期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：29
DOI：10.1073/pnas.2205636119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Nonlinear three-wave mixing is a fundamental physical pathway in nonlinear optical materials, providing a route for producing a high-energy photon through two input photons. This report proposes a generalized phase-matching theory that evaluates second-order nonlinear optical properties for arbitrary polarization structures. It predicts light amplification pathways by using polarization helices, which are justified by experiments based on spontaneous helielectric nematic fluids. The unique polar electric field switching of the helielectrics enables the dynamic tuning of the emitted nonlinear light. The discovery not only introduces a general principle for nonlinear optical calculation but also contributes to a significant advance in diversifying the category and structure of polar materials.
Second-order optical nonlinearity is the essential concept for realizing modern technologies of optical wavelength conversion. The emerging helical polarization fluid, dubbed helielectric nematic, now makes it possible to design and easily fabricate various polarization structures and control their optical responses. The matter family is demonstrated as an ideal liquid platform for nonlinear optical conversion and amplification with electric-reconfigurable tunability. We here develop a universal phase matching theory and reveal a nonclassic chirality-sensitive phase-matching condition in the polarization helices through both the numerical calculation and the experimental validations. The nonlinear optical amplification can be dramatically modulated with a contrast ratio of >100:1 by an in-plane electric field. Furthermore, we employ the director relaxation under electric fields coupled with nonlinear optical simulation to clarify the topology–light interactions.
