Time-resolved two-photon excitation of long-lifetime polaritons

TL;DR

This paper reports time-resolved two-photon excitation measurements of long-lifetime polaritons, revealing an angle-dependent process into lower polariton states involving exciton states, which is symmetry-forbidden at normal incidence.

Contribution

It demonstrates the direct two-photon excitation into lower polariton states at non-zero angles, highlighting the role of state mixing and symmetry considerations.

Findings

Two-photon excitation into lower polaritons is angle-dependent.

Excitation into the $1s$ exciton state is observed at non-zero angles.

Symmetry forbids this process at normal incidence, but it becomes allowed otherwise.

Abstract

Recent studies of two-photon excitation of exciton-polaritons in microcavities have considered the possibility of an allowed absorption process into the $2p$-state of the excitons which participate in the polariton effect. Here we report time-resolved measurements of two-photon excitation directly into the lower polariton states invoking the $1s$ state of the excitons. Although this process is forbidden by symmetry for light at normal incidence, it is allowed at non-zero angle of incidence due to state mixing.