When using linear quadratic Gaussian (LQG) control on each mode, the higher-order disturbance model not only requires non-negligible identification effort but also leads to the calculations of high-order control matrix, which greatly increases the computational burden of the real-time processor. To address this problem, we propose a hybrid control method for adaptive optics (AO) system, which is feasible from an implementation viewpoint. This method combines the optimal modal gain integral control (OMGI) and LQG control algorithm, and designs the control strategy of the corresponding mode according to whether the mode is affected by narrow-band disturbances. The performances of the proposed control method are evaluated using the on-sky measurement data recorded by the 1-m New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO). The results show that 95.85% of disturbances are effectively filtered by the hybrid control method. Compared with the full-OMGI, the narrow-band disturbances at different frequencies are significantly suppressed. And compared with the full-LQG, the execution time of identification procedure is reduced by 37.77% and the control calculation time is reduced by 73.8%, which is more beneficial for the real-time mitigation of disturbance.

In order to make the resolution of segmented telescopes close to the diffraction limit of equivalent aperture, each sub-mirror must have extra high coplanar precision. In this paper, aiming at the co-phasing problem of segmented telescopes, first, the principle of co-phasing detection technology of pupil plane and focal plane in segmented telescopes optical co-phasing detection technology is studied. Then, the advantages and disadvantages, application fields and future development trends are summarized. Finally, solutions are provided on the detection problems of large piston error and large tip-tilt error respectively.

In this paper, the dielectric properties of aqueous glucose solution with a broadband of 200 MHz--10 GHz are measured using a network analyzer. The measurement results show that when the frequency is constant, the dielectric constant and conductivity of the solution tend to decrease as the glucose concentration increases. The single-order Debye model and second-order polynomial are used to fit the measurement data of the dielectric properties of the aqueous glucose solution at each concentration. The relationship between dielectric properties and concentration and frequency is effectively quantified. Based on the parameters of the Debye model, a three-dimensional earlobe dispersion model and an antenna transceiver structure are established. The simulation results show that the S21 signal and glucose concentration maintain a stable and regular response relationship over a wide frequency band, which can be expressed by a quadratic polynomial. This microwave non-invasive blood glucose detection method based on S21 can be used to evaluate unknown blood glucose concentrations.

The transmission of signal in optical fiber is affected by Kerr nonlinear damage, resulting in nonlinear spectrum broadening effect, resulting in information leakage out of band and incomplete information in the receiving end. The traditional nonlinear compensation method processes the signal at the receiving end by inverting the channel transfer function, but the effect is not ideal. In order to solve this problem, first, the optimization algorithm is used to find out the out of band adjoint signal which can compress the original signal to another Nyquist bandwidth in the digital reverse channel transmission; Second, the compressed Nyquist signal is sent in the sender; Finally, the original signal is recovered by Nyquist filtering at the receiving end. Simulation results show that the performance of the proposed algorithm is better than that of reverse transmission method in the band-limited systems, and the gain of the error vector amplitude is 3.17 dB in the standard single-mode fiber with the length of 800 km.

The polarization-coupling distribution in fiber coil and beat length of used fiber are achieved by testing polarization-maintaining fiber coils using white light interferometry. The polarization-coupling distribution of the fiber coil is obtained through this test, which is helpful in identifying the principal external factors affecting the polarization-maintaining ability of the fiber coil. By identifying the polarization-coupling peak produced by the two fusion splice points at both ends of the fiber coil and the white light interferometer, the optical path difference of the optical signal transmitted by the two orthogonal polarization axes of the fiber coil is obtained, and the beat length of the fiber coil is calculated. The experiment shows that the angle error can be recognized effectively when the angle is 0.13°. The results show that the polarization-coupling distribution and beat length of the fiber coil can be measured simultaneously using a white light interferometer, providing a simple and effective method for characterizing the polarization characteristics of the polarization-maintaining fiber coil.

As a new security technology in the physical layer of optical communication, quantum noise stream cipher combines mathematical complexity and physical complexity. The quantum noise stream cipher has the advantages of high security, high speed, long span, flexible structure, and high compatibility with the existing optical fiber communication systems. This paper presents the current research status and the basic principle of the quantum noise stream cipher. In the aspect of key negotiation, we compare the Y-00 protocol of quantum noise stream cipher with the BB84-type protocol of quantum key distribution and summarize the quantum noise stream cipher’s key technical schemes. Additionally, we introduce a typical application of quantum noise stream cipher and propose an endogenously secure optical communication system with a unified negotiation channel and transmission channel. The experimental verification is demonstrated, and finally, the development trend of a quantum noise stream cipher is analyzed.

