相干布居数拍频(coherent population beating,CPB)现象,产生于一个Λ型三能级原子系统中,当双色相干激光场的频率差和两基态能级频率间隔近失谐的时候,原子在激发态能级上的布居数会产生一个弛豫振荡,且振荡频率等于失谐量.当将此现象运用于原子标准频率的提取时,CPB频标的稳定度与CPB信号的幅度及信噪比直接相关.本文理论推导了描述CPB现象的表达式,数值模拟并实验研究了87Rb基态超精细子能级的相干性对CPB信号的影响,通过控制与基态子能级共振相干激光场的抽运时间来控制能级的相干程度,观测不同相干程度对CPB信号质量的影响.研究结果表明CPB信号振荡的幅度与基态子能级相干程度成正比关系.要改善CPB信号信噪比、提高原子频标稳定度,建立、提高和保持基态超精细能级的相干性是关键.本文还讨论了CPB现象用于弱磁场测量及其他方面应用的可行性.
Research on chip-scale atomic clocks （CSACs） based on coherent population trapping （CPT） is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance＇s collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.
