In numerical and experimental analyses, we studied the effect of misaligning the cylindrical mirror rotation in shaping system on the far-field spot and beam quality of the laser during beam shaping based on Huygens--Fresnel diffraction theory. Increasing the rotation angle not only rotated and tilted the far-field spot of the shaping beam, but also elongated and defocused the spot. This aberration derives from the superposition of astigmatism and defocusing caused by rotating the cylindrical mirror. The results show that misaligned rotation also defocuses the shaping system with cylindrical mirror. We then quantitatively analyzed the correlation among the normalized phase coefficient and focal spot, in which the normalized phase coefficient is related with the center wavelength of the laser, size of the shaping beam, distance of the cylindrical mirrors and magnification factor. From the correlation coefficient, we can evaluate the sensitivity of the shaping system to the cylinder-mirror rotation disorder. Finally, we verified our calculated results using a corresponding experimental device. The experimental results agreed well with the calculated results.

The basic working principle and mathematical model for a fast-steering mirror driven by PZT, which is a type of mirror widely used in optical-axis control systems, are analyzed, and the identification process of genetic algorithms in the model is described. A system for measuring the frequency response of a large-aperture fast-steering mirror driven by PZT is set up to realize parameter identification for the transfer function. The frequency response of the identified transfer function and the actual measured data are compared, and the identification accuracy of multiple resonance points in the system is analyzed. The experimental results show that at each resonance point, the frequency response of the transfer function obtained by the genetic algorithm is consistent with the measured data. The results also show that the transfer function obtained by this algorithm can analyze the dynamic characteristics of optical axis control system more accurately, and we can design advanced control algorithm, thus improving the performance of the optical-axis control system.

In order to meet the control requirements of the surface accuracy and structural stability of large aperture mirrors for laser devices, a multi-point mounting method with decoupling of multiple degrees of freedom of the mirror is proposed. The control of multiple degrees of freedom of mirror is realized by limiting position to avoid the additional surface shape caused by mounting. The effectiveness of the proposed method has been analyzed by finite element method, and the feasibility of the analysis method and the mounting method has been verified through experiments. The results show that the additional surface shape brought by the mounting method of the mirror is small, which meets the requirement of the low-stress additional mounting surface of the mirror. On the basis, the surface shape of the mirror placed at a tilt angle of 45° is simulated, and the influences of the position distributions of different mounting points on the surface accuracy of the mirror are explored. Simulation results show that in order to ensure the surface accuracy of the mirror, at least one mounting point should be located on the longer side of the mirror. These results have important guiding significance for the mounting design of large aperture mirrors.

Fluorescence immunochromatographic quantitative detection technology has been widely used in the field of clinical detection, such as for the screening and detection of the new coronavirus pneumonia. To improve the detection accuracy, a fluorescence immunochromatographic quantitative detection method based on fluorescence microscope digital image processing is proposed. Initially, the luminous flux loss equation of the microscopy system is constructed. Then, the RGB components in the original image are extracted according to the digital image features output by the area array CCD, and the quantum response rate curve of the area array CCD is fitted after weighting to compensate. Finally, the relative intensity of the fluorescence signal is obtained, and the concentration of the analyte is inversed according to the intensity of the fluorescence signal. After experimental verification, it can be observed that the coefficient of variation of the test results is 3.04%, and the linear fitting coefficient is >0.99. This detection method can accurately detect the analyte with a minimum mass concentration of 0.1 ng/mL. It is suitable for CCD imaging fluorescent microscope system and has certain reference significance for fluorescence detection.

Intravascular optical coherence tomography (IVOCT) is of great significance for early diagnosis of cardiovascular diseases and imaging probes are the core components of IVOCT systems. For this purpose, an IVOCT probe driven by a miniature propeller was proposed in this paper. Instead of using electric devices such as micromotors that provided power for beam scanning in traditional endoscopic probes, the probe utilized the kinetic energy of the fluid that flushed away the blood in the imaging of the IVOCT system to drive the propeller installed at the probe end, thereby driving the right-angle prism on the propeller shaft to rotate and realizing the scanning imaging of beams for the vessel walls. Moreover, we improved the driving efficiency of fluid by optimizing the design of the propeller. For the probe, the outer diameter is 1.5 mm and the highest scanning speed can reach 491 r/s. Finally, the imaging ability of the IVOCT system integrating the probe was well verified by the clear tomographic images of the samples like white tapes, green onion tubes, and in vitro artery vessels of chicken hearts.

An innovative joint estimation algorithm for coherent optical filter bank-based multicarrier systems with offset quadrature amplitude modulation was proposed. The training sequence design enables simultaneously time synchronization and channel estimation. Thus, the proposed algorithm effectively improves spectral efficiency. First, the conjugate symmetry condition of the time domain waveform was derived from the system model. Based on the derived condition, a time synchronization method was proposed. The proposed method combines the pseudo-random sequence with conjugate symmetry to improve time synchronization accuracy. Then, channel estimation was performed based on the principle of dual-dependent pilots. The method avoids the impact of intrinsic imaginary interference and maintains the conjugate symmetry of the time domain waveform. Finally, numerical simulations were performed to investigate the system''s transmission performance. The simulation results demonstrate that the proposed algorithm can effectively accomplish joint estimation of the time offset and channel response.

