Unconventional modes in lasers with spatially varying gain and loss

TL;DR

This paper introduces a new class of lasing modes in spatially inhomogeneous gain media, characterized as surface modes localized at gain boundaries, expanding understanding of unconventional lasing phenomena.

Contribution

It identifies and characterizes surface lasing modes arising from spatial gain variations and links them to transmission resonances and PT-symmetric cavity modes.

Findings

Surface modes are localized at gain boundaries.

These modes originate from transmission resonances.

Connection established with PT-symmetric cavity modes.

Abstract

We discuss a class of lasing modes created by a spatially inhomogeneous gain profile. These lasing modes are "extra modes", in addition to, and very different from, conventional lasing modes, which arise from the passive cavity resonances. These new modes do not have high intensity across the entire gain region, but instead are localized at the gain boundary and throughout the gain-free region. They are surface modes, originating from the transmission resonances of the gain-free region. Using an S-matrix description we connect these surface modes to the lasing modes in PT-symmetric (balanced gain-loss) cavities.