Based on the von Karman spectral model, a step-by-step phase screen method is employed in this study to simulate the propagation characteristics of radially-polarized vector beams with different orders in the Kolmobarov’s atmospheric turbulence. Furthermore, the Stokes vectors, scintillation index, and radial deviations of gravity centers of beams are analyzed. The simulation results show that the maximum discriminating distance of the ring features of the radially-polarized vector beam under an atmospheric turbulence is larger than that of the scalar vortex beam, and its scintillation index and the radial deviation of the gravity center of beams are smaller than those of scalar vortex beams. High-order beam can maintain its ring shape features at a larger distance than that of a low-order beam, and the scintillation index and the radial deviation of gravity center of beam for high-order beams are observed to be smaller. The Stokes vectors images of the radially-polarized vector beams get diffused and distorted. In conclusion, the radially-polarized vector beams have better turbulence resistance than the scalar vortex beams under an atmospheric turbulence, and high-order beams exhibit better properties than low-order beams in some way.

The directional polarimetric camera (DPC) aboard the GF-5 satellite is the first domestic space-born instrument with operational multi-spectral, multi-directional, and polarimetric observations. A series of algorithms used for DPC measurements were formulated to acquire cloud detection results, cloud thermodynamic phase distribution, and cloud optical thickness of the observed zones. The cloud detection results were derived from the reflectance at 670 and 865 nm, the geometric normalized polarized radiance was obtained at 490 nm, and the linear degree of polarization was obtained at 865 nm. The cloud thermodynamic phase was derived from the normalized polarized radiance at 865 nm; the cloud optical thickness was obtained from the reflectance at 670 and 865 nm and results of cloud thermodynamic phase. Because of the lack of L1 data of DPC, the algorithms were applied to POLDER data to validate their feasibility. Results indicated that the consistency of “cloudy judgment” and “clear judgment” was 93.3% and 92.9%, respectively. Further, the consistency of “water clouds,” “ice clouds,” and “mixed-phase clouds” was 87.4%, 76.6% and 22.8%, respectively. The correlation coefficient of the optical thickness was 0.89, which demonstrates the feasibility of the proposed algorithms. The proposed algorithms can develop the operational cloud production of DPC.

A lidar system that combines backscattering, side-scattering, and Raman-scattering lidars has two obvious advantages in detecting the extinction coefficients of tropospheric aerosols: 1) the lidar ratio (LR) does not need to be assumed in the retrieval of aerosol extinction coefficients; 2) there are no near-ground transition and blind areas. Herein, we obtain the 146-day data by using an integrated lidar system in Hefei city from January 2017 to December 2018. We retrieve and statistically analyze the extinction coefficients of aerosols to get the average LR of aerosols of 68.4 sr, the monthly distribution of average LR , and the monthly, seasonal, and annual average profiles of aerosol extinction coefficients. Some cases show that the aerosol extinction coefficient versus height and time is very complicated under 0.6 km altitude, which cannot be detected by the traditional backscattering lidar. Moreover, the errors in the aerosol extinction coefficient retrieved from the empirical LR are analyzed by comparison. The obtained results provide a scientific basis for studying air pollution transmission and control.

Herein, to address the challenge in measuring the small-angle backscattering intensity of water bodies, the water Scheimpflug lidar system was designed based on the Scheimpflug imaging principle. The design, simulation, and construction of this water Scheimpflug lidar were presented, and the flume experiments were conducted on deionized water, tap water, and river water. Moreover, the distance correction method under the condition of multi-measurement media was discussed in detail. The variations in width and intensity of the backscattered beam were compared with the measured data by the spectrophotometer. Results indicate that the width and intensity of a laser beam can represent the beam attenuation and simultaneously characterize the backscattered optical intensities in different water bodies. Furthermore, the data from the spectrophotometer have a good consistency with those from the water Scheimpflug lidar system.

