Geometry-Controlled Nonlinear Optical Response of Quantum Graphs

TL;DR

This study investigates how the geometry of quantum wire networks influences their nonlinear optical properties, revealing that specific geometries can significantly enhance hyperpolarizabilities, with potential for designing systems with ultralarge nonlinear responses.

Contribution

It introduces a novel analysis of geometry effects on quantum graphs' nonlinear optical responses, demonstrating significant hyperpolarizability enhancements through geometric optimization.

Findings

Certain geometries greatly enhance first hyperpolarizability.

Second hyperpolarizability remains negative or zero across geometries.

Optimized loop geometries rival top chromophores in nonlinear response.

Abstract

We study for the first time the effect of the geometry of quantum wire networks on their nonlinear optical properties and show that for some geometries, the first hyperpolarizability is largely enhanced and the second hyperpolarizability is always negative or zero. We use a one-electron model with tight transverse confinement. In the limit of infinite transverse confinement, the transverse wavefunctions drop out of the hyperpolarizabilities, but their residual effects are essential to include in the sum rules. The effects of geometry are manifested in the projections of the transition moments of each wire segment onto the 2-D lab frame. Numerical optimization of the geometry of a loop leads to hyperpolarizabilities that rival the best chromophores. We suggest that a combination of geometry and quantum-confinement effects can lead to systems with ultralarge nonlinear response.