Search Results (118)

Underwater laser imaging is widely used for deep-sea exploration, autonomous underwater navigation, and inspection of marine infrastructure, where high-precision observation under optically challenging conditions is required. These imaging systems are inherently limited by absorption attenuation, volume scattering, and backscattered noise, leading to reduced visibility, low contrast, and loss of structural details. In this study, we propose a Polarization-Constrained Multi-Scale Defogging and Restoration (PCMS-DR) algorithm designed for turbid and heterogeneous aquatic environments, specifically targeting submerged engineered structures, pipelines, and other objects of interest. The method integrates polarization feature constraints with multi-scale decomposition, enabling robust separation of backscattered light and target-reflected signals while preserving high-frequency structural information. To quantitatively evaluate the proposed framework, two complementary validation strategies are adopted. First, polarization-resolved Monte Carlo photon propagation simulations are conducted to generate physically consistent synthetic underwater laser images for controlled analysis under different scattering conditions. Second, real-world validation is performed using 12 self-acquired coastal underwater laser imaging scenes collected under representative aquatic environments. The simulation and experimental datasets are analyzed separately to ensure that the quantitative evaluation accurately reflects both physical restoration capability and practical applicability. Quantitative results from the Monte Carlo simulation experiments demonstrate that the proposed PCMS-DR method achieves a peak PSNR of 26.52 dB and an SSIM of 0.836 under representative low-turbidity conditions, outperforming polarization-only and multi-scale-only baselines. In addition, evaluation on the self-acquired real underwater laser imaging dataset containing 12 coastal scenes indicates an average backscatter suppression ratio of 22.3% and a local contrast enhancement ratio of 1.62. These results confirm that the proposed method improves image visibility and structural preservation across both controlled simulations and practical imaging scenarios. Furthermore, evaluation on 12 real coastal underwater laser imaging scenes demonstrates an average backscatter suppression ratio of 22.3% and a local contrast enhancement ratio of 1.62, indicating improved visibility, contrast, and structural fidelity. The principal novelty of the proposed framework lies in the unified integration of polarization-constrained backscatter modeling, multi-scale transmission estimation, and physically guided detail restoration within a single optimization framework. The experimental results demonstrate that the proposed PCMS-DR framework provides physically interpretable and effective restoration performance under the tested turbidity range for underwater laser imaging applications. Full article

Single-event burnout (SEB) remains a persistent threat to SiC power MOSFETs in space, yet rapid evaluation of SEB susceptibility without costly heavy-ion campaigns is challenging. This work demonstrates that femtosecond laser two-photon absorption (TPA) can fill that role for a commercial 1200 V SiC MOSFET—provided the laser energy is correctly mapped to heavy-ion linear energy transfer (LET). We derive an equivalent LET model that incorporates the thermal spike effect, giving LET_eq = Γ₁E₀² + Γ₂E₀⁴, which corrects the classical square law at high excitation intensities where it fails. Three ionization-driven failure signatures emerge: drain-to-gate and drain-to-source single-event leakage current (SELC), and SEB. The SEB threshold saturates near 500 V once LET exceeds 25 MeV·cm²/mg—roughly 42% of the device’s 1200 V rating. From these thresholds, we define a safe operating area: below 200 V is safe, 200–600 V risks SELC degradation, and above 600 V carries high SEB risk. Benchmarking against published heavy-ion data shows SEB threshold agreement within 15%, and within 5% at high LET. We stress that the TPA method captures ionization-driven effects only; it does not replicate displacement damage. These results support rapid, laser-based screening of SiC power devices for radiation hardness. Full article

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

Passively mode-locked lasers, as essential tools for generating ultrashort pulses, have found widespread applications in industrial manufacturing, optical communications, biomedical imaging, and fundamental scientific research. Saturable absorbers serve as the key components governing the performance of such laser systems. Conventional saturable absorber materials, including semiconductor saturable absorber mirrors, carbon nanotubes, and graphene, however, suffer from inherent limitations in operational wavelength range, damage threshold, and environmental stability. In recent years, two-dimensional transition metal carbides and nitrides, known as MXenes, have emerged as a promising class of materials to address these challenges. Their unique metallic conductivity, broadband saturable absorption, ultrafast carrier dynamics, excellent thermal management capability, and versatile chemical tunability offer unprecedented opportunities for advanced saturable absorber applications. This review systematically summarizes the recent progress of MXene-based saturable absorbers, with an emphasis on their distinctive advantages in extending the mode-locked wavelength range, enhancing output pulse stability, and increasing the optical damage threshold. Furthermore, strategies for performance optimization through surface terminal group engineering, defect modulation, and heterostructure design are discussed in depth. Finally, the future prospects and key challenges toward industrial implementation of MXenes in ultrafast photonics are outlined, aiming to stimulate further advancements in high-performance ultrafast laser technology. Full article

