http://hdl.handle.net/10366/4101 2026-05-09T22:27:33Z 2026-05-09T22:27:33Z Pablos Marín, José Miguel http://hdl.handle.net/10366/170441 2026-03-14T03:03:31Z 2025-01-01T00:00:00Z

[EN] In this thesis we present fundamental research at the intersection of High Harmonic Generation (HHG) and Artificial Intelligence (AI), demonstrating the potential of combining both fields to model and understand ultrafast physical phenomena. Throughout this work, the major result was to accurately and efficiently describe both the microscopic quantum dynamics and the macroscopic propagation effects of HHG within the development of an AI-based model trained with exact results from the Three-Dimensional Time-Dependent Schrödinger Equation (3D-TDSE). This approach drastically reduces computational costs (from months to hours or even minutes) while retaining the quantum-level precision, that enables us further exploration of the HHG process. This hybrid AI-3D-TDSE model is capable of predicting the atomic dipole acceleration as a function of the amplitude and phase of the driving laser field. Beyond its simplicity, once trained, the neural network effectively replaces the 3D-TDSE at every point of the generating medium. Afterwards, the HHG emissions can be propagated to the far field through the integral solution of Maxwell’s equations. The model has been successfully validated in theoretical and experimental contexts. It was first employed to simulate and analyze HHG driven by structured laser beams of vortices with different Orbital Angular Momentum (OAM), accurately reproducing the spatial intensity distributions, OAM spectra, and temporal emission profiles of synthesized attosecond pulses. Moreover, it has been used as theoretical backup of experiments generating HHG with Hermite-Gauss (HG) driving beams, where the harmonic propagation give rise to an interference pattern between the different lobes of the HHG beams formed in the near field. Subsequently, the model was extended to mixed gaseous media, revealing a regime of coherent interference between species that acts as a natural spectral filter. These results highlight the potential of the developed framework for control the HHG emission, along with the attosecond pulse characteristics. The results presented here show that integrating AI into strong-field physics not only accelerates computation but defines other paths to follow in the standard simulation methodologies. Although this model is not general, it is perfectly suited to compute macroscopic HHG driven by structured laser pulses. Looking ahead, future efforts may include extending the model to incorporate non-linear propagation of the driving beam in dense media, accounting for dispersion from both neutral atoms and free electrons, both affected by the gas pressure. In such a case, a comprehensive analysis over the required dataset must be performed, as the number of free parameters increases abruptly. Another direct extensions of the model could be the addition of the wavelength and polarization of the driving beam, giving rise to a further generalization of the methodology here developed. From another perspective, the development of AI tools in HHG and attosecond science can be use to develope diagnostic techniques to characterize the properties of the Extreme Ultraviolet (EUV) emission in experiments. Attosecond light science faces several challenges in the development of characterization techniques that can retrieve spatiotemporally the properties (polarization, intensity, and phase) of attosecond pulses. AI may open the route for in situ measurements that can rely on accurate predictions.

2025-01-01T00:00:00Z Martín Hernández, Rodrigo http://hdl.handle.net/10366/170430 2026-03-14T03:03:25Z 2025-01-01T00:00:00Z

