In this paper, complex modes in a linear chain of gold nanospheres are analyzed, accounting for metal losses. Dispersion
diagrams are computed for travelling modes with both longitudinal and transverse (with respect to the array axis)
polarization states. The procedure outlined in this work allows for the description of single mode evolution varying
frequency, thus the modal dispersion diagrams are composed by the superposition of all the different modes in the one
dimensional array. Each nanoparticle is modeled as an electric dipole, by adopting the single dipole approximation, and
the complex zeroes of the homogeneous equation characterizing the field in the periodic structure are computed. The
Ewald method is employed to analytically continue the periodic Green's function into the complex spectral domain and
to achieve rapid convergence. Full characterization of the modes is provided in terms of their direction of propagation
(forward/backward), their guidance and radiation properties (bound/leaky), the position of their wavenumber on the
Riemann sheet (proper/improper), and also in terms of their possible physical excitation in the structure by a source in
proximity of the array or a defect (physical/nonphysical modes). Understanding the modes excitable in this kind of
structures is essential for possible applications in which the linear chain can be employed, from near-field enhancement
to SERS, and innovative sensors.
KEYWORDS: Optical spheres, Silver, Near field, Metals, Terahertz radiation, Near field optics, Super resolution, Optical imaging, Image enhancement, Particles
Recently there has been a number of studies of single-layer and double-layer arrays of small resonant particles made of a
noble metal. The intense interest to these structures is caused by their promising properties for near-field enhancement
and subwavelength imaging applications, especially in the optical range. They have substantial advantages over the
structures containing DNG (double negative) materials as they are easier in fabrication and may mitigate the problem of
losses. So far the super-resolution properties were theoretically investigated only for the arrays of a finite extent. In this
work we consider single-layer and multilayer infinite arrays. This formulation allows to build a highly effective
algorithm and to consider both the problem of excitation of a periodic structure by a single dipole and the modal
properties of the structure. The field produced by a single dipole source is effectively described by using the array
scanning method, accelerated by the Ewald method. Each subwavelength sphere is represented as an electric dipole
scatterer. Special attention is given to the investigation of the number of layers influence on local field enhancement and
to the study of the field distribution between the layers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.