Modeling of a continuous superradiant laser on the sub-mHz $^1$S$_0\,\rightarrow\,^3$P$_0$ transition in neutral strontium-88

TL;DR

This paper proposes a design for a continuous superradiant laser on a narrow strontium transition, aiming to enhance optical clock stability by overcoming pulsed superradiance limitations through simulation and modeling.

Contribution

It introduces a novel combined approach of high-flux cold atom beam and bowtie cavity design, with models predicting sub-100 mHz linewidth and stable continuous operation.

Findings

Estimated laser linewidth below 100 mHz

Predicted output power of hundreds of femtowatts

Feasibility demonstrated through simulation of cooling and loading processes

Abstract

Continuous superradiance using a narrow optical transition has the potential to improve the short-term stability of state-of-the-art optical clocks. Even though pulsed superradiant emission on a mHz linewidth clock transition has been shown, true continuous operation, without Fourier limitation, has turned out to be extremely challenging. The trade-off between maintaining a high atomic flux while minimizing decoherence effects presents a significant obstacle. Here, we discuss the design of a machine that could overcome this problem by combining a high-flux continuous beam of ultra cold strontium atoms with a bowtie cavity for the generation of superradiant lasing. To evaluate the feasibility of our design, we present simulation results for continuous high-efficiency cooling, loading, and pumping to the upper lasing state inside the bowtie cavity. We then present two different models for stimulating the generated superradiant field by taking into account position-dependent shifts, collisional decoherence, light shifts, and atom loss. Finally, we estimate a laser linewidth of less than 100 mHz, limited by atom number fluctuations, and resulting in an output power of hundreds of fW.