Unleashing infinite momentum bandgap using resonant material systems

The realization of photonic time crystals is a major opportunity but also comes with significant challenges. The most pressing one, potentially, is the requirement for a substantial modulation strength in the material properties to create a noticeable momentum bandgap. Reaching that noticeable bandgap in optics is highly demanding with current, and possibly also future, material platforms since their modulation strength is small by tendency. Here we demonstrate that by introducing temporal variations in a resonant material, the momentum bandgap can be drastically expanded, potentially approaching infinity with modulation strengths in reach with known low-loss materials and realistic laser pump powers. The resonance can emerge from an intrinsic material resonance or a suitably spatially structured material supporting a structural resonance. Our concept is validated for resonant bulk media and optical metasurfaces and paves the way toward the first experimental realizations of photonic time crystals

Parametric Mie resonances and directional amplification in time-modulated scatterers

We provide a theoretical description of light scattering by a spherical particle whose permittivity is modulated in time at twice the frequency of the incident light. Such a particle acts as a finite-sized photonic time crystal and, despite its sub-wavelength spatial extent, can host optical parametric amplification. Conditions of parametric Mie resonances in the sphere are derived. We show that time-modulated materials provide a route to tailor directional light amplification, qualitatively different from that in scatterers made from a gain media. We design two characteristic time-modulated spheres that simultaneously exhibit light amplification and desired radiation patterns, including those with zero backward and/or vanishing forward scattering. The latter sphere provides an opportunity for creating shadow-free detectors of incident light.Comment: 8 pages, 4 figure

Mie Resonances and Kerker Effects in Parametric Time-Modulated Spheres

Publisher Copyright: © 2022 IEEE.We provide a theoretical description of light scattering by a spherical particle whose permittivity is modulated with twice the frequency of the incident light. Such a sphere acts as a finite-size photonic time crystal and permits optical parametric amplification. We show that the control of the temporal modulation strength provides a qualitatively new route to spectrally overlap different parametric Mie resonances in the sphere for controlling its far-field pattern and satisfying the Kerker scattering conditions.Peer reviewe

Scattering of light by spheres made from a time-modulated and dispersive material

Publisher Copyright: © 2021 IEEE.We derive the dispersion relation of eigenmodes propagating in a time-varying and dispersive medium. We use these eigenmodes to analytically study the scattering of light by a sphere made from a time-varying and dispersive medium. These results are compared to full-wave optical simulations and excellent agreement is observed. With that, we provide tools and outline a path towards further explorations of light scattering by time-varying finite particles.Peer reviewe

Boosting third-harmonic generation by a mirror-enhanced anapole resonator

We demonstrate that a dielectric anapole resonator on a metallic mirror can enhance the third harmonic emission by two orders of magnitude compared to a typical anapole resonator on an insulator substrate. By employing a gold mirror under a silicon nanodisk, we introduce a novel characteristic of the anapole mode through the spatial overlap of resonantly excited Cartesian electric and toroidal dipole modes. This is a remarkable improvement on the early demonstrations of the anapole mode in which the electric and toroidal modes interfere off-resonantly. Therefore, our system produces a significant near-field enhancement, facilitating the nonlinear process. Moreover, the mirror surface boosts the nonlinear emission via the free-charge oscillations within the interface, equivalent to producing a mirror image of the nonlinear source and the pump beneath the interface. We found that these improvements result in an extremely high experimentally obtained efficiency of 0.01%