The project tackled the longstanding challenge of demonstrating the non-dissipative transfer of orbital angular momentum orbital angular momentum from light to a mechanical oscillator - an open question in optical physics. Initial experimental tests using a mesoscale torsional pendulum (a centimeter-long wire with a millimeter-scale mirror) revealed that the low-frequency torsional signal expected from light-induced torque was overwhelmed by ambient mechanical noise. This outcome highlighted the need for a microscale system to achieve a sufficient signal-to-noise ratio.
In response, the project developed and validated torsional micropendulums fabricated via direct laser writing. These microstructures exhibited torsional oscillations in the kilohertz range, enabling the effective filtering of mechanical noise even in ambient (non-vacuum) conditions. To support experimental design and interpretation, a theoretical model of optical torque transfer was developed, confirming the expected dynamics of light–matter angular momentum coupling.
A key materials-related outcome was the identification of pure SZ2080 photopolymer as a suitable medium for device fabrication. Unlike earlier microdevices made with addition of a photoinitiator, the new micropendulums reliably withstood high optical intensities, ensuring stable and repeatable measurements. All fabrication data have been made openly available on Zenodo, promoting transparency and reproducibility.
To conduct and automate the experiments, the project built a custom optoelectronic pump–probe system that enabled the precise excitation of micropendulums via orbital angular momentum transfer and the automated measurement of amplitude and phase spectra. Robust and precise, the system remains operational at the host laboratory, supporting ongoing research in optomechanics and integrated photonics. All accompanying Python automation scripts are also available on Zenodo.
A major scientific milestone was achieved with the first experimental demonstration of torsional oscillations driven by non-dissipative transfer of orbital angular momentum - a result that complements the classic 1935 Beth experiment, which confirmed such transfer for spin angular momentum. A journal article reporting this breakthrough is in preparation, with submission expected by the end of 2025.
Throughout the project, the researcher conducted two visits to Vilnius University Laser Research Center, acquiring practical expertise in direct laser writing, refining device design, and fabricating the core samples used in the experiments. These visits also helped reinforce collaboration between the host SINGULAR group (LOMA, Bordeaux, France) and the Laser Nanophotonics group (Vilnius, Lithuania).
The project also fostered international scientific dialogue through exchanges with the research teams of Prof. Filippo Romanato (Padua, Italy) and Prof. Yujie Chen (Guangzhou, China) on ongoing experiments involving optical torque and orbital angular momentum multipliers.
To support dissemination and outreach, a dedicated project website was launched to share research progress, background information, and public-facing materials:
https://geotkach.github.io/oscillight-msca/(opens in new window).
Finally, the project designed a prototype torsional micropendulum for optical excitation at oblique incidence, offering greater flexibility in future experimental configurations. Although fabrication via direct laser writing is still under refinement, the prototype points to a promising direction for continued development.
