High-performance laser system for compact cold-atom optical clock

We demonstrate a straightforward frequency-locking technique that employs external modulation saturation absorption spectroscopy to achieve a high-performance 780 nm laser system. By externally modulating the laser frequency through a fiber electro-optic modulator, this scheme can stabilize multiple transitions of the 87Rb D2 line with excellent performance. Experimental results establish fractional frequency instability of 2.21 × 10-13 at 1 s with a linewidth of 1.46 kHz for the cycling transition 5S1/2(Fg = 2) → 5P3/2(Fe = 3). Notably, we have locked the system to the repumping transition 5S1/2(Fg = 1) → 5P3/2(Fe = 2), achieving a record-low instability of 1.98 × 10-12 at 1 s averaging time. This simplified laser system, featuring exceptional short-term frequency stability and multi-frequency locking capability, serves as a critical subsystem for the compact cold-atom optical clock, enabling advanced precision metrology applications. Furthermore, its metrological performance enables immediate applications in other quantum sensors, such as Rydberg electrometry, atomic magnetometry, and matter-wave interferometry.