Air pollution greatly impacts the productivity and life of people. Aerosol is an important pollutant and cannot be ignored. It is significant to improve the detection accuracy of atmospheric aerosol concentrations, especially low-concentration aerosols. In this study, filament-induced fluorescence spectrum (FIFS) of NaCl aerosol is preprocessed and combined with partial least squares (PLSR) to establish a prediction model and explore the impact of different preprocessing methods on the detection accuracy of the model. To choose the preprocessing method, this study divides the preprocessing methods into three aspects according to their effects: scattering correction, smoothing and denoising, and baseline correction, and the significance of peak algorithm is proposed. The optimal preprocessing method is selected after comparing no preprocessing, single preprocessing, and combined preprocessing and analyzing the influence of different preprocessing methods on the accuracy of FIFS spectral prediction model. The experimental results show that the combined preprocessing of multiple methods reduces the root mean square error to 0.03 compared with no preprocessing, and the relative prediction error is reduced by 60%. Compared with the direct observation of spectral signal selection preprocessing method, the best preprocessing method can be selected more accurately according to the improvement of spectral signal-to-noise ratio and the modeling effect of predicted components. The present study provides a reference for the analysis and research of low-concentration air pollutants.

Doping of silicon clusters with transition metals can enhance the stability of such clusters and confer many peculiar physical and chemical properties. Therefore, this method occupies an important position in the fields of new energy and materials science. Herein, we report the geometric structures as well as electronic and thermodynamic properties of CoSi16- and Co2Si322- clusters using the particle swarm optimization algorithm CALYPSO searching method and density functional theory. Results indicate that the lowest structures of the CoSi16- and Co2Si322- clusters exhibit the highly symmetric D2d and D2h point structures, respectively, in which the Co atom is completely encapsulated in Si cages. Based on these structures, various electronic properties, including the magnetic properties and bond order, are systemically evaluated. In addition, the photoelectron spectra, infrared spectra, and Raman spectra are recorded to identify the main characteristic peaks of the two systems. Finally, the thermodynamic properties of the two systems are investigated. Moreover, the temperature dependence of Cv and S for the CoSi16- and Co2Si322- clusters is discussed.

The generation of high-order harmonics from planar molecules H32+ with different molecular configurations is studied using the numerical solution of the time-dependent Schr?dinger equation. The results show that planar molecules H32+ emit both odd and even harmonics, and the relative yields of odd and even harmonics are sensitive to orientation angles and molecular configuration. A simple method is proposed, based on the above results, to detect the position of atomic nucleus via odd and even high-order harmonic spectra. Bond lengths and angles from oriented asymmetric planar molecules can be reconstructed using odd-even harmonics at different angles. Meanwhile, probing the polycentric molecular structure in attoseconds using a high-order harmonic spectrum is helpful.

Coherent laser communication has the advantages of high speed and long-distance transmission capabilities, both of which play an important role in inter-satellite communication. A coherent optical communication system makes full use of information on light intensity, phase, frequency, and polarization, which cannot only improve the efficiency of frequency band utilization, but also extend the relay distance across which optical communication is possible. As a type of multi band modulation, quadrature phase shift keying (QPSK) modulation and demodulation can greatly improve the utilization of spectrum resources. Aiming to resolve the problem of the response rate of QPSK modulation and demodulation in coherent optical laser communication, an improved Costas loop is proposed in this study. The results of the experiment verify the entire QPSK modulation and demodulation system and the performance feasibility of the improved Costas loop.

A new model of high-sensitivity elliptical side-core photonic crystal-fiber sensor is designed. A circular hole and three elliptical holes of different sizes constitute the elliptical side-core photonic crystal-fiber air hole, where the e, e1, and e2 are the ellipticities of the elliptical holes, and the gold-nano-film is coated in the left elliptical hole with the ellipticity e. The finite element analysis software, COMSOL, is used to numerically analyze the sensing characteristics of the sensor. We found that the resonant peak of surface plasmon resonance has a high sensitivity to the change in the refractive index of the measured liquid; the sensitivity of the photonic crystal-fiber sensor varies with ellipticities e, e1 and the gold-nano-film thickness. Within the refractive index range of 1.40-1.42, the sensor sensitivity increases with increasing e1; within the refractive index range of 1.42-1.43, the sensor sensitivity initially decreases and then increases with increasing e1. When ellipticity e1 is 1.2, and the refractive index is 1.43, the sensitivity reaches as high as 31800 nm/RIU (refractive index). At a refractive index of 1.38-1.43, the sensor sensitivity increases with increasing ellipticity e. When ellipticity e is 2.3, the sensitivity reaches as high as 33200 nm/RIU. When the refractive index is 1.42-1.43, the sensor sensitivity decreases with an increase in the gold-nano-film thickness. When the refractive index is 1.43, and the gold-nano-film thickness is 40 nm, the sensor sensitivity reaches as high as 34600 nm/RIU.

