Fig. 1. Experimental setup. (a) Schematic diagram of frequency shift device; (b) physical image of large aperture saturated absorption optical path

Fig. 2. Energy level transfer diagram

Fig. 3. Relationship between modulation output and power of each level of FEOM

Fig. 4. Relationsheep between saturated absorption signal and spot diameter. (a) Changes of transition signal with spot diameter; (b) changes of SNR of saturated absorption signal stripe with spot diameter; (c) relationsheep between saturated absorption error signal and laser power when spot diameters are 3 mm and 8 mm, respectively; (d) changes of error signal slope with laser power

Fig. 5. Saturated absorption signals before and after modulation. (a) Signal before modulation; (b) signal after modulation; (c) signal with increased spot diameter after modulation; (d) error signal after modulation

Fig. 6. Cold atom cloud in MOT center

Fig. 7. Change of signal with time during frequency stabilization. (a) Saturation absorption error signal (illustration: acquisition error signal) (Note: error signal after locking slightly deviates from 0 is due to small gain of laser locking control system, which does not affect normal operation of experiment); (b) number of atoms falling into detection zone

Fig. 8. Main optical link of atomic fountain clock. (a) Optical path; (b) all fiber link