A classical model of the upper bounds of the cascading contribution to the second hyperpolarizability

TL;DR

This paper examines the limits of molecular cascading effects on second hyperpolarizability, revealing that cascading cannot surpass the fundamental limit but can aid in designing materials with large third-order responses when direct contributions are absent.

Contribution

It provides a theoretical analysis of the upper bounds of cascading contributions to second hyperpolarizability, clarifying their role in nonlinear-optical material design.

Findings

Cascading can lower the direct contribution at high hyperpolarizability values.

Cascading contributes when the direct second hyperpolarizability is zero.

Cascading cannot exceed the fundamental nonlinear-optical limit.

Abstract

We investigate whether microscopic cascading of second-order nonlinearities of two molecules in the side-by-side configuration can lead to a third-order molecular nonlinear-optical response that exceeds the fundamental limit. We find that for large values of the second hyperpolarizability, the side-by-side configuration has a cascading contribution that lowers the direct contribution. However, we do find that there is a cascading contribution to the second hyperpolarizability when there is no direct contribution. Thus, while cascading can never lead to a larger nonlinear-optical response than for a single molecule with the same number of electrons, it may provide design flexibility in making large third-order susceptibility materials when the molecular second hyperpolarizability vanishes