Phonon-Assisted Lasing in ZnO Microwires at Room Temperature

TL;DR

This paper demonstrates room temperature phonon-assisted whispering gallery mode lasing in ZnO microwires, showing how free exciton recombination with phonon emission can achieve laser action in high-quality microresonators.

Contribution

It reports the first observation of phonon-assisted WGM lasing in ZnO microwires at room temperature, highlighting the role of phonon scattering and resonator quality in laser operation.

Findings

Lasing occurs above a threshold of ~100 kW/cm^2.

Lasing modes are WGM-related and linearly polarized perpendicular to the wire axis.

Spectral and emission pattern changes confirm laser operation.

Abstract

We report on room temperature phonon-assisted whispering gallery mode (WGM) lasing in ZnO microwires. For WGM laser action on the basis of the low gain phonon scattering process high quality resonators with sharp corners and smooth facets are prerequisite. Above the excitation threshold power $P_{\textit{Th}}$ of typically $100\,kW/cm^2$, the recombination of free excitons under emission of two longitudinal optical phonons provides sufficient gain to overcome all losses in the microresonator and to result in laser oscillation. This threshold behavior is accompanied by a distinct change of the far and near field emission patterns, revealing the WGM related nature of the lasing modes. The spectral evolution as well as the characteristic behavior of the integrated photoluminescence intensity versus the excitation power unambiguously prove laser operation. Polarization-resolved measurements show that the laser emission is linear polarized perpendicular to the microwire axis (TE).