Enhanced Nonlinear Yield from Barium Titanate Metasurface Down to the Near Ultraviolet

Abstract

Metasurfaces are artificial nanopatterned two-dimensional architectures that can offer a solution to the bottleneck problem of bulky optical elements. They have the ability of wavefront shaping and light sub-wavelength manipulation because they are formed of resonantly scattering elements. Recently, the properties of metasurfaces gained interest for nonlinear optics in the efforts to miniaturize nonlinear optical devices while maintaining high photon-photon interactions. Here we develop a new type of nonlinear metasurface based on the metal oxide barium titanate, which demonstrates an efficient nonlinear optical response over a broad spectral range, from near-ultraviolet to the visible range, where metals and semiconductors typically have losses. Contrary to previously demonstrated nonlinear plasmonic metasurfaces, these dielectric metasurfaces are less sensitive to surface roughness and gain their optical nonlinearity from the noncentrosymmetric crystal structure of the ferroelectric barium titanate.

Engineering of the Second‐Harmonic Emission Directionality with III–V Semiconductor Rod Nanoantennas

“…To measure the SHG intensity we use a home built nonlinear microscope [58,59] equipped with a tunable Ti:Sapphire laser, which covers the region from 700 to 1080 nm, combined with an optical parametric oscillator system that covers the region from 1080 to 1600 nm. [60,61] The SHG responses from the structures were measured by sweeping the excitation wavelengths in the region from 800 to 1400 nm with steps of 10 nm (see more details in the Experimental Section). Figure 2 presents the experimental and simulation results for the SHG spectra from single nanoantenna, symmetric and asymmetric dimers, and insets with corresponding scanning electron microscopy (SEM) images of fabricated structures.…”

“…Additionally, for every 50 nm, we recorded the SHG polar plots as a dependence of the SHG intensity with respect to the polarization of the incoming excitation. [59][60][61] The shape of the SHG polar response originates from the geometry of the nanoantennas, responsible of the Mie modes (see Figure S2.1, Supporting Information), and the material crystal structure. To identify the impact of the crystal structure, we consider the polar response far from dominating Mie resonances.…”

Barium Titanate Nanostructures and Thin Films for Photonics

“…c) Refractive index of BaTiO 3 thin films (sub-micrometer thickness) produced by different fabrication methods. The refractive indices data are obtained from the references as indicated: molecular beam epitaxy (MBE), [53] pulsed laser deposited (PLD), [54] amorphous barium titanate fabricated by a sol-gel technique, [56] polycrystalline (poly-C) and amorphous sputtered thin films of 1-5 µm thickness, [59] nanoparticle films deposited by spin-coating of solvothermal synthesized particles of a diameter of 5 nm (circles) [57] and hydrothermally grown (triangular) of a diameter of 50 nm. [58] www.advancedsciencenews.com www.advopticalmat.de…”

“…The highest refractive index is achieved via molecular beam epitaxial growth. [53] Then, methods associated with the use of PLD systems [54] or metal organic chemical vapor deposition [55] show reduced refractive indexes, whereas sol-gel [56] and nanoparticle-films [57,58] have the smallest value of the refractive index. The decreased refractive index comes from the deviation of a pure monocrystalline film.…”

“…Timpu et al [54] developed the first all-dielectric BaTiO 3 based metasurface, which supported SHG signal, from near-ultraviolet up to the visible range. A bilayer film of BaTiO 3 and Si 3 N 4 nanostructured to an array of nanodisks via e-beam lithography.…”