Tunable virtual gain in resonantly absorbing media

TL;DR

This paper explores how virtual gain, a phenomenon where absorbing media mimic amplification, can be tuned and observed in resonant media at different light intensities, enabling dynamic control of optical responses.

Contribution

It provides a theoretical analysis of virtual gain in two-level resonant media, highlighting its dependence on light intensity and population inversion, and shows how it can be controlled without traditional gain media.

Findings

Virtual gain is most observable at low intensities in absorbing media.

The virtual gain can be tuned dynamically via population inversion.

Resonant absorbing media can mimic gain-like responses without instability.

Abstract

Virtual gain refers to the simulation of real light amplification using radiation with exponentially decaying amplitude, so that its complex frequency corresponds to the scattering pole. We theoretically study virtual gain in a two-level resonant medium for different regimes of light-matter interaction depending on the radiation intensity. We show that virtual gain at the pole can be most clearly observed for low intensities, when the medium is absorbing, in contrast to the saturated medium at high intensities. The efficiency of virtual gain can be tuned with the light intensity and can be controlled dynamically through the population inversion of the medium. Our results show that resonantly absorbing media paradoxically mimics gain-like response, which admit a number of related phenomena and methods to mold both optical signals and material properties without relying on instability-prone gain media.