Atmospheric coherence length is an important parameter for evaluating the effect of adaptive phase correction in a laser transmission system, so there is a high research value to measure and analyze the atmospheric coherence length. In this paper, a system for measuring atmospheric coherence length by differential image motion method is designed and built to carry out field experiments in Xi'an area, and the variation trend of atmospheric coherence length within the whole day in Xi'an area is analyzed. Results show that although the values of atmospheric coherence length measured in different directions are different, the overall variation trend is the same, and the variation is more stable at night than at day. These results have a reference value for the construction of urban wireless optical transmission systems.

In this work, an automatic power line extraction method based on airborne LiDAR point cloud data is proposed. First, spatial partitioning of LiDAR data was performed. Second, according to the horizontal distribution characteristics of power lines in three-dimensional space, an improved Euclidean clustering algorithm was used to realize rough extraction of the power lines. Third, using the connection between a power line and a power tower, the spatial coordinate position at the top of the power tower was estimated. Then, the improved Euclidean clustering algorithm was used to realize single power line extraction, and the model was used to combine a straight line and parabola to obtain the centerline equation of a single power line and its radius. Finally, a power line adapter was developed at the insulator according to the power line equation and radius, and the complete point cloud of a single power line was obtained. Experiment results show that compared with the classification effect of support vector machines combined with the geometric feature method, the proposed method can extract complete power lines automatically, quickly, and accurately from power line inspection data, which has application value in power patrol.

Based on the references of average aerosol extinction coefficient per unit mass concentration in dry environment and baked aerosol scattering extinction coefficient in wet environment respectively, corresponding the two kinds of aerosol extinction hygroscopic growth factor, i.e. f1(RH) and f2(RH), had been proposed. By utilizing the hourly data from nephelometer and aethalometer, as well as the coincidental environmental and meteorological data, including atmospheric visibility, relative humidity, NO2 mass concentration, and PM10 mass concentration, in Chengdu from October 2017 to December 2017, the comparative study on the two kinds of aerosol extinction hygroscopic growth factors was systematically carried out. The results showed that both f1(RH) and f2(RH) could well characterize the optical effect of aerosol hygroscopicity, and their coefficient of determination was 0.90 (passed the significance test of α=0.01). By multi-model comparison, the quadratic polynomial function was proved to best fit the variation of both f1(RH) and f2(RH) with relative humidity. The ratio of average f1(RH) to average f2(RH) increased with the increase of relative humidity. Further research indicated that the significant response of baked aerosol scattering extinction coefficient to the variation of relative humidity was fundamental for the above inconsistency between f1(RH) and f2(RH).

Spectral analysis is used to present the design flow of a non-coated photopic visual illumination sensor. The sensor matching error is evaluated by calculating the relative deviation of central wavelength, full width at half maxima, and the integral area in 380-780 nm band between theoretical relative spectral response and apparent photopic visual spectral efficiency function. Using the combination of blue glass QB21, yellow glass LB9, LB16, and LXD44MQ silicon photocell, the theoretical relative spectral response of the illumination sensor is compared with the spectral efficiency function of the photopic illumination spectrum. The relative deviations of the central wavelength, full width at half maxima, and the integral area in 380-780 nm band are 0.36%, 5.00%, and 14.15%, respectively. With TES 1330A illuminometer as the standard reference, the average absolute error and relative error of 10 groups measured in the range of 0-2000 lx are 7.82 lx and 1.77%, respectively. Results show that the proposed method is feasible and can be used as a reference for the design and development of related illumination sensors.

This study proposes a sheet strain sensor comprising two glass-fiber flakes, a silica fiber Bragg grating, and two glass-fiber tubes that is packaged by a high temperature-resistant adhesive. The strain sensor contains no metal material, facilitating resistance to strong power and electromagnetic interference. Three sensor prototypes are manufactured and arranged on a constant strength cantilever beam for comprehensive performance test. Experimental results show that all three sensors possess good measuring repeatability (repeatability error 0.999), and consistency for measuring sensitivities. The sensors also demonstrate good temperature compensation ability (within 22 pm) and creep resistance. These test results indicate that the proposed sensor has a superior measurement performance and can meet the requirements of long-term strain monitoring for electric power facilities in the wild.

