Electronic population transfer via impulsive stimulated x-ray Raman scattering with attosecond soft-x-ray pulses

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Coherent Control of Vibrational State Population in a Nonpolar Molecule

A coherent control scheme for the population distribution in the vibrational states of nonpolar molecules is proposed. Our theoretical analysis and results of numerical simulations for the interaction of the hydrogen molecular ion in its electronic ground state with an infrared laser pulse reveal a selective two-photon transition between the vibrational states via a coupling with the first excited dissociative state. We demonstrate that for a given temporal intensity profile the population transfer between vibrational states, or a superposition of vibrational states, can be made complete for a single chirped pulse or a train of chirped pulses, which accounts for the accumulated phase difference due to the AC Stark effect. Effects of a spatial intensity (or, focal) averaging are discussed

Measuring the complete transverse spatial mode spectrum of a wave field

We put forward a method that allows the experimental determination of the entire spatial mode spectrum of any arbitrary monochromatic wave field in a plane normal to its propagation direction. For coherent optical fields, our spatial spectrum analyzer can be implemented with a small number of benchmark refractive elements embedded in a single Mach-Zehnder interferometer. We detail an efficient setup for measuring in the Hermite-Gaussian mode basis. Our scheme should also be feasible in the context of atom optics for analyzing the spatial profiles of macroscopic matter waves

Dipole spectrum structure of non-resonant non-pertubative driven two-level atoms

We analize the dipole spectrum of a two-level atom excited by a non-resonant intense monochromatic field, under the electric dipole approximation and beyond the rotating wave approximation. We show that the apparently complex spectral structure can be completely described by two families: harmonic frequencies of the driving field and field-induced nonlinear fluorescence. Our formulation of the problem provides quantitative laws for the most relevant spectral features: harmonic ratios and phases, non-perturbative Stark shift, and frequency limits of the harmonic plateau. In particular, we demonstrate the locking of the harmonic phases at the wings of the plateau opening the possibility of ultra-short pulse generation through harmonic filtering

Quantum field theory of photons with orbital angular momentum

A quantum-field-theory approach is put forward to generalize the concept of classical spatial light beams carrying orbital angular momentum to the single-photon level. This quantization framework is carried out both in the paraxial and nonparaxial regimes. Upon extension to the optical phase space, closed-form expressions are found for a photon Wigner representation describing transformations on the orbital Poincaré sphere of unitarily related families of paraxial spatial modes

Quantum-path signatures in attosecond helical beams driven by optical vortices

High-order harmonic generation (HHG) driven by beams carrying orbital angular momentum has been recently demonstrated as a unique process to generate spatio-temporal coherent extreme ultraviolet (XUV)/x-ray radiation with attosecond helical structure.Weexplore the details of the mapping of the driving vortex to its harmonic spectrum. In particular we show that the geometry of the harmonic vortices is complex, arising from the superposition of the contribution from the short and long quantum paths responsible of HHG. Transversal phase-matching and quantum path interferences provide an explanation of the dramatic changes in theXUVvortex structure generated at different relative positions of the target respect to the laser beam focus. Finally, we show how to take advantage of transversal phase-matching to select helical attosecond beams generated from short or long quantum paths, exhibiting positive or negative temporal chirp respectively.CH-G acknowledges fruitful discussions with Mette B Gaarde and support from the Marie Curie International Outgoing Fellowship within the EUSeventh Framework Programme for Research and Technological Development (2007–2013), under REA grant Agreement No 328334 CH-G, JSR and LP acknowledge support from Junta de Castilla y León (Project SA116U13) and MINECO (FIS2013-44174-P). AP acknowledges financial support of the US Department of Energy, Basic Energy Sciences, Office of Science, under contract No DE-AC02- 06CH11357

Two-center Interferences in Photoionization of Dissociating H2+_2^+ Molecule

We analyze two-center interference effects in the yields of ionization of a dissociating hydrogen molecular ion by an ultrashort VUV laser pulse. To this end, we performed numerical simulations of the time-dependent Schr\"odinger equation for a H$_2^+$ model ion interacting with two time-delayed laser pulses. The scenario considered corresponds to a pump-probe scheme, in which the first (pump) pulse excites the molecular ion to the first excited dissociative state and the second (probe) pulse ionizes the electron as the ion dissociates. The results of our numerical simulations for the ionization yield as a function of the time delay between the two pulses exhibit characteristic oscillations due to interferences between the partial electron waves emerging from the two protons in the dissociating hydrogen molecular ion. We show that the photon energy of the pump pulse should be in resonance with the $\sigma_g - \sigma_u$ transition and the pump pulse duration should not exceed 5 fs in order to generate a well confined nuclear wavepacket. The spreading of the nuclear wavepacket during the dissociation is found to cause a decrease of the amplitudes of the oscillations as the time delay increases. We develop an analytical model to fit the oscillations and show how dynamic information about the nuclear wavepacket, namely velocity, mean internuclear distance and spreading, can be retrieved from the oscillations. The predictions of the analytical model are tested well against the results of our numerical simulations

