arXiv subjects

Albert Mathew

Publications and source records attributed to Albert Mathew.

4 recordsLinked to original sources

arXiv2026

Asymmetric high-harmonic generation from subwavelength bianisotropic resonators

High-harmonic generation (HHG) enables attosecond light pulses and table-top sources of coherent extreme-ultraviolet and soft X-ray radiation. Although HHG has long been associated with gases and plasma, nanostructured solids are emerging as new alternative sources enabling both the enhancement and control of HHG. Here, we experimentally demonstrate and theoretically describe that a single dielectric subwavelength resonator can act as a direction-selective high-harmonic source, enabling control over multiple harmonic orders through the excitation and hybridization of Mie modes. The resonator's geometrical volume is $0.12 \lambda^3$, and its optical mode volume is $0.03 \lambda^3$ at its pump wavelength. Structural asymmetry of the resonator along the propagation direction translates into different mode coupling under opposite illumination directions, resulting in pronounced forward-backward asymmetry in the generation of the third, fifth, and seventh harmonics. These results establish bianisotropic subwavelength resonators as a platform for flexible asymmetric generation of high harmonics, expanding the toolbox for controlling strong-field light-matter interactions with Mie-resonant nanophotonics.

physics.optics↗

arXiv2026

Intrinsic chirality of dielectric metasurfaces unlocked by resonant chiral modes

Controlling optical chirality at the subwavelength scales is essential for many applications of nanophotonic structures in polarization optics, sensing, and nonlinear photonics. Achieving a strong chiroptical response in planar dielectric metasurfaces without intrinsically chiral building blocks (or "meta-atoms") remains challenging. The recent theoretical study [ACS Photonics 12, 6717 (2025)] predicted that bilayer metasurfaces with rotated C$_4$-symmetric apertures can exhibit pronounced chiral response originating from resonant chiral photonic modes realizing maximum chirality under the mode strong coupling. That observation uncovers a novel mechanism of metasurface chirality. Here, we confirm experimentally this novel concept and demonstrate resonantly enhanced circular dichroism in the near-infrared frequency range. We fabricate a free-standing silicon membrane metasurface that is nominally achiral. When out-of-plane symmetry is broken by a thin PMMA layer, it unlocks and activates a strong chiral response. The observed circular dichroism is explained by the properties of chiral photonic modes, and it is governed by interlayer coupling and symmetry breaking, in agreement with theoretical predictions. These results establish bilayer metasurfaces as a simple and versatile platform for engineering strong mode-induced chirality in compact planar photonic metadevices.

physics.optics↗

arXiv2025

Nonreciprocal metasurfaces with epsilon-near-zero materials

Nonreciprocal optics enables asymmetric transmission of light when its sources and detectors are exchanged. A canonical example -- optical isolator -- enables light propagation in only one direction, similar to how electrical diodes enable unidirectional flow of electric current. Nonreciprocal optics today, unlike nonreciprocal electronics, remains bulky. Recently, nonlinear metasurfaces opened up a pathway to strong optical nonreciprocity at the nanoscale. However, demonstrations to date were based on optically slow nonlinearities involving thermal effects or phase transition materials. In this work, we demonstrate a nonreciprocal metasurface with an ultra-fast optical response based on indium tin oxide in its epsilon-near-zero regime. It operates in the spectral range of 1200-1300 nm with incident power densities of 40-70 GW/cm$^2$. Furthermore, the nonreciprocity of the metasurface extends to both amplitude and phase of the forward/backward transmission opening a pathway to nonreciprocal wavefront control at the nanoscale.

physics.optics↗

arXiv2024

Wide-bandgap optical materials for high-harmonics generation at the nanoscale

High-order harmonics generation (HHG) is the only process that enables table-top-size sources of extreme-ultraviolet (XUV) light. The HHG process typically involves light interactions with gases or plasma-material phases that hinder wider adoption of such sources. This motivates the research in HHG from nanostructured solids. Here we investigate theoretically material platforms for HHG at the nanoscale using first-principle supercomputer simulations. We reveal that wide bandgap semiconductors, aluminium nitride AlN and silicon nitride SiN, are highly promising for XUV light generation when compared to one of the most common nonlinear nanophotonic material -- silicon. In our calculations we assume excitation with 100 fs pulse duration, 10^13 W/cm^2 peak power and 800 nm central wavelength. We demonstrate that in AlN material the interplay between the crystal symmetry and the incident light direction and polarization can enable the generation of both even and odd harmonics. Our results should advance the developments of high-harmonics generation of XUV light from nanostructured solids.

physics.optics↗