In a traditional direct detection (DD) optical communication system, performance loss is inevitably caused by the interaction between dispersion and square-law detection of a photodetector. Based on a DD optical communication system using Stokes space multiplexing, a spectrum compression algorithm is proposed to optimize the phase of a transmitted signal sequence, which transforms a three-dimensional Stokes space signal to a four-dimensional Jones spatial signal with 3/4 bandwidth, thus enabling the dispersion pre-compensation without performance loss and extra hardware cost. Since this ideal spectrum compression requires global optimization algorithm with high complexity, we propose a simplified look-up-table based phase optimization algorithm. Simulation results show that when the optimization length is 7 symbols, the difference between the peak and the valley of the spectrum is about 17 dB, which effectively decreases the bandwidth requirement of the transmitter.

With the development of aerospace manufacturing and high-performance aircraft, large-curvature plate-shell structure has been widely used. Aiming at the problem of assembly deformation caused by factors such as prestress and size and position deviation. a fiber Bragg grating sensor is used to study the surface reconstruction algorithm of plate-shell structure. The relationship between wavelength shift and curvature is established, and the curvature data required for the surface reconstruction algorithm is obtained. Segment fitting algorithm is applied to calculate the coordinate increment of all measuring points to realize the curve reconstruction. On this basis, the measured surface of the plate-shell structure is reconstructed, and the theoretical data at the measuring points of the ANSYS simulation surface is compared with the data of the actual reconstructed deformation surface. The results show that the algorithm is highly effective and provides technical support for the deformation prediction and modification of plate-shell structures.

In this study, a cascaded dual micro-ring resonator with the same radius is used to implement an n>1 order optical time-domain differentiator. The effects of differentiation accuracy, energy efficiency, and input signal on the differentiation results of the cascaded dual-ring differentiator were analyzed using the principle of minimum average deviation. In comparison with a single micro-ring, the average absolute deviation of differential waveform can be reduced from 5.67% to 0.67%. Within the range of 1n<2 differential orders, the overall average absolute deviation of the differentiator does not exceed 2.3% and the cross-correlation coefficients are greater than 99%. The differential accuracy is improved, the input signal pulse width is less affected the defferentiation order of the cascaded dual micro-ring defferentiator, and the applicable input-signal pulse width range is larger. Simultaneously, by adjusting the coupling state of a loop in the cascade structure, the differentiation order of the differentiator can be changed to realize a tunable high-precision fractional differentiator.

Based on the optical thin film theory, the optical characteristic matrix method was used to derive a mathematical model of the reflection-induced retardance and incident angle of the high-reflection film for air-gap Fabry-Perot (F-P) etalon. The change in the reflection-induced retardance at incident angle ranging 0°-3° was analyzed using TFCalc membrane design software, and the mathematical model was verified. Results show that the reflection-induced retardance and the incident angle exponentially increase, and the reflection-induced retardance is close to 2.88×10 -3 rad when the incident angle is 3°. The experiment setup of the F-P interference imaging optical path, demonstrates that the F-P etalon interval is (2015.50919±0.00002) μm and the relative error limit is approximately 8.6×10 -9. Compared with the measurements that do not consider the reflection phase shift [the interval is (2015.50864±0.00082) μm and the relative error limit is approximately 9×10 -7], the measurement accuracy shows significant improvement.

In the field of industry, the technology of direct part marking with traceability has been paid more and more attention. However, many product components have requirements of size restriction for direct part marking, thus the information storage capacity has been restricted. In order to improve the data storage density of direct part marking, the concept of color two-dimensional barcode is introduced into the technology of direct part marking, and the color Data Matrix two-dimensional barcodes are designed by direct part marking. The laser marking experiment of color two-dimensional barcodes on titanium alloy materials are carried out with nanosecond laser marking equipment, and the laser marking of color two-dimensional barcodes are successfully implemented, and barcodes’ qualities are evaluated. In order to further verify the reliability of barcodes, the images of two-dimensional barcodes marked by laser are collected for choosing whether to carry out barcode reconstruction before information extraction according to the evaluation results to verify barcodes information. The verification results prove that the processed color Data Matrix two-dimensional barcodes are reliable, and the color direct part marking technology is feasible, which can be promoted and applied in the field of industrial direct part marking.

