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Posted: Sep 22, 2011

Research highlights advances in nano-optics - nanoplasmonics and metamaterials

(Nanowerk News) Light-matter interaction at the nanometer scale has turned into a very fast-growing field of research known as nano-optics. To highlight breakthroughs in the specific areas of nano-optics known as nanoplasmonics and metamaterials, the editors of the Optical Society's (OSA) open-access journal Optical Materials Express (OMEx) have published a special Focus Issue on Nanoplasmonics and Metamaterials. The issue is organized and edited by Guest Editor Romain Quidant of the Institute of Photonic Sciences and the Catalan Institute for Research in Advanced Studies, Spain, and OMEx Associate Editor Vladimir Drachev of Purdue University, USA.
"Research in nanoplasmonics and metamaterials is very well representative of the tremendous increase of activities in nano-optics," said Drachev. "Both are expected to have a strong impact on our society, especially in the areas of chip-scale and high-integration density optical interconnects, advanced materials for photovoltaics, and bio-medical applications."
The first main motivation behind such enthusiasm for nano-optics comes from the potential of the field to extend concepts and functionalities of conventional optics down to the nanometer scale; toward ultra-compact photonic devices that are not limited by diffraction. Beyond miniaturization, an additional motivation arises from the rich new physics involved when matter is downsized to dimensions that are much smaller than the light wavelength.
"At this very exiting stage of research in nanoplasmonics and metamaterials, further advances are in part conditioned by the development of new optical materials with improved properties, as well as advances in nanofabrication techniques to increase the quality of constitutive nano-units," said Quidant. "We have seen a noteworthy advance in materials research the past few years. As such, we put together this special issue now to address these advances and highlight the future of this dynamic field."
Nanoplasmonics studies the optical properties of nanoscale systems supporting surface plasmons, and gained a lot of attention after the discovery of surface-enhanced Raman scattering (SERS) in the 1970s. Benefiting from recent advances in nanofabrication techniques, research in nanoplasmonics has recently been very successful in using noble metal (especially silver and gold) nanostructures to control light fields well beyond the limit of diffraction. Such control has already contributed to enhanced light interaction with tiny amounts of matter down to the single-molecular level.
In the field of metamaterials, researchers aim at designing ensembles of sub-wavelength units that behave as effective materials featuring properties that are not found in nature. Artificial materials have recently regained a huge interest triggered by provocative theoretical proposals such as superlensing and invisibility at optical frequencies, as well as the successful experimental demonstration of negative refraction.
Key Findings & Select Papers
In the fields of plasmonics and plasmonic metamaterials, reduction in metal losses is important and crucial for potential applications. It will bring the technology from the proof-of-principle research to system-qualified development. In their paper, Purdue University researchers Naik, Kim and Boltasseva explore the use of alternative materials such as conducting oxides and transition-metal nitrides that feature lower intrinsic absorption than conventional plasmonic metals. Paper: "Oxides and nitrides as alternative plasmonic materials in the optical range," Optical Materials Express, Vol. 1, Issue 6, pp. 1090-1099.
Dopant concentration dependence of aluminum-doped zinc oxide (ZnO) performance as a metal alternative is studied by Frölich and Wegener. This group from the Karlsruhe Institute of Technology demonstrates applicability of the atomic layer deposition technique for 3-D design of metamaterials. Paper: "Spectroscopic characterization of highly doped ZnO films grown by atomic-layer deposition for three-dimensional infrared metamaterials," Optical Materials Express, Vol. 1, Issue 5, pp. 883-889.
Kehr et al. develop lenses with sub-diffraction resolution (superlenses) for terahertz spectral range based on phonon resonances of perovskite-type oxides. This collaborative team from the U.K., U.S., and Germany uses a unique near-field microscopy tool with a free-electron tunable laser for their research. Paper: "Microspectroscopy on perovskite-based superlenses." Optical Materials Express, Vol. 1, Issue 5, pp. 1051-1060.
Alternatively, Campione, Albani, and Capolino study another approach in which the metal losses are compensated by the introduction of a gain material. The authors predict the possibility of designing loss-compensated metamaterials, made of a 3-D lattice of nanoshells, that exhibit permittivity near zero with moderate losses at optical frequencies by using optically pumped fluorescent dye molecules in the cores of the metamaterial constituent nanoshells. Paper: "Complex modes and near-zero permittivity in 3D arrays of plasmonic nanoshells: loss compensation using gain," Optical Materials Express, Vol. 1, Issue 6, pp. 1077-1089.
The ability to define nano-units with a very high accuracy and reproduce them with ease and low cost over large areas will become a key ingredient toward the elaboration of future optical devices based on plasmonics and metamaterials. A collaborative team led by Noginov develops a new approach along this direction. In their paper, Barnakov et al. discuss a fabrication method based on silver-filled alumina templates as a way to achieve curved metamaterials. Paper: "Toward Curvilinear Metamaterials Based on Silver-Filled Alumina Templates," Optical Materials Express, Vol. 1, Issue 6, pp. 1061-1064.
Another collaborative team led by Linden reports on a powerful technique for the spatial and spectral mapping of the plasmonic modes of lithographically defined photonic meta-atoms. In this paper, Cube et al. show the importance of advanced characterization tools such as electron energy-loss spectroscopy (EELS) combined with transmission electron microscopy, capable to probe with a sub-wavelength resolution the properties of individual nano-units in metamaterials. Paper: "Spatio-spectral characterization of photonic meta-atoms with electron energy-loss spectroscopy," Optical Materials Express, Vol. 1, Issue 6, pp. 1009-1018.
Source: Optical Society of America
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