SNOM characterization of a potential low cost thin gold coated micro-structured grating using a commercial CD substrate

J. Barrio^a, T.P.J. Han^b, J. Lamela^a, C. de las Heras^a, G. Lifante^a, M.A. Sánchez-Alejo^c, E. Camarillo^d and F. Jaque^b,e

^a Departamento de Física de Materiales, Facultad de Ciencias. Universidad Autónoma de Madrid, 28049-Madrid, Spain.

^b Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow G4 ONG, Scotland, UK.

^c Posgrado en Ciencia e Ingeniería de Materiales, UNAM.

^e Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049-Madrid, Spain.

Received 8 December 2014;
accepted 1 July 2015

Abstract

In this work near-field optical measurements of a corrugated grating coated with a 30 nm thick gold film are presented. The grating was made using the polycarbonate corrugated substrate of a commercially available recordable CD as template. This has been proved to be a versatile and low cost technique in producing large 1.6 μm period gratings. The study was carried out using a Scanning Near-Field Optical Microscope (SNOM) working in both collection and reflection modes at two different wavelengths, 532 nm and 633 nm. The results illustrate that the intensity patterns of near-field images are strongly polarization-dependent, even showing different periodicity of the localized fields for orthogonal polarization states. When electric field of the light is polarized parallel to the grooves, the periodicity of the SNOM images is coincident with the grating period, whereas when the light is polarized perpendicular to the grooves the SNOM pattern shows a periodicity twice that of the corresponding topography of the grating. Numerical simulations of the SNOM data based on a two-dimensional Finite Difference Time-Domain (2D-FDTD) model have been realized. The results of the simulations are in good agreement with the experimental data, emphasizing the need of performing numerical simulation for the correct interpretation of SNOM data.

Keywords: Scanning near field optical microscopy (SNOM); grating; finite difference time domain technique (FDTD).

PACS: 07.79.Fc; 42.79.Dj; 42.25.Fx; 42.25.Bs

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Acknowledgments

This work has been partially supported by Ministerio de Ciencia e Innovación (project TEC2010-21574-C02-01) and Comunidad de Madrid (P2009/TIC-1476), Spain. E. Camarillo G. recognizes to DGAPA-UNAM support for a sabbatical year at UAM.

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