With molecular dynamics simulations, we calculate the probability as well as the angle and energy distributions when the reflection and resputtering of Mo/Si atoms occur. Four types of collisions are considered: Mo-on-Mo, Mo-on-Si, Si-on-Mo, and Si-on-Si. We find that the lower the amount of energy transferred to the substrate is, the more likely it is for reflection to occur, but the less likely for resputtering. Moreover, the effect of incident angle on the reflection and resputtering probabilities is related to the types of sputtered atoms and substrate atoms. However, the higher the incident energy is, the higher the reflection and resputtering probabilities are. Finally, by the magnetron sputtering experiment, we fabricate the Mo/So multilayer samples on substrates with different inclination angles, and the experimental result verifies the simulation result. This study should be helpful in simulation of magnetron sputtering deposition and the optimization of deposition process.

In this paper, a sensing simulation method for fiber Bragg grating (FBG)-based mechanical structures, based on Livelink data interaction, is proposed. The proposed simulation method combines the FBG sensing simulation model with the COMSOL finite element multiphysical field coupling model using the Livelink module. An interactive model based on the combination of COMSOL and MATLAB was established to realize the simulation analysis of the FBG sensing signal from mechanical structures under multiple physical fields such as stress and temperature. Moreover, an efficiency optimization module based on an adaptive sliding window was adopted to improve the speed of simulation of the FBG reflectivity spectrum. Finally, a typical H-beam structure and FBG sensors were used to verify the FBG-based mechanical structure sensing simulation model. Results show that the error of the FBG center wavelength offset between simulation and experiment is less than 4.6%, and the root-mean-square error is less than 0.0048. In an impact-loading experiment, simulation results were in good agreement with the measured data, which further verifies the correctness of the simulation method proposed in this paper. Furthermore, this simulation method can lay the foundation for the arrangement of FBG sensor networks.

This study proposes a method for space optical information encoding communication based on optical bright-ring lattices. Based on an objected-oriented computer-generated holography method, a computer-generated hologram of four simple-mode optical bright-ring lattices is generated and loaded into a reflection-type spatial light modulator (SLM), which modulates the incident light and experimentally reconstructs the aforementioned four simple-mode optical bright-ring lattices. The four optical bright-ring lattice modes correspond to four different quaternary numbers and can be easily identified. By employing the proposed system, a 32 pixel×56 pixel image with a 256 grayscale is encoded and transmitted in space through optical bright-ring lattice mode combination. A charge-coupled device (CCD) at a distance of 2 m from the transmitting terminal is used to capture the optical bright-ring lattice images, which can be easily decoded with no errors in the computer even with partial interference. On this basis, a single optical bright-ring lattice is extended to 2×2 and 4×4 arrays, which can increase the transfer efficiency and system capacity by 4 and 16 times, respectively. Results provide some theoretical and experimental foundations for researches on encoding and communication of optical bright-ring lattices.

Traditional methods of infrared and visible image fusion generally possess disadvantages of low contrast, inconspicuous thermal infrared target, and insufficient details and textures. To address these problems, an infrared and visible image fusion method based on multiscale low-rank decomposition was proposed in this study. First, multiscale low-rank decomposition was used to decompose the infrared and visible images into multilevel local parts (saliency parts) and global low-rank parts, respectively. Second, optimal fusion rules were designed to effectively integrate the complementary information of infrared and visible images by comprehensively analyzing the characteristics of decomposed images. Finally, the fusion of the images was reconstructed according to the proposed fusion rules. The proposed fusion method was tested and verified using an open dataset. Experimental results show that the proposed method can obtain fusion images with clear targets and rich details. Further, it produced an enhanced visual effect and higher accuracy compared with other state-of-the-art fusion methods.

