To clarify the reliability of laser energy density as the basis for optimizing selected laser melting process, temperature field, melt pool size, and densification of selected laser melted specimens at different scan speeds with constant energy density were investigated through numerical simulation and experiments using cobalt-chromium alloy powder. The results show that the laser energy density is not a reliable parameter that affects the melt pool size and relative density of selected laser melted parts. In addition, the scanning speed of laser plays a crucial role in modulating the melting and solidification processes of the powder and melt pool size. When the laser energy density is the same, as the laser scanning speed increases, the melt pool size increases, and the density of the sample increases accordingly.

Herein, the prediction accuracy of three tropospheric refractive index profile models commonly used at home and abroad was analyzed using the measured data of the tropospheric zenith delay and meteorological environment obtained from 11 international global positioning system service stations in China. Moreover, the applicability of the models was evaluated in high altitude areas and with seasonal changes. Results show that the exponential and segmented models achieve a higher accuracy at high altitude areas, while the Hopfield model shows greater advantages in areas other than high altitudes. Generally, the accuracy of the segmented and Hopfield models is higher in spring and winter and lower in summer and autumn. The accuracy of the exponential model shows a negligible relation with the season. The findings of this study have important reference values for the application research of the tropospheric refraction error correction model.

The potential energy curves for seven Λ-S electronic states (X2Σ+, B2Σ+, C2Δ, F2Σ+, A2Π, D2Π, and E2Π) of strontium chloride (SrCl) molecule are investigated using the multireference configuration interaction method (MRCI). Davidson correction (+Q), core-valence correction, and spin-orbit coupling effect are considered in the calculation. Based on the obtained potential energy curves of Λ-S states, the vibration energy levels, wave functions, and spectroscopic parameters are determined by solving the Schrödinger equation using the discrete position presentation method. The calculated values agree substantially with experimental and theoretical values. Additionally, the transition dipole moments, Franck-Condon factors, and radiative lifetime of the SrCl molecule are explored. Due to the significant diagonal distribution of the Franck-Condon factors (f00=0.96959) and short radiative lifetimes (τ=31.05 ns) of the A2Π (ν′=0) →X2Σ+(ν″=0) transition, the SrCl molecules are suitable for rapid laser cooling. Therefore, this study presents a three-laser scheme for laser cooling of SrCl molecules. The calculated pump and repump wavelengths of the laser-driven cycling are668.2 nm (λ00), 682.0 nm (λ01), and 681.5 nm (λ12).

Optical fiber sensors have the advantages of high sensitivity, high-inherent insulation, and good anti-electromagnetic interference ability compared to standard monitoring technologies. However, humidity sensors based on fiber Bragg gratings are easily affected by temperature and stress, resulting in issues such as significant humidity measurement errors and low stability. This paper proposes a fabrication method based on a single grating half-coated temperature and humidity sensor to solve these problems. First, a moisture-sensitive material is coated on half of the grating, and the other half is a bare grating area. Then, the bare grating reflection spectrum peak curve is then Gaussian fitted to establish the functional relationship between ambient temperature and center wavelength λ. Finally, the relationship between the area S enclosed by the grating reflection spectrum curve and the peak power under various environmental humidity conditions is analyzed. The function model of the area S and the relative humidity of the environment is established. The sensor is tested by a temperature and humidity generator. The experimental result shows that the sensor has good repeatability in the range of 10%‒90%RH (%RH is relative humidity). The humidity monitoring sensitivity is 2.95/%RH, and the response time is 6.6 min, which matches the temperature and humidity monitoring requirements in storage and other fields while also providing a new solution for temperature and humidity monitoring in related fields.

A novel sensor structure, D-type surface plasmon resonance (SPR) sensor based on regular hexagon photonic crystal fiber (PCF), is proposed to measure the refractive index (RI) and temperature simultaneously, and measure the refractive index and temperature dynamically in a large range. It can simultaneously detect the refractive index of 1.230—1.355 and the temperature of 5—85 ℃. The results show that when RI is in the range of 1.330—1.355, the sensitivity is 1645.7 nm/RIU; the maximum sensitivity in the whole detectable range is 1497.6 nm/RIU. When the temperature range is 20—60 ℃, the sensitivity can reach up to -2.68 nm/℃,and the sensitivity can reach up to -3 nm/℃ in the whole measurable range. The superiority of this structure is that it is sensitive to a large dynamic detection range of RI and temperature with relatively high sensitivity.

Layered decoding algorithm layers the check matrix and updates the messages by layer, which accelerating the decoding convergence rate. However, since message updates in each layer is based on the upper layer, it is unavoidable to introduce the irrelevant information of the upper level, which reduces the proportion of effective details of the current layer. Aiming at the problem, this paper presents a layered-sorted min-sum ascend (LS-MS-A) decoding algorithm that introduces an ascending layer-weight scheduling strategy. It first updates the layer with smaller weight and reduces the interference of irrelevant information from the upper layer to the effective information of the current layer, thus, speeding up the decoding convergence rate. According to the simulation results, under the premise of ensuring the system reliability, compared with the layered minimal sum decoding algorithm, when the code length is 256 and the code rate is 0.5, LS-MS-A can improve the decoding convergence speed by about 9%. When up to 512 and the code rate is 0.75, the decoding convergence speed can be improved by about 15%.

