Near-field surface plasmon effects on Au-double-slit diffraction for polychromatic light
© Han; licensee Springer. 2014
Received: 24 June 2014
Accepted: 23 September 2014
Published: 9 October 2014
The surface plasmon effects on near-field diffraction for polychromatic light are studied. An Au-double-slit is used as the model and Fresnel integral is employed to perform the theoretic analysis. The results are illustrated with numerical examples and they show that, compared with the normal double-slit, the plasmon effect changes the spectral shift from redshift to blueshift and also enhances the intensity peak. This effect can be used in optical data transmission or specific spectral selectors.
The study of surface plasmons has gained much attention since the discovery of optical transmission enhancement through subwavelength apertures in metal films, which can be explained with the excitation of surface plasmons by the incident optical field on a metal-dielectric interface. For a nanostructure metallic double-slit, these plasmon waves travel toward the slits and couple with the field directly transmitted through the slits. In this way, the spectra and even the spatial coherence can be modulated. In the past, the spectral changes induced by normal aperture diffraction have been intensively studied, and an interesting phenomenon called ‘spectral switch’ was discovered. Also, some related applications were suggested, such as lattice spectroscopy or optical data transmission scheme. Recently, the effect of surface plasmons with Au-double-slit for polychromatic light was studied in the far-field, which also showed the spectral switch and was controlled by an electro-optic setup. However, in order to enhance the signal intensity and to use this type of optical device in micro/nanoscale, it is worth investigating the plasmonic effects in the near-field (or the so-called Fresnel zone), which is the topic of this work. The results show that the behavior of near-field diffracted spectral intensity with plasmonic effect differs substantially from that without the effect.
Results and discussion
The plasmonic effect on the diffracted spectral behavior of Au-double-slit in the near-field is studied. The analytic formulations for both Au and normal cases are derived by applying Fresnel approximation to the Fresnel diffraction integral. It is found that the incident spectral intensity is enhanced and blueshifted right after the Au-double-slit. Also, the numerical results show that the spectral switch can be found when the lateral positions vary and that the surface plasmons can affect both the magnitude of the diffracted spectral intensity and the spectral shifts, which benefit the control of spectra with plasmons and the potential applications in nano-optic devices.
Pin Han is now a professor and the head of the Graduate Institute of Precision Engineering, National Chung Hsing University. His main interests of research are optical engineering, optical design, and light wave propagation.
This study was supported by the National Chung Hsing University, Taiwan and the Ministry of Science and Technology of R.O.C. under contract No. NSC 101-2221-E-005 -062 -MY3 and NSC 102-2622-E-005-013-CC3.
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