Using the ultraviolet band observations from the ocean color satellites,this study has employed a coupled ocean-atmosphere vector radiative transfer model to analyze the ultraviolet polarization characteristics of 355-nm and 385-nm radiation measured at the top of atmosphere (TOA). Results showed that atmospheric molecules contributed most toward the polarization of the ultraviolet radiation reaching the ocean color satellite sensors. Compared with the condition that solely accounts for atmospheric molecules, aerosols, air-sea surface, and water body could also weaken the total degree of polarization (DOP) of ultraviolet radiation reaching the ultraviolet satellite sensors. The total DOP of 355-nm and 385-nm radiation varied in the range of 0%-70% with different TOA viewing zeniths. Compared with the visible band of 412 nm that is usually set by ocean color satellite sensors, the TOA DOP of ultraviolet radiation reaching the satellite sensors exhibited insignificant differences under the same condition.

This paper describes the use of a self-made meteorological radiosonde for turbulence analysis to measure profiles of the turbulence parameter Cn2 and meteorological parameters such as temperature, wind speed, and wind direction in Lhasa, Tibet. The trends of variation of turbulence intensity and meteorological parameters with height are analyzed. A comparison of the turbulence characteristics in the morning and evening reveals that a strong turbulence layer appears at 8-15 km at both these durations, but the turbulence intensity above 8 km in the morning is greater than that in the evening. Furthermore, based on the Hufnagel-Vally 5/7 model, the Cn2 Lhasa model is fitted using the statistical average of all radiosonde data. The statistical analysis results show that the Cn2 Lhasa model can effectively estimate the turbulence intensity above Lhasa. Finally, a comparison of the radiosonde data of Lhasa and Gaomeigu reveals that the wind speed in Lhasa is lower and favorable for astronomical observations, but the turbulence in Lhasa is stronger and reduces the quality of astronomical observations. These results provide a foundation for the study of turbulence profiles, observatory site selection, and support for the application of electro-optical engineering in Lhasa.

In this study, the atmosphere major greenhouse-gases monitor instrument (GMI) loaded on the GF-5 satellite platform is used to measure the column concentration of atmospheric greenhouse gases CO2 and CH4. To ensure the accuracy of the greenhouse gas inversion in GMI remote sensing data, the influence of aerosol and other factors in greenhouse gas inversion on inversion results is analyzed and used as the correction factor of the inversion algorithm. Given this, the GMI inversion results are verified using the total carbon column observing network (TCCON) site. Furthermore, results show that the GMI near-infrared inversion results exhibit a low bias with -1.06±2.93×10 -6(-0.26±0.72%), and the inversion accuracy is within 1%.

Phytoplankton specific absorption coefficient is an important optical parameter associated with phytoplankton biomass and absorption spectrum. The quantitative analysis of specific absorption coefficients of phytoplankton populations makes up for the deficiency of specific absorption spectra of phytoplankton populations in Yellow Sea and Bohai Sea, and provides a new idea for monitoring the phytoplankton population concentration. Combined with the phytoplankton absorption coefficient and pigment concentration data collected during the cruise in Yellow sea and Bohai Sea in June, 2016, CHEMTAX software is used to analyze the concentrations of eight dominant alga species in Yellow Sea and Bohai Sea. The multiple linear regression analysis of the absorption coefficient and concentration data of algal species is carried out by using the LOO-CV method, the specific absorption spectra of each algae are extracted, and the total absorption spectra are reconstructed. The results show that the model inversion is effective, and the reconstructed absorption spectrum is consistent with the measured spectra in blue and red wavebands. In addition, when analyzing the contribution of dominant alga species to phytoplankton absorption coefficient, it is found that among all dominant alga species, the dinoflagellate gives the greatest contribution to phytoplankton absorption, followed by cyanobacteria.

