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      Minimal spaser threshold within electrodynamic framework: Shape, size and modes

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          Abstract

          It is known (yet often ignored) from quantum mechanical or energetic considerations, that the threshold gain of the quasi‐static spaser depends only on the dielectric functions of the metal and the gain material. Here, we derive this result from the purely classical electromagnetic scattering framework. This is of great importance, because electrodynamic modelling is far simpler than quantum mechanical one. The influence of the material dispersion and spaser geometry are clearly separated; the latter influences the threshold gain only indirectly, defining the resonant wavelength. We show that the threshold gain has a minimum as a function of wavelength. A variation of nanoparticle shape, composition, or spasing mode may shift the plasmonic resonance to this optimal wavelength, but it cannot overcome the material‐imposed minimal gain. Furthermore, retardation is included straightforwardly into our framework; and the global spectral gain minimum persists beyond the quasi‐static limit. We illustrate this with two examples of widely used geometries: Silver spheroids and spherical shells embedded in and filled with gain materials.

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          Most cited references 22

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          Active nanoplasmonic metamaterials.

          Optical metamaterials and nanoplasmonics bridge the gap between conventional optics and the nanoworld. Exciting and technologically important capabilities range from subwavelength focusing and stopped light to invisibility cloaking, with applications across science and engineering from biophotonics to nanocircuitry. A problem that has hampered practical implementations have been dissipative metal losses, but the efficient use of optical gain has been shown to compensate these and to allow for loss-free operation, amplification and nanoscopic lasing. Here, we review recent and ongoing progress in the realm of active, gain-enhanced nanoplasmonic metamaterials. On introducing and expounding the underlying theoretical concepts of the complex interaction between plasmons and gain media, we examine the experimental efforts in areas such as nanoplasmonic and metamaterial lasers. We underscore important current trends that may lead to improved active imaging, ultrafast nonlinearities on the nanoscale or cavity-free lasing in the stopped-light regime.
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            General properties of local plasmons in metal nanostructures.

             Feng Wang,  Y Shen (2006)
            Under the quasistatic approximation, the characteristics of a local plasmon resonance of a metal nanostructure exhibit several general properties. The resonance frequency depends on the fraction of plasmon energy residing in the metal through the real dielectric function of the metal. For a given resonant frequency, the Q factor of the resonance is determined only by the complex dielectric function of the metal material, independent of the nanostructure form or the dielectric environment. A simple result describing the effect of optical gain on the Q factor is also obtained.
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              Stimulated emission of surface plasmons at the interface between a silver film and an optically pumped dye solution.

              Surface plasmons (SPs) are surface-bound electromagnetic waves supported by metals, offering the possibility of strong spatial confinement of electromagnetic fields on the micro- and nanoscales. They suffer, however, from strong damping caused by internal absorption and radiation losses. Here we demonstrate amplification of SPs by stimulated emission, which marks a possible solution to this problem. We use an attenuated-total-reflection setup to detect stimulated emission of SPs at the interface between a silver film and an optically pumped dye solution acting as the amplifying medium. Clear evidence of stimulated emission is provided by an excellent agreement of the experimental observations with a theoretical analysis. Amplification of SPs can be considered analogous to photon amplification in a laser, thereby suggesting novel approaches in the field of nano-optics.
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                Author and article information

                Journal
                Ann Phys
                Ann Phys
                10.1002/(ISSN)1521-3889
                ANDP
                Annalen Der Physik
                John Wiley and Sons Inc. (Hoboken )
                0003-3804
                1521-3889
                07 December 2015
                April 2016
                : 528
                : 3-4 ( doiID: 10.1002/andp.v528.3-4 )
                : 295-306
                Affiliations
                [ 1 ] Institute of Applied PhysicsJohannes Kepler University Linz Altenbergerstraße 69 4040 LinzAustria
                [ 2 ] Soft Matter PhysicsJohannes Kepler University Linz Altenbergerstraße 69 4040 LinzAustria
                Author notes
                [* ]Corresponding authors E‐mail: nikita.arnold@ 123456jku.at
                Article
                ANDP201500318
                10.1002/andp.201500318
                4834728
                27158151
                © 2015 The Authors. Annalen der Physik published by Wiley‐VCH Verlag GmbH & Co. KGaA Weinheim

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                Page count
                Pages: 12
                Product
                Funding
                Funded by: European Research Council
                Award ID: 257158
                Categories
                Original Paper
                Original Papers
                Custom metadata
                2.0
                andp201500318
                April 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.8.6 mode:remove_FC converted:18.04.2016

                Physics

                spaser, localized surface plasmon, laser threshold, plasmonics, retardation

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