Temperature and stress are easily to cause cracks in concrete bridges and endanger the safety of bridges, but traditional strain measurement methods are difficult to apply on a large scale in actual projects. The weak fiber Bragg grating(wFBG) array strain measurement technology has the advantages of easy networking, high-precision, multiple measurable points, strong reliability, strong anti-interference ability, excellent corrosion resistance, wide measurement range and long-distance measurement. It can be widely promoted in the field of large civil engineering strain measurement. In this paper, first, the relationship between strain and wavelength is determined through wFBG strain-wavelength calibration experiments, and a high-precision large-capacity demodulation system is constructed. Then, the feasibility and superiority of wFBG array strain measurement are verified by strain measurement experiment in T-beam loading and unloading process. Finally, an array of 4118 wFBGs is used to monitor the bridge strain on the Hangzhou Xiasha Bridge.

Distributed optical fiber sensing technology has been widely used in the safety monitoring of pipeline transportation. Accurately extracting and classifying the characteristics of different optical fiber vibration signals is a research hotspot in recent years. Aiming at the defects that the traditional time-frequency analysis method needs to manually set the basis function and cannot eliminate the interference of high-frequency noise when studying the optical fiber vibration signal, the local mean decomposition (LMD) method with adaptive characteristics is used to process the signal, and a new method based on LMD is proposed in this paper. Decomposed feature extraction and recognition methods. First, LMD is performed on the original signal to obtain several product function components; then, the signal is reconstructed by the principle of autocorrelation, and the sample entropy features and energy features of the reconstructed signal are extracted; finally, the above features are fused and sent to the support vector machine for training recognition. The experimental results show that the method can effectively identify different vibration types, and has a high accuracy rate.

To ease the polarization fading phenomenon of weak fiber Bragg grating array, the influence of the polarization variation of the light pulses induced by the birefringence effect on the interference intensity is analyzed theoretically, and the coupling coefficient of the alternating item is found to cause the distortion of phase signal, which is demodulated by the zero difference symmetry algorithm. In order to reduce the impact of the polarization fading phenomenon, we propose a kind of polarization compensation method based on real-time polarization measurement, by which the coupling coefficient of the alternating item is eliminated. The simulation results show that the polarization compensated zero difference symmetry algorithm can achieve stable demodulation results in a large dynamic range, and solve the large-range jump problem of the signals in the demodulation process of the conventional zero difference symmetric algorithm.

Aiming at the problem that the peak-to-average power ratio in the orthogonal frequency division multiplexing system of visible light communication is too high, this paper proposes an improved Polar codes scheme to reduce the peak-to-average power ratio. The peak-to-average ratio growth index and amendment bits are introduced into the Polar codes encoding process. First, the scheme calculates the peak-to-average ratio growth index of a large number of Polar symbols in offline form to obtain the best index of amendment. This process is realized by Monte Carlo simulation. Second, in the system transmission process, the channel matching is performed through the signal-to-noise ratio feedback information, and the optimal correction set is obtained by looking up the table. Finally, the corresponding correction bit is bit-flipped to reduce the peak-to-average ratio. This solution is able to use the traditional decoding solution of the Polar codes to jointly decode the information and amendment bits, so there is no need to transmit auxiliary information, and the complexity of the encoding and decoding process does not increase. The simulation results show that when the code length is 1024, the number of subcarriers is 256, and the number of amendment bits is selected as 32, the proposed correction scheme can reduce the peak-to-average ratio by 4.9 dB without affecting the decoding complexity, and has a smaller block error rate performance advantage compared to the same type of scheme.

In order to solve the problem of the spectrum fragmentation in elastic optical networks, a fragmentation-aware routing and spectrum allocation algorithm for maximizing service carrying capacity is proposed in this paper. In the routing stage, K-shortest path routing algorithm is utilized to calculate K alternative paths with the minimum hops offline for connection requests. In the spectrum allocation stage, the factors such as the duration of the arriving request and established connections are considered to evaluate the service carrying capacity of the free spectrum block (SB). From available SBs of the selected path, we select the scheme that is beneficial to maximize the service carrying capacity of the free resource in the relevant paths after the lightpath is established for the connection establishment. Simulation results show that the algorithm can reduce the bandwidth blocking probability and the link average fragmentation ratio and improve the resource utilization.

Based on the spectral peak point characteristics of Chinese speech, this study proposes a syllable matching algorithm to improve the matching effect of Chinese speech syllables in noisy environments. First, a discrete cosine transform is used to extract the speech signal envelope spectrogram, and the human ear masking effect is used for spectral energy judgment to obtain the extreme value points of spectral energy in each frame. Then, the syllable signal is corresponded to a binary sequence by performing binary quantization in the logarithmic frequency range. Finally, the syllable matching result is determined based on the template comparison of the binary sequence. The results show that the proposed algorithm outperforms the conventional methods for matching syllables in the noiseless Chinese speech. Additionally, it has a high matching accuracy at low signal-to-noise ratios.

The focusing precision of the linear Fresnel collector has an important effect on the photothermal efficiency. Moreover, the partial hot spot caused by the partial focus of the concentrator causes an unbalanced expansion of the absorber, which causes severe damage to the collector's structure. Therefore, it is crucial to analyze the concentrating error of the collector. According to the characteristics of the linear Fresnel heat collecting system, the main factors affecting the light-gathering precision of the Fresnel collector are discussed through mechanism analysis. All the factors are analyzed and simulated by MATLAB software, and it is concluded that the main factors that cause the concentration deviation of the collector are the north-south arrangement deviation of the linear Fresnel mirror field, dynamic displacement deviation of the reflection center of the primary mirror, and dynamic variation of the light path of the reflected light. The concentrated light deviation caused by the north-south deviation of the mirror field layout is normally distributed at noon and varies with the latitude. Meanwhile, the effect of the dynamic displacement deviation of the reflection center of the primary mirror on the focusing precision is greater in the morning and evening, and it is asymmetric in the morning and afternoon with the maximum error approaching 0.08°. The influence of light path variation of the reflected light on the concentrating error is mainly reflected in the annual time axis. Through simulation analysis and field testing, the linear compensation algorithm was used to compensate the target tracking angle of the collector's primary mirror. After the compensation, the maximum concentration error of the heat collecting system was less than 0.06°.

