Free-electron induced mode mixing and surface-polariton enhanced reflected THz-field

The main result of this talk is the prediction of large enhancements at the band edges of a coupled Bloch-surface-plasmon-polariton band in the spectrum of the reflected far electromagnetic field due to anti-crossing gaps induced by the strong coupling between the continuous surface-plasmon-polariton mode and the discrete Bloch-like modes. The existence of these Bloch-like modes is a direct consequence of the nonlocal mixing of specular and diffraction modes of the reflected electromagnetic field by free-electron induced optical polarization and the interference of a pair of surface optical-polarization waves with opposite Bragg order numbers in the presence of a grating. The interference of these two counter-propagating surface waves leads to the formation of a Wannier-like state with associated electromagnetic fields localized within the grating-gap regions. The effects of the sheet density, grating period and absorption loss on the optical enhancements of both transmitted and reflected electromagnetic fields are investigated.