Search Results (359)

Optical coherence tomography (OCT) employs light to acquire high-resolution 3D images and is widely applied in fields such as ophthalmology and forensic science. A popular technique for visualizing the top view (en face) is to slice it with flat horizontal plane or apply statistical functions along the depth axis. However, when the target appears as a thin layer, strong reflections from other layers can interfere with the target, rendering the flat-plane approach ineffective. We apply Otsu-based thresholding to extract the object’s foreground, then use least squares (with Tikhonov regularization) to fit a polynomial curve that describes the sample’s structural morphology. The surface is then used to obtain the latent fingerprint image and its residues at different depths from a translucent tape, which cannot be analyzed using conventional en face OCT due to strong reflection from the diffusive surface, achieving FSIM of 0.7020 compared to traditional en face of 0.6445. The method is also compatible with other signal processing techniques, as demonstrated by a thermal-printed label ink thickness measurement confirmed by a microscopic image. Our approach empowers OCT to observe targets embedded in samples with arbitrary postures and morphology, and can be easily adapted to various optical imaging technologies. Full article

Topological orientation structures in chiral nematic liquid crystals, such as torons, exhibit promising optical properties and are of increasing interest for applications in photonic devices. However, despite this attention, their polarization and phase dynamics during formation remain insufficiently explored. In this work, we investigate the dynamic optical response of a toron generated by focused femtosecond infrared laser pulses. A custom-designed polarization holographic microscope is employed to simultaneously record four polarization-resolved interferograms in a single exposure. This enables the real-time reconstruction of the Jones matrix, providing a complete description of the local polarization transformation introduced by the formation of the topological structure. The study demonstrates that torons can facilitate spin–orbit coupling of light in a manner analogous to q-plates, highlighting their potential for advanced vector beam shaping and topological photonics applications. Full article

We report on the preparation and characterization of a new family of hydrogen-bonded nematogenic liquid crystalline dimers. The dimers are supramolecular complexes that consist of a benzoic acid derivative, acting as the proton donor, featuring a spacer with seven methylene groups and a terminal decyloxy chain, paired with an azopyridine derivative as the proton acceptor. The latter was either fluorinated or nonfluorinated with variable alkoxy chain length. The formation of a hydrogen bond between the individual components was confirmed using FTIR and ¹H NMR spectroscopy. All supramolecules were investigated for their liquid crystalline behaviour via a polarized optical microscope (POM) and differential scanning calorimetry (DSC). All materials exhibit enantiotropic nematic phases as confirmed by X-ray diffraction (XRD) and POM investigations. The nematic phase range depends strongly on the degree and position of fluorine atoms. Additionally, the supramolecules demonstrated a rapid and reversible transition between the liquid crystal phase and the isotropic liquid state because of trans-cis photoisomerization upon light irradiation. Therefore, this study presents a straightforward approach to design photo-responsive nematic materials, which could be of interest for nonlinear optics applications. Full article

An oceanographic cruise with 34 stations was conducted in the central-southwestern region of the Gulf of Mexico from February 19 to 10 March 2013. This study included the measurement of hydrographic and phytoplankton bio-optical parameters, and pigment samples were collected at two depth levels (10 and 50 m). Our results showed a warm and nutrient-depleted water column associated with low chlorophyll a (<1 mg Chla m⁻³) and average values of a_ph440 (0.01 ± 0.008, m⁻¹) and a_d350 (0.04 ± 0.02, m⁻¹). In addition, nano-microphytoplankton abundance and pigments were analyzed using a light microscope and HPLC, respectively. Overall, the Gulf of Mexico exhibited oligotrophic characteristics, with Chla (0.17 ± 0.11 mg m⁻³) and NO₃⁻ (0.03 ± 0.001 µM), except at 50 m depth in some stations north of Yucatán and in Campeche Bay and at surface level off the Tamaulipas shelf. In these three regions, values of a_ph(440), a_d(350), (Chla) and phytoplankton abundance (>12 × 10³ cells L⁻¹) were observed near river mouths and under seasonal oceanographic forcings, which increased the growth and diversity of phytoplankton. The most relevant pigments found were DVchla (0.06 ± 0.13 mg m⁻³), Chlb (0.16 ± 0.21 mg m⁻³), Zea (0.06 ± 0.03 mg m⁻³), and Hex-fuco (0.02 ± 0.02 mg m⁻³); these are associated with the presence of Prochlorococcus, chlorophytes, Synechococcus, prymnesiophytes, and diatoms. Through the bio-optical variability, we determined the ecological geography of phytoplankton in four different spectral shapes, where M1 and M2 represent the group of cyanobacteria (Prochlorococcus and Synechococcus) and M3 and M4 represent a mixture of diatoms, dinoflagellates, and chlorophytes. In conclusion, we consider that oceanographic processes such as cyclonic and anticyclonic structures and permanent rivers determine the favorable changes in phytoplankton (>nutrients, Chla, a_ph440) and an increment in the number of phytoplankton spectral shapes). Full article

