Anomalous optical properties of absorptive modulated metal film under surface plasmon polariton excitation conditions Alexandre V. Kats and Alexey Y. Nikitin Usikov Institute for Radiophysics and Electronics National Academy of Science of Ukraine, 12 Ak. Proskury St., 61085, Kharkov, Ukraine ABSTRACT The detailed theoretical analysis of the fine optical phenomena caused by surface plasmon polariton (SPP) excitation in a metallic film with weakly modulated dielectric permittivity is made for both symmetrical and nonsymmetrical dielectric arrangements. SPP modes in the film are close to those existing at an interface between metal and dielectric half spaces (these polaritons are weakly coupled under the symmetrical surrounding), and the effect of enhanced light transmission (ELT) caused by photon-SPP-photon transformations can occur. The advantage of the approach used is that we present the most interesting results in a simple analytical form. The dispersion relation for the film SPP for both arrangements is investigated. On this basis the comprehensive examination of the ELT effect is performed. The parameters of the problem (optimal film thickness, optimal modulation amplitude) responsible for total suppression of the zeroth- and/or nonzeroth-order reflected waves and maximal transmission are found. The results are of essential interest for optical nano-devices design. Keywords: Surface plasmon polariton, enhanced light transmission, metal film 1. INTRODUCTION After the first observation of the ELT through the metallic subwavelength holearray, 1, 2 a great deal of attention is devoted to this problem. This experiment was repeated more than once by those who had pioneered the ELT phenomenon, 3–5 and by others, see, for instance 6, 7 (the ELT was examined in the millimeter wave range as well 8 ). Some authors examined reflectivity from the hole arrays in metal films 5, 9 ; certain polarization properties, 10 and entanglement of photons in such films. 11 The investigations were devoted to measurements and calculations of transmission and reflection properties of metal films with other types of a periodic modulation. Specifically, the films having the modulated optical index of the metal, 12–14 dielectric pillars, 15, 16 relief corrugations 17–19 (in particular, the corrugations in the form of a set of concentric circular grooves surrounding a single subwavelength aperture 20 ), periodically allocated slits in the metal film 21–23 and arrays of metallic nanoparticles 24, 25 were examined. The ELT was also observed in non-zeroth diffraction orders by two different groups of authors 16, 19 (the independent detailed theoretical description of this effect was given in Ref. 26). The theoretical papers relevant to this subject present in main cases numerical simulations (see the description of numerical diffraction methods in monographs 27, 28 ). To the best of the authors’ knowledge there are only three papers 12, 13, 29 describing the qualitative physical picture of the effect. Different theories were proposed to explain the ELT: waveguide mode excitation, see for instance Refs. 29, 30; SPP modes excitation 12, 13, 26, 31, 32 ; and excitation of SPPs which are coupled through the waveguide modes of nanoholes (or slits), see. 4, 33 The authors can refer to the papers containing more or less detailed surveys of literature: Ref. 13 discusses some disagreements between recent papers; Ref. 34 presents a review of recent experimental and theoretical papers and applied aspects of the problem. In the present paper we consider the diffraction problem on a periodically modulated metal film both for oblique and normal incidence. To provide an analytical treatment we use the assumption of a large magnitude of the complex dielectric permittivity module (that is valid for metals in the visible and infrared regions of the spectra) and the smallness of the dielectric permittivity modulation. In our approach we neglect the dielectric Further author information: A.V.Kats: E-mail: avkats@online.kharkiv.com, Telephone: (38 057) 706 1812, 744 8331, Fax: Fax: (38 057) 744 1105, Address: PO Box 8847, 61002, Kharkov, Ukraine A.Yu.Nikitin: E-mail: alexey@ire.kharkov.ua, Telephone: (38 057) 744 8331, Fax: (38 057) 744 1105, Address: 13 Zolotoy Pereulok, 61140, Kharkov, Ukraine