High-harmonic generation from subwavelength silicon films Kent Hallman, Sven Stengel, Wallace Jaffray, Federico Belli, Marcello Ferrera, et al. Nanophotonics, 2025 Recent years have witnessed significant developments in the study of nonlinear properties of various materials at the nanoscale. Often, experimental results on harmonic generation are reported without the benefit of suitable theoretical models that allow assessment of conversion efficiencies compared to the material’s intrinsic properties. Here, we report experimental observations of even and odd harmonics up to the 7th, generated from a suspended subwavelength silicon film resonant in the UV range at 210 nm, the current limit of our detection system, using peak power densities of order 3 TW/cm2. We also highlight the time-varying properties of the dielectric function of silicon, which exhibits large changes under intense illumination. We explain the experimental data with a time domain, hydrodynamic-Maxwell approach broadly applicable to most optical materials. Our approach accounts simultaneously for surface and magnetic nonlinearities that generate even optical harmonics, as well as linear and nonlinear material dispersions beyond the third order to account for odd optical harmonics, plasma formation, and a phase locking mechanism that makes the generation of high harmonics possible deep into the UV range, where semiconductors like silicon start operating in a metallic regime.
Harmonic generation from aluminium and gold nanolayers and nanogratings: bound and hot electron contributions International Conference on Metamaterials Photonic Crystals and Plasmonics, 2025
Quasi three dimensional gold plasmonic metasurfaces for enhanced harmonic generation and light conversion to UV International Conference on Metamaterials Photonic Crystals and Plasmonics, 2025
Below the surface: Unraveling the intricacies of the nonlinear optical properties of aluminum through bound electrons M. Scalora, K. Hallman, S. Mukhopadhyay, S. Pruett, D. Zappa, et al. APL Photonics, 2024 By uncovering novel aspects of second harmonic generation in aluminum, we show that there are unusual and remarkable consequences of resonant absorption, namely an unexpectedly critical role that bound electrons play for light–matter interactions across the optical spectrum, suggesting that a different basic approach is required to fully explain the physics of surfaces. We tackle an issue that is never under consideration given the generic hostile conditions to the propagation of light under resonant absorption. Unlike most noble metals, aluminum displays Lorentz-like behavior and interband transitions centered near 810 nm, thus splitting the plasmonic range in an atypical manner and setting its linear and nonlinear optical properties apart. Studies of aluminum nanostructures having complex topologies abound, as do reported inconsistencies in the linear spectral response of surface plasmons and harmonic generation. Our experimental observations of second harmonic generation from aluminum nanolayers show that bound electrons are responsible for a unique signature neither predicted nor observed previously: a hole in the second harmonic spectrum. A hydrodynamic-Maxwell theory explains these findings exceptionally well and becomes the basis for renewed studies of surface physics.
Tailoring gold plasmonic metasurfaces for efficient harmonic generation S. Mukhopadhyay, C. Cojocaru, M. A. Vincenti, K. Hallman, A. Mihi, et al. International Conference on Transparent Optical Networks, 2024 Harmonic generation on metal surfaces is an important field of research that explores the fundamental properties of surface physics. Surface plasmonic resonances and their spatial and temporal properties together with metasurfaces properties enable a wider understanding and control of light-matter interactions at the nanoscale. We report a combined experimental-theoretical investigation to monitor and control nanoscale electron dynamics with plasmons using ultrafast optical pulses in the visible and UV ranges. Our unique microscopic, hydrodynamic model for linear and nonlinear interactions in metal surfaces validates our experimental results. This work is part of an ongoing study of exploring nonlinear frequency conversion in the surface of metals and their intrinsic properties, starting from simple nanolayers and proceeding to two dimensional or more complicated nanostructures, as we explore, compare and discuss their efficiency, tailorability and applications.
Strong nonlinear efficiency enhancement in the visible and UV ranges from plasmonic gold nanogratings European Quantum Electronics Conference Eqec 2023 in Proceedings Conference on Lasers and Electro Optics Europe CLEO Europe 2023 and European Quantum Electronics Conference Eqec 2023 Part of Conference on Lasers and Electro Optics Europe CLEO Europe 2023 and European Quantum Electroni, 2023
Large Enhancement in Visible to UV Nonlinear Frequency Conversion by a Plasmonic Gold Nanograting International Conference on Metamaterials Photonic Crystals and Plasmonics, 2023