Based on the interference fringe visibility of the ultra-small GRIN fiber probe, we study the influence of the GRIN fiber probe on the F-P interference signal. Furthermore, we analyze a theoretical formula of the fringe visibility of the ultra-small GRIN fiber probe based on the Gaussian beam and establish a corresponding test experimental system for verification. The experimental results show that for the ultra-small GRIN fiber probe with a focal spot diameter of 15 µm, the fringe visibility remains above 0.8 within a cavity length of 600-1350 µm. However, for single-mode fiber probes, the fringe visibility remains at 0.8 within a cavity length range of 130-530 µm. Therefore, the proposed ultra-small GRIN fiber probe improves the fringe visibility of the F-P interferometer for a long cavity length. This paper provides the theoretical foundation for further research into the application of the ultra-small GRIN fiber probe, which requires a long initial cavity length or a large dynamic range.

Wire breakage may occur in steel strands in complex engineering environments. In order to effectively identify broken wire signals, a self-sensing steel strand with fiber Bragg grating (FBG) strain sensor embedded and pre-stressed to the center wire of the steel strand is fabricated in this paper. The sensitivity of self-sensing steel strand to the identification of broken wire signals is analyzed to explore the correlation between the damage area and location of cables and the strength of broken wire signals. Taking the damage area, damage location and sensor location of ordinary steel strands as research variables, three groups of tension wire breaking tests are carried out on cables composed of 16 ordinary steel strands and 3 self-sensing steel strands. The test results show that the respective sensing strands can accurately identify the broken wire signal, and the identification of broken wire signal is independent of the distribution position of FBG measuring points in the self-sensing steel strand. The time period of the broken wire signal detected by each sensor is basically the same, and the strength of the broken wire signal collected by the FBG sensor is related to the location and degree of the common steel strand damage.

To improve the temperature sensitivity and data integrity of the fiber laser, a fiber laser temperature sensing system based on beat frequency demodulation is proposed. The fiber Bragg grating (FBG) in the fiber laser resonator is used for temperature sensing. The wavelength change of FBG is successively transformed into the wavelength change of the resonator and the frequency shift of the fiber laser beat frequency signal, which greatly improves the sensitivity of the system. The Python program is used to realize the second-time data automatic collection and saving, thus improving the working efficiency. The error caused by large frequency jitter can be avoided by demodulating the temperature signal through the rectangular frame center position method instead of direct peak value finding method. Compared with optical demodulation technology, the system uses mature electrical demodulation technology to demodulate instead of expensive wavelength demodulation instrument, reducing the cost of modulation. The experimental results show that the system has high sensitivity and measurement accuracy. The average sensitivity of the system is 74.087 kHz/℃. The measurement accuracy of the system is 0.47×10-3 ℃.

Semiconductor optical amplifier (SOA) can be used to generate narrow optical pulse with steady high extinction ratio and has been widely used in the field of optical fiber sensing. However, most of current schemes only employ SOA in unidirectional modulation for pulse generation. Based on the feature that SOA can work in both directions, this paper proposes a bidirectional narrow pulse modulation of SOA to further enhance the extinction ratio of optical pulse. A fiber optic mirror is used to reflect the optical pulse generated by unidirectional modulation back to the SOA for the second pulse modulation. The experimental results show that compared with unidirectional modulation, bidirectional modulation achieves a maximum extra gain of 6.18 dB at low input optical power. For pulsed light with an input peak power of 6 dBm, the bidirectional absorption can further weaken the leakage light intensity by more than 30 dB, and the overall absorption rate reaches more than 72 dB.

