Oral presentation

Session Information

Location: Science and Cultural Center - FORTH
Day: 2. Thursday 17th
Time: 12:10-12:30
Chairperson: to be announced…

Presentation Details

Presentation Type: Oral presentation
Title: Topological Phase Structures of Conical Refraction Beams: Fractional Orbital Angular Momentum as a Continuous Vortex Parameter for Sensing
Abstract: Topological textures in light fields such as vortices, phase singularities, and structured wavefronts carrying orbital angular momentum (OAM), have emerged as powerful probes of nanoscale material properties. While Laguerre-Gaussian (LG) modes remain the canonical vortex platform, their integer topological charge represents a discrete parameter space that may not fully exploit the richness of optical topology available in more complex beam geometries. Here we explore conical refraction (CR), the phenomenon arising when light propagates along the optical axis of a biaxial crystal, as a route to continuous, fractional OAM states, opening a broader topological parameter space for structured-light sensing. Using the Belsky–Khapalyuk–Berry diffractive theory of conical refraction, we characterise three distinct CR beam families , Lloyd, Poggendorff, and Raman, each carrying a unique topological fingerprint encoded in their azimuthal phase structure. Unlike LG beams, whose vortex charge is fixed by the generation condition, CR beams generate fractional topological charges that vary continuously with the crystal parameter, enabling systematic exploration of an extended vortex phase space. Full interferometric phase retrieval reveals sub-wavelength azimuthal phase gradients characteristic of each family, and we examine how these gradients respond to nanoscale refractive-index perturbations. Experimentally, the Poggendorff CR configuration demonstrates markedly enhanced phase-gradient contrast compared to LG beams under equivalent conditions, with refractive-index discrimination reaching a microscopic level. We further examine the propagation behaviour of all three CR families through heterogeneous, weakly scattering media, including thin cultures of healthy fibroblasts and melanoma cells, and characterise how the topological structure of each beam family evolves and encodes information about the scattering environment. These results position CR-generated fractional OAM as a distinct and underexplored class of optical topological texture, with open questions around vortex stability, phase evolution under disorder, and sensing functionality at the nanoscale that we hope will stimulate discussion within the POLYTOPO community, especially for biomedical applications.

Presenter

Ms Fatima Khanom
Aston University | United Kingdom

Authors

1. Galiakhmetova, Diana | Aston Institute of Photonic Technologies, Aston University, Birmingham, United Kingdom
2. Khanom, Fatima | Aston Institute of Photonic Technologies, Aston University, Birmingham, United Kingdom
3. Mohamed, Nawal | {Affiliation3:value}
4. Singh, Shakti | Aston Institute of Photonic Technologies, Aston University, Birmingham, United Kingdom
5. Mylnikov, Valentin | Ioffe Physical-Technical Institute, Saint Petersburg, Russia Aston Institute of Photonic Technologies
6. Sokolovskii, Grigorii | Ioffe Physical-Technical Institute, Saint Petersburg, Russia Aston Institute of Photonic Technologies
7. Meglinski, Igor | Aston Institute of Photonic Technologies, Aston University, Birmingham, United Kingdom
 8. Rafailov, Edik | Aston Institute of Photonic Technologies, Aston University, Birmingham, United Kingdom