In this study, a mathematical model of the relationship between the bandwidth integral diffraction efficiency (PIDE) and the incident angle with the substrate material of a multilayer diffractive optical element (MLDOE) for a two-band system is established. A method for selecting a double-band oblique incident MLDOE substrate material is proposed; this method selects the best base material combination of the dual-band MLDOE. The proposed method and the mathematical model solve the problem in which the improper selection of the substrate material leads to a decrease in the diffraction efficiency and bandwidth integral diffraction efficiency of the MLDOE when light is obliquely incident. In addition, the method provides theoretical guidance for the application of MLDOE in multi-band and wide-band systems. According to the method, an MLDOE suitable for a medium wave infrared (MWIR) of 3.7-4.8 μm and a long wave infrared (LWIR) of 7.7-9.5 μm is designed, and a 10× hybrid zoom lens is designed using the diffraction element for the dual-band. The results show that the modulation transfer function (MTF) of the system at the Nyquist frequency of the MWIR is greater than 0.52 and the MTF at the Nyquist frequency of the LWIR is greater than 0.35.

Radial velocity measurements errors caused by lighting instabilities severely limit the precision improvement in instruments; however, fiber scrambling is an effective method to enhance the stability of instrumental illumination. To provide a reliable experimental reference for the operation of a high resolution spectrograph upgrade and a new high precision radial velocity instrument design, the near field and far field scrambling properties of a single circular fiber, single octagonal fiber, circular-octagonal-circular fiber cascade connection system, double circular fiber scrambler, circular-octagonal hybrid double-fiber scrambler, and double octagonal fiber scrambler were studied in detail. The results showed that the octagonal fiber improved the near field scrambling compared to single circular fiber, the double-fiber scrambler could improve both near field and far field scrambling, and the double octagonal fiber scrambler optimally performed for both near field and far field. Furthermore, the prototypes of the double-fiber scramblers, including ball lens system and twin lens system, were also assessed herein. The throughput was observed to be 55% and 80%, respectively.

A composite structural strain sensor is proposed, which incorporates a high-sensitivity fiber Fabry-Pérot interferometer (FPI) into the fiber Sagnac interferometer (FSI). The sensitivity of the FPI strain sensor is greatly improved by the vernier effect, which is caused by the superposition of the FPI and calibrated FSI spectra. The results of theoretical calculation show that, the sensitivity of the composite structure sensor can be regulated by the free spectral range difference between two sets of interference spectra. Further, the experiment results show that, the sensitivity of the composite structure sensor is increased 19.7 times compared with that of a single FPI strain sensor, reaching 65.1 pm·με-1. The composite structure sensor plays an important role in scenarios requiring high sensitivity measurement and accurate measurement.

Automatic segmentation of brain tumor images is difficult to achieve owing to the diversity in tumor shapes and severe imbalance in the segmentation categories. Conventional convolutional neural network can hardly predict high precision segmentation images. To solve the abovementioned problems, an improved model based on the original three-dimensional (3D)-Unet was proposed, which replaced the conventional convolution module with a hybrid dilated convolution module to exponentially increase the receptive field of neurons, reducing the network depth and avoiding scenarios wherein small targets could not be recovered during up-sampling. Furthermore, the hybrid loss function was used to replace the original Dice loss function to increase the penalty faced by the model when classification errors of sparse classes occurred, forcing the model to learn the features of these classes better. Experiment results showed that the hybrid dilated convolution module and the hybrid loss function could respectively improve the prediction accuracy of the whole tumor region and the core tumor region. Multiple performance parameters of brain tumor automatic segmentation were improved using this 3D-HDC-Unet model.

Automated segmentation of retinal blood vessels plays an important role in the diagnosis of diseases such as diabetes and hypertension. Existing algorithms have insufficient ability to segment blood vessels into small blood vessels and lesions. In this paper, a retinal vessel segmentation method based on an improved holistically nested edge detection (HED) network is proposed to solve the segmentation problem. In the proposed method, firstly a residual deformable convolution block is used instead of the ordinary convolution block to enhance the ability of the model to capture the shape and size of the blood vessel; Subsequently, the original pooling layer is replaced by a dilated convolution layer to preserve the spatial locations of blood vessels; finally, an HED network framework with a short connection structure at the bottom is used for feature extraction and fusion of pre-trained networks, in which the model can better fuse the high-level structural information of the blood vessels and low-level details of the blood vessels in the retinal image extracted by the backbone network. By verifying the digital retinal images for vessel extraction (DRIVE) and the structured analysis of the retina (STARE) datasets, the sensitivities are 81.75% and 80.68%, the specificities are 97.67% and 98.38%, the accuracies are 95.44% and 96.56%, and the area under curve (AUC) of receiver operating (ROC) are 98.33% and 98.12%, respectively. The proposed method achieves comprehensive segmentation performance, which is superior to that of other advanced methods.

