Tailoring optical nonlinearities of LiNbO3 crystals by plasmonic silver nanoparticles for broadband saturable absorbers

The synthesis of Au-NPs by ion implantation in the crystalline GaN and characterisation of their optical properties

Nanostructured surfaces with embedded noble metal nanoparticles is an attractive way for manipulation with the optical properties of wide bandgap semiconductors applied in optoelectronics, photocatalytic processes or for Surface-Enhanced Raman spectroscopy. Ion implantation offers an effective way for nanoparticle preparation without the use of additional chemicals that offers precise control of nanoparticle depth distribution. The aim of this study is a synthesis of the gold nanoparticles in GaN by implantation of 1.85 MeV Au ions with high fluences up to 7×1016 cm-2 and study of optical properties of Au implanted GaN. Implanted crystals were annealed at 800 °C in an ammonia atmosphere for 20 min to support Au nanoparticle creation and GaN recovery. The structure characterisation has been realized by Rutherford backscattering spectroscopy in channelling mode and it showed the formation of two separated disordered regions – the surface region and buried layer. The lower implantation fluences induce damage mainly in a buried layer; however, the increase of the Au-ion fluence leads to the increase of surface disorder as well. Further, the increase of the Au-ion fluence induces the Au dopant shift to the surface and multimodal Audepth profiles. TEM analyses confirmed the formation of Au nanoparticles in the implanted samples after annealing with sizes up to 14 nm. The increase of light absorption and modification of GaN bandgap of the Au modified GaN was deduced from the change in optical transmission spectra between 370 – 1400 nm.

Surface Plasmon Resonance and Increased Interfacial Electron Transfer of 3D AgNWS@TiO2NS Structure for Enhanced Photocatalytic and DSSC Properties

Ag nanowires coated with TiO2 nanosheets (AgNWS@TiO2NS, AWT) have been successfully synthesized via a one-pot hydrothermal synthesis. Importantly, the prepared AWT shows enhanced photocatalytic activity compared with Degussa P25, which is attributed to its continuous hierarchical structures, special conductive channel and localized surface plasmon resonance (SPR). Additionally, these prepared AWT were exploited as an electron conductor and scattering material in the TiO2 composite photoanodes of dye-sensitized solar cells (DSSCs). The highest energy conversion efficiency of 6.98% was achieved when the AWT doping rate in the photoanode slurry was 5 wt%. Both enhanced Isc and Voc are attributed to the increased photo-absorption efficiency from the localized SPR. The potential enhanced light-scattering effect and faster photoelectric transmission efficiency of the AWT in the photoanode.

Measurement of non-linear optical properties in graphene oxide using the Z-scan technique

We report the value of non-linear optical parameters in graphene oxide (GO) using the Z-scan technique. The value of the non-linear refractive index η₂, non-linear absorption coefficient β and the complex value of third order susceptibility χ⁽³⁾ in samples with different concentrations of GO diluted in distilled water were determined. The value of these parameters were obtained directly from the measurement of normalized transmittance of each sample as a consequence of its non-linear response when are exposed to electromagnetic radiation from a Nd:YAG laser emitting at 532 nm in CW mode. In addition, we found that the parameters η₂, β and χ⁽³⁾ growth by increasing excitation laser power, where β showed an high order of magnitude around ~10^-2 cm/W.

A Novel Hierarchical Nanostructure for Enhanced Optical Nonlinearity Based on Scattering Mechanism

Surface modification of nonlinear optical materials (NOMs) is widely applied to fabricate diverse photonic devices, such as frequency combs, modulators, and all-optical switches. In this work, a double-layer nanostructure with heterogeneous nanoparticles (NPs) is proposed to achieve enhanced third-order optical nonlinearity of NOMs. The mechanism of modified optical nonlinearity is elucidated to be the scattering-induced energy transfer between adjacent NPs layers. Based on the LiNbO₃ platform, as a typical example, double layers of embedded Cu and Ag NPs are synthesized by sequential ion implantation, demonstrating twofold magnitude of near-infrared enhancement factor and modulation depth in comparison with a single layer of Cu NPs. With the elastic collision model and thermolysis theory being considered, the shift of the localized surface plasmon resonance (LSPR) peak reveals the formation mechanism of the double-layer nanostructure. Utilizing the enhanced optical nonlinearity of LiNbO₃ as modulators, a Q-switched mode-locked waveguide laser at 1 µm is achieved with shorter pulse duration. It suggests potential applications to improve the performance of nonlinear photonic devices by using double-layer metallic nanostructures.

Plasmonic Ag nanoparticles embedded in lithium tantalate crystal for ultrafast laser generation

We report the Ag nanoparticles (NPs) embedded in LiTaO₃ (AgNP:LT) by direct Ag⁺ ion implantation. Transmission electron microscope imaging indicates that the embedded Ag NPs have an average diameter of 3.65 nm. The linear optical absorption spectrum of AgNP:LT peaking at 477 nm is observed owing to the typical effect of localized surface plasmon resonance. Z-scan investigation shows ultrafast saturable absorption of AgNP:LT at the near infrared 1 μm wavelength, which enables AgNP:LT to be a new saturable absorber (SA) for the generation of 1 μm Q-switched mode-locked pulsed laser with pulse duration of 35 ps and repetition rate of 8.74 GHz. This work not only opens a new way to tailor the nonlinearity of LiTaO₃ by embedding Ag⁺ NPs, but also develops AgNP:LT as a new SA for ultrafast laser generation.