Terahertz wave generation by the upper hybrid wave

This paper investigates the excitation of terahertz radiation (in the form of a magnetosonic wave) by the interaction of the upper hybrid (pump) wave and the extraordinary wave (laser). The ponderomotive force due to the nonlinear interaction between the pump wave and the extraordinary wave (laser) generates a nonlinear current at the difference frequency. If the appropriate phase matching conditions are satisfied and the frequency of the pump is appropriate, then this difference frequency can be brought in the terahertz range. The extraordinary wave propagates perpendicular to the static magnetic field and is polarized perpendicular to the static magnetic field. The expressions for the coupling coefficients of the three-wave interaction have been derived. The analytical expression for the electric vector of the terahertz wave has been obtained. By changing the strength of the magnetic field, one can enhance or suppress the terahertz emission. For the typical laser plasma parameters used here (plasma density n0=5.3x1018 cm-3, pump wave frequency (ω0)=1.810x1014 rad/s, normalized pump wave amplitude μ=0.4, and applied magnetic field B0=105, 150, and 205 kG for T=1 KeV), the generated terahertz emission can be at the power level of gigawatts. The power spectrum of the generated radiations is also given. The expression for growth rate of this decay instability is also calculated; we have found that the value of decay growth rate comes out to be of the order of 108 s-1.