Aiming at the problem that the detection performance is affected by the deformation of the rotating shaft of the pulsed laser circumferential detection system under the condition of high-speed rotation, the mechanical model of the high-speed shaft is established to derive the theoretical formula of the bending deformation of the shaft. Combined with the echo power equation of the planar expansion target, the imaging model of target detection is established under the rotation axis offset. The influence of the deformation of the shaft on the amplitude voltage of the echo signal and the imaging position is simulated. The results show that when the motor speed reaches 40000 r/min, the angular displacement of the rotating shaft at the total reflection plane mirror reaches 0.013 rad, and the deformation along the Y axis reaches 0.88 m; the amplitude voltage of the echo signal gradually decreases with the increase of the speed; the spatial imaging point has a position jitter of 0.004 m at 40000 r/min.

In this paper, we introduce Lambert-Beer law into bidirectional reflectance distribution function in order to deduce a mathematical model for calculating the backscatter cross section of spherical cooperative target. And based on this theoretical basis, the experimental system that for measuring the backscatter cross section of spherical cooperative target is established. Using this test system, the relative intensity spectral data of echo signal of the spherical cooperative target with different materials was measured. At the same time, the spot images of spherical cooperative targets corresponding to the three typical emission power of 50 mW, 80 mW, and 300 mW are collected. According to the spectral data analysis, the backscattering cross sections of the cooperative targets with different materials are calculated. The results show that the laser radar cross section of the spherical cooperative target with refractive index of 1.46, 1.51, and 1.93 increases linearly with the increase of laser power. When the laser power is constant, the laser radar cross section of the spherical cooperative target with refractive index of 1.93 is significantly larger than that of the spherical cooperative target with refractive index of 1.46 and 1.51. This research provides a theoretical basis and data reference for the theoretical research and experimental measurement of the laser radar cross section.

Spot size and collimation performance of excitation light are important indexes to evaluate the performance of fluorescence excitation light path of nucleic acid detection system. This paper introduces a calibration method of fluorescence excitation light path performance for nucleic acid detection system. Firstly, the excitation light spot model and optical path collimation model are established, and the numerical calculation is carried out by MATLAB. Then, the accuracy of the model is preliminarily verified by ZEMAX ray tracing simulation. Finally, the excitation light path collimation performance test platform is built, and the industrial cameras are used to collect the light spot for experimental verification. The maximum output spot of the excitation light path is 2.23 mm, and the output angle is 1.72°. The results show that the established spot model and optical path collimation model can be used to calibrate the excitation optical path performance of nucleic acid detection instrument, which can effectively solve the problem that the spot is difficult to be accurately controlled, and provides a new idea for optical path collimation evaluation.

For on-axis three mirror astigmatism (TMA) space camera with large aperture and long focus, the secondary mirror support is a big mass cantilever. In order to improve the dynamic characteristics and ensure support structure stability, a lightweight support structure with high stiffness and stability is designed by theory and finite element analysis. The assemble weighs less than 4.5 kg. The analysis and test results show that the frequency of the first mode is 104 Hz and the dynamic characteristic is good. The dimension stability is less than 3 μm through dynamic vibration and thermal vacuum circle by self-designed method and device, and the structure size does not change. Stability test results show that the barrel design is reasonable and has high stability. At present, the support structure is adopted in some high resolution space camera, which would be referenced by high resolution, lightweight, and agile camera design.

We use the chaotic laser with low coherence property to achieve speckle suppression. In particular, we use laser diodes commonly used in laser display to generate chaotic laser by diodes with optical feedback perturbation and diodes with electrical chaotic signal modulation. The effects of bias current and feedback strength in the optical feedback system, and the bias current and modulation amplitude in the modulation system on speckle suppression are studied, respectively. Moreover, the speckle suppression effects of two systems are compared. The experimental results show that the chaotic laser generated by two methods effectively suppresses the speckle noise, and the speckle contrast of speckle patterns is reduced by more than 0.9, the maximum spectrum can be expanded to 4.6 nm by using chaotic laser, and the coherence length is reduced from 441 μm to 87 μm.

A system is reported in which a semiconductor optical amplifier is used to generate laser signal. The system mainly uses a terahertz laser which can generate two different frequencies and whose frequencies can be adjusted. The optical signal generated by the laser is converted into a stable electrical signal by a photodiode. As a low-noise radio frequency source, electrical signal can generate ultra-short pulse signal with low jitter and high repetition rate. Then, theoretical analysis and simulation experiment are carried out for each part of the system. According to Gaussian pulse theory, the parameters of pulse function in steady state are obtained. Finally, the single pulse and continuous pulse with different modulation frequency are simulated. The change of pulse is analyzed by changing the value of each parameter. The simulation results show that high repetition rate continuous ultrashort optical pulses can be obtained in the range of 10-30 GHz.

