Blue SHG enhancement by silver nanocubes photochemically prepared on a RbTiOPO4 ferroelectric crystal

Giant Second Harmonic Generation Enhancement by Ag Nanoparticles Compactly Distributed on Hexagonal Arrangements

The association of plasmonic nanostructures with nonlinear dielectric systems has been shown to provide useful platforms for boosting frequency conversion processes at metal-dielectric interfaces. Here, we report on an efficient route for engineering light-matter interaction processes in hybrid plasmonic-χ⁽²⁾ dielectric systems to enhance second harmonic generation (SHG) processes confined in small spatial regions. By means of ferroelectric lithography, we have fabricated scalable micrometric arrangements of interacting silver nanoparticles compactly distributed on hexagonal regions. The fabricated polygonal microstructures support both localized and extended plasmonic modes, providing large spatial regions of field enhancement at the optical frequencies involved in the SHG process. We experimentally demonstrate that the resonant excitation of the plasmonic modes supported by the Ag nanoparticle-filled hexagons in the near infrared region produces an extraordinary 10⁴-fold enhancement of the blue second harmonic intensity generated in the surface of a LiNbO₃ crystal. The results open new perspectives for the design of efficient hybrid plasmonic frequency converters in miniaturized devices.

Hybrid Plasmonic-Ferroelectric Architectures for Lasing and SHG Processes at the Nanoscale

Coherent light sources providing sub-wavelength confined modes are in ever more demand to face new challenges in a variety of disciplines. Scalability and cost-effective production of these systems are also highly desired. The use of ferroelectrics in functional optical platforms, on which plasmonic arrangements can be formed, is revealed as a simple and powerful method to develop coherent light sources with improved and novel functionalities at the nanoscale. Two types of sources with sub-diffraction spatial confinement and improved performances are presented: i) plasmon-assisted solid-state nanolasers based on the interaction between metallic nanostructures and optically active rare earth doped ferroelectric crystals and ii) nonlinear radiation sources based on quadratic frequency mixing processes that are enhanced by means of localized surface plasmon (LSP) resonances. The mechanisms responsible for the intensification of the radiation-matter interaction processes by LSP resonances are discussed in each case. The challenges, potential applications, and future perspectives of the field are highlighted.

Single crystal structure and optical properties of nonlinear optical crystal Rb0.94Ti0.94Ta0.06OPO4

SHG efficiency of Rb_0.94Ti_0.94Ta_0.06OPO₄ is about 1.4 times that of RTP.

Electrostatic Force-Driven Oxide Heteroepitaxy for Interface Control

Oxide heterostructure interfaces create a platform to induce intriguing electric and magnetic functionalities for possible future devices. A general approach to control growth and interface structure of oxide heterostructures will offer a great opportunity for understanding and manipulating the functionalities. Here, it is reported that an electrostatic force, originating from a polar ferroelectric surface, can be used to drive oxide heteroepitaxy, giving rise to an atomically sharp and coherent interface by using a low-temperature solution method. These heterostructures adopt a fascinating selective growth, and show a saturation thickness and the reconstructed interface with concentrated charges accumulation. The ferroelectric polarization screening, developing from a solid-liquid interface to the heterostructure interface, is decisive for the specific growth. At the interface, a charge transfer and accumulation take place for electrical compensation. The facile approach presented here can be extremely useful for controlling oxide heteroepitaxy and producing intriguing interface functionality via electrostatic engineering.

Anisotropic enhancement of Yb3+ luminescence by disordered plasmonic networks self-assembled on RbTiOPO4 ferroelectric crystals

Increasing Yb³⁺ absorption efficiency is currently desired in a number of applications including bio-imaging, photovoltaics, near infrared driven photocatalysis or ultra-short pulsed solid-state lasers. In this work, silver nanoparticles, which are connected forming disordered networks, have been self-assembled on Yb³⁺ doped RbTiOPO₄ crystals to produce a remarkable enhancement of Yb³⁺ absorption, and hence in the photoluminescence of this ion. The results are interpreted taking into account the near-field response of the plasmonic networks, which display strong amplification of the electric field at the maximum of Yb³⁺ excitation at around 900 nm, together with the anisotropic character of the Yb³⁺ transitions in RbTiOPO₄. We show that in the near field regime, the scattering of the plasmonic networks produces additional polarization field components to those of the incident field, which allows access to the largest transition dipolar moment of Yb³⁺ ions in RbTiOPO₄. As a result, a much more efficient route for Yb³⁺ excitation takes place at the immediacy of the plasmonic networks. This work provides fundamental insights for improving the optical properties of rare earth ions by the suitable design of metallic nanoparticle arrangements, and constitutes a promising step towards the development of new multifunctional solid-state lasers.

2D Arrays of Hexagonal Plasmonic Necklaces for Enhanced Second Harmonic Generation

Hexagonal plasmonic necklaces of silver nanoparticles organized in 2D superlattices on functional ferroelectric templates are fabricated in large-scale spatial regions by using a surfactant-free photo-deposition process. The plasmonic necklaces support broad radiative plasmonic resonances allowing the enhancement of second harmonic generation (SHG) at the ferroelectric domain boundaries. A 400-fold SHG enhancement is achieved at the near-UV spectral region with subsequent interest for technological applications.

Plasmonic enhancement of second harmonic generation from nonlinear RbTiOPO4 crystals by aggregates of silver nanostructures

We demonstrate a 60-fold enhancement of the second harmonic generation (SHG) response at the nanoscale in a hybrid metal-dielectric system. By using complex silver nanostructures photochemically deposited on the polar surface of a ferroelectric crystal, we tune the plasmonic resonances from the visible to the near-infrared (NIR) spectral region, matching either the SH or the fundamental frequency. In both cases the SHG signal at the metal-dielectric interface is enhanced, although with substantially different enhancement values: around 5 times when the plasmonic resonance is at the SH frequency or up to 60 times when it matches the fundamental NIR radiation. The results are consistent with the more spatially-extended near-field response of complex metallic nanostructures and can be well explained by taking into account the quadratic character of the SHG process. The work points out the potential of aggregates of silver nanostructures for enhancing optical nonlinearities at the nanoscale and provides an alternative approach for the development of nanometric nonlinear photonic devices in a scalable way.