In this paper, the symbolic structures of 19 typical intensity modulation schemes are introduced, and their slot error rate (SER) models in a Gaussian channel, weak-turbulence channel, and moderate-turbulence channel are derived and numerical simulations are performed. The results show that with the increase in the signal-to-noise ratio (SNR), the SER of each modulation mode initially decreases, but then, gradually plateaus. When SER stabilizes, the SNR requirement increases with the increase in turbulence intensity. The SER of pulse position modulation (PPM) is the smallest in all three channels. When the modulation order is small, the SER of differential amplitude PPM is the largest, and when the modulation order is large, the SER of on-off keying(OOK) is the largest, while SERs of the other methods are in-between, arranged hierarchically as the modulation order increases. These research results will serve as a reference for the design of practical laser communication systems.

A fourth-order pulse amplitude modulation faster-than-Nyquist (4PAM-FTN) rate atmospheric optical transmission system was proposed to improve the transmission rate. The theoretical bit error rate (BER) equation in a log-normal fading channel was derived. Then, the influence of transmission distance and laser wavelength on the system BER performance was discussed. Furthermore, the relationship between the acceleration factor and the transmission rate was analyzed. Monte Carlo simulation results reveal that the BER is proportional to the transmission distance, but inversely proportional to the acceleration factor and the laser wavelength. When the acceleration factor is 0.9, the system shows a 6.1% transmission rate gain with an almost invariable BER performance, and when the acceleration factor is 0.83, it achieves a 16.7% transmission rate gain.

Two methods for the edge extraction of optical pupils in optical scanning holographic systems were proposed, and the holographic information of objects was obtained based on double pupil heterodyne detection. First, LG beam-axis cone lens pupil and aperture filter were used as two pupils to form a composite light field, which was able to scan the object to extract edge information. Second, when the aperture filter was unchanged, the other pupil used a power amplitude-type pupil with function distribution and edge information extraction. Computer simulation experiments show that the edge extraction qualities of the two pupils described in this paper are improved in comparison with the use of a ring pupil, and digital image processing is not required, which simplifies the experimental steps.

A three-dimensional measurement method based on three channel binary fringe defocused projection is proposed in this work. The phase-shifting fringes are encoded into three color channels. At the projector, the binary digital images separated from three channels are used as input. The defocusing fringes of three channels are projected sequentially in a single camera frame time, and the fusion color fringe images of three channels are obtained by color camera. The color three channel fringes are decoupled and the aliasing effect of color channels in the measurement system is calibrated with a black and white camera. Phase calculation and three-dimensional reconstruction are performed based on decoupled fringe information. The results suggest that compared with the traditional color projection measurement, the speed and rebuilding accuracy of the proposed method are greatly improved, and the proposed method is suitable for measuring color objects and dynamic objects.

The supervised classification technology of remote sensing images is widely used in the field of information extraction and change detection, in which the selection of training samples is very important, and the quality of training samples directly determines the accuracy of classification. However, due to the limitation of conditions and human error, some impure or wrong training samples may be selected, resulting in a decrease in classification accuracy. In order to solve this problem, the median absolute deviation method is used to detect and eliminate impure and wrong training samples in the supervised classification of remote sensing images based on the spectral information of the image. The optical remote sensing image data obtained from Landsat-8 in some areas of Nanchang city is selected, the support vector machine is used to supervise and classify the two situations that contain abnormal training samples and eliminate abnormal training samples, and compare the classification results. Experimental results show that the classification accuracy of removing abnormal training samples is significantly better than that of abnormal training samples.

This paper studied a new self-mixing interference (SMI) sensing technology based on the measurement of laser diode junction voltage. The SMI signal was obtained by measuring the variation of laser diode junction voltage. Conventional SMI technology usually employs a detection scheme that utilizes the photocurrent from an external or integrated photodiode (PD) to obtain the SMI signal. In this paper, the SMI signal was obtained by measuring the PN junction voltage of a vertical-cavity surface-emitting laser(VCSEL), which simplifies the structure of the SMI system and improves the system reliability. The signal-to-noise ratio of the system were evaluated, and the junction voltage signal of the laser diode was compared with the photocurrent signal of integrated PD, the results were found to be consistent.

The microstructure and properties of laser cladding 316L stainless steel coating under three magnetic field intensities are compared. The surface morphologies, metallographic structures, and friction and wear morphologies of the three cladding layers are characterized via three-dimensional laser scanning confocal microscopy, metallurgical microscopy, and scanning electron microscopy, respectively. Results show that the application of magnetic field can reduce the surface roughness of the cladding layer and optimize the surface morphology. The grains in the cladding layer are considerably refined when the magnetic field intensity becomes 400 mT. In addition, the number of pores and cracks decreases. The average microhardness increases by 25% to become 573 HV, and the wear resistance is considerably improved.