A vector system that uses a single laser source and a dual-polarized Mach-Zehnder modulator (MZM) to generate two channels of optical radio frequency signals at different frequencies is experimentally studied. Using the optical subcarrier multiplexing technology, two channels of quadrature phase shift keying (QPSK) signals can be carried by two optical subcarriers with different frequencies based on a modulator and an optical carrier. The polarization multiplexing technology is used to overcome crosstalk of optical signals with different frequencies, and the signals can be successfully transmitted over an 80-km-long single-mode fiber (SMF). In the experiment, 15- and 30-GHz QPSK signals are modulated using a dual-polarized MZM based on a single sideband modulation format. After the 80-km SMF transmission, the 15-GHz QPSK signal transmission performance is better than that of the 30-GHz signal. When the input power of a photodetector (PD) is more than -10.2 dBm, the bit error rate (BER) of a system after demodulation is less than 3.8×10 -3. The system has the advantages of simple structure, low complexity, and few electrical and optical devices, which effectively reduce cost and play a considerable role in the development of future access networks.

In order to overcome the influence of atmospheric turbulence and mechanical platform vibration in free space optical communication system, a nutation coupling scheme based on peak power feedback and fast mirror is proposed in this work, and the nutation experimental platform is built. A sine disturbance of a certain frequency and amplitude is introduced through a fast reflector to conduct a dynamic tracking experiment. The results show that the maximum coupling range of the system can reach 1.1 mrad when the coupling efficiency is not less than 55% in the tracking state. At the same time, the designed tracking algorithm can correct the large disturbance and reduce the mean square error of the received optical power of the detector from 9.91% in open-loop to 0.81% in closed-loop. The nutation coupling efficiency of the system under different signal-to-noise ratios is tested. The results show that the coupling efficiency decreases with the decrease of signal-to-noise ratio.

In this paper, a low crosstalk 3-LP mode 12-core fiber based on heterogeneous structure is designed. The core adopts a heterogeneous ring refractive index distribution without trench-assisted structure, which is simple in structure and can increase the effective mode area of the core. COMSOL software is used to analyze the performance of crosstalk and effective mode area of heterogeneous cores. The results indicate that the inter-core crosstalk of the heterogeneous core LP01, LP11, and LP12 modes are lower than -0.78, -0.66, and -0.4 dB/km, respectively, and their effective mode areas are 150, 166, and 200 μm 2, respectively. With a square lattice core arrangement, a low crosstalk 3-LP mode 12-core fiber design with a cladding diameter of about 213.8 μm and a relative core multiplexing factor of 26.9 can be realized, providing device support for the upgrade and expansion of communication capacity.

This study introduces an end-to-end communication learning system based on a generative adversarial network (GAN) after discussing the advantages of laser link communication. This improves the real-time and global optimization of the communication system. Moreover, this study introduces the Wasserstein GAN to resolve mode collapse and training instability in the training and application of a traditional GAN. Finally, the Wasserstein GAN is applied to the end-to-end communication system, and the experimental results show that the Wasserstein GAN can effectively simulate an additive Gaussian white noise channel and a lognormal channel, thus avoiding the training instability and mode collapse of the traditional GAN.

Taking the shape perception and visualization reconstruction of the structure in the spacecraft as the research background, a plate-shaped structure deformation monitoring system based on a quasi-distributed fiber Bragg grating sensor network and a coordinate conversion surface reconstruction algorithm are proposed. First, the finite element analysis software ABAQUS is used to simulate and analyze the deformation state of the four-side fixed plate structure, and the position of the fiber grating sensor is determined. Then, the strain detection principle of the fiber Bragg grating and the three-dimensional surface reconstruction algorithm based on coordinate transformation are studied and analyzed. Finally, a set of deformation detection systems is built, and relevant experiments are carried out. The results show that the root mean square error of the shape variable of the measured point is no more than 0.04 mm, and the relative error is no more than 3.5%. The system can be applied to the deformation detection of the plate structure in the spacecraft.

