Extremely long range surface polaritons in a thin corrugated metal film Alexander V. Korovin V.Ye. Lashkarev’s Institute for Physics of Semiconductors, National Academy of Science of Ukraine, 41 prospect Nauki, Kiev 03680, Ukraine article info Article history: Received 9 October 2011 Received in revised form 4 July 2012 Accepted 6 July 2012 Available online 17 August 2012 Keywords: Long range surface plasmon polaritons Propagation length Corrugated film abstract The essential increase of propagation length of a long range surface plasmon polariton in a thin symmetrically corrugated plasmon-carrying film embedded in a dielectric medium is theoretically predicted. The calculations are based on the differential formalism for the system of Maxwells equations where the solution for electromagnetic fields is written as a superposition of partial plane waves in the presentation of a curvilinear non-orthogonal coordinates system for simplifying the boundary conditions. The spectral and angular dependencies of p-polarized light transmittance/ reflectance demonstrate that the in-plane shift between both profiles of corrugated film drastically changes the surface plasmon polariton propagation length from minimum of the asymmetric profile to maximum of the symmetric one. The obtained results were qualitatively explained using the model of weakly coupled photonic wells. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Considerable interest to nanoplasmonics has been stimulated by recent experiments on overcoming the classical diffraction limit for the light propagation in a plasmon-carrying structure in the regime of the surface plasmon polariton (SPP) excitation (see, for example, review [1]). Polaritons are quasiparticles manifesting strong interaction of photons and excitations in a matter (pho- nons, excitons, magnons, plasmons, etc.). Surface polaritons can only propagate along the interface between two different media and they are characterized by very high confinement of electric field at the interface and relatively low propagation losses [2]. In particular, SPPs are the surface electromagnetic waves that are located at interface between dielectric and plasmon-carrying media (metals or heavily doped semiconductors). They are observed up to the visible. In the case of a thin plasmon-carrying film the interaction between the single interface SPP (SISPP) at opposite film surfaces splits SISPP in two surface modes, if the surrounding dielectrics are almost the same identical. These split modes are characterized by the different propagation lengths and they are termed the long- range and short-range surface plasmon polaritons (LRSPPs and SRSPPs) in comparison with SISPP. For the first time this SPP splitting was theoretically predicted by Sarid [3] in the case of stratified structure, the SPPs in which are excited by evanescent waves at the attenuated total reflection regime of surface polariton. Similarly, the excitation of split SPPs by plane waves via the grating coupler effect was numerically studied in free standing thin corrugated metal films with a sinusoidal modulation [4,5] or the ridge-like modulation [6]. From practical point of view, the LRSPPs can be used as element of the extremely sensitive sensor [7]. Also, the use of semiconductor ultra-thin films opens the possibility to surface polariton UV optics that is compatible with standard Si technology [8]. The interaction of SPPs at opposite sides of plasmon-carrying film was also numerically analyzed in corrugated symmetric/asymmetric film, the profiles of which possess additional first harmonic, 2k g (where k g is the grating vector) [9]. This 2k g modulation opens up the SPP band gaps and leads to the anti-crossing between the dispersion branches of LRSPPs and SRSPPs. If a thin plasmon-carrying film is enclosed between different dielectrics, the SISPPs at opposite film sides are different and their interaction leads to their repulsion. The coupling between incident light and SISPPs in the case of a metal film with shifted profiles in an asymmetric dielectric environment was examined experimentally in the Kretschmann–Raether configuration. Such silver film was produced by evaporating metal on the grating partly at oblique incidence using the shadow of grating wires and partly at normal incidence to produce a continuous metal layer [10]. Theore- tical simulations was performed for thin metal films, which are corrugated on one or both surfaces in the framework of the coordinate transformation procedure developed by Chandezon et al. [11] and extended by Preist et al. for arbitrary profiled multilayer structures [12]. The results of theoretical calculations of Schroter and Heitmann [10] were replicated by Hooper and Sambles [13] with revised explanation in the framework of the iterative series solution method [14]. There are many different types of the electromagnetic modes such as waveguide, surface polariton, local excitations, etc. Over- all electromagnetic modes are characterized by the strong loca- lization of electromagnetic field in a small volume. By analogy with quantum well for electrons the structures with 1D confined Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optcom Optics Communications 0030-4018/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2012.07.087 E-mail address: Korovin@isp.kiev.ua Optics Communications 285 (2012) 5191–5197