Decoherence Effects of Terahertz Generation in Solids under Two-Color Femtosecond Laser Fields

We theoretically investigate terahertz emission from solid materials pumped by intense two-color femtosecond laser field in the presence of decoherence effects. Quantum-mechanical simulations are based on the length gauge semiconductor Bloch equations describing the optical excitation and decoherence with phenomenological dephasing and depopulation times. Contributions of interband and intraband mechanisms are identified in time domain, and the latter has dominated THz generation in solid-state systems. It is found that dephasing is crucial for enhancing asymmetric intraband current and deduced that solid-state materials with short dephasing time and long depopulation time would be optimal selection for strong-field terahertz generation experiments.