The excitation of terahertz (THz) plasmons by a pre-bunched relativistic electron beam propagating in a parallel plane semiconducting guiding system is studied. It is found that the n-InSb semiconductor strongly supports the confined surface plasmons in the terahertz frequency range. The growth rate and efficiency of the THz surface plasmons increase linearly with modulation index and show the largest value as modulation index approaches unity. Moreover, the growth rate of the instability scales as one-third power of the beam density and inverse one-third power of the THz radiation frequency.

The generation of Terahertz (THz) radiation by a density modulated relativistic electron beam (REB) using rippled density plasma, oriented at a suitable angle along the direction of radiation wave, is being investigated in this paper. The non-linear interaction of density modulated REB with ripple density plasma modifies the dispersion relation of the radiation wave co-propagating with the beam wave. Using fluid equations model, it is found that the requisite ripple wavelength decreases as the ripple angle increases and becomes steeper for resonant THz radiation emission. Thus, the radiation wavelength in terahertz range can be tuned by varying the ripple wavelength and beam energy. In addition, it is investigated that the growth rate of THz radiation emission scales as the one-third power of beam current, two-third power of ripple plasma density, and one-third power of modulation index. The output power and efficiency of THz radiation emission depend on the modulation index and reach the largest value when modulated beam velocity is comparable with the phase velocity of the wave as the modulation index approaches unity.

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