Investigation on Miniaturized Optical System for Rapid Steering Fountain Clock

The Rapid Steering Fountain Clock is a frequency reference device pivotal for steering hydrogen maser time-keeping. To fulfill time-keeping demands, enhancing the operational reliability and stability of the rapid-steering fountain clock is crucial. The optical system, being the most vulnerable component, is susceptible to environmental factors like temperature, causing fluctuations in atomic cloud temperature and atomic number, thereby deteriorating frequency stability. This study proposes a miniaturized optical system for the rapid-steering fountain clock, achieved by lowering light height, minimizing light path, reducing elastic adjustment frames, and optimizing optical path layout. Utilizing new designs such as waveplate polarizing beamsplitter combination, vertically positioned acousto-optic modulator, and double-pass through cat-eye acousto-optic modulator, all optical devices are integrated onto a 400mm×600mm optical bench with a standard 25 mm hole spacing. The entire optical system, wrapped in foam, underwent temperature fluctuation testing, revealing that with a 12 ℃ temperature change, the optical power fluctuation post-optical fiber in the longest optical path is below 6.6%, significantly improving the compactness and stability of the fountain clock optical system. When applied to the rapid-steering rubidium fountain clock, a daily atomic number fluctuation of 5.28% and a fountain clock frequency daily stability of 5.57E-16 were achieved.