Fig. 1. Schematic of single photon heterodyne velocity measurement experimental system

Fig. 2. Photograph of single photon heterodyne velocity measurement experimental system

Fig. 3. Data processing flow of coherent beat signal spectrum analysis

Fig. 4. The spectrums of the beat frequency signal under PCR of 134，270，428，545，640，800，902 and 920 kHz，respectively，DCR=1.8 kHz

Fig. 5. The signal amplitude，noise amplitude and SNR of spectrum under different PCR，DCR=1.8 kHz

Fig. 6. The spectrums of the beat frequency signal under PCR of 200，350，490，610，720，830，902，920，928，946，965，978，992，994，997 and 1 009 kHz，DCR=52.4 kHz

Fig. 7. Enlarged partial view of harmonic components in Fig.6（j），（m），（p）

Fig. 8. The signal amplitude，noise amplitude and SNR of spectrum under different PCR，DCR=52.4 kHz

Fig. 9. The spectrum of the beat frequency signal under different photon count rates，DCR=194.4 kHz

Fig. 10. The signal amplitude，noise amplitude and SNR of spectrum under different PCR，DCR=194.4 kHz