In this study, we propose a method for multi-angle digital radiography (DR) scanning inclusion detection of low-density powder materials considering the problems such as large inclusion detection errors and low stability caused by the usage of different single scanning angles. First, multi-angle DR detection is performed with respect to the measured object. Then, the scale-invariant feature transform (SIFT) feature matching method is used to find the inclusion images at different angles. Further, the maximum size of the inclusions at different angles is automatically selected as approximate value. Finally, a relation between the inclusion area and rotation angle is established under different angles and the maximum inclusion area and rotation angle are predicted. The experimental results prove that the proposed method can solve the problem of low efficiency associated with computed tomography (CT) and can improve the accuracy and stability of detection when compared with the single-scan detection method. A high degree of confidence is associated with the prediction at a small rotation angle, which indicates that the proposed method can meet the demands of inclusion detection in practical applications.

In this study, an adaptive multiple-gain imaging method was proposed based on a pushbroom imaging spectrometer to meet the demands of high dynamic range (DR) monitoring using an ocean color remote sensor. Further, the advantage of the pixel-by-pixel adaptive readout method was explained by analyzing the differences in case of DR and the signal-to-noise ratio (SNR), and the corresponding system design was presented. The limit of full well charge was determined based on the ocean imaging scene, and the optimal number and proportion of gains were obtained via system simulation based on the constraints associated with respect to SNR and DR. The results denote that the optimal imaging effect can be obtained when the number of gains is four and the full well charges are 2.5 Me - (ultra-low gain), 500 ke - (low gain), 100 ke - (medium gain), and 20 ke - (high gain). Based on this setting, the total DR of the spectral imaging system can become 116 dB; the average SNR of each channel under typical radiance becomes 767.37. Furthermore, the medium-resolution atmospheric radiation transfer model was used to verify this imaging mode. The conditions with respect to the channels meet the requirements of DR and SNR, except for the 10th channel of the cloud that appears to be out of saturation.

In this study, we propose an infrared target modeling method based on deep learning. Further, we design a conditional double adversarial autoencoding network by combining the adversarial concepts with autoencoding. By using the trained network, the expected infrared target images can be easily generated by inputting category labels and the random variables that satisfy a certain distribution. The effectiveness of the proposed model is verified using a self-built infrared dataset. The conducted experiments prove that the generated target images exhibit considerable authenticity and diversity. Finally, the randomly generated target images as supplement the small data set can effectively improve the problem of lack of training data and improve the accuracy of the recognition algorithm in the infrared imaging system.

A manufacturing-aid optical coherence tomography (M-OCT) method is proposed to achieve imaging with high-resolution, non-destructivity, full-depth, and large-volume. This method combines the discrete manufacturing principle and microtomography. High-resolution images are obtained by OCT in the discrete manufacturing process. OCT scan and discrete manufacturing are conducted simultaneously or alternately, which combines the image mosaic algorithm, the full-depth three-dimensional (3D) image of the manufacturing samples is obtained at the same time as the manufacturing is completed. Polymer scaffolds are constructed using the 3D printing technology for M-OCT verification, and the imaging results are consistent with those of microcomputed tomography (Micro-CT). Moreover, when compared with Micro-CT, M-OCT can more clearly distinguish the stack-fusion state of adjacent layers of materials and the manufacturing defects. The thickness of the printing layer, the pore diameters and the strut diameters of different regions are quantified using the high-resolution imaging results of M-OCT. The large-volume and high-resolution OCT provides a new method for monitoring the discrete manufacturing processes such as 3D printing, cell assembly, biological manufacturing, and automatic biopsy and the non-destructive tests.