[EN] This thesis presents a theoretical study of strong-field light-matter interactions driven by structured light, in two different scenarios. The first part focuses on the generation and amplification of strong, locally isolated, magnetic fields through the interaction of structured light beams with matter, and the exploration of one of their potential applications. Structured light beams offer the possiblity to decouple spatially the electric and magnetic field components carried by a laser beam. We investigate the amplification of the paraxial longitudinal magnetic field component of azimuthally polarized vector beams. This magnetic field is maximum in an electric field singularity and, therefore, it is locally isolated from the surrounding electric field distribution. Our study suggests that the longitudinal magnetic field carried by an azimuthally polarized laser beam can be enhanced through the interaction with tailored metallic nanoantennas. The potential applications of these strong and ultrafast isolated magnetic fields could range from the control of the magnetization dynamics in magnetic materials to atomic and molecular spectroscopy or particle manipulation. As a potential application, we explore the use of intense isolated magnetic fields to assist the high-order harmonic generation (HHG) process. Our results demonstrate that HHG assisted by magnetic fields lead to the emission of ultra-broadband, attochirp-free HHG spectra, and consequently, to near Fourier-limited attosecond pulses. The second part of this thesis is devoted to the study of HHG driven by various types of structured light fields, and the influence of these driving fields on the spatial and temporal properties of the resulting high-photon-energy radiation. We follow a double-folded strategy: the generation of novel complex structured light fields at the attosecond scale and the enhancement of the intensity and focusing properties of attosecond HHG sources. We introduce the use of hollow Gaussian driving beams in HHG to increase the intensity of attosecond pulses. Hollow Gaussian beams allow to deliver a larger amount of energy at the target compared to standard Gaussian beam schemes, while keeping the intensity below the barrier suppression regime. Our theoretical simulations demonstrate that this configuration allows for more compact HHG setups with shorter driving laser beamlines and, combined with the enhanced refocusing properties of the harmonics, lead to the generation of attosecond pulses with up to three times more peak intensity. This intensity gain could potentially allow HHG sources to become better suited for applications where high photon fluxes are required, such as nanoimaging, metrology or spectroscopy. Preliminary experimental results performed at the group of Profs. Anne L’Huiller and Cord L. Arnold, at Lund University (Sweden), corroborate the properties of the high-order harmonics driven by hollow Gaussian beams. Subsequently, we investigate the up-conversion of near-infrared spatiotemporal optical vortices (STOVs) to the extreme-ultraviolet through HHG, with high topological charges. A comprehensive theoretical framework is developed to describe the generation and propagation dynamics of extreme-ultraviolet STOVs through HHG. Our theoretical simulations are in excellent agreement with the first experimental observations of HHG driven by STOVs, performed by the group of Profs. Margaret M. Murnane and Henry C. Kapteyn at the Univeristy of Colorado at Boulder (United States). Finally, we propose a novel scheme for the generation of extreme-ultraviolet STOVs via HHG, in which all harmonic orders are emitted in the far field with the same topological charge. This approach paves the way for the synthesis of STOVs at attosecond timescales. These attosecond pulses with non-trivial topologies, coupled in the temporal and spatial domains, could be of high interest for spatiotemporal probing ultrafast electronic dynamics in novel materials or in helical circular dichroism experiments. This thesis work involves the development and understanding of several advanced numerical methods and models, such as the implementation of highly-parallelized codes for calculating the HHG response based on the three-dimensional (3D) time dependent Schrödinger equation, the development of software for computing the strong field approximation (SFA) using graphical processing units (GPUs), or the use of state-of-the-art particle-incell codes for laser-plasma interactions. In combination with thetools already existing at the Laser Applications and Photonics group (ALF) at Universidad de Salamanca, these methods have enabled the simulation of extreme scenarios for the strong-field interaction of structured laser light with matter.; [ES] Esta tesis presenta un estudio teórico de las interacciones luzmateria de campos intesos mediante luz estructurada, en dos escenarios diferentes. La primera parte se centra en la generación y amplificación de campos magnéticos intensos y localmente aislados a través de la interacción de haces de luz estructurada con la materia, así como en la exploración de una de sus posibles aplicaciones. Los haces de luz estructurada ofrecen la posibilidad de desacoplar espacialmente las componentes eléctrica y magnética de un haz láser. Investigamos la amplificación de la componente magnetica longitudinal, en régimen paraxial, en haces vectoriales con polarización azimutal. Esta componente del campo magnético alcanza su valor máximo en una singularidad del campo eléctrico y, por lo tanto, queda localmente aislado de la distribución eléctrica circundante. Nuestro estudio sugiere que el campo magnético longitudinal, transportado por un haz láser azimutalmente polarizado, puede ser amplificado mediante la interacción con nanoantenas metálicas diseñadas a medida. Las posibles aplicaciones de estos campos magnéticos intensos y ultrarrápidos podrían abarcar desde el control de la dinámica de magnetización en materiales magnéticos, hasta la espectroscopía atómica y molecular o la manipulación de partículas. Como una potencial aplicación, exploramos el uso de campos magnéticos intensos y aislados para asistir el proceso de generación de armónicos de orden elevado (HHG, por sus siglas en inglés). Nuestros resultados demuestran que el proceso HHG asistido por campos magnéticos intensos, resulta en la emisión de espectros de armónicos de orden elevado extensos sin attochirp y, en consecuencia, a la producción de pulsos de attosegundos cercanos al límite de Fourier. La segunda parte de esta tesis está dedicada al estudio del proceso HHG usando diversos tipos de campos de luz estructurada, y a la influencia de dichos campos sobre las propiedades espaciales y temporales de la radiación de alta energía resultante. Seguimos una estrategia doble: la generación de nuevos campos de luz estructurada complejos en la escala de attosegundo y la optimización de la intensidad y propiedades de focalización de las fuentes de pulsos de attosegundo. En primer lugar, introducimos el uso de hollow-Gaussian beams como haz incidente en el proceso HHG para incrementar la intensidad de los pulsos de attosegundo. Estos haces permiten entregar una mayor cantidad de energía al blanco en comparación con los esquemas gaussianos tradicionales, manteniendo la intensidad por debajo del régimen de supresión de barrera. Nuestras simulaciones teóricas demuestran que esta configuración permite sistemas HHG más compactos y que, combinados con las propiedades de refocalización de los armónicos generados, resultan en pulsos de attosegundo hasta tres veces más intensos. Esta ganancia de intensidad podría permitir que las fuentes HHG se adapten mejor a aplicaciones que requieren flujos altos de fotones, como nanoimagen, metrología o espectroscopía. Los resultados experimentales preliminares realizados en el grupo de los Profs. Anne L’Huiller y Cord L. Arnold, en la Universidad de Lund (Suecia), corroboran las propiedades de los armónicos de orden elevado generados mediante hollow-Gaussian beams. Posteriormente, investigamos la conversión de vórtices espaciotemporales ópticos (STOVs, por sus siglas en inglés) desde el infrarrojo cercano al ultravioleta extremo a través del proceso HHG, con carga topológica alta. Desarrollamos un marco teórico para describir la dinámica de generación y propagación de STOVs en el ultravioleta extremo mediante HHG. Nuestras simulaciones teóricas concuerdan de manera excelente con las primeras observaciones experimentales de HHG generados mediante STOVs, realizadass por el grupo de los Profs. Margaret M. Murnane y Henry C. Kapteyn de la Universidad de Colorado en Boulder (Estados Unidos). Finalmente, proponemos un esquema para la generación de STOVs en el ultravioleta extremo mediante HHG en el que todos los armónicos se emiten en el campo lejano con la misma carga topológica. Esta configuración permite la síntesis de STOVs en escalas de attosegundo. Estos pulsos de attosegundo con topologías no triviales, acopladas en los dominios espacial y temporal, podrían resultar de gran interés para el estudio de dinámicas electrónicas ultrarrápidas en nuevos materiales o en experimentos de dicroísmo circular helicoidal. Esta tesis implica la comprensión y el desarrollo de diversos métodos y modelos numéricos avanzados, tales como la implementación de códigos altamente paralelizados para calcular la respuesta HHG basados en la ecuación de Schrödinger dependiente del tiempo en tres dimensiones, el desarrollo de software basado en unidades de procesamiento gráfico (GPU, por sus siglas en inglés) para el cálculo de la aproximación de campo fuerte (SFA, por sus siglas en inglés), o el uso de códigos de última generación de particle-in-cell para simulaciones de interacción láser-plasma. En combinación con las herramientas existentes en el grupo de Aplicaciones de Láser y Fotónica (ALF) de la Universidad de Salamanca, estos métodos han permitido la simulación de escenarios extremos para la interacción de luz láser estructurada, en el régimen de campo intensos, con la materia.