Two-Photon Polymerization (2PP) has been established in recent decades as one of the most promising additive manufacturing processes for the fabrication of freeform 3D micro- and nanostructures. In 2PP, the photochemical reaction, induced by the absorption of the energy of two photons, is confined to a small and well-defined region of the space known as voxel, enabling the manufacture of 3D features with high accuracy and resolutions in the submicrometric range. Unfortunately, 2PP shows some drawbacks, among which its low productivity appears as one of its main limitations nowadays. In this regard, different approaches have recently been explored aiming at increasing 2PP throughput, like the use of Spatial Light Modulators (SLMs), which allows dynamically adjusting the shape of the laser beam into different geometries, patterns or even complex images. In this work an experimental 2PP setup comprising a femtosecond visible laser in combination with high accuracy linear stages and different optical solutions including an SLM has been used to explore the improvement achieved in productivity and additional advantages for the manufacturing of different 2.5 and 3D microstructures. A commercial photoresist has been used as base for these experiments, adjusting its photoinitiator content to obtain the optimal sensitivity to the wavelength provided by the laser. Full article

Three ethynyl-extended benzanthrone derivatives with benzonitrile (Dye A), thiophene (Dye B), and methyl propiolate (Dye C) as substituents were synthesized and investigated to illustrate structure–property relationships governing their nonlinear optical (NLO) behavior. The third-order nonlinear absorption and refractive index of three dyes were studied using open- and closed-aperture z-scan measurements under 532 nm continuous-wave laser excitation. All dyes exhibited reverse saturable absorption dominated by two-photon absorption, with Dye A showing the highest nonlinear absorption coefficient (βeff = 2.3 × 10⁻⁵ cm/W) and two-photon response, attributed to its extended conjugation and smaller HOMO−LUMO gap (6.45 eV). Closed-aperture Z-scans revealed strong nonlinear refraction (n₂), with the thiophene-substituted Dye B displaying the largest n₂ (14.8 × 10⁻⁹ cm²/W) and third-order susceptibility (χ³ = 3.1 × 10⁻⁶ esu). The evaluated optical switching figures of merit met the requirements for all-optical switching and optical limiting. DFT and TDDFT calculations demonstrated that donor substitution and conjugation length govern electronic structure, charge transfer character, and global reactivity descriptors. Enhanced electronic softness and hyperpolarizability in Dye B further support its superior refractive nonlinearity. These results establish clear structure–property correlations and highlight donor engineering as an effective strategy for developing organic nonlinear optical and photonic materials. Full article

Efficient ozone synthesis has always been the pursuit of ozone workers and the foundation for the industrial application of ozone reactors. Recently, with continuous breakthroughs in materials and catalyst research, as well as the rapid development of advanced characterization technologies, introducing catalysts into dielectric barrier discharge (DBD) to build a DBD–catalyst coupled system has developed into an advanced means of improving ozone synthesis and attracted widespread attention. This review aims to provide a systematic summary for the research status of the DBD–catalyst coupled system in the field of ozone synthesis. Firstly, the structure of DBD reactors (type and shape of the electrode, etc.), catalyst types and the coupling method of DBD and catalysts (such as catalyst packing, catalyst coating/film) for the DBD–catalyst coupled system are discussed. Subsequently, the relevant mechanisms involving plasma gas-phase reactions and gas–solid interface reactions for elevating discharge ozone synthesis through coupling catalysts with DBD are summarized and analyzed. Afterwards, the research status of the DBD–catalyst coupled system in the field of ozone synthesis is surveyed. At present, the optimal ozone synthesis performance of the reactor with packed catalyst in air plasma (γ-Al₂O₃ sphere) is 0.96 g/Nm³ and 103 g/kWh, and in oxygen plasma (SiO₂ particle) is 130 g/Nm³ and 91 g/kWh, respectively. For the reactor coupled with a catalyst coating, the performance reaches 19.3 g/Nm³ and 320 g/kWh in oxygen plasma (TiO₂). Then, advanced plasma parameter detection techniques (i.e., optical emission spectroscopy and two-photon absorption laser-induced fluorescence) are expatiated to observe the changes in plasma parameters within the discharge system and then provide strong support for further in-depth research and analysis of the enhancement mechanism of coupling catalysts on ozone synthesis. Finally, a short conclusion, together with the current challenges and future opportunities of the DBD–catalyst coupled system in improving ozone synthesis, are proposed. Full article