Hydrogen-bonded cross-linked main chain azobenzene (azo) photoactive polymers have broad application prospects in flexible actuators, optical actuators, and other fields. Most of the research on this kind of photoresponsive material is mainly focused on air, and exploration in solvents remains underexplored. In this paper, azobenzene polyamide ester semicrystalline polymer (PEA-6T) with hydrogen-bond cross-linking was synthesized by Michael addition polymerization. The uniaxially oriented polymer film with high orientation (48.85%) and fast response (5 s under UV light and 55 s under visible light) was obtained by a simple solution casting/mechanical stretching method. Compared with PEA-2T and PEA-4T, PEA-6T exhibits enhanced mechanical properties (elastic modulus increased by 17.4%; yield strength increased by 34.1%; breaking strength increased by 75.4%; elongation at break increased by 33.8%; toughness increased by 101.3%; photoinduced stress increased by 43.5%) and reduced light response time (decreased by 58.3% in ultraviolet light and 50% in visible light) due to the elongation of the compliant chain length. The thin PEA-6T film exhibited light-induced deformation not only in air but also in polar solvents such as water, methanol, ethanol, butanol, and saline solutions (e.g., normal saline, 0.9 wt% NaCl, and simulated seawater, 3.5 wt% NaCl). In addition, polarizing optical microscope (POM) observations showed that the brightness and texture direction of the films remained stable (Δ_Brightness < 5%), the light response time was consistent (6 s under UV light, 65 s under visible light), the light-induced stress retention rate was 95%, and the films exhibited good solvent resistance. This study bridges the research gap in azobenzene photoresponsive materials in solvent environments, and the material shows potential for applications in marine equipment coatings or biomedical actuators. Full article

The production of agricultural residues causes environmental pollution, especially in regions with intensive horticultural production. The solution is to maximise the use of residues, applying the ‘zero waste’ model and using them to develop construction materials. Natural fibres used to reinforce materials have environmental and economic benefits due to their low cost. This research presents an innovative characterisation using an inverted-plate optical microscope, a high-resolution scanning electron microscope (HRSEM) and a 3D X-ray microscope. A physico-mechanical and chemical characterisation of horticultural fibres was also conducted. The fibres analysed were those produced in the highest quantities, including those from tomatoes, peppers, zucchinis, cucumbers and aubergines. The viability of these natural fibres for use as reinforcements in biocomposites was investigated. The analysis centred on studying the microstructure, porosity, chemical composition, tensile strength, water absorption and environmental degradation of the natural fibres. The results showed a porosity ranging from 47.44% to 61.18%, which contributes to the lightness of the materials. Cucumber stems have a higher tensile strength than the other stems, with an average value of 19.83 MPa. The SEM analysis showed a similar chemical composition of the scanned fibres. Finally, the life cycle of the materials made from horticultural residue was analysed, and negative GWP (global warming potential) CO2eq values were obtained for two of the proposed materials, such as stabilised soil reinforced with agricultural fibres and insulation panels made of agricultural fibres. Full article

Extreme ultraviolet (EUV) imagers are key tools to monitor the space environment and forecast space weather. EUV filters are important components to block radiation in the ultraviolet (UV), visible, and near-infrared (IR) regions. In this study, various characterization methods were proposed for the nickel mesh-supported indium (In) filter, and their spectral characteristics were comprehensively studied. The material and thickness of the filter were chosen based on atomic scattering principles, determined through theoretical calculation and software simulation. The metal film was deposited using the vacuum-resistive thermal evaporation method. The measured transmission of the filter was 10.06% at 83.4 nm. The surface elements of the sample were analyzed using X-ray photoelectron spectroscopy (XPS). The surface and cross-sectional morphologies of the filter were observed using a scanning electron microscope (SEM). The impact of the oxide layer and carbon contamination on the filter’s transmittance was investigated using an ellipsometer. A multilayer “In-In₂O₃-C” model was established to determine the thickness of both the oxide layer and carbon contamination layer on the filter. This model introduces the filling factor based on the original model and considers the diffusion of the contamination layer, resulting in more accurate fitting results. The transmittance of the filter in the visible light range was measured using a UV-VIS spectrophotometer, and the measurement error was analyzed. This article provides preparation methods and test methods for the 83.4 nm EUV filter and conducts a detailed analysis of the spectral characteristics of the prepared optical filters, which hold significant value for space exploration applications. Full article