Aiming at the existence of various morphological noise points and a large amount of redundant data in the original point cloud scanned in the field, this paper proposes a simplification optimization strategy for point clouds based on comprehensive algorithms such as method library, cloth simulation filtering, and curvature classification. First, sparse noise points at long distances are removed by statistical filter. Second, passthrough filter is used to segment point cloud blocks with close distances and large density , and cloth simulation filtering algorithm is used to remove such noise points, and then using radius filter to remove the close distance noise points around the target point cloud. Finally, the redundant data of the point cloud is removed based on curvature-grading compression method and compared with two traditional compression methods for experimental comparison and analysis. Experimental results show that the simplification optimization strategy proposed in this paper can effectively remove the noise points in the point cloud, while retaining most of the characteristic points of the point cloud, it can minimize the redundancy of the point cloud data and improve the data quality of point cloud model reconstruction.

As the booming of personalized customization and special functions of three-dimensional (3D) printed parts, single material 3D printed parts can no longer meet the demand of actual working conditions, and 3D printing technology of multi-material parts has become a research hotspot in the rapid prototyping industry. Modeling is one of the key technologies for 3D printing of multi-material parts. In this paper, first, a method of gradient source modeling based on control points is proposed. In geometric modeling, this method considers that spatial geometric models are composed of points in space, and in material modeling, and the idea of “gradient source” is used to represent multi-material parts with color gradient according to the formula of material component gradient change. Then, VS2013 and OpenGL programming languages are used for visual modeling representation and analysis of single gradient source parts. Finally, on the basis of single-gradient source modeling, two different gradient sources are weighted by using operation symbol “?”, and three kinds of material parts are presented and analyzed visually. The multi-material parts manufactured by the proposed modeling method by optical processing technology can well avoid adverse effects such as stress concentration and thermal failure caused by the rapid change of material composition in the multi-material parts.

The main research is to realize the fabrication of Fabry-Pérot(FP) optical microcavity array based on CO2 laser processing. Firstly, by combining CO2 laser micromachining and mask, an array-type concave structure was prepared on the glass substrate, and the characteristics of the structure were analyzed. Measurement and simulation analysis results show that the concave structure can be approximated to a Gaussian surface with depth ranging from 0.042 μm to 0.64 μm and full width at half maximum height ranging from 11.30 μm to 16.60 μm, the bottom of the structure can be approximated as a spherical surface. Secondly, FP microcavity array was prepared by dielectric coating and microcavity assembly, using a flat mirror-concave mirror microcavity assembly form to form an FP stable cavity. Finally, the generation of optofluidic laser in the FP microcavity array was realized.

The methods of underlying welding including laser welding and laser-MIG hybrid welding in combination with methods of filling welding including laser-MIG hybrid welding and MIG welding(melt inert-gas welding),are used to complete the welding of 15-mm-thick 316L austenitic stainless steel. The microstructure and mechanical properties of the weld joints in each group were studied. The results show that the weld joint obtained by all laser-MIG hybrid welding has the best formation. There is cellular structure in the center of laser-MIG hybrid welding layer, while the MIG welding layer is almost all columnar crystal structure. The tensile strength of the filling layer welded by hybrid welding is higher than that welded by MIG, while the strength of the underlying layer welded by laser is comparable to that welded by hybrid welding, and all fractures are ductile fractures. The micro-hardness of the weld center of the two different underlying layers is higher than that of the base metal, the micro-hardness of the weld center of the hybrid welding filling layer is slightly higher than that of the base metal, and the micro-hardness of MIG filling layer is lower than that of the base metal.

The YAG laser Thomson scattering system is designed to measure the time evolution of electron density of capacitive-coupled plasma (CCP). CCP is generated in a plate electrode device under vacuum which is powered by 300 W radio-frequency power supply. A silicon avalanche photodiode (APD) with a max conversion gain of 5.0×10 5 V/W is used to measure the Nd∶YAG laser Thomson scattered signal in the wavelength range of 200 nm to1000 nm. In order to increase the intensity of the Thomson scattering signal, an optical oscillating cavity is set on both sides of the plasma generator to extend the contact length between the driving laser and the plasma and to amplify the Thomson scattering signal to increase the total emission intensity of the signal light. In addition, a signal collection system and a multistage filter system are positioned at the front-end of APD to improve the signal-to-noise ratio. Finally, we develop an inverse algorithm to calculate electron density of CCP based on the Thomson scattering principle, and the calculation results are compared with the measurement results of the Langmuir probe, which verifies the effectiveness of the algorithm.

