Crossover from exciton-polariton condensation to photon lasing in an optical trap

TL;DR

This study demonstrates how optical trapping techniques enable the observation of a crossover from exciton-polariton condensation to photon lasing in a microcavity, revealing a two-threshold behavior with potential for novel photonic phases.

Contribution

It compares single-spot and ring-shaped excitation methods, showing how optical trapping influences the transition between exciton-polariton condensation and photon lasing.

Findings

Ring-shaped excitation induces two-threshold behavior.

Exciton-polariton condensate appears at the first threshold.

Photon lasing occurs at the second threshold.

Abstract

Optical trapping has been proven to be an effective method of separating exciton-polariton condensates from the incoherent high-energy excitonic reservoir located at the pumping laser position. This technique has significantly improved the coherent properties of exciton-polariton condensates, when compared to a quasi-homogeneous spot excitation scheme. Here, we compare two experimental methods on a sample, where a single spot excitation experiment allowed only to observe photonic lasing in the weak coupling regime. In contrast, the ring-shaped excitation resulted in the two-threshold behavior, where an exciton-polariton condensate manifests itself at the first and photon lasing at the second threshold. Both lasing regimes are trapped in an optical potential created by the pump. We interpret the origin of this confining potential in terms of repulsive interactions of polaritons with the reservoir at the first threshold and as a result of the excessive free-carrier induced refractive index change of the microcavity at the second threshold. This observation offers a way to achieve multiple phases of photonic condensates in samples, e.g., containing novel materials as an active layer, where two-threshold behavior is impossible to achieve with a single excitation spot.