The surface scattering of structural components in satellite optical communication systems will directly affect the transmission efficiency of signals. Therefore, based on the self-built bidirectional reflection distribution function (BRDF) measurement system, the surface properties of titanium alloy and aluminum alloy structural parts are measured in this paper. The influence of the structure surface roughness and incident angle on the BRDF distribution at the 1550 nm laser communication wavelength is analyzed. The BRDF model of the surface of the structural part is established, and the optimal model parameters are obtained by the simulated annealing algorithm. The experimental results show that the relative root mean square error between the modeling results and the measured results is better than 7.26%. The ABg model parameters fitted according to the measured data provides the necessary data parameters for the stray light tracing calculation and system design in practical engineering applications.

In order to reduce miss distance errors of the photoelectric tracking stabilization platform for airborne laser communication, an observer-based internal model control strategy with two degrees of freedom is proposed. The strategy takes the velocity loop simplified using the current loop as the control object, uses the two-degree-of-freedom internal model control to correct the system, and introduces the observer-based control law into the two-degree-of-freedom internal model control to reduce the model error and influence of external disturbances on system performance. The high performance of the proposed strategy is validated by simulation and experiment. The experimental results show that the improved internal model control is better than the traditional internal model control in terms of anti-interference ability, robustness, and tracking performance. Bringing the improved internal model control algorithm into the actual system also has good tracking performance, and its tracking accuracy is about 143 μrad, which is about 24% higher than that of traditional internal model control.

Aiming at improving the measurement of wavelength modulation via laser absorption spectroscopy, a non-dispersive multi-wavelength second-harmonic measurement method is proposed. By adjusting the relative position between the spectral lines, the demodulation of the multispectral line modulation signal can be achieved without the need for a grating or other spectroscopic devices, and the gas temperature can then be measured online. Based on the 7185.60 cm-1/7444.35 cm-1 H2O absorption spectrum, the influence of the modulation coefficient and the relative position between the spectral lines on the measurement are discussed. Further, the second-harmonic extraction method under different modulation frequency conditions is analyzed using the modulation signal spectrogram. A numerical simulation method is used to establish a complex flow-field change model in the pulse detonation process. The proposed method is used to measure gas temperature during the pulse detonation process, and its correctness is verified in this study. The research results are of great significance to the measurement of wavelength modulation under complex environmental conditions.

In this study, we propose an orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) system based on low density parity check code (LDPC) coded with probabilistic shaping (PS) for optimizing the transmission performance of the OFDM signal. We theoretically analyze the PS technology and the generation and demodulation principle of the PS-OFDM signal. The average power of the modulated OFDM signals for the same transmission power decreased by approximately 20% after PS with a 6.7% extra overhead. Compared with a normal OFDM-RoF system, the proposed PS-OFDM-RoF system can reduce the transmitting power of OFDM signals, and it has a better peak-to-average power ratio (PAPR) performance. Furthermore, a 25 GHz verification RoF system with a data rate of 2.5 Gbps is established for analyzing the transmission characteristics of the PS-OFDM signals. The measured bit error rate curves at different fiber lengths show that a PS-OFDM-RoF system based on LDPC can effectively improve the sensitivity of the receiver and increase the reliable transmission distance of the system.

The optical frequency scanning interference absolute distance measurement system needs to correct the optical frequency scanning nonlinearity and refine the signal distance spectrum so that it has low data collection and processing efficiency. Therefore, it is difficult to meet the length measurement requirements in large-scale digital manufacturing scenarios. This paper designs a data collection and processing system introducing auxiliary interference signals as the digital signal acquisition system clock, and the nonlinearity of the frequency sweep is corrected meanwhile in the signal collection process, and hence the efficiency of the designed system is high. Sparse fast Fourier transform is used to determine the range of the spectrum refinement interval. Based on the zoom fast Fourier transform, the refinement of the distance spectrum is realized and the efficiency of precise distance calculation is effectively improved. The experimental results show that the data processing speed of the designed system is more than 10 times faster compared with traditional systems using the chirp Z transform. Compared with the commercial interferometer, in the equivalent space distance range of 15.4-16.1 m, the error of the measurement is kept within 10 μm, and the measurement repeatability is better than 6 μm.

