Effect of the electron drift in graphene on the polarization conversion of a normally incident wave

The polarization conversion of an electromagnetic wave normally incident on graphene with a direct electric current is investigated in the hydrodynamic approach. It is shown that the dynamic conductivity of graphene depends on the direction of electron drift even in the absence of spatial dispersion (i.e., for long electromagnetic waves). This changes the polarization of electromagnetic radiation at terahertz frequencies. The real part of the dynamic conductivity of graphene with electron drift can be negative, which leads to amplification of terahertz wave.