In this paper, a new structure of kilowatt-level cladding power stripper is proposed based on spiral flow channel water-cooling technology, and its heat dissipation performance is studied. First, the structure is compared with the traditional water-cooled cladding power stripper and the heat sink endothermic cladding power stripper to verify its practicability and superiority. Second, by studying the parameters of the spiral flow channel, it is found that the initial temperature of the heat sink has no significant effect on the heat dissipation performance of the stripper. The large diameter spiral cooling pipe and the appropriate initial temperature of the cooling water will help heat dissipation. Finally, it is experimentally found that the stripper can effectively strip the cladding power below 4200W under optimized conditions. When stripping 1000 W cladding power, the peak temperature of the striper is 300.49K, the temperature valley is 284.29K, and the temperature difference is 16.2K. Under the same power, compared with the above-mentioned traditional stripper, the peak temperature is reduced by up to 15.1%, the temperature valley is reduced by up to 10.3%, and the temperature difference is reduced by up to 73.4%.

In order to study the high-cycle fatigue properties of AlSi7Mg alloy fabricated by selective laser melting (SLM), the static tensile test and fatigue test under different stress loadings were performed on the as-built specimens. The microstructure and fatigue fracture morphology of the as-built specimens were observed by metallographic microscope and electron microscope, and the fatigue failure mechanisms were investigated. The results show that the tensile properties of SLM AlSi7Mg specimens are significantly higher than those of cast AlSi7Mg, and the tensile strength and yield strength are lower than those of SLM AlSi10Mg, but their fatigue limits are similar. Compared with traditional manufacturing method, the microstructure of the specimens is divided into three regions, namely the fine zone, coarse zone, and heat-affected zone. The Si phase is uniformly embedded in α-Al matrix in a network structure. Through fracture morphology analysis, it is found that the fatigue cracks of SLM AlSi7Mg specimens are initiated at the defects such as pores and inclusion, and propagate radially in a semicircle manner. When the remaining section cannot bear the fatigue load, the samples fracture instantaneously, and the fracture zone has the morphology characteristics of cleavage surface and dimple. Comparing the as-built specimens of SLM AlSi7Mg and SLM AlSi10Mg, it is found that the macroscopic differences between the tensile properties and fatigue properties of the two specimens are currently small. The microstructure of specimens formed by SLM is similar and contains a large number of scattered defects.

The 5A06 Al alloy samples with preset grooves are repaired by using laser cladding. The microstructures and tensile properties of these repaired samples are investigated by using metallurgical microscopy and scanning electron microscopy. The β phase in the heat affected zone during repair grows as a result of heat input. When the line energy reaches 166.7 J/mm, the β phase size increases to larger than 1 μm. The microstructure of repaired zone is composed of α phase, β phase within α grains, and Al-Si eutectic phase along α phase grain boundary. The lack-of-fusion defects are effectively suppressed when laser power is 1400 W and the pore defects result in the tensile strength and elongation of the repaired zone lower than those of base metal.

Graphene/polylactic acid single-component composites and graphene/nano-Fe3O4/polylactic acid two-component composites were rapidly prepared using fused deposition molding technology, and the effect of graphene content on absorbing properties was examined. Single-component samples exhibit better wave absorption performance with an 8% mass fraction of graphene. In the two-component composite, with a constant nano-Fe3O4 mass fraction, increasing graphene content obviously improves the wave absorption performance of the sample. Furthermore, the wave absorption performance of two-component composite samples is better than that of the single-component composite sample. Folds formed by graphene coating on the substrate surface can increase the number of multiple reflections of electromagnetic wave. However, when graphene content is too large, electron scattering, which is generated by graphene agglomeration, affects the wave absorption effect. Compared with the single-component composite sample, the two-component composite sample has more types of micro interfaces under the dual action of graphene and nano-Fe3O4, which renders electromagnetic wave propagation path more complex, thereby consuming more energy. Therefore, compounding different types of absorbing agents can effectively improve the wave absorption performance of the material.

With anhydrous citric acid and o-phenylenediamine as carbon sources, solvent-dependent emitting carbon nanodots are prepared by the one-step solvothermal method. The morphology and structure of the prepared carbon dots are characterized using atomic force microscope. It is found that the carbon quantum dots have a uniform height around 1.5 nm, and are mainly consist of few layers of graphene. The optical features of as-prepared carbon quantum dots are further confirmed by photoluminescence (PL) spectra and UV-visible (UV-Vis) absorption spectroscopy. It is found that the main absorbance is attributed to the carbon core and the surface states, and the maximum absorption occurs at wavelengths of 285 nm and 430 nm. In addition, the fluorescent emission in organic solvents peaks at 515 nm and its corresponding emission wavelength is the luminescence wavelength of surface defect state. With the increase of water content in the system, the emission peak red-shifts and the maximum emission intensity gradually decreases. When the water content (volume fraction) is in the range from 10% to 100%, the fluorescence signal intensity is linearly proportional to water content, and the detection limit of water content is 0.1% under the optimal condition. The experimental results confirm that these novel carbon quantum dots have a potential application as a probe and a sensor for the real-time quantitative detection of water content in various organic solvents. The results obtained here not only broaden the application range of carbon nanodots, but also provide a simple and effective method to detect water content in organic solvents.

