Stability improvement of ⁴⁰Ca⁺ optical clock by using a transportable ultra-stable cavity

The instability of the clock laser is one of the primary factors limiting the instability of the optical clocks. We present an ultra -stable clock laser based on a 30 -cm -long transportable cavity with an instability of -3 x 10-16 at 1 s-100 s. The cavity is fixed by invar poles in three orthogonal directions to restrict the displacement, meeting the requirements of transportability and low vibration sensitivity. By applying the ultra -stable laser to a transportable 40Ca+ optical clock with a systematic uncertainty of 4.8 x 10-18 and using the real-time feedback algorithm to compensate the linear shift of the clock laser, the short-term stability of the transportable 40Ca+ root Variation Selector-2 root Variation Selector-2 optical clock has been greatly improved from 4.0 x 10-15/ i/s to 1.16 x 10-15/ i/s, measured at -100 s-1000 s of averaging time, enriching its applications in metrology, optical frequency comparison, and time keeping. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement