Symmetry-sensitive plasmonic enhancement of nonlinear optical intensity in nano-micro hierarchical structures on silver

Side edge emission from a waveguide substrate

In this study, we fabricated embedded titanium dioxide (TiO₂) nanograting structures with slanted cross section on a silicon dioxide (SiO₂) substrate using electron beam lithography (EBL) and reactive ion etching (RIE) methods, and we analyzed their optical signals. The surface morphologies of the embedded TiO₂ nanograting structures were monitored by a scanning optical microscope (SEM). By focusing the transverse electric (TE) polarized beam with the wavelength λ=633nm at the incident angle θ=22.0^∘ from the rear side of TiO₂ face, we could observe +1st and -2nd diffraction orders with diffraction efficiencies (I/I_total): I₁=23% and I₂=19%, respectively, on a SiO₂/TiO₂ interface. Diffraction beams were waveguided to both left and right directions in a SiO₂ substrate via total internal reflection (TIR); next, two guided beams were emitted from the side edges of the substrate. This work is expected to develop a highly efficient two-way waveguide optical interconnector.

Optical Third Harmonic Generation Using Nickel Nanostructure-Covered Microcube Structures

We investigated the optical third harmonic generation (THG) signal from nanostructure-covered microcubes on Ni. We found that the hierarchical structures greatly change the third-order optical nonlinearity of the metallic surface. While the symmetry and lightning rod (LR) effects on microstructures did not significantly influence the THG, the localized surface plasmon (LSP) effect on the nanostructures enhanced it. By removing the nanostructures on the hierarchical structures, THG intensity could be strongly suppressed. In the present paper, we also discuss the mechanism that enhances THG in nano/micro structures.

Nonlinear optics on nano/micro-hierarchical structures on metals: focus on symmetric and plasmonic effects

In this review, the authors study their creation of nano/micro-hierarchical structures on Ag and Ni substrates by femtosecond laser treatment and their investigation of their optical second-harmonic generation (SHG) signal intensities by SHG spectroscopy. The authors obtained the nanostructure-covered microgroove and microcube structures. These hierarchical surface structures were found to modify significantly the optical nonlinearity of the metal surfaces. The macroscopic symmetry of the surface’s shapes influenced SHG, and the excitation of surface plasmons enhanced SHG. On the other hand, the nanostructures on the microstructures had an additional effect on the generated SHG. For the microcube structures, the additional SHG emission was suppressed by removing a large amount of nanostructures. Left SHG was discussed by the effect of the propagating delay.