In the process of using molecular beam epitaxy (MBE) technology to grow GaSb thin film materials, we use a reflection high-energy electron diffractometer (RHEED) to realize real-time monitoring of GaSb thin film preparation. We obtain the relationship between the growth parameters and the diffraction pattern change and determine the the temperature of deoxidation layer by analyzing and studying the deoxidation layer on substrate and its growth process based on the RHEED diffraction oscillation pattern. By calculating the growth rate, the optimization of source temperature, beam-to-current ratio, and growth temperature are optimized. Preliminary characterization and analysis of the surface quality of GaSb epitaxial film using double crystal X-ray diffraction (XRD) technology show that GaSb epitaxial film can meet the device preparation requirements and provide experimental basis for the next step of preparing quantum wells and superlattice structures by molecular beam epitaxy.

Herein, a heterojunction AlGaAs/GaAs PIN diode material structure for a millimeter wave switch and limiter applications is designed, and the two main factors (i.e., the Al doping concentration and I-layer thickness) that influence the performance of the diode are analyzed and optimized. Furthermore, the verification device is fabricated via molecular beam epitaxy and semiconductor process flow sheet technique. We test the device, and the test results show that the opening voltage of the PIN diode is 1.06 V, and the breakdown voltage is 26. The insertion loss of the diode is approximately 1 dB and the isolation degree is 12 dB (when the frequency is 30 GHz), both of which are observed in the frequency range of 1-40 GHz. Thus, the designed device is suitable for millimeter wave switch and limiter circuits.

In this study, composite conductive films doped using poly(3,4-ethylenedioxythiophene) (PEDOT) and various concentrations of graphene oxide (GO) for dye-sensitized solar cells (DSSC) were prepared by the potentiostatic method. The structure and morphology of the composite films were characterized and the square resistance of the different films was measured using a four-probe apparatus. The effect of GO doping concentrations on the properties of the films was investigated, and the optimum preparation process was obtained. The results indicate that the composite film deposited at a GO concentration of 0.3g/L has the best properties, and the film has a high specific surface area, good electrical properties, low charge transfer resistance (5.23Ω·cm 2), because of the doping of GO. The composite film shows good redox catalytic properties. Compared with pure PEDOT, the photoelectric conversion efficiency of the DSSC assembled with the composite film as counter electrode increases from 4.43% to 6.23% with a fill factor of 0.68.

The purpose of this article was to estimate the effect of Er,Cr∶YSGG laser ablation on the surface crystal structure of human dentin with X-ray diffractometer (XRD). Er,Cr∶YSGG laser with different energy densities were used to ablate human dentin, and XRD was used to analyze the changes of crystal structures, average particle size, and lattice parameters of hydroxyapatite (HA) crystals before and after laser irradiation. The results show that the average size of HA particles in dentin inorganic phase decreased slightly after laser irradiation with different energy densities, but the cell parameters did not change significantly. Based on XRD data, the ellipsoidal HA grain morphology of dentin before and after laser irradiation were obtained by Rietveld full pattern fitting of Popa model. The surface morphology and microstructure of dentin after laser irradiation were observed by scanning electron microscopy. It was found that the surface roughness of dentin increased obviously, there was no stained layer on the surface, no carbonization phenomenon and crack, and no obvious melting phenomenon. This study showed that the inorganic phase did not change after Er,Cr∶YSGG laser ablation of human dentin, HA grains did not recrystallize, and large area melting was not observed on the dentin surface.

To correct the dynamic aberrations introduced by an airborne conformal optical window that changes with viewing angle, a method for aberration correction of the conformal optical system based on computational imaging is proposed herein. By establishing an incoherent imaging system model, the principle and imaging process of the wavefront encoding system to eliminate the dynamic aberrations of the conformal optical window are given, and the design criteria of the conformal optical system based on computational imaging and the optimization process of the mask are clarified, and the transmission capability of the system is quantitatively analyzed by using the tilted edge method. Experimental results show that the dynamic aberration of the airborne conformal optical system can be corrected using the computational imaging method, and there is no need to add complex correctional devices, the system has the advantages of a simple structure and strong stability.

