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Lasers and nanostructured polymers and compounds: influence of properties and parameters

A study of the formation of Laser Induced Periodic Surface Structures (LIPSS) using near-infrared femtosecond pulsed laser irradiation on poly(ethylene terephthalate) (PET) films deposited over gold substrates has been carried out. We report the influence of the gold substrate roughness and the PET film thickness on LIPSS formation and analyze it in terms of the features of the electric field distribution obtained by computer simulations using COMSOLTM. We obtain LIPSS with periods close to the irradiation wavelength as long as the aforementioned substrate and film parameters remain below certain threshold values, in particular for polymer thicknesses below 200 nm and substrate roughness of few nm. However, experiments show the impossibility of LIPSS formation for rough substrates as well as thick films above these threshold values. In our numerical simulations, we notice the generation of Surface Plasmon Polariton (SPP) in the film-substrate interface that gives rise to a periodical field pattern on the surface of the thin film. This periodicity is broken for a certain level of substrate roughness or film thickness. Moreover, the evolution of the period of the SPP as the substrate roughness and film thickness change for given laser parameters is qualitatively in good agreement with the experimental LIPSS period (below but close to the irradiation laser wavelength). In conclusion, the experimental findings are explained by the formation and behavior of SPP in the thin film-substrate interface. On these grounds, we propose that, for our case of study, this SPP formation and the subsequent inhomogeneous rise in temperature induced by the periodic field on the surface of the sample is the leading mechanism contributing to LIPSS formation.

More information at:  

Prada-Rodrigo, J., Rodríguez-Beltrán, R. I., Ezquerra, T. A., Moreno, P., & Rebollar, E. (2023). Influence of film thickness and substrate roughness on the formation of laser induced periodic surface structures in poly(ethylene terephthalate) films deposited over gold substrates. Optics & Laser Technology, 159, 109007. https://doi.org/10.1016/j.optlastec.2022.109007
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V Photo Contest “Day of Light”

On the occasion of the proclamation of May 16 as “International Day of Light and Light-Based Technologies” by the United Nations Organization, the Master’s Degree in Laser Physics and Technology” announces the V edition of the Photo Contest “Day of the light”.

In the organization of the contest and formation of the jury participate:

The contest is open to undergraduate, master’s or doctoral students, professors and members of the university community of the University of Salamanca and the University of Valladolid, as well as graduates of the Master’s Degree in Laser Physics and Technology who are not part of the jur

The participation period is open until May 12. Each participant can send up to two photographs to each of the established categories:

  • Technologies of light and Optical Phenomena
  • The laser

4 prizes will be awarded:

  • First prize in the Light Technologies and Optical Phenomena category: 200 euros.
  • Second prize in the Light Technologies and Optical Phenomena category: 100 euros.
  • First prize in the Laser category: 200 euros.
  • Second prize in the Laser category: 100 euros.

In addition, those winners who are undergraduate, master’s or doctoral students will receive one year of free subscription to the Royal Spanish Physics Society with online access to the Physics Journal. The winning photographs will be published in the Pure and Applied Optics magazine of the Spanish Optical Society (SEDOPTICA).

The complete rules of the competition are available on the website of the Master’s Degree in Physics and Technology of Lasers (laser.usal.es/posgrado)

Organizacion concurso 2023
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Use of ultrashort laser pulses as a standard for fracture resistance testing

The use of fracture mechanics for rationalizing the fracture behavior of cemented carbides is valid, as far as sharp cracks, free of residual stresses and subjected to a well-defined stress state are used for assessing fracture toughness. However, machining a very sharp notch on the surface of hardmetals for fracture toughness testing has been a critical issue during many years. Within this context, introduction of surface “through-thickness” _micronotches (SEμVNB) by means of ultrashort pulsed laser ablation (UPLA) is here proposed, implemented and analyzed as an innovative precracking-like route within flexural testing procedures for appropiated evaluation of fracture toughness of cemented carbides. UPLA parameters used for introducing the micronotch are optimized in terms of induced damage ahead of the notch tip. For comparison purposes, fracture toughness is also determined by means of flexural testing of previously cracked single-edge notch beams (SENB-Cracked) as well as specimens with V-notch tips sharpened through diamond polishing using a razor blade, and Palmqvist indentation microfracture method. The satisfactory agreement found between values measured using UPLA-micronotched and SENB-Cracked (reference) specimens allows to conclude that flexural testing of SEμVNB samples is a valid methodology for reliable determination of fracture toughness of hardmetals. This is feasible because of the extremely short time of laser-matter interaction. It yields small and somehow controlled damage in front of the notch tip as a result of shock wave propagation during ablation, which translates into effective precracking of SEμVNB specimens