In this study, to address the issue of imaging distortion that occurs when visual measurements are applied in inhomogeneous refractive index environments, an inhomogeneous refractive index field produced in the inhomogeneous temperature field is developed, and the trajectory of light in the refractive index field is investigated, and the image distortion is corrected according to the trajectory's deviation. The spatial refractive index field produced using the nonuniform temperature field is reconstructed using the background schlieren method. The light emitted by the spatial point is abstracted as light rays and reproduces the light in the inhomogeneous temperature gradient environment according to the Runge-Kutta method. The world coordinates of the point are computed based on the PnP (perspective-n-point) algorithm and the pixel coordinates of the same point in the image before and after correction. Experimental findings demonstrate that the method can efficiently decrease the measurement error and correct the measured image's distortion.

Phase retardation is an important indicator of polarizing optical elements. To measure the phase retardation of the polarizing element accurately and quickly, a method with phase compensation and cascade modulation for detecting the phase retardation of the polarizing elements is proposed. In this method, a photo-elastic modulator (PEM) and an electro-optical modulator (EOM) are used as the cascade modulation element of the phase delay detection system, and a Soleil-Babinet phase compensator is used to compensate phase retardation for the sample. Using digital phase lock technology and a field-programmable gate array (FPGA)-based on-chip programmable system, it detects the phase parameters of the Soleil-Babinet phase compensator corresponding to the extreme point of light intensity and performs data processing to realize the detection of the phase retardation of the sample. Experiments show that the maximum relative error of using this method to measure the phase delay of a sample is 0.857% and the measurement accuracy is 99.143%, which verifies that the combination of the polarization modulation and compensation methods to measure the phase retardation has high accuracy, and the influence of the compensator itself on the measurement error is reduced.

In this paper, a new fast center extraction algorithm of structured light stripe is proposed, which can extract the center of structured light stripe quickly under complex motion blur. This paper analyzes the causes of blurred motion imaging of line structured light and the gray value distribution law of the light stripe section in the image, and designs a P-tile threshold segmentation algorithm based on the theoretical light stripe imaging width, which solves the difficulty of extracting the light stripe area caused by the different light stripe imaging width and irregular brightness change in the case of motion blur. According to the characteristics of the light stripe image, the positioning speed of the light stripe is improved by the improved region growth algorithm, and the center of the structured light stripe is extracted according to the gray value distribution of the light stripe section. The experimental results show that the improved P-tile threshold segmentation algorithm is more effective than the extreme value method and Otsu method when segmenting the optical stripe region under motion blur. Our center extraction method provides faster speed and better precision, and has practical value in high-speed industrial measurement of structured light.

According to the contradiction between measurement efficiency and accuracy in the multi-line structured light measurement, a fast measurement results of the measurement method base on region digital image correlation matching is proposed in this paper. The bilateral filter and Otsu thresh method are used to preprocess the image, and the gray centroid method is utilized to extract the initial point of the stripe center. The bicubic interpolation method is adopted to improve the local neighborhood resolution of the center initial point for the reuse of the gray centroid method in the local neighborhood to improves the accuracy of the center point extraction. Based on the center line extracted from the left image, the digital image correlation method is used to search for stereo matching points corresponding to the reference near the center line of the right image, which greatly reduced the search range of the digital image correlation method and improved measurement efficiency and stereo matching accuracy. The measurement experimental result of the standard block gauge show that the centerline extraction speed of the method is 3.29 times that of the Steger method, and compared with the traditional epipolar constrained stereo matching method, the root mean square error of this method is reduced by 68.57%.

The accuracy of the phase retardation of a wave plate, which is an important technical parameter, directly affects the performance of the entire polarization optical system. It may be necessary to measure the wave plate before use. Based on the curve distribution characteristics of the polarization interference spectrum, a method for measuring the phase retardation of a wave plate is presented. In this method, the wave plate to be measured is placed between a polarizer and an analyzer, and the transmission spectrum curve in a certain spectral range is measured using a spectrophotometer. Based on an accurate estimation of the wavelengths of certain points with specific transmission from the transmission spectrum curve, the thickness, absolute phase retardation, order, and effective phase retardation of the wave plate can be obtained simultaneously. Theoretical analysis and experimental results show that the proposed method has advantages such as, suitability for zero-order or multi-order crystal wave plate with any phase retardation, high measurement precision, and ease of operation. Furthermore, it has no strict requirements for the directions of the fast axis of the wave plate and the transmission axes of the polarizer and the analyzer.

