Search Results (238)

The linear and third-order nonlinear optical (NLO) properties of a water-soluble perylenediimide derivative, N,N′-di(2-(trimethylammonium iodide) ethylene) perylenediimide (TAIPDI), doped with semiconductor nanoparticles (NPs), were systematically investigated under femtosecond laser excitation. ZnO and TiO₂ NPs were synthesized using a pulsed laser ablation technique. Nanocomposite systems were prepared by incorporating different concentrations of ZnO and TiO₂ NPs into the TAIPDI dye solution. The optical properties were characterized using UV–visible absorption spectroscopy together with open- and closed-aperture Z-scan measurements at 800 nm. Linear absorption measurements revealed concentration-dependent modifications in the optical band gap, indicating electronic interaction between the dye molecules and the semiconductor NPs. Open-aperture Z-scan results demonstrated strong nonlinear absorption (NLA) behavior dominated by two-photon absorption and excited-state absorption processes. Closed-aperture measurements showed a negative nonlinear refractive (NLR) index, corresponding to self-defocusing behavior. Both the NLA coefficient and the NLR index increased with increasing NP concentration, resulting in a significant enhancement of the third-order nonlinear susceptibility of the nanocomposite systems. In addition, optical limiting measurements revealed a pronounced reduction in the limiting threshold with increasing nanoparticle concentration, demonstrating improved laser attenuation capability. These findings indicate that ZnO@TAIPDI and TiO₂@TAIPDI nanocomposites are promising candidates for applications in optical limiting, all-optical switching, and advanced photonic devices. Full article

An optical lens focuses light and a similar device can be developed to focus surface water waves. A detailed description of such hydrodynamic lenses is given, for which the focusing is induced by shaping the bathymetry of the bottom. Classically, the Luneburg lens uses a specific radial variation of the refractive index. The modified Luneburg lens (MLL) introduces an extra degree of freedom, permitting the focal point to be tuned. It is shown how to design the MLL for water waves, and then its performance is evaluated. Compared with a simple parabolic-shaped mount, the MLL is shown to be free of spherical aberration, resulting in a focus with larger intensity and smaller size of the focal point. Moreover, the focusing properties can be tuned and enhanced thanks to the possibility of changing the position of the focal point. The focusing quality of the MLL is described in all water-depth regimes (covering dispersive and non-dispersive waves) and the focusing of linear and nonlinear waves is revealed experimentally. The option of moving the focal point outside the lens, where the water depth is constant, may be useful when locating devices for harvesting wave energy. Full article

The topological properties of vector optical fields are traditionally considered strictly conserved during continuous deformations and linear propagation. However, while structured light has been extended into nonlinear regimes, previous studies have predominantly focused on the intensity modulation of specific orbital angular momentum (OAM) components and the pure frequency conversion of structured light. The critical question of whether macroscopic topological invariants remain robust or experience fundamental breakdown during nonlinear light–matter interactions remains largely unexplored. To address this specific gap, we propose and generate multiple fractional vector optical fields (MF-VOFs), establishing their dynamic topological evolution and inherent conservation laws in free space. It should be noted that our experimental results are limited to free-space propagation. Strikingly, we report a significant departure from this paradigm during light–matter interactions: topological nonconservation anomalies manifest when these optical fields interact with nonlinear materials via second- and third-harmonic generation. Through a comprehensive quantitative analysis of the OAM spectrum, we confirm that the asymmetrical reconstruction and spatial transition of the total OAM along the propagation direction serve as the physical origins driving this topological symmetry breaking. These findings provide a fundamentally novel perspective on topological manipulation in nonlinear optical processes, offering advanced strategies for complex structured light generation and high-dimensional optical information processing. Full article

Locusta migratoria manilensis causes frequent locust outbreaks in China. This study addresses technical barriers to developing monitoring and control methods based on optical traps. We examined the synergistic effects of spectral light and linear polarized light, and their relationship to visual aggregation under partially polarized illumination. Results showed that the coupling of unpolarized and polarized components within partially polarized light determines the effectiveness of polarized spectral vector illumination on locust aggregation sensitivity. Spectral characteristics modulate polarization-dependent visual sensitivity and affect synergy between spectral and polarized light. The induction of aggregation depended on both the spectral properties of partially polarized light and the illumination parameters. Among the tested conditions, unpolarized violet light combined with linearly polarized orange light at a 270° vector angle produced the strongest time-dependent effect, followed by unpolarized orange light combined with linearly polarized violet light at 0°. The combined stimulation of spectral and polarized-light-triggered aggregation through polarization-enhanced polarotaxis and spectrum-driven phototaxis. This behavior appears to result from nonlinear regulation between unpolarized and polarized components, which increases directional sensitivity for orientation. These findings show that partially polarized light can effectively trap locusts, promote aggregation, and interfere with navigation, providing a basis for improved optical control strategies. Full article