More information at:  

Ortiz-Membrado, L., Liu, C., Prada-Rodrigo, J., Jiménez-Piqué, E., Lin, L. L., Moreno, P., Wang, M. S., & Llanes, L. (2022). Assessment of fracture toughness of cemented carbides by using a shallow notch produced by ultrashort pulsed laser ablation, and a comparative study with tests employing precracked specimens. International Journal of Refractory Metals and Hard Materials, 108, 105949. https://doi.org/10.1016/j.ijrmhm.2022.105949
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ALF-USAL researchers participate in the annual meeting of the European Optical Society (EOSAM 2022)

From September 12 to 16, the annual meeting of the European Optical Society (EOSAM 2022) was held in Porto (Portugal). The Laser and Photonics Applications group (ALF – USAL) has participated in this conference presenting some of the most recent results of the research it is currently carrying out.

The works presented were:

  • Marina Fernández Galán, Enrique Conejero Jarque, Julio San Román. Pulse self-compression down to the sub-cycle regime in hollow capillary fibers with decreasing pressure gradients. TOM 8 Non-linear and Quantum Optics – Oral contribution (Abstract).
  • Miguel López Ripa, Iñigo J. Sola, Benjamín Alonso. Ultraestable spatiotemporal characterization of optical vortices in the visible and near infrared. TOM 13 Advances And Applications of Optics and Photonics – Oral contribution (Abstract). 
  • Rodrigo Martín Hernández, Luis Plaja, Carlos Hernández García. Fourier-limited attosecond pulse generation with magnetically pumped high-order harmonic generation. TOM 8 Non-linear and Quantum Optics – Oral contribution (Abstract)
  • Luis Plaja, Ana García Cabrera, Roberto Boyero-García, Óscar Zurrón, Julio San Román, Carlos Hernández García. Multi-beam vortex generation induced by the non-linear optical anisotropy of graphene. TOM 8 Non-linear and Quantum Optics – Poster (Abstract)
  • Victor W. Segundo Staels, Enrique Conejero Jarque, Daniel Carlson, Michaël Hemmer, Henry C. Kapteyn, Margaret M. Murnane, Julio San Román. Supercontinuum generation in the enhanced frequency chirp regime in multipass cells. TOM 8 Non-linear and Quantum Optics – Oral contribution (Abstract)
  • Carlos Hernández García. Novel ultrafast structured EUV/x-ray sources from nonlinear optics. TOM 13 Advances And Applications of Optics and Photonics – Oral contribution (Abstract). 
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adminALF-USAL researchers participate in the annual meeting of the European Optical Society (EOSAM 2022)

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.
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Castilla y León Televisión echoes the meeting of the expert committee of the ATTOSTRUCTURA project

The television channel Castilla y León Television publishes on its website the news about the meeting of the expert council of the ATTOSTRUCTURA project.

You can read the press release and watch the video on their website.

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adminCastilla y León Televisión echoes the meeting of the expert committee of the 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.

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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.

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The OSAL Student Chapter of Salamanca winner of the second Foton 2022 prize awarded by the CSIC

The OSAL Student Chapter of the University of Salamanca has been awarded second place at the Foton 2022 Awards in the Foton Emitted category, for its informative video “The colors in soap bubbles”.

The jury has positively valued “his ability to disclose to the general public, explaining the operation of the phenomenon of interference of light with an accessible and attractive example” in addition to his creativity when showing the colors that are produced in the bubbles.

The video explains the thin film interference phenomenon, which is responsible for the appearance of colors in soap bubbles and which also appears in other situations such as puddles or butterfly wings.

You can see this video (and other very interesting ones too) on the page of the OSAL Student Chapter of Salamanca and read the complete review of the award on the CSIC website.

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adminThe OSAL Student Chapter of Salamanca winner of the second Foton 2022 prize awarded by the CSIC

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).

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