Spectral self-action of THz emission from ionizing two-color laser pulses in gases

The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and finite-difference-time-domain simulations in 1D and 2D geometries. We show that produced THz signals interact with free electron trajectories and thus influence significantly further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action plays a key role in the observed strong spectral broadening of the generated THz field. Diffraction limits the achievable THz bandwidth by efficiently depleting the low frequency amplitudes in the propagating field.Comment: 12 pages, 6 figure

Slow light in molecular aggregates nanofilms

We study slow light performance of molecular aggregates arranged in nanofilms by means of coherent population oscillations (CPO). The molecular cooperative behavior inside the aggregate enhances the delay of input signals in the GHz range in comparison with other CPO-based devices. Moreover, the problem of residual absorption present in CPO processes, is removed. We also propose an optical switch between different delays by exploiting the optical bistability of these aggregates.Comment: 4 pages, 4 figure

Guide to Jupyter Notebooks for educational purposes

Actualización del "Manual de uso de IPython Notebook para docentes" publicado” (http://eprints.ucm.es/29686). Esta nueva edición del manual cuyo titulo es “Manual de uso de Jupyter Notebook para aplicaciones docentes” incluye como elemento principal la transición que hubo desde el software IPython Notebook hasta el software Jupyter Notebook con posterioridad al 2013 cuando se redactó el manual original. Otra extensión fundamental que se ha incluído en el nuevo manual es el estudio sobre gestión de cursos y herramientas de autocorrección realizado en nuestro proyecto “Nuevas herramientas de software libre para la corrección automática de ejercicios complejos” (2015)”

Manual de uso de Jupyter Notebook para aplicaciones docentes

Actualización del "Manual de uso de IPython Notebook para docentes" publicado” (http://eprints.ucm.es/29686). Esta nueva edición del manual cuyo titulo es “Manual de uso de Jupyter Notebook para aplicaciones docentes” incluye como elemento principal la transición que hubo desde el software IPython Notebook hasta el software Jupyter Notebook con posterioridad al 2013 cuando se redactó el manual original. Otra extensión fundamental que se ha incluído en el nuevo manual es el estudio sobre gestión de cursos y herramientas de autocorrección realizado en nuestro proyecto “Nuevas herramientas de software libre para la corrección automática de ejercicios complejos” (2015)”

Directionality of THz emission from photoinduced gas plasmas

Forward and backward THz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semi-analytical model based on Jefimenko's equation and rigorous Maxwell simulations in one and two dimensions. We find the emission in backward direction having a much smaller spectral bandwidth than in forward direction and explain this by interference effects. Forward THz radiation is generated predominantly at the ionization front and thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model

Increasing applicability of slow light in molecular aggregate nanofilms with two-exciton dynamics

We study the slow-light performance in the presence of exciton – exciton interaction in films of linear molecular aggregates at the nanometer scale. In particular, we consider a four-level model to describe the creation/annihilation of two-exciton states that are relevant for high-intensity fields. Numerical simulations show delays comparable to those obtained for longer propagation distances in other media. Two-exciton dynamics could lead to larger fractional delays, even in presence of disorder, in comparison to the two-level approximation. We conclude that slow-light performance is a robust phenomenon in these systems under the increasing complexity of the two-exciton dynamics

The Hall of the Kingdoms of the Buen Retiro Palace as an improvised 3D-model room (1779-1803)

[EN] During the Modern Age, various European courts consolidated the tradition of the manufacture of plans-reliefs of fortified cities as a complement to other forms of representation (maps and plans) used within the military field. In this context, the Hall of Kingdoms of the Buen Retiro Palace functioned as an improvised 3D-model room at the end of the 18th century. The plan-relief of Cadiz was installed therein as the sole model built as part of the global project promoted by King Charles of Spain III in 1776 for the manufacture of models of strongholds of the kingdom. After the usefulness of this first model was questioned, the project was abandoned, although the room did later house another seven models. The identity of these deposited models, the time period, and the circumstances under which this room was utilised as a 3D-model room constitute the subject of this research.[ES] Durante la Edad Moderna diversas cortes europeas consolidaron como tradición la fabricación de planos en relieve de ciudades fortificadas, complemento a otras formas de representación -mapas y planos- empleadas dentro del ámbito militar. En este contexto, el Salón de los Reinos del Palacio del Buen Retiro funcionó como un improvisado cuarto de modelos a finales del siglo XVIII. En él quedó instalado el modelo de Cádiz, único elaborado al amparo del proyecto global para la fabricación de maquetas de plazas fuertes del Reino, promovido por Carlos III (1776). Tras cuestionarse la utilidad de este primer modelo el proyecto fue abortado, si bien la estancia albergó siete modelos más con posterioridad. La identidad de las maquetas depositadas, el periodo de tiempo y las circunstancias en las que fue utilizado como cuarto de modelos son objeto de investigación.Granado-Castro, G.; Aguilar-Camacho, J.; Cabrera-Revuelta, E. (2023). El Salón de los Reinos del Palacio del Buen Retiro como improvisado cuarto de maquetas (1779-1803). EGA Expresión Gráfica Arquitectónica. 28(49):138-149. https://doi.org/10.4995/ega.2023.19030138149284

Competition between the Modulation Instability and Stimulated Brillouin Scattering in a Broadband Slow Light Device

We observe competition between the modulation instability (MI) and stimulated Brillouin scattering (SBS) in a 9.2-GHz broadband SBS slow light device, in which a standard 20-km-long single-mode LEAF fibre is used as the SBS medium. We find that MI is dominant and depletes most of the pump power when we use an intense pump beam at ~1.55 {\mu}m, where the LEAF fibre is anomalously dispersive. The dominance of the MI in the LEAF-fibre-based system suppresses the SBS gain, degrading the SBS slow light delay and limiting the SBS gain-bandwidth to 126 dB \cdot GHz. In a dispersion-shifted highly nonlinear fibre, the SBS slow light delay is improved due to the suppression of the MI, resulting in a gain-bandwidth product of 344 dB \cdot GHz, limited by our available pump power of 0.82 W

Evolution of the Correlation between Orthogonal Polarization Patterns in Broad-Area Lasers

We measure polarization-resolved instantaneous patterns in a large-aspect ratio quasi-isotropic Nd:YAG laser. High correlation between the instantaneous orthogonal polarization patterns recorded at the earlier stages of the laser pulse has been found due to the strong cross saturation between both polarization modes

THz and far-infrared radiation from ionizing multi-color pulses

International audienceResearch on intense terahertz (THz) electromagnetic sources has received an increasing attention owing to numerous applications, for example, in time-domain spectroscopy, biomedical imaging or security screening. Here, THz emission in gases via ionizing multi-color femtosecond pulses is analyzed by means of semi-analytical models and finite-difference-time-domain simulations in 1D and 2D geometries. We find the emission in backward direction having a much smaller spectral bandwidth than in forward direction and explain this by interference effects. Forward THz radiation is generated predominantly at the ionization front and thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model. Moreover, we show that produced THz signals interact with free electron trajectories andthus influence significantly further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action plays a key role in the observed strong spectral broadening of the generated THz field in forward direction. Diffraction limits the achievable THz bandwidth by efficiently depleting the low frequency amplitudes in the propagating field