This paper reports the design of a planar coding target with holographic property. The local code of the coding target can be used to determine the position of the imaging portion on the target and the overall state of the target. The target can be used for pose measurement and can improve the measurement range and measurement accuracy. To solve the decoding and matching problem of the coding target, a decoding algorithm based on target image backprojection correction and correlation matching is proposed. In this algorithm, the target image is reconstructed in three-dimensional space by perspective transformation. Subsequently, it is rotated and corrected in the three-dimensional space, and then projected back onto the original image surface. Improving the correlation matching algorithm, only the marker points on the coding target are considered, greatly improving the matching efficiency. The proposed decoding and matching method demonstrate good matching effect and high matching efficiency in experiments. The image backprojection correction method can also be applied in photogrammetry for coding target decoding and matching. This method is not limited by encoding rules and can effectively improve the decoding accuracy rate.

In this paper, a theoretical modeling analysis of LiNbO3 integrated Y-waveguide based on a distributed polarization crosstalk analyzer was conducted using the Jones matrix and experimentally verified. Results of experiments show that the polarization crosstalk analyzer can evaluate the overall extinction ratio of Y-waveguide and test the crosstalk value of a defect inside the Y-waveguide, which compensates for the deficiency of the intensity extinction ratio tester. Finally, the rationality of test results of the Y-waveguide was verified by single polarization fiber. The distributed polarization crosstalk analyzer has great significance for screening LiNbO3 integrated optical chips with better performance in practical applications.

Using actively Q-switched self-Raman lasers to suppress the main frequency-shifted Raman mode, so that the Raman mode with relatively lower gain coefficient is stimulated Raman scattering to output Raman light with a new wavelength. First, the theoretical derivation of the actively Q-switched normalized rate equations with two Raman modes are deduced, and the normalized Raman gain coefficient, normalized loss ratio, and normalized initial population inversion density are evaluated by the basic parameters of typical experiment and common crystals. Secondly, the influence of normalized variables on the output characteristics of two Raman light pulses are studied through numerical simulation, and the range of parameters that can realize the stimulated Raman scattering of the Raman mode with relatively lower gain coefficient is found. Finally, the normalized variable values derived from the experimental parameters are numerically simulated. The results are analyzed and the optimization scheme is given.

Because of the poor wear resistance and low hardness of magnesium alloys, the modification of their surface using laser remelting technology is particularly beneficial, especially, the influence of the laser power factor is important. To investigate the influence of the power factor in laser remelting on the microstructure, hardness, and friction and wear properties of rare-earth magnesium alloys, the laser remelting experiments with Mg-1.85Y-7.91Zn-0.75Zr (mass fraction,%) alloy were conducted under different laser powers using a 3 kW DILAS semiconductor laser. The structure, morphology, phase composition, and distribution of the samples were observed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). Microhardness tests were conducted to measure the Vickers hardness and elucidate the effects of different laser powers on the structure and mechanical properties of the alloy. The results show that the macrostructure of the alloy after the remelting process becomes finer and with increasing laser power, the grain increases and the second phase becomes more dispersed. Hardness and wear resistance are enhanced because of fine-grained strengthening, solid solution strengthening, and dispersion strengthening. Among the changes, under laser powers of 800, 1000, 1200, and 2000 W, the average Vickers hardness values of the remelted fine crystal region are 90.97, 93.47, 94.20, and 95.53, respectively, whereas the average Vickers hardness value of the coarse crystal base material is only 63.90. When the alloy is laser-remelted under a power of 2000 W, it exhibits a hardness 49.50% greater than that of the base material. As the power is increased, the wear resistance is enhanced and the wear gradually transitions from adhesive to abrasive wear. The laser remelting technology substantially strengthens the rare-earth magnesium alloy, and increasing the laser power can dramatically increase the hardness, antifriction, and antiwear properties of the alloy.