Aluminum ion optical clock transition has a natural linewidth of 8 mHz. The detection laser's linewidth must be ~1 Hz to obtain the optical clock transition spectral line. The semiconductor laser has a linewidth of 500 kHz and a long-term drift of 90 MHz/h. The laser frequency is locked on the Fabry-Pérot (F-P) cavity to meet the requirements of aluminum ion spectral detection. One of the main noises of the F-P cavity is vibration noise. To reduce the vibration sensitivity of the F-P cavity, this study theoretically analyzes the vibration sensitivity of the F-P cavity with stable laser frequency. The finite element method is used to investigate the relationships between the elastic deformation of the F-P cavity as well as its shape and support position. An F-P cavity is designed with a laser vibration sensitivity of 0.53 kHz/(m·s2) at a laser wavelength of 534 nm. It provides a theoretical foundation for realizing low vibration noise lasers and has important applications in the fields of atomic clocks and precise spectrum measurement.

In order to obtain the best technological parameters of laser cladding FeCrNiSi powder on Q690, an optimization method of laser cladding parameters based on response surface method (RSM) and second generation non-dominated sorting genetic algorithm (NSGA-Ⅱ) algorithm is proposed. By designing the Box-Benhnken experiment scheme in response surface method, the proxy model between the input variables (laser power, scanning speed, and powder feeding rate) and the response values (dilution, heat affected zone depth, and microhardness) is established, and the process parameters were optimized by NSGA-Ⅱ. The results show that the optimal parameters are obtained when the laser power is 1950 W, the scanning speed is 19 mm/s, and the powder feeding rate is 2.4 r/min. Under these conditions, the dilution rate of the cladding specimen decreases by 22.4%, the depth of the heat affected zone decreases by 17.9%, and the microhardness increases by 4.2%.

In order to explore the high-quality forming process of micro-holes, the picosecond laser combined with helical drilling technology was used to carry out the basic experiments of micro-hole forming. The shape (taper and size) of the micro-hole can be controlled by changing the deflection angle and translation of the wedge prism in the optical path of the rotating optical system. Taking 1-mm 304 stainless steel as an example, the influence of processing parameters such as laser pulse energy, defocusing amount, repetition frequency and laser helical drilling speed on the quality of micro-hole processing was studied. According to the experimental results, laser pulse energy is the key factor of micro-hole forming quality, defocusing amount can change the taper of the micro-hole to a certain extent, and the repetition frequency and rotation speed of the laser determine the thermal influence of the micro-hole and the thickness of the recasting layer. While laser pulse energy is 141 µJ, repetition frequency is 66.67 kHz, defocusing amount is +0.1 mm, and laser helical drilling speed is 8000 r/min, the high-quality micro-holes with pore diameters ranging from 100 to 300 μm and controllable tapers can be obtained.

The transmissive glass grating is commonly used in compact micro spectrometers and spectroscopy systems which can simplify the structure of optical system and reduce the complexity and expense of modulation. Traditional manufacturing methods have been unable to meet the increasing demands of modern industry due to the brittle and hard characteristics of glass materials. The transmission quartz glass gratings were etched using a femtosecond laser with wavelength of 1040 nm, repetition rate of 100 kHz, and pulse width of 388 fs. And the effects of laser power P, scanning speed v, and repeated scanning layer N on the etching depths and widths of quartz glass gratings have been investigated. Furthermore, the diffraction efficiency of the etched quartz glass grating sample was measured using a helium-neon laser (wavelength: 632.8 nm). The grating diffraction pattern was recorded by a CCD, and the diffraction efficiency was calculated using the gray-scale center of gravity method. In the experiment, under the condition that laser power was 442 mW, scanning speed was 380 mm/s, and scanning times was 10, the etched grating width d was 5.67 μm and the grating period D was 8.17 μm. The testing results show that the zero-order, positive first-order and negative first-order diffraction efficiency of the quartz glass grating are 24.98%,31.80% and 31.04 %, respectively.

In order to study the effect of height on the residual stress distribution in laser-deposited thin-walled parts, a fully coupled thermomechanical finite element model is built to simulate the temperature and stress fields in the laser-deposited 316L stainless steel thin-walled parts. The simulated results are compared with the experimental results to verify the model. The results show that as the height increases, the longitudinal stress distribution along the height direction gradually changes from uniformly distributed larger tensile stress to smaller tensile stress at the bottom and larger tensile stress at the top. The vertical stress at the boundary increases as the height increases, and the size of the zone with large tensile stress gradually increases. The longitudinal stress along the length decreases slightly as the height increases. The longitudinal stress in the lower layer gradually decreases due to thermal cycling caused by deposition. As the height increases, the vertical stress distribution at the bottom of the thin-walled part gradually becomes tensile stress at both ends and compressive stress in the middle, and the stress increases with the increase of height.

Laser cladding technology was used to prepare a Co-based alloy coating on a GCr15 bearing steel substrate. The microstructure, microhardness, and dry friction of the coating, and wear experiments were performed using various loads. The results show that the microstructure is in the form of plane, columnar, dendrite, and equiaxed crystals from the bottom to the top of the cladding layer. This is due to the solid solution strengthening of alloy elements, dispersion strengthening of carbide hard phase, and fine grain strengthening of microstructure, and the average microhardness of the coating is approximately 1.36 times higher than that of GCr15 bearing steel. With the increase of external load, the average friction coefficient of the laser cladding layer is increased, the friction coefficient decreases from 0.342 to 0.261, and the fluctuation amplitude decreases gradually, while the wear rate increases to 27.93 × 10-2 mm3·N-1·m-1. The wear mechanism of the coating varies with the load. The coating wears primarily due to abrasive wear and minor oxidation wear under a 150 N load. When the load increases to 300 N, the coating primarily wears due to oxidation and adhesive wear. For a 450 N load, the worn form of the coating is primarily due to microcutting and strong plastic deformation, with a smooth and flattening wear surface due to the formation of stable oxide enamel and work hardening layers.

