Exploring the Nature of High-Order Cavity Polaritons under the Coupling-Decoupling Transition

TL;DR

This study experimentally investigates high-order cavity polaritons in multimode cavities, revealing a transition between coupled and decoupled regimes as cavity thickness varies, with notable spectral and dynamical changes.

Contribution

It demonstrates the coupling-decoupling transition in multimode cavities experimentally, highlighting spectral and ultrafast dynamical differences with fixed coupling strength.

Findings

Spectral response varies during the transition despite constant coupling strength.

Pronounced upper-polariton emission observed in multimode cavities.

Ultrafast spectra change significantly across the transition.

Abstract

Recently, we predicted theoretically that in cavities that support several longitudinal modes, strong coupling can occur in very different manners, depending on the system parameters. Distinct longitudinal cavity modes are either entangled with each other via the material or independently coupled to the exciton mode. Here we experimentally demonstrate the transition between those two regimes as the cavity thickness is gradually increased while maintaining fixed coupling strength. We study the properties of the system using reflection and emission spectroscopy and show that even though the coupling strength is constant, different behavior in the spectral response is observed along the coupling-decoupling transition. In addition, we find that in such multimode cavities pronounced upper-polariton emission is observed, in contrast to the usual case of a single-mode cavity. Furthermore, we address the ultrafast dynamics of the multimode cavities by pump-probe spectroscopic measurements and observe that the transient spectra significantly change through the transition.