Design of nonlinear optical response of multipole-type excitons by film thickness and incident pulse width

TL;DR

This paper theoretically explores how film thickness and pulse width influence the nonlinear optical response of excitons confined in thin films, revealing optimal conditions for maximizing nonlinear signals despite damping.

Contribution

It introduces a theoretical model analyzing the nonlinear optical responses of confined excitons considering polarization, damping, and film parameters, highlighting optimal conditions for signal enhancement.

Findings

Fast-decay radiative modes dominate Kerr spectra even with high damping.

Optimal pulse width and film thickness maximize nonlinear signal intensity.

Confined excitons exhibit unique coupled states affecting nonlinear optical responses.

Abstract

We theoretically investigate the nonlinear optical pulse responses of excitons in a thin film where the excitonic center-of-mass motion is confined. A large interaction volume between excitons and radiation yields particular coupled states with radiative decay times reaching several femto-seconds. By considering two polarization directions of light, we reveal that these fast-decay modes dominantly survive in an optical Kerr spectra even under a massive nonradiative damping $\Gamma=30$ meV. The results clearly show that there is an optimal combination of the incident pulse width and the film thickness for maximizing the integrated intensity of nonlinear signals.