Localized modes revealed in Random Lasers

TL;DR

This paper demonstrates that in strongly scattering media, individual lasing modes can be spatially localized using non-uniform gain, leading to lower thresholds and improved efficiency, advancing the understanding of random laser modes.

Contribution

The study reveals that all lasing modes in a low-dimensional random laser are spatially localized when gain competition is managed, enabling better control and efficiency.

Findings

All lasing modes are spatially localized with non-uniform gain.

Selective excitation reduces lasing threshold significantly.

Spatial location of modes boosts laser power efficiency.

Abstract

In sufficiently strong scattering media, light transport is suppressed and modes are exponentially localized. Anderson-like localized states have long been recognized as potential candidate for high-Q optical modes for low-threshold, cost effective random lasers. Operating in this regime remains however a challenge since Anderson localization is difficult to achieve in optics and nonlinear mode interaction compromise its observation. Here, we exhibit individually each lasing mode of a low-dimension solid-state random laser by applying a non-uniform optical gain. By undoing gain competition and cross-saturation, we demonstrate that all lasing modes are spatially localized. We find that selective excitation reduces significantly the lasing threshold while lasing efficiency is greatly improved. We show further how their spatial location is critical to boost laser power-efficiency. By efficiently suppressing spatial hole burning effect, we can turn on the optimally-outcoupled random lasing modes. Our demonstration opens the road to the exploration of linear and nonlinear mode interactions in the presence of gain, as well as disorder-engineering for laser applications.