Using fundamental principles to understand and optimize nonlinear-optical materials

TLDR

Nonlinear‑optical research has largely relied on empirical methods, yet exact calculations of fundamental efficiency limits reveal that optimizing materials requires a blend of theoretical guidance and practical synthesis. The paper aims to apply fundamental principles to understand and optimize the nonlinear‑optical response of materials, offering practical guidelines for new material design. The authors use exact fundamental limits and a scale‑invariant figure of merit to identify the properties that make a material optimal for nonlinear‑optical response, reviewing a decade of progress. The fundamental approach is already producing practical guidelines for designing new nonlinear‑optical materials.

Abstract

Our approach to the problem of understanding the nonlinear-optical response of a material focuses on fundamental concepts, which are exact and lead to broad results that encompass all material systems. For example, one can calculate precisely and without approximation the fundamental limit of the efficiency of any optical phenomenon. Such limits, in turn, when built into a scale-invariant figure of merit can be used to determine what makes a material optimal for maximizing a desired property, such as its nonlinear-optical response. However, since the results are broad and general (for example, fundamental guidelines for making better quantum systems may demand a particular shape of an electron cloud or energy level spacing), the difficulty arises in implementing such fine tuning using the approaches available to the synthetic chemist or nanotechnologist. Undoubtedly, an intimate interplay of empirical and fundamental approaches will need to be applied to the problem of optimizing molecules and materials. Much of the work in the field of nonlinear optics has by necessity focused on empirical approaches. Our work focuses on the fundamental approach, which is beginning to bear fruit in providing practical guidelines for making new materials. This paper reviews progress made over the last decade.