Fig. 1. The fitted curve of the response bandwidth of the air coherent detection technique with different pulse durations of the probe laser

Fig. 2. The THz pulse distortions induced by air coherent detection technique with different probe laser pulses（50 fs，100 fs，150 fs，and 200 fs），the input THz pulse has a central frequency of 2 THz（black line），（a）shows their time waveforms，（b）shows their frequency spectra，and（c）shows their pulse energy loss，0 fs duration in（c）means the initial normalized THz pulse energy

Fig. 3. The THz pulse distortions induced by air coherent detection technique with different probe laser pulses（50 fs，100 fs，150 fs，and 200 fs），the input THz pulse has a central frequency of 5 THz，（a）shows their time waveforms，（b）shows their frequency spectra，and（c）shows their pulse energy loss

Fig. 4. The THz pulse distortion induced by the different probe laser pulses（50 fs，100 fs，150 fs，and 200 fs），the input THz pulse has a central frequency of 8 THz，（a）shows their time waveforms，（b）their frequency spectra，and（c）their pulse energy loss

Fig. 5. The evolutions of THz pulse frequency redshift（a）and its pulse energy loss（b），X-axis is the central frequency of input THz pulses from 1 THz to 10 THz，and Y-axis is the duration of the probe laser pulses from 30 fs to 220 fs