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- ItemLaser stripping of hydrogen atoms by direct ionization([London] : IOP, 2015) Brunetti, E.; Becker, W.; Bryant, H.C.; Jaroszynski, D.A.; Chou, W.Direct ionization of hydrogen atoms by laser irradiation is investigated as a potential new scheme to generate proton beams without stripping foils. The time-dependent Schrödinger equation describing the atom-radiation interaction is numerically solved obtaining accurate ionization cross-sections for a broad range of laser wavelengths, durations and energies. Parameters are identified where the Doppler frequency up-shift of radiation colliding with relativistic particles can lead to efficient ionization over large volumes and broad bandwidths using currently available lasers.
- ItemSub-laser-cycle control of coupled electron–nuclear dynamics at a conical intersection([London] : IOP, 2015) Richter, Maria; Bouakline, Foudhil; González-Vázquez, Jesús; Martínez-Fernández, Lara; Corral, Inés; Patchkovskii, Serguei; Morales, Felipe; Ivanov, Misha; Martín, Fernando; Smirnova, OlgaNonadiabatic processes play a fundamental role in the understanding of photochemical processes in excited polyatomic molecules. A particularly important example is that of radiationless electronic relaxation at conical intersections (CIs). We discuss new opportunities for controlling coupled electron–nuclear dynamics at CIs, offered by the advent of nearly single-cycle, phase-stable, mid-infrared laser pulses. To illustrate the control mechanism, a two-dimensional model of the NO2 molecule is considered. The key idea of the control scheme is to match the time scale of the laser field oscillations to the characteristic time scale of the wave packet transit through the CI. The instantaneous laser field changes the shape and position of the CI as the wave packet passes through. As the CI moves in the laser field, it 'slices' through the wave packet, sculpting it in the coordinate and momentum space in a way that is sensitive to the carrier-envelope phase of the control pulse. We find that the electronic coherence imparted on the sub-laser-cycle time scale manifests during much longer nuclear dynamics that follow on the many tens of femtosecond time scale. Control efficiency as a function of molecular orientation is analyzed, showing that modest alignment is sufficient for showing the described effects.
- ItemSignatures of attosecond electronic–nuclear dynamics in the one-photon ionization of molecular hydrogen: analytical model versusab initiocalculations([London] : IOP, 2015) Medišauskas, Lukas; Morales, Felipe; Palacios, Alicia; González-Castrillo, Alberto; Plimak, Lev; Smirnova, Olga; Martín, Fernando; Ivanov, Misha YuWe present an analytical model based on the time-dependent WKB approximation to reproduce the photoionization spectra of an H2 molecule in the autoionization region. We explore the nondissociative channel, which is the major contribution after one-photon absorption, and we focus on the features arising in the energy differential spectra due to the interference between the direct and the autoionization pathways. These features depend on both the timescale of the electronic decay of the autoionizing state and the time evolution of the vibrational wavepacket created in this state. With full ab initio calculations and with a one-dimensional approach that only takes into account the nuclear wavepacket associated to the few relevant electronic states we compare the ground state, the autoionizing state, and the background continuum electronic states. Finally, we illustrate how these features transform from molecular-like to atomic-like by increasing the mass of the system, thus making the electronic decay time shorter than the nuclear wavepacket motion associated with the resonant state. In other words, autoionization then occurs faster than the molecular dissociation into neutrals.
- ItemTwo-particle quantum correlations in stochastically-coupled networks([London] : IOP, 2019) de J León-Montiel, Roberto; Méndez, Vicenç; Quiroz-Juárez, Mario A.; Ortega, Adrian; Benet, Luis; Perez-Leija, Armando; Busch, KurtQuantum walks in dynamically-disordered networks have become an invaluable tool for understanding the physics of open quantum systems. Although much work has been carried out considering networks affected by diagonal disorder, it is of fundamental importance to study the effects of fluctuating couplings. This is particularly relevant in materials science models, where the interaction forces may change depending on the species of the atoms being linked. In this work, we make use of stochastic calculus to derive a master equation for the dynamics of one and two non-interacting correlated particles in tight-binding networks affected by off-diagonal dynamical disorder. We show that the presence of noise in the couplings of a quantum network creates a pure-dephasing-like process that destroys all coherences in the single-particle Hilbert subspace. Moreover, we show that when two or more correlated particles propagate in the network, coherences accounting for particle indistinguishability are robust against the impact of off-diagonal noise, thus showing that it is possible, in principle, to find specific conditions for which many indistinguishable particles can traverse stochastically-coupled networks without losing their ability to interfere. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
- ItemAll-optical spatio-temporal control of electron emission from SiO2 nanospheres with femtosecond two-color laser fields([London] : IOP, 2019) Liu, Qingcao; Zherebtsov, Sergey; Seiffert, Lennart; Skruszewicz, Slawomir; Zietlow, Dominik; Ahn, Seongjin; Rupp, Philipp; Wnuk, Pawel; Sun, Shaohua; Kessel, Alexander; Trushin, Sergei; Schlander, Annika; Kim, Dongeon; Rühl, Eckart; Ciappina, Marcelo F.; Tiggesbäumker, Josef; Gallei, Markus; Fennel, Thomas; Kling1, Matthias F.Field localization by nanostructures illuminated with laser pulses of well-defined waveform enables spatio-temporal tailoring of the near-fields for sub-cycle control of electron dynamics at the nanoscale. Here, we apply intense linearly-polarized two-color laser pulses for all-optical control of the highest energy electron emission from SiO2 nanoparticles. For the size regime where light propagation effects become important, we demonstrate the possibility to control the preferential emission angle of a considerable fraction of the fastest electrons by varying the relative phase of the two-color field. Trajectory based semi-classical simulations show that for the investigated nanoparticle size range the directional steering can be attributed to the two-color effect on the electron trajectories, while the accompanied modification of the spatial distribution of the ionization rate on the nanoparticle surface has only a minor effect. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft
- ItemRecombination dynamics of clusters in intense extreme-ultraviolet and near-infrared fields([London] : IOP, 2015) Schütte, Bernd; Oelze, Tim; Krikunova, Maria; Arbeiter, Mathias; Fennel, Thomas; Vrakking, Marc J. J.; Rouzée, ArnaudWe investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in Schütte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed Ar–Xe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell.