Quasi-continuous sub-$\mu$K strontium source without a high-finesse cavity stabilized laser

TL;DR

This paper presents a compact, robust method for producing ultra-cold strontium atoms using a fiber-based frequency comb as a stable frequency reference, eliminating the need for high-finesse cavity-locked lasers.

Contribution

It introduces a novel, cavity-free, fiber-based frequency comb system for stable laser cooling of strontium, enabling field-deployable continuous cold atom sources.

Findings

Achieved sub-$$K temperatures in strontium samples.

Demonstrated quasi-continuous outcoupling from the MOT.

System performance comparable to cavity-locked laser setups.

Abstract

We demonstrate a quasi-continuous sub-$\mu$K strontium source achieved without the use of a high-finesse cavity-locked laser. Our frequency reference is based on a dispersion-optimized, fiber-based frequency comb that enables sub-kHz linewidths. The long-term stability of the comb is defined by an external RF reference: either a 10 MHz RF signal from the Dutch Metrology Institute (VSL), or a tunable RF source whose long-term stability is maintained by monitoring and stabilizing the position of a narrow-line magneto-optical trap (MOT). The comb-stabilized system is benchmarked against a conventional cavity-locked laser and achieves comparable performance in broadband and single-frequency MOTs using the narrow $^1$S$_0$ $\rightarrow$ $^3$P$_1$ laser cooling transition. We generate high-flux, sub-$\mu$K samples of all three bosonic strontium isotopes and demonstrate quasi-continuous outcoupling from the MOT. These results highlight the system's suitability for compact, robust, and field-deployable continuous cold atom devices.