Fig. 1. Schematic of laser automatic frequency stabilization system

Fig. 2. Flow chart of laser automatic frequency stabilization

Fig. 3. Flow chart of dual feedback PZT

Fig. 4. Variance of saturated absorption signal during lock loss and re-lock of laser

Fig. 5. Saturated absorption curve and error signal curve during peak search. (a) Saturation absorption curve; (b) error signal curve

Fig. 6. Variance of saturated absorption signal with time during closed-loop operation of fountain atomic clock

Fig. 7. Error signal during frequency stabilization

Fig. 8. Laser frequency stability

Fig. 9. Closed-loop results of fountain atomic clock in Shanghai and Beijing