Benefiting from large intrinsic nonlinearities, low absorption, and high field enhancement abilities, all-dielectric nanoantennas are considered essential for efficient nonlinear processes at subwavelength volumes. In particular, when the dielectric nanoantenna supports the nonradiating anapole mode, characterized by a minimum in the extinction cross section and a maximum electric energy within the material, third harmonic generation (THG) processes can be greatly enhanced. In this work, we demonstrate that a higher-order anapole mode in a 200 nm thick germanium nanodisk delivers the highest THG efficiency on the nanoscale at optical frequencies. By doubling the diameter of a disk supporting the fundamental anapole mode, we discover the emergence of an anapole mode of higher order, with a valley in the extinction cross section significantly narrower than that of the fundamental anapole. Under this condition, we observe a highly improved electric field confinement effect within the dielectric disk, leading to THG conversion efficiencies as large as 0.001% at a third harmonic wavelength of 550 nm. In addition, by mapping the THG emission across the nanodisk, we are able to unveil the anapole near-field intensity distributions, which show excellent agreement with numerical simulations. Our findings remarkably expand contemporary knowledge on localized modes in dielectric nanosystems, revealing crucial elements for the elaboration of highly efficient frequency upconversion nanodevices.

3D vectorial holography reconstructs an arbitrary 3D vectorial field–carrying wavefront using machine learning inverse design.

Dielectric nanoantennas excited at Mie resonances are becoming suitable candidates for nonlinear optical effects due to their large intrinsic nonlinearity and capability to highly confine electromagnetic fields within subwavelength volumes. In this work, we show that a single Ge nanodisk, recently demonstrated as an efficient source of third-harmonic generation (THG), can also be exploited for four-wave mixing (FWM) phenomena. The high field enhancement inside the disk yields effective third-order susceptibilities as high as 2 × 10^–8 esu (2.8 × 10^–16 m²/V²), which were determined by single pump wavelength THG measurements tuned to high-order Mie modes. A similar nonlinear optical response is observed in the case of degenerate FWM where two different pump wavelengths are coupled to a single high-order resonant mode. However, when the two pump wavelengths are coupled to different high-order modes, the FWM process is partially suppressed due to a diminished near-field spatial overlap of the mixed wavelengths within the disk. This investigation reveals useful pathways for the optimization of third-order optical processes in all-dielectric nanostructures.

A crystalline gallium phosphide nanodisk is shown to be the most efficient sub–100-fs nanoscale all-optical switch.

Metal halide perovskites are promising candidates as photocatalysts due to their uniquely outstanding photophysical properties; however, the catalytic efficiency is limited by severe charge recombination. Herein, we show that carbonized polymer dots (CPDs) can act as an efficient charge modulator to stabilize photo-generated carriers in methylamine lead triiodide (MAPbI₃) perovskites through ultra-fast hole transfer, and thus increase the rate of visible light-driven photocatalytic HI splitting 35-fold. The optimized CPD/MAPbI₃/Pt hybrid photocatalytic system exhibits an impressive H₂ evolution rate of 11 497 μmol h⁻¹ g⁻¹, a solar-to-hydrogen conversion efficiency of 2.15%, and an apparent quantum yield of 53.6% at 420 nm, which are among the highest values for metal halide perovskite photocatalysts. Moreover, the presented strategy of hole extraction via CPDs can be universally applied to improve the performance of previous electron-manipulated MAPbI₃-based photocatalytic systems. The easy-to-prepare and bandedge-tunable CPDs with excellent charge-transfer ability may bring new insights in developing high-performance perovskite photocatalysts.

Surface-enhanced Raman scattering (SERS) nanoprobes show promising potential for biosensing and bioimaging applications due to advantageous features of ultrahigh sensitivity and specificity. However, very limited research has been reported on the SERS photostability of nanoprobes upon continuous laser irradiation, which is critical for high-speed and time-lapse microscopy. The core–shell off-resonant gap-enhanced Raman tags (GERTs) with built-in Raman reporters, excited at near-infrared (NIR) region but with a plasmon resonance at visible region, allow decoupling the plasmon resonance behaviors with the SERS performance and therefore show ultrahigh Raman photostability during continuous laser irradiation. In this work, we have synthesized five types of off-resonant GERTs with different embedded Raman reporters, numbers of shell layer, or nanoparticle shapes. Via thorough examination of time-resolved SERS trajectories and quantitative analysis of photobleaching behaviors, we have demonstrated that double metallic-shell GERTs embedded with 1,4-benzenedithiol molecules show the best photostability performance, to the best of our knowledge, among all SERS nanoprobes reported before, with a photobleaching time constant up to 4.8 × 10⁵ under a laser power density of 4.7 × 10⁵ W cm⁻². Numerical calculations additionally support that the local plasmonic heating effect in fact can be greatly minimized using the off-resonance strategy. Moreover, double-shell BDT-GERTs are highly potential for high-speed and high-resolution Raman-based cell bioimaging.