Journal of Nonlinear Optical Physics & Materials

Adsorption and photocatalytic are commonly used methods for the removal of dye contained in industrial wastewater. Therefore, this study aimed to combine reduced Graphene Oxide (rGO) with Titanium Oxide (TiO₂) through various compositions using the hydrothermal method to obtain a catalyst of rGO/TiO₂ nanocomposites for the removal of contaminants from wastewater. The synthesized rGO/TiO₂ nanocomposites were mixed with methylene blue (MB) to reduce their content in water under dark conditions and UV light irradiation. The change of the optical properties of MB under both conditions was also examined, where a decrease in absorbance was observed. Under UV light irradiation, the maximum wavelength $({\lambda }_{max})$ of MB shifted from 664nm to 649nm but remained constant at 664nm in dark conditions. The results of optical characterizations confirmed that the adsorption of MB by rGO/TiO₂ nanocomposites under dark conditions did not change the MB structure. However, a significant degradation was observed with photocatalytic process under UV light irradiation. Nanocomposites rGO/TiO₂ with rGO 60% and TiO₂ 40% (GT40) have better performance in reducing MB under UV light irradiation.

Gold-doped TiO₂ nanoparticles (NPs) were synthesized using a hydrothermal precipitation decomposition method. The synthesized Au–TiO₂ NPs have two crystalline structures, anatase and rutile. The X-rays were used to investigate the structural properties of the samples. The XRD confirmed the incorporation of Au in TiO₂. The diffuse reflection spectroscopy (DRS) technique was used to investigate the samples’ linear optical properties and band gaps. The optical properties revealed an extended tailing with a surface plasmon resonance (SPR) absorption peak. The bandgap was redshifted due to the Au incorporation. The reflection Z-scan (RZ-scan) technique was employed to study the nonlinear optical refraction and absorption coefficients of Au-doped TiO₂ NPs at 514nm wavelength. The nonlinear reflection and absorption coefficients were calculated by fitting theoretical equations to the experimental data. Hence, the nonlinear properties of gold-doped TiO₂ nanoparticles may find potential applications for optoelectronic devices such as optical switches and safety devices against high-power laser beams.

Three-dimensional numerical simulation on the waveguide formation written directly by 320nm ultraviolet laser in congruent lithium niobate (LN) crystal is presented. With the recent development of praseodymium (Pr)-doped laser crystal, the 320 nm UV laser has become easily available today. Though the absorption coefficient of this wavelength laser in LN is relatively low at room temperature, which might deter the direct waveguide writing fabrication, the situation will be much different when temperature rises. The absorption coefficient of this laser in LN will increase significantly under elevated temperature. When the temperature-dependent absorption coefficient is taken into consideration, the coupling of temperature and absorbed laser power will bring about interesting absorption characteristics. That is, the penetration depth of the laser will be affected by its power and the focus condition. In this work, we investigate the waveguide formation process in heated LN crystal via the lithium ion thermal-diffusion model. Cases where the laser is focused onto the surface and into the crystal are studied separately. The results show that when extra heated, the LN crystal can strongly absorb the 320nm laser focused on the surface and then form surface waveguides. Besides, when focused into the crystal, the laser will penetrate into the crystal and create internal high-temperature area with appropriated power and focusing parameter. However, in this case, only a relatively small refractive index change is obtained, which is not large enough to support efficient waveguide mode.

Dual-spectral narrow bandwidth surface lattice resonance (SLR) sensors consisting of semiconductor/SiO₂ nanoparticle dimer arrays are proposed to achieve two high figures of merit (FOM). We demonstrate that FOM can be optimized by the change of semiconductor nanoparticles’ shape. The best shape of Si nanoparticles with high FOM is pillar because of the narrowest FWHM of SLR. The FOM of Si/SiO₂ nanopillar dimer array can reach a value of 180 due to the high sensitivity and narrow bandwidth. Besides, the influences of different structural parameters (such as the gap of the Si nanopillars in each dimer, Si nanopillars’ diameter and height) on FOM of Si/SiO₂ nanopillar dimer arrays are investigated. In the trade-off between the strong SLR and the high FOM, the gap of 50nm, the Si nanopillars’ diameter of 80nm, and the Si nanopillars’ height of 100nm, are chosen as suitable values. Furthermore, a comparison of FOM between Si, Ge, GaAs nanopillars with fixed sizes is implemented to select the appropriate materials. The best semiconductor material to obtain a high FOM is Si because of a narrower FWHM and higher sensitivity. This work is of great significance for the design of multi-spectral SLR sensors.

