ИСТИНА

The idea to amplify subterahertz electromagnetic pulses in nonequilibrium plasma channels created in noble gases by the photoionization process in the intense ultrashort laser pulse was first proposed in [1]. The characteristic feature of noble gas cross sections is the presence of the Ramsauer minimum and a range with large positive value of derivative in some energy range. If one places peak of photoionization in the above mentioned energy range the amplification of low frequency radiation can be reached. The detailed study of amplification process during the propagation of THz pulses in plasma channels has been done in [2]. The current study is devoted to the amplification of ultrashort subterahertz pulses (including one-cycle) in nonequilibrium nitrogen plasma. Possibility of amplification in nitrogen is caused by the existence of the rapidly increasing range of transport cross section as well (between 1.5-2.2 eV). Due to the fast relaxation of electron energy distribution function (EEDF) forced by the vibrational excitations of nitrogen molecules in the range of 2-4 eV amplification is possible during the short time of order of picoseconds which enables to amplify extremely short subterahertz pulses. The specificity of ultrashort pulse amplification is the main issue of current investigation. References 1. A. V. Bogatskaya, E. A. Volkova, A. M. Popov., Jetp Lett., 97, p. 388 (2013). 2. A.V. Bogatskaya., I.V. Smetanin, E.A. Volkova, and A.M. Popov., Laser and Particle Beams, 33, p. 17 (2015).