Crack tip deformation field measurements are crucial for the quantitative study of material fracture characteristics and behavior. Subset-based digital image correlation (DIC) is commonly used for this purpose; however, results obtained across the crack are meaningless and are faced with under-match problems in measuring complex deformation fields around the crack. To solve these problems, we propose the Hermite-element based regularized global DIC (HRGDIC) method for deformation field measurements around the crack. HRGDIC uses the high order Hermite element function to construct each finite element in global DIC, and it establishes an iteration method that simultaneously considers the gray-scale error and the displacement field smoothness. During each iteration, the generalized cross-validation method is used to obtain the optimum regularization parameter. Therefore, the proposed HRGDIC method can not only handle the complex high-gradient deformation around the crack tips but also produce smoothed displacement and strain fields at the end of the iterations. Simulations and experimental results of crack tip deformation images show that compared with the traditional local DIC, the proposed HRGDIC has higher measurement accuracy, and it is an effective method for solving the high-gradient deformation field measurement problems around crack tips.

To screen the high reliability and stability devices from the scientific grade area detectors for the aerospace application, the environmental stress screening tests such as temperature cycling, random vibration, and burn-in are performed on the space-borne area charge coupled device (CCD). A system for area CCD image acquisition is designed, and the electro-optical parameters of a CCD are tested before and after screening based on the segmented illumination light source and the continuous tunable monochromatic light source. The differences of dark currents, photo response non-uniformity, quantum efficiencies, linearity errors, and other parameters of the area CCD before and after the environmental reliability tests are compared, the environmental adaptability of the area CCD is analyzed, and thus the quality defects and the early failures are eliminated. Subsequently, the detectors with an optimal performance are extracted from the participating area CCD and used in the space-borne directional polarimetric camera for atmospheric remote sensing observation. The experimental results show that the maximum change of quantum efficiency between pre- and post-screening for the ultimate optimal detector is -2.56%, the photo response non-uniformity is smaller than 3%, the linearity error is smaller than 1%, and the dark current is 889.22 electron·(pixel·s -1) -1 after screening. These research results provide significant reference data for the standardization establishment of low-level CCD screening methods and performance assessment techniques in aerospace field.

To improve the tribological properties of TC4 surfaces, a TC4+Ni60+Ni-MoS2 multi-component composite self-lubricating wear-resistant coating was prepared on the TC4 surface by the TruDisk4002 coaxial powder feeding fiber laser. The microstructure and the tribological performance of this coating were also analyzed. The results show that there are no cracks but a few pores within the coating. The main precipitation phases of the coating are TiC, Ti2Ni, Ti2SC, and α-Ti, and they are uniformly and compactly distributed within the coating. Ti2SC and Ti2Ni form the Ti2SC-Ti2Ni mosaic structure composite phase, and the misfit between (01 1ˉ0 )Ti2SC and (001 )Ti2Ni is 3.18%. Ti2SC and Ti2Ni form the coherent interface relationship. The coating micro-hardness is obviously higher than that of the substrate. The Ti2SC-Ti2Ni mosaic composite phase can effectively improve the anti-friction and wear resistance of coatings, and the wear mechanism of coatings is abrasive wear.

In this study, the laser deposited AlSi10Mg alloys are formed under different cooling conditions to investigate the effect of the substrate cooling condition on the deposition qualities and properties. Further, we analyze the temperature variation during the forming process, morphologies, microstructures, and tensile properties of the formed specimens using the temperature testing systems, an optical microscope, a scanning electron microscope, and a universal material testing machine, respectively. The results denote that the deposition efficiency increases and the defect rate decreases when a reasonable substrate cooling temperature is considered. The deposition layer structure can be significantly altered when the cooling conditions are changed. In addition, the dendrite space of the deposition specimen is observed to decrease. The tensile strength and yield strength of the specimens fabricated under the cooling condition are improved by approximately 4% and 7%, respectively, when compared with those of the specimens fabricated without applying any cooling conditions. Furthermore, the fracture mode of the specimens is ductile fracture.