2025-01-01T00:00:00Z Merchán Corral, Rosa Pilar Santos Sánchez, María Jesús Reyes Ramírez, Israel Medina Domínguez, Alejandro Calvo Hernández, Antonio http://hdl.handle.net/10366/170014 2026-02-25T01:02:05Z 2017-02-15T00:00:00Z

[EN]The annual performance, fuel consumption and emissions of a hybrid thermosolar central tower Brayton plant is analyzed in yearly terms by means of a thermodynamic model. The model constitutes a step forward over a previously developed one, that was satisfactorily validated for fixed solar irradiance and ambient temperature. It is general and easily applicable to different plant configurations and power output ranges. The overall system is assumed as formed by three subsystems linked by heat exchangers: solar collector, combustion chamber, and recuperative Brayton gas-turbine. Subsystem models consider all the main irreversibility sources existing in real installations. This allows to compare the performance of a real plant with that it would have in ideal conditions, without losses. Furthermore, the improved version of the model is capable to consider fluctuating values of solar irradiance and ambient temperature. Numerical calculations are presented taking particular parameters from a real installation and actual meteorological data. Several cases are analyzed, including plant operation in hybrid or pure combustion modes, with or without recuperation. Previous studies concluded that this technology is interesting from the ecological viewpoint, but that to be compelling for commercialization, global thermal efficiency should be improved (currently yearly averaged thermal efficiency is about 30% for recuperative plants). We analyze the margin for improvement for each plant subsystem, and it is concluded that, the Brayton heat engine, by far, is the key element to improve overall thermal efficiency. Numerical estimations of achievable efficiencies are presented for a particular plant and real meteorological conditions.

2017-02-15T00:00:00Z Fernández Galán, Marina http://hdl.handle.net/10366/169668 2026-02-11T01:01:28Z 2022-01-01T00:00:00Z

[ES] Los pulsos láser ultracortos con duraciones límite por debajo del ciclo óptico son una herramienta indispensable para el avance de la ciencia ultrarrápida y prometen desvelar las dinámicas atómicas más fundamentales de la materia en la escala de tiempo sub-femtosegundo. Sin embargo, su generación y manipulación aún está limitada a montajes extremadamente costosos y complejos como los denominados sintetizadores de varios canales espectrales. En este trabajo estudiamos, a través de simulaciones numéricas, la generación de pulsos sub-ciclo en el infrarrojo cercano por medio de una técnica mucho más compacta: la auto-compresión solitónica en fibras huecas rellenas de gas con un gradiente de presión decreciente hasta vacío. En contra de lo que habitualmente se pensaba, demostramos la viabilidad de esta técnica en configuraciones experimentales estándar y proponemos una ruta general para encontrar, en cualquier situación, los parámetros del pulso inicial y de la fibra que optimizan el proceso. Comparando los resultados con los obtenidos en la situación más habitual de presión constante, demostramos también que el empleo de un gradiente decreciente favorece de forma natural el proceso de auto-compresión y retrasa la aparición de efectos indeseados como la fisión solitónica por la dispersión de orden alto o la ionización. Esto permite la generación de pulsos sub-ciclo de gran calidad, con duraciones menores, mayores potencia pico, espectros más anchos y un perfil temporal más limpio que los que se obtienen cuando el gas en el interior de la fibra se mantiene a presión constante.