Theoretical approach for Electron Dynamics and Ultrafast Spectroscopy (EDUS)

In this manuscript, we present a theoretical framework and its numerical implementation to simulate the out-of-equilibrium electron dynamics induced by the interaction of ultrashort laser pulses in condensed-matter systems. Our approach is based on evolving in real time the density matrix of the system in reciprocal space. It considers excitonic and nonperturbative light−matter interactions. We show some relevant examples that illustrate the efficiency and flexibility of the approach to describe realistic ultrafast spectroscopy experiments. Our approach is suitable for modeling the promising and emerging ultrafast studies at the attosecond time scale that aim at capturing the electron dynamics and the dynamical electron−electron correlations via X-ray absorption spectroscopyG.C., M.M., and A.P. acknowledge Comunidad de Madrid through TALENTO Grant Ref 2017-T1/IND-5432 and 2021- 5A/IND-20959, Grants Ref RTI2018-097355-A-I00 and ref PID2021-126560NB-I00 (MCIU/AEI/FEDER, UE), and computer resources and assistance provided by Centro de Computación Científica de la Universidad Autónoma de Madrid (FI-2021-1-0032), Instituto de Biocomputación y Física de Sistemas Complejos de la Universidad de Zaragoza (FI-2020-3-0008), and Barcelona Supercomputing Center (FI2020-1-0005, FI-2021-2-0023, FI-2021-3-0019). J.J.P., J.J.E.-P., and A.J.U.-Á . acknowledge funding from Grant No. PID2019- 109539GB-C43 (MCIU/AEI/FEDER, UE), the María de Maeztu Program for Units of Excellence in R&D (Grant No. CEX2018-000805-M), the Comunidad Autónoma de Madrid through the Nanomag COST-CM Program (Grant No. S2018/NMT-4321), and the Generalitat Valenciana through Programa Prometeo/2021/01. F.M. acknowledges the MICIN project PID2019-105458RB-I00, the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2016-0686), and the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M). R.E.F.S. acknowledges support from the fellowship LCF/BQ/PR21/11840008 from “La Caixa” Foundation (ID 100010434

Generation and Applications of Extreme-Ultraviolet Vortices

Vortex light beams are structures of the electromagnetic field with a spiral phase ramp around a point-phase singularity. These vortices have many applications in the optical regime, ranging from optical trapping and quantum information to spectroscopy and microscopy. The extension of vortices into the extreme-ultraviolet (XUV)/X-ray regime constitutes a significant step forward to bring those applications to the nanometer or even atomic scale. The recent development of a new generation of X-ray sources, and the refinement of other techniques, such as harmonic generation, have boosted the interest of producing vortex beams at short wavelengths. In this manuscript, we review the recent studies in the subject, and we collect the major prospects of this emerging field. We also focus on the unique and promising applications of ultrashort XUV/X-ray vortex pulsesA.P. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 702565. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007-2013), under REA grant Agreement No 328334. We acknowledge support and from Junta de Castilla y León (Project SA046U16) and MINECO (FIS2013-44174-P, FIS2015-71933-REDT, FIS2016-75652-P)

El grupu neandertal de la Cueva d'El Sidrón (Borines, Piloña).

Na monografía clásica de Puig y Larraz (1896: 250-252) amiéntense delles cavidaes del Conceyu de Piloña2 , pero non la Cueva d’El Sidrón (Fig. 1). Esta conocíase, ensin dulda, dende la Guerra Civil y el maquis al servir d’abellugu a persiguíos políticos, y guarda una alcordanza imborrable nuna de les sos múltiples entraes, yá qu’ellí ta enterrada Olvido Otero González (1908-1938). Per El Sidrón pasaron munches persones a lo llargo de los años, pero en 1994 prodúxose’l descubrimientu per parte d’unos espeleólogos xixoneses d’unos güesos humanos que dieron un importante xiru a la conocencia de los nuesos antepasaos neandertale