The Sixth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics – Metamaterials 2012 - consisted of a 4-day conference September 17th-22nd and a 2-day Doctoral School (21–22 September). Organized by the Metamorphose Virtual Institute and hosted by the National Research University of Information Technologies, Mechanics and Optics and St. Petersburg Electrotechnical University "LETI", this Congress follows the success of Metamaterials 2007-2011 and continues the traditions of the series of International Conferences on Complex Media and Metamaterials (Bianisotropics) and Rome International Workshops on Metamaterials and Special Materials for Electromagnetic Applications and Telecommunications.
The 2012 congress comprises 3 Invited Plenary Talks, 3 Invited Keynote Talks, 37 Invited Talks, 8 Extended Oral Talks, 189 accepted oral and 88 accepted poster presentations grouped in 3 poster sessions, 45 parallel sessions, and 2 plenary sessions. The conference is comprised of more than 300 contributions from all around the globe. Discussions included a variety of topics in different areas of physics, ranging from acoustic to optical and UV metamaterials, and provided visitors with a wonderful opportunity to recognize the current state of the art in the metamaterials world.
The Center for Metamaterials and Integrated Plasmonics had two attendees recount their experience at Metamaterials’ 2012 and discuss specific lectures that resonated with them;
Tremendous plenary talks were presented by Alexandra Boltasseva an Assistant Professor in the School of Electrical and Computer Engineering and Birck Nanotechnology Center at Purdue University specializing in nanophotonics, plasmonics and metamaterials. Her seminar “Plasmonic Metamaterials: Looking beyond Gold and Silver”. Federico Capasso, the Robert Wallace Professor of Applied Physics at Harvard University presented “Beam Shaping and Wavefront Engineering with Phase Discontinuities”. His research covers a broad range of topics from applications to basic science in the areas of electronics, photonics, nanoscale science and technology including plasmonics, metamaterials and the Casimir effect.
At several Nonlinear Metamaterials sessions, the topic of nonlinear response in metamaterials, ranging from harmonic generation to tunability-- from soliton propagation in chiral media to nonlinear cloaking were mentioned. Merging the ideas of nonlinear optics with plasmonics concepts, Yuri Kivshar’s group presented the analysis of modulations instability in plasmonic nanoparticles chains. The suggested model allows investigating a nonlinear temporal dynamics of the particle dipole moment oscillations in a chain of metallic nanoparticles driven by an external optical field. The study revealed the possibility of generating oscillons in such system-- the nearly stationary oscillating regions strongly localized in all directions. Such localized particle-like states can organize into simple patterns, with the examples of polarization patterns formation given by the authors. While one-dimensional localized states are observed in many systems, solitary waves in optical fibers or in water being some examples, few examples of such two-dimensional localized states are known. Owing to the novelty of the media suggested by the authors for oscillons generation, the process received the name plasmon oscillons.
Another work from the same group described a possibility of nonlinear cloaking by incorporating a layer of a nonlinear material with a near-zero refractive index in a multi-shell nanowire design. The authors demonstrated manipulation of the scattering cross-section of such system by adjusting the intensity of the incident field, owing to the energy exchange between the multipole modes of the structure.
While metamaterials are mostly known as artificial media with naturally unavailable electromagnetic properties, they are quickly expanding their presence in other areas of material research, in particular acoustics and thermodynamics. This expansion is accelerating, and in this year’s Metamaterials Congress, acoustic metamaterials required three separate sessions, and one more special session was allotted to “unconventional” metamaterials. No doubt, it won’t take long for some of these unconventional materials to become widespread.
“On the acoustic metamaterial side, all presentations were outstanding” expressed Research Faculty member Yaroslav Urzhumov . Sanches-Dehesa (Polytechnical Univ. of Valencia) reported novel acoustic cloaks designed for operation in air. In general, acoustic cloaking requires materials with effective density less than the density of ambient medium. Very few materials are lighter than air, but amongst those materials is… warm air, that’s right. The Spanish group suggests that warmed air is useful not only for optical mirages, but also for acoustic cloaking, and reported a smart temperature-gradient acoustic cloak in which effective density and speed of sound are controlled by heat.