For investigating the fuel spray characteristics of the nozzle designed for the aero-engine, the off-axis particle field holographic measuring system is used on an engine test-bed. The spray structure, atomized particles locations, amounts, and sizes distribution in space under different experimental conditions are obtained quantitatively. Experimental results show that under normal temperature and pressure conditions, the atomization field formed by this type of nozzle is distributed in a hollow cone. The atomized particles are concentrated on the surface of the cone. The diameter of the particles is mostly between 60 μm and 80 μm, with the distance from the nozzle increases, the particle diameter decreases and approaches the same, showing a uniform atomization effect. When the injection pressure is low, a vortex ring similar to the mainstream ring appears downstream of the dense vortex ring near the nozzle area. As the injection pressure increases, the number of vortex rings near the nozzle is reduced, the ripples and filaments of the liquid film are increased, and the mainstream ring is not observed downstream. The atomization structure on both sides of the jet is not completely symmetrical. Under the working conditions of 800 K and 5.5 kPa high temperature pure air flow, the average diameter of atomized particles in the combustion chamber is reduced to about 12 μm, and the atomization quality is significantly improved.

In order to obtain pulse lasers with narrow pulse width, good waveform symmetry, and stable output performance, a 1064 nm double passively Q-switched laser based on graphene quantum dots and molybdenum disulfide was designed. The laser used a simple linear cavity structure, with 808 nm LD as the pump source and Nd∶YVO4 as the gain medium. Graphene quantum dots and molybdenum disulfide were obtained by hydrothermal method and lithium-ion intercalation method respectively. Saturable absorbers were prepared through spin coating and drying process, which were used as passively Q-switched devices. Compared with the single passively Q-switched laser, the output pulse width of the double passively Q-switched laser was narrower and the pulse waveform symmetry was better. When the pump power was 12.9 W, the pulse width of Q-switched laser was 180 ns, the repetition rate was 1085 kHz, the signal-to-noise ratio was 44 dB, and the average output power was 595 mW.

In order to study the new wavelength output of the alkali metal rubidium vapor laser and its possible applications, the two-photon excitation and four-wave mixing process of 5 2S1/2→6 2D5/2 and 5 2S1/2→6 2D3/2 in the rubidium atomic system produced laser output with four wavelengths of 358.7 nm, 359.1 nm, 420.3 nm, and 421.7 nm, obtained the best resonance position and resonance linewidth of 6 2D5/2 and 6 2D3/2 energy levels, and studied the generated four-wave mixing laser. The signal intensity changes with the temperature of the system and the energy of the single pulse of the pump light. An abnormal transition of 6 2D5/2→6 2P1/2 is found when the system temperature is higher than 185 ℃ and a preliminary explanation is given. Experimental results show that this technology of generating blue-violet lasers through four-wave mixing of rubidium vapor can provide a new laser source for marine resource exploration, high-density information storage, and underwater laser communications.

Herein, an FV520B steel joint is formed through laser backing welding and cold metal transfer (CMT) filler welding. Microstructures and properties of the joints at different processing parameters are studied. Microstructures of the fusion zone (FZ) obtained using laser backing welding mainly comprise lath martensites, which are arranged in a parallel form in the primary austenite grains, and δ ferrites, which are situated at the primary austenite grain boundaries and lath martensite interfaces. Some continuous and discrete δ ferrites are located at the fusion line of laser welding. The weld width, weld penetration, and the width of heat-affected zone (HAZ) increase with the increase of the heat input of the CMT filler welding. Moreover, the microstructural characteristics of the HAZ and FZ of laser backing welding gradually disappear. When the heat input of CMT filler welding is lower, the grains in the heat-affected laser welding fusion zone (HALWFZ) close to the filler welding fusion line exhibit an equiaxed shape because of the high temperature reheating. Furthermore, the size of the equiaxed grains decreases with the increase of distance to the filler welding fusion line. When the heat input of CMT filler welding is higher, the columnar grain microstructures in the laser welding fusion zone transfer into the larger equiaxed grains. Compared with the single laser welding, the hardness of the weld cross-section exhibits more uniform distribution in the horizontal direction after the filler welding. With the increase of heat input of filler welding, the average hardness of HALWFZ initially increases and then decreases. The average hardness of the filler welding fusion zone (FWFZ) is lower than that of the laser welding fusion zone (LWFZ). Moreover, the average hardness of the LWFZ presents the lowest value in the vicinity of the filler welding fusion line. After filler welding, the strength of laser backing welding area is higher than that of the base metal, whereas the strength of filler welding area is lower than that of the base metal. The impact toughness of laser backing welding area increases with the heat input of filler welding. Electrochemical corrosion results show that with the increase in the heat input, the corrosion potential of LWFZ initially increases and then decreases. The LWFZs before and after filler welding both exhibit a superior corrosion resistance than the base-metal substrate.

