上海天文台时间频率研究室以原有被动型氢钟物理部分为基础,开展了脉冲微波式氢原子钟的研究.设计电路产生2个相干微波脉冲,连续激励氢原子跃迁,模拟“双腔共振”,使氢原子发生Ramsey干涉,压缩氢原子跃迁谱线宽度,以期提高氢原子钟短期稳定度指标.具体做法为:用DDS产生扫频电路,混频生成1.420 405 GHz激励信号后,再用CPLD产生脉冲时序控制数字衰减器,将激励信号衰减为脉冲形式,激励氢原子发生Ramsey干涉,导出微波信号并进行相关处理就可以产生Ramsey条纹.已观测到Ramsey干涉条纹,其中心峰宽度为1.2 Hz,相比传统被动型氢原子钟压缩了60％.%Time & frequency research center in Shanghai Astronomical Observatory has carried out theoretical analysis and relative research on pulsed microwave hydrogen maser based on conventional passive hydrogen clock. Circuit is designed to generate two coherent pulses. The pulses simulating two coherent microwave fields can successively stimulate hydrogen atomic transition to induce Ramsey interference. It could compress the line width of atomic transition spectrum so as to improve the stability performance of hydrogen maser. The concrete method is generating sweep signals by DDS, mixing it to detecting signals in 1.420 405 GHz, outputting timing sequence by CPLD to make the digital attenuator attenuating detecting signals to pulsed form, inducing Ramsey interference with the pulsed detecting signals, exporting the microwave signal from cavity and doing some processing to generate Ramsey fringes. So far, Ramsey fringes have been observed and the line width of the central fringe is about 1.2 Hz, which is 60% narrower than that of the continuous microwave in the same condition.
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