Molecular nonlinear optics: recent advances and applications

Abstract

The field of nonlinear optics continues to evolve and impact many fields and particularly has promising applications in the biomedical field. Furthermore, a major application, all-optical switching, has still not been realized because of the lack of a suitable material with high nonlinear figure of merit. This review focuses specifically on molecular materials that provide an opportunity for optimization of optical nonlinearity at two levels: microscopic and bulk. We present essential physics at these two levels and describe how the relationship between microscopic and bulk levels can be exploited to design new materials with enhanced optical nonlinearity. In this context, we introduce recent advances in multiscale modeling. The emphasis in this review is placed on third-order optical nonlinearity that governs all-optical processes. We discuss the current status of nonlinear optical studies on new molecular systems and the challenges to be met. This review covers newly emergent promising directions, together with their most impactful applications, and thus is beyond the comprehensive account of all the progress that has been made in the area of molecular nonlinear optics. Therefore, novel directions for enhancing molecular nonlinearities are presented, which include twist-motif chromophores, synergistic coupling between bond length alternation and high density of states, microscopic cascading, hybridization of states, etc. We then present some specific, promising nonlinear media. In this context, metamaterials and metasurfaces are also discussed, as they play an important role in the enhancement of nonlinearities and light manipulations. Another new direction covered is chiral nonlinearity. Finally, we present some selected major applications of nonlinear optics, specifically in optical signal processing, optical limiting, biophotonics, and upconversion random lasing. The review concludes with the authors’ views on the future perspective.