Substrates of 30CrMnSiA and 30CrMnSiNi2A high-strength steels were repaired by a multilayer laser-cladding process using 30CrMnSiA alloy powders. The microstructures and mechanical properties of the cladding layers, substrates, and heat-affected zones were analyzed. The cladding layers on both the 30CrMnSiA and 30CrMnSiNi2A substrates exhibited a mainly sorbite microstructure. As the number of cladding layers increased, the sorbite and martensite contents on the 30CrMnSiA substrate decreased and increased, respectively, and a mainly martensite microstructure was observed in the cap layer. In the heat-affected zone (HAZ) of the 30CrMnSiA substrate, the microstructure was mainly martensite and small amount of blocky ferrite, and the ferrite was identified as the unmelted phase of the original ferrite matrix. In contrast, as the number of cladding layers on the 30CrMnSiNi2A substrate increased, the martensite content gradually increased, but sorbite remained the dominant microstructure. In the heat-affected zone of the 30CrMnSiNi2A substrate, the microstructure was mainly sorbite and coarse-grained martensite. The mechanical properties of the high-strength steels were also analyzed. The microhardness values were larger in the cladding layer on the 30CrMnSiA substrate than those on the 30CrMnSiNi2A substrate, and the softening phenomenon of the heat-affected zone was more obvious on the 30CrMnSiNi2A substrate than that on the 30CrMnSiA substrate. The tensile strength of the cladded sample on 30CrMnSiA substrate was over 90% of the substrate, and the impact toughness and elongation of the cladded samples were better than those of the 30CrMnSiA substrate. On the 30CrMnSiNi2A substrate, the cladding improved the impact toughness but significantly reduced the tensile strength and elongation. The results confirmed the suitability of 30CrMnSiA powders for laser-cladding repair of 30CrMnSiA steel. However, when the powders were used to repair 30CrMnSiNi2A steel, the heat input of the multilayer laser-cladding must be lowered to reduce the width of heat-affected zone, the formation of coarse-grained martensite, and the matensite decomposition.

Dynamic compression tests with a high strain rate (1000--4200 s -1) were carried out on the as-deposited and heat-treated samples of AerMet100 ultrahigh strength steel fabricated by laser additive manufacturing using a split Hopkinson pressure bar (SHPB), and the microstructures and impact fractures of the samples were observed. The results show that the strain rate sensitivity of the AerMet100 steel samples fabricated by laser additive manufacturing is high, and the strain rate hardening effect of the material is obvious. Heat treatment can improve the dynamic impact performance of the laser additive manufactured AerMet100 steel. After solid solution treatment at 885 ℃ for 1 h, oil quenching, cryogenic treatment at -73 ℃ for 1 h, and tempering at 482 ℃ for 5 h, the AerMet100 ultrahigh strength steel samples fabricated by laser additive manufacturing show the optimal combination of strength and toughness and an excellent dynamic impact performance. When the tempering temperature increases to 494 ℃, the dynamic compression strength of the samples decreases.

To study the effect of energy ratio coefficient (the ratio of laser power to arc power) on pores during the aluminum alloy laser-MIG hybrid welding process, 6 mm thick 6061 aluminum alloy laser-MIG hybrid welded joints were measured using X-ray nondestructive testing and metallographic microstructure observation. Pores under the energy ratio coefficient of 4.0, 3.5, and 3.1 were analyzed. It was observed that the laser power has a significant effect on the bottom weld width in the cross-setion of the weld and increasing the arc power can effectively deepen the hybrid zone. Under the higher-energy ratio coefficient, the diameter of the pores inside the weld is larger, but the number of pores is smaller, contributing to low porosity. The pores in the weld cross-section are mainly distributed in the upper part of the weld and less in the lower part. However, when the energy ratio coefficient is reduced to 3.1, the distribution of pores tends to be uniform, the number of pores in the lower part significantly increases, and the number of process pores increases. These results show that increasing the energy ratio of laser power during laser-MIG is beneficial to reduce the porosity.

In this study, the Cu-Hf alloy and low carbon steel are respectively welded using a high-power fiber laser. The morphological characteristics of keyholes obtained by freezing and preserving the keyholes in a molten pool are compared. The results show that the keyholes can be retained in both materials, and the diameter of a keyhole is obviously greater than that of a spot. The shape of the keyhole retained in the Cu-Hf alloy is similar to that of a “gourd” with the intersection of big and small rings. The diameter of the small ring located in front of the welding direction is equivalent to that of the spot, and the diameter of the large ring is in the order of a millimeter. In low carbon steel, the laser output time to retain a keyhole is very short, the solidation time of the molten pool is long, and only the large circle area of the keyhole can be retained. Further analysis shows that a keyhole morphology can be divided into two parts: the laser direct-action area and vapor pressure maintaining area. In numerical simulations, the morphological characteristics of a keyhole must be considered when building a suitable heat source model for laser welding.

A local shielding gas model is proposed herein to address the easy oxidation of titanium alloys during the laser cladding process in an open environment. The effective protection ranges provided by the local shielding gas nozzle under different gas flow rates are analyzed with the Fluent software, and the mathematical model of the effective protective length of the airflow is established through the third-order polynomial fitting. Then, the response surface method is used to establish the quadratic regression model between the process parameters, including the shielding gas flow and the length of the high-temperature region to be protected during the laser cladding. The local shielding gas model for titanium-alloy laser cladding in an open environment is established through the analysis of the above two models. The single-pass cladding layer obtained through the verification test exhibits a good morphology and a bright-silver metallic luster on the surface, indicating that the molten pool and its surrounding high-temperature area are effectively protected during the cladding process. The local shielding gas model established can be used to guide the selection of the shielding gas flow rate required in the laser cladding process in an open environment.

