A phenomenological model of the terahertz radiation of the plasma channel of a femtosecond filament has been elaborated that satisfactorily describes the experimental results of the detection of low-frequency radiation in air. The angular distributions of the terahertz radiation intensity in the absence and presence of an external electrostatic field have been obtained. The dependence of the divergence angle of the terahertz radiation on the filament parameters has been determined.
Bibliographical noteFunding Information:
This work was supported by the Russian Founda tion for Basic Research (project nos. 09 02 01200 a and 09 02 01522 a), the Council of the President of the Russian Federation for Support of Young Scien tists and Leading Scientific Schools (project no. MK 2213.2010.2), and the Ministry of Education and Sci ence of the Russian Federation (state contract no. 02.740.11.0223).