The uniformity of local photoelectric properties in infrared detectors is critical for detection sensitivity. However, micro-nano-scale surface abnormalities introduced during mercury cadmium telluride (HgCdTe) fabrication systematically degrade in-plane photoelectric response consistency. To overcome the optical diffraction limits of standard far-field metrology, we utilized a cryogenic scattering-type scanning near-field optical microscopy (Cryo-SNOM) system to achieve the first super-resolution, in situ imaging of local near-field photocurrent in HgCdTe photoconductive detectors at 10 K. Device-level measurements reveal that sub-wavelength surface protrusions (~tens of nanometers high) act as strong recombination centers, suppressing local photocurrent and causing a consistent 10~20% relative signal attenuation compared to planar regions. Power and bias-dependent testing indicate these defects function as unsaturated linear recombination states. Increasing bias voltage amplifies the coupling between the external field and the defect’s built-in field, broadening the local depletion region and driving a non-linear escalation in the attenuation ratio. This study establishes quantitative engineering tolerances for morphological deviations at the nanoscale, providing critical criteria for the chip integration, structural optimization, and precision manufacturing of high-performance infrared sensing arrays. Full article

The paper introduces a non-linear method for modeling the luminance coefficient (Qd) of asphalt (bituminous) mixtures using a Generalized Additive Model (GAM). Developed from observations after three and six months of service, the model accounts for the effects of aggregate luminance, binder content, and air voids, as well as temporal and non-linear dependencies. It showed a high goodness-of-fit (R² = 0.91) and strong predictive accuracy (RMSE = 4.8 mcd/m²/lx). The analysis revealed that the service period significantly influences luminance, with values after six months being, on average, 12.6 mcd/m²/lx higher than at three months. The impact of aggregate luminance was non-linear, displaying a saturation effect, while asphalt content and air voids varied in their influence over time. Results indicate that the factors affecting bituminous mixture luminance are complex and vary over time; moreover, high aggregate luminance alone does not guarantee a high Qd. Applying the additive model confirms the importance of accounting for non-linear effects and temporal interactions when assessing road surface optical properties. Full article

This work establishes a map between deposition, structure, and properties that enables the design of Ni-P coatings for advanced surface engineering applications. The coatings were electrodeposited on 316L stainless steel substrates using electrolytes of different phosphorus contents, achieved by systematically varying the phosphorous acid (H₃PO₃) concentrations. The influence of phosphorus content and intrinsic pH on elemental composition, cathodic current efficiency (CCE), thickness, microstructure, surface topography, crystalline structure, optical properties, and tribological behavior was investigated. The incorporation of phosphorus follows the H₃PO₃ concentration increase in a non-linear trend, achieving a maximum value of 22.17 at.% P at the highest bath concentration. The CCE presented an opposite trend, decreasing from approximately 96% to 40%, due to intense activity of hydrogen evolution reactions, and evidencing indirect phosphorus incorporation mechanisms. A transition from crystalline to amorphous structures was observed as the phosphorus content increased, being accompanied by grain refinement and significant roughness reduction to a minimum Sa = 8 ± 1 nm at ~15 at.% P. The optical properties, such as diffuse reflectivity and CIE Lab* color coordinates, were strongly correlated to surface roughness and microstructural evolution, demonstrating the influence of phosphorus through structural changes. Tribological behavior of the coatings revealed a complex interplay between composition, roughness, and wear mechanisms. The lower and more stable coefficients of friction were observed for high phosphorus coatings, although their durability depended on the balance between brittleness and grain refinement. The results demonstrate the combined role of phosphorus concentration and intrinsic pH changes as an effective tool for tailoring the structural, optical, and tribological properties of electrodeposited Ni-P coatings. Full article

Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under electric dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high-temperature fabrication processes. In this work, heterostructures made of two distinct amorphous materials, namely SiO₂ and TiO₂, were prepared through plasma-enhanced atomic layer deposition (PEALD) with deposition temperature of 100 °C. By using the uniaxial dispersion model, we characterized the form birefringence of the deposited films, which can play a crucial role for the phase-matching condition in nonlinear waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective bulk second-order susceptibility, ${\chi }_{zzz}^{\left(2\right)}$ = 1.30 ± 0.13 pm/V, at a wavelength of 1032 nm. Noteworthy, we observed strong SHG signals from two-component nanolaminates, which are several orders of magnitude larger than those from single layers. The SHG signals from our samples only require the broken inversion symmetry at the interface. Here, optical properties of nanocomposites can be precisely engineered using the promising PEALD technology. Full article

