Publications by Year: 2017

Pantazopoulos PA, Stefanou N, Almpanis E, Papanikolaou N. Photomagnonic nanocavities for strong light-spin wave interacton. Physical Review B. 2017;96(10):104425 (9 pages).Abstract
The interaction of visible and near-infrared light with spin waves in appropriately designed dual nanocavities, for both photons and magnons, is investigated by means of rigorous calculations, correct to arbitrary order in the magneto-optical coupling parameter. It is shown that the concurrent localization of the interacting photon and magnon fields in the same region of space for a long period of time enhances their mutual interaction, provided that specific selection rules are fulfilled. Our results provide evidence for the occurrence of strong effects, beyond the linear response approximation, which lead to enhanced modulation of light by spin waves through multimagnon absorption and emission processes by a photon.
Alevizaki A, Sainidou R, Rembert P, Morvan B, Stefanou N. Acoustic properties of double-porosity granular polymers. Physical Review B. 2017;95(21):214306 (10 pages).Abstract
Using an extension of the full elastodynamic layer-multiple-scattering method to structures of fluid-saturated poroelastic spherical bodies, a comprehensive theoretical study of the acoustic response of double-porosity submerged liquid-saturated granular polymeric materials of specific morphology consisting of touching porous polymer spheres arranged in a fcc lattice, beyond the long-wavelength effective-medium description, is presented. Calculated transmission and absorption spectra of finite slabs of these materials are analyzed by reference to the acoustic modes of the constituent porous spherical grains as well as to relevant dispersion diagrams of corresponding infinite crystals, and a consistent interpretation of the results is provided. In particular, it is shown that resonant modes with very long lifetime, localized in the spheres in the form of slow longitudinal waves, which are peculiar to poroelastic materials, are formed when the viscous length is much shorter than the radius of the inner pores of the spheres. These modes, which can be easily tuned in frequency by adjusting the intrinsic porosity of the spheres, induce some remarkable features in the acoustic behavior of these double-porosity materials, such as narrow dispersionless absorption bands and directional transmission gaps.
Almpanis E, Pantazopoulos PA, Papanikolaou N, Yannopapas V, Stefanou N. A birefringent etalon enhances the Faraday rotation of thin magneto-optical films. Journal of Optics. 2017;19(7):075102 (8 pages).Abstract
The magneto-optical response of a Faraday-active Fabry–Pérot etalon with birefringent mirrors is studied by means of electrodynamic simulations using the finite-element and the scattering-matrix methods. The specific structure under consideration consists of a magnetic garnet film sandwiched between two metallic layers, patterned with periodically spaced parallel grooves on their outer sides. Our results are analyzed by reference to the properties of the individual structural components and a consistent interpretation of the different spectral features observed is provided. It is shown that, by properly adjusting the geometrical parameters involved, strong Faraday rotation enhancement can be obtained through constructive synergy between the Fabry–Pérot resonant mode of the magneto-optical nanocavity and the slot plasmon mode localized in the grooves.
Toumazatou A, Arfanis MK, Pantazopoulos PA, Kontos AG, Falaras P, Stefanou N, Likodimos V. Slow-photon enhancement of dye sensitized TiO2 photocatalysis. Materials Letters. 2017;197:123-126.Abstract
Photonic band gap engineered TiO2 inverse opals were fabricated using self- assembled polystyrene films as sacrificial templates with controlled optical properties, aimed at the identification of the slow-photon effect on dye sensitized TiO2 photocatalysis. The materials’ photocatalytic efficiency was evaluated using Raman spectroscopy, on methylene blue photodegradation following both UVA and monochromatic visible light illumination. Contrary to UVA, where no photonic effect could be traced, laser irradiation within the slow-photon energy range of the TiO2 inverse opals, resulted in a marked increase of the dye photosensitized degradation rate, outperforming not only compact nanocrystalline films but also the benchmark mesoporous Aeroxide® P25 TiO2 films. This effect provides direct evidence for the presence of slow photons that amplify the interaction of visible light with the adsorbed dye molecules on the periodically structured TiO2 film.