Nonlocal mode mixing and surface-plasmon-polariton-mediated enhancement of diffracted terahertz fields by a conductive grating

Abstract

This work generalizes our previous study of the effect of plasma-wave induced longitudinal fields ͓D. H. Huang et al. J. Appl. Phys. 100, 113711 ͑2006͔͒. We incorporate a conductive grating on top of a conducting sheet for generating and mixing Bragg modes arising from a reflected and/or transmitted electromagnetic field. It also generalizes our recent work on the coupling of electronically modulated two-dimensional plasmons with the surface plasmon ͓G. Gumbs and D. H. Huang, Phys. Rev. B 75, 115314 ͑2007͔͒ by including the retardation and longitudinal-field effects in calculating the diffracted near and far electromagnetic fields. The main result of this paper is the prediction of large enhancements at the band edges of a coupled Bloch-surfaceplasmon-polariton band in the spectrum of the reflected far electromagnetic field due to anticrossing gaps induced by the strong coupling between the continuous surface-plasmon-polariton mode and discrete Blochlike 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 counterpropagating 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, plasmon instability, grating period, angle of incidence, and absorption loss on the optical enhancements of both transmitted and reflected electromagnetic fields are investigated.

Surface-plasmon mediated near-field light diffraction

“…If the array is infinite and all the slits, as well as the filled dielectric materials, are identical for a periodic system, 11,12,19,20 the continuous variable β becomes a discrete reciprocal wave number j(2π/D) where D is the array period and j = 0, ±1, · · · .…”

Comparing the image potentials for intercalated graphene with a two-dimensional electron gas with and without a gated grating

“…12,13 We assume that the periodic potential is along the x direction and that the modulated sheet density can be described by n 2D ͑x͒ = ͚ n=−ϱ ϱ n exp͑inGx͒, where the real-value n is the nth Fourier component of n 2D ͑x͒, G =2 / d is the reciprocal-lattice vector, and d is the period of the potential. In this case, we have as the potential outside the layered system ͑see the Appendix for details͒,…”

Tunable surface plasmon instability leading to emission of radiation

“…In addition to the work cited above, the role played by plasma excitations in the THz response of 2D microstructures has received considerable attention, [7][8][9][10][11][12][13][14][15][16] as well as plasmon properties in fullerenes. [17][18][19] Plasmon modes of quantum-well transistor structures in the THz range may be excited with the use of far-infrared (FIR) light and other means.…”