Excitation of Surface Plasmons on a Metal Grating and Its Application to an Index Sensor

Yoichi OKUNO
Rui HU
Sailing HE
Toyonori MATSUDA

IEICE TRANSACTIONS on Electronics   Vol.E90-C    No.7    pp.1507-1514
Publication Date: 2007/07/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.7.1507
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electromagnetic Theory
metal grating,  surface plasmon,  resonance absorption,  mode conversion,  index sensor,  Yasuura's method,  

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Excitation of plasmons on the surface of a metal grating placed in planar or conical mounting is investigated in detail. Most of the results of numerical computations are compared with experimental data. When a TM wave illuminates a metal grating, total or partial absorption of incident light occurs at angles of incidence at which the plasmon surface waves are excited. In planar mounting the absorption is generally strong and nearly total absorption is observed. While in conical mounting, it is not so strong as that in the planar mounting case and a considerable amount of incident power is reflected. This, however, is accompanied by enhanced TM-TE mode conversion and the greater part of the reflected wave is in the TE polarization. The reciprocal of the TM-wave efficiency, hence, is a practical measure in finding the angles of incidence at which the plasmons are excited. Because the angles are sensitive functions of the refractive index of a material over the grating surface, this phenomenon can be used as an index sensor.