Second-order processes in organic thin films

This research project focuses on developing organic thin films with strong second-order optical nonlinearities using physical vapor deposition, specifically thermal evaporation. The goal is to create materials suitable for advanced photonic devices without the need for electrical poling, which is typically required to achieve the necessary noncentrosymmetric structure.

We demonstrate that by leveraging the spontaneous orientation of polar molecules during the deposition process, we can obtain thin films with bulk second-order susceptibilities exceeding 20 pm/V. This approach breaks the out-of-plane symmetry, resulting in films with nonlinear properties comparable to or exceeding those of established materials like lithium niobate and aluminum nitride. For this project, we investigate various molecules, fabrication conditions, and substrate treatments to optimize the nonlinear coefficients. We also explore coevaporation techniques, combining molecules with strong spontaneous orientation and high hyperpolarizability to enhance overall nonlinearities.

The significance of this work lies in its potential to simplify the fabrication of nonlinear optical materials for integrated photonics. By eliminating the need for electrical poling and demonstrating compatibility with existing photonic fabrication processes, this approach opens up new possibilities for heterointegration on various photonic platforms. While the current results are promising, further optimization of molecular design and deposition conditions could lead to even higher $\chi^{(2)}$ values, potentially surpassing those of state-of-the-art nonlinear optical materials.

Collaborators on this project are the Perepichka Group @ McGill University and the Martel Group @UdeM.

The initial work for this project was published in ACS Photonics: https://pubs.acs.org/doi/full/10.1021/acsphotonics.4c01190