Femtosecond laser micromachining is a manufacturing method that uses ultra-short pulse width and ultra-high energy laser to accurately remove materials. In this paper, considering the mutual temperature induction among the components of the face gear material 18Cr2Ni4WA, the energy coupling model of femtosecond laser ablation of face gear material is established, and the change process of electron temperature and lattice temperature under different energy densities is simulated and analyzed. The results show that electron temperature increases rapidly with the increase of laser energy density and is much higher than the lattice temperature. The laser with energy of 0.320-5.255 J/cm2 is used to observe the ablation morphology of face gear tooth surface and detect the tooth surface roughness. The results show that the ablation morphology is smooth and the minimumroughness is 0.265 μm, which is basically consistent with the simulation analysis results of the energy coupling model, and provide a basis for improving the research of face gear surface quality.

Aiming at the problem of short-term superhydrophilicity and long wettability transition period of laser etched metal surface, we optimized the laser etching parameters to construct micro/nano layered papillary structures on the surface of red copper, and manufactured the superhydrophilic samples. After being thermally oxidized for 3 h at high temperature under water vapor environment, the samples were annealed with ethanol for 15 min in a 150 ℃ tubular furnace. The water contact angle on the surface of the samples increased from (4.0±0.7)° before annealing to (150.7±0.6)° after annealing, and the sample surface changed rapidly from superhydrophilic to superhydrophobic, which greatly improved the wettability transformation efficiency.

In this paper, 316L stainless steel samples are fabricated by selective laser melting technology, and the microstructure of samples are analyzed by scanning electron microscope and optical microscope. The effects of laser power and line energy density (LED) on the upper surface morphology of the sample are studied. With laser power and scanning speed as input, the roughness of upper surface of forming samples are predicted based on genetic algorithm optimized back propagation (GA-BP) neural network, The experimental results show that the LED has a great influence on the surface morphology and forming defects of fabricated samples. When the LED is 240 J/m, the melt track is smooth and continuous. The mean absolute percentage error of the GA-BP neural network prediction model is 6.34%.

In order to improve the up-conversion fluorescence intensity of rare earth ions doped micro/nano materials, a series of NaYF4∶Yb3+, Tm3+ and NaLuF4∶Yb3+, Tm3+ microcrystals are synthesized by oleic acid and ethanol assisted hydrothermal method. The hydrothermal products are annealed at low temperature. At the same time, the morphology of the microcrystals is fine-tuned by controlling the doping amount of Yb3+ to achieve spectral regulation. The results of spectral studies show that the fluorescence intensity of the samples annealed at low temperature is significantly enhanced compared with that of the parent crystals. A series of NaLuF4∶Yb3+, Tm3+ microcrystals are synthesized by hydrothermal method using sodium citrate as surfactant, and the fluorescence intensity is further improved, and the fluorescence intensity increased with the increase of Yb3+ concentration. Subsequently, Ho3+ is introduced into the NaLuF4∶Yb3+, Tm3+ system to regulate the fluorescence color and luminous intensity by adjusting the doping amount of Tm3+ and Ho3+. The changes of fluorescence intensity and color under different doping amounts are studied by laser spectroscopy. Taking into account the excellent fluorescence properties of NaLuF4∶Yb3+, Tm3+, which is made for safety ink and applied to anti-counterfeiting, showing its potential application in the anti-counterfeiting field.

In order to study the high-temperature tensile properties of GH3039 superalloy treated by laser shock peening (LSP), the GH3039 superalloy samples are first peened by a high-energy laser beam. Then, the relaxation behavior of residual stress on the surface of LSP GH3039 after exposure at 600 ℃ for different time, the change in grain size of LSP GH3039 after exposure at 600 ℃ for 5 h, and the high-temperature tensile properties and fractures of GH3039 before and after LSP are compared and analyzed. The results show that after LSP impact, the grains in the near surface of GH3039 are significantly refined, and the residual compressive stress is found in the surface layer of the impact area at a depth of around 1.7 mm. After exposure at 600 ℃ for 5 h, the average grain size of LSP GH3039 increases from 20.5 μm to 28.8 μm, much smaller than the average grain size (47.9 μm) of the base metal. With the increase of exposure time, the relaxation rate of the surface residual stress of LSP GH3039 decreases, which shows a continuous decreasing trend. Compared with that of the base metal, the average ultimate tensile strength of the laser treated sample at 600 ℃ increases by 7.9%, which is attributed to grain refinement and residual compressive stress induced by laser impact treatment.

To explore the overall situation of terahertz wave inhibition of K562 cell viability gene expression and reveal its possible key signaling pathways. In this study, terahertz wave was used to intervene K562 cells, RNA sequencing technology was used to analyze the overall differences in gene expression changes, and bioinformatics method was used to analyze the enrichment and clustering characteristics of differentially expressed genes. Under certain conditions, 1131 differentially expressed genes were screened, among which 216 expressed genes were up-regulated and 915 expressed genes were down-regulated. The results of gene ontology enrichment analysis showed that differentially expressed genes were mainly concentrated in DNA-binding transcriptional activator activity, RNA polymerase-DNA binding, transcription factor activity, protein folding, covalent chromatin modification and histone modification, etc. The signaling pathway analysis results of Kyoto Encyclopedia of Genes and Genomes showed that the differentially expressed genes were mainly concentrated in mitogen-activated protein kinase, C-type lectin receptor, Notch, Janus-activated kinase singal transducers and activators of transcriprion and transforming growth factor-β signaling pathways which are closely related to the proliferation and apoptosis of K562 cells. The study has certain reference value for revealing the effect of terahertz wave on organism.