In an effort to resolve the biocompatibility problems of Zr-based bulk metallic glasses in biomedical applications as implant materials, a nanosecond laser was employed to produce dimple and groove textures on a Zr sample surface. The biocompatibility characteristics of the sample surface were evaluated by a cell viability test, cell alignment, and morphology observation. Moreover, the surface modifications induced biocompatibility enhancement mechanism were discussed from the perspective of the surface morphology evolution. The results show that, compared with an untreated sample, the laser-induced groove pattern could significantly enhance osteoblast adhesion on the sample surface and cell viability, which is mainly attributed to the remarkably improved surface roughness. However, the modification effect of the laser-induced dimple pattern on cell viability was undesirable. In addition, the laser-induced grooves and the micro-nanostructures attached in the grooves are the main reasons why the osteoblasts are distributed along the groove direction in or around the grooves.

We have experimentally implemented a difference-frequency-generated mid-infrared (MIR) source based on synchronously pulsed pumping. The passive synchronization between polarization-maintaining Er- and Yb-doped mode-locked fiber lasers was realized by using all-optical modulation technique via master-slave injection. By combining spectral broadening of highly nonlinear fiber and wide-band tunable filter, we could obtain broadly tunable MIR picosecond laser from 2940 nm to 3260 nm. The average power was 580 mW to 926 mW,and the maximum pump conversion efficiency was 41%. In the experiment, the injection of low-power synchronous induced pulses could substantially reduce the pumping threshold for the MIR parametric generation, which would relax the requirement of strong pump field to realize efficient MIR generation.

Low dispersion mirrors with broad bandwidth and high damage threshold are indispensable optical components in a petawatt (PW) laser system. Here, we systematically investigate the optical properties, dispersion characteristics, damage resistance characteristics and damage mechanisms of metal-dielectric mirrors, dielectric mirrors and ternary composite mirrors. The dielectric films can improve the damage thresholds of metal films. The transmission efficiency and damage threshold of silver-dielectric mirrors are higher than those of Au and Al. The typical damage morphology of near threshold metal-dielectric mirrors under the action of femtosecond lasers is bulge, and the reason is that the metal layer absorbs a lot of energy and causes the thermal stress damage. In ternary composite mirrors, the existence of the protective HfO2 layers makes the electric field in Ta2O5 decrease, the initial damage layer is transferred to HfO2, and the threshold increases without sacrificing reflection bandwidth and dispersion performance.

Herein, a dual-lens laser profile measurement method was proposed to solve the problem of light stripe occlusion in the single-lens laser triangulation method. First, we experimentally observed and explored the distribution of light stripe in the sensor and its reasons for the formation. Moreover, we analyzed the surface morphology of the object, the relation between the optical system and light stripe distribution, and the light stripe distribution effect on three-dimensional reconstruction. Then, based on the direct incidence laser triangulation principle, a dual-lens measuring system was designed. Morphological processing combined with a gray-scale centroid method and other algorithms was used to extract the center coordinates of the light stripe. Finally, the dual-lens data were fused based on the minimization of variance. Experimental results show that the proposed dual-lens can solve the problem of large-area morphology loss caused by light stripe occlusion and reconstruct the complete envelope of the object's surface morphology. Furthermore, the associated data loss ratio was less than 0.5%.

In the study, a method to analyze the effect of position sensitive detector (PSD) on the performance of laser tracing measurement system is proposed. The PSD measurement principle is analyzed, and the PSD measurement model is established in the laser tracing measurement system. A simulation model of the laser tracking measurement system is built using Matlab/Simulink software, and the influence of the displacement voltage conversion coefficient of PSD on the performance of the laser tracing measurement system is simulated and analyzed. Simulation results show that when the displacement voltage conversion coefficient αp is 1000 m/V, the response time of PSD is short, the overshoot of the dynamic response of the laser tracing measurement system is low, the stability time is short, and the dynamic overshoot error is small. Experimental results show that the greater the αp, the greater the voltage error output by the PSD photoelectric conversion circuit, and the greater the impact on the performance of the laser tracing measurement system. When αp=1000 m/V, the error of the output voltage of the PSD photoelectric conversion circuit is the lowest, and the stabilization time is the shortest.

