Room-temperature condensation in whispering gallery microresonators assisted by longitudinal optical phonons

TL;DR

This paper demonstrates room-temperature condensation of whispering gallery modes in ZnO microwires, facilitated by interactions with longitudinal optical phonons, leading to coherent UV lasing with spatial coherence.

Contribution

It reveals a novel room-temperature condensation mechanism in microresonators involving LO phonons and multimodal WGM systems in ZnO microwires.

Findings

Condensation occurs below the first LO phonon replica of ZnO excitons.

Lasing modes exhibit spatial coherence.

Multimodal WGM interactions with LO phonons enhance condensation probability.

Abstract

We report condensation of hexagonal whispering gallery modes (WGM) at room temperature in ZnO microwires that embody nearly perfect polygonal whispering gallery microresonators. The condensate regime is achieved in the UV spectral range only at energies below the first longitudinal optical (LO) phonon replica of the free ZnO A-exciton transition and at non-zero wave vectors. We demonstrate that the multimodality of the WGM system and the high population of free excitons and phonons with various momenta strongly enhance the probability of an interaction of quasiparticles of the cavity exciton-photon system with LO phonons. We further examine the far-field mode pattern of lasing WGM and demonstrate their spatial coherence.