Anisotropic Confinement of Chromophores Induces Second-Order Nonlinear Optics in a Nanoporous Photonic Metamaterial

TL;DR

Embedding chromophores in nanoporous silica creates anisotropic conditions that induce second-order nonlinear optical effects, such as second-harmonic generation, by confining and orienting molecules at the nanoscale.

Contribution

This work demonstrates a novel method to induce nonlinear optics in isotropic materials through nanoscale confinement and molecular orientation control.

Findings

Nanoporous silica with conical channels exhibits SHG due to molecular orientation.

Confinement induces non-centrosymmetric dipolar order in chromophores.

The approach enables designing nonlinear optical materials via nanoporosity and molecular confinement.

Abstract

Second-order nonlinear optics is the base for a large variety of devices aimed at the active manipulation of light. However, physical principles restrict its occurrence to non-centrosymmetric, anisotropic matter. This significantly limits the number of base materials exhibiting nonlinear optics. Here, we show that embedding chromophores in an array of conical channels 13 nm across in monolithic silica results in mesoscopic anisotropic matter and thus in a hybrid material showing second-harmonic generation (SHG). This non-linear optics is compared to the one achieved in corona-poled polymer films containing the identical chromophores. It originates in confinement-induced orientational order of the elongated guest molecules in the nanochannels. This leads to a non-centrosymmetric dipolar order and hence to a non-linear light-matter interaction on the sub-wavelength, single-pore scale. Our study demonstrates that the advent of large-scale, self-organised nanoporosity in monolithic solids along with confinement-controllable orientational order of chromophores at the single-pore scale provides a reliable and accessible tool to design materials with a nonlinear meta-optics.