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Polarization and frequency-controlled amplification in a nonequilibrium plasma in the presence of an external magnetic field

The method of controlling the spectral and polarization characteristics of a terahertz (THz) pulse during its amplification in nonequilibrium magnetized plasma is investigated. The physical mechanism involves the well-known cyclotron resonance, which has been demonstrated to strongly influence the features of nonequilibrium plasma — in particular, its amplifying and focusing ability. According to the suggested model, a static magnetic field is applied along the propagation direction of a femtosecond UV laser, which creates a nonequilibrium plasma channel. The seed linearly polarized THz pulse propagates in the channel after the ionizing UV pulse. The conducted numerical simulations are based on the self-consistent solution of the kinetic Boltzmann equation and second-order wave equation for THz pulse propagation. It is shown that by varying the magnetic field strength one can control the pulse carrier frequency as well as change the polarization to a circular one. For long THz pulses, the presence of a magnetic field provides the possibility to detune the ellipticity degree at the output of the plasma channel.