The cavity ring-down method has an extremely high measurement sensitivity to the absorption of a medium in the cavity and can be used to accurately measure cavity loss. Based on the theories of free carrier absorption and resonant cavity, this study establishes a theoretical model of an optical cavity ring-down to measure the properties of semiconductor materials and derives the functional relationship among the cavity ring-down signal, semiconductor material characteristic parameters, and cavity structure parameters. Simulation analysis and experimental verification are performed. Simulation results show that the cavity ring-down method can be used to accurately measure semiconductor material properties, such as doping concentration and resistivity. Meanwhile, based on the proposed method, the doping concentration and resistivity of a crystalline silicon wafer are determined experimentally to be (2.65±0.38)×1016 cm-3 and (0.61±0.07) Ω?cm respectively, exhibiting the high application potential of this method for measuring semiconductor material properties.

Laser diode (LD) end-pumped square YAG/Yb∶YAG composite crystal is taken as the study specimen. Based on the theory of heat conduction and working characteristics of continuous LD end-pumped square YAG/Yb∶YAG, the effects of pump power, thickness, and section size of YAG crystal on temperature, thermal stress, and thermal deformation of laser crystal is systematically investigated using finite element method. The pump spot radius of collimation focused using an optical coupling system is 400 μm in the calculation process. The findings show that when the size of Yb∶YAG crystal is 4 mm×4 mm×1 mm, and the thickness of YAG crystal is 0.1 mm, the maximum temperature rise in YAG/Yb∶YAG square crystal increases from 37.19 ℃ to 82.92 ℃ with the increase in pump power from 60 W to 80 W. When the YAG crystal's thickness increases from 0 mm to 0.5 mm, the maximum thermal stress changes from 26.93 MPa to 10.438 MPa, and the maximum temperature decreases by 18.18 ℃, but the thermal deformation due to thermal stress remains unchanged. The use of square YAG/Yb∶YAG composite crystal can efficiently decrease the maximum thermal stress and temperature rise in laser crystal, which has guiding significance for the design and high power output of all-solid Yb∶YAG laser.

Laser shock peening (LSP) is an advanced surface modification technique for anti-fatigue manufacturing. In this paper, the orthogonal test method was employed to investigate the distribution of residual stress on the surface of 2050 aluminum-lithium alloy. The correspondingly optimal LSP parameters were obtained. Furthermore, the fatigue life extension was verified with these parameters. Results show that there is a strong correlation between the LSP-induced residual stress and the geometric characteristics of the specimen. For the LSP parameters which affected residual stress, the effect of overlapping rate is greater than laser energy, and further more significant than impact times. The optimal LSP parameters are laser power density of 5.30 GW·cm-2, overlapping rate of 50%, and peened twice. With the optimal LSP parameters, the fatigue life increased by 22% and 63% at 260 MPa and 200 MPa stress level, respectively.

To obtain transparent polycarbonate (PC) welding samples without adding additional absorbents, 1710 nm and 1910 nm lasers were used to study the transmission welding of PC. The qualities of obtained welding samples were verified by the corresponding weld appearance and the strength of each sample. The experimental results show that the PC welding samples obtained by 1710 nm laser and 1910 nm laser have close strength and desired welding effect. The maximum tensile force of 1334.4 N was obtained by the 1710 nm laser with parameters as follows: 20 W power, 6.5 mm/s welding speed, and -6 mm defocusing amount, and the strength of the welding sample reached 60.9% of the PC substrate.

Laser polishing, as a noncontact green processing technology, can replace the traditional polishing technology. In this paper, the surface of DC53 hardened steel is continuously polished by a laser with a 1064 nm wavelength to investigate the effect of laser polishing on the surface quality of DC53 hardened steel. Additionally, the surface roughness, hardness, Young's modulus, corrosion resistance of the material, and the changes in the subsurface microstructure of the processed surface after laser polishing are thoroughly investigated. The experimental results show that the average roughness is reduced from 4.829 μm to 0.505 μm at a rate as high as 90% when the laser power is 180 W, the laser scan speed is 20 mm/s, and the laser scan interval is 0.06 mm. Simultaneously, the surface hardness and corrosion resistance of the material after laser polishing are reduced compared with the initial sample, the hardness of the molten zone is reduced by 40%, and the self-corrosion potential is reduced by 4%.

