Mainz 2026 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 17: Photonics and Biophotonics I
Q 17.6: Talk
Tuesday, March 3, 2026, 12:15–12:30, P 3
Colloidal Self-Assembly for 3D Second-Harmonic Photonic Crystals — •Thomas Kainz1, Ülle-Linda Talts2, Helena Weigand2, Rachel Grange2, Ullrich Steiner1, and Viola Vogler-Neuling1 — 1Adolphe Merkle Institute and NCCR Bio-inspired Materials, University of Fribourg, CH-1700 Fribourg, Switzerland — 2Institute for Quantum Electronics, Department of Physics, ETH Zürich, CH-8093 Zürich, Switzerland
Three-dimensional nonlinear (second-harmonic) photonic crystals can simultaneously generate different nonlinear processes. However, creating large crystals in all three dimensions presents a considerable challenge, primarily due to the chemical inertness of metal oxides. This study presents the first demonstration of colloidal-crystal templating into a second-order optical material. Self-assembled polystyrene opal templates are infiltrated with barium titanate sol-gel, resulting in an inverse fcc network of tetragonal barium titanate after calcination. Our samples have unprecedented sizes (>3000 unit cells in x, y directions and >100 in z) and reflectivity values above 80%. We engineered the final linear photonic bandgap and measured the second-harmonic generation (SHG) over it, including its intensity under polarization and its power dependence. We successfully replicated the photonic network into a second-order material and demonstrated, for the first time, a linear photonic band gap from a fully scalable three-dimensional photonic crystal made of a nonlinear optical material. We present the influence of a stopband on the SHG generation, with edge enhancement and inhibited spontaneous emission.
Keywords: 3D nonlinear photonic crystal; Second-harmonic generation; Colloidal self-assembly; Polystyrene opals; Inhibited spontaneous emission