A terahertz quantum cascade laser (THz-QCL) is a kind of semiconductor laser, which is suitable to realize the self-mixing interference. In this work, an experimental method based on self-mixing interference effect is demonstrated for the measurements of the emission spectrum, linewidth enhancement factor, and feedback optical coupling coefficient of a THz-QCL. We set up the optical path for self-mixing interferometry with THz-QCL to obtain the self-mixing interference signal with high signal-to-noise ratio as well as its variance with feedback optical distance, based on voltage driven by THz-QCL. By analyzing the self-mixing interference signal, the lasing spectra of THz-QCL under different operating currents and temperatures are obtained accurately. The resolution of spectra is inversely proportional to feedback optical distance. In addition, we investigate the linewidth enhancement factor of THz-QCL and the feedback optical coupling coefficient based on the self-mixing interference signal. The self-mixing interferometry demonstrated here is expected to be further developed into one used for terahertz spectral identification and measurement.

This study presents a high-sensitivity detection method for a specific biological molecule using a graphene-based optical biosensor. The use of functionalized magnetic nanoparticles as biological molecule carriers, which can be immobilized on the graphene surface under a magnetic field, improves the graphene surface-modification process. The effectiveness of our proposed method was successfully verified in an Ochratoxin A detection experiment. We obtained a detection limit of 0.01 ng·mL -1 for Ochratoxin A, a good response in the range of 0.01--5 ng·mL -1, and a good function of the biomolecule specificity. We believe that the proposed method can expand the scope of applications of graphene-based optical biosensors, simplify the biomolecule-sensing process, and improve the sensitivity of graphene-based optical biosensors.

There exist various kinds of spatial frequency errors on the ultra-precision machined surfaces, which seriously influence their performances. According to different performances of workpieces, it is necessary to use an effective decomposition method to extract the topography containing the spatial frequency errors at specific frequency bands. The traditional spatial frequency error decomposition method has the serious problem of modal aliasing. In order to solve this problem, an adaptive bidimensional variational mode decomposition (BVMD) algorithm is proposed to decompose a three-dimensional surface topography. First, image continuation and self-convolution Hanning window are introduced to preprocess the truncation errors when collecting 3D topographic data. Then, the particle swarm annealing optimization algorithm is used to optimize the penalty coefficient and the number of decomposition layers in the BVMD algorithm. Among them, the fitness function of the optimization algorithm is constructed by taking KL divergence among modal components as aliasing indicators, introducing the minimum risk Bayesian decision theory, and combining KL divergence with reconstruction errors. Finally, the measured topography of the ultra-precision machined surface is analyzed and compared with those by the discrete wavelet decomposition method and the bidimensional empirical mode decomposition methods. The results show that the KL divergence by the proposed method is several hundred, much higher than those by the other two methods. The proposed method has a good inhibition ability for frequency error modal aliasing, and can effectively decompose the spatial frequency errors of an ultra-precision machined surface.

In this study, we design a metal-dielectric-metal (MDM) waveguide side-coupled square ring resonator with a rectangular-groove (RG). Its effective length is accurately derived through the F-P theory and a tunable multimode plasmonic filter is realized based on this structure. Based on numerical calculations and theoretical analysis, the extra non-integer resonant modes are obtained beyond the conventional integer modes. The wavelength of each non-integer resonant mode red-shifts with the increase of the RG's length because RG has the maximal effect on the magnetic field when it is located at antinodes of the magnetic fields. However, the integer modes are not sensitive to RG and their wavelengths are fixed because RG has the minimal effect on the magnetic field when it is placed on the nodes of the magnetic fields. The number of modes and their field distributions can be adjusted by changing the shape, position, and number of RGs. Compared with the conventional resonators, the proposed structure and the corresponding results are extremely useful for the design of optoelectronic devices as they can provide more channels to flexibly manipulate the resonant wavelengths.

