“Structuring ultrafast laser pulses for their application in attosecond science”

Carlos Hernández-García
University of Salamanca

Ultrafast laser technology has transformed our understanding of science, enabling the observation and control of matter on femtosecond (10⁻¹⁵ s) and attosecond (10⁻¹⁸ s) timescales. The generation of attosecond pulses through high harmonic generation (HHG)—recognized with the 2023 Nobel Prize in Physics—has established a foundation for attosecond science as a transformative field impacting applied —photonics, nanotechnology, spectroscopy, imaging— and fundamental—physics, chemistry, biology— fields. A pivotal development in attosecond science is the capability of structuring ultrafast laser sources, particularly in their spin and orbital angular momentum properties. These advances enable time-dependent studies of chiral systems, magnetic materials, and ultrafast electronic and spin dynamics with unprecedented precision. The ability to generate structured attosecond pulses via HHG has driven several breakthroughs in nonlinear optics, allowing the creation of EUV/soft x-ray pulses with tailored angular momentum and spatiotemporal profiles. In this talk we will review several works that have boosted the field of attosecond structured pulses during the last decade. We will focus not only in the ability to tailor the angular momentum properties of attosecond pulses, but also on how through the topology of the EUV/soft x-ray pulses we can retrieve information about ultrafast electronic dynamics of matter. Since the early work on HHG driven by vortex beams, the use of driving field configurations with custom orbital angular momentum properties has opened opportunities for controlling spatiotemporal high-order harmonic properties. Notable advancements include the generation of attosecond vortices with controlled polarization, high harmonic pulses with time-dependent orbital angular momentum or self-torque, EUV vector harmonic pulses, attosecond vortex pulse trains, spatially-structured harmonic beams from graphene, or EUV spatiotemporal and spatiospectral optical vortices.

“Light Manipulation in Multilayered Photonic Structures”

Emiliano Descrovi
Politecnico di Torino and European Optical Society

Recent results on light manipulation by means of Bloch surface waves (BSW) on multilayers are presented. Planar multilayers sustaining either TE or TM-polarized BSW offer new opportunities for light management at the micro and nanoscale. BSWs can be considered as the dielectric equivalent of Surface Plasmon for metals. Compared to SPPs, BSWs present some advantages, such as lower absorption, narrower mode resonances, stronger near-field surface enhancement effects, longer propagation length, spectral and polarization tunability. In this talk, I will show how light can be confined and propagated by means of BSW coupling, in a 2D optics fashion, wherein light is flowing on an almost flat surface with weak perturbations. In addition, I will discuss how the presence of the high photonic LDOS associated to BSW can change the emission behavior of organic dipoles located on the multilayer surface. The concept of a BSW planar cavity is introduced and the corresponding effects on the spectral and temporal signature of emitters located therein will be discussed. In addition, chiral diffractive gratings will be demonstrated to provide an outcoupling mechanism for BSW resulting in free-space propagating beams carrying specific orbital angular momenta. The presented results have potential applications in the domain of engineered sources for telecommunications and quantum technologies.

“Future Perspectives of Optical Fiber Sensors”

Orlando Frazão
Institute for Systems and Computer Engineering, Technology and Science

Optical fiber sensors (OFS) still play a crucial role due to their unique advantages. They are immune to electromagnetic interference, making them ideal for applications in aerospace, power grids, and medical fields. Additionally, they enable long-distance remote sensing and are widely used in structural health monitoring for bridges and pipelines. Their high precision and sensitivity allow for the detection of small variations in temperature, pressure, and strain, while their resistance to extreme environments makes them essential in nuclear plants, deep-sea exploration, and space missions. They are also lightweight and miniaturized, favoring biomedical and aerospace applications. However, they face challenges such as high costs, complex integration, and competition from wireless and IoT sensors. Despite this, they continue to dominate areas like structural monitoring, oil and gas, biomedicine, defense, and aerospace. Therefore, optical fiber sensors remain relevant, especially where precision, durability, and remote sensing are indispensable, with their future depending on cost reduction and integration with smart sensor networks.

