Matthieu Guer, a member of the École Nórmale Supérieure de Lyon who is doing a research stay in the Laser and Photonics Applications group (ALF – USAL), will give the seminar entitled “How do photons combine in non-perturbative physics?”.
The seminar will take place on Thursday, February 24 at 09:15 in Aula VII in the Trilingual Building of the University of Salamanca.
In spite of having an extremely short life, of just a few quadrillionths of a second, ultrashort femtosecond laser pulses have become an indispensable tool in many areas of science and technology, as they allow to probe the most fundamental properties of matter on ultrafast time scales.
Generating these such short pulses of light in a controlled manner and with a good quality is not an easy task, and in the last years various strategies have been proposed. The main idea is to generate a very wide light spectrum, made up of many frequencies, by means of nonlinear processes starting from a narrower one, and then correcting its phase to synchronize all the frequencies, giving rise to an ultrashort pulse. A widely used method to achieve this large spectral broadening is to propagate an initial light pulse through a hollow cylindrical fiber filled with a gas. In this case, one of the parameters that most influences the propagation is the pressure of the filling gas, which allows for a continuous tuning of the dispersion and the intensity of the nonlinear effects experienced by the pulse. In particular, if the fiber and gas parameters are carefully chosen, the incident pulse can broaden its spectrum while correcting its phase due to the interaction between the linear and nonlinear processes. In this way, the pulse reduces its duration on its own, in a process known as soliton self-compression.
Usually, these experiments are carried out keeping the gas at constant pressure, homogeneously filling the fiber. However, in one of our latest studies we have shown that applying a decreasing pressure gradient, causing the gas concentration to gradually decrease during propagation, can improve the quality of the self-compressed pulses and reduce their duration even more than constant pressure.
You can look up for all the details of this work at:
F. Galán, E. C. Jarque, and J. San Roman, Optimization of pulse self-compression in hollow capillary fibers using decreasing pressure gradients, Optics Express 30(5), 6755–6767 (2022). https://doi.org/10.1364/OE.451264
The University of Salamanca (Spain) invites application for a 3-year PhD Student position to obtain a PhD degree in Physics, starting in September 2022. The position is part of the project ATTOSTRUCTURA, “Structured attosecond pulses for ultrafast nanoscience”, funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 851201), supervised by Dr. Carlos Hernández-García, and with a duration of 5 years.
Application deadline: May 2nd 2022
The PhD candidate will enroll the project “Structured attosecond pulses for ultrafast nanoscience” at the Laser Applications and Photonics Research group (ALF-USAL) at University of Salamanca (https://laser.usal.es/alf/en/home/). The candidate will find a dynamic and international working environment, and will enrol in the theoretical group. ALF-USAL is an interdisciplinary Optics research group with expertise in both theory (strong-field physics, nonlinear optics, ultrafast phenomena, attosecond science) and experiments (ultrashort pulse characterization, pulse shaping, photonic crystals, ultrashort micro-machining). The candidate will explore the generation and ultrashort structured pulses and their application in ultrafast magnetism, an emerging field that is opening exciting scenarios in laser-matter interaction at the most fundamental level, merging the fields of Optics and Magnetism.
Some of the recent results have been published in high impact factor scientific journals:
-“Generation of extreme-ultraviolet beams with time-varying orbital angular momentum”, L. Rego, K. M. Dorney, N. J. Brooks, Q. Nguyen, C-T. Liao, J. San Román, D. E. Couch, Allison Liu, E. Pisanty, M. Lewenstein, L. Plaja, H. C. Kapteyn, M. M. Murnane, C. Hernández-García, Science 364, eaaw9486 (2019). Highlighted in the media:
-“Controlling the polarization and vortex charge of attosecond high-harmonic beams via simultaneous spin-orbit momentum conservation”, K. M. Dorney, L. Rego, N. Brooks, J. San Román, C-T. Liao, J. L. Ellis, D. Zusin, C. Gentry, Q. Nguyen, J. M. Shaw, A. Picón, L. Plaja, H. C. Kapteyn, M. M. Murnane, C. Hernández-García, Nature Photonics 13, 123–130 (2019).
-“Extreme-Ultraviolet Vector-Vortex Beams from High Harmonic Generation“, Alba de las Heras, Alok P. Pandey, Julio San Román, Javier Serrano, Elsa Baynard, Guillaume Dovillaire, Moana Pittman, Charles Durfee, Luis Plaja, Sophie Kazamias, Olivier Guilbaud, Carlos Hernández-García, Optica 9, 71-79 (2022).
-“Necklace-structured high harmonic generation for low-divergence, soft X-ray harmonic combs with tunable line spacing”, Laura Rego, Nathan J. Brooks, Quynh L. D. Nguyen, Julio San Román, Iona Binnie, Luis Plaja, Henry C. Kapteyn, Margaret M. Murnane, Carlos Hernández-García, Science Advances 8, eabj7380 (2022).