To solve the problems of the lack of a model and inaccurate axis extraction of an airplane, a method for rendezvous analysis pose attainment of classified lines is proposed. In this method, first, a rotation matrix is obtained by deriving the unique correspondence between the pose definition and the progressive rotation of Euler angles in the reference coordinate system, and the lines are classified based on the carried pose information. Furthermore, a method for non-axis rendezvous analysis pose attainment, which uses the relative pose relationship between the feature line and the intersecting axis as input value for rotation transformation and obtains the rotation matrix by improving the feature line vector in the reference system, is implemented. Then, the pose rotation matrix is obtained by the modified Rodrigues transformation using the vector space relationship between the synchronous rotations of the two lines. The pose information can be analyzed using the solving time matrix. Tests show that the stability of the proposed algorithm is better than that of the model matching method, and its processing efficiency is considerably increased. Moreover, it has obvious advantages in terms of anti-occlusion, feature location, and tracking, which provides a new direction for the optical pose processing of the range.

Based on a theoretical model of a 2-μm thulium-doped mode-locked fiber laser and nonlinear Schr?dinger equation (NLSE), this study analyzed the evolution conditions of self-similar pulses in the laser. The peak power output of the self-similar pulse was approximately 22.66 W. Further, the effects of parameters, such as net dispersion, length of dispersion-compensation fiber, and gain coefficient on self-similar pulses were simultaneously studied. The results show that increasing the net dispersion in the cavity and the length of the dispersion-compensation fiber increases the pulse width and decreases the energy of the single pulse. Moreover, increasing the small-signal gain coefficient increases both the pulse width and energy of the single pulse.

A 12CrNi2 alloy steel, which was composed of a major ferrite and minor austenite, has been fabricated by means of the laser additive manufacturing technology. The microstructure of distinct interlayer heat-affected zone consists of coarse ferrite and a small amount of austenite comparing to the microstructure of inner deposited layer. The microstructure of as-deposited steel was homogenized after isothermal quenching treatment, and meanwhile the strength was improved significantly. The evolution process of the microstructure and morphology of the bainite with the isothermal quenching temperature and time and its effect on the yield strength and tensile strength as well as the elongation of the alloy steel are reported. And the optimized heat treatment process with good comprehensive mechanical properties is proposed.

Herein, the finite element method (FEM) is used to simulate a single-layer and multi-track temperature field considering the powder-to-solid transition and latent heats of melting at different scanning speeds. The generation of defects, anisotropy of microstructure, and mechanical properties are experimentally analyzed. Results show that increasing the laser scanning speed tends to reduce the wettability of the liquid phase and increase porosity. Moreover, the depth and width of molten pool gradually decrease, which hinders the formation of good metallurgical bonding. Numerous cellular and dendrites are formed in the molten pool, and the high temperature gradient tends to induce planar or cellular dendrites, while the low temperature gradient tends to induce dendritic dendrites. The simulation also demonstrates that the average grain size, grain orientation, strain distribution, and the distribution of the boundary-misorientation angle on the cross-section and longitudinal section show some differences owing to differences in the temperature gradient along different directions. Furthermore, the transverse samples display a higher yield strength, but the ductility is significantly lower than that of vertical samples containing elongated columnar grains along the building direction.

In this study, a cobalt-based/graphene oxide (GO) composite coating has been fabricated on the surface of the TC4 substrate/titanium alloy via laser cladding. The scanning speed of V1=6 mm/s, feeding rate of V2=1.2 r/min, and spot diameter of D=4 mm remain constant, and four different laser power settings of P1 =1000 W, P2=1300 W, P3=1600 W, and P4=1900 W are selected to investigate the effect of laser power on the microstructure and mechanical properties of the cobalt-based/GO composite coating. The results prove that the cladding layer mainly comprises the TiC, Co2Ti, γ-Co, α-Ti, and Cr3C2 phases. GO reacted with the TC4 matrix under the reaction of low power to in situ composites TiC. Furthermore, it interacts with the semi-solid Co2Ti structure and decomposes rapidly under a high-power reaction, mainly generating the Co2Ti structure. When the laser power is P2=1300 W, the cladding effect is optimal and the forming structure is uniform; subsequently, the cladding cobalt-based/GO coating is metallurgically bonded to the TC4 substrate. The microhardness of the cladding layer is 1100 HV0.2, which is 2.82 times that of the matrix having a microhardness of 390 HV0.2.