In this study, a nano-circular resonant cavity filter embedded with a symmetrical sector metal block based on metal-insulator-metal (MIM) is developed using the finite element method. It is found that by changing parameters such as the sector resonance angle, circular resonant cavity radius, coupling distance, and refractive index of medium in the resonant cavity, one can effectively adjust the transmissivity characteristics of the proposed structure. The filter shows two significant resonance peaks with the transmissivity up to 76% and quality factor to 40, which is suitable for efficiently achieving a tunable dual-channel bandpass filter. The parameters of the proposed structure are adjusted and optimized to enable the corresponding resonant wavelengths distributed in the 850 nm and 1310 nm optical communication windows of near-infrared band optical fiber communication. This structure provides an important theoretical basis for designing the next-generation high-performance nano-plasmonic filters in the field of optical communication.

In this study, an optical structure design and optical radiometric-calibration method for a hyperspectral-imaging lidar system are proposed. Using the proposed method, the central wavelength and bandwidth of each receiving channel were directly determined using a scanning monochromator. The system-calibration coefficients of each channel were measured in the laboratory using the hyperspectral-image lidar equation and excluding the influence of atmosphere extinction. Simulation results show that the synthetic uncertainty is 0.87% and the extended uncertainty (k=2) is 1.73%. Furthermore, a novel technique was used to monitor the emitted laser-pulse power in real time during the flight experiment. Based on echo-signal intensity information from the detector, the hyperspectral reflectance of the earth's surface can be accurately retrieved, and the high-precision terrain acquisition and super-fine surface classification can be realized.

Solar diffuser reflectance degradation monitor (SDRDM) is used to gain the reflectance of a solar diffuser (SD). The transmittance of the sun view port and the relative bidirectional reflectance distribution function (BRDF) of the solar diffuser vary with the angle. Therefore, the SDRDM observation signals are affected by the angle of the incident light. The effect factor is called the SDRDM angle factor (abbreviated as the angle factor). This study proposes a method for calculating the SDRDM angle factor using on-board data employed on the premise that the solar diffuser plate does not decay in the early orbit stage. The same solar angle ratio calculation is used, thereby verifying the stability of the solar diffuser reflector without discussing the angle factor. The angle factor is calculated and compared with laboratory measurements. Results show that the deviation between the calculated values and the measured values of the laboratory is less than 0.5%. The angle factor measured prior to the launch can be used to calculate the BRDF degradation factor of the SD.

In this study, we propose an exhaled CO2 gas measurement system based on a mid-infrared hollow waveguide fiber. A distributed-feedback (DFB) laser with a central wavelength of 2.73 μm and a 1-m hollow waveguide fiber were used in the proposed system. The exhaled CO2 gas was measured in real time via calibration-free wavelength modulation spectroscopy (CF-WMS). The linearity with respect to the CO2 concentration obtained via CF-WMS and the prepared standard CO2 gas concentration is 0.9999. Further, when the volume fraction is 0%--6%, the maximum absolute error between the measurement results and the volume fractions of the standard gas is 0.01%. The precision of the CO2 volume fraction retrieved via CF-WMS is 1.01×10 -5, and the CO2 gas detection limit is 1.3×10 -6 at an optimal integration time of 26.00 s. Subsequently, the measurement accuracy and measurement sensitivity of CF-WMS and the traditional calibrated wavelength modulation spectroscopy (WMS) were compared. The obtained results demonstrate that the measurement accuracy and measurement sensitivity of CF-WMS are twice and 1.4 times those of WMS, respectively. The background CO2 volume fraction obtained via CF-WMS is observed to remain stable at approximately 3.8×10 -4 during real-time measurement of the exhaled CO2 gas; further, the CO2 volume fraction observed immediately after exhalation remains stable at approximately 5.7%.

In this study, we establish a theoretical model of pulse compression and focusing process in an ultrahigh peak power laser system and simulate the dispersion process of parallel grating pair compressor and the focusing process of parabolic mirror based on ray-tracing method and Fraunhofer far-field diffraction. The wavefront distortion for a square diameter is described using the Square-Radial polynomial. The effect of four different wavefront distortions in near-field on the far-field spatio-temporal distribution is analyzed, and the error tolerance is provided under different conditions.