2022-01-01T00:00:00Z Berrah, Chahinez http://hdl.handle.net/10366/169591 2026-02-08T03:03:29Z 2025-01-01T00:00:00Z

[ES] Esta tesis se centra principalmente en la generación, detección, caracterización y aplicación eficientes de pulsos láser ultracortos en el procesamiento de diversos materiales para aplicaciones biológicas y médicas. Para ello, se empleó un oscilador láser de Ti:Zafiro amplificado mediante un sistema de amplificación de pulsos, logrando duraciones de pulso cortas en el rango de femtosegundos, con una frecuencia de repetición de 5 kHz y una energía de hasta 1,6 mJ por pulso. Estos pulsos se sintonizan espectralmente mediante un amplificador paramétrico. La longitud de onda del pulso se modula mediante procesos no lineales, lo que permite sintonizarlo en un rango de 240 a 2400 nm. Este mecanismo permite que el láser de Ti:Zafiro sirva como fuente de pulsos ópticos ultracortos. Instrumentos como FROG o SPIDER se utilizan habitualmente para identificar pulsos ultracortos. Estos pulsos se caracterizan por su duración extremadamente corta, lo que permite la monitorización de procesos físicos, químicos y biológicos ultrarrápidos. Además, presentan un amplio ancho de banda espectral, alta intensidad y energía de pico debido a su concentración en un período de tiempo reducido. Se han caracterizado y optimizado numerosos parámetros experimentales, como el tamaño y la potencia del haz láser, la geometría de enfoque, el tiempo de tratamiento, las fibras ópticas utilizadas, entre otros, para lograr los objetivos deseados. Recientemente, las técnicas ópticas se han aplicado ampliamente en el diagnóstico, pronóstico y tratamiento médicos. Diversas técnicas de imagen óptica y espectroscopía han alcanzado un éxito significativo en la investigación médica y biológica. La fluorescencia con resolución temporal es una de estas técnicas y constituye una herramienta poderosa para el estudio de tejidos y células. El primer capítulo de esta tesis describe la fluorescencia con resolución temporal de dos muestras diferentes, BODIPY y DEXTRAN-TR, tras la excitación con un haz láser ultrarrápido. Optimizamos la configuración experimental para las mediciones de fluorescencia de los fluoróforos BODIPY y DEXTRAN-TR y diseñamos un programa MATLAB que permite la reconstrucción de la función de fluorescencia real. Este enfoque busca que esta técnica sea compatible con diversas aplicaciones biomédicas. Este trabajo tiene como objetivo investigar, desarrollar y validar la aplicación de la fluorescencia con resolución temporal en vasos sanguíneos, diagnóstico de tejidos médicos y cirugía oncológica. La configuración experimental se optimizó para maximizar la fluorescencia y determinar la resolución espectral. La fibra óptica fue uno de los componentes más importantes responsables de esto. El núcleo de la fibra actúa como una rendija de entrada y, por lo tanto, su tamaño afecta la precisión del dispositivo. Cuanto más estrecha y pequeña sea la abertura del núcleo, menor será la cantidad de fluorescencia capturada y mayor la resolución espectral. Por el contrario, cuanto más grande sea el núcleo de la fibra, mayor será la cantidad de luz capturada, que es el resultado deseado, obteniendo una señal de fluorescencia de mayor intensidad y logrando una mejor relación señal-detector. Para este propósito, se utilizaron fibras con un tamaño de rendija de 10 micrómetros y una resolución de entre 0,4 y 0,8 nanómetros. También se presentaron métodos de análisis, filtrado y procesamiento de datos para eliminar el ruido significativo y mostrar los tiempos de vida de la fluorescencia de las dos muestras. Las aplicaciones más importantes de esta tecnología se demostraron en la terapia fotodinámica basada en BODIPY, las sondas BODIPY para membranas lipídicas y los sensores de pH fluorescentes basados en BODIPY para membranas lipídicas. También se destacó la importancia del colorante DEXTRAN-TR en la adhesión celular, la diferenciación y el mantenimiento tisular, y el reconocimiento y la clasificación celular, además de medir la permeabilidad vascular y evaluar el equilibrio iónico. Esta técnica revela las propiedades únicas de los fluoróforos estudiados midiendo la intensidad de fluorescencia en función de la longitud de onda de la luz, midiendo así la fluorescencia transitoria resuelta en el tiempo a longitudes de onda específicas, caracterizando posteriormente estos fluoróforos y extrayendo sus propiedades más importantes. El segundo capítulo de esta tesis presenta un método flexible, preciso y reproducible para la fabricación de membranas porosas de PDMS mediante ablación láser de pulsos ultracortos, propuesto como una alternativa a las técnicas convencionales. Se microtaladraron de forma sistemática membranas de PDMS con espesores de 25, 50 y 100 microm para investigar la influencia de los principales parámetros del láser - energía por pulso y tiempo de apertura del obturador - sobre las dimensiones, geometría y calidad de los orificios consecuentes. Los resultados indican que la energía del pulso es el factor dominante que afecta a las dimensiones de los agujeros, mientras que los tiempos de apertura por encima de 1000 ms y el espesor de la membrana cuentan con un rol secundario. Se ha apreciado como una mayor energía total aportada incrementa el ángulo de conicidad de los orificios, y que la extensión de la zona afectada térmicamente está directamente relacionada con el diámetro del haz láser y el espesor de la membrana. Se desarrolló un modelo numérico para simular el proceso de ablación, incorporando el efecto de apantallamiento por plasma, y mostrando que la eliminación de material depende fuertemente de la energía del pulso. A partir de los datos experimentales, se formuló un modelo empírico para estimar la energía por pulso óptima para fabricar membranas con orificios de 10 microm de diámetro y una separacion de 40 microm. Las predicciones del modelo mostraron buena concordancia con las mediciones experimentales en cuanto al diámetro de salida de los orificios, mientras que se observaron mayores desviaciones en el diámetro de entrada. Finalmente, para