Electron trajectory backanalysis for spectral profile in two-color terahertz generation

The gas-phase medium ionized by two-color femtosecond field produces supercontinuum radiation ranging from the terahertz to midinfrared band. Under the strong-field approximation, the electron trajectory backanalysis is exploited to interpret the spectral profile of terahertz radiation. Meanwhile, the electron trajectory method can correlate terahertz spectral profiles and photoelectron momentum distributions (PEMDs). The coherent superposition of electron trajectories released from the consecutive cycles is found to induce the high-frequency cutoff and sharpen the spectral bandwidth of supercontinuum radiation, tightly coinciding with the intercycle interference fringes in PEMDs. The trajectory analysis exhibits that single electron interference plays an important role in the terahertz generation process. Our method provides an intuitive interpretation in terms of electron trajectory perspective and sheds light on the microscopic mechanisms of terahertz generation.