximum ionization to characteristic parameters of the
cluster
Irradiation of benzene molecules by ion-induced and light-induced intense fields
Benzene, with its sea of delocalized -electrons in the valence orbitals,
is identified as an example of a class of molecules that enable establishment
of the correspondence between intense ion-induced and laser-light-induced
fields in experiments that probe ionization dynamics in temporal regimes
spanning the attosecond and picosecond ranges.Comment: 4 ps figure
How to observe the Efimov effect
We propose to observe the Efimov effect experimentally by applying an
external electric field on atomic three-body systems. We first derive the
lowest order effective two-body interaction for two spin zero atoms in the
field. Then we solve the three-body problem and search for the extreme
spatially extended Efimov states. We use helium trimers as an illustrative
numerical example and estimate the necessary field strength to be less than 2.7
V/angstrom.Comment: 4 pages, 2 postscript figures, psfig.sty, revte
Exact field ionization rates in the barrier suppression-regime from numerical TDSE calculations
Numerically determined ionization rates for the field ionization of atomic
hydrogen in strong and short laser pulses are presented. The laser pulse
intensity reaches the so-called "barrier suppression ionization" regime where
field ionization occurs within a few half laser cycles. Comparison of our
numerical results with analytical theories frequently used shows poor
agreement. An empirical formula for the "barrier suppression ionization"-rate
is presented. This rate reproduces very well the course of the numerically
determined ground state populations for laser pulses with different length,
shape, amplitude, and frequency.
Number(s): 32.80.RmComment: Enlarged and newly revised version, 22 pages (REVTeX) + 8 figures in
ps-format, submitted for publication to Physical Review A, WWW:
http://www.physik.tu-darmstadt.de/tqe
Hypoxia inducible factor-1-alpha (HIF-1 alpha) is related to both angiogenesis and inflammation in rheumatoid arthritis
Adherence to a treat-to-target strategy in early rheumatoid arthritis:results of the DREAM remission induction cohort
INTRODUCTION: Clinical trials have demonstrated that treatment-to-target (T2T) is effective in achieving remission in early rheumatoid arthritis (RA). However, the concept of T2T has not been fully implemented yet and the question is whether a T2T strategy is feasible in daily clinical practice. The objective of the study was to evaluate the adherence to a T2T strategy aiming at remission (Disease Activity Score in 28 joints (DAS28) < 2.6) in early RA in daily practice. The recommendations regarding T2T included regular assessment of the DAS28 and advice regarding DAS28-driven treatment adjustments. METHODS: A medical chart review was performed among a random sample of 100 RA patients of the DREAM remission induction cohort. At all scheduled visits, it was determined whether the clinical decisions were compliant to the T2T recommendations. RESULTS: The 100 patients contributed to a total of 1,115 visits. The DAS28 was available in 97.9% (1,092/1,115) of the visits, of which the DAS28 was assessed at a frequency of at least every three months in 88.3% (964/1,092). Adherence to the treatment advice was observed in 69.3% (757/1,092) of the visits. In case of non-adherence when remission was present (19.5%, 108/553), most frequently medication was tapered off or discontinued when it should have been continued (7.2%, 40/553) or treatment was continued when it should have been tapered off or discontinued (6.2%, 34/553). In case of non-adherence when remission was absent (42.1%, 227/539), most frequently medication was not intensified when an intensification step should have been taken (34.9%, 188/539). The main reason for non-adherence was discordance between disease activity status according to the rheumatologist and DAS28. CONCLUSIONS: The recommendations regarding T2T were successfully implemented and high adherence was observed. This demonstrates that a T2T strategy is feasible in RA in daily clinical practice
Femtosecond laser pulse shaping for enhanced ionization
We demonstrate how the shape of femtosecond laser pulses can be tailored in
order to obtain maximal ionization of atoms or molecules. For that purpose, we
have overlayed a direct-optimization scheme on top of a fully unconstrained
computation of the three-dimensional time-dependent Schrodinger equation. The
procedure looks for pulses that maintain the same total length and integrated
intensity or fluence as a given pulse that serves as an initial guess. It
allows, however, for changes in frequencies -- within a certain, predefined
range -- and overall shape, leading to enhanced ionization. We illustrate the
scheme by calculating ionization yields for the H2+ molecule when irradiated
with short (~5 fs), high-intensity laser pulses
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