Modeling and analysis of an ultra-stable subluminal laser

TL;DR

This paper presents a highly stable subluminal laser design utilizing a composite gain spectrum, significantly reducing frequency sensitivity to cavity length changes and narrowing linewidth, with potential for various practical applications.

Contribution

It introduces a novel composite gain profile combining broad and narrow spectra, enhancing laser stability and linewidth reduction, supported by both analytical and numerical models.

Findings

Stability enhanced by a factor up to 10^5

Fundamental linewidth reduced by the same factor

Close agreement between idealized and physical models

Abstract

We describe a subluminal laser which is extremely stable against perturbations. It makes use of a composite gain spectrum consisting of a broad background along with a narrow peak. The stability of the laser, defined as the change in frequency as a function of a change in the cavity length, is enhanced by a factor given by the group index, which can be as high as 105 for experimentally realizable parameters. We also show that the fundamental linewidth of such a laser is expected to be smaller by the same factor. We first present an analysis where the gain profile is modeled as a superposition of two Lorentzian functions. We then present a numerical study based on a physical scheme for realizing the composite gain profile. In this scheme, the broad gain is produced by a high pressure buffer-gas loaded cell of rubidium vapor. The narrow gain is produced by using a Raman pump in a second rubidium vapor cell, where optical pumping is used to produce a Raman population inversion. We show close agreement between the idealized model and the explicit model. A subluminal laser of this type may prove to be useful for many applications.