validar la viabilidad biológica de las membranas producidas, se cultivaron células madre mesenquimales derivadas de tejido adiposo humano sobre las láminas de PDMS procesadas con láser y se integraron en dispositivos órgano-en-chip (Organ-on-chip, OoC). Las células mostraron una fuerte adhesión y una alta actividad metabólica, lo que confirma la idoneidad de este método de fabricación basado en láser para la manufactura de membranas de PDMS en sistemas OoC.; [EN] This thesis focuses primarily on the efficient generation, detection, characterization, and application of ultrashort laser pulses in the processing of various materials for biological and medical applications. For this purpose, a Ti:Sapphire laser oscillator amplified using a pulse amplification system was used, achieving short pulse durations in the femtosecond range with a repetition rate of 5 kHz and energy up to 1.6 mJ per pulse. These pulses are spectrally tuned using a parametric amplifier. The pulse wavelength is modulated through nonlinear processes, allowing it to be tuned within a range of 240 to 2400 nm. This mechanism enables the Ti:Sapphire laser to serve as a source of ultrashort optical pulses. Instruments such as FROG or SPIDER are typically used to characterize ultrashort pulses. These pulses are characterized by their extremely short duration, which allows for the monitoring of ultrafast physical, chemical, and biological processes. They also have a wide spectral bandwidth, high intensity, and high peak energy due to the energy being concentrated within a narrow time period. Many experimental parameters such as laser beam size and power, focusing geometry, treatment time, optical fibers used, and others have been characterized and optimized to achieve the desired goals. Recently, optical techniques have been widely applied in medical diagnosis, prognosis, and treatment. Several optical imaging and spectroscopy techniques have achieved significant success in medical and biological research. Time-resolved fluorescence is one of these techniques, and it is a powerful tool for studying tissues and cells. The first chapter of this thesis describes time-resolved fluorescence of two different samples, BODIPY and DEXTRAN-TR, after excitation with an ultrafast laser beam. We optimized the experimental setup for fluorescence measurements of both BODIPY and DEXTRAN-TR fluorophores and designed a MATLAB program that allows reconstruction of the real fluorescence function. This approach aims to make this technique compatible with various biomedical applications. This work aims to research, develop, and validate the application of time-resolved fluorescence within blood vessels, medical tissue diagnosis, and cancer surgery. The experimental setup was optimized to maximize fluorescence and determine the spectral resolution. The optical fiber was one of the most important components responsible for this. The fiber core acts as an input slit, and therefore its size affects the accuracy of the device. The narrower and smaller the opening of the core, the smaller the amount of fluorescence captured and the greater the spectral resolution. Conversely, the larger the fiber core, the greater the amount of light captured, which is the desired result, obtaining a higher-intensity fluorescence signal and achieving a better signal-to-detector ratio. For this purpose, fibers with a slit size of 10 micrometers and a resolution ranging from 0.4 to 0.8 nanometers were used. Data analysis, filtering, and processing methods were also presented to eliminate significant noise and display the fluorescence lifetimes of the two samples. The most important applications of this technology were demonstrated in BODIPY-based photodynamic therapy, BODIPY probes for lipid membranes, and fluorescent pH sensors based on BODIPY for lipid membranes. The importance of DEXTRAN-TR dye in cell adhesion, tissue differentiation and maintenance, and cell recognition and sorting were also highlighted, in addition to measuring vascular permeability and assessing ionic balance. This technique reveals the unique properties of the studied fluorophores by measuring the fluorescence intensity as a function of light wavelength, thus measuring the time-resolved transient fluorescence at specific wavelengths and then characterizing these fluorophores and extracting their most important properties. The second chapter of this thesis presents a flexible, precise and reproducible method for fabricating porous polydimethylsiloxane (PDMS) membranes using ultrashort pulse laser ablation, proposed as an alternative to conventional techniques. PDMS membranes with thicknesses of 25, 50 and 100 microm were systematically microdrilled to investigate the influence of key laser parameters - pulse energy and shutter time - on the dimensions, geometry and quality of the resulting holes. Results indicate that pulse energy is the dominant factor affecting pore dimensions, while shutter time above 1000 ms and thicknessplay a secondary role. Higher total energy increases the taper angle of the pores and the extent of the heat-affected zone is directly related to both the laser beam diameter and membrane thickness. A numerical model was developed to simulate the ablation process, incorporating plasma shielding and showing that material removal is strongly pulse energy-dependent. Based on experimental data, an empirical model was also developed to estimate the optimal pulse energy required to fabricate membranes with 10 microm hole diameters and 40 microm spacing. The model predictions showed good agreement with experimental measurements for the exit hole diameters, while larger deviations were observed for entry diameters. Finally, to validate the biological viability of the manufactured membranes, human adipose tissue-derived mesenchymal stem cells were cultured on the laser-processed PDMS films integrated into Organ-on-Chip (OoC) devices. The cells exhibited strong cell adhesion and high metabolic activity, confirming the suitability of this laser-based fabrication method for the development of PDMS membranes in OoC systems.

