Enhanced electromagnetic field-particle interactions in a waveguide

R. Gomez-Medina, P. San Jose, A. Garcia-Martin, M. Lester, M. Nieto Vesperinas(*) and J.J. Saenz

Dept. Fisica de la Materia Condensada, Univ. Autonoma de Madrid, 28049-Madrid, Spain.

(*)Inst. Ciencia de Materiales, C.S.I.C, Campus de Cantoblanco, 28049-Madrid, Spain.

The physical interactions between dielectric particles and electromagnetic modes in a waveguide are analyzed. In analogy with attractive defects in electronic wires [1], the coupling of the scattered field with the waveguide modes always induce resonant states of the scatter-guide system close to the onset of new modes. We analyze thisresonant phenomenon in terms of the transport eigenchannels (i.e., eigenstates of the transmission matrix). Just at the resonant condition, one of the channels is completely close while all the others transmit without any scattering. This is a very general phenomenon depending only on the existence of quasi-bound states [2]. As we will show, the analysis of the scattering induced by a small surface bump in an otherwise perfect waveguide shows the same behaviour close to the onset of a new mode.

The strong scatterer-field interactions at the resonance condition are analyzed in terms of the spatial field distribution around the scatterers. For a uniform random distribution of those defects, the scatter-guide resonances are shown to be responsible of the oscillating behaviour of different transport coefficients (mean free path, localization length,...) as a function of the wavelength or the waveguide width [3].


[1] C. S. Chu and R.S. Sorbello, Phys. Rev. B 40, 5491 (1989); P.F. Bagwell, Phys. Rev. B 41, 10354 (1989).
[2] Ch. Kunze and R. Lenk, Solid State Commun. 84, 457 (1992).
[3] A. Garcia-Martin et al., Appl. Phys. Lett. 71, 1912 (1997), Phys. Rev. Lett. 81, 329 (1998), ibid. (2000) (in press).