Fig. 1. (a) Average light intensity signal after combination; (b) average light intensity signal after combination (without direct current component Aref2)

Fig. 2. Experimental setup of real-time monitoring system for center frequency of pulse laser

Fig. 3. Real-time display of calculation result of center frequency

Fig. 4. Test program of performance for beat frequency measurement system

Fig. 5. Average light intensity of combined beam generated by frequency shifting, chopping and self-heterodyne

Fig. 6. Results of measurement by maximum method with sampling rate of 2 GSa·s-1. (a) Center frequency of 104 pulses; (b) frequency number distribution of center frequency

Fig. 7. Measurement results of continuous laser beat frequency. (a) Beat frequency signal of continuous laser; (b) center frequency of beat frequency signal of continuous laser

Fig. 8. Spectra of the beat frequency signal under different sampling rates. (a) Sampling rate is 2 GSa·s-1; (b) sampling rate is 1 GSa·s-1