Colloidal Self-Assembly as Templating for 3D Second-Harmonic Photonic Crystals

Three-dimensional nonlinear (second-harmonic) photonic crystals can simultaneously generate different non-linear processes, such as second-harmonic generation (SHG), optical parametric amplification, and other sum- and difference-frequency processes [1], [2]. However, creating large crystals in all three dimensions, mainly in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$z$</tex> direction, presents a considerable challenge, primarily due to the chemical inertness of metal oxides [3]–[5].