In order to solve the problem imprecise alignment and uneven grinding thickness in the automatic grinding system of the locomotive, a algorithm based on the laser scanning technology for the center axis of the grinding tool in the normal direction of the grinding point is proposed in this paper. First, the normal vector of the three-dimensional model of the workpiece to be polished obtained by scanning by the line laser sensor is calculated, and the 6 methods of obtaining normal is compared to obtain the optimal algorithm to calculate the normal coordinates of each point on the model. Then, through hand-eye calibration, the normal coordinates and the center axis coordinates of the grinding tool can be converted to each other, and the two can achieve precise alignment by using offline programming. Finally, a grinding model is established to obtain the ideal grinding thickness by calculation, and the grinding thickness values of the precise and imprecise alignment are measured. Experimental results show that, compared with imprecise alignment algorithm, the algorithm can well solve the problem of uneven grinding thickness and achieve the grinding effect consistent with the ideal grinding.

Graphene is a special two-dimensional material, and has excellent physical properties. Combining graphene with micro-nano devices has become a hot research topic. In the mid-infrared to terahertz band, surface plasma can be excited in graphene, which can be applied to multi-functional tunable devices. In this paper, we propose a broadband light modulator working in the infrared waveband, which combines graphene plasma with silicon based subwavelength metallic gratings. By applying a bias voltage on graphene to change the Fermi level, the transmission light can be modulated within the wavelength range from 7 to 22 μm, and the modulation depth can reach up to 99.96% (33.77 dB).

In this study, the IES TM-30-18 gamut index is used to characterize the gamut area of LED sources. Simultaneously, the spectra of 20 sample light sources at four color temperatures are simulated by the superposition of monochromatic light spectra in a 380--780 nm band with a 5-nm interval, and the change of the gamut area is calculated. The results show that the color gamut area of a light source increases after the monochromatic light of 380--465 or 605--780 nm superimposes on the spectrum of each sample light source, and decreases with the monochromatic spectral of a 470--600 nm band. A light box matching is performed to match the superimposed spectrum, and the visual experiment of color brightness and preference is conducted. The experimental results show that the brightness and color preference of the spectra with an increased color gamut area are better than those with a decreased gamut area. When two monochromatic lights with different peak wavelengths and amplitude powers are superimposed at the same time, the color temperature of the light sources can be kept substantially unchanged, whereas, the color gamut can be increased by 2--10. The relationship between the spectral distribution and gamut area is obtained by simulating the source spectrum after superimposing monochromatic light, which is of great significance for optimizing the color gamut area and visual effects of the LED light sources.

Considering the poor mode-field confinement characteristics of graphene-coated circular nanowire structures and the difficulty of coupling them with commonly used linearly polarized light sources, two types of graphene-coated elliptical nanowire pairs are proposed in this work. Finite element modeling is used to study the dependence of the graphene plasmon mode characteristics on the geometric and physical parameters of the structures. Simulation results show that the arrangement direction of the double elliptical nanowires, distance between the nanowires, ratio of the long and short axes of the ellipse, and graphene chemical potential have a significant effect on the transmission performance of the plasmon mode. The proposed graphene-coated elliptical nanowire pairs can realize long-distance transmission and subwavelength confinement, and it has potential application value in the fields of tunable nanophotonic devices and infrared sensing.

Outer and inner radius of hard-edge annular aperture as well as decay factor as main effection factors for the abruptly autofocusing property of circular Airy beam (CAB) carrying hard-edge annular aperture are all considered. Conclusion has been achieved that, putting hard-edge annular aperture on CAB will enhance its first autofocusing peak intensity and suppresses the further autofocusing peak intensity, and its first autofocusing peak intensity will also be generally increased under the condition of different decay factors. These conclusions have potential applications in particle manipulation.

The diffusion property of wave functions in the non-periodic quantum walks is investigated in detail. The numerical results show that the multipath coherent superposition state can be precisely controlled by using position-dependent unitary evolution. Different evolutionary operations lead to the phenomenon of constructive or destructive interference and thus it affects the diffusion property. The diffusion speed of the walker can be changed by adjusting the evolution parameters of the system. The research on the diffusion speed of quantum walks is helpful to design new algorithms based on quantum walks.

The scan line filtering algorithm can simplify the filtering problem to a certain extent and achieve improved filtering results in complex terrains. However, it is difficult to filter out some noise points under the ground and points with large difference between positive and negative slope angles. To resolve these problems, a vertex vector angle-scan line filtering algorithm is proposed, where the vertex vector angle and height difference threshold are used to perform postprocessing on the scan line, further improving the filtering effect. The traditional algorithm is compared with the improved algorithm through experiments, proving that the latter can achieve improved filtering results.

