Light by light diffraction in vacuum

We show that a laser beam can be diffracted by a more concentrated light pulse due to quantum vacuum effects. We compute analytically the intensity pattern in a realistic experimental configuration, and discuss how it can be used to measure the parameters describing photon-photon scattering in vacuum. In particular, we show that the quantum electrodynamics prediction can be detected in a single-shot experiment at future 100-PW lasers such as ELI or HIPER. On the other hand, if carried out at one of the present high-power facilities, such as OMEGA EP, this proposal can lead either to the discovery of nonstandard physics or to substantial improvement in the current limits by PVLAS collaboration on the photon-photon cross section at optical wavelengths. This example of manipulation of light by light is simpler to realize and more sensitive than existing, alternative proposals, and can also be used to test Born-Infeld theory or to search for axionlike or minicharged particles.Ministerio de Ciencia e Innovación | Ref. FIS2008-01001Universidade de Vig

Self-trapping of vortex crystals via competing nonlinearities

We investigate the existence of self-trapped nonlinear waves with multiple phase singularities. Working with the cubic-quintic nonlinear Schrödinger equation, we focus on configurations with an antivortex surrounded by a triangular arrangement of vortices within a hosting soliton. We find stationary patterns that can be interpreted as stable self-trapped vortex crystals, constituting the first example of a configuration of this sort with space-independent potentials. Their stability is linked to their norm, transitioning from unstable to stable as their size increases, with an intermediate region where the structure is marginally unstable, undergoing a remarkable and puzzling self-reconstruction during its evolutionXunta de Galicia | Ref. ED431B 2021/22Agencia Estatal de Investigación | Ref. PID2020-118613GB-I0

On vortex and dark solitons in the cubic–quintic nonlinear Schrödinger equation

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGWe study topologically charged propagation-invariant eigenstates of the 1+2-dimensional Schrödinger equation with a cubic (focusing)–quintic (defocusing) nonlinear term. First, we revisit the self-trapped vortex soliton solutions. Using a variational ansatz that allows us to describe the solutions as a liquid with a surface tension, we derive a simple formula relating the inner and outer radii of the bright vortex ring. Then, using numerical and variational techniques, we analyse dark soliton solutions for which the wave function density asymptotes to a non-vanishing value. We find an eigenvalue cutoff for the propagation constant that depends on the topological charge l. The variational profile provides simple and very accurate results for l ≥ 2. We also study the azimuthal stability of the eigenstates by a linear analysis finding that they are stable for all values of the propagation constant, at least for small l.Ministerio de Ciencia e Innovación | Ref. PID2020-118613GB-I00Xunta de Galicia | Ref. ED431B 2021/2

Polygons of quantized vortices in Bose-Einstein condensates with a circular trap

We consider a disk-shaped cold atom Bose-Einstein condensate with repulsive atom-atom interactions within a circular trap, described by a two-dimensional time-dependent Gross-Pitaevskii equation with cubic nonlinearity and a circular box potential. In this setup, we discuss the existence of a type of stationary nonlinear waves with propagation-invariant density profiles, consisting of vortices located at the vertices of a regular polygon with or without an antivortex at its center. These polygons rotate around the center of the system and we provide approximate expressions for their angular velocity. For any size of the trap, we find a unique regular polygon solution that is static and is seemingly stable for long evolutions. It consists of a triangle of vortices with unit charge placed around a singly charged antivortex, with the size of the triangle fixed by the cancellation of competing effects on its rotation. There exist other geometries with discrete rotational symmetry that yield static solutions, even if they turn out to be unstable. By numerically integrating in real time the Gross-Pitaevskii equation, we compute the evolution of the vortex structures and discuss their stability and the fate of the instabilities that can unravel the regular polygon configurations. Such instabilities can be driven by the instability of the vortices themselves, by vortex-antivortex annihilation or by the eventual breaking of the symmetry due to the motion of the vortices.Xunta de Galicia | Ref. ED431B 2021/22Agencia Estatal de Investigación | Ref. PID2020-118613GB-I0

Filamentation processes and dynamical excitation of light condensates in optical media with competing nonlinearities

We analyze both theoretically and by means of numerical simulations the phenomena of filamentation and dynamical formation of self-guided nonlinear waves in media featuring competing cubic and quintic nonlinearities. We provide a theoretical description of recent experiments in terms of a linear stability analysis supported with simulations, showing the possibility of the observation of modulational instability suppression of intense light pulses traveling across such nonlinear media. We also show a mechanism of indirect excitation of light condensates by means of coalescence processes of nonlinear coherent structures produced by managed filamentation of high-power laser beams.Ministerio de Educación y Ciencia | Ref. FIS2006-04190Xunta de GaliciaMinisterio de Educación y Ciencia | Ref. FIS2007-6256