An ultrafast laser system combined with an optical delay line allowed ablation and in-scription at 1 kHz and 1 GHz pulse burst within transparent polyimide films. The two-photon-induced absorption results in clean surface ablation, while inscription results in polymer decomposition, creating carbonised regions within the polymer. Three pulse bursts at 1 GHz increased the observed coupling to the material significantly. Modified regions (with linewidths down to a few microns) were investigated using optical microscopy, white light interferometry, SEM and Raman spectroscopy, supporting the increasing carbon density relative to the pristine polymer. As depth of field was only a few microns at high NA, 3D micro-structuring was achieved. Polymer decomposition produces gaseous products, resulting in internal stress and thus affecting inscription fidelity. An inscribed subsurface electrode with dimensions of 5 mm × 0.3 mm × 3 μm connected to conducting vias had a resistance of R = 10.6 ± 0.2 kΩ, along with resistivity of ρ ~ 0.19 Ω cm; hence, it had DC conductivity, σ ~ 5.3 Scm⁻¹. This conductivity is similar to that of bulk graphite and could well form the basis of future flexible sensors, demonstrating single-step 3D subsurface inscription of carbon or laser-induced graphene structures. Full article

Organic photovoltaic materials and nonlinear optical materials share inherent commonalities in molecular characteristics—such as strong light absorption, high charge carrier mobility, and tunable energy levels. Therefore, this study selects a bithiophene-fused ring system with photovoltaic application potential as the research subject. Using TTTTB6-2CHO (TB1) and IDTTB6-2CHO (TB2) as comparative molecules, their nonlinear optical properties in the near-infrared region were systematically investigated. Transient absorption spectroscopy results demonstrate that TB1 exhibits strong and persistent excited-state absorption within the spectral range of 650–900 nm, endowing it with excellent two-photon absorption performance (a cross-section of up to 5591 GM at 650 nm) and an ultralow optical limiting threshold (0.00147 J/cm² under 800 nm femtosecond laser irradiation). The findings of this study not only confirm the feasibility of developing nonlinear optical materials from photovoltaic candidate molecules but also highlight the effectiveness of the “thiophene-for-benzene substitution” strategy in significantly enhancing optical nonlinearity. These results provide valuable design principles for the development of multifunctional organic optoelectronic materials, particularly for application scenarios such as laser protection. Full article

The rapid development of detection technologies has increased the demand for multispectral camouflage materials capable of broadband concealment and effective thermal management. To address the conflicting optical requirements between infrared camouflage and LiDAR camouflage, we propose a composite design combining a germanium–ytterbium fluoride (Ge/YbF₃) selective emitter with an amorphous silicon (a-Si) two-dimensional periodic microstructure. The multilayer film, optimized using the transfer-matrix method and a particle swarm optimisation algorithm, achieves low emissivity in the 3–5 μm and 8–14 μm infrared atmospheric windows and high emissivity within 5–8 μm for radiative cooling, while introducing a narrowband absorption peak at 1.55 μm. Additionally, the a-Si microstructure provides strong narrowband absorption at 10.6 μm via a grating-resonance mechanism. FDTD simulations confirm low emissivity in the infrared windows, high absorptance at LiDAR wavelengths, and good angular and polarization robustness. This work demonstrates a multifunctional photonic structure capable of integrating infrared camouflage, laser camouflage, and thermal-radiation control. Full article

High-speed silicon (Si) photonic transmitters operating in the O-band require higher on-chip optical power to support advanced modulation formats and ever-increasing line rates. A straightforward approach is to operate laser diodes at higher output power or employ more specialized sources, but this raises cost and exacerbates nonlinear effects such as self-phase modulation, two-photon absorption, and free-carrier generation in high-index-contrast Si waveguides. This paper proposes a low-cost 4 × 1 tree-cascade multimode interference (MMI) power combiner on a Si-on-insulator platform at 1310 nm wavelength that enables coherent power scaling while remaining fully compatible with standard commercial O-band lasers. The device employs adiabatic tapers and low-loss S-bends to ensure uniform field evolution, suppress local field enhancement, and mitigate nonlinear phase accumulation. The optimized layout occupies a compact footprint of 12 µm × 772 µm and achieves a simulated normalized power transmission of 0.975 with an insertion loss of 0.1 dB. Spectral analysis shows a 3 dB bandwidth of 15.8 nm around 1310 nm, across the O-band operating window. Thermal analysis shows that wavelength drift associated with ±50 °C temperature variation remains within the device bandwidth, ensuring stable operation under realistic laser self-heating and environmental changes. Owing to its broadband response, fabrication tolerance, and compatibility with off-the-shelf laser diodes, the proposed combiner is a promising building block for O-band transmitters and photonic neural-network architectures based on cascaded splitter and combiner meshes, while preserving linear transmission and enabling dense, large-scale photonic integration. Full article

