Specific features of terahertz radiation emitted from laser sparks induced in gases by femtosecond laser pulses with linear polarization

The increasing interest to the terahertz radiation is connected with it´s unique potential for lots of applications such as identification and detection of different objects and materials for the problems of security, biology, chemistry. Some of the most promising alternative for terahertz waves generation are laser plasma methods. Recently in Institute of Applied Physics RAS new experimental data were obtained. In the common scheme of generation (50 fs, 2.5 mJ linear polarized laserpulse, 80-400mm focal length lens) a radiation pattern with strong cylindrical assymetry depending on optic polarization was obtained. This effect could not be explained in terms of ponderomotive force like due to it´s axisymmetric character. Here the authors will discuss the process of electric current formation during the ionization in a given optic field and selfconsistent dynamics of electrons in plasma column with low frequency electromagnetic field. In the assumption of instantaneous electron appearance we used a semi-classical model based on Boltzman equation for electrons with the source of particles defined according to Keldysh law.