Tiemo Bückmann of Martin Wegener’s group (Karlsruhe Institute of Technology) reported fabrication of three-dimensional pentamode metamaterials, mysterious media proposed in 1995 by Graeme Milton that remained entirely hypothetical until this work. The group uses advanced direct laser writing optical lithography to sculpt non-trivial three-dimensional microstructures. Pentamode metamaterials are so far the only known elastic (non-fluid-like) media capable of implementing the famous transformation acoustics recipes in the exact fashion.
Quantum metamaterials are quickly moving into the mainstream: several groups report studies of enhanced Purcell effect in plasmonic metamaterials and propose various quantum-mechanical uses to this enhancement. A multiple university collaboration represented by speaker Pavel Ginzburg focuses on spontaneous two-photon emission processes and shows the effect of plasmonic nanostructures on these processes. Alexander Poddubny (Russia) and his collaborators from the UK and Australia develop a theory of Purcell effect in hyperbolic metamaterials, which were recently proposed as strong enhancers of spontaneous emission. Casimir effect and its control with metamaterials remains an attractive topic for many scientists, including the group of Costas Soukoulis (Greece/USA), Christopher Wilson (Sweden), Mario Silveirinha (Portugal), and C. T. Chan (Hong Kong). Falk Lederer's group developed a theoretical framework establishing an analytic relation between the enhancement factors of higher-order multipolar fields in the vicinity of optical nanoantennas and the modification of the emission rates in a quantum mechanical multilevel system. As an example, the authors show that a properly designed nanoantenna can excite dipole-forbidden transition in a three-level system due to the enhanced electric quadruple fields. The derived approach is quite general and can be similarly used for the analysis of the enhancement of a variety of other low-rate processes.
Jensen Li, of City University of Hong Kong, presented a novel concept he calls “coiling space”, which enables acoustic metamaterial resonators with deeply subwavelength dimensions. These maze-like structures contain fluid-filled labyrinths made of solid walls, which force the sound to travel much longer distance than the straight line across the structure, thus creating geometric resonances on greatly reduced spatial scales. As a result, the structures exhibit highly unusual effective properties like large refractive index (slow speed of sound), low effective density and negative refraction.
The electromagnetic and optical metamaterials were classified into “Transformation Optics”, “Optical and UV”, “Plasmonic”, “Terahertz”, “Nonlinear”, “Tunable”, “Chiral”, “Quantum” and “Graphene-based”. On the Transformation Optics front, several new concepts are moving forward, including the field-transformation and metasurface approaches. The group of Andrea Alu (University of Texas) uses the latter concept to design ultra-slim “mantle cloaks”, which are being proposed for microwave (antennas) and optical invisibility applications. Sebastien Guenneau reported his recent work in transformation thermodynamics, whose perhaps cutest application includes making objects that “repel” heat.
The conference proved to provide a unique forum to share the latest results of the rapidly developing field of metamaterials research worldwide and bring together the engineering, physics, and material science communities working in the field of artificial electromagnetic materials and their applications from radio to optical frequencies. The success of the conference series allows Metamorphose Virtual Institute, as a non-for-profit international association, to provide fi nancial support to a number of participants and particularly students, operate European Doctoral Programme on Metamaterials (EUPROMETA) and deliver other services to the community.
Dr. Ekaterina Poutrina presented "Enhancing nonlinear response with metamaterials: from nonlinear parameters engineering to one-way imaging"
Abstract: We first summarize the approaches developed in our group allowing for the description of a nonlinear metamaterial media in terms of the effective nonlinear susceptibilities. We subsequently discuss the nonlinear magneto-electric coupling and demonstrate that it can lead to a non-reciprocal nonlinear imaging using a three- or four-wave mixing process, producing an image either on reflection or on transmission.
Dr. Yaroslav Urzhumov presented "Optically large three-dimensional directional cloaks: off-normal incidence performance study"
Abstract: In this paper we study a generalization of directional, optically large eikonal-limit cloaks based on conformal maps, to three dimensions. The cloak is a spherical shell filled with a graded isotropic dielectric whose distribution is cylindrically, although not spherically, symmetric. Due to lack of spherical symmetry, the structure has low visibility only for a limited range of incidence angles. We employ a 2.5D full-wave modelling technique, which exploits cylindrical symmetry but still allows arbitrary non-symmetric excitations, to estimate visibility of a cloak with respect to a mon-ochromatic plane wave incident at various angles. With respect to a certain visibility measure, the structure has a reduced visibility for angles up to 3 degrees.