“Applications of Gallium Oxide-Based Photomemristors in Neuromorphic Engineering”

Marina Sparvoli
Universidade de São Paulo

Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor material that has garnered significant attention in the field of high-voltage and high-frequency power electronics. Five main crystalline phases of Ga2O3 have been identified, including the corundum (𝛼), monoclinic (𝛽), defect spinel (𝛾), cubic (𝛿), and orthorhombic (ɛ) phases. Their thermodynamic stability follows the order of 𝛾, 𝛿, 𝛼, ɛ, and 𝛽. Notably, the monoclinic 𝛽-Ga2O3 phase is the most stable, particularly at high temperatures, while the other phases are metastable above room temperature and tend to transform into the 𝛽 phase under specific thermal conditions. In this study, thin films were deposited using the RF sputtering technique at three different power levels: 200, 300, and 400 W. The films were deposited onto p-type silicon substrates over a process duration of 30 minutes. For analysis, Rutherford Backscattering (RBS) techniques, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were employed, confirming the 𝛽 phase. Through UV-Vis spectroscopy, the reflectance of the material was obtained, enabling the calculation of the bandgap. After depositing metallic contacts, the IxV curve was obtained to study the material non-linear behavior and light response. The three devices were subjected to electrical characterization in order to obtain key parameters such as SET and RESET voltages. It was observed that the photomemristors exhibited threshold switching behavior and photoelectric response. The devices were also evaluated in conjunction with an RC circuit, which emulates the dynamics of the neuronal membrane.

“Ultrafast structural dynamics in solids driven by femtosecond laser pulses: from nonthermal bond breaking to surface nanostructuring”

Martin E. Garcia
University of Kassel

When solids are exposed to ultrashort, intense laser pulses, they are driven into an extreme nonequilibrium state: the electronic system is heated within femtoseconds to temperatures of tens of thousands of Kelvin—far exceeding the surface temperature of the Sun—while the ionic lattice remains initially cold and undisturbed. In this short-lived, transient regime, the hot electrons dramatically alter the interatomic bonding landscape, exerting strong forces on the ions. These forces can trigger ultrafast structural phase transitions that are inaccessible under thermodynamic equilibrium conditions. Such «nonthermal» phenomena can be effectively described using approaches based on Density Functional Theory (DFT).
However, DFT simulations are inherently limited to small systems (typically fewer than ~1000 atoms) and are not yet capable of fully capturing the energy exchange between electrons and ions.

Almost simultaneously with the bond modification, the sudden increase in electronic temperature enhances electron-phonon coupling, leading to stronger electron-ion collisions. These collisions initiate a flow of energy from the electronic system into the lattice, culminating in a thermalized state within a few picoseconds. At this point, both subsystems reach a common elevated temperature, giving rise to “thermal” structural responses such as melting, ablation, dislocation formation, and nanocrystallization. Both the energy exchange- and the “thermal” processes are well captured by two-temperature model molecular dynamics (TTM-MD) simulations, which, based on classical interatomic potentials, enable the study of systems containing hundreds of millions of atoms. However, such models cannot account for the initial laser-induced bond changes and associated nonthermal transformations.

In this talk, we will review the current theoretical frameworks for describing both “nonthermal” and “thermal” laser-induced phenomena and present recent efforts toward a unified description that bridges the gap between electronic excitation and large-scale material response. Particular emphasis will be placed on the role of machine learning–based interatomic potentials—especially neural network potentials—which, when properly trained on DFT data, provide a powerful route to scale quantum-accurate descriptions to previously inaccessible time and length scales.

“Physical principles of optical interferometry for surface topography measurement”

Peter de Groot
Zygo Corporation and SPIE

The story of modern surface-measuring interferometry is a remarkable journey through the history of optics, beginning with the discovery of interference fringes and leading up to present-day methods. Today, laser interferometers and white-light interference microscopes are benchmark tools for high-precision measurements of form and roughness for everything from optical components with sub-nanometer tolerances to highly structured, additively manufactured parts. While basic concepts begin with a Michelson interferometer for perfectly flat and smooth mirrors, the topic becomes more complicated and interesting with real, three-dimensional (3D) surface structures. These surfaces diffract light over a range of angles, encoding topography information in a complex scattered light field. This light is then collected and imaged onto a camera, which inevitably filters the scattered light, leading to variations in response depending on spatial frequency. Furthermore, even for low spatial frequencies, data processing that converts measured light intensities to height data can suffer from measurement nonlinearities and uncertainty, particularly with parts that have semi-transparent coatings or variations in material composition over the measured area.
In our research at Zygo, in collaboration with international partners, we are building a better understanding of the fundamental metrological characteristics of topography-measuring interferometers. A suite of modeling techniques tackles these issues, from conventional or “elementary” Fourier optics to full 3D transfer functions and methods for solving the inverse problem for complex surface structures. Key aspects of our work include the translation of complex physics concepts into new capabilities, as well as meaningful, easily understood specifications and guidance for optimizing instrument setup for specific measurement tasks. Tools include open-source software models as well as engagement with international standards organizations such as ISO, for consistency and confidence in the use of interferometers for areal surface topography measurement.