Two-photon polymerization (2PP) is revolutionizing micro- and nanoscale manufacturing by enabling true 3D fabrication with feature sizes far below the diffraction limit—capabilities that traditional lithography cannot match. By using ultrafast femtosecond laser pulses and nonlinear absorption, 2PP initiates polymerization only at the laser’s focal point, offering unmatched spatial precision. This paper highlights key advancements driving the field forward: the development of new materials engineered for 2PP with improved sensitivity, mechanical strength, and the introduction of high-speed, parallelized fabrication strategies that significantly enhance throughput. These innovations are shifting 2PP from a prototyping tool to a viable method for scalable production. Applications now range from custom biomedical scaffolds to complex photonic and metamaterial structures, demonstrating their growing real-world impact. We also address persistent challenges—including slow writing speeds and limited material options—and explore future directions to overcome these barriers. With continued progress in materials and hardware, 2PP is well positioned to become a cornerstone of next-generation additive manufacturing. Full article

This study details how 3-(naphthalen-2-yl)-1-phenylprop-2-en-1-one (3NPEO) behaves in terms of photophysics when exposed to different solvents. The solvatochromic effect study reveals significant polarity shifts in the excited states of the 3NPEO compound, likely due to an intramolecular proton transfer mechanism. Measurements of dipole moments provide insight into their resonance structures in both ground and excited states. Electrochemical analysis revealed a reversible redox process, indicating a favorable charge transport potential. HOMO and LUMO energies of the compound were computed via oxidation and reduction potential standards. 3NPEO exhibits optimal one-photon and two-photon absorption characteristics, validating its suitability for visible wavelength laser applications in photonic devices. Furthermore, molecular docking and dynamics simulations demonstrated strong interactions between 3NPEO and the progesterone receptor enzyme, supported by structure–activity relationship (SAR) analyses. In vitro cytotoxicity assays on the MDAMB-231 breast cancer cell line showed moderate tumor cell inhibitory activity. Apoptosis studies confirmed the induction of both early and late apoptosis. These findings suggest that 3NPEO holds promise as a potential anticancer agent targeting the progesterone receptor in breast cancer cells. Overall, the findings highlight the substantial influence of solvent polarity on the photophysical properties and the design of more effective and stable therapeutic agents. Full article

This study explores the optical properties of a close-packed monolayer composed of core/shell-alloyed CdSeS/ZnS quantum dots (QDs) of two different sizes and compositions. The monolayers were self-assembled in a stacked configuration at the water/air interface using Langmuir–Blodgett (LB) techniques. Under continuous 532 nm laser illumination on the red absorption edge of the blue-emitting smaller QDs (QD450), the red-emitting larger QDs (QD645) exhibited oscillatory temporal dynamics in their photoluminescence (PL), characterized by a pronounced blueshift in the emission peak wavelength and an abrupt decrease in peak intensity. Conversely, excitation by a 405 nm laser on the blue absorption edge induced a drastic redshift in the emission wavelength over time. These significant shifts in emission spectra are attributed to photon- and anisotropic-strain-assisted interlayer atom transfer. The findings provide new insights into strain-driven atomic rearrangements and their impact on the photophysical behavior of QD systems. Full article

The current study presents the results of a methodical investigation into the ionization of rare gas atoms, specifically focusing on argon. In this study, two configurations are examined: ionization via a near-infrared (NIR) laser field alone, and ionization caused by extreme ultraviolet (XUV) radiation in the presence of a strong, synchronized NIR pulse. The theoretical investigation is conducted using an ab initio method to solve the time-dependent Schrödinger equation within the single active electron (SAE) approximation. The simulation results show a sequence of above-threshold ionization (ATI) peaks that shift to lower energies with increasing laser intensity. This behavior reflects the onset of the Stark effect, which modifies atomic energy levels and increases the number of photons required for ionization. An examination of the two-color photoionization spectrum, which includes sideband structures and harmonic peaks, shows how the ionization probability is redistributed between the direct path (single XUV photon absorption) and sideband pathways (XUV ± n × IR) as the intensity of the infrared field increases. Quantum interference between continuum states is further revealed by the photoelectron angular distribution, clearly indicating the control of ionization dynamics by the IR field. Full article