Periodic Reporting for period 4 - ATTOSTRUCTURA (Structured attosecond pulses for ultrafast nanoscience)
Periodo di rendicontazione: 2024-09-01 al 2025-08-31
Since the invention of the laser in 1960, our ability to harness light for practical applications has increased exponentially. For many years, however, interest in the spatial profile of laser beams was dominated by the quest for smoother, cleaner Gaussian beams—free of undesired spatial inhomogeneities—because they can be focused to a minimum-size spot. By contrast, advanced applications benefit from non-uniform intensity, phase, or polarization distributions. Paradigmatic examples include optical tweezers and adaptive-wavefront optics. Control of light in its transverse dimension has therefore spurred the development of techniques for structuring, sculpting, or tailoring beams. The general term structured light refers to beams with non-homogeneous, non-trivial distributions of intensity, phase and/or polarization in the plane transverse to propagation.
Recent advances in structured laser pulses in the ultrafast regime—down to femtoseconds (1 fs = 10⁻¹⁵ s)—together with improved understanding of their nonlinear interaction with solids and gases, have enabled the up-conversion of structured light into the extreme-ultraviolet (EUV), an attractive domain for manipulating magnetic and chiral systems on ultrafast timescales. Reaching this milestone was non-trivial: most generation techniques are wavelength-dependent and inefficient at high frequencies. Consequently, generating structured light in these extreme regimes must be accompanied by theoretical efforts to understand topology and the conservation rules governing spin–orbit exchange between light and matter.
ATTOSTRUCTURA aims to develop novel ultrafast structured-light tools and to explore their application in ultrafast magnetism. Thanks to high-harmonic generation (HHG), it is now possible to produce attosecond pulses structured in polarization and orbital angular momentum (OAM). We seek to push these capabilities to their limits, devising strategies for attosecond/X-ray sources with controlled angular momentum. We also design new HHG schemes in atomic and solid systems where structured pulses grant access to previously unexplored ultrafast phenomena. Finally, we explore scenarios of ultrafast magnetism that leverage structured laser pulses.
Conclusions of the action. We have established a coherent theoretical, computational, and experimental pathway for structured-light–driven HHG and its applications. In particular, we developed new theoretical frameworks for simulating HHG with structured beams in gaseous and solid targets; generated new forms of ultrafast, high-frequency structured light—such as vector–vortex beams, spatiotemporal EUV vortices, attosecond STOVs (spatiotemporal optical vortices), and attosecond skyrmions; pioneered the use of structured light at the nanoscale to enhance attosecond pulse sources (e.g. frequency content and peak intensity); and established a practical route to high-frequency structured-light generation in solids via HHG. These advances laid the groundwork for proposed attomagnetism experiments based on isolated magnetic pulses with controlled polarization. We uncovered a scenario in which nonlinear magnetization switching can be driven by circularly polarized magnetic fields. Finally, we developed the multi-platform HHGstudio app to support researchers and experimentalists in modeling HHG and proposing new schemes in attosecond science.
Recent advances in structured laser pulses in the ultrafast regime—down to femtoseconds (1 fs = 10⁻¹⁵ s)—together with improved understanding of their nonlinear interaction with solids and gases, have enabled the up-conversion of structured light into the extreme-ultraviolet (EUV), an attractive domain for manipulating magnetic and chiral systems on ultrafast timescales. Reaching this milestone was non-trivial: most generation techniques are wavelength-dependent and inefficient at high frequencies. Consequently, generating structured light in these extreme regimes must be accompanied by theoretical efforts to understand topology and the conservation rules governing spin–orbit exchange between light and matter.
ATTOSTRUCTURA aims to develop novel ultrafast structured-light tools and to explore their application in ultrafast magnetism. Thanks to high-harmonic generation (HHG), it is now possible to produce attosecond pulses structured in polarization and orbital angular momentum (OAM). We seek to push these capabilities to their limits, devising strategies for attosecond/X-ray sources with controlled angular momentum. We also design new HHG schemes in atomic and solid systems where structured pulses grant access to previously unexplored ultrafast phenomena. Finally, we explore scenarios of ultrafast magnetism that leverage structured laser pulses.
Conclusions of the action. We have established a coherent theoretical, computational, and experimental pathway for structured-light–driven HHG and its applications. In particular, we developed new theoretical frameworks for simulating HHG with structured beams in gaseous and solid targets; generated new forms of ultrafast, high-frequency structured light—such as vector–vortex beams, spatiotemporal EUV vortices, attosecond STOVs (spatiotemporal optical vortices), and attosecond skyrmions; pioneered the use of structured light at the nanoscale to enhance attosecond pulse sources (e.g. frequency content and peak intensity); and established a practical route to high-frequency structured-light generation in solids via HHG. These advances laid the groundwork for proposed attomagnetism experiments based on isolated magnetic pulses with controlled polarization. We uncovered a scenario in which nonlinear magnetization switching can be driven by circularly polarized magnetic fields. Finally, we developed the multi-platform HHGstudio app to support researchers and experimentalists in modeling HHG and proposing new schemes in attosecond science.