Non-invasive blood glucose detection based on optical measurement is a research hotspot in the biomedical field at present. However, due to the problems of low signal-to-noise ratio, background noise interference and low accuracy, the non-invasive blood glucose detection method is still in the experimental stage and cannot be applied in clinical practice. To solve these problems, a non-invasive blood glucose detection method based on visible image is proposed. By using the collected scattering images and the gradient boosting decision tree algorithm, the regression model of the relationship between the characteristic parameters of the scattering images and the blood glucose concentration is established, and the accuracy of the model is verified by the phantom experiment. Experimental results show that the relationship between visible scattering images and glucose concentration can be modeled by the gradient boosting regression model, with a consistency determination coefficient up to 0.929 and an average absolute error of glucose detection accuracy of 0.156 g·L -1.

Skull registration is one of the important steps in the process of craniofacial restoration. The accuracy of skull registration directly affects the outcome of craniofacial restoration. In order to improve the registration accuracy and convergence speed of skull point cloud model, a registration algorithm based on the hierarchical optimization strategy is proposed. The registration process is divided into two processes, coarse registration and fine registration. The different optimization strategies are used for optimization. Firstly, the geometric features are extracted based on the neighborhood of points, and then the eigenvectors consisting of mean curvature, Gauss curvature, normal vector angle, and principal curvature are obtained. Further, the feature similarity is calculated by distance function to establish matching point pairs, and k-means algorithm is used to eliminate the mismatching point pairs. Then the quaternion method is used to calculate the rigid body transformation relationship between the skull point clouds to achieve skull coarse registration. Finally, the improved iterative closest point (ICP) algorithm is improved by the introducing k-d tree and geometric feature constraints. The improved ICP algorithm is used to achieve accurate skull registration. The experimental results show that it is effective to use the k-means algorithm to eliminate the mismatched point pair optimization strategy. It is also effective to add the k-d tree and geometric feature constraint optimization strategy to the fine registration process. Compared with ICP algorithm, the matching rate and registration accuracy of this algorithm are improved by 17% and 51%, respectively, and the time-consuming is reduced by 31%. Compared with other classical registration algorithms and improved ICP algorithm, the efficiency of the proposed algorithm is the best. In order to verify the universality of the algorithm, the terra cotta warriors fragment data is also used to verify, and the proposed algorithm achieves good results and optimal performance. Therefore, the proposed algorithm is an effective point cloud registration method.

In this study, a transmission type long-wavelength infrared microscopic imaging optical system operating in wavelengths of 15-35 μm is designed to meet the demand for cooled staring focal plane array detector containing long-wavelength infrared 32×32 pixel elements and exhibiting an elemental size of 50 μm×50 μm. The designed system adopts disposable imaging and comprises a series of lenses. A cold diaphragm is positioned at exit pupil of the optical path. Symmetrical double gluing lens combination is introduced into the system to correct the aberration. Further, an optical passive compensation technique is employed to realize anti-thermal aberration at temperatures of -20 ℃ to 40 ℃. The simulation results show that the designed system exhibits a modulation transfer function (MTF) value of 0.369 and an encircled energy concentration of >80% at a characteristic frequency of 10 lp·mm -1 when its center wavelength, focal length, numerical aperture, effective magnification, and spatial resolution are 27 μm, 14 mm, 0.25, 10, and 0.1 mm, respectively. Furthermore, a clear distinguishable image can be obtained using the designed system. The designed system satisfies the requirement of short structure and high resolution of cold optical system.

In this study, we design nanostructured antireflection multiwavelength micro-optics that can be used in fiber-optic communication systems. The finite-difference time-domain method was used to search for a moth-eye nanostructure that exhibited a significantly reduced reflectivity in the wavelength range from 1250 to 1650 nm. Further, a multiobjective optimization algorithm was developed for optimizing the wideband reflectance at an oblique incidence from 0° to 30°; this optimization was implemented for a parameter space in which the geometrical arrangement, radius, height, and period of the nanopillars could be included. Subsequently, at a wavelength of 1550 nm, a near-zero reflectance (0.012%) was obtained via simulation, whereas an experimental value of 0.157% was obtained when the samples fabricated based on the optimal design was used. Furthermore, this discrepancy between the simulated and experimental results was analyzed by considering the change in the reflective index with the wavelength.

