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26 August 2005 Linear and non-linear near field behaviour on random metal films and surfaces
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We have developed a new detection scheme based on a scanning near-field optical microscope to image both the linear and the non-linear (e.g. second harmonic generation (SHG)) on surfaces with sub-wavelength resolution. The microscope we used here scatters the evanescent waves that contain sub-wavelength information with the apex of a metallic tip. The resolution of this microscope is directly given by the size of the radius of curvature of the metal tip end (about 5 nm). Our set-up is applied to the optical study of crystalline films and random metal surfaces. Using thin SBN films (Strontium Barium Niobate) we demonstrate that near-field optics is a surface sensitive measurement. The ability to perform high quality and highly resolved images is transposed to increase the resolution of imaging in the THz domain. It is also used in the visible domain on random metal films. Several studies have demonstrated that random metal surfaces show localization of the electric field on small area called "hot spots" where the electric field can exceed the applied field by several orders of magnitude. Position of the hot spots depends on film structure, on the polarization and wavelength of the illuminating laser beam. In addition, these random metal films are known to be the source of nonlinear optical effects. We are currently working to precisely locate the respective position of the linear and non-linear hot spots on silver.
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Laurent Williame, Romain Lecaque, Eric Le Moal, Emmanuel Fort, Samuel Gresillon, Jean-Claude Rivoal, and Claude Boccara "Linear and non-linear near field behaviour on random metal films and surfaces", Proc. SPIE 5928, Plasmonic Nano-imaging and Nanofabrication, 592801 (26 August 2005); doi: 10.1117/12.613884;

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