Superradiant lasing in inhomogeneously broadened ensembles with spatially varying coupling.

Anna Bychek,Christoph Hotter,David Plankensteiner,Helmut Ritsch

doi:10.12688/openreseurope.13781.2

Abstract

Background: Theoretical studies of superradiant lasing on optical clock transitions predict a superb frequency accuracy and precision closely tied to the bare atomic linewidth. Such a superradiant laser is also robust against cavity fluctuations when the spectral width of the lasing mode is much larger than that of the atomic medium. Recent predictions suggest that this unique feature persists even for a hot and thus strongly broadened ensemble, provided the effective atom number is large enough. Methods: Here we use a second-order cumulant expansion approach to study the power, linewidth and lineshifts of such a superradiant laser as a function of the inhomogeneous width of the ensemble including variations of the spatial atom-field coupling within the resonator. Results: We present conditions on the atom numbers, the pump and coupling strengths required to reach the buildup of collective atomic coherence as well as scaling and limitations for the achievable laser linewidth. Conclusions: We show how sufficiently large numbers of atoms subject to strong optical pumping can induce synchronization of the atomic dipoles over a large bandwidth. This generates collective stimulated emission of light into the cavity mode leading to narrow-band laser emission at the average of the atomic frequency distribution. The linewidth is orders of magnitudes smaller than that of the cavity as well as the inhomogeneous gain broadening and exhibits reduced sensitivity to cavity frequency noise.

Highlights

Collective stimulated emission of coherent light by atoms inside an optical cavity is a fundamental phenomenon studied for decades in quantum optics [1,2,3,4,5,6,7]
Such a superradiant laser typically operates in a bad-cavity regime, where the cavity mode is much broader than the natural linewidth of the atoms providing the gain
We study a model of a superradiant laser and focus on inhomogeneity among the atomic ensemble

Summary

INTRODUCTION

Collective stimulated emission of coherent light by atoms inside an optical cavity is a fundamental phenomenon studied for decades in quantum optics [1,2,3,4,5,6,7]. We numerically investigate the dynamics of an atomic medium with a wide range of resonance frequencies and show how the intensity of the pumping rate can lead to cooperative effects among the atoms such that superradiant lasing is achieved. (e-f) The mean photon number and the linewidth as functions of the atom-cavity coupling strength g and pumping rate R. The mean intra-cavity photon number and the laser linewidth ∆ν (the FWHM of the spectrum) are depicted in Figure 2 as functions of the number of atoms, pumping rate, and atom-cavity coupling strength. The lasing threshold the collective emission of light with an ultra-narrow linewidth is observed In this collective regime the phases of the atomic dipoles are synchronized via photon exchange through the cavity which leads to the buildup of a collective dipole among the atoms. We will consider the atoms to be subject to distinct frequency shifts and different couplings to the resonator mode

ATOMIC ENSEMBLES WITH INHOMOGENEOUS BROADENING

INHOMOGENEOUSLY BROADENED ENSEMBLES WITH VARIABLE COUPLING

CONCLUSIONS