In this work, Cs was used as the N-dopant and B3PyPPM was used as the electron transport layer material to prepare a green phosphorescent organic light-emitting device. Experiments show that N-doping improves device efficiency and alleviates the efficiency roll-off of the device. In order to investigate the reasons for the performance improvement of N-doped devices, tests of Lambertian, open-circuit voltage, and conductivity were conducted. Experiments confirm that Cs-doped devices can improve conductivity and promote the injection and transmission of electrons, so more electrons can recombine with holes to form excitons, the device performance is improved and the efficiency roll-off is alleviated.

This paper proposes a graphene gap waveguide structure comprising graphene-covered nanowires and graphene layers. The propagating properties of the fundamental mode and their dependence on the structural and material parameters are studied in detail by the finite element method. Results show that the nanowire radius, gap distance, nanowire permittivity, and chemical potential of graphene have a significant impact on the mode transmission properties. By optimizing parameters, the proposed structure can simultaneously achieve long-range propagation of graphene plasmons and deep subwavelength confinement of the mode field. The application of graphene plasmons for the deep-subwavelength transmission of mid-infrared waves offers a theoretical basis and guidance for the design and high-density integration of photonic devices beyond the diffraction limit.

In this study, the third-order nonlinearity and optical bistability effect of mono-layer graphene was investigated. Using theoretical analysis and numerical simulation, the threshold value of the optical bistability of mono-layer third-order nonlinearity graphene can be tuned by changing its Fermi energy, relaxation time, two-photon absorption coefficient, and temperature. We demonstrate that the larger Fermi energy level,the higher temperature and the larger threshold value of the optical bistability. Further, a higher two-photon absorption coefficient corresponds to a higher low threshold of the bistability. Moreover, the relaxation time and two-photon absorption coefficient can significantly alter the light transmissivity of the graphene structure, although the light transmissivity is insensitive to the temperature of the graphene material. Results offer a theoretical basis for designing nanophotonic devices with micro-nano structure such as optical switches and optical sensors.

Phase-modulated Doppler lidar could benefit from both direct detection Doppler lidar and coherent detection Doppler lidar. However, owing to the lack of dynamic range of its own frequency-shift measurement, its practical application is limited. In this paper, a star map method to measure the signal optical frequency shift was proposed, which used the changing of phase-modulation discriminate parameters in the two- or three-dimensional coordinate system. Furthermore, the models of its measurement sensitivity and error were derived. The proposed method could not only effectively maintain the advantages of the conventional method but also greatly improve the dynamic range of the frequency-shift measurement.Theoretical research showed that the method could increase the measurement dynamic range by approximately nine times. The correctness and effectiveness of the proposed method were experimetnally proven by measuring actual targets.

In this study, we propose an on-board relative radiometric method based on a solar diffuser to correct the non-uniformity of the pixel response of the linear array CCD detector based on the imaging optical system of the push-room optical remote sensor. The proposed method uses laboratory integrating sphere calibration data as a reference standard to perform flat-field correction on the onboard calibration data, and the influences of the stray light in the field of view of the camera and the distribution of the bidirectional reflectance distribution function (BRDF) on the relative calibration results are eliminated; further, we obtain the relative calibration coefficients of each pixel, which can be applied to three different objects, i.e., the ocean, the Gobi desert, and the cloud. The results prove that the various vertical striping noises in the raw image can be effectively eliminated and that the image streaking metrics with respect to each scene is better than 0.0045 after relative calibration. Based on the solar diffuser, relative radiometric calibration for the linear array CCD detector in the large dynamic range can be realized, exhibiting considerable timeliness and calibration accuracy.

The traditional optical particle counting method is limited by the bandwidth of particle echo pulse. Therefore, it cannot be directly applied to the measurement of particle number at the back end of the ultrafine particle condensation growth system. In this paper, based on the principle of particle light scattering, a particle optical counting module by using the scheme of high-bandwidth particle echo pulse is designed. At a sampling flow rate of 0.3 L·min -1, the echo pulse half-width of the 15 μm standard polystyrene particle is 650 ns, which improves the efficiency of particle counting. In order to improve the upper limit and accuracy of the particle number concentration measurement, a particle coincidence correction method based on probability statistics is proposed. The upper limit of the particle number concentration measurement is 2×10 5 cm -3 by using this correction method. Experiments in the self-developed butanol-based ultrafine particle condensation growth system are conducted. The results show that the correlations between the self-developed system and the ambient air concentration measurement devices TSI-3788 and Airmous-A20 both exceed 0.98 , and in contrast, that between the self-developed system and the vehicle emission solid particle number concentration measurement device MEXA-200SPCS is up to 0.96. Thus, the accuracies of the designed optical particle counting module and the coincidence correction method are verified.