Herein, a dual-lens laser profile measurement method was proposed to solve the problem of light stripe occlusion in the single-lens laser triangulation method. First, we experimentally observed and explored the distribution of light stripe in the sensor and its reasons for the formation. Moreover, we analyzed the surface morphology of the object, the relation between the optical system and light stripe distribution, and the light stripe distribution effect on three-dimensional reconstruction. Then, based on the direct incidence laser triangulation principle, a dual-lens measuring system was designed. Morphological processing combined with a gray-scale centroid method and other algorithms was used to extract the center coordinates of the light stripe. Finally, the dual-lens data were fused based on the minimization of variance. Experimental results show that the proposed dual-lens can solve the problem of large-area morphology loss caused by light stripe occlusion and reconstruct the complete envelope of the object''s surface morphology. Furthermore, the associated data loss ratio was less than 0.5%.

Elastic constants are important parameters to describe the mechanical properties of metal foils. To accurately measure the elastic constants of metal foils, a nondestructive testing method is proposed based on laser ultrasonic technology. First, the inverse problem of elastic modulus calculation is solved numerically. Second, the ultrasonic fields excited by a pulse laser on 20 μm thick foils of Mg-Li alloy, 304 stainless steel and 6061 aluminum alloy are calculated by the direct coupling finite element method. The simulated Lamb wave speed is brought into the numerical calculation program to get the calculation values of elastic modulus and Poisson''s ratio which are subsequently compared with the model specifications. Finally, the effectiveness of the numerical method for inverse problems is verified by the experimental measurement of aluminum alloy foils. The results show that the elastic modulus and Poisson''s ratio of foils can be accurately obtained by the numerical method. These results provide a certain reference for evaluating the mechanical properties of metal foils through the measurement of elastic constants.

As a result of low accuracy and susceptibility to noise interference of traditional bearing fault diagnostic algorithms, a diagnosis method combining empirical mode decomposition and convolutional neural network is proposed. First, fiber Bragg grating (FBG) is used to obtain the vibration signal of the bearing, and then empirical mode decomposition is used to decompose the signal into multiple intrinsic mode function (IMF) components. After the extraction of useful signals, based on the structural characteristics of IMF components, the IMF components are combined into a matrix and input into the improved convolutional neural network for fault classification and recognition. The results show that the proposed method can effectively identify normal, faulty, and composite faulty bearings. Furthermore, the recognition accuracy of the proposed method is greater than 91%.

To enable the real-time traceability of measurements of the modulated phase distribution produced by a liquid crystal optical phased array (LCOPA), a spatial high-resolution phase measurement method based on optical combs, which combines spatial chirp and dual-comb interferometry techniques, is proposed herein. Theoretical simulation analysis is conducted to study the influence of the parameters of the grating and optical comb light source on the system''s spatial resolution and measurement field of view. Theoretical simulation results show that the field of view measured using this method can reach more than 100 mm, and the spatial resolution is better than 2 μm. Further, experimental results show that this method can enable the rapid measurement (microsecond timescale) of the modulation phase distribution generated by a multichannel LCOPA driving electrode. Thus, the proposed method is expected to provide an effective way for the development and performance evaluation of LCOPA devices.

As the line laser sensor can be only installed beside rails during dynamic inspection, it cannot ensure the intersection line of line laser measurement plane and wheel surface to be through wheel center, which causes the affine distortion of large number of wheel profiles and makes it difficult to use the traditional iterative closest point (ICP) algorithm to register the measured profile and to ensure the accuracy and robustness of measurement. In this paper, an algorithm of reweighted scaling iterative closest point based on region of interest (ROI-RSICP) is proposed to achieve accurate registration of worn wheel profiles with affine distortion. First, according to the wear characteristics of wheel profiles and a large number of worn wheel profile data, the PointNet deep learning network is adopted to divide the collected wheel profile point sets into two parts: wear region of interest (ROI) and non-wear part. Then, the ROI-RSICP method is proposed by assigning different values of weight to ROI and non-wear part to achieve accurate registration of the worn wheel profiles with affine distortion and the standard wheel profiles. Finally, the Hausdorff distance algorithm is used to visualize the wheel profile wear. The results of ICP algorithm, scaling ICP algorithm, ROI-RSICP algorithm and the 4th kind of inspector are compared in the experiment, which verifies the superiority of the proposed algorithm for dynamic inspection of worn wheel profiles with affine distortion.

At present, the economic loss caused by the forgery of ink marks is increasing annually. This study presents a method for identifying ink marks using swept source optical coherence tomography (SSOCT). To acquire the back-scattered light intensity from ink marks written on white paper, a custom-built SSOCT system was used. The attenuation coefficient of each ink mark was obtained by data fitting, which was used to distinguish ink marks written with different brands of ink of the same color. Experiments show that the attenuation coefficient of PILOT ink, Deli ink, and Hero ink is in the range of 0.1333--0.1434, 0.1501--0.1695, and 0.1748--0.1892, respectively. We reconstructed X-Y cross-sectional images of characters written using different brands of ink. The ink marks can be distinguished successfully by the proposed method, which validates its feasibility.