The spray-dried potato starch was produced by gelatinizing native potato starch at two concentrations of 3% and 5% at 75 °C for 30 min, followed by drying in a pilot-scale spray dryer. X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy were applied to characterize native potato starch and spray-dried (SD) potato starch powders. The physical properties of the starches, including moisture content, color, bulk density, tapped density, particle size parameters, water holding capacity, and hygroscopicity, were investigated. XRD, DSC, and FTIR revealed the formation of a semi-crystalline to amorphous structure in the spray-dried starch powders. Microscopic examination showed that the starch granules of native potato starch were spherical and regular in shape, while spray-dried (SD) starch powders displayed wrinkled granules. The moisture content of the spray-dried powders was significantly lower than that of the native starch, while the native starch had higher particle size values [D(4.3)] compared to the spray-dried powders. Higher water holding capacity values were also recorded in the spray-dried starches compared to the native starch. Regarding the color parameters, statistical analysis revealed similar values for lightness (L*) and yellowness (YI) indices, while significant differences were found in hue angle (H°), a*, and b* values. A principal component analysis (PCA) was carried out to investigate the relationships among the physical properties of the native potato starch and spray-dried starch powders. The findings of the present study highlight the potential application of physically modifying starch through the spray-drying process. Full article

Photic retinopathy is an uncommon clinical entity characterized by retinal damage brought on by excessive exposure to light without protection. It encompasses several distinct clinical categories, including solar maculopathy, handheld laser maculopathy, arc welding maculopathy, and iatrogenic macular degeneration. These clinical entities result from exposure to diverse light sources, such as solar radiation, laser pointers, welding arcs, and operating microscopes during ophthalmic procedures. Patients typically present with bilateral but asymmetric symptoms, including reduced visual acuity, central or paracentral scotomas, photophobia, metamorphopsia, and headaches. After exposure, most people can recover on their own in a matter of weeks to six months without the need for special care. However, thanks to their anti-inflammatory properties, several clinical cases reporting the use of steroids for acute photic retinopathy have been documented in the scientific literature, together with the use of antioxidants. The purpose of this review is to provide an update on this phototoxic maculopathy, describing its different clinical entities, diagnosis, and treatment options, and also focusing on the role of optical coherence tomography for its management. Full article

Three-dimensional (3D) cellular models, such as spheroids, serve as pivotal systems for understanding complex biological phenomena in histology, oncology, and tissue engineering. In response to the growing need for advanced imaging capabilities, we present a novel multi-modal Raman light sheet microscope designed to capture elastic (Rayleigh) and inelastic (Raman) scattering, along with fluorescence signals, in a single platform. By leveraging a shorter excitation wavelength (532 nm) to boost Raman scattering efficiency and incorporating robust fluorescence suppression, the system achieves label-free, high-resolution tomographic imaging without the drawbacks commonly associated with near-infrared modalities. An accompanying Deep Image Prior (DIP) seamlessly integrates with the microscope to provide unsupervised denoising and resolution enhancement, preserving critical molecular details and minimizing extraneous artifacts. Altogether, this synergy of optical and computational strategies underscores the potential for in-depth, 3D imaging of biomolecular and structural features in complex specimens and sets the stage for future advancements in biomedical research, diagnostics, and therapeutics. Full article

