Localized Light Focusing and Super Resolution Readout via Chalcogenide Thin Film
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0918-H06-01-G07-01
Localized Light Focusing and Super Resolution Readout via Chalcogenide Thin Film Junji Tominaga1, Paul Fons1, Takayuki Shima1, Kazuma Kurihara1, Takashi Nakano1, Alexander Kolobov1,2, and Stephane Petit1 1 Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8562, Japan 2 Laboratory of Physical Chemistry for Material Condense, University of Montlellier II, Montpellier, Montpellier Cedex 5, France
ABSTRACT We have demonstrated that certain chalcogenide layers within a spinning super-RENS optical disc allow to squeeze the 650 nm laser beam to a spot size as fine as 50 nm using a 15-nm chalcogenide film. The near-field light was focused at a depth of just over 30 nm after passing through a chalcogenide film. Finite-difference time-domain (FDTD) simulations also reproduced these results. We suggest that a conductive ring aperture generated in the chalcogenide layers plays an important role in the localized light focusing.
INTRODUCTION It is well known [1] that due to its wave nature, light cannot be focused into a spot smaller than a certain size, as specified by Abbe’s far-field diffraction limit whose numerical value is determined by the wavelength (λ) of the light used and the numerical aperture (NA= n sinα ) of the lens, D= λ/(2NA). Here n and α are the refractive index and incident angle of the light, respectively. The optical far-field limit (Fraunhofer) can be differentiated from the near-field (Fresnel) limit in terms of the dimensionless Fresnel number (F=a2/Lλ) where a is the aperture size, L is the distance from aperture to the observation point, and λ is the wavelength. For the Fraunhofer (Fresnel) limit, this can be expressed as F
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