Feasibility of Extreme Ultraviolet Active Optical Clock

We propose an experimental scheme of vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) optical frequency standards with noble gas atoms. Considering metastable state 3P2 noble atoms pumped by a conventional discharging method, the atomic beam is collimated with transverse laser cooling at the metastable state and enters into the laser cavity in the proposed setup. Due to stimulated emission from the metasable state to the ground state inside the laser cavity consisting of VUV reflection coating mirrors, our calculations show that with enough population inversion to compensate for the cavity loss, an active optical frequency standard at VUV and XUV is feasible.