Abstract:

THz emission of atoms in intense femtosecond Gaussian-enveloped laser pulses is investigated by solving time-dependent Schrödinger and Dirac equations (TDSE). It is deduced from the one-component laser field that the excitations of electron to the continuum and high Rydberg states are essential for the THz emissions. Upon this conclusion, an alternative description of the four-photon process is proposed to explain the significant enhancement of THz emissions by mixing the fundamental and its second order harmonic laser fields. This mechanism is confirmed with the help of a short-range shallow potential model. Besides, a biased electric field is also used to destroy the symmetry of the atomic system such that three-photon processes dominate in this situation. Finally a 5THz frequency laser field is superposed on the fundamental laser field to induce the generation of second harmonics which may involve both the three-and four-photon photon process discussed in the present study.
 
 
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