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Optics Near Surfaces and at the Nanometer Scale

par Guy Molénat - publié le

This new book, of which one of the three authors is a researcher at CEMES, explores the physical phenomena underlying the optical responses of nanoscale systems. Important aspects of wave optics on surfaces and at small scales are discussed, such as the optical interference near surfaces, how imaging optical fields can be used to enhance resolution, the consequences of the finite size of the focal spot and the physical origin of the index of refraction based on an ensemble of discrete scatterers.

The finite width of a beam incident on a reflecting surface creates a zone where the incident and reflected beams overlap. In this overlap zone, the two beams interfere, giving rise to a surface standing wave and we can take advantage of surface standing waves to enhance the optical response of adsorbed nanoparticles or molecules.

In chapter three we describe how interference effects can be exploited to improve image resolution in optical microscopy. Using an optical scanning probe in collection mode, lateral standing waves can be recorded at variable distances from the surface. We then show how an intermediate field region outside the near field region can be defined. In the intermediate field region, amplitude variations across the image are considerable at distances smaller than five times the wavelength of the incident beam. This enables a smooth transition between indirect (diffraction) and direct images. Furthermore, we explain how the image of the particle can be reconstructed. Resolution can be as high as that observed in near field optics, with the added advantage that no feedback signal between the probe and surface is required.

Chapter four considers the consequence of the finite size of the focal spot in optical spectroscopy. Changing the position of the nanotube within the focal spot leads to spectral shifts when displacing in a particular direction but not in the direction perpendicular to it. This means that when using a grating spectrometer, apparent shifts in spectral positions can occur if the nano emitters are smaller than the size of the focal spot. The associated spectral shifts are small but cannot be ignored when studying strain or doping induced effects in optical spectra of nano-objects.

The final chapter goes into details of how the index of refraction can be related to scattering by an ensemble of discrete scatterers. We start by considering a plane of scatterers after which we introduce the third dimension. We then go on to show how the phase shift is related to the finite speed of light and the physical dimension of the interacting medium.

 

Book reference : Optics Near Surfaces and at the Nanometer Scale, Bacsa, Wolfgang, Bacsa, Revathi, Myers, Tim, SpringerBriefs in Physics, ISSN : 2191-5423

Link : https://www.springer.com/gp/campaign/surface-interface-science/blog2

Contact : Wolfgang Bacsa [at] cemes.fr