Photothermal microactuators are extensively utilized in optical microelectromechanical systems and microrobotics. A waveguide-type excitation photothermal U-shaped microactuator, with strong controllability and large displacement, is constructed using the narrow-band wave-absorbing properties of functional dyes, and the temperature and displacement changes in the actuator are simulated in this paper. A narrow-band response photothermal microactuator with a single arm length and radius of 5.8 mm and 200 μm, respectively, is constructed. The experimental findings indicate that the actuator produced using the proposed scheme has the benefits of large displacement response, high energy utilization rate, low production cost, and high integration. Driven using a 100 mW laser, the actuator's free end can attain a displacement of 100-160 μm in the violet (408 nm) or red (638 nm) band, which is much greater than the displacement (20 μm) produced by the beam in the non-corresponding band.

A passively Q-switched (PQS) Tm∶YAP laser in the 2 μm waveband is introduced. A linear cavity structure of the Tm∶YAP laser is chosen in the experiment. A laser diode with an output central wavelength of 792 nm is used as the pump source, and a saturable absorber prepared by a new two-dimensional material of black phosphorus is used as a PQS modulation device for the Tm∶YAP laser. In the continuous wave mode, an output power of 1.0 W is obtained with an output central wavelength of 1994.8 nm from the Tm∶YAP laser under the pump power of 8.8 W, corresponding to a slope efficiency of 17.3%. Under the PQS regime, an average output power of 0.9 W and a minimum pulse width of 1.3 µs at 135.8 kHz are acquired from the Tm∶YAP laser at 1986.7 nm under the pump power of 8.8 W, corresponding to a slope efficiency of 14.2%. In addition, the beam quality factor of Mx2=1.10 and My2=1.06 are measured from the PQS Tm∶YAP laser under an average output power of 0.9 W.

Weld seam tracking is the key technology for achieving automated welding. In this paper, a seam tracking method based on a line array camera and a feature recognition algorithm is constructed to provide gapless seam recognition under laser welding. The workpiece surface image is captured by a line array camera and denoised by mean filtering. By analyzing the gray value of the image, the change in the gray value of the image, the gray gradient of the image, and the width of the weld area, the weld track is identified, and the identification and tracking of the gapless weld are realized. Welding experiments are conducted, and the results show that the error of the weld identification method based on a line array camera is less than 0.05 mm. Weld seam tracking experiments on welds with different a gap are conducted, and the results show that the proposed method has a good recognition effect for welds with a gap less than 0.3 mm.

To investigate the forming rules of laser additive manufacturing thin-walled parts on a nonhorizontal substrate and expand the extensive use of laser additive repair technology, the forming experiments of thin-walled parts were conducted on an inclined substrate from 0° to 150°, based on the inside-beam powder feeding technology. The forming rules of thin walls under different inclination angles were examined, and the forces of a molten pool under the nonhorizontal substrate were investigated. The experimental findings demonstrate that the total width and height of thin walls increase, and the length of the molten pool decreases with the increase of substrate inclination angle. The forming part’s tail collapse becomes severe with the increasing substrate inclination angle. A slope with a 21° maximum angle is obtained when the substrate angle is 150°. The study findings offer reference value for laser additive manufacturing and repair on the nonhorizontal substrate.

A pulsed fiber laser with a wavelength of 1064 nm is used to clean the epoxy silicone paint on the surface of KMN steel. The overlap ratio and energy density are selected as variable parameters, and the samples are cleaned in one pass and two passes under different parameters. The effects of laser cleaning parameters on the substrate surface roughness and the adhesion of the recoating paint are investigated, as well as the trends and reasons for the variation of substrate surface Vickers hardness with the cleaning parameters. The results show that with an energy density of 4.73 J/cm2 and an overlap ratio of 0.4-0.7, the paint cannot be removed by a single pass cleaning, and a second pass cleaning is required to remove the residual paint chips. When the overlap ratio of the second cleaning is less than 0.5 and the energy density is less than 4.25 J/cm2, the substrate surface melting causes a minor decrease in the surface roughness, but the adhesion of the recoating paint is unaffected at surface roughness of more than 0.6. When the overlap ratio of the second cleaning is greater than 0.5 and the energy density is greater than 4.25 J/cm2, the surface tensile stress caused by melting and solidification of the substrate surface, as well as the phase change and grain growth in the heat-affected zone, resulting in a lower hardness on the substrate surface compared to the interior.