Combined with the high quality Fabry-Perot (F-P) optical microcavities, we studied the thermal stability of G-quadruplex DNA structure laser-based high resolution melting (HRM) analysis. DNA solutions with three different concentrations of K+, which corresponds to different thermostablility of the G-quadraplux DNA structure in the solution, are studied. Experimental results show that DNA structure with different K+ concentrations can be well distinguished by laser-based HRM curves. Further, by analyzing the laser thresholds of different DNA solutions at arbitrary temperature, it is found that the melting temperature of the curves can be well decreased by using a lower pump energy.

The holographic waveguide used in near-eye display technology is usually planar, making it difficult to fit the user's head. Although the holographic waveguide with a curved surface can better fit the curve of the user's head, its design is very difficult owing to the complex light transmission process in the waveguide. To establish the imaging design method of a curved holographic waveguide, the key transmission process of light in a curved holographic waveguide is analyzed, the ray-tracing mathematical model suitable for a curved holographic waveguide is proposed, and the ray-tracing algorithm for the light transmission process in a curved holographic waveguide is established. Then, the design of the curved holographic waveguide is realized. Based on the algorithm, the optical systems of spherical and cylindrical surface holographic waveguides are designed and the ray-tracing simulation is performed. According to the design results, the cylindrical curved holographic waveguide elements are fabricated and demonstrated in the optical system. The observation results verify the feasibility of the proposed method.

Double-telecentric lenses present the advantages of low distortion and large depth of field. Therefore, they are widely applied in the online detection of the machine vision industry. This study presents an optical design for a three-magnification double-telecentric system based on machine vision. The telecentric system is divided into objective and eyepiece parts by setting a refractive prism as the boundary. Different optical magnification in the original system could be realized by replacing the eyepiece, which ensures the applicability of the telecentric systems in outline and detail. In this study, we designed a three-magnification double-telecentric system with high definition and low distortion using the optics design software. In the proposed system, the working distance is 110 mm and the object fields of view are 100 mm and 25 mm. The optical magnifications are -0.11, -0.24, and -0.44. The system achieves low distortion (0.3 at 145 lp/mm). Additionally, it meets other design requirements. Furthermore, the relationship between fields of view and optical design is investigated.

In order to meet the needs of repair and surface modification of copper contacts in high voltage switchgears, carbon nanotubes (CNTs)/Cu composite coating is prepared on the surface of Cu substrate by laser-assisted low pressure cold spraying with CNTs as reinforcing phase and Cu as bonding phase. First, the surface of CNTs is metallized by electroless-plating of copper to improve the density of CNTs and the interfacial bonding between CNTs and Cu. Then, the spraying distance, scanning speed, and laser irradiation power are optimized. Finally, the microstructure of the composite coating is analyzed by energy dispersion spectroscopy (EDS) and scanning electron microscope (SEM). The results show that the interfacial bonding between the coating and the substrate is the best when the spraying distance is 15 mm. With the increase of scanning speed, the internal of the coating has relatively good compactness and coating/interface bonding state, and the surface of the coating is smooth. With the increase of laser irradiation power, the thickness and width of the coating first increase and then decrease, and the coating thickness reaches the maximum at 800 W. Due to the softening effect of laser heating and the protective effect of copper films on the surface of CNTs, CNTs can be evenly dispersed in the composite coating and maintain the structural integrity.

We quantitatively investigated the effect of wavelength, core radius, and shell thickness on the photothermal properties of a single Au nanoshell using Mie theory, a size-dependent dielectric function, and heat equation to determine the maximum surface temperature change and optimal particle size under continuous laser excitation. First, the intensity and position of the resonance peak can be adjusted by changing the core radius and shell thickness of the Au nanoshell. The required particle surface temperature variation also can be obtained. Then, the maximum particle surface temperature change per unit incident light intensity γmax at four typical wavelengths (800, 808, 820, and 1064 nm) in the near-infrared region and the corresponding optimal particle size is obtained to analyze the application of the photothermal properties of the particles. Finally, the particle size distribution with a particle surface temperature change per unit incident light intensity greater than 0.9γmax at the above wavelength is given. This research is essential for photothermal therapy, plasmonic-assisted photocatalysis, and particle synthesis.

The research of optical angular momentum and spin-orbit coupling under non-paraxial conditions will help people understand the phenomenon of light in sub-wavelength structures. The evanescent wave in the near field may produce strong spin-orbit coupling. In this paper, based on the angle spectrum diffraction theory and Parseval theorem, the near field evolution characteristics of propagating waves, evanescent waves and angular momentum of Laguerre-Gaussian vector vortex beams on high-order Poincaré sphere are analyzed in detail, as well as the spin-orbit coupling caused by evanescent waves. The results show that the evanescent wave action near the source plane of the beam with sub-wavelength waist width is strong, and dominates the total optical field. Moreover, the orbital angular momentum contains the contributions of both the transverse and longitudinal electric fields in the near field, and the transverse spin angular momentum in the evanescent wave is related to the transverse polarization state, furthermore there is a phenomenon of spin direction locking. The research provides a theoretical support for the study and application of vector vortex beams in sub-wavelength structures.

