Absorption-induced confinement of lasing modes in diffusive random medium

TL;DR

This study numerically investigates how local absorption in diffusive random media confines lasing modes within the pumped region, altering mode characteristics and enabling discrete lasing peaks.

Contribution

It reveals that absorption-induced reabsorption confines lasing modes, significantly differing from passive quasimodes, and reduces effective system size.

Findings

Lasing modes are confined within the pumped volume despite extended passive quasimodes.

Absorption broadens decay rate distribution, promoting discrete lasing peaks.

Reabsorption suppresses feedback from unpumped regions, effectively reducing system size.

Abstract

We present a numerical study of lasing modes in diffusive random media with local pumping. The reabsorption of emitted light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasimodes of the passive system (without gain or absorption). Even if all the quasimodes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absorption broadens the distribution of decay rates of quasimodes and facilitates the occurrence of discrete lasing peaks.