Fig. 1. Absolute frequency locking setup for the ML.

Fig. 2. (a) Profile of the custom-built astigmatism Herriott cell. (b) Space and energy distributions of the light spot of the astigmatism Herriott cell shown in (a).

Fig. 3. (a) Schematic of the noise test of the CO2 cell. (b) Experimental results of CO2 cell noise test. Detailed MPI noise is also shown, of which the amplitude is about 2 mV.

Fig. 4. Relationship between the error signal and the relative frequency.

Fig. 5. (a) Frequency stabilization test of the ML. (b) Details of the beat note shown in (a). (c) Allan deviation of the ML.

Fig. 6. OPLL system for the offline-seeder laser and online-seeder laser; LO, local signal; PFD, phase-frequency detector.

Fig. 7. (a) Frequency drift of online-seeder laser when offset locked to the ML at 760 MHz after being divided by eight using the OPLL setup shown in Fig. 6. (b) Frequency drift of offline-seeder laser when offset locked to the ML at 7.616 GHz after being divided by 64 using the OPLL setup shown in Fig. 6.