The research of 369.5 nm laser stabilizing method and its influence on ytterbium ion optical clock

The 369.5 nm laser serves as the cooling laser for ytterbium-ion optical clocks, and its frequency instability directly affects the intensity of ion fluorescence. This paper compares two stabilization methods for a 369.5 nm frequency-tripled fiber laser: locking to a femtosecond optical frequency comb (FOFC) and locking to a wavelength meter. The FOFC-locked laser achieves a frequency instability of 2.85 × 10−13 at 1 s, three orders of magnitude lower than that of the wavelength meter-locked laser. Fluorescence variations from a single Yb+ ion are monitored under both locking schemes; the FOFC lock produces less than half the fluorescence fluctuation observed with the wavelength meter lock, thereby improving the signal-to-noise ratio. The reduced fluorescence noise lowers the quantum projection noise of the Yb+ optical clock, enabling the attainment of lower overall clock instability.