| Time（frequency）is one of the seven base quantities defined by the International System of Units and has the highest level of measurement accuracy among all physical quantities.High-performance time and frequency are crucial national strategic resources and have emerged as focal points of international competition in quantum technology.The compact cesium beam atomic clock,commonly known as the compact cesium clock,is a primary frequency standard capable of generating and maintaining real-time high-precision time-frequency signals with exceptional accuracy and mid-to-long-term stability.The compact cesium beam clock is the main timekeeper in the calculation of International Atomic Time and serves as the core clock in standard time generation systems worldwide.Compact magnetic-state-selection cesium beam atomic clocks have served as primary timekeeping devices in most countries for a long time;however,the advances in laser technology have led to the development of compact optically pumped cesium beam atomic clocks,which offer several advantages over their magnetic-state-selection counterparts.The preparation of the atomic state in these clocks employs optical pumping rather than atomic-state magnetic screening,thereby eliminating the need for bulky state-selected magnets.This change significantly increases the population of atoms in clock transitions and thus improve the theoretical frequency stability.In addition,compact optically pumped cesium beam atomic clocks employ laser detection for clock transitions rather than electron multiplier detection,thereby overcoming domestic technological challenges and extending the overall lifespan of the clock.This dissertation addresses the key technological challenges involved in engineering compact optically pumped cesium beam atomic clocks,provides a detailed study of a transition that is insensitive to fluctuations in the static magnetic fields,and proposes and experimentally demonstrates a highly sensitive method for measuring atomic microwave fields.Partial core components or modules of the cesium beam tube,laser system,and electronic system have also been developed.Integrating of the systems locks the Ramsey clock transition signal,and thus,the frequency stability performance of our compact optically pumped cesium beam atomic clocks was measured as:<5×10-12（1 s）、<3.5×10-12（10 s）、<8.5×10-13（100 s）、<2.7×10-13（1000 s）、<8.5×10-14（10000 s）.The research contents of this dissertation are organized as follows.（1）Study of the Zeeman effect.The dependence of the ground state transition frequency of cesium atoms（?=±1,?8）=0)on the static magnetic field is calculated using the Breit-Rabi formula,the Zeeman frequency shift of the conventional0-0 clock transition（?=±1,?8）=0,8)=0)and that of non-0-0 transitions are compared,the advantages of non-0-0 transitions as clock transitions are elucidated.Non-0-0 transitions exhibit a smaller offset in the Zeeman frequency shift under specific static magnetic fields.（2）Study of magnetic resonance in a microwave-excited cesium atomic beam.This study investigates the effect of the strength of the microwave magnetic field on the transition probability of the ground state of the cesium atoms using atomic density matrix and atomic flight time distribution models.Experimental setups for cesium atomic beam with Rabi and Ramsey magnetic resonances are constructed.The optimal operating strength of the microwave magnetic field in compact optically pumped cesium beam atomic clocks is determined by measuring and analyzing the impact of the microwave magnetic field on the fluorescence signal of the atomic beam.In addition,a novel method for the detection of microwave fields based on the atomic beam,which offers a high signal-to-noise ratio,is developed and experimentally demonstrated by using the field sensitivity of beam fluorescence.（3）Study of spatial distribution of atomic beams.To achieve a highly collimated cesium atomic beam,we use the Monte Carlo method to simulate the angular distribution and flux characteristics of the atomic beam that traverses multiple layers of collimating micropores.These simulations accurately predict the atomic utilization and consumption rates,allowing the lifetime of compact optically pumped cesium beam atomic clocks to be calculated.（4）Development of a laser system for a compact optically pumped cesium beam atomic clock.The laser system is responsible for providing pumped light to"purify"the atomic energy levels and detect light for extracting the clock transition signal,thus playing a crucial role in the compact optically pumped cesium beam atomic clocks.A comprehensive investigation of various laser frequency-locking techniques established a strategy for the development of laser systems using atomic-beam fluorescence stabilization.We introduce a compact optical system,develop a laser frequency stabilization circuit,and experimentally ensure compliance with engineering application requirements for compact optically pumped cesium beam atomic clocks.（5）Development of an electronic system for a compact optically pumped cesium beam atomic clock.The electronic system integrates physical and optical systems into a cohesive unit to enable the clock to generate a stable standard frequency signal.This dissertation describes the development of digital servo circuits,microwave signal sources,and standard signal generation circuits for the electronic system.All implemented electronic system modules were successfully employed in the closed-loop locking of the clocks. |
