A survey of atomic frequency standards

摘要: The survey reviews the historical background and development of atomic frequency standards leading to most recent achievements. A qualitative discussion underlying principles is also included. Modern produced in United States are illustrated, performance data reflecting present state art presented. comparison different types complicated by many quantitative factors relating physical characteristics which differ each case. However, on a basis it may be stated that rubidium gas cell are, at time, compact, light weight oscillators, they have high level short-term stability. long-term stability this case exceeds best quartz crystal oscillators two or more orders magnitude without need for long warm-up stabilization periods. Calibration terms primary standard required. cost less than other standards. Cesium beam somewhat larger heavier standards, limited shot noise cesium tube resonance signal. term very high, limits not yet been measured averaging has degree intrinsic reproducibility qualifies service as calibration. hydrogen maser, present, highest stability, when compared with commercially It largest influenced advanced characteristics. New developments progress include thallium controlled active maser. Along these advances, new improvements will continue made various established likely their relative qualities remain approximately same, absolute values advanced.