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

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

A quantitative theory-versus-experiment comparison for the intense laser dissociation of H2+

A detailed theory-versus-experiment comparison is worked out for H$_2^+$ intense laser dissociation, based on angularly resolved photodissociation spectra recently recorded in H.Figger's group. As opposite to other experimental setups, it is an electric discharge (and not an optical excitation) that prepares the molecular ion, with the advantage for the theoretical approach, to neglect without lost of accuracy, the otherwise important ionization-dissociation competition. Abel transformation relates the dissociation probability starting from a single ro-vibrational state, to the probability of observing a hydrogen atom at a given pixel of the detector plate. Some statistics on initial ro-vibrational distributions, together with a spatial averaging over laser focus area, lead to photofragments kinetic spectra, with well separated peaks attributed to single vibrational levels. An excellent theory-versus-experiment agreement is reached not only for the kinetic spectra, but also for the angular distributions of fragments originating from two different vibrational levels resulting into more or less alignment. Some characteristic features can be interpreted in terms of basic mechanisms such as bond softening or vibrational trapping.Comment: submitted to PRA on 21.05.200

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

Characterizing a source of fission fragments for a gas jet

A model for the rate at which various primary fission products stop in the gas of the source chamber of a gas jet has been constructed. It describes the absorption of fission fragments in Al foils placed between the 235 U deposit and the gas chamber as well as the penetration of fragments through the gas. The model is based on reported ranges (mean values as a function of A and the dispersion in ranges) and measured activities of Kr and Xe.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43112/1/10967_2005_Article_BF02060552.pd

The Australian Sony PlayStation Case and the Implementation of the Australia-US Free Trade Agreement (AUSFTA)

In this paper, we consider the definition of 'Technological Protection Measure' and the meaning of 'Effective Technological Measure' (ETM) in Article 17.4.7 of the Australia-United States Free Trade Agreement (AUSFTA). We consider the effect of the recent High Court decision in Stevens v Kabushiki Kaisha Sony Computer Entertainment [2005] HCA 58 and the emphasis of the court on upholding consumer interests. We also consider the recommendations of the House of Representatives Standing Committee on Legal And Constitutional Affairs (LACA) with respect to Art 17.4.7, and the way in which these recommendations can be implemented to protect the legitimate interests of both copyright holders and consumers, while staying within the boundaries of our international obligations. We conclude that the recommendation that liability for circumvention of technological measures should be linked to copyright infringement, and that the LACA recommendation, the text of the AUSFTA, and a recent US Court of Appeals decision in StorageTek v Custom Hardware Engineering ((2005) 421 F.3d 1307) all provide support for this proposition

Étude expérimentale du spectre des électrons d'autoionisation en radioactivité β

Following already published experiments on 32P, 35S, 147Pm, results are given for 90Y, 143Pr and 22Na. The intensities of the X, K or L lines, are in good agreement with the theory of autoionisation. On the other hand the continuous spectra, between 1 and 13 keV, of autoionisation electrons emitted simultaneously with β radiation disagree with theoretical predictions. (The intensity is greater, the spectral distribution is different, and the law of variation versus Z is inverted.) This could be explained by a contribution from external electronic shells considerably more important than that predicted by the autoionisation theory.Faisant suite à des expériences déjà publiées sur le 32P, 35S, 147Pm, les résultats sont donnés pour le 90Y, 143Pr et 22Na. Contrairement aux intensités des raies X, K ou L, qui sont en bon accord avec la théorie de l'autoionisation, les spectres continus, mesurés entre 1 et 13 keV, des électrons d'autoionisation émis simultanément avec le rayonnement β sont en contradiction avec les prévisions théoriques (intensité plus grande, distribution spectrale différente et loi inversée en fonction de Z). Ceci s'expliquerait par une contribution des couches externes du cortège électronique considérablement plus importante que celle prévue par la théorie de l'autoionisation

Étude expérimentale du spectre des électrons d'autoionisation en radioactivité β

Continuum spectra, between 1 and 13 kV, of autoionisation electrons are given for 6 radioelements (3 already published). A disagreement results from comparison with theory; this could be explained by a more important contribution of the external electronic shells.Les spectres continus, entre 1 et 13 kV, des électrons d'autoionisation sont donnés pour 6 radioéléments β (3 déjà publiés). Comparaison avec la théorie, d'où il ressort un désaccord qui pourrait s'expliquer par une contribution beaucoup plus importante des couches externes du cortège électronique

Étude de la période de décroissance du niveau de 57 keV lié à la désintégration du MTh2

Le rayonnement sortant d'une source de M Th2 est compté à l'aide d'un compteur Geiger dans un angle solide 4 π. Un temps mort, imposé au compteur, peut varier de 2.10-4 à 1 s; l'étude du nombre des impulsions enregistrées permet de conclure que la période du niveau de 57 keV est supérieure à 0,5 s