arXiv subjects

Rodrigo Martín-Hernández

Publications and source records attributed to Rodrigo Martín-Hernández.

7 recordsLinked to original sources

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2026

Scaling law from orbital angular momentum conservation in harmonic and high-order harmonic generation driven by spatiotemporal light fields

Nonlinear photon upconversion processes driven by diverse forms of structured light are receiving increasing attention. In harmonic and high-order harmonic generation (HG and HHG) with Laguerre-Gauss (LG) beams, linear scaling the driver topological charge (TC) with the harmonic order is equivalent to driver orbital angular momentum (OAM) per photon scaling, and constitutes a proof of OAM conservation. However, with generic driving fields, such as non-LG vortices or spatiotemporal optical vortices, TC and OAM per photon may scale or not in a process in which the OAM is conserved. We find the physical magnitude that scales with generality when the OAM, either longitudinal or transverse, or its intrinsic part, is conserved. This new rule allows for the wealth of phenomena observed in HHG that are unintelligible from the rigid LG rule.

physics.optics↗

arXiv2025

Compact, intense attosecond sources driven by hollow Gaussian beams

High-order harmonic generation (HHG) enables the up-conversion of intense infrared or visible femtosecond laser pulses into extreme-ultraviolet attosecond pulses. However, the highly nonlinear nature of the process results in low conversion efficiency, which can be a limitation for applications requiring substantial pulse energy, such as nonlinear attosecond time-resolved spectroscopy or single-shot diffractive imaging. Refocusing of the attosecond pulses is also essential to achieve a high intensity, but difficult in practice due to strong chromatic aberrations. In this work, we address both the generation and the refocusing of attosecond pulses by sculpting the driving beam into a ring-shaped intensity profile with no spatial phase variations, referred to as a Hollow Gaussian beam (HGB). Our experimental and theoretical results reveal that HGBs efficiently redistribute the driving laser energy in the focus, where the harmonics are generated on a ring with low divergence, which furthermore decreases with increasing order. Although generated as a ring, the attosecond pulses can be refocused with greatly reduced chromatic spread, therefore reaching higher intensity. This approach enhances the intensity of refocused attosecond pulses and enables significantly higher energy to be delivered in the driving beam without altering the focusing conditions. These combined advantages open pathways for compact, powerful, tabletop, laser-driven attosecond light sources.

physics.optics↗

arXiv2024

Generation of intense, polarization-controlled magnetic fields with non-paraxial structured laser beams

The ability to spatially separate the electric and magnetic fields of a light beam enables the inspection of laser-matter interactions driven solely by optical magnetic fields. However, magnetic field excitations are commonly orders of magnitude weaker than those driven by the electric field. Several studies have already demonstrated the isolation of an intense, linearly polarized magnetic field using structured light. In this work, we report the generation of isolated high intensity magnetic fields with controlled polarization state in the non-paraxial regime using structured laser beams. Our theoretical findings highlight a significant enhancement in the amplitude of the longitudinal magnetic field carried by an azimuthally polarized laser under tight-focusing conditions. Furthermore, by implementing a multiple-beam configuration, we achieve precise control over the polarization state and amplitude of the spatially isolated magnetic field. We report the generation of polarization-controlled magnetic fields reaching up to tens of Tesla, even from moderately intense laser beams of $\sim 10^{12} \, \mathrm{W}/\mathrm{cm}^2$. Our study paves the way for ultraintense interactions with circularly polarized magnetic fields from a feasible experimental setup point of view, particularly interesting to probe ferromagnetic materials and chiral media.

physics.optics↗

arXiv2024

All-optical non-linear chiral ultrafast magnetization dynamics driven by circularly polarized magnetic fields

Ultrafast laser pulses provide unique tools to manipulate magnetization dynamics at femtosecond timescales, where the interaction of the electric field -- such as excitation of spin carriers to non-equilibrium states, generation of localized charge currents, demagnetization, or inverse Faraday effect -- dominates over the magnetic field. Recent proposals using structured laser beams have enlightened the possibility to generate intense femtosecond magnetic fields, spatially isolated from the electric field. Here we demonstrate the relevance of this novel scenario to femtomagnetism, unveiling the purely precessional, non-linear, chiral response of the magnetization when subjected to circularly polarized magnetic fields. This fundamental result not only opens an avenue in the study of laser-induced ultrafast magnetization dynamics, but also sustains technological implications as a route to promote all-optical non-thermal magnetization switching both at shorter timescales -- towards the attosecond regime -- and at THz frequencies.

cond-mat.mes-hall↗

arXiv2024

Optical Magnetic Field Enhancement using Ultrafast Azimuthally Polarized Laser Beams and Tailored Metallic Nanoantennas

Structured light provides unique opportunities to spatially tailor the electromagnetic field of laser beams. This includes the possibility of a sub-wavelength spatial separation of their electric and magnetic fields, which would allow isolating interactions of matter with pure magnetic (or electric) fields. This could be particularly interesting in molecular spectroscopy, as excitations due to electric and -- usually very weak -- magnetic transition dipole moments can be disentangled. In this work, we show that the use of tailored metallic nanoantennas drastically enhances the strength of the longitudinal magnetic field carried by an ultrafast azimuthally polarized beam (by a factor of $\sim65$), which is spatially separated from the electric field by the beam's symmetry. Such enhancement is due to favorable phase-matching of the magnetic field induced by the electronic current loops created in the antennas. Our particle-in-cell simulation results demonstrate that the interaction of moderately intense ($\sim10^{11}$ W/cm$^2$) and ultrafast azimuthally polarized laser beams with conical, parabolic, Gaussian, or logarithmic metallic nanoantennas provide spatially isolated magnetic field pulses of several tens of Tesla.

physics.optics↗

arXiv2022

Extension of the bright high-harmonic photon energy range via nonadiabatic critical phase matching

Extending the photon energy range of bright high-harmonic generation to cover the entire soft X-ray region is important for many applications in science and technology. The concept of critical ionization fraction has been essential, because it dictates the maximum driving laser intensity that can be used while preserving bright harmonic emission. In this work, we reveal a second, nonadiabatic critical ionization fraction that substantially extends the maximum phase-matched high-harmonic photon energy, that arises due to strong reshaping of the intense driving laser field. We validate this understanding through a systematic comparison between experiment and theory, for a wide range of pulse durations and driving laser wavelengths. In particular, high harmonics driven by intense few-cycle pulses experience the most pronounced spectral reshaping, significantly extending the bright photon energy range. We also present an analytical model that predicts the spectral extension that can be achieved for different driving lasers. This reveals an increasing role of nonadiabatic critical phase matching when driven by few-cycle mid-infrared lasers. These findings are important for the development of high-brightness soft X-ray sources for applications in spectroscopy and imaging.

physics.optics↗