Nanosecond Ramsey spectroscopy for Ca beam optical clocks

Atomic beam optical clocks offer continuous operation, simplified structure, and excellent short- to mid-term stability, making them promising candidates for next-generation optical flywheel clocks. However, the atomic utilization efficiency in current thermal beam optical clocks remains below 1%, limiting their further performance enhancement. Therefore, maximizing the utilization of atoms within the atomic beam has become a critical problem. In this work, we propose an innovative nanosecond Ramsey spectroscopy for Ca beam optical clocks, which enables the full utilization of atoms with all transverse velocities. The spectral amplitude is enhanced 2300 times compared to conventional Ca beam optical clocks, and the frequency stability can reach the quantum projection noise limit of $$1.2\times 1{0}^{-17}/\sqrt{\tau }$$ in theory, comparable to the best cold-atom optical clocks. This approach paves the way for high-precision, transportable flywheel optical clocks.