摘要
Atomic clocks operating at microwave region,are divided into two categories according to the mode of operation,namely the passive mode,in which the standard frequency of a clock signal is locked on to a very narrow atomic spectral line such as in cesium beam
Atomic clocks operating at microwave region, are divided into two categories according to the mode of operation, namely the passive mode, in which the standard frequency of a clock signal is locked on to a very narrow atomic spectral line such as in cesium beam and rubidium gas cell clocks, and the active mode, where the atomic ensemble itself can produce a high stable and accurate standard frequency signal such as hydrogen maser. The hydrogen maser has been the most stable atomic clock for nearly half a century, and has been applied in a variety of scientific research fields.
