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

Abstract

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.

Multiband dynamics of extended harmonic generation in solids under ultraviolet injection

“…where k is the crystal momentum, m (or n) is the band indice, ρ mn is the density matrix element, with m = n representing interband polarization and m = n population, E is the band dispersion, F(t) is the electric field, d is the transitional dipole moment (TDM), T 2 is the empirical dephasing time and k ′ = k + A(t) is the crystal momentum in the moving frame. Note that T 2 is set to infinity unless otherwise stated and the influence of shorter dephasing time [53] will be illustrated later. The total current can be split into the interband and intraband contributions:…”

Investigation of the Spatio-Temporal Characteristics of High-Order Harmonic Generation Using a Bohmian Trajectory Scheme

“…More crucially, this theory considers ionized electrons to be free electrons traveling in a laser field, ignoring the influence of coulomb potential. The phase of harmonic emission is also affected by the change in coulomb potential, which in turn influences the intensity and interference structure of harmonics [35][36][37][38]. HHG obtained in the experiment is a coherent superposition of all atomic harmonics in the gas target so that the precision of the harmonic phase of a single atom will affect the accuracy of the harmonic calculation as a whole [39].…”

Modulation of High-Order Harmonic Generation from a Monolayer ZnO by Co-rotating Two-Color Circularly Polarized Laser Fields

“…In the past decade, a large number of theoret-ical and experimental studies related to HHG have been carried out for series of solid materials with different band gaps and properties. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Among them, two-dimensional crystal materials have become popular target for solid high-order harmonics due to their unique electronic structure, excellent optical properties, strong electron-electron interaction, and negligible propagation effects. [49,50] In addition, polarization characteristics of high-order harmonics of two-dimensional materials have a strong tunability, and it is possible to utilize two-dimensional materials to generate circularly polarized high-order harmonics.…”