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A new method of measuring aerosol optical properties from digital twilight photographs
摘要： An optimal-estimation algorithm for inferring aerosol optical properties from digital twilight photographs is proposed. The sensitivity of atmospheric components and surface characteristics to brightness and color of twilight sky is investigated, and the results suggest that tropospheric and stratospheric aerosol optical thickness (AOT) are sensitive to condition of the twilight sky. The coarse–fine particle volume ratio is moderately sensitive to the sky condition near the horizon under a clean-atmosphere condition. A radiative transfer model that takes into account a spherical-shell atmosphere, refraction, and multiple scattering is used as a forward model. Error analysis shows that the tropospheric and stratospheric AOT can be retrieved without significant bias. Comparisons with results from other ground-based instruments exhibit reasonable agreement on AOT. A case study suggests that the AOT retrieval method can be applied to atmospheric conditions with varying aerosol vertical profiles and vertically inhomogeneous species in the troposphere.
关键词： tropospheric and stratospheric AOT,aerosol optical properties,digital twilight photographs,coarse–fine particle volume ratio,radiative transfer model
更新于2025-09-04 15:30:14
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Materials Science and Technology of Optical Fabrication || Surface Roughness
摘要： Because it influences optical-scatter losses and downstream laser modulation [1], the surface roughness of an optical-glass component is an important parameter for many optical systems (including lasers and telescopes). During optical polishing, a number of interactions between the workpiece, polishing slurry, and pad may influence the resulting workpiece roughness at different spatial scale lengths. The phenomena affecting large spatial scale length (>1 mm) on the workpiece (i.e. surface figure) are described in Chapter 2 (see Figure 2.1). By contrast, in this chapter, the phenomena and process parameters affecting short spatial scale lengths (<1 mm) (i.e., surface roughness from AFM2 scale roughness to μ-roughness) are described (see Figure 1.8). Fine-scale roughness, typically measured by atomic force microscopy (AFM), is referred to as AFM1 (≤5 μm) and AFM2 roughness (≤50 μm), as represented on the right of the plot. Roughness at this scale is influenced by parameters such as the single-particle removal function, Beilby layer properties, slurry particle size distribution (PSD), pad topography, pad mechanical properties, and slurry particle redeposition. The next higher spatial scale length (the micrometer to millimeter range, known as micro- or μ-roughness), is usually measured by white-light interferometry (Figure 1.8). μ-Roughness is affected not only by the smaller spatial-scale length phenomena given above, but also by factors governing slurry-interface interactions, such as the spatial distribution of slurry particles present at the interface. These parameters and phenomena are listed Figure 4.1, consisting of a schematic of the workpiece–lap interface at the spatial scale length of interest that influences the final polished surface roughness. Figure 4.1 provides a valuable outline for this chapter.
关键词： Optical Polishing,Slurry PSD,Pad Topography,AFM,μ-Roughness,Surface Roughness
更新于2025-09-04 15:30:14
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Graphene Oxide as an Optical Biosensing Platform: A Progress Report
摘要： A few years ago, crucial graphene oxide (GO) features such as the carbon/oxygen ratio, number of layers, and lateral size were scarcely investigated and, thus, their impact on the overall optical biosensing performance was almost unknown. Nowadays valuable insights about these features are well documented in the literature, whereas others remain controversial. Moreover, most of the biosensing systems based on GO were amenable to operating as colloidal suspensions. Currently, the literature reports conceptually new approaches obviating the need of GO colloidal suspensions, enabling the integration of GO onto a solid phase and leading to their application in new biosensing devices. Furthermore, most GO-based biosensing devices exploit photoluminescent signals. However, further progress is also achieved in powerful label-free optical techniques exploiting GO in biosensing, particularly using optical fibers, surface plasmon resonance, and surface enhanced Raman scattering. Herein, a critical overview on these topics is offered, highlighting the key role of the physicochemical properties of GO. New challenges and opportunities in this exciting field are also highlighted.