The pollution of atmospheric particulate matter in the Beijing-Tianjin-Hebei (BTH) region is very serious, which has an impact on the climate, environment, and human health. To quickly and accurately evaluate particulate pollution in the BTH region using remote sensing technology, this article verifies the accuracy of the global 1 km resolution MCD19A2 aerosol optical depth (AOD) product released by NASA and analyzes its reliability in the BTH region. At the same time, the correlation between the AOD product and the air quality index (AQI) is analyzed to explore the indication function for air pollution. The spatial distribution data of MCD19A2 AOD and the measured data of aerosol robotic network (AERONET) in the BTH region from 2014 to 2018 are obtained for validation, and the two types of data are processed by space-time transformation to achieve accurate matching. Validation results show that MCD19A2 products have achieved higher accuracy and stability in the BTH region. It's correlation coefficient, root mean square error, mean absolute error, and within expected errors are 0.9504, 0.1243, 0.0863, and 82.26%, respectively. Based on AOD results at different scales, correlation analysis performed with AQI data suggests higher correlation, which indicates that the MCD19A2 data has a direct indication of air pollution. This study can provide some references for the research of aerosol characteristics and air quality monitoring.

During the development of Ti∶sapphire laser crystals, the research of defects always plays a pivotal role in their performances. In recent years, some new optical phenomena have been observed in highly Ti-doped sapphire crystals, which indicates that the change in the internal defect structure may induce some influences on laser performances. This article introduces the research progress of defects in Ti∶sapphire laser crystals and also makes a brief discussion.

As one of the basic characteristics of magnetic materials, magnetic field has attracted people's attention, and has been widely used in military, medicine, industry, and other field. The basic principles, development process, and application prospects of the high sensitivity micro-optical-atomic magnetometer are sorted out. First, the working mechanism and system composition of the miniature optical-atomic magnetometer are described. Second, the development processes of key technologies such as atomic gas cell fabrication and optimization methods, atomic gas cell heating methods, and magnetic field signal detection methods are discussed. Finally, the latest research progress of the magnetometer is reviewed, and the application prospects of the miniature optical-atomic magnetometer are prospected.

In this paper, recent research progress of optical wireless communications in unmanned aerial vehicles (UAVs) was reviewed. By means of wireless optical technology, technical challenges and key enabling technologies were also surveyed for implementing robust and wideband communication links between UAV and satellite, UAV and UAV, and UAV and terrestrial terminals. The mechanisms and schemes of modeling, parameter optimization, and experimental testing under different UAV optical wireless link configurations were described in detail. Additionally, the key development trends of high-speed and high-reliability UAV-based wireless optical communication technology in modular implementation, high altitude platforms applications, and others were discussed.

The micro-ring resonator is an important device for the integration of silicon photonic chips. Based on the principle of micro-ring resonators, the paper mainly describes the research significance and development process of high-quality factor micro-ring resonators in the mid-infrared field, and analyzes the advantages and disadvantages of micro-ring resonators in different material systems in terms of technology and practical applications; then, we introduce the theoretical research of the cascaded micro-ring resonator based on the Vernier effect in the field of sensing and filtering in the mid-infrared region; the generation principle and development history of the mid-infrared Kerr optical frequency comb are reviewed, and we theoretically prove the germanium strip waveguide micro-ring can realize a wide-spectrum optical frequency comb with a bandwidth close to an octave at a pump power as low as 80 mW. Finally, we summarize the research progress and prospect the future applications.

In this paper, laser-induced breakdown spectroscopy (LIBS) is summarized from two aspects. The first is the advantages of LIBS qualitative analysis method in element rapid monitoring and drawing the relative content distribution diagram of elements based on high spatial resolution ability of LIBS to comprehensively observe the distribution of elements in different parts of plant organs. The second is the progress and existing problems of LIBS in quantitative analysis of nutrient elements and heavy metals in soil and plants. The sensitivity of this technology to the determination of metal elements is better than that of nonmetallic elements. For the determination of nonmetallic elements, inert gases are need to eliminate atmospheric effects; for the determination of metal elements, the effects of self-absorption of metal elements can be solved by uncalibrated LIBS and optical thin LIBS.

