Continuous-wave virtual-state lasing from cold ytterbium atoms

TL;DR

This paper demonstrates a novel continuous-wave laser using a virtual lower level in cold ytterbium atoms, enabled by two-photon processes and magneto-optical trapping, with potential applications in precision measurement.

Contribution

It introduces a new lasing mechanism involving virtual levels in cold atoms, realized in a magneto-optical trap without additional repumping, expanding laser technology possibilities.

Findings

Lasing verified by threshold behavior and photon correlations.

The process runs continuously without additional repumping.

Potential adaptation to other atomic transitions like the ytterbium clock transition.

Abstract

While conventional lasers are based on gain media with three or four real levels, unconventional lasers including virtual levels and two-photon processes offer new opportunities. We study lasing that involves a two-photon process through a virtual lower level, which we realize in a cloud of cold ytterbium atoms that are magneto-optically trapped inside a cavity. We pump the atoms on the narrow $^1$S$_0$ $\to$ $^3$P$_1$ line and generate laser emission on the same transition. Lasing is verified by a threshold behavior of output power vs.\ pump power and atom number, a flat $g^{(2)}$ correlation function above threshold, and the polarization properties of the output. In the proposed lasing mechanism the MOT beams create the virtual lower level of the lasing transition. The laser process runs continuously, needs no further repumping, and might be adapted to other atoms or transitions such as the ultra narrow $^1$S$_0$ $\to$ $^3$P$_0$ clock transition in ytterbium.