Taking the WC nozzle with obvious difference in laser shock resistance performance used in laser jet solder ball bonding as the research object, the difference between microstructure and composition was observed by means of scanning electron microscope/energy dispersive X-ray spectrometer. Combined with the theory of material beam interaction, the micro mechanism of the influence of Co content and microcracks on the laser resistance of WC nozzle was studied. The test results show that WC particle size, through microcrack, and metal binder Co content are obviously different. The analysis shows that the through microcracks caused by excessive sintering pressure will produce light trapping phenomenon to the laser, and form a heat affected zone with higher temperature around it, in which the Co with lower melting point is easy to melt. Near the heat affected zone at the front end of the nozzle small hole, the molten Co and tin ball are prone to metallurgical reaction, forming tin, and the nozzle will fail in severe cases. The more serious the crack and the higher the Co content, the worse the resistance to laser shock of WC nozzle. Therefore, reducing Co content and sintering pressure can effectively improve the laser shock resistance of the nozzle.

The joining of dissimilar materials, especially metals and glass, is widespread in various industrial products. Ultrafast laser welding of heterogeneous materials is a fast, clean, and non-contact technique that has been extensively studied in recent years. In this study, molecular dynamics methods are used for simulating the femtosecond laser action at the interface between aluminum and quartz glass. The simulation constructed a Lennard-Jones (LJ) interaction potential for quartz glass according to its melting point and elastic constants. The construction of the LJ interaction potential between aluminum and quartz glass is based on the adhesion work between the two materials, thus simplifying and accelerating the simulation process while maintaining the macroscopic properties. A small-scale molecular dynamics simulation of the femtosecond laser action at the aluminum and quartz glass interface is performed using the two-temperature model coupled to molecular dynamics method. After femtosecond laser irradiation, the local transient temperature in the welding zone and stress are as high as 10000 K and 20 GPa, respectively, and diffusive movement of aluminum atoms to the quartz glass side occurs. The continuous collision of high-temperature particles causes the mixing zone of aluminum and quartz glass to expand, and the center of the mixing zone of the two materials moves toward the quartz glass side. The simulation reveals the molecular dynamics evolution of the femtosecond laser-action aluminum-quartz glass interface on the picosecond time scale at the microscopic level, providing a theoretical basis for femtosecond laser welding of dissimilar materials.

Aluminum alloy is an excellent lightweight metal material with low density, high specific strength, and good corrosion resistance. In order to improve the mechanical properties of aluminum alloy fabricated by laser selective melting (SLM), this paper proposed a strengthening method of aluminum alloy material in which Cu element was used as simple particle, and explored the influence of the proportion of Cu element on the forming quality and properties of aluminum alloy fabricated by SLM. The results showed that the doping of Cu powder can refine the microstructure grain of aluminum alloy simply and effectively, and improved the tensile strength of aluminum alloy material. Al2Cu phase could effectively refine the grain and form a more compact micro equiaxed crystal structure in the overlapping area. With the increase of the content of copper powder, the Al2Cu phase generated in the structure gradually increased, and the grain size gradually decreased from 3.30 μm to 2.12 μm. The microstructure was refined. The sample containing 5% copper powder had the highest tensile strength of 460 MPa, which was 20.4% higher than that without copper powder. However, after excessive copper powder was dopped, the performance of the sample was reduced to a certain extent due to the presence of un-melted particles. This study is of great significance to further improve the mechanical properties of aluminum alloy fabricated by SLM.

In this study, 18Ni300 maraging steel powders and micron silicon carbide (SiC) powders are sintered using selective laser melting technology. Furthermore, the effects of adding different volume fractions of SiC for roughness, microstructure, and mechanical properties are investigated. The results reveal that with the increase in SiC volume fraction, the swelling and spheroidization of the top surface are aggravated, the surface roughness and pores become larger, and the side powder adhesion is serious. Additionally, the solidification structure changes from cellular crystals to columnar crystals and then to dendrites, and the samples of hardness and tensile strength are higher than those without SiC powders. When the volume fraction of SiC powders is 0.5, the hardness and tensile strength samples are the highest, reaching 371.1 HV and 1.51 GPa, which are 7% and 54.8% higher than the sample without SiC powders, respectively. Therefore, while the addition of SiC powders increases the top surface roughness and porosity, it can transform and refine the grain, increase the dislocation density and improve mechanical properties, and then enhance the comprehensive performance of the sample.