关键词： bioanalytical applications,2D materials,label-free biosensors,optical devices,physicochemical properties
更新于2025-09-04 15:30:14
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Comparison of MultiColor fundus imaging and colour fundus photography in the evaluation of epiretinal membrane
摘要： Purpose: To compare MultiColor fundus imaging (MC) and colour fundus photography (CFP) for the evaluation of epiretinal membrane (ERM). Methods: In this retrospective study, 192 eyes (181 patients) that underwent vitrectomy for ERM were imaged using Spectralis optical coherence tomography (for MC) and AFC-210 digital camera (for CFP) 1 week before vitrectomy. Two investigators independently determined the rate of delineability and ERM area for each modality. Results: The intergrader agreement rates for delineability were very high for both image modalities. The rate of delineability of ERM (%) was higher for MC than for CFP, for both investigators [70.8% versus 52.6% and 73.4% versus 53.6% (both p –)]. Epiretinal membrane (ERM) area measurement showed high agreement between investigators for MC (p = 0.466) but di?ered signi?cantly between the investigators for CFP (p –). The ERM area determined on MC was signi?cantly wider than that on CFP for both investigators (p – for investigator 1 and p – for investigator 2). Conclusion: The ERM area is more clearly detectable and widely demarcated in MC than in CFP images. MultiColor imaging (MC) may be more sensitive and accurate for early detection of ERM and ERM area measurement.
关键词： MultiColor imaging,spectral-domain optical coherent tomography,epiretinal membrane,colour fundus photography
更新于2025-09-04 15:30:14
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Effects of sintering process on the structural, dielectric and optical absorption properties of KNbO <sub/>3</sub> -based ceramics
摘要： The influence of the sintering temperature and the dwell time on the structural, optical and dielectric properties of [KNbO3]0.8[Ba(Ni0.5Nb0.5)O3?δ]0.2 ceramics (KBNNO) was systematically investigated. X-ray diffraction measurements of the ceramic bodies sintered at different temperatures indicated that all samples presented a cubic-like structure. However, the results remarkably revealed that both the sintering temperature and the dwell time are crucial factors that must be taken into account for “tuning” the optical response of the KBNNO ceramics. It was concluded that fine distortions in the (Nb,Ni)O6 octahedral site, induced by sintering temperature and dwell time, promoted subtle changes in the local crystal field and, consequently, in the optical properties of the KBNNO. The mechanisms responsible for the observed spectral features of KBNNO were discussed by considering absorbance spectra of NiNb2O6 ceramics and allowed ligand-field transitions. The comparison between both optical spectra revealed a notable similarity between them. Since the octahedral site in KBNNO is equivalent to the nickel columbite structure, it was inferred that the spectral behavior is mainly driven by the same two contributions: one major associated to a distorted octahedral configuration and one minor related to spin-orbit coupling effects. In accordance with X-ray diffraction data, the temperature dependence of the dielectric properties corroborated that the KBNNO present a cubic-like phase in the whole temperature range investigated.
关键词： Ferroelectrics,Ceramic processing,Optical properties
更新于2025-09-04 15:30:14
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High energy shift in the optical conductivity spectrum of the bilayer graphene
摘要： We calculate theoretically the optical conductivity in the bilayer graphene by considering Kubo-Green-Matsubara formalism. Different regimes of the interlayer coupling parameter have been considered in the paper. We show that the excitonic effects substantially affect the optical conductivity spectrum at the high-frequency regime when considering the full interaction bandwidth, leading to a total suppression of the usual Drude intraband optical transition channels and by creating a new type of optical gap. We discuss the role of the interlayer coupling parameter and the Fermi level on the conductivity spectrum, going far beyond the usual tight-binding approximation scheme for the extrinsic bilayer graphene.