2025-01-01T00:00:00Z Delgado Notario, Juan Antonio Stephen, R. Power Knap, Wojciech Pino, Manuel Vaquero Monte, Daniel Taniguchi, Takashi Velázquez Pérez, Jesús Enrique Meziani, Yahya Moubarak Alonso Gonzalez, Pablo Caridad Hernández, José Manuel http://hdl.handle.net/10366/169326 2026-01-28T01:00:33Z 2025-01-01T00:00:00Z

[EN]Moiré superlattices formed at the interface between stacked 2D atomic crystals offer limitless opportunities to design materials with widely tunable properties and engineer intriguing quantum phases of matter. However, despite progress, precise probing of the electronic states and tantalizingly complex band textures of these systems remain challenging. Here, we present gate-dependent terahertz photocurrent spectroscopy as a robust technique to detect, explore, and quantify intricate electronic properties in graphene moiré superlattices. Specifically, using terahertz light at different frequencies, we demonstrate distinct photocurrent regimes, evidencing the presence of avoided band crossings and tiny (∼1 to 20 meV) inversion-breaking global and local energy gaps in the miniband structure of minimally twisted graphene and hexagonal boron nitride heterostructures, key information that is inaccessible by conventional electrical or optical techniques. In the off-resonance regime, when the radiation energy is smaller than the gap values, enhanced zero-bias responsivities arise in the system due to the lower Fermi velocities and specific valley degeneracies of the charge carriers subjected to moiré superlattice potentials. In stark contrast, the above-gap excitations give rise to bulk photocurrents-intriguing optoelectronic responses related to the geometric Berry phase of the constituting electronic minibands. Besides their fundamental importance, these results place moiré superlattices as promising material platforms for advanced, sensitive, and low-noise terahertz detection applications.

2025-01-01T00:00:00Z Ordoñez Mendieta, Ángel José Sánchez Hernández, Esteban http://hdl.handle.net/10366/168013 2025-11-28T01:01:33Z 2021-02-04T00:00:00Z

[EN]As grid parity is reached in many countries, photovoltaic self-consumption is raising great interest. Currently, there is a big number of new projects being developed in Spain thanks to the new regulation. From the experience of the monitoring of one full year of operation of a self-consumption PV plant in a university building, a regulatory, energy, and economic analysis is made for this type of building. It has been carried out by simulating the behavior of the building with installations within the range of PV powers allowed in the Spanish regulation. The analysis shows the good fitting between the new Royal Decree of Self-Consumption and the new Building Code. The economic analysis proves that the new simplified compensation method gives the best economic return for this use of the buildings when the PV production is matched with the consumption. The time of return of investment is between 8 and 9 years, and the levelized cost of electricity (LCOE) is into the range of the pool market price of electricity. These results show the profitability of PV self-consumption for this type of building.