In this study, a multicomponent composite film system based on alginate, chitosan, κ-carrageenan, agar, and Rapana venosa protein hydrolysate (RVPH) was developed, and the effect of RVPH incorporation (0–1.5%) on molecular interactions, microstructure, and functional performance was evaluated using FTIR, SEM, mechanical testing, optical analysis, and water-related measurements. FTIR results indicated that RVPH interacted with the polysaccharide matrix mainly through hydrogen bonding and ionic interactions without causing chemical degradation. SEM analysis revealed concentration-dependent microstructural changes, with smoother morphologies at low RVPH levels and increased roughness and heterogeneity at higher concentrations. These structural differences were reflected in the functional properties. All films exhibited high swelling and water solubility. Optical properties were significantly affected by RVPH. Mechanical properties exhibited a non-linear response, with numerical variations observed but no statistically significant differences (p > 0.05). The EDAS and SWARA methods were employed to determine the optimal incorporation level of RVPH in the film formulations. Among the RVPH-containing films, the formulation incorporating 1% RVPH was identified as the most suitable alternative. Full article

High-order Poincaré sphere (HOPS) beams have attracted tremendous interest due to their complex polarization and phase characteristics. However, manipulating the second harmonics generation (SHG) of HOPS beams is still challenging. Here, we developed a vector-coupled wave model to predict petal-shaped intensity patterns and reveal a linear correlation between petal number and topological order (n = 2 → 4). Moreover, we experimentally investigated the multidimensional regulation of SHG in HOPS beams through tailored phase-matching strategies. By employing three distinct configurations—(i) type-I phase matching, (ii) type-II phase matching, and (iii) orthogonally arranged BBO crystals based on Type-I phase matching—we establish a comprehensive framework for controlling the spatial and polarization properties of SHG in n = 2 HOPS beams. These results advance the manipulation of structured light in nonlinear optics, providing insights for optimizing applications in optical communication and polarization imaging. Full article

Interest in non-centrosymmetric crystalline materials exhibiting second harmonic generation (SHG) has increased due to their potential applications in optical sensing and biosensing. Saccharide-based metal complexes are particularly attractive systems, as chiral sugars can promote non-centrosymmetric crystal packing. In this work, a new lanthanum–β-d-fructose compound, [La(C₆H₁₂O₆)(H₂O)₅]Cl₃ (LaFRUCl), was synthesized using a simple and low-cost method and characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ and consists of infinite (La³⁺–fructose)_n chains extending along the [001] direction, forming a one-dimensional Metal–Organic Framework. The nonlinear optical response was evaluated using the Kurtz–Perry powder technique with a Nd:YAG laser (1064 nm) and compared to a sucrose reference. The measured SHG efficiency is comparable to that of previously reported alkaline earth metal–sugar analogs. While the compound’s SHG emission is significant, evaluation of its structural stability under aqueous or physiological conditions is be required before considering biological applications. Full article

The interaction between plasmonic nanoparticles and organic dye molecules plays an important role in varied photonic and optoelectronic applications. In this work, we systematically investigate the optical properties of a water-soluble perylenediimide derivative, N,N′-di(2-(trimethylammonium iodide) ethylene) perylenediimide (TAIPDI), in the presence of different concentrations of silver nanoparticles (AgNPs) under femtosecond (fs) laser excitation. The AgNPs were synthesized via the laser ablation technique. The influence of AgNP concentration on the linear, fluorescence, and nonlinear optical properties of the TAIPDI dye was explored through UV–visible absorption spectroscopy, fluorescence emission measurements, and open- and closed-aperture Z-scan techniques. The Ag NP–TAIPDI dye hybrid systems (Ag@TAIPDI nanocomposites) exhibited pronounced reverse saturable absorption and self-defocusing behavior, indicating a negative nonlinear refractive index. Both the nonlinear absorption coefficient and refractive index increased markedly with rising AgNP concentration, leading to a significant enhancement in the third-order nonlinear susceptibility. Fluorescence studies further revealed a concentration-dependent emission enhancement due to metal-enhanced fluorescence arising from surface plasmon resonance-induced local field amplification. The Ag@TAIPDI nanocomposites also demonstrated strong optical limiting performance, with the limiting threshold decreasing as the AgNP concentration increased. These findings highlight the synergistic role of plasmon–exciton coupling and thermal lensing in enhancing the nonlinear response of such nanocomposites. The results establish AgNPs–TAIPDI dye hybrid systems as promising materials for all-optical switching, optical limiting, and photonic device applications. Full article

