Systematic study of terahertz wave generation in laser-included plasma

THz wave generation in laser-included plasma has attracted considerable attention recently and the intense THz waves generated from air-induced plasma, serving as broadband THz source for sensing and imaging applications, has attracted more and more researchers’ interests in recent years. In our experiment, terahertz is detected using THz Air-Biased Coherent Detection (THz-ABCD) method. This method can achieve the third-order nonlinear susceptibility tensor to produce field-induced optical second harmonic photons. In the THz-ABCD system, red-shift is observed in frequency spectra with enhanced pump power and decreased bandwidth. After changing the probe power, the red-shift in frequency spectral can also observed with enhanced probe power, but the bandwidth is broadening as the prober power increasing. We further explore of these phenomena through intense self-phase modulation of the optical pulse in the plasma and the collision behavior. This study reveals that we can control THz intensity and bandwidth by changing pump power and probe power in the ABCD system.