The candidate will explore the application of Artificial Intelligence to the Physics behind the generation of ultrashort structured pulses, an emerging field that is opening exciting scenarios in laser-matter interaction at the most fundamental level, merging the fields of Optics and Computing Sciences. The candidate will be advised thus by two experts in each of those fields:
Interested candidates should send a CV (maximum 3 pages), a complete list of grades during his/herdegree and Master program, a personal statement with interests and reasons for applying, and two recommendation letters to Dr. Carlos Hernández-García at alf@usal.es.
For further information and inquiries see Euraxess web page, or contact Dr. Carlos Hernández-García at alf@usal.es.
SELECTION PROCESS
The selection process is governed by the principles of publicity, equality, merit, and ability, constituting the effect one selecting body composed of representatives of the group of research of USAL.
The selection process will consist of two phases:
SELECTION COMMISSION
The selection commission will be made up of the two co-advisors, Dr. Javier Serrano and Dr. Carlos Hernández-García, and one member of the research team Laser Applications and Photonics Research group (ALF-USAL) at Universidad de Salamanca.
More information about the project, the position and the application process can be found Euraxess web page.
The newspaper El Mundo in its supplement Innovadores Castilla y León publishes a report on the new investigation being carried out by the ALF – USAL Group.
This research demonstrates the production of a type of laser beam in the extreme ultraviolet with a special design in phase and polarization.
In this type of beam, the polarization distribution is linked to the phase structure. These light forms are called vector vortices, because the structure is analogous to that of a whirlpool with different directions of vibration. It is, therefore, a light beam that combines the properties of the orbital angular momentum of light associated with the optical vortices with those of the spin angular momentum of the light particles, which defines the polarization.
The study from which the results presented in the publication have been obtained is the result of the collaboration between the ALF – USAL Group with the Paris-Saclay University and the Colorado School of Mines and is part of the European project ERC ATTOSTRUCTURA (851201)
You can read the article below and consult the review published on the article on our website.
On February 2nd, Carlos Hernández García, Ramón y Cajal researcher, member of the Laser and Photonic Applications research group and principal investigator of the Attostructura project (ERC 851201) gave the seminar “Structuring ultrafast laser light through highly nonlinear physics” within the cycle of seminars of the Rocasolano Institute of the CSIC.
The degree of control we have achieved over the manipulation of light is truly amazing. Initiated by our Greek ancestors using mirrors to guide light, we live in a world where the most advanced laser technology allows us to create and sculpt light beams with great precision. In particular, nowadays we can create ultrashort attosecond pulses (with durations of trillionths of a second), of very high frequencies (up to the soft X-rays), and with increasingly complex spatial structures thanks to our ability to harness their angular momentum. In this talk we will review our recent work in the generation of structured ultrashort laser pulses. Thanks to the highly nonlinear process of high harmonic generation, we can tailor the spin and orbital angular momentum properties of extreme ultraviolet/soft x-ray laser pulses directly at their generation. By properly controlling the process of high harmonic generation, from the driving laser beam to the target (gas or solid), different families of structured ultrashort laser beams can be created: self-torqued beams, vector-vortex beams, tunable high-frequency combs, or hexagonal harmonic beams. These new optical tools allow us to fantasize of new laser-matter interaction processes at the nanoscale, whose physical laws are yet to be discovered. For example, structured laser pulses offer an appealing alternative to study sub-femtosecond magnetization dynamics, where a complete understanding of the electronic and spin interactions remains unexplored
You can see the full video of the seminar on this page or on Youtube channel of the Rocasolano Institute.
Several media outlets have echoed the publication of a new research article by the ALF – USAL Group in the prestigious Optica magazine. It demonstrates the production of a type of laser beam in the extreme ultraviolet with a special design in phase and polarization.
In this type of beam, the polarization distribution is linked to the phase structure. These light forms are called vector vortices, because the structure is analogous to that of a whirlpool with different directions of vibration. It is, therefore, a light beam that combines the properties of the orbital angular momentum of light associated with the optical vortices with those of the spin angular momentum of the light particles, which defines the polarization.
The authors explain that “the fundamental idea is to control the properties of ultraviolet light by acting on the initial infrared light, thanks to the fact that all the information is encoded in the physical laws of conservation.” In fact, in this study a new conserved quantity is also discovered in the harmonic generation process, the Pancharatnam topological charge, which includes in its definition both the spin and the orbital angular momentum of the light beam.
The study from which the results presented in the publication have been obtained is the result of the collaboration between the ALF – USAL Group with the Paris-Saclay University and the Colorado School of Mines and is part of the European project ERC ATTOSTRUCTURA (851201)
Full report can be read at Salamanca24horas or Divulgación Científica de la USAL web page.
