Effects of polarization and laser profile on THz radiation generation through three-color laser pulses in ordinary and extraordinary modes.

THz radiation through a novel scheme based on a three-pulse configuration in two-dimensional ordinary and extraordinary modes was investigated. The electromagnetic radiation driven by the linear and nonlinear current density created by the laser-induced plasma mechanism has been evaluated. The numerical findings of the present study show that the electric field of THz radiation is significantly improved compared to the two-color scheme if the third harmonic is included. The asymmetric three-color femtosecond laser fields can be used to control the polarization state, radiation power, and the directivity of the THz radiation. With adjustable time delays between pulses, the polarization controllability of THz radiation from plasma, based on experimental conditions, can be achieved. With this scheme, not only tuning to circularly polarized THz radiation is feasible, but also linear or elliptical polarization can be realized by adjusting time delays. The effects of different laser profiles and wavelengths on ionization rate are considered. Variation of the electric field of the generated THz waves for both ordinary and extraordinary modes of photocurrent mechanism is examined numerically for various spatial laser profiles. The study indicates that a laser pulse profile can be used to control THz radiation. [ABSTRACT FROM AUTHOR]