A polarization multiplexed metasurface is designed to focus red, green and blue light. This metasurface adjusts the rotation angle of titanium dioxide nano-pillars to achieve the modulation of incident light based on the geometric phase principle. The high polarization conversion efficiency can be achieved by only three different nano-pillar sizes. This metasurface can focus three-color light on the different positions of the same focal plane and thus to realize the control of focus position based on the polarization response characteristics. The metasurface device designed here can be used as a compact optical device in the fields of portable imaging systems, polarized devices, encrypted information transmission, and so on.

In recent years, the generation, transport, and harvesting of hot carriers in surface plasmon (SP) enhanced metal nanostructures have been extensively and deeply studied. Among them, a new photoelectric conversion mechanism based on electronic tunneling and thermal emission effect, combined with planarization manufacture and complementary metal oxide semiconductor (CMOS) compatible integration, is expected to be an alternative scheme for silicon-based infrared photoelectric detection. At present, these detectors are mainly used in metal-semiconductor Schottky junction photovoltaic devices, which have weak photoelectric response. In this paper, a novel photoconductive device based on metal-silicon composite disordered nanostructures is reported. Due to the localized hot spot effect of the disordered surface plasmon and the significant photoconductivity gain of the multiple interdigital metal semiconductor metal (MSM) structures, the broad-band strong photoelectric response of the silicon sub-band gap is obtained experimentally. Finally, the photocurrent responsivity of the hot carrier mediated multiple interdigital MSM devices is as high as 2.50 A/W at 1310 nm.

Sagnac interferometers have important applications in the field of optical filtering. Based on the 3D silicon nitride waveguide platform, we obtained a new Sagnac-like resonance filter system by using a two-layer multi-microring system. In the new system, the bottom main microring cavity was coupled via feedback with the top input/output waveguide and the single/double sub-microrings, respectively. Furthermore, two light waves transmitting in the opposite direction were generated in the coupling area and interfered with each other, thereby a filter structure with adjustable filtering waveforms and resonance peak positions is realized. In this paper, a transmission matrix and an iteration method were used to analyze the output spectra, and the output waveform was designed by changing the coupling coefficient between the waveguide and the microcavity. Besides, the phase of the main microcavity was modulated by the metal heating electrode to regulate the resonance peak position. The theoretical analysis and experimental characterization results show that the dense filtering effect of the device can be effectively improved by adding top sub-microrings and thus the 3D integrated structure can provide greater design freedom. The related multi-microring resonance filter system can be widely used in optical communication, optical sensing, and other fields.

A sub-wavelength periodic grating has special characteristics that a traditional grating does not have. We, therefore, fabricated a sub-wavelength, metal, nanograting polarizer on a square of polycarbonate (PC) using nano-imprinting technology. The grating period is 278 nm, depth is 110 nm, duty cycle is 0.5, and deposited aluminum-metal layer is 70 nm thick. The performance of the sub-wavelength metal grating polarizer was tested using a spectroscopic test system. The experimental results show that when the incident wavelength is 600 nm, a double-layer flexible grating polarizer acquires good polarization characteristics. Its transmission efficiency for TM-polarized light is as high as 55%, and the extinction ratio is as high as 32 dB. The performance of the polarizer was tested using a six-channel sensor made in the laboratory. The test results show that the average error of the polarizer is 0.2002°, maximum error is 1.105°, and standard error is 0.7255°. The manufacturing process only involves two steps: the nano-imprinting process and the metal-evaporation process; it does not involve coating, stripping, or etching an imprint adhesive. So the manufactured gratings have obvious advantages for low-cost mass production of large-area polarizers, which can be widely used in the production of semiconductor optoelectronic devices such as optical-detection devices and optoelectronic switching devices.

Based on the MgO∶LiNbO3 crystal, the critical phase matching technology and the semi-monolithic cavity structure are used to perform external cavity frequency doubling and generate 532 nm laser. The mismatch of the frequency-doubling cavity modes caused by the thermal lens effect is theoretically analyzed. When the higher fundamental frequency light is injected into the frequency-doubling cavity, the mode matching is performed again to mitigate the effect of mode mismatch on the frequency doubling conversion efficiency. Finally, the frequency doubling process with the maximum frequency doubling conversion efficiency of (49.3±0.45)% is achieved and the corresponding output power is 567.0 mW. Furthermore, the model cleaner can not only improve the 532 nm laser beam quality but also reduce the intensity noise to realize the output power of 470 mW and the beam quality factor of 1.05 for the low-noise green laser, whose shot noise limit is reached at an analysis frequency of 1.65 MHz. The whole frequency doubling system possesses a compact structure, a stable output power, and can supply an effective pump field for the quantum squeezed light source, and thus it can play an important role in quantum precision measurement and quantum information fields.

