Fig. 1. Principle diagram of laser automatic frequency locking based on MTS

Fig. 2. Theoretical curves and linear characteristics of MTS signal at different modulation frequencies（all curves are normalized）

Fig. 3. Structure diagram of laser automatic frequency locking system

Fig. 4. Schematic diagram of automatic frequency locking state machine

Fig. 5. The flow chart of locking the frequency point to be locked in the similarity recognition state

Fig. 6. The characteristic spectrum and the received spectrum slide convolution and show a peak at the overlap

Fig. 7. Structure diagram of beat frequency optical path

Fig. 8. Beat frequency fluctuation and Allan variance of stability under different integration time before and after frequency locking in short time

Fig. 9. Beat frequency fluctuation and Allan variance of stability under different integration time before and after frequency locking in long time

Fig. 10. The process of laser unlocking and relocking caused by artificially blocking the emitted light

Fig. 11. Beat frequency fluctuation in the process of laser relocking after unlocking and Allan variance of stability under different integration time after relocking