Strong-coupling-assisted formation of coherent radiation below the lasing threshold

TL;DR

This paper demonstrates that by leveraging strong light-matter coupling and time-modulated pumping, coherent radiation can be achieved below the traditional lasing threshold, resulting in narrower linewidths and enhanced coherence.

Contribution

It introduces a novel method to generate coherent radiation below the lasing threshold using strong coupling and pump modulation, surpassing conventional laser limitations.

Findings

Linewidth reduced by two orders of magnitude

Coherence function improved from two to one

Coherent radiation achieved below lasing threshold

Abstract

The creation of nanoscale lasers that operate above a coherent threshold is a challenging problem. We propose a way to circumvent this issue using systems in which a strong coupling regime is achieved between the light and the active medium. In the strong coupling regime, energy oscillations take place between the EM field in the cavity and the atoms. By applying appropriate time modulation to the pumping, it is possible to control these energy oscillations in such a way that coherence in the laser system appears below the lasing threshold. We show that in this approach, the radiation linewidth is two orders of magnitude smaller than the linewidth of a conventional laser for the same photon number. In addition, the second order coherence function of the output radiation is reduced from two to one before the system reaches a positive population inversion. Our results pave the way for the creation of nanoscale sources of coherent radiation that can operate below the lasing threshold.