The photon kinetic approach toward terahertz radiation

Abstract

A one dimensional spatiotemporal model for the femtosecond laser pulse interaction with air is developed in which the laser pulse propagation as well as the plasma formation and evolution accompanied with the THz radiation are investigated numerically. The photon kinetic approach based on the Klimontovich kinetic equation for the photons is used to describe the ultrashort laser pulse propagation while the Ammosov–Delone–Krainov approach accompanied with the plasma fluid equations is used to investigate the plasma formation and evolution, respectively. It is noteworthy that the model main focus was on the investigation of the long standing disagreement on the mechanisms of air-plasma THz radiation. Therefore, the three mechanisms of plasma current radiation, four-wave mixing by third order nonlinear susceptibility, and the interaction with the self exited plasma wave were inserted into the model, and their contributions to the THz emission were computed and compared. Our obtained results show that the interaction with the plasma wave plays no role in THz generation, while the nonlinear polarization and the plasma current are the two competing mechanisms, which both have significant roles in air plasma THz radiation.