Nickel–phosphorus (NiP) alloys have been widely used in many engineering fields such as aerospace, automotive, and optics; however, it is difficult to study the material removal mechanism and microscopic size changes in the polishing process of nickel–phosphorus alloys through simple experiments. In light of these difficulties, there is a need to improve our understanding of the surface friction and wear mechanisms of NiP materials. In the present study, molecular dynamics simulations are employed for the first time to investigate the material removal mechanism, mechanical response, phase transformation, and stress distribution of two NiP alloys with different phosphorus contents during the nano-polishing process by adjusting the polishing depth and speed. Our simulation results indicate that the mechanical response of the low-phosphorus alloy is slightly higher than that of the high-phosphorus NiP alloy. Larger polishing depths and higher speeds reduce the surface quality and lead to increased residual stress. The findings presented herein provide an atomic-level understanding of the material removal mechanism of NiP alloys via MD methodology and offer valuable guidance for selecting alloys with an appropriate NiP ratio as engineering materials and for developing processing methods to improve surface quality. Full article

In this paper, we propose a scheme based on the spin Hall effect of light (SHEL) for characterizing aligned polymers. Poly (3-hexylthiophene) (P3HT) films were prepared via the solution shear coating method. The experimental results obtained by using SHEL indicated that the alignment of polymer chains could be enhanced by UV irradiation and was positively correlated with the irradiation time, which was consistent with the measurements of the UV–Vis spectrometer and the polarizing optical microscope (POM). Compared with other optical methods, such as POM that characterizes aligned samples using light intensity, the amplified shift in SHEL can significantly reduce technical noise and exhibit high sensitivity. Even for the weak alignment film, this method can still recognize its alignment and achieve a signal-to-noise ratio (SNR) of 30 dB. This renders SHEL a highly precise technique for studying aligned polymers, which is valuable for the development of organic electronics. Full article

To push the boundaries of confocal microscopy beyond its current limitations by predicting sensor responses for complex surface geometries, we build digital twins using three rigorous models, the finite element method (FEM), Fourier modal method (FMM), and boundary element method (BEM) to model light–surface interactions. Fourier optics are then used to calculate the sensor signals at the back focal plane and at the detector. A 3D illumination model is applied to 2D periodic structures for FEM and FMM modelings and to 3D aperiodic structures for BEM modeling. The lateral and vertical scanning processes of the confocal microscope are achieved through focal-point shifts of the objective, using plane-wave illuminations with varying incident and azimuthal angles. This approach reduces the need for repeated, time-intensive rigorous simulations of the scattering process when a fine scanning is desired. Furthermore, we give an in-depth description of a novel confocal microscopy method using FMM. For rectangular grating surfaces, the three models yield identical, highly accurate results, as validated by measured results. Simulations of the instrument transfer function, tilted gratings, and gratings with edge rounding offer insights into some experimentally observed effects. This research therefore provides a promising approach for correcting systematic errors in confocal microscopy. Full article

We investigate the resonant characteristics of planar surfaces and distinct edges of structures with the excitation of phonon-polaritons. We analyze two materials supporting phonon-polariton excitations in the mid-infrared spectrum: silicon carbide, characterized by an almost isotropic dielectric constant, and hexagonal boron nitride, notable for its pronounced anisotropy in a spectral region exhibiting hyperbolic dispersion. We formulate a theoretical framework that accurately captures the excitations of the structure involving phonon-polaritons, predicts the response in scattering-type near-field optical microscopy, and is effective for complex resonant geometries where the locations of hot spots are uncertain. We account for the tapping motion of the probe, perform analysis for different heights of the probe, and demodulate the signal using a fast Fourier transform. Using this Fourier demodulation analysis, we show that light enhancement across the entire apex is the most accurate characteristic for describing the response of all resonant excitations and hot spots. We demonstrate that computing the demodulation orders of light enhancement in the microscope probe accurately predicts its imaging. Full article

In the present investigation, high stability Vitreloy Zr₄₄Ti₁₁Cu₁₀Ni₁₀Be₂₅ bulk metallic glass has been subjected to severe shear deformation by high-pressure torsion for 0.1 revolutions under an applied pressure of 4 and 8 GPa. The fully glassy nature of the as-cast glass has been confirmed by X-ray powder diffraction and differential scanning calorimetry. Deformation-induced surface features on an internal plane of the deformed disk-shaped specimens were studied in detail at the macroscopic level by optical reconstruction method and at microscopic scales by white-light optical profilometry. Shear and compressive strain components were measured based on surface changes and it was determined that compressive strain gradient with 0.2–0.4 strain change builds up toward the disk edge, while only part of the nominal shear deformation occurs in the disk interior. The effect of strain localization in the Vitreloy bulk metallic glasses has been quantified by a surface distortion model based on simple shear. The model was then validated experimentally by the reconstructed z-profiles. Full article