2021-02-04T00:00:00Z Parra Domínguez, Javier Sánchez Hernández, Esteban Ordoñez Mendieta, Ángel José http://hdl.handle.net/10366/168007 2025-11-27T01:01:04Z 2023-07-04T00:00:00Z

[EN]The deployment of distributed and affordable renewable energy has led to the development of the prosumer concept in the field of energy. To better understand its relevance and to analyse the main trends and research developments, a systematic literature review was performed. This work gathered 1673 articles related to this topic that were analysed following the PRISMA methodology with the help of VOSviewer 1.6.18 bibliometric software. These papers are classified into four clusters: smart grids, microgrids, peer to peer networks, and prosumers. The first two clusters show a certain degree of maturity, while the latter maintain a growing interest. The analysis of the articles provides a broad view of the prosumer’s role in energy and its potential, which is not limited to simple energy exchanges. Furthermore, this systematic review highlights the challenges, not only technical but also in terms of electricity market design and social aspects. The latter require further research, as society is undergoing a paradigm shift in the way in which energy is produced and used. How this shift occurred will determine whether it can lead to true prosumer empowerment and a fairer energy transition.

2023-07-04T00:00:00Z Delgado Notario, Juan Antonio López Díaz, David McCloskey, David Caridad Hernández, José Manuel http://hdl.handle.net/10366/166706 2025-07-30T00:02:20Z 2024-01-01T00:00:00Z

[EN] The photothermal conversion in plasmonic nanohelices is studied, unveiling how helical nanostructures made from metals with a notable interband activity -such as cobalt (Co) and nickel (Ni)- exhibit a remarkable temperature rise 𝚫T up to ≈1000 K under illumination. Such outstanding 𝚫T values exclusively occur at wavelengths close to their localized plasmon resonances (𝚫T is significantly lower off resonance), and therefore the photothermal conversion of these nanoparticles is spectrally selective. The exceptional and spectrally selective temperature rise is demonstrated at near infrared (NIR) wavelengths, which prompts the use of Co and Ni helical nanoparticles in a wide range of photothermal applications including solar energy conversion, seawater desalination, catalysis, or nanomedicine.

2024-01-01T00:00:00Z Velázquez Pérez, Jesús Enrique Titov, O.Yu Gurevich, Yuri G. http://hdl.handle.net/10366/163269 2025-04-30T19:46:09Z 2023-01-01T00:00:00Z

[EN]Solar cells rely on photogeneration of charge carriers in p-n junctions and their transport and subsequent recombination in the quasineutral regions. Several basic issues concerning the physics of the operation of solar cells remain obscure. This paper discusses some of those unsolved basic problems. In conventional solar cells, recombination of photogenerated charge carriers plays a major limiting role in the cell efficiency. High quality thin-film solar cells may overcome this limit if the minority diffusion lengths become large as compared to the cell dimensions, but, strikingly, the conventional model fails to describe the cell electric behavior under these conditions. A new formulation of the basic equations describing charge carrier transport in the cell along with a set of boundary conditions is presented. An analytical closed-form solution is obtained under the linear approximation. It is shown that the calculation of the open-circuit voltage of the solar cell diode does not lead to unphysical results in the new given framework.

2023-01-01T00:00:00Z Castelló, O. López Baptista, Sofia M. Watanabe, K. Taniguchi, T. Díez Fernández, Enrique Velázquez Pérez, Jesús Enrique Meziani, Yahya Moubarak Caridad Hernández, José Manuel Delgado Notario, Juan Antonio http://hdl.handle.net/10366/163234 2025-04-30T19:46:09Z 2024-01-01T00:00:00Z

[EN]In recent years, graphene field-effect-transistors (GFETs) have demonstrated an outstanding potential for terahertz (THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune (decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors.

2024-01-01T00:00:00Z Delgado Notario, Juan Antonio Calvo Gallego, Jaime Velázquez Pérez, Jesús Enrique Ferrando-Bataller, Miguel Fobelets, Kristel Meziani, Yahya Moubarak http://hdl.handle.net/10366/162271 2025-04-30T19:46:09Z 2020-01-01T00:00:00Z

[EN]Plasma waves in semiconductor gated 2-D systems can be used to efficiently detect Terahertz (THz) electromagnetic radiation. This work reports on the response of a strained-Si Modulation-doped Field-Effect Transistor (MODFET) under front and back sub-THz illumination. The response of the MODFET has been characterized using a two-tones solid-state continuous wave source at 0.15 and 0.30 THz. The DC drain-to-source voltage of 500-nm gate length transistors transducing the sub-THz radiation (photovoltaic mode) exhibited a non-resonant response in agreement with literature results. Two configurations of the illumination were investigated: (i) front side illumination in which the transistor was shined on its top side, and (ii) back illumination side where the device received the sub-THz radiation on its bottom side, i.e., on the Si substrate. Under excitation at 0.15 THz clear evidence of the coupling of terahertz radiation by the bonding wires was found, this coupling leads to a stronger response under front illumination than under back illumination. When the radiation is shifted to 0.3 THz, as a result of a lesser efficient coupling of the EM radiation through the bonding wires, the response under front illumination was considerably weakened while it was strengthened under back illumination. Electromagnetic simulations explained this behavior as the magnitude of the induced electric field in the channel of the MODFET was considerably stronger under back illumination.

