Investigation of entire-space terahertz emission from gas filament excited by a two-color field

By using the finite-difference time-domain (FDTD) method, this paper studys the entire-space distribution of terahertz emission generated by a two-color field induced micro-plasma based on photocurrent model. The spatial distributions of terahertz spectra and waveforms versus emission angle are investigated in three planes perpendicular with each other for the first time, and the results show that terahertz emission mainly focuses on forward direction with polarization same as the excitation field. When emission angle increasing, the bandwidth narrows, the peak frequency red shifts, the emission intensity decreases, and the obtained results are accurately explained based on coherent superposition mechanism. In addition, through comparing theoretical results with experimental data, the correctness of terahertz emission distribution in entire space is comfirmed.