In order to obtain optimal process parameters of the laser cladding Ni35WC11 coating, a single factor control method is adopted. Three process parameters, including laser power, powder feeding rate and scanning speed, are used as control variables. The dilution ratio, height and width of the cladding layer are used as reference indexes for orthogonal range analysis. The results show that the influences of powder feeding rate, scanning speed and laser power on the reference indexes decrease gradually. The optimal parameters obtained by single factor and orthogonal analysis are laser power of 1500 W , powder feeding rate of 2 g/s and scanning speed of 4 mm/s. Samples are prepared according to these parameters. The hardness of the as-prepared cladding layer is about 710 HV, the self-corrosion potential is -0.72 V, and the self-corrosion current density is 0.96 A/cm 2, indicating the cladding layer obtained under optimal parameters has high hardness, uniform structure, and strong corrosion resistance.

This study proposes a graphene monolayer/few layered Ti3C2Tx MXene/silver film as a new plasmonic hybrid nanostructure. The feasibility of two-dimensional Ti3C2Tx MXene in the ultrasensitive detection of surface plasmon resonance (SPR) was confirmed using the transfer matrix method. Calculation results show that both the photon absorption and energy loss are balanced by optimizing the thickness of Ti3C2Tx MXene and the silver film. In addition, under an excitation wavelength of 632.8 nm, the optimal sensing configuration is monolayer graphene/3-layered Ti3C2Tx MXene/35-nm silver film, which can produce an ultralow (approaching zero) SPR reflectivity (3.48×10 -9). For a minute variation in the refractive index (as small as 0.0012 RIU), the proposed configuration can produce a differential phase response up to 110.55°and provide a phase detection sensitivity as high as 9.21×10 4 (°)/RIU. In comparison with the conventional sensing configuration with angular modulation, the proposed configuration can provide an enhancement factor that is four orders of magnitude higher. Therefore, our proposed configuration has potential application in ultrasensitive biochemical detection.

In this study, we systematically calculate the conduction band structure of biaxial tensile strain paralleled to (001),(110), and (111) crystal planes and uniaxial tensile strain paralleled to [001], [110], and [111] crystal direction in Ge1-xSnx alloys based on the deformation potential theory. Results indicate that the descent speed in the Γ valley is faster than that in the L valley in the case of biaxial tensile strain paralleled to (001) and (110) crystal planes and uniaxial tensile strain paralleled to [001] crystal direction in Ge1-xSnx. However, the descent speed in the L valley is faster than that in the Γ valley in the case of biaxial tensile strain paralleled to (111) crystal plane and uniaxial tensile strain paralleled to [110] and [111] crystal directions in Ge1-xSnx. The strategy of tuning Ge1-xSnx alloy into a direct band gap material is proposed for reducing Sn composition based on biaxial tensile strain paralleled to (001) and (110) crystal planes and uniaxial tensile strain paralleled to [001] crystal direction in Ge1-xSnx alloy which will provide references for the experimental preparation and device simulation.

In a stimulated emission depletion (STED) microscopy, a periodically arranged optical lattices is used as fluorescence depletion pattern to achieve parallelized multi-point fluorescence depletion, which can effectively improve the time resolution of imaging. We propose a simple optical system model of microscopic imaging system in parallelized STED microscopy and derive out a formula to illuminate the effect mechanism of tube lens and microscope objective on parallelized fluorescence depletion pattern periodicity in the model. Then we work out the optimum optical parameters which are used to generate a parallelized fluorescence depletion pattern with smaller periodicity from our formula. The numerical simulation result shows that square lattice-like parallelized fluorescence depletion pattern with a periodicity as small as 276 nm× 276 nm was generated with our method.

The broadband yellow-orange laser is an important fluorescent source in the fields of biomedicine. Based on broadband quasi-phase matching technology of periodically polarized lithium niobate (MgO∶PPLN) crystal, a modeling scheme based on apodization step chirped MgO∶PPLN is proposed. In the chirped MgO∶PPLN, broadband sum frequency of C-band (1525-1565 nm) and 980nm laser is realized. The genetic algorithm is used to optimize the tracking rate and the increment of chirp period range. The spectral output with conversion efficiency of -11 dB, band top fluctuation of 0.047 dB and band width of 6 nm is obtained near the wavelength of 600 nm. This work provides a broadband yellow-orange all-solid-state laser output design with high conversion efficiency and low band top ripple.