Detecting photon-photon scattering in vacuum at exawatt lasers

In a recent paper, we have shown that the QED nonlinear corrections imply a phase correction to the linear evolution of crossing electromagnetic waves in vacuum. Here, we provide a more complete analysis, including a full numerical solution of the QED nonlinear wave equations for short-distance propagation in a symmetric configuration. The excellent agreement of such a solution with the result that we obtain using our perturbatively motivated variational approach is then used to justify an analytical approximation that can be applied in a more general case. This allows us to find the most promising configuration for the search of photon-photon scattering in optics experiments. In particular, we show that our previous requirement of phase coherence between the two crossing beams can be released. We then propose a very simple experiment that can be performed at future exawatt laser facilities, such as ELI, by bombarding a low power laser beam with the exawatt bump.Xunta de GaliciaMinisterio de Educación y Ciencia | Ref. FIS2007-29090-EMinisterio de Educación y Ciencia | Ref. FIS2007-6256Ministerio de Educación y Ciencia | Ref. TIN2006-12890Ministerio de Educación y Ciencia | Ref. FIS2005-0118

Point cloud simulator for space in-orbit close range autonomous operations

In recent years, many different in-orbit close-range autonomous operations have been developed for multiple purposes, such as rendezvous and docking operations or ADR operations. In both cases, the systems have to calculate the relative position between the spacecraft and the target in order to control the orbital manoeuvres and the physic interaction between both systems. One of the sensors used for the pose calculation for these operations are LiDAR sensors, developing pose calculation algorithms that process the point cloud acquired by these sensors. One of the main problems for the development and testing of these algorithms is the lack of real data acquired in orbit and the difficulty of acquiring this data. This makes it fundamental to develop a simulator to generate realistic point clouds that can be used to develop and test pose calculation algorithms. This work presents a simulator developed for this purpose, that is the generation of realistic point clouds for algorithm development for pose calculation using LiDAR sensors for space in-orbit close range autonomous operations. The simulator uses the LiDAR sensor specifications, in order to introduces measurement errors and the scanning pattern, and 3D model of the satellite or object that is scanned.Universidade de Vigo | Ref. 58550

Vortex revivals and Fermi-Pasta-Ulam-Tsingou recurrence

We study the self-trapped vortex-ring eigenstates of the two-dimensional Schrödinger equation with focusing Poisson and cubic nonlinearities. For each value of the topological charge l, there is a family of solutions depending on a parameter that can be understood as the relative importance of the cubic term. We analyze the perturbative stability of the solutions and simulate the fate of the unstable ones. For l=1 and l=2, there is an interval of the family of eigenstates for which the initial profile breaks apart but subsequently reconstructs itself, a process that can be interpreted as a nontrivial nonlinear oscillation between the vortex and an azimuthon. This revival provides a compelling realization of a recurrence of the Fermi-Pasta-Ulam-Tsingou type. Outside this interval, the vortices can be stable (for small cubic terms) or unstable and nonrecurrent (for large cubic terms). We argue that there is a crossover between these regimes that resembles a strong stochasticity threshold. For l≥3, all solutions are unstable and nonrecurrent. Finally, we comment on the possible experimental implementation of this phenomenon in the context of nonlinear laser beam propagation in thermo-optical media.Agencia Estatal de Investigación | Ref. FIS2017-83762-PXunta de Galicia | Ref. ED431B 2018/5

Analysis of key variables for energy efficiency in warships

The purpose of this work is to investigate the effect of environmental variables on the electric energy expenditure of a typical surface warship. Studies with similar objectives are much more frequent for merchant ships, but warship operations have peculiarities that will be emphasised. In particular, they spend large fractions of their life cycle at port, during which the vessel remains active. First, a discussion of the embarked systems is presented, pointing out the importance of auxiliary systems and, in particular, heating, ventilation and air conditioning. Quantitative estimates of the energy consumption of those systems are provided. Then, using data taken during real operations of a frigate of the Spanish Navy, correlations are computed between power consumption and different environmental variables. As a novelty, the analysis is carried out separating the different modes of operation of the ship. This leads to interesting conclusions, including a considerable positive correlation between seawater temperature and fuel consumption when the vessel is in port. The effect of a moored ship on the surrounding seawater temperature is studied by a numerical computation. The results suggest that the position of sea chests may be consequential for energy efficiency.Xunta de Galicia | Ref. ED431B 2018/57Agencia Estatal de Investigación | Ref. FIS2017-83762-PMinisterio de Economía y Competitividad | Ref. FPDI-2013-17516Ministerio de Economía y Competitividad | Ref. ENE 2013-48015-C3-1-

Indoor air quality analysis using recurrent neural networks: a case study of environmental variables

In the pursuit of energy efficiency and reduced environmental impact, adequate ventilation in enclosed spaces is essential. This study presents a hybrid neural network model designed for monitoring and prediction of environmental variables. The system comprises two phases: An IoT hardware–software platform for data acquisition and decision-making and a hybrid model combining short-term memory and convolutional recurrent structures. The results are promising and hold potential for integration into parallel processing AI architectures