关键词： interlayer coupling,excitonic effects,Kubo-Green-Matsubara formalism,bilayer graphene,optical conductivity
更新于2025-09-04 15:30:14
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Studies on growth and characterization of (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate: a nonlinear optical material
摘要： Hydrazone compound (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate (DMABHBH) was synthesized and single crystals of DMABHBH were grown by solvent evaporation method at room temperature. Molecular structure of DMABHBH compound was confirmed by 1H and 13C nuclear magnetic resonance techniques. The presence of functional groups was confirmed by Fourier transform infrared and FT Raman spectral analyses. The X-ray crystal structure was elucidated at 173 K by single crystal X-ray diffraction and the results were compared with the corresponding values obtained at 298 K. The compound crystallizes in the chiral monoclinic space group P21. Mechanical stability of the grown crystals was estimated from the Vicker’s microhardness test. Powder second harmonic generation efficiency of DMABHBH is about 1.1 times that of potassium dihydrogen phosphate. DMABHBH is found to show optical limiting behavior at high input light intensities, the third order nonlinear optical absorption coefficient measured using open aperture Z-scan studies, is 0.95 × 10?11 m/W. Anti-bacterial activity was studied using the well and disc diffusion methods.
关键词： X-ray diffraction,Mechanical properties,Nonlinear optical material,Thermal analysis,Antibacterial activity,Hydrazone,Crystal growth
更新于2025-09-04 15:30:14
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Error Assessment Model for the Inverse Kinematics Problem for Stewart Parallel Mechanisms for Accurate Aerospace Optical Linkage
摘要： In this work we develop a mathematical model to estimate the error for inverse kinematics problem for Gough-Stewart parallel mechanisms. We propose the estimation error method to include manufacture, assembly, backlash, and sensing errors. We provide the error transmission matrices for the length of each leg of the hexapod, which permits evaluation of the accuracy error in the position of each one, given a desired position and orientation of the mobile platform. We also present numerical modelling in order to estimate the accuracy of the methodology herein proposed, for specific attitude operations corresponding to performing a successful ground-LEO nanosatellite optical link. In such a case, we were able to provide the required tolerances for the actuators in order to guarantee an orientation precision requirement of the order of milliradians.
关键词： parallel mechanisms,Gough-Stewart platform,aerospace optical linkage,error assessment,inverse kinematics
更新于2025-09-04 15:30:14
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Use of optical fluorescence agents during surgery for pituitary adenomas: current state of the field
摘要： Introduction Differentiation of normal pituitary from abnormal tumor tissue remains a surgical challenge despite improvements in optical visualization technology for pituitary adenoma (PA) surgery. During neurosurgical procedures for other tumor types, 5-aminolevulinic acid (5-ALA) has become a focus of investigation based on its high specificity in differentiating tumor tissue. However, the role of 5-ALA and other optical fluorescent agents in PA surgery remains less clear. Objective To perform a systematic review on the use of various optical fluorescent agents in PA surgery. Method Using PRISMA guidelines, a systematic literature review to identify reports describing 5-ALA and other optical agents for fluorescence-guided surgery for PA was performed. Eleven research studies met inclusion criteria and were reviewed. Results In two studies, 5-ALA was not shown to be effective in aiding PA resection using standard neurosurgical endoscopic/microscopic approaches. 5-ALA photodynamic therapy was evaluated in two in-vitro models with inconsistent results. Intraoperative use of indocyanine green (ICG) concluded with varying results, but showed a tendency towards improved differentiation of functional PA. OTL38 showed potential for intraoperative identification of nonfunctioning PA, particularly in tumors with high folate receptor expression. One study reported clinically useful fluorescence following sodium fluorescein administration. Conclusion We conclude that selected optical fluorescent agents, including ICG and folate receptors, are most likely to hold promise for clinical use in differentiating PA from normal tissue.
关键词： Pituitary adenoma,Fluorescence guided surgery,Optical fluorescence agents,5-Aminolevulinic acid
更新于2025-09-04 15:30:14
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Retinal and Macular Ganglion Cell Count Estimated With Optical Coherence Tomography RTVUE-100 as a Candidate Biomarker for Glaucoma
摘要： To evaluate the ability of total and macular estimated retinal ganglion cell (RGC) counts to discriminate between healthy and glaucomatous eyes. To determine threshold markers of the estimated RGCs taking into account age dependence.
关键词： ganglion cells,optical coherence tomography,glaucoma
更新于2025-09-04 15:30:14