The clinical application of penicillin is very extensive, and it is extremely important for the authenticity identification of such drugs and the identification of drug content. In this paper, the self-built terahertz time-domain spectroscopy system is used to test and analyze the pure penicillin sodium and amoxicillin capsules from three different manufacturers. The absorption spectra of four drugs in the range of 0.2-1.4 THz and the obvious absorption peaks are obtained. At the same time, the changes of absorption peak intensity of pure penicillin sodium and amoxicillin with different contents under the same mass are tested, and the corresponding relationship between the mass and intensity is clearly obtained. Finally, the intensities of three amoxicillin drugs are put together for comparison, and the correspondence between the content and the intensity can be visually seen. Spectroscopic study results on pure penicillin sodium and amoxicillin show that terahertz spectroscopy can be used for qualitative identification and quantitative analysis of penicillin drugs, which is of great significance to the substance identification of penicillin drugs.

In this study, microwave plasma chemical vapor deposition was used to control the trace impurities for preparing high-quality single-crystal diamond materials, the structural and optical properties of which were comprehensively evaluated. Further, the impurity contents of the crystals were analyzed using ultraviolet (UV)-visible absorption spectroscopy and photoluminescence spectra. The crystal structures and quality of the single crystals exhibiting different qualities were analyzed based on the Raman spectrum, X-ray rocking curve, and X-ray white-light morphology beam. Subsequently, the crystal structures and defects of a single-crystal diamond exhibiting different qualities were evaluated under a polarizing microscope. The obtained high-purity single-crystal diamond contains a few defects and impurities, and its dislocation stress field is uniformly distributed in the aggregate state. The maximum transmittances of single-crystal diamonds with high purity and low-doped nitrogen in the UV visible near-infrared (UV-visible-NIR) band are 71.58% and 71.27%, respectively, which are approximately similar to the theoretical value of transmittance (71.6%) for diamond. In the intrinsic infrared absorption band, the lattice symmetry of high-purity diamond crystals is better, whereas the absorbance is smaller than that of low-concentration nitrogen-doped single-crystal diamonds. The high-quality single-crystal diamond film prepared by controlling the trace impurities is expected to be used as an optical detector probe and an optical window.

A full-energy dynamic model is developed to simulate the behavior and evolution of a free electron laser(FEL)pulse induced photoelectron wave-packet within an external single-cycle terahertz field, and the streaked photoelectron energy spectrum is significantly broadened at the zero crossing of terahertz vector potential, which could be used to retrieve the FEL pulse length. Further analysis and comparison of the pulse recovery errors of photoelectron wave packets with different pulse lengths at different delays, and the accuracy requirements of time synchronization in actual measurement are evaluated. In addition, a scheme for measuring the double -pulse delay is proposed, and the accuracy of the scheme is verified by numerical calculations.

X-ray fluorescence imaging (XRFI) is a promising diagnostic method with respect to the geometrically complex fluids in high-energy-density physics, including experimental astrophysics and inertial confinement fusion, because of its capability of detecting localized information. In this study, we have conducted a proof-of-principle experiment with respect to XRFI at the Shenguang-Ⅲ prototype laser facility. In this experiment, a static object comprising poly-4-methyl-1-pentene foam and titanium dioxide nanoparticles was pumped with vanadium plasma radiation, resulting in the emission of titanium K-shell fluorescent photons. A flat-crystal spectrometer dispersed and imaged these fluorescent photons, and one-dimensional spatially resolved intensity profiles were successfully obtained. Further, the fluorescent intensity profiles were quantitatively simulated based on the theories related to fluorescence production and flat-crystal imaging, denoting good agreement with the experimental results. This research is directly useful for the application of XRFI to hydrodynamic experiments in case of complex geometries.