We employ terahertz time-domain spectroscopy (THz-TDS) combined with chemometrics to identify Calculus bovis and its confounding substances, and obtain the THz-TDS of Coptidis rhizome, Rhubarb, Cattail pollen, Calculus bovis, artificial Calculus bovis, and adulterate Calculus bovis. The random forest (RF) classification model and the support vector machine (SVM) model which adopts three kinds of parameter optimization are established, respectively. The classification and identification of the THz absorption spectra of six kinds of matter are conducted. In addition, the RF model based on the synthetic minority over-sampling technique (SMOTE) is proposed to solve the problem that the recognition rate of the RF model decreases due to the serious unbalanced sample dataset. The results show that both the RF model and the SVM model can achieve a recognition rate of about 95.00%. However, the RF model can run much faster, whose running time is only 2% of that of the optimal PSO-SVM model. The RF model based on the SMOTE technique can effectively solve the problem of low recognition rate caused by unbalanced data. The recognition rate increases from 84.17% to 94.17%, and the operation speed is basically constant. The research conclusion provides a new approach for the identification of rare Chinese medicine using terahertz spectroscopy.

The laser induced breakdown spectroscopy (LIBS) method is used for the rapid and green identification of Gannan navel orange juices. The sugar contents and Ca,K,Zn element contents of healthy and Huanglongbing navel oranges are experimentally measured. In addition, the differences in sugar and element contents are analyzed. The LIBS data of navel orange juice is first collected, which is then preprocessed by the nine-point smoothing (9SM) method combined with multivariate scattering correction (MSC). Finally, the principal component analysis (PCA) method combined with the multi-layer perceptron (MLP) neural network and radial basis function (RBF) neural network model is used for rapid identification of healthy and Huanglongbing navel orange juice. The results show that the PCA-MLP model is superior to the PCA-RBF model in the identification effect of healthy and Huanglongbing navel oranges. The identification accuracies of healthy and Huanglongbing navel oranges on the training dataset are 93.8% and 93.4%, respectively. In contrast, the identification accuracies of healthy navel oranges and Huanglongbing navel oranges on the prediction dataset are 93.9% and 94.8%, respectively. The LIBS detection results confirm that the Huanglongbing results in the change in pulp quality of navel oranges. The further spectral preprocessing and the classification model are used to distinguish the juices of Huanglongbing oranges and healthy navel oranges in quality and thus the product qualification ratio of factory orange juices is increased.

As a semiconductor material, Cu(In,Ga)Se2 (CIGS) nano film plays an important role in the field of solar cells. In this paper, a series of CIGS thin film samples were deposited using the magnetron sputtering technology under different sputtering powers, working pressures, and sputtering time. Laser-induced breakdown spectroscopy (LIBS) was quantitatively analyze the atomic concentration ratios of Ga to In+Ga and Cu to In+Ga in CIGS thin film samples. Then combined with the single calibration curve drawn under each sputtering parameter, a merged calibration curve of two content ratios was drawn, and the fitting coefficient of the merged calibration curve reached more than 0.99, indicating that the fitting effect is good. Moreover, the three samples of CIGS thin films under random sputtering parameters were used to assess the accuracy of LIBS by comparing the analysis results of energy dispersive X-ray spectroscopy (EDS) and LIBS. The errors of the analytical results were all less than 5%, verifying the accuracy of LIBS. This research provides a new method for the rapid analysis of CIGS thin film and the timely determination of performance and develops new applications of LIBS technology in the field of thin film semiconductor materials.

Differential optical absorption spectroscopy (DOAS) is a spectroscopic measurement technique that uses the narrow-band absorption characteristics of gas molecules to derive gas concentrations. This paper introduces the basic principles of DOAS, and develops a program in MATLAB to analyze DOAS data for benzene, toluene and xylenes (BTX). Moreover, the hypothetical and retrieved values of BTX concentration are compared, and the effects of the change in the incident light intensity and particle parameters on concentration retrieval are studied. Results show that the retrieved values are consistent with the hypothetical values of the BTX concentration, indicating the accuracy of the BTX-DOAS data processing program. Preconditions that cannot be directly deduced theoretically in DOAS are validated using a numerical simulation.

In this work, a quick and quantitative detection method for three common flavors, i.e., coumarin, vanillin, and ethyl maltol, in flavor adulterated Pu'er tea is established. The Fourier transform near-infrared spectroscopy combined with the partial least squares method is used to quantitatively analyze the flavor adulterated Pu'er tea. The quantitative analysis models for three adulterated flavor components are established, and the predictive capabilities of the quantitative analysis models built with different pre-processing methods and without spectral pre-processing are compared. The results show that the predicted root mean square errors of the three flavors of coumarin, vanillin, and ethyl maltol by combining different spectral pre-processing methods are 0.1461, 0.1678, and 0.1800, respectively, and the prediction determination coefficients are 0.7989, 0.7350, and 0.6938, respectively. The detection limit of three flavors is 0.2 mg/g. The near-infrared spectroscopy combined with the partial least squares quantitative analysis can achieve rapid detection and analysis of the three flavors in adulterated Pu'er tea.