Optical resonance in a narrow slit in a thick metallic screen

Interaction of TM-polarized waves with a subwavelength thick metallic slit has been analyzed. A Fabry-Perot-like behavior is reported. The resonance peaks, however, have very low magnitude and a systematic shift towards longer wavelengths is observed. The slit being narrow, this shift can be interpreted as the result of an aperture effect. Spectral transmission from a periodic array of such slits features the same peaks with a high increase in their magnitude, confirming that a grating acts as an amplifier of those resonances. Such a mechanism might explain the enhancement of the transmission observed in recent experiments [T.W. Ebbesen, H.J. Lezec, H.F Ghaemi, T.Thio, and P.A. Wolff, Nature (London) 391, 667 (1998)].