Faster light with competing absorption and gain

TL;DR

This paper experimentally demonstrates significant pulse peak advancements in a fast-light medium with competing absorption and gain, achieving enhancements far beyond previous limits and exploring the transition between fast and slow light.

Contribution

It introduces a novel experimental setup using potassium-based four-wave mixing to enhance pulse advancement through competing absorption and gain effects.

Findings

Pulse peak advancements up to 88% of input pulse width

Enhancement occurs even with unity total gain, making the medium transparent

Fast light optimized for large pulse widths

Abstract

We experimentally investigate the propagation of optical pulses through a fast-light medium with competing absorption and gain. The combination of strong absorption and optical amplification in a potassium-based four-wave mixing process results in pulse peak advancements up to $88\%$ of the input pulse width, more than $35 \times$ that which is achievable without competing absorption. We show that the enhancement occurs even when the total gain of the four-wave mixer is unity, thereby rendering the medium transparent. By varying the pulse width, we observe a transition between fast and slow light, and show that fast light is optimized for large pulse widths.