In this paper, based on the frequency selection surface (FSS) of the traditional resonant split ring, on the basis of the finite element method and the semi-resonant ring periodic aperture structure, the Floquent period condition is used to simulate the infinite space element, and the scattering parameter and bandpass characteristics of the structure are obtained through the frequency domain solver. The shape of the structural unit is expanded to a crescent-shaped double-layer structure with reverse openings on the upper and lower surfaces, and the FSS of a multilayer semi-resonant ring coupling structure with a flat top transmission passband is optimized. The simulation results show that when the transverse magnetic wave is incident vertically, the resonant frequency of the semi-resonant ring structure is stable at 9 THz, the return loss at the center frequency is -22 dB, and it has good angular stability. The double-layer crescent-shaped structure can achieve multiple narrowband passbands at the resonance points of 5.9 THz, 10 THz and 11.7 THz, respectively. The multi-layer FSS structure has a transmission coefficient of less than -3 dB in the frequency range from 6.35 THz to 9.35 THz, and has good polarization stability. It provides a theoretical basis and technical support for the applications of FSS in the fields of terahertz non-destructive testing, communication and sensing.

The sag of high-voltage transmission lines is an important indicator for the lines design and operation. Moreover, it is related to the safety of the lines operation and is controlled within the range specified by the design. Transmission lines sag measurement is a key research topic for domestic and international power departments and research organizations. In this paper, a capillary fiber-based high-voltage transmission lines sag sensor is designed. The sensor has advantages of a large mode area, strong anti-electromagnetic field interference ability, and real-time online monitoring. The experimental results show that when the sag radius of the sensor is less than 15 cm, the monitoring sensitivity is 2.552 dB/cm, and the linear correlation coefficient is 0.9635. The higher the sensitivity of the capillary fiber optic sensor, the smaller the sag curvature radius of the sensor and the greater the bending degree. The experimental phenomenon is consistent with the theoretical analysis results, indicating its practical applicability.

The temperature-pressure cross-sensitivity problem in a frequency-modulated continuous-wave (FMCW) interference fiber pressure sensor is addressed in this study using a real-time temperature drift compensation method. The reference and pressure sensors are bonded and placed in the same temperature field. The temperature drift correction principle is evaluated using the relationship between the cavity length changes of the two sensors and the temperature. Further, the temperature drift of the pressure sensor is corrected in real-time using the temperature drift compensation method. The experimental results show that the pressure measurement error of the method decreases from 9.21% to 0.32% in the heating process, the pressure measurement error decreases from 3.33% to -0.24% in the cooling process, and the pressure drift of the pressure sensor is less than 0.1 kPa within 60 min of cooling. The temperature compensation method significantly improves the measurement accuracy of the FMCW interference fiber pressure sensor.

Aiming at the low positioning accuracy of distance vector hop (DV-Hop) algorithm in wireless sensor networks, a DV-Hop positioning algorithm based on double communication radius and improved gray wolf algorithm is proposed in this paper. First, the position of the beacon node is broadcast with the double communication radius, and the hop number between the beacon node and the unknown node is obtained, so as to get the distance between the beacon node and the unknown node. Then, an improved gray wolf algorithm is used to estimate the location of unknown nodes. Simulation results show that the improved DV-Hop algorithm has better positioning accuracy and stability than the traditional DV-Hop algorithm and similar algorithms.

The propagation of intense femtosecond laser pulses in atmospheric air can lead to a channel with high laser intensity, high plasma density, and capability for remote generation and control, namely filament. When the filaments interact with the materials, high laser intensity can excite the materials and induce the finger-print fluorescence of the materials. Supercontinuum can also be generated during filamentation which can cover the entire atmospheric optical transmission windows. The supercontinuum provides an idea source for sensing multiple atmospheric components through differential optical absorption spectroscopy. Intense femtosecond laser filamentation provides a new approach for atmospheric sensing of multiple phases and multiple components. In this paper, we focus on the new atmospheric sensing techniques based on intense femtosecond lasers, namely, remote femtosecond laser filament induced breakdown spectroscopy and filament induced supercontinuum Lidar. The working principles, the methods for spectral measurement and analysis as well as the recent research progress are briefly reviewed. Finally, the scientific and technique problems and future development of intense femtosecond laser remote atmospheric sensing are discussed.

At present, most of the wireless solutions applied in various medical scenarios are based on the conventional radio frequency technology paradigm, which have to face several potential risks, such as electromagnetic interference and medical data leakage. On the other hand, wireless optical technology has many inherent advantages, such as abundant spectrum resources, high security, anti-electromagnetic interference, and no spectrum regulation. Therefore, for sufficiently illustrating the potentialities of this technology, the academia and industry are actively incorporating various wireless optical schemes into electromagnetic sensitive medical scenarios from multiple dimensions. In order to clearly present the state of art of the wireless optical application in medical scenarios, this paper sorted out the medical wireless optical active links, the passive links, the relay links, and the relevant experimental prototypes. In addition, the main technical challenges and potential solutions for the further development of healthcare wireless optical technology are presented.

The performance of indirect X-ray detector (IXD) has been improved with the gradual improvement of imaging requirements in medical diagnosis, industrial non-destructive testing, safety monitoring, and scientific research, which promotes the further development of low radiation dose, high resolution, and fast real-time X-ray imaging detection technology. As the core devices of IXD, scintillation screen and image sensor have developed rapidly with the progress of scintillator materials, semiconductor manufacturing process, and integrated circuit technology. In order to realize the effective transmission of image between scintillation screen and image sensor, three coupling modes are usually adopted: fiber coupling, optical lens coupling, and direct coupling. This paper mainly introduces the research progress of scintillation screen and image sensor, as well as the structure and characteristics of the three coupling modes, and prospects the future development trend of IXD.