In order to optimize the process parameters of aspherical lens molding process, a two-dimensional axisymmetric model is established by MSC.Marc software. Based on five-element generalized Maxwell viscoelastic model, a finite element simulation of the molding process of D-ZK3 glass materials is carried out. The changes in equivalent stress of glass preform and dies, and the influence of molding temperature, molding rate, and friction factor on the equivalent stress are analyzed. The results show that the equivalent stress at the edge of the lens is larger than that at the center of the lens, and the equivalent stress at the center point of the upper surface is greater than that at the center point of the lower surface. The equivalent stress of the lens and the die increases with the increase of molding rate and friction coefficient, and decreases with the increase of molding temperature. The equivalent stress of the die is larger than that of the lens. Orthogonal test shows that the molding temperature and molding rate are the main factors affecting the equivalent stress of the glass preform. Combined with practical application, the most suitable molding parameters are molding temperature of 580 ℃, molding rate of 0.1 mm/s, and friction factor of 0.2.

The off-axis reflective optical system overcomes the material limitation of traditional refractive system and has the advantages of large aperture, small volume, lightweight and non-chromatic aberration. With the extensive application of freeform surface, which has very high degree of freedom, it has corrected the asymmetric aberration introduced by off-axis system, which has become a research hotspot. Aiming at the complex problem of solving the off-axis three-mirror initial structure, this paper introduces several common design methods of off-axis reflection system, which can be summarized as two ideas from the design principle: first, the initial structure of coaxial system is established according to aberration theory, and the off-axis optimization of optical system is carried out to achieve non-central occlusion; the second is to directly construct a simple optical system without central obscuration, using the complex surface for aberration optimization in the optimization process. According to the two kinds of design theory, the optical systems with different structures are designed as examples. The optimization process and image quality evaluation function show that both methods can meet the design targets, but the optimization process is different, and the construction results are almost equivalent. Among them, the first method is more advantageous in aberration optimization, which is suitable for optical systems with small off-axis angle; the second method avoids complex off-axis optimization and is suitable for compact optical systems.

Theoretical analysis of the coplanar waveguide photoconductive switch based on InGaAs material system is carried out, and the transmission performance of the radio-frequency (RF) signal in the dark state without illumination and the bright state with laser irradiation is studied. A laser pulse trigger switch with a working wavelength of 1550 nm, a pulse width of 96 fs and a repetition rate of 103.2 MHz is used to sample the 445 MHz RF signal. Experimental results confirm that the high-speed photoconductive switch can realize the bandpass sampling of the RF signal, while reducing the carrier lifetime of the switch, which is conductive to achieving higher frequency signal sampling.

Based on the advanced microwave scanning radiometer 2 (AMSR2) first level brightness temperature data, the influence of radio frequency interference (RFI) signal on AMSR2 7.3 GHz channel measurement data over East Asian Ocean is evaluated with generalized RI index identification method, and the results are compared with those obtained by spectrum difference method. The results show that the location and time variation characteristics of the RFI signal contamination detected by the two methods are almost the same, but the RFI signal detected by the generalized RI index recognition method has larger intensity, wider range and more pixels. At the same frequency, more RFI signals are observed by vertical polarization than by horizontal polarization. The distribution of RFI signals over East Asian Ocean shows a long and narrow strip with a northeast to southwest trend, and its position and range vary with the observation time. For AMSR2, the 7.3 GHz RFI signal on the ocean surface only appears in the descending orbit observation and is mainly from the downlink signal of the stationary satellite over the equator reflected by the ocean surface.

The measurement of atmospheric wind field is of great significance for global climate change, sea storm detection, accuracy of daily weather forecast, and even national military security. Space-based coherent wind light detection and ranging (LiDAR) has attracted wide attention due to its high time-space resolution, high sensitivity, real-time detection, and small volume. Most spacecraft have micro-vibration disturbance sources, which can influence the signal-to-noise ratio (SNR) of coherent wind LiDAR. Based on the principle analysis of coherent wind LiDAR system, this paper analyzes the influence of satellite micro-vibration on the signal-to-noise ratio of the coherent wind LiDAR, based on the measured data of a certain type of micro-vibration. The experimental results show that satellite micro-vibration has a certain effect on the signal-to-noise ratio of coherent wind LiDAR. When the mismatch angle is 3.77 μrad, the signal-to-noise ratio fluctuates between -1.5 dB and 1.36 dB, and the impact is relatively weak. From a micro-vibration perspective, a satellite platform can meet the detection requirements of a coherent wind LiDAR.

