Prospects for an Active Optical Clock Based on Cavityless Lasing

Active optical clocks take advantage of the substantial suppression of cavity pulling in the bad-cavity lasing regime and feature the simple structure and excellent portability. In the extreme case, where the cavity mirror reflection approaches zero and cannot support any quasi-bound modes for light waves, conventional bad-cavity lasers become the cavityless lasing and the cavity pulling vanishes. Consequently, the laser frequency is determined entirely by the atomic transition. This work is dedicated to theoretically explore the potential application of the cavityless lasing in active optical clocks. Without loss of generality, Cs atoms with well-established quantum control techniques are employed as the gain medium that is pumped by a 459-nm laser. The clock laser wavelength is 1470 nm. The simulation shows that the frequency stability of the clock laser with feasible physical quantities reaches 3.4x10-14$3.4\times 10<^>{-14}$ at 1 s of averaging time, one order of magnitude better than the recently demonstrated compact passive optical clocks that are built upon a two-photon transition in a hot Rb vapor and upon the modulation transfer spectroscopy of thermal Cs atoms. Such compact cavityless lasing-based active optical clocks have the broad application prospect in satellite navigation and communications and promise an architecture for the integrated photonic metrology. Cavity noise strongly influences the short-term performance of local oscillators in conventional passive optical clocks through the cavity pulling. The pulling effect vanishes in the cavityless lasing whose central frequency is completely determined by the atomic transition. Active optical clocks based on the cavityless lasing possess advantages of simple structure, compact size, and potentially high stability.image