Laboratory of Quantum Optics

Structured light as a tool for the formation and analysis of new states of matter

Project Overview and Funding Information

This project focuses on the interaction between structured light and matter, with particular emphasis on the transfer of orbital angular momentum (OAM) from photons to atomic and magnetic systems. When interacting with matter, photons can transfer not only energy and linear momentum, but also spin and orbital angular momentum, enabling novel pathways for controlling electronic and magnetic properties at the nanoscale.

The project was funded through a competitive national research call (ARRS project J1-3012) and builds upon prior developments in the generation of OAM-carrying light beams in the visible and XUV spectral ranges. The present work extends these concepts to ultrafast and element-selective regimes using high-order harmonic generation (HHG) and free-electron laser (FEL) sources.

The overall objective was to move from proof-of-principle demonstrations toward the development of new experimental methods for ultrafast magnetism, nanoscale magnetic field generation, and topological imaging based on OAM transfer.a.

Project's team

The project was carried out by an interdisciplinary team with expertise in ultrafast optics, atomic and molecular physics, magnetism, and XUV spectroscopy.

  • University of Nova Gorica (UNG) – experimental activities, HHG-based XUV sources, ultrafast magnetism
  • Jožef Stefan Institute (JSI) – atomic and condensed matter physics, experimental support
  • University of Halle – theoretical modeling and quantum dynamics
  • CEA Paris and University of Cergy-Pontoise – structured light and OAM beam generation
  • Elettra Sincrotrone Trieste (FERMI FEL) – XUV and EUV experiments at seeded FEL sources

Detailed information on project members and their affiliations is available through the SICRIS system: https://cris.cobiss.net/ecris/si/sl

Scientific Objectives and Work Program

The project was structured around three main scientific goals (SGs):

SG1 – Generation of Steady-State Nanoscale Magnetic Field Pulses

SG2 – OAM Diffraction for Topological Reconstruction and Magnetic Helicoidal Dichroism

SG3 – Fundamental Laws Governing OAM Transfer to Atoms

Project Phases and Their Realization

Phase 1: Ultrafast Magnetic Field Generation (SG1)

A novel laser-based scheme was developed to generate localized, steady-state magnetic fields at the nanometer scale with tunable durations ranging from femtoseconds to nanoseconds. By combining XUV excitation with infrared vortex pulses, circulating electronic wave packets were induced in helium atoms, resulting in nanoscale current loops and ferromagnetically aligned magnetic moments.

The approach was validated through a combination of experimental photoemission measurements and ab initio time-dependent Schrödinger equation simulations, showing excellent quantitative agreement. The induced magnetization persists beyond the driving laser pulse duration, demonstrating the feasibility of steady-state ultrafast magnetic field generation without external magnetic fields.

Phase 2: OAM-Based Diffraction Imaging and Magnetic Helicoidal Dichroism (SG2)

This phase resulted in two major experimental breakthroughs.

First, OAM-based extreme ultraviolet ptychography was demonstrated using spiral zone plates, achieving a ~30% improvement in spatial resolution compared to conventional Gaussian illumination. This enables sub-100 nm, time-resolved imaging over extended sample areas.

Second, time-resolved magnetic helicoidal dichroism (MHD) was experimentally observed in resonant EUV scattering experiments. Ultrafast laser excitation induced transient rearrangements of magnetic vortex structures, including the formation of metastable surface spin textures with reversed chirality. These results demonstrate the optical preparation of complex spin states without external magnetic fields, with relevance for ultrafast spintronics and data storage.

Phase 3: Fundamental Studies of OAM Transfer to Atoms (SG3)

The third phase addressed the fundamental possibility of OAM-driven atomic transitions that are forbidden within conventional dipole and multipole selection rules. The target transition was the excitation of helium from the 1s² ground state to the 1s2s metastable state using twisted XUV light.

To enable this experiment, a high-pressure open glass microcell was developed in collaboration with IFN Milan. The microcell allows controlled gas densities up to 120 mbar and was validated using interferometric calibration and synchrotron spectroscopy. Initial measurements revealed novel high-density effects, including modified Fano resonances and molecular-like spectral features.

Further developments included the integration of microelectrodes fabricated via FLICE technology to enable in situdetection of metastable atoms. While the final demonstration of OAM-induced monopole transitions is still ongoing, the necessary experimental infrastructure and detection capabilities were successfully established.

Scientific Results and Impact

The project has significantly advanced the understanding of structured light–matter interaction, ultrafast magnetization dynamics, and nanoscale imaging. Two of the three main objectives were fully achieved, resulting in new experimental methodologies with broad applicability in atomic physics, magnetism, and ultrafast spectroscopy. The partial completion of SG3 lays a solid foundation for future investigations into angular momentum transfer at the atomic scale

Publications Resulting from the Project

  • J. Wätzel et al., Phys. Rev. Lett. 128, 157205 (2022).
  • M. Pancaldi et al., Single-shot Ptychography with Extreme Ultraviolet OAM Beams, Optica 11, 3 (2024).
  • M. Fanciulli et al., Time-Resolved Magnetic Helicoidal Dichroism with EUV OAM Beams, Phys. Rev. Lett., in press.

The project was funded by the “Javna agencija za raziskovalno dejavnost Republike Slovenije”.

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