Intensity-Tunable All-Glass Kerr Meta-Optics

This thesis investigates intensity-tunable all-glass metaoptics based on the Kerr nonlinear response of fused silica. Phase-sensitive characterization methods were developed, combining modal decomposition for structured beams with ultrafast off-axis digital holography. Low-energy measurements of structured-light metasurfaces validated the platform and methodology for high-energy experiments.

The intensity-dependent response of fused-silica nanopillars was studied using FDTD simulations, which predicted only a small Kerr-induced phase shift before the expected damage threshold. Simulations with implanted gold nanoparticles predicted a five-orders-of-magnitude increase of the nonlinear response, while revealing critical simulation limitations. This motivated a high-energy two-dimensional experimental phase library as a function of nanopillar size and incident intensity. The measured response was larger than predicted and dependent on sample orientation, indicating additional contributions beyond the nanopillar Kerr response.

Measurements showed increasing thermal contributions with repetition rate at high intensity. The critical rate for thermal accumulation was predicted as 1.8 Hz, consistent with single-shot measurements following the 2 Hz curve. Simulations of phase response with incidence angle showed a weak dependence for small angles, at low or high intensity. Simulated optical vortices underwent intensity-dependent radial reshaping while preserving their topological charge, and metalenses showed focal displacement and deformation. The experimental library was interpreted as a two-intensity phase space for designing tunable devices.

Arbitrary phase transformations are not accessible, although a preliminary 800 µm -diameter metalens produced a simulated focal shift from 89 mm to 143 mm with focal degradation. This demonstrates partial intensity-dependent focal tuning, while identifying the main limitations of the approach. Overall, this work establishes a path towards intensity-tunable all-glass metaoptics by combining measured nanopillar responses with nonlinear substrate propagation.