This paper addresses the problem of the lack of single point cloud data for archeological site data archiving and model reconstruction, using the ruins of Banteay Srei in Angkor, Cambodia as a case study, and proposes a complete and efficient digital recording and reconstruction plan. By combining the ground-based lidar point cloud and the UAV-image visual point cloud, the key issues, such as the registration and fusion of the laser and the visual point clouds, and model construction and repair in the model reconstruction process can be solved, and a three-dimensional model of the target object obtained. Based on this, the proposed model application can produce a scene-roaming animation and vertical profile view that can provide an enhanced static and dynamic data basis for the protection, restoration, and research of the Angkor Banteay Srei. The proposed scheme can also provide data foundation and technical reference for data collection, digital archiving, data analysis, scene display, and relic restoration for ancient heritage protection, and further promote the application of the lidar technology to these fields.

Laser powder bed fusion (L-PBF) can accurately and efficiently produce complicated structures made of various medical metals, giving orthopedic implants with customized macro and micro geometry, so that they can quickly respond to personalized clinical treatment needs according to the specific physiological environment, and accelerate the process of bone repair and reconstruction to the greatest extent. This article firstly introduces the current development of metal orthopedic implants fabricated by the L-PBF from the perspective of biomaterials, structural design and manufacturing process in general. Then, it discusses the unique processing characteristics and mechanical properties of non-degradable metals such as titanium and tantalum alloys and biodegradable metals such as magnesium and zinc alloys. Finally, the future development of the L-PBF in the field of orthopedic implants preparation is prospected.

A common strategy for mixture composition analysis based on Raman spectroscopy is to construct the spectral database of pure substances and calculate the spectral similarity of the mixture to be identified and the pure substances in the database. However, influenced of the performance of the measuring instrument and the mutual interference of the components of the mixture, the spectrum of the substance contained in the mixture to be identified will have different degrees of distortion compared with the corresponding pure substance spectrum in the database, bringing great difficulties in component identification. To address this problem, a method to improve the identification accuracy of components in mixtures using the spectral data of known mixtures is proposed herein. The spectral peak information, including Raman shift and full width at half maximum, of the pure substance in the database is used to study the correspondence of the spectral peaks of the known mixture to the specific substances of the mixture. The spectral feature parameters of the pure substance, the known mixture, and the mixture to be identified are constructed using the Raman shift of the spectral peak, the full width at half maximum, and the peak intensity, respectively and the fuzzy membership function is used to calculate the spectral similarity between the mixture to be identified, the pure substance, and the substances contained in known mixture based on calculated feature parameters. Furthermore, suspected components contained in mixture to be identified are determined based on the spectral similarity. Based on the spectral database of 204 pure substances and 8 known mixtures, the experimental results for 81 unknown mixtures reveal that the proposed method can reduce the calculation error of similarity caused by spectral distortion and can improve the identification accuracy. Compared with search strategy based on the database of pure substance, the identification accuracy obtained using the proposed method increases from 76.34% to 92.83%.

To identify different Xinjiang jujube varieties, a hyperspectral technique and machine learning algorithms were employed to obtain and analyze the spectral data of Jinsi-jujube, Jun-jujube, and Tan-jujube. First, the original spectra were preprocessed using various data preprocessing methods, including multiplicative scatter correction (MSC), standard normal variate transformation (SNV), first-derivative (1-Der), and Savitzky-Golay (SG) smoothing. The effects of the preprocessing methods on modeling were investigated. Then, the samples were divided into calibration and prediction sets using sample set partitioning methods based on joint X-Y distance (SPXY). The jujube variety identification models were established based on linear discriminant analysis (LDA), K-nearest neighbor (KNN), and support vector machine (SVM) algorithms using the preprocessed full-band spectra. The results demonstrate that 1-Der outperformed other preprocessing methods mentioned above. Next, the characteristic bands were extracted from the full-band spectra using principal component analysis (PCA), successive projections algorithm (SPA), and competitive adaptive reweighted sampling (CARS). Then, the jujube variety identification models were established based on the characteristic bands. The CARS-based models achieved the highest accuracy in the models established based on several characteristic band extraction methods. Finally, taking the SVM model as an example, the model runtime was compared. The time required by the SVM model based on the characteristic bands was much shorter than the time required by the model based on the full-band spectra.

Combined with laser-induced breakdown spectroscopy (LIBS) technology, the laser cleaning online monitoring system is designed to monitor the quality of laser cleaning in real time. The fiber laser uses in the experiment can be processed and applied in a multidimensional space. First, we determine the laser cleaning speed value and study the change law of LIBS with laser single pulse energy density, which can characterize the cleaning effect of carbon fiber composite materials. Then, during data analysis processing, the method of removing the background by mean smoothing is used to process the continuous background of the envelope-like spectrum. The density-based spatial clustering of applications with noise algorithm is used to realize the separation of spectral noise and effective data. The Pearson coefficient analysis method determines the best ablation times for laser cleaning, and provides a basis for the automatic optimization control of the laser cleaning process. Finally, a scanning electron microscope is used to analyze the surface morphology of the carbon fiber, which confirmes the effectiveness of LIBS technology to monitor the laser cleaning effect online.