ALF results

It was not everything perfect

It was not everything perfect
 
Nowadays, the high-order harmonic generation process is an extended useful tool for the study of femtosecond dynamics. Nevertheless, there are still many doubts regarding the electron behavior inside different types of mediums.
 
Recent studies in solid targets have revealed new scenarios with extraordinary electronic dynamics compared with atoms or molecules. The process in solids can be explain through a semiclassical point of view using the electron trajectory from the excitation until the recombination with its hole in real space; the so-called perfect recollisions. However, recent studies have confirmed that part of the high-order harmonic emissions comes from trajectories where the electron and hole do not overlap in real space; the so-called imperfect recollisions.
 
In this work, we demonstrate the existence of imperfect recollisions when the medium is a single-layer graphene, and the driving laser pulse is linearly polarized. Graphene, compared to other solids, presents a singular structure band with points where the valence and conduction band are in contact. Our study has a great relevance because until this moment there were studies only with finite-gap solids and huge Berry curvature or using a driving field with elliptical polarization. We truly believe that this work takes a new step in the full understanding of the ultrafast dynamics driven by intense laser pulses in solids.
 

More information at:

Boyero-García, Roberto, Ana García-Cabrera, Oscar Zurrón-Cifuentes, Carlos Hernández-García, y Luis Plaja. «Non-classical high harmonic generation in graphene driven by linearly-polarized laser pulses». Opt. Express 30, n.o 9 (abril de 2022): 15546-55. https://doi.org/10.1364/OE.452201.
29 July, 2022 admin , No comments
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Meeting in Salamanca of the Scientific Advisory Committee of ATTOSTRUCTURA project

Meeting in Salamanca of the Scientific Advisory Committee of ATTOSTRUCTURA project

Next August will be thirty months since the ATTOSTRUCTURA project began, which means that half of its duration has already elapsed.

For this reason, the first meeting of the project’s scientific advisory committee has been held. The committee, made up of external researchers who are experts in the different fields of the project, has the objective of evaluating the development of the project, the results obtained to date and, if necessary, proposing changes or modifications in the lines of research. In this way, it is intended to ensure that the project achieves the best possible results while maintaining the highest level of excellence.

The members of the scientific advisory committee are:

  • Prof. Jon Marangos (chairman) –  Imperial College (London, UK)
  • Dra. Alicia Palacios – Universidad Autónoma de Madrid (Madrid, Spain)
  • Prof. Misha Ivanov – Instituto Max Born de Óptica No Lineal y Espectroscopía de Pulso Corto en la Asociación de Investigación de Berlín (Berlin, Germany)
  • Catedrático Jamal Berakdar – Instituto de Física, Universidad Martin-Luther (Halle – Wittenberg, Germany)

The meeting, which took place on Friday, July 22, in the Board Room of the Faculty of Sciences, began with an open-door session in which the status of the project and the main results obtained to date were presented. The videos of that session will be available on the project website.

On the occasion of the meeting, Carlos Hernández García (principal investigator of the project) speaks in this video recorded by the audiovisual services of the University of Salamanca, about the project, its objectives and the results obtained.

25 July, 2022 admin , , No comments
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ALF-USAL researchers participate in the XXXVIII Biennial Meeting of the Royal Spanish Society of Physics (Murcia)

ALF-USAL researchers participate in the XXXVIII Biennial Meeting of the Royal Spanish Society of Physics (Murcia)

From July 11 to 15, the XXXVIII Biennial Meeting of the Royal Spanish Society of Physics was held. The Laser and Photonics Applications group (ALF – USAL) has participated in said biennial, presenting some of the most recent results of the research it is currently carrying out.

The works presented were:

  • Luis Sánchez-Tejerina, Rodrigo Martín-Hernández, Rocío Yanes, Luis Plaja, Luis López-Díaz, Carlos Hernández-García. “Magnetic order excitation by magnetic fields from sub-picosecond structured laser pulses”. S15 Novel frontiers and challenges in magnetism – Oral contribution. (Abstract)
  • Rodrigo Martín-Hernández, Luis Sánchez-Tejerina, Enrique Conejero Jarque, Luis Plaja , Carlos Hernández-García. “Spatial isolation of femtosecond magnetic needles driven by azimuthally-polarized laser beams“, S15 Novel frontiers and challenges in magnetism – Oral contribution. (Abstract). Prize for the best oral contribution in the Symposium “Novel Frontiers and Challenges in Magnetism” awarded by the Spanish chapter of IEEE Magnetics.
  • Miguel López-Ripa, Íñigo J. Sola, Benjamín Alonso. “In-line and ultraestable spatiotemporal characterization of constant and time-varying optical vortices“, S9 Quantum Optics and Nonlinear Optics – Oral contribution (Abstract)
  • V. W. Segundo Staels, E. Conejero Jarque, J. San Roman. “Use of gas-filled multipass cells to generate clean supercontinuum spectra“, S9 Quantum Optics and Nonlinear Optics – Oral contribution. (Abstract)
  • Luis Sánchez-Tejerina, Rodrigo Martín-Hernández, Rocío Yanes, Luis Plaja, Luis López-Díaz, Carlos Hernández-García. “Non-linear, purely magnetic magnetization response to femtosecond structured laser pulses“, S9 Quantum Optics and Nonlinear Optics – Oral contribution. (Abstract)
  • Rodrigo Martín-Hernández,Luis Plaja, Carlos Hernández-García. “Magnetically-pumped High Harmonic Generation with circularly polarized driving fields”, S9 Quantum Optics and Nonlinear Optics – Oral contribution. (Abstract)
  • Ana García-Cabrera, Roberto Boyero-García, Óscar Zurrón Cifuentes, Julio San Román, Carlos Hernández-García, Luis Plaja. “Multi-vortex high-harmonic beams from graphene’s anisotropy“, S9 Quantum Optics and Nonlinear Optics – Oral contribution. (Abstract)
  • Alba de las Heras, Alok Kumar Pandey, Julio San Román, Javier Serrano, Luis Plaja. “Extreme-ultraviolet scalar and vectorial vortices with very high topological charge“, S9 Quantum Optics and Nonlinear Optics – Oral contributionl. (Abstract). Winner of the “Young Researchers” contest in the student category.
  • Ignacio Lopez-Quintas, Warein Holgado, Rokas Drevinskas, Peter G. Kazansky, Íñigo J. Sola, Benjamín Alonso. “Collinear optical vortices with tailored topological charge generated by angular momentum transfer“, S9 Quantum Optics and Nonlinear Optics – Poster. (Abstract)
  • Javier Serrano, Carlos Hernández-García. “High-performance simulations of high-order harmonic generation based on artificial intelligence“, S9 Quantum Optics and Nonlinear Optics – Poster. (Abstract)
  • Rosa Ana Pérez-Herrera, Alba de las Heras, María-Baralida Tomás, Beatriz Santamaría, Clara Benedí-García, Ana I. Gómez-Varela, Verónica González-Fernández, Martina Delgado-Pinar. “The future researchers in Optics and Photonics: gender bias in the PhD theses defended in Spain in 2015-2020“, S2 Women in Physics – Oral contribution. (Abstract). 