We investigate the effect of gold nanoparticles capped by Citrate (Au-CA) and 3-MPA (Au-MPA) addition into PEDOT:PSS as an anode buffer layer (ABL) in the structure of an inverted hybrid solar cell. The localized surface plasmon resonance (LSPR) excited in AuNP is expected to accelerate the transfer of holes to the anode (Ag), increasing the mobility of charge carriers in this type of solar cell. The measured UV–visible absorption spectra show typical representation of the PEDOT:PSS mixtures, which changed due to modification of Au-NP’s concentrations. The maximum absorption peak of Au-CA solution ($d=\sim 13.8$nm) is located around 522nm, while Au-MPA solution ($d=\sim 25.7$nm) is located around 528nm. These peaks are found to be red-shifted including the absorbance intensity increased when they are modified with that of PEDOT:PSS. Under the illumination of 100mW/cm² simulated solar irradiation, the fabricated solar cell device exhibits an increase of Power Conversion Efficiency (PCE) value from 1.02% to 2.38% for the device with the addition of 20.0v/v% Au-CA and to 2.44% for the device with the addition of 2.0v/v% of Au-MPA. In our case, the enhancement of open circuit voltage ($V_{\mathrm{\text{OC}}}$) and short circuit current density ($J_{\mathrm{\text{SC}}}$) together occurs as a result of localized electric field effects from AuNP that influence charge transport and also the work function at the interface between PEDOT:PSS and the Ag-electrode. In our result, the fabricated solar cell with the addition of Au-MPA into the device structure shows a better performance efficiency of about 2.44% in comparison to the device with the addition of Au-CA of about 2.38%.

The development of crystal fabrication and characterization approaches makes it possible to study novel materials with enhanced linear and nonlinear optical properties. The solution growth method was adopted in the present investigation to create Barium thiourea chloride (BTCL), a metal–organic single crystal. Structural, optical, and thermal characteristics of the BTCL crystals were evaluated by XRD analysis, Fourier transform infrared spectroscopy, UV–Vis spectrometry, photoluminescence, SHG, and thermal analyses. The XRD method was applied to investigate the structural characteristics of the BTCL, which is related to the monoclinic structure. The FT-IR spectral investigation was conducted to observe the vibrational modes in BTCL. The optical measurements showed the transmittance in the near-UV and visible spectrums. Optical characteristics include bandgap, refractive index, extinction coefficient, optical, and electrical conductivities, and dielectric constants were obtained. The PL curve showed two notable emission peaks at 482.5nm and 491nm. The ability to generate second harmonics was investigated using the Kurtz and Perry method, and the SHG was more than 1.79 times the KDP sample. The thermal behavior of the BTCL was evaluated by TGA/DTA measurements. The Coats–Redfern relation was used to estimate the activation energy of the thermal system and the value was determined to be 9.48KJ/mol. The findings indicate that the BTCL crystals possess excellent optical transparency, higher SHG potency, and good thermal stability, which are suitable for use in photonic structures.

Ultrafast reverse saturable absorption (RSA) in chromophore-based borondipyrro- methenes (BODIPYs) derivatives, 1,7-Diphenyl-3,5-bis(9,9-dimethyl-9H-fluoren-2-yl)- boron-diuoride-azadipyrromethene (ZL-61) and 1,7-Diphenyl-3,5-bis(4-(1,2,2-triphenyl- vinyl)phenyl)-boron-diuoride azadipyrromethene (ZL-22), has been theoretically analyzed with femtosecond (fs) laser pulses at 800 nm and 850 nm. The results are in good agreement with the reported experimental results. The effect of input pulse intensity, pulse width, nonlinear absorption (NLA) coefficients, sample thickness and laser pulse shaping on transmittance has been studied and optimized for high contrast and low-power operation. All-optical fs NOT and the universal NOR and NAND Boolean logic gates have been designed with ZL-61 and ZL-22. The logic gates with top-hat input pulse profile have a sharp switch ON/OFF time compared to the Gaussian input laser profile. Ultrafast operation at relatively low pump intensities opens up exciting prospects for the applicability of BODIPY derivatives for ultrafast low-power all-optical computing and information processing.

This paper derives optical soliton solutions for the nonlinear Schrödinger equation in optical metamaterials. A thorough examination of various nonlinearities is conducted, spanning those governed by the Kerr law, power law, parabolic law, dual power law, quadratic–cubic law, non-local law, and polynomial law. The optical soliton solutions are derived utilizing the addendum to Kudryashov’s method. Through the selection of specific parameter values, the analysis demonstrates the presence of straddled solutions, bright solitons, and singular solitons. Furthermore, the paper outlines the necessary conditions for the existence of soliton pulses. Additionally, the stability of the nonlinear Schrödinger equation with Kerr law nonlinearity is analyzed. Our results are compared with the related findings in the literature, underscoring the novelty and importance of our work.