arXiv subjects

Nikolaos Stefanou

Publications and source records attributed to Nikolaos Stefanou.

4 recordsLinked to original sources

arXiv2026

Perturbative Born theory for light scattering by time-modulated scatterers

We present a theoretical framework for electromagnetic scattering by particles with a permittivity that is periodically varying in time, based on a perturbative approach. Within this framework, we derive explicit expressions for the scattering matrix of the dynamic system in a first-order Born approximation, relating it directly to the corresponding static problem. We show that inelastic scattering amplitudes are governed by overlap integrals between static modes at the input and output frequencies. Using this insight, we analyze scattering from a time-modulated, isotropic, dielectric sphere and a high-permittivity dielectric cylinder, and demonstrate how modal orthogonality can suppress inelastic channels, while appropriate tuning of geometric parameters can significantly enhance them. In particular, we show that cylindrical resonators support strong inelastic scattering when resonance-to-resonance optical transitions, induced by the temporal variation, involve a high-Q supercavity mode. Comparison with full time-Floquet calculations confirms that the first-order Born approximation remains quantitatively accurate for modest modulation amplitudes and provides clear physical intuition for frequency conversion and resonance-mediated scattering processes in time-modulated photonic resonators.

physics.optics↗

arXiv2019

Designing Si sphere metagratings: From perfect reflection to large-angle diffraction

A thorough theoretical study of the optical properties of periodic Si nanosphere arrays is undertaken, placing particular emphasis on the synergy between electric and magnetic Mie resonances, which occur in high-refractive-index nanoparticles and can lead to a rich variety of phenomena ranging from perfect reflection to controlled diffraction. By means of systematic calculations using the layer-multiple-scattering method that we properly extended so as to describe periodic arrays with many scatterers per unit cell, in conjunction with finite-element simulations, we optimized surfaces of Si nanospheres that efficiently channel the transmitted light into a single, first-order diffraction beam, following simple design rules based on physical insight. Our results provide compelling evidence that Huygens' metasurfaces consisting of simple Si nanosphere dimer lattices constitute a promising platform for large-angle unidirectional deflection of transmitted light in the visible, at wavelengths shorter than the diffraction edge of the lattice.

physics.optics↗

arXiv2019

High-efficiency triple-resonant inelastic light scattering in planar optomagnonic cavities

Optomagnonic cavities have recently been emerging as promising candidates for implementing coherent microwave-to-optical conversion, quantum memories and devices, and next generation quantum networks. A key challenge in the design of such cavities is the attainment of high efficiencies, which could, e.g., be exploited for efficient optical interfacing of superconducting qubits, as well as the practicality of the final designs, which ideally should be planar and amenable to on-chip integration. Here, on the basis of a novel time Floquet scattering-matrix approach, we report on the design and optimization of a planar, multilayer optomagnonic cavity, incorporating a Ce:YIG thin film, magnetized in-plane, operating in the triple-resonant inelastic light scattering regime. This architecture allows for conversion efficiencies of about 5%, under realistic conditions, which is orders of magnitude higher than alternative designs. Our results suggest a viable way forward for realizing practical information inter-conversion between microwave photons and optical photons, mediated by magnons, with efficiencies intrinsically greater than those achieved in optomechanics and alternative related technologies, as well as a platform for fundamental studies of classical and quantum dynamics in magnetic solids, and implementation of futuristic quantum devices.

physics.optics↗

arXiv2019

Layered optomagnonic structures: Time Floquet scattering-matrix approach

A fully dynamic theoretical approach to layered optomagnonic structures, based on a time Floquet scattering-matrix method, is developed. Its applicability is demonstrated on a simple design of a dual photonic-magnonic cavity, formed by sandwiching a magnetic garnet thin film between two dielectric Bragg mirrors, subject to continuous excitation of a perpendicular standing spin wave. Some remarkable phenomena, including nonlinear photon-magnon interaction effects and enhanced inelastic light scattering in the strong-coupling regime, fulfilling a triple-resonance condition, are analyzed and the limitations of the quasistatic adiabatic approximation are established.

cond-mat.mes-hall↗