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Nano-Optics of Surface Plasmon Polaritons Anatoly V Physics Reports 408 (2005) 131–314 www.elsevier.com/locate/physrep Nano-optics of surface plasmon polaritons Anatoly V. Zayatsa,∗, Igor I. Smolyaninovb, Alexei A. Maradudinc aSchool of Mathematics and Physics, The Queen’s University of Belfast, Belfast BT7 1NN, UK bDepartment of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA cDepartment of Physics and Astronomy and Institute for Surface and Interface Science, University of California, Irvine, CA 92697, USA Accepted 1 November 2004 editor: D.L. Mills Abstract A surface plasmon polariton (SPP) is an electromagnetic excitation existing on the surface of a good metal. It is an intrinsically two-dimensional excitation whose electromagnetic field decays exponentially with distance from the surface. In the past, it was possible to study only the (far-field) scattered light produced by the interaction of surface polaritons with surface features. Only with the development of scanning near-field optical microscopy did it become possible to measure the surface polariton field directly in close proximity to the surface where the SPP exists. Here we overview the near-field studies of surface polaritons on randomly rough and nanostructured surfaces, theoretical models of SPP interaction with surface features, and SPP applications in novel photonic technologies. Surface polariton scattering, interference, backscattering, and localization will be discussed, as well as concepts of surface polariton optics and polaritonic crystals. Surface polaritons are finding an ever increasing number of applications in traditional domains of surface characterization and sensors as well as in newly emerging nano-photonic and optoelectronic technologies. © 2004 Elsevier B.V. All rights reserved. PACS: 73.20.Mf; 78.66.−w; 07.79.Fc Keywords: Surface plasmon polaritons; Scanning near-field optical microscopy; Nano-optics ∗ Corresponding author. E-mail address: [email protected] (A.V. Zayats). 0370-1573/$ - see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physrep.2004.11.001 132 A.V. Zayats et al. / Physics Reports 408 (2005) 131–314 Contents 1. Introduction ..........................................................................................133 1.1. Surface electromagnetic waves at a dielectric–metal interface ............................................134 1.1.1. Surface plasmon polaritons ..................................................................135 1.1.2. Surface plasmons ..........................................................................138 1.1.3. A metal film on a dielectric substrate ..........................................................139 1.1.4. Localized surface plasmons..................................................................142 1.1.5. Optical excitation of surface plasmon polaritons ................................................144 1.2. Scanning near-field optical microscopy ...............................................................146 2. Surface polariton scattering .............................................................................149 2.1. Single scattering regime: the SPP interaction with individual defects ......................................151 2.1.1. The interaction of a surface plasmon polariton with a single surface defect ..........................151 2.1.2. The propagation of a surface plasmon polariton near an index step .................................163 2.1.3. The interaction of a surface plasmon polariton with a subsurface defect .............................169 2.1.4. Near-field imaging of the SPP interaction with a single surface defect ..............................175 2.1.5. Interference of surface plasmon polariton beams ................................................179 2.2. Multiple scattering regime: backscattering of surface plasmon polaritons ..................................185 2.2.1. Enhanced backscattering of surface polaritons on a randomly rough surface .........................186 2.2.2. Direct observation of SPP backscattering with SNOM ...........................................192 2.3. Multiple scattering regime: surface polaritons localization on rough surfaces ...............................196 3. Two-dimensional optics of surface polaritons ..............................................................202 3.1. The interaction of surface plasmon polaritons with material and/or geometrical discontinuities in their propagation path ...........................................................................202 3.1.1. The impedance boundary condition ...........................................................203 3.1.2. Modal expansions (discrete) .................................................................205 3.1.3. Modal expansions (continuous) ..............................................................211 3.2. Elements of SPP optics ............................................................................214 4. Near-field microscopy of surface plasmon polaritons and characterization of metal surfaces .......................218 4.1. Characterization of metallic nanostructures via local excitation of surface polaritons .........................219 4.2. Imaging of thin film interfaces with air–metal and glass–metal surface polaritons ...........................221 4.3. Fractal properties of rough surfaces and SPP scattering .................................................222 5. Surface polaritons on periodically structured surfaces .......................................................226 5.1. Surface polaritonic crystals .........................................................................228 5.1.1. One-dimensional periodic surface profile ......................................................228 5.1.2. Two-dimensional periodic surface profile ......................................................234 5.2. Imaging of the SPP Bloch waves ....................................................................237 5.3. Waveguiding in line-defects of a SPP crystal ..........................................................239 6. Enhanced optical properties mediated by surface plasmon polaritons ...........................................243 6.1. Surface plasmon polaritons and the enhanced backscattering of light from a randomly rough metal surface ....................................................................................243 6.2. Surface plasmon polaritons and the enhanced optical transmission of periodically structured films .............257 6.2.1. Optical transmission of a metal film with a periodic hole array: a near field view .....................257 6.2.2. The origin of the enhanced transmission through periodically nanostructured metal films ..............262 6.2.3. Polarization effects in the light transmission through a polaritonic crystal ...........................265 6.2.4. Light-controlled transmission of polaritonic crystals .............................................269 7. Nonlinear optics of surface plasmon polaritons .............................................................274 7.1. Second harmonic generation in reflection from rough metal surfaces ......................................275 7.1.1. Second harmonic generation from metallic diffraction gratings ....................................281 7.1.2. Second harmonic generation at randomly rough metal surfaces ....................................286 7.2. Near-field second-harmonic generation at metal surfaces ................................................291 A.V. Zayats et al. / Physics Reports 408 (2005) 131–314 133 7.3. Near-field SHG from metallic diffraction gratings ......................................................296 8. SPP interrogation using other scanning probe microscopy techniques ..........................................298 8.1. Influence of surface polaritons on the tunneling current of STM ..........................................298 8.2. Light emission induced by the electron tunneling in STM: a role of surface plasmon polaritons ................304 9. Conclusion ...........................................................................................306 Acknowledgements .......................................................................................307 References ..............................................................................................308 1. Introduction In its simplest form a surface plasmon polariton (SPP) is an electromagnetic excitation that propagates in a wave like fashion along the planar interface between a metal and a dielectric medium, often vacuum, and whose amplitude decays exponentially with increasing distance into each medium from the interface [1–3]. Thus, a SPP is a surface electromagnetic wave, whose electromagnetic field is confined to the near vicinity of the dielectric–metal interface. This confinement leads to an enhancement of the electromagnetic field at the interface, resulting in an extraordinary sensitivity of SPPs to surface conditions. This sensitivity is extensively used for studying adsorbates on a surface, surface roughness, and related phenomena. Surface plasmon polariton-based devices exploiting this sensitivity are widely used in chemo- and bio-sensors [4]. The enhancement of the electromagnetic field at the interface is responsible for surface-enhanced optical phenomena such as Raman scattering, second harmonic generation (SHG), fluorescence, etc. [1,5]. The intrinsically two-dimensional nature of SPPs provides significant flexibility in engineering SPP- based all-optical integrated circuits
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