Tunable third-harmonic generation from polaritons in the ultrastrong coupling regime

TL;DR

This paper demonstrates tunable third-harmonic generation in polaritonic microcavities with ultrastrong coupling, achieving significant nonlinear enhancement by embedding nonlinear dye in a high-Q cavity, enabling efficient visible spectrum conversion.

Contribution

It introduces a method to achieve ultrastrong coupling with a high normalized ratio and demonstrates tunable third-harmonic generation with substantial enhancement in a polaritonic system.

Findings

Achieved a normalized coupling ratio of 62%, the highest reported.

Observed tunable third-harmonic generation across the visible spectrum.

Internal conversion enhancements exceeded three orders of magnitude.

Abstract

Strong inter-particle interactions between polaritons have traditionally stemmed from their exciton component. In this work, we impart a strong photonic nonlinearity to a polaritonic mode by embedding a nonlinear polymethine dye within a high-Q all-metal microcavity. We demonstrate nonlinear microcavities operating in the ultrastrong coupling regime with a normalized coupling ratio of 62\%, the highest reported to date. When pumping the lower polariton branch, we observe tunable third-harmonic generation spanning the entire visible spectrum, with internal conversion enhancements more than three orders of magnitude larger than in bare films. Transfer matrix calculations indicate that the observed enhancements are consistent with the enhanced pump electric field.