The thermal state of powder arriving in a molten pool is crucial to the forming precision and quality of the cladding layer for off-axis laser cladding. Aiming at the different melting behavior of powder under the action of light powder, an infrared thermal imaging acquisition system and a high speed camera process acquisition system for the laser cladding process with off-axis powder feeding were built. The light powder thermal interaction under different laser powers and defocus amounts was studied. Three typical characteristic stages of powder melting were established. The influence of laser power and defocus amounts on the duration of the characteristic stage of powder melting was examined. Finally, the relationship between the thermal state of powder and characteristic stage was obtained. The findings depict that with the increase in laser power, the number of melted powder in the interaction space increases and the powder temperature uniformity decreases, and the number of liquid powder particles increases with an increase in defocus and the temperature inhomogeneity of powder decreases. The smaller the laser power or larger the defocusing amount, the time required for the temperature to rise and the solid powder's melting increases. The powder's probability of entering the molten pool in solid state increases. The thermal states of powder arriving at the molten pool under different laser parameters are obtained, providing an experimental basis for the powder melting behavior analysis.

Detection of ice on the skin surface of aircraft in the stationary state is a challenging task. In this study, an ultrasonic guide detection technique is proposed to distinguish among three ice types (glaze ice, mixed ice, and rime ice on plate-like structure surfaces) and determine the ice thickness by extracting the characteristic parameters of the time and frequency domains. First, the S0 mode signal of the ultrasonic Lamb wave is acquired using ABAQUS simulation software. The degree of S0 mode amplitude attenuation influenced by the ice thickness and type is observed in the time domain. In the frequency domain, the ice coefficient is introduced to realize nonlinear mapping on the ice thickness and type. Subsequently, experimental verification is performed on the three ice thickness types with Lamb waves. A comparison with the simulation results indicates that the method is feasible. Finally, a method of analyzing the type and thickness of ice is described.

This study aims to improve the mechanical properties and microstructure of M2 high-speed steel tool materials prepared using three-dimensional printing technology and promote the development of three-dimensional printing technology for metal tool materials. M2 high-speed steel samples were prepared using laser selective melting under different substrate materials and powder feeding speeds. The mechanical properties and microstructure of the samples were characterized and observed. The results show that the thermal expansion coefficient of 316L stainless steel substrate is about 57.27 % higher than that of M2 high-speed steel substrate. The thermal conductivity of 316L stainless steel substrate is 17.28 % lower than that of M2 high speed steel substrate, which reduces the thermal stress produced during the preparation process. Remaining stress is released more fully with slow cooling. Therefore, 316L stainless steel substrate is conducive to forming M2 high-speed steel samples. With the decrease of powder feeding speed, the real-time heat treatment time in the printing process will be greatly increased, which leads to a slight decrease in the hardness of the material but a more compact microstructure, a decrease in cracks, pores, and other defects, and an increase in the tensile strength. The Rockwell hardness of the sample obtained by the experiment is up to (58.97 ± 0.28) HRC, and the tensile strength can reach (937 ± 118) MPa. The microstructure presents a network structure with many martensite columnar crystals, and the needle width is less than 1 μm. The main phases include α-Fe, austenite, martensite, and MC carbides.

The dynamic equation of the semiconductor laser system is a critical theoretical basis for investigating chaotic lasers, whose calculation accuracy directly determines the simulation reliability of the chaotic laser generated by the system. In this study, different semiconductor laser systems are evaluated and compared based on the two widely used methods of photoelectric field decomposition: amplitude-phase decomposition and real-imaginary part solution. The comparison shows that the computational results of both methods have a minimal difference in the case of low complexity of output light, but a significant difference exists in the case of high complexity. Furthermore, the numerical simulation of the photoelectric field using the real-imaginary part solution has higher precision and is more suitable than the amplitude-phase decomposition for analyzing semiconductor laser systems that generate chaotic lasers with higher complexity.

A visible/infrared integrated space remote-sensing imