arXiv subjects

Aitor De Andrés

Publications and source records attributed to Aitor De Andrés.

3 recordsLinked to original sources

arXiv2026

Ultrafast excitation of Bloch plasmon polaritons in hyperbolic metamaterials with an extreme ultra-violet transient grating

Manipulating materials properties with light drives advances in materials science and photonics. Hyperbolic metamaterials are promising candidates as next-generation quantum optical media. They support Bloch plasmon polaritons, which are characterized by potentially infinite wave-vectors and long lifetimes, but cannot be excited through direct light illumination due to momentum mismatch. Here, we experimentally show that a transient grating, formed via interference of fully coherent seeded free-electron laser pulses in a thin insulator film, enables the excitation of Bloch plasmon polaritons in an underlying hyperbolic metamaterial. Finite element simulations confirm the role of the transient grating in facilitating phase-matching and mode excitation. Our findings demonstrate a route to spatiotemporally excite Bloch plasmon polaritons modes, offering an alternative to permanently nanostructured gratings and potentially enabling ultrafast control of optical modes excitation.

physics.optics↗

arXiv2025

Polarization conversion using hybrid near-zero and high-index metamaterials

Near-zero-refractive index materials display unique optical properties such as perfect transmission through distorted waveguides, cloaking, and inhibited diffraction. Compared to conventional media, they can fundamentally behave differently to light impinging from air, owing to the phenomenon of total external reflection. This makes them attractive for evanescent wave phenomena without prism coupling or sub-wavelength air gaps. Here, we introduce a strategy for linear-to-circular polarization conversion based on this effect. Practically realizable device designs are presented using hybrid structures of near-zero index and high index materials in a simple planar geometry. Our results predict polarization conversion in both reflection and transmission configurations based on naturally available epsilon-near-zero materials and illustrate the role of loss in limiting performance. Although the operation wavelength is limited to the epsilon-near-zero region, the concept can be implemented from the terahertz to optical domains using tunable epsilon-near-zero materials.

physics.optics↗

arXiv2025

Ultrafast interband transitions in nanoporous gold metamaterial

Nanoporous metals have emerged as promising functional architectures due to their tunable optical and electronic properties, high surface areas, and versatile use in real-life applications such as sensing, catalysis, and biomedicine. While the optical and morphological properties of nanoporous metals have been extensively studied, their electronic properties at ultrafast timescales remain largely unexplored. Here, we study the transient response of a nanoporous gold metamaterial and compare it with the ultrafast dynamics of a continuous gold film. We unravel that the nanoporous sample supports lower energy interband transitions, due to a much higher electron temperature in the nanoporous material, which causes an enhanced redistribution of electron density around the Fermi level. The experimental results are consistent with the two-temperature model, which highlights the role of nanoscale porosity in enabling the more efficient generation of hot carriers, thus allowing lower energy photons to induce interband transitions. Our findings demonstrate that nanoporosity affects fundamental ultrafast electronic processes and introduces this platform as temporal metamaterial allowing the emergence of tunable electronic properties not supported by the bulk counterpart. Furthermore, we present new insights into ultrafast electronic properties of nanoporous metals, which can impact several areas, from photochemistry and catalysis to energy harvesting and opto-electronics.

cond-mat.mes-hall↗