199,379 research outputs found
Comparative time-resolved photoemission from the Cu(100) and Cu(111) surfaces
No full textCitation: Ambrosio, M. J., & Thumm, U. (2016). Comparative time-resolved photoemission from the Cu(100) and Cu(111) surfaces. Physical Review A, 94(6), 14. doi:10.1103/PhysRevA.94.063424Motivated by the striking dependence of the valence electronic structure of transition metal surfaces on their crystallographic orientation, and by emerging experiments on laser-assisted extended ultraviolet (XUV) photoemission from solid surfaces, we calculate photoemission spectra from Cu(100) and Cu(111) surfaces as a function of the photoelectron final kinetic energy and the delay between the ionizing attosecond XUV pulse train and assisting infrared (IR) laser pulse. Our numerical simulations predict distinct differences in delay-dependent photoelectron energy distributions and photoemission time delays for Cu(100) and Cu(111) surfaces. These differences can be scrutinized experimentally with existing technology in a suggested in situ comparative RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) configuration by placing the two surfaces on a sliding platform while keeping all optical components and pathlengths fixed. Our calculations also show that the inclusion of the Fresnel-reflected incident IR pulse at the metal-vacuum interface modifies photoelectron spectra and photoemission time delays in a characteristic way that reveals the degree of spatial location of the initial electronic states
Probing O+ 2 potential curves with an XUV-IR pump-probe experiment
No full textCitation: Cörlin, P., Fischer, A., Schönwald, M., Sperl, A., Mizuno, T., Thumm, U., . . . Moshammer, R. (2015). Probing O+ 2 potential curves with an XUV-IR pump-probe experiment. 635(11). doi:10.1088/1742-6596/635/11/112060Upon ionization of ground state O2 molecules in a short XUV pulse, we observe a time-dependent vibrational wave packet in the potential of the binding O+ 2 (a4?u) state. Our pump-probe delay dependent kinetic-energy-release (KER) spectra are in qualitative agreement with the results of coupled-channel simulations that are based on calculated Born-Oppenheimer potential-energy curves (PECs). Using a Morse potential adjusted to the experimental data most features of the experimental spectra are reproduced quantitatively. © Published under licence by IOP Publishing Ltd
Probing calculated O-2(+) potential-energy curves with an XUV-IR pump-probe experiment
No full textCitation: Corlin, P., Fischer, A., Schonwald, M., Sperl, A., Mizuno, T., Thumm, U., . . . Moshammer, R. (2015). Probing calculated O-2(+) potential-energy curves with an XUV-IR pump-probe experiment. Physical Review A, 91(4), 8. doi:10.1103/PhysRevA.91.043415We study dissociative photoionization of molecular oxygen in a kinematically complete XUV-IR pump-probe experiment. Detecting charged fragments and photoelectrons in coincidence using a reaction microscope, we observe a pump-probe delay-dependent yield of very low energetic O+ ions which oscillates with a period of 40 fs. This feature is caused by a time-dependent vibrational wave packet in the potential of the binding O-2(+)(a(4)Pi(u))state, which is probed by resonant absorption of a single infrared photon to the weakly repulsive O-2(+)(f(4)Pi(g)) state. By quantitative comparison of the experimental kinetic-energy-release (KER) and quantum-beat (QB) spectra with the results of a coupled-channel simulation, we are able to discriminate between the calculated adiabatic O-2(+) potential-energy curves (PECs) of Marian et al. [Marian, Marian, Peyerimhoff, Hess, Buenker, and Seger, Mol. Phys. 46, 779 (1982)] and Magrakvelidze et al. [Magrakvelidze, Aikens, and Thumm, Phys. Rev. A 86, 023402 (2012)]. In general, we find a good agreement between experimental and simulated KER and QB spectra. However, we could not reproduce all features of the experimental data with these PECs. In contrast, adjusting a Morse potential to the experimental data, most features of the experimental spectra are well reproduced by our simulation. By comparing this Morse potential to theoretically predicted PECs, we demonstrate the sensitivity of our experimental method to small changes in the shape of the binding potential
Dissociation dynamics of noble-gas dimers in intense two-color IR laser fields
No full textWe numerically model the dissociation dynamics of the noble-gas dimer ions He[subscript 2]+, Ne[subscript 2]+, Ar[subscript 2]+, Kr[subscript 2]+, and Xe[subscript 2]+ in ultrashort pump and probe laser pulses of different wavelengths. Our calculations reveal a distinguished “gap” in the kinetic energy spectra, observed experimentally for the Ar[subscript 2] dimer [ J. Wu et al. Phys. Rev. Lett. 110 033005 (2013)], for all noble-gas dimers for appropriate wavelength combinations. This striking phenomenon can be explained by the dissociation of dimer ions on dipole-coupled Born-Oppenheimer adiabatic potential curves. Comparing pump-probe-pulse-delay-dependent kinetic-energy-release spectra for different noble-gas dimer cations of increasing mass, we discuss increasingly prominent (i) fine-structure effects in and (ii) classical aspects of the nuclear vibrational motion