This paper proposes a short-term photovoltaic (PV) power prediction method that integrates aerosol optical feature mining with a dual-channel attention mechanism to address the complex non-linear attenuation effects of atmospheric aerosols and the limitations of existing models in handling sudden meteorological changes and aerosol evolution. Using the optical properties of aerosols and clouds (OPAC) database, a high-dimensional aerosol optical feature set is constructed, which is subsequently optimized using the minimum redundancy maximum relevance (mRMR) algorithm. The prediction scenarios are categorized into polluted and clean regimes through K-means clustering. A dual-channel encoder–decoder network, combining bidirectional long short-term memory (BiLSTM) and iTransformer, is developed to capture high-frequency meteorological volatility and low-frequency aerosol evolution. A bidirectional cross-attention mechanism enables deep feature interaction between the optical and meteorological channels. The method is validated using in situ measurements from a PV station in Hebei, China, along with aerosol data from the Copernicus Atmosphere Monitoring Service (CAMS) and meteorological data from the ECMWF Reanalysis v5 (ERA5). Experimental results demonstrate an average reduction of approximately 29.83% in mean absolute error (MAE) on polluted days and 15.22% on clean days. Interpretability analysis reveals distinct physical mechanisms driving the predictions, emphasizing the role of extinction on polluted days and scattering on clean days. Full article

This paper presents a comprehensive analysis and simulation of a cost-effective optical Intensity-Modulation/Direct-Detection (IM/DD) Orthogonal Frequency Division Multiplexing (OFDM) system. Implemented via a MATLABR2024a and OptiSystem 23 co-simulation environment, the study evaluates a 4-QAM modulated link over a 120 km transmission distance, providing detailed investigations into signal spectral properties and constellation characteristics. To address the critical performance limitation posed by high Peak-to-Average Power Ratio (PAPR), a novel Hybrid Whale Optimization Algorithm with Selective Mapping (HWOA-SLM) is proposed. Simulation results demonstrate that the proposed scheme significantly outperforms conventional reduction techniques; specifically, at a Complementary Cumulative Distribution Function (CCDF) of 10⁻² and a fixed computational budget of 256 evaluations, the HWOA-SLM achieves a PAPR reduction gain of 3.9 dB relative to the original OFDM signal. Furthermore, in terms of algorithmic efficiency, it outperforms standard Genetic Algorithm (GA) and WOA-based SLM techniques by approximately 0.4 dB under identical computational budgets. Parametric analysis further confirms that increasing population size and iteration numbers consistently improves convergence, thereby minimizing non-linear distortions and enhancing signal integrity. Moreover, the technique exhibits superior Bit Error Rate (BER) performance, delivering Optical Signal-to-Noise Ratio (OSNR) gains of 0.63 dB, 1.31 dB, and 2.0 dB over standard WOA-SLM, GA-SLM, and conventional SLM, respectively. Conclusively, the HWOA-SLM offers a favorable trade-off between computational complexity and reduction efficiency, validating its potential for reliable, high-speed optical communication networks. Full article

The synthesis of continuous non-linear metal nanostructures at the micro and nanoscale remains a challenging frontier in nanotechnology due to inherent synthetic constraints. This study introduces an innovative chemical methodology for fabricating continuous rings and diverse geometries via the chemical fusion of gold nanorods (AuNRs) on a solid substrate. Initially, aqueous solutions of cetyltrimethylammonium bromide (CTAB)-coated AuNRs were deposited and dried on a solid substrate, resulting in the self-assembly of ring-like arrays. Subsequent chemical growth of the AuNRs in all dimensions was achieved using an aqueous solution of Au(I)/CTAB/Ascorbic Acid (AA), enabling their fusion into continuous structures. This approach permits the formation of arbitrary shapes by pre-arranging AuNRs, thereby opening new avenues for the exploration of non-linear nanostructures with potentially novel plasmonic and electronic properties. The capability to engineer such complex nanostructures is pivotal for advancing fields such as photonics, electronics, and sensing, where the unique optical and electronic properties of gold nanostructures can be exploited for cutting-edge applications. Furthermore, this technique shows a significant promise for the fabrication of various micro- and nanodevices and the seamless interconnection of components in integrated electronic circuits, potentially leading to more efficient and miniaturized electronic systems. The broader implications of this research are significant, offering a potential pathway to the development of nanomaterials and devices that could benefit various industries and technological processes. Full article