Due to the wide spectral bandwidth of ultra-short and ultra-intense laser facility, the use of traditional spatial filter lens groups to expand the beam will cause the accumulation of chromatic aberrations of the device, which will seriously affect the quality of the terminal focal spot. In this paper, the main technology and research progress of eliminating chromatic aberration in ultra-short and ultra-intense laser facilities are reviewed, and both the advantages and disadvantages of several main schemes are compared and summarized. On this basis, a scheme for dynamic and accurate compensation of the chromatic aberration of the facility is proposed, which has been verified and used in actual engineering. This paper also analyses and prospects the development direction of chromatic aberration compensation.

Compared with single vortex beam, vortex beam array has multiple phase singularities, which can not only increase information transmission capacity, but also increase the number of particles captured and observed. At present, there are various methods for generating vortex beam array in the field of optics, such as interferometry, Talbot effect method, optical wedge diffraction method, mode conversion method, Dammann vortex grating method, computational holography method, spatial light modulation method, and metamaterial pattern method. In this paper, the theoretical model, experimental principle, experimental results, and research status of these methods are introduced in detail, and their application prospects are presented.

The ideal surface has strong polarization properties, but the actual surface is usually rough, resulting in significant shadowing and severe diffuse reflection. In order to accurately characterize the polarization properties of rough surfaces, based on the micro-facet model, an improved six-parameter polarization bidirectional reflection distribution function (pBRDF) model is established considering the shadowing effect and diffuse reflection. Based on this, the expression of the optical reflection polarization degree of rough surface is derived. The degree of polarization of aluminum and black lacquer materials is simulated to invert the complex refractive index. The results show that the proposed model simulation value is more consistent with the experimental measurement value, and the complex refractive index inversion accuracy is higher. The pBRDF measurement is carried out on the 45# steel material, and the distribution of polarization degrees under different incident angles reflection angles and roughness is analyzed. The experimental results show that the simulation values of the six-parameter model can be well matched with the experimental measurements, and the accuracy of the model is increased by modeling the diffuse reflection part. This work can be used as a theoretical basis and method for the detection and analysis of rough surfaces.

According to the theory of Mie scattering, a polarization nephelometer composed of 532 nm laser as light source and charge-coupled device as detector was designed. Standard polystyrene latex (PSL) particles with particle size of 2 μm was measured, and the scattering phase function of the PSL was obtained. Compared with the theoretical scattering phase function of 2 μm spherical particles with polarization angle of 0° and 90°, the fitting degree was 87.3% and 88.4%, respectively. Chahine iteration algorithm was used to inverse the particle size of the PSL, the measured particle size was 1.94 μm, which was close to the real particle size. The results of polar nephelometer were compared with those of wide range particle size spectrometer and scanning electron microscopy. The results show that the detection precision of the device is high and not affected by subjective factors. The device is of great significance for the accurate detection of particle size, which has good application potential in related field.

In the atmospheric pollutants, there are many harmful gas components that is difficult to distinguish the absorption peaks of different components obtained by infrared and terahertz spectral detection. This paper designs an algorithm for analyzing the proportion of different substances in the measured spectrum based on the theoretical spectrum of the substances that may be included in the measured spectrum. The overdetermined equations constructed by using the corresponding relationship between experimental peaks and different theoretical peaks are solved based on genetic algorithm and simulated annealing algorithm, so the contribution of theoretical spectra of various materials in the experimental spectrum is obtained. In order to verify the accuracy of the proposed algorithm, we use this algorithm to analyze the experimental spectra of the water vapor system composed of known water clusters. The results show that the proposed algorithm can get the specific gravity of different components better and has stronger practicality.