Article review published on the article can be consulted on our website.
The prestigious journal Optica has just published a new article demonstrating the generation of high-frequency light with multiple vibration directions and a spiral phase structure. The research is the result of an international theoretical-experimental collaboration between the Laser and Photonics Applications Group of the University of Salamanca, the University of Paris-Saclay and the Colorado School of Mines. This work was developed within the European project ERC ATTOSTRUCTURA.
One of the great advantages of laser light is that we can shape its spatial properties, with the aim of exploring new scenarios in light-matter interaction and optimizing some applications such as imaging techniques or optical communications.
In this work we organize the distribution of the phase (the instantaneous oscillation position) in the form of a helix, which is the characteristic of optical vortices or “tornadoes of light”. In addition, we configure different polarizations (oscillation directions) in a single laser beam. Forms of light that combine both properties are called vector-vortex beams.
In the high-frequency regime, it is more challenging to structure laser light, since most conventional devices are not efficient for ultraviolet radiation, X-rays or gamma rays. However, we can circumvent this problem thanks to the generation of high-order harmonics. This nonlinear optics process, in which a high-intensity visible or infrared laser interacts with the atoms of a gas, allows us to up-convert the properties into the extreme ultraviolet or X-rays.
Our work demonstrates that we can generate vector-vortex beams in the extreme ultraviolet thanks to the physical conservation laws in high-order harmonic generation. Our theoretical proposal of a new conserved quantity, the Pancharatnam topological charge, in high harmonic generation has been confirmed experimentally in the laboratory of Paris-Saclay.
More information at:
Download the full paper at Gredos @Universidad de Salamanca: http://hdl.handle.net/10366/146004
Jorge Souto, from the University of Valladolid, will give the seminar entitled “Degradation of laser diodes: physical models and resolution by finite element methods (FEM)” on December 14 at 11:30.
The seminar is open to all who want to attend, it will take place in the Aula Sancho Guimerá (Exactas) of the Faculty of Sciences of the University of Salamanca.
The entire seminar will be uploaded to this website and to the YouTube channel of the ALF-USAL group.
Javier Serrano, member of the Laser and Photonics Applications group and researcher in the ATTOSTRUCTURA project (ERC 851201), will give the seminar entitled “Deep Learning and harmonic generation” on December 17 at 10:00.
The seminar will take place in Room III of the Faculty of Sciences of the University of Salamanca.
For those who cannot attend, the entire seminar will be uploaded to this website and to the YouTube channel of the ALF-USAL group.
The XIII National Meeting of Optics (#RNO2021) ended last week after three days full of interesting contributions and work.
It is with great regret that we say goodbye to this edition, although we do so with a bittersweet feeling since Ana García Cabrera, doctoral student and member of the GIR Aplicaciones Lásica y Fótonica was chosen as the winner of the RNO2021 award in the category of Quantum and Nonlinear Optics.
Ana presented her work “Ultrafast Talbot Spectroscopy” of which she is co-author along with Carlos Hernández – García and Luis Plaja. You can read the summary below.
Abstract:
High-order harmonic generation is an extraordinary tool that allows for the production of high-frequency coherent radiation in the form of very short pulses that can be used to unveil the properties of matter at the nanoscale. High-order harmonic generation occurs during the interaction of an intense laser with the atoms in matter. First, the laser distorts the atomic potential, releasing the electron through tunnel ionization. Then, the electron is accelerated by the laser field and redirected to rescatter with its parent ion, leading to the emission of radiation in the form of harmonics of the incident laser’s frequency. In the spatial scale where this process occurs, the electrons behave as waves and, therefore, they experience some phenomena that are typically observed in light, like the Talbot effect. The (optical) Talbot effect leads to the formation of a series of self-images of a periodic field distribution —like that in a diffraction grating— at regular distances.
In this work, we simulate an experiment of matter Talbot imaging with the ionized electronic wavefunction in a crystal during the high-order harmonic generation. The periodic wavefunction in the crystal is released by the laser field and, upon its evolution, it experiences the formation of Talbot self-images over time. The temporal modulations in the harmonic signal, caused by the matter Talbot effect, leave a trace in the harmonic spectrum that depends on the band occupation of the crystal. Therefore, we propose a new spectroscopic tool, ultrafast Talbot spectroscopy, based on the already known Talbot -Lau interferometry.
You can consult the article that she has published about this same work in the following link or download it from the institutional repository of the University of Salamanca GREDOS.
Ana García-Cabrera et al 2021 New J. Phys. 23 093011
We congratulate Ana and the rest of the congress winners and finalists!
All the details of the congress can be consulted on its website and its Twitter account (hashtag #RNO2021)