Anomalous ring-down effects and breakdown of the decay rate concept in optical cavities with negative group delay

TL;DR

This paper investigates the unusual ring-down effects in optical cavities with negative group delay, revealing non-exponential decay and the breakdown of the traditional decay rate concept through theory, simulation, and experiment.

Contribution

It provides the first combined theoretical and experimental demonstration of anomalous ring-down effects caused by negative group delay in optical cavities.

Findings

Non-exponential cavity decay observed.

Additional resonance peaks in transmission.

Breakdown of the decay rate concept.

Abstract

Propagation of light pulses through negative group velocity media is known to give rise to a number of paradoxical situations that seem to violate causality. The solution of these paradoxes has triggered the investigation of a number of interesting and unexpected features of light propagation. Here we report a combined theoretical and experimental study of the ring-down oscillations in optical cavities filled with a medium with such a strongly negative frequency dispersion to give a negative round-trip group delay time. We theoretically anticipate that causality imposes the existence of additional resonance peaks in the cavity transmission, resulting in a non-exponential decay of the cavity field and in a breakdown of the cavity decay rate concept. Our predictions are validated by simulations and by an experiment using a room-temperature gas of metastable helium atoms in the detuned electromagnetically induced transparency regime as the cavity medium.