Chirped seeded free-electron lasers: self-standing light sources for two-colour pump-probe experiments

We demonstrate the possibility to run a single-pass free-electron laser in a new dynamical regime, which can be exploited to perform two-colour pump-probe experiments in the VUV/X-ray domain, using the free-electron laser emission both as a pump and as a probe. The studied regime is induced by triggering the free-electron laser process with a powerful laser pulse, carrying a significant and adjustable frequency chirp. As a result, the emitted light is eventually split in two sub-pulses, whose spectral and temporal separations can be independently controlled. We provide a theoretical description of this phenomenon, which is found in good agreement with experiments performed on the FERMI@Elettra free-electron laser

Realidad Aumentada y stellarium: astronomía para niños y niñas de cinco años

Los educadores están llamados a favorecer la alfabetización digital, introduciendo las distintas herramientas tecnológicas con fines educativos ya que son parte del uso cotidiano de los niños y niñas. La Realidad Aumentada y el programa Stellarium, son poderosas herramientas para la enseñanza de la Astronomía, ya que permiten observar las estrellas, constelaciones y sistema solar, facilitando la explicación de los fenómenos celestes al educador/a. El presente estudio tuvo como objetivo analizar la intervención educativa con Realidad Aumentada y el programa Stellarium, en el desarrollo de lenguaje astronómico, específicamente el aspecto semántico y morfosintáctico sobre el sistema solar, estrellas y constelaciones, para niños y niñas de cinco años de edad. La intervención educativa fue llevada a cabo en el Aula Didáctica de la Universidad de Playa Ancha y aplicada a los niños y niñas del Nivel de Transición Mayor, de tres establecimientos municipales: Liceo San Felipe y las Escuelas Almendral y José Bernardo Suárez. Por medio de un estudio cuasi experimental (pre y post test), se analizó el avance que tuvieron los cincuenta y tres niños y niñas que participaron del estudio a través de dos test. Los resultados obtenidos evidenciaron el avance en el lenguaje científico al reconocer elementos del universo —aspecto semántico— expresar ideas y explicaciones sobre eventos astronómicos —aspecto morfosintáctico— que los niños y niñas conoció en la intervención educativa.// Educators are called to favor digital literacy, introducing the different technological tools for educational purposes since they are part of the daily use of children. Augmented reality and the Stellarium program are powerful tools for teaching astronomy, since they allow observing the stars, constellations and solar system, facilitating the explanation of celestial phenomena to the educator. The objective of this study was to analyze the educational intervention with augmented reality and the Stellarium program, in the development of astronomical language, specifically the semantic and morphosyntactic aspect of the solar system, stars and constellations, for five-year-old boys and girls. The educational intervention was carried out in the Didactic Classroom of the University of Playa Ancha and applied to the children of the Major Transition Level, of three municipal establishments: Liceo San Felipe and the Almendral and José Bernardo Suárez Schools. Through a quasi-experimental study (pre and post test), the progress of the fifty-three boys and girls who participated in the study through two tests was analyzed. The results obtained evidenced the progress in scientific language by recognizing elements of the universe —semantic aspect— expressing ideas and explanations about astronomical events —morphosyntactic aspect— that children knew in the educational intervention

Transient polarization dynamics in a CO2_2 laser

We study experimentally and theoretically the polarization alternation during the switch-on transient of a quasi-isotropic CO$_2$ laser emitting on the fundamental mode. The observed transient dynamics is well reproduced by means of a model which provides a quantitative discrimination between the intrinsic asymmetry due to the kinetic coupling of molecules with different angular momenta, and the extrinsic anisotropies, due to a tilted intracavity window. Furthermore, the experiment provides a numerical assignment for the decay rate of the coherence term for a CO$_2$ laser.Comment: 14 pages, 6 figures, submitted to Opt. Com

Delayed Self-Synchronization in Homoclinic Chaos

The chaotic spike train of a homoclinic dynamical system is self-synchronized by re-inserting a small fraction of the delayed output. Due to the sensitive nature of the homoclinic chaos to external perturbations, stabilization of very long periodic orbits is possible. On these orbits, the dynamics appears chaotic over a finite time, but then it repeats with a recurrence time that is slightly longer than the delay time. The effect, called delayed self-synchronization (DSS), displays analogies with neurodynamic events which occur in the build-up of long term memories.Comment: Submitted to Phys. Rev. Lett., 13 pages, 7 figure

Spectro-temporal shaping of seeded free-electron laser pulses

We demonstrate the ability to control and shape the spectro-temporal content of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser (FEL). The control over the spectro-temporal properties of XUV light was achieved by precisely manipulating the linear frequency chirp of the seed laser. Our results agree with existing theory, which allows retrieving the temporal properties (amplitude and phase) of the FEL pulse from measurements of the spectra as a function of the FEL operating parameters. Furthermore, we show the first direct evidence of the full temporal coherence of FEL light and generate Fourier limited pulses by fine-tuning the FEL temporal phase. The possibility to tailor the spectro-temporal content of intense short-wavelength pulses represents the first step towards efficient nonlinear optics in the XUV to X-ray spectral region and will enable precise manipulation of core-electron excitations using the methods of coherent quantum control.Comment: 5 pages, 3 figure