Fig. 1. THz waveforms from femtosecond laser ionized Ar-gas plasma and THz wave peak-to-peak amplitude for different laser intensities. (a) THz waveforms; (b) dependence of THz wave peak-to-peak amplitude on laser intensity

Fig. 2. THz waveforms from femtosecond laser ionized Ar-gas plasma under different E_DC and THz waveform without E_DC shown in inset. (a) Positive electric field; (b) negative electric field

Fig. 3. Linear dependence of THz wave peak-to-peak amplitude on external electric field

Fig. 4. THz waveforms and angle dependence of peak-to-peak amplitude when E_DC＝1.0 kV/cm. (a) THz waveforms with or without laser field at acceleration stage; (b) THz wave peak-to-peak amplitude versus θ

Fig. 5. THz wave peak-to-peak amplitude of laser plasma radiation before and after applied electric field