Accurate estimation of soil moisture content (SMC) is of great significance for precision agriculture and water resources management in arid areas. Traditional estimation methods and field measurements are time consuming and labor intensive. Therefore, we obtain hyperspectral image data of winter wheat plots in Fukang City, Xinjiang by unmanned aerial vehicle platform, and the original hyperspectral data are preprocessed through first derivative, second derivative, absorbance, first derivative of absorbance (FDA), and second derivative of absorbance. Random forest (RF), gradient boosted regression tree (GBRT), and extreme gradient boost (XGBoost) are used to select the importance of feature variables. A model is established based on geographical weighted regression (GWR). The results show that the pretreatment effect of FDA is the best. The model based on FDA-GBRT is optimal. The determination coefficient (R2) of the modeling set and the verification set are 0.890 and 0.891, respectively, and the quartile interval reaches 3.490. Compared with RF and XGBoost algorithms, the advantages of the GBRT algorithm are more prominent. The R2 of most of the model modeling set and the verification set are greater than 0.600. This indicates that the GWR model is effective in predictive modeling of SMC and can provide theoretical support for the management and protection of agro ecosystem in arid regions.

In this study, the concentration levels of NO2, O3, and SO2 at the crossroad of Haier Road and East Yinchuan Road, Qingdao, are continually monitored in real-time based on the long path differential optical absorption spectroscopy (LP-DOAS) from 2017 to 2018. The concentration levels of NO2, O3, and SO2 obtained using LP-DOAS are compared with those obtained at the environmental monitor station, and a good agreement between these is found. The correlation coefficients of NO2 and O3 hourly average results are 0.78 and 0.798, respectively, and the correlation coefficients of monthly average results of these are 0.91 and 0.84, respectively. The diurnal variation of NO2 concentration presents two peaks, i.e., in the morning and evening. Compared with the real-time traffic flow, NO2 concentration is strongly positively correlated with traffic flow, and the correlation coefficient is 0.95. There is a significant weekend effect in the NO2 concentration on working days relative to weekends.

In this study, we design a solar spectrum synthesis method based on monochrome LEDs to solve the problem of spectral discontinuity associated with white LED. The proposed method ensures the fitting of the solar spectrum by constructing a monochromatic LED spectral model by the least squares algorithm considering the maximum correlation index R2 as the optimization target. Based on the ideal peak-wavelength equal-interval LED fitting, the simulation experiment is solved to obtain an optimal fitting solution for a non-equal-interval monochrome LED. Thus, we obtain an optimum number (27) of monochrome LED combinations, and the maximum correlation index R2 is 0.9576. Furthermore, the spectral fitting result of two groups of 17 monochromatic LED combinations obtained by decreasing experiment is analyzed. The mixed spectrum meets the Class-A-level standard requirements of AM1.5. Thus, the best fit of various LEDs is achieved with respect to the solar spectrum, and the difficulty of engineering implementation is reduced.

Anthracnose is one of the most common diseases of camellia oleifera, so it is of great significance to quickly detect it. In this paper, a new method for the detection of anthracnose in camellia anthracnose leaves is proposed. First, laser induced breakdown spectroscopy is used to quickly and non-destructively diagnose the Mn element content in the leaves of normal and infected anthracnose camellia oleifera leaves. The true content of Mn element in the samples is analyzed by flame atomic absorption spectrometry. Second, different pretreatment methods, such as smoothing, denoising, normalization, baseline correction, first-order derivation noise reduction, and second-order derivation noise reduction, are used to preprocess the spectral data. Partial least squares (PLS) method is used to establish a quantitative model. Interval partial least-squares regression (iPLS) method is utilized to filter the spectral data. Finally, combined with 7-point smoothing and first derivative noise reduction, the quantitative model is established based on iPLS. The results show that the modeling effect of the sixth subinterval is the best when it is divided into 24 subintervals, the modeling correlation coefficient is 0.9076, the modeling root mean square error is 0.2090 μg/mg, the prediction correlation coefficient is 0.8947, and the prediction root mean square error is 0.2100 μg/mg.

In this study, we develop optical color modulation films in accordance with colorimetry to address the problem of low photon quantity observed in a low-light-level system. This system comprises a six-color filter, promoting color rendition. Further, we develop a data acquisition and iteration method model, which can be used to obtain the film design of the optical color modulation films by analyzing the spectral properties and combining the Essential Macleod film design software with the Mathcad engineering calculation software. The films are deposited via electron beam evaporation. Subsequently, we combine the quartz crystal deposition monitoring technology with the optical deposition monitoring technology to control the film thickness. Furthermore, optical color modulation films can be developed by performing inverse analysis with respect to film stacks. The obtained films pass the spectrum test and satisfy the application requirements.