Dissociation spectrum of H2+_2^+ 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 $\lambda \sim 790$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 ($\lambda \sim 790$nm). Integrating over the laser focal volume, for the intensity $I \sim 3 \times 10^{15}$W cm$^{-2}$, 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

Nuclear classical dynamics of H2_2 in intense laser field

In the first part of this paper, the different distinguishable pathways and regions of the single and sequential double ionization are determined and discussed. It is shown that there are two distinguishable pathways for the single ionization and four distinct pathways for the sequential double ionization. It is also shown that there are two and three different regions of space which are related to the single and double ionization respectively. In the second part of the paper, the time dependent Schr\"{o}dinger and Newton equations are solved simultaneously for the electrons and the nuclei of H$_2$ respectively. The electrons and nuclei dynamics are separated on the base of the adiabatic approximation. The soft-core potential is used to model the electrostatic interaction between the electrons and the nuclei. A variety of wavelengths (390 nm, 532 nm and 780 nm) and intensities ($5\times10^{14}$ $Wcm^{-2}$ and $5\times10^{15}$ $Wcm^{-2}$) of the ultrashort intense laser pulses with a sinus second order envelope function are used. The behaviour of the time dependent classical nuclear dynamics in the absence and present of the laser field are investigated and compared. In the absence of the laser field, there are three distinct sections for the nuclear dynamics on the electronic ground state energy curve. The bond hardening phenomenon does not appear in this classical nuclear dynamics simulation.Comment: 16 pages, 7 figure

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

Adherence to a Treat-to-Target Strategy in Early Rheumatoid Arthritis: Results of the DREAM Remission Induction Cohort

Introduction\ud 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. \ud \ud Methods\ud 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. \ud \ud Results\ud 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. \ud \ud Conclusions\ud 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 practic

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

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

Correlation dynamics between electrons and ions in the fragmentation of D2_2 molecules by short laser pulses

We studied the recollision dynamics between the electrons and D$_2^+$ ions following the tunneling ionization of D$_2$ molecules in an intense short pulse laser field. The returning electron collisionally excites the D$_2^+$ ion to excited electronic states from there D$_2^+$ can dissociate or be further ionized by the laser field, resulting in D$^+$ + D or D$^+$ + D$^+$, respectively. We modeled the fragmentation dynamics and calculated the resulting kinetic energy spectrum of D$^+$ to compare with recent experiments. Since the recollision time is locked to the tunneling ionization time which occurs only within fraction of an optical cycle, the peaks in the D$^+$ kinetic energy spectra provides a measure of the time when the recollision occurs. This collision dynamics forms the basis of the molecular clock where the clock can be read with attosecond precision, as first proposed by Corkum and coworkers. By analyzing each of the elementary processes leading to the fragmentation quantitatively, we identified how the molecular clock is to be read from the measured kinetic energy spectra of D$^+$ and what laser parameters be used in order to measure the clock more accurately.Comment: 13 pages with 14 figure