In addition, Carlos Hernández García participated in the organization of the congress as part of the scientific committee.

25 July, 2022 admin , , , No comments
adminALF-USAL researchers participate in the XXXVIII Biennial Meeting of the Royal Spanish Society of Physics (Murcia)

High fashion jewelry in non-linear optics

High fashion jewelry in non-linear optics

Sterling silver jewelry, rose gold with exclusive designs, rings, earrings, bracelets… made out of light? Like a high fashion jewelry workshop, the Laser and Photonics Applications research group of the University of Salamanca (ALF-USAL) focuses its efforts on designing light jewels through non-linear optics. Jewels, not only for their beauty in the form of high-frequency lasers, but also for their usefulness in observing and controlling unknown processes in nature. In fact, the design of coherent and high-frequency laser light beams (towards the X-rays) has become a unique tool to access processes that take place in very small sizes (nanometers) and in very short times (trillionths of seconds).

The theoretical-experimental collaboration between ALF-USAL and the group of Profs. Murnane and Kapteyn at the University of Colorado at Boulder (USA) have been developing fine jewelry for the last few years. After generating high-frequency rings with properties never seen before (see references [1,2]), the researchers have gone a step further, entering the world of necklaces. The design of an infrared laser in the form of a necklace allows to control the frequency and divergence (or spatial size) of the X-rays that are produced after the non-linear process of high-order harmonic generation. In this work, published in the journal Science Advances, the researchers also demonstrate that the spectral content of these X-ray lasers can be calibrated by means of the number of beads in the necklace. One more step in the high fashion jewelry with lasers that tries to help in the understanding of the fastest processes of nature.

More information in:

“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).

References::

[1] “Generation of extreme-ultraviolet beams with time-varying orbital angular momentum”, Laura Rego, Kevin M Dorney, Nathan J Brooks, Quynh Nguyen, Chen-Ting Liao, Julio San Román, David E Couch, Allison Liu, Emilio Pisanty, Maciej Lewenstein, Luis Plaja, Henry C Kapteyn, Margaret M Murnane, Carlos Hernández-García,   Science 364, eaaw9486 (2019).

[2] “Controlling the polarization and vortex charge of attosecond high-harmonic beams via simultaneous spin-orbit momentum conservation”, Kevin M. Dorney, Laura Rego, Nathan J. Brooks, Julio San Román, Chen-Ting Liao, Jennifer L. Ellis, Dmitriy Zusin, Christian Gentry, Quynh L. Nguyen, Justin. M. Shaw, Antonio Picón, Luis Plaja, Henry C. Kapteyn, Margaret M. Murnane, Carlos Hernández-García, Nature Photonics 13, 123–130 (2019).

25 April, 2022 admin , No comments
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Jila Press Release – A Necklace Made of Doughnuts

Jila Press Release – A Necklace Made of Doughnuts

Our friends and frequent collaborators from JILA (University of Colorado) echo the paper “Necklace-structured high-harmonic generation for low-divergence, soft x-ray harmonic combs with tunable line spacing” recently published in ScienceAdvances.

You can read his review at the following link: https://jila.colorado.edu/news-events/articles/necklace-made-doughnuts

More information at:

Rego, L., Brooks, N. J., Nguyen, Q. L. D., San Roman, J., Binnie, I., Plaja, I., Kapteyn, H. C., Murnane, M. M., & Hernández-García, C. (2022). Necklace-structured high-harmonic generation for low-divergence, soft x-ray harmonic combs with tunable line spacing. Science Advances, 8(5), eabj7380. https://doi.org/10.1126/sciadv.abj7380
24 February, 2022 admin , No comments
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Compressing light pulses in pressure gradients

Compressing light pulses in pressure gradients

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

Download the full paper at Gredos @Universidad de Salamanca: http://hdl.handle.net/10366/148576
 
21 February, 2022 admin , No comments
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