We developed advanced computational tools and theory to simulate and control ultrafast structured laser pulses, focusing on macroscopic high-harmonic generation (HHG). We combined microscopic models—SFA, TDSE (single- and multi-electron), and density-matrix—with Maxwell-integral macroscopic descriptions on high-performance computing. We introduced AI-assisted HHG to accelerate simulations and access macroscopic TDSE. We built a nonlinear-propagation HHG code essential to demonstrations of isolated attosecond pulses in semi-infinite cells, and developed diagnostics for full spatiotemporal characterization. Using these tools, we designed and enabled ultrafast structured EUV light: vector–vortex beams; harmonics with ultra-high topological charge; necklace-driven harmonics with controllable spacing/divergence; and spatiotemporal optical vortices (STOVs) in the EUV, including attosecond STOVs. We established a 3D description of tightly focused structured beams down to nanometric scales to explore spin–orbit effects and magnetic-dipole transitions, and showed that polarization textures can be imprinted into the EUV via HHG, yielding attosecond light skyrmion pulses. We explored structured-light HHG in solids: 3D TDSE for 2D materials (with macroscopic propagation) and solid targets to imprint angular momentum onto EUV sources, culminating in topological high-harmonic spectroscopy to probe anisotropic nonlinear response and electron dynamics. We also proposed the use of intense, isolated, circularly polarized magnetic pulses in nanostructures to drive a nonlinear, purely magnetic chiral mechanism. This could enable all-optical magnetization switching on femtosecond timescales without thermal effects. Finally, we released HHG Studio 1.0 a multi-platform, user-friendly app for HHG (Oct 2025; >80 beta testers). The overall scientific output comprises 43 peer-reviewed articles (Nature Photonics, Science Advances, Optica, Phys Rev Lett, etc.) and 4 manuscripts under review. Multiple dissemination activities aimed to both specialized and general public were performed.
The field of structured ultrafast pulses (down to the attosecond timescale), and their interaction with nanostructures, are at the focus of interest in the non-linear optics community. ATTOSTRUCTURA is ideally placed to add value by tackling some very prominent current scientific challenges. The scientific and the technological activities within the Action drive a new direction in the field of light-matter interaction, a field of relevance not only for fundamental physics but also other disciplines ranging from material science, chemistry, and biology to optoelectronics and spintronics.
ATTOSTRUCTURA produced highly specialized software products covering high harmonic generation in a broad range of situations, from the most common set-ups to structured hard x-rays scenarios. Advanced computational tools, including high performance computing and artificial intelligence, are opening exciting possibilities to tackle macroscopic strong-field scenarios that were not theoretically accessible some years ago. A multiplatform, open-source, user-friendly version of the high harmonic generation code has been developed, HHG Studio, https://laser.usal.es/hhgstudio(si apre in una nuova finestra).
In collaboration with our experimental collaborators, we have proposed a new set of experiments that can benefit from the uniqueness of structured electromagnetic fields in diverse fields, in particular, in femtosecond, or even attosecond, ultrafast magnetism. Our first micromagnetic simulations results demonstrated that all-optical magnetization switching can be achieved through the use of structured laser pulses. These results imply the first theoretical proposal for ultrafast magnetic switching through the use of isolated magnetic fields. However, the generation of such ultrafast magnetic fields is challenging, and though the theoretical blue-skies have been established, more efforts towards realistic experimental realizations with state-of-the-art laser technology are required.
ATTOSTRUCTURA produced highly specialized software products covering high harmonic generation in a broad range of situations, from the most common set-ups to structured hard x-rays scenarios. Advanced computational tools, including high performance computing and artificial intelligence, are opening exciting possibilities to tackle macroscopic strong-field scenarios that were not theoretically accessible some years ago. A multiplatform, open-source, user-friendly version of the high harmonic generation code has been developed, HHG Studio, https://laser.usal.es/hhgstudio(si apre in una nuova finestra).
In collaboration with our experimental collaborators, we have proposed a new set of experiments that can benefit from the uniqueness of structured electromagnetic fields in diverse fields, in particular, in femtosecond, or even attosecond, ultrafast magnetism. Our first micromagnetic simulations results demonstrated that all-optical magnetization switching can be achieved through the use of structured laser pulses. These results imply the first theoretical proposal for ultrafast magnetic switching through the use of isolated magnetic fields. However, the generation of such ultrafast magnetic fields is challenging, and though the theoretical blue-skies have been established, more efforts towards realistic experimental realizations with state-of-the-art laser technology are required.