Variation of light extinction properties of monodisperse Au-Ag alloy nanospheres with particle size and wavelength are analyzed based on Mie theory. In the theoretical calculations, the dielectric function of Au-Ag alloy nanoparticles is corrected for the effect of the reduced mean free path of the free electrons in metal nanoparticles. Three fitting equations for determining particle size and concentration methods based on the extinction properties are proposed in this paper, including resonance wavelength method, dual-wavelength extinction method, and improved dual-wavelength extinction method. The results show that as long as the extinction spectrum of the particles is measured, the particle size and concentration can be retrieved by using the fitting equations. In addition, comparing the sensitivity and the particle size range of three methods are found that the resonance wavelength method is easier and faster than other methods.

To establish the near infrared measurement model of nicotine content in e-liquid, 63 samples with different nicotine contents and tastes were collected. After eliminating the abnormal samples via Monte Carlo cross validation, the interval partial least squares (iPLS), and synergy interval partial least squares (SiPLS) methods were used to select the optimal wavelength, and subsequently, the correction model was established. The results show that iPLS identified the characteristic wavelength bands of 1090?1228 nm and 1370?1508 nm. By combining the different bands, SiPLS determined the optimal bands as 1126?1240 nm, 1358?1414 nm, and 1474?1530 nm. When compared with the full-spectrum PLS model, the variables used in the SiPLS-PLS model reduced by two-thirds and the mean square error of prediction value reduced from 1.188 to 0.963; thus, improving the accuracy of the model.

A structure of the front semicircle and rear trapezoidal dual-interface grating monocrystalline silicon thin film solar cell was designed. The structure and the control group were simulated by the finite-difference time-domain method. It is shown that the dual-interface has better light-trapping performance than the single-interface grating structure by analysis of the short circuit current density and absorption spectrum. The absorption enhancement mechanism of the structure at long wavelength (750-1100 nm) was analyzed by using electromagnetic field distribution. In addition, for the front semicircle rear trapezoidal grating structure, the left and right slope of rear trapezoidal grating and the offset degree of front and rear gratings under the same period are further optimized. The results show that the irregular trapezoidal gratings have better light-trapping performance, and through the absorption efficiency cloud diagram, the best effect can be found when the offset degree is at 40 nm. The optimal short-circuit current density reaches 20.17 mA/cm2, which is 58.1% higher than the planar structure by calculation and analysis. The research results have certain guiding significance for the grating structure design of thin film solar cells.

In this paper, a design method of multi-focal intraocular lens is proposed. Dammann zone plate, which consists of a series of concentric rings, is a practical optical element which introduces the phase modulation idea of Dammann grating into the traditional band plate. Through modulating the diffraction order, it can produce a series of axial focal spot distribution in the light field behind the focusing lens. Moreover, by combining the focusing lens with different numerical apertures, the intensity distribution of the focal spot will also change to a certain extent. Through theoretical simulation and experimental verification, it provides an effective design method for fabrication of multi-focus intraocular lens. The multi-focus intraocular lens has five focal points, which can improve cataract patients' vision at different distances simultaneously and provide them with clearer and more detailed images.

Aiming at the problem that the accuracy of the traditional Kubelka-Munk(K-M) theory spectral prediction model is not ideal when performing offset printing spot color ink spectrum prediction, a color spectrum prediction method for offset printing spot color ink is proposed by constructing a base ink database based on piecewise linear interpolation method, combined with modifying the K-M model with the Stearns-Noechel(S-N) transfer function. The study used 64 spot colors obtained by mixing a certain series of spot color inks of Siegwerk brand as the target color samples for training, carried out two-color, three-color, and four-color mixed spectrum prediction research respectively, and obtained three quantities of primary color inks when mixed . The optimal paper-based weights are -0.5, -0.1, 0.2, respectively. Bringing the best paper-based weight into the prediction model, and using CIE1976 color difference, CIEDE2000 color difference and root mean square error(RMSE) as evaluation indicators, two, three, and four-color spot colors with known formulas were randomly selected for accuracy testing experiments. The experimental results show that compared with the traditional K-M method, the CIE1976 color difference, CIEDE2000 color difference and RMSE of the method proposed in this study are reduced from 5.748, 3.471 and 0.048 to 2.077, 1.441 and 0.011, respectively. Compared with the traditional K-M method, the prediction accuracy of this method is greatly improved, and it can better realize the spectrum prediction of the mixed color of offset printing ink with higher accuracy.

In this paper, the sound-light fusion effect has been studied based on physiological parameters and subjective emotional changes. The influence of western major music, western minor music, 3 kinds of monochromatic lighting (wavelengths of 623, 537, 445 nm) and 2 kinds of white lighting with different color temperatures (color temperature of 3000, 6000 K) on the human body is systematically discussed. The experimental results show that people's physiological response to music is stronger than that of the lighting stimulus. The physiological perception under dual-factor stimulation is stronger than that of single-factor, and sound plays a major role in the sound-light fusion environment. Music and light interact when they stimulate emotions at the same time. The superposition of two positively related emotional environmental factors can strengthen the effect on emotions. It provides theoretical support and opinions for the design of music and light show or immersive interactive lighting.