Dissociation dynamics of diatomic molecules in intense laser fields: a scheme for the selection of relevant adiabatic potential curves
No full textWe investigated the nuclear dynamics of diatomic molecular ions in intense laser fields by analyzing their fragment kinetic-energy release (KER) spectra as a function of the pump-probe delay τ . Within the Born-Oppenheimer (BO) approximation, we calculated ab initio adiabatic potential-energy curves and their electric dipole couplings, using the quantum chemistry code GAMESS. By comparing simulated KER spectra as a function of either τ or the vibrational quantum-beat frequency for the nuclear dynamics on both individual and dipole-coupled BO potential curves with measured spectra, we developed a scheme for identifying electronic states that are relevant for the dissociation dynamics. We applied this scheme to investigate the nuclear dynamics in O[subscript 2][superscript +] ions that are produced by ionization of neutral O[subscript 2] molecules in an ultrashort infrared (IR) pump pulse and dissociate due to the dipole coupling of molecular potential curves in a delayed IR probe laser field
THE ROLE OF PATENTS IN INFORMATION AND COMMUNICATION TECHNOLOGIES: A SURVEY OF THE LITERATURE
No full textDuring the last few decades, the number of patents in information and communication
technologies has increased considerably. An increasing number of patents and the associated
fragmentation of IP rights have generated a series of potentially problematic consequences. Patent
thickets, royalty stacking, the emergence of patent assertion entities, increased patent litigation –
particularly around standard essential patents – and the difficulties with defining fair, reasonable,
and nondiscriminatory licensing terms are some of the most debated issues in the literature that we
review in this paper. We devote a specific section of our survey to patent quality, currently one of the
most debated issues surrounding the patent system. In our analysis, we mix theoretical and empirical
arguments with a more policy-oriented reasoning. This allows us to better position the different issues
in the relevant political and economic context
Electronic structure effects in spatiotemporally resolved photoemission interferograms of copper surfaces
No full textCitation: Ambrosio, M. J., & Thumm, U. (2017). Electronic structure effects in spatiotemporally resolved photoemission interferograms of copper surfaces. Physical Review A, 96(5), 051403. https://doi.org/10.1103/PhysRevA.96.051403Attosecond photoelectron spectroscopy allows the observation of electronic processes on attosecond time scales (1as=10−18 s), as has been demonstrated in proof-of-principle experiments that probe the electronic dynamics in isolated atoms with unprecedented accuracy. Its recent expansion to solid targets is starting to allow the distinction of ultrafast collective electronic processes in matter with added spatial resolution, probing the electronic band structure and dielectric response in nanoplasmonically enhanced light-induced processes of relevance for photocatalysis, optoelectronics, and light harvesting. Based on a quantum-mechanical model for photoelectron emission by an attosecond pulse train from the d band of a Cu(111) surface into a delayed assisting laser pulse, we calculate two-pathway two-photon interferograms as functions of the photoelectron energy and pulse delay. Our results scrutinize the dependence of observable photoelectron interferograms on the electronic structure of and electron transport in the substrate and agree well with experimental spectra and semiclassical Monte Carlo simulations of Lucchini et al. [Phys. Rev. Lett. 115, 137401 (2015)]
Dissertatio Theologica De Lege Ceremoniali Et Forensi / Ad disputandum proposita, Praeside Theodoro Thummio ... Respondente M. Georgio Alberto ... ad diem Iunii ...
No full textEnergy-resolved attosecond interferometric photoemission from Ag(111) and Au(111) surfaces
No full textCitation: Ambrosio, M. J., & Thumm, U. (2018). Energy-resolved attosecond interferometric photoemission from Ag(111) and Au(111) surfaces. Physical Review A, 97(4), 043431. https://doi.org/10.1103/PhysRevA.97.043431Photoelectron emission from solid surfaces induced by attosecond pulse trains into the electric field of delayed phase-coherent infrared (IR) pulses allows the surface-specific observation of energy-resolved electronic phase accumulations and photoemission delays. We quantum-mechanically modeled interferometric photoemission spectra from the (111) surfaces of Au and Ag, including background contributions from secondary electrons and direct emission by the IR pulse, and adjusted parameters of our model to energy-resolved photoelectron spectra recently measured at a synchrotron light source by Roth et al. [J. Electron Spectrosc. 224, 84 (2018)]. Our calculated spectra and photoelectron phase shifts are in fair agreement with the experimental data of Locher et al. [Optica 2, 405 (2015)]. Our model's not reproducing the measured energy-dependent oscillations of the Ag(111) photoemission phases may be interpreted as evidence for subtle band-structure effects on the final-state photoelectron-surface interaction not accounted for in our simulation
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