2020-01-01T00:00:00Z Abidi, El Hadj Khan, Ayaz H. Delgado Notario, Juan Antonio Clericò, Vito Calvo Gallego, Jaime Taniguchi, Takashi Watanabe, Kenji Otsuji, Taiichi Velázquez Pérez, Jesús Enrique Meziani, Yahya Moubarak http://hdl.handle.net/10366/162266 2026-01-27T10:17:43Z 2024-01-01T00:00:00Z

[EN]An asymmetric dual-grating gate bilayer graphene-based field effect transistor (ADGG-GFET) with an integrated bowtie antenna was fabricated and its response as a Terahertz (THz) detector was experimentally investigated. The device was cooled down to 4.5 K, and excited at different frequencies (0.15, 0.3 and 0.6 THz) using a THz solid-state source. The integration of the bowtie antenna allowed to obtain a substantial increase in the photocurrent response (up to 8 nA) of the device at the three studied frequencies as compared to similar transistors lacking the integrated antenna (1 nA). The photocurrent increase was observed for all the studied values of the bias voltage applied to both the top and back gates. Besides the action of the antenna that helps the coupling of THz radiation to the transistor channel, the observed enhancement by nearly one order of magnitude of the photoresponse is also related to the modulation of the hole and electron concentration profiles inside the transistor channel by the bias voltages imposed to the top and back gates. The creation of local n and p regions leads to the formation of homojuctions (𝑛𝑝 , 𝑝𝑛 or 𝑝𝑝+) along the channel that strongly affects the overall photoresponse of the detector. Additionally, the bias of both back and top gates could induce an opening of the gap of the bilayer graphene channel that would also contribute to the photocurrent.

2024-01-01T00:00:00Z Minin, Igor V. Minin, Oleg V. Delgado Notario, Juan Antonio Calvo Gallego, Jaime Velázquez Pérez, Jesús Enrique Ferrando-Bataller, Miguel Meziani, Yahya Moubarak http://hdl.handle.net/10366/162257 2025-04-30T19:46:10Z 2020-01-01T00:00:00Z

[EN]Herein, a simple terahertz (THz) receiver that uses subwavelength focusing of the THz beam on the detector area is proposed. As a proof of concept, a THz detection system with an original optical coupling scheme is implemented, where the signal to be detected is coupled to a THz detector through a mesoscale dielectric particle lens. Coherent detection is successfully demonstrated with an enhancement of the detector sensitivity of about 4.3 dB, compared with that of a direct detection system with the slight decreasing (≈1.67 times) of noise equivalent power value. The results show that the proposed method can reduce the size and increase the sensitivity of various THz systems, including imaging, sensing, and ranging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, security, etc.

2020-01-01T00:00:00Z Delgado Notario, Juan Antonio Clericò, Vito Díez Fernández, Enrique Velázquez Pérez, Jesús Enrique Taniguchi, Takashi Watanabe, Kenji Otsuji, Taiichi Meziani, Y. M. http://hdl.handle.net/10366/162235 2025-04-30T19:46:10Z 2020-01-01T00:00:00Z

[EN]A graphene-based field-effect-transistor with asymmetric dual-grating gates was fabricated and characterized under excitation of terahertz radiation at two frequencies: 0.15 THz and 0.3 THz. The graphene sheet was encapsulated between two flakes of h-BN and placed on a highly doped SiO2/Si substrate. An asymmetric dual-grating gate was implemented on the h-BN top flake. Even though no antenna was used to couple the incoming radiation, a clear gate-bias-dependent photocurrent was measured under excitation at 0.3 THz up to room temperature. We subsequently demonstrated that the device can be used for terahertz sensing and inspection of hidden metallic objects at room temperature.

2020-01-01T00:00:00Z Raposo Funcia, Víctor Javier López Díaz, Luis Martínez Vecino, Eduardo http://hdl.handle.net/10366/161241 2024-12-18T01:01:24Z 2024-01-01T00:00:00Z

[ES] El principal objetivo de este trabajo ha sido fomentar la participación de los estudiantes en el desarrollo de las clases. Para ello hemos introducido herramientas de gamificación en el aula en asignaturas del área de Electromagnetismo impartidas en el Grado en Fisicas. La principal herramienta utilizada ha sido la aplicación Kahoot! pero también se han utilizado cuestionarios dentro de la plataforma Studium. Ambos sistemas constituyen una herramienta de encuestas en tiempo real donde los estudiantes pueden afianzar los conocimientos adquiridos de forma entretenida, como si fuera un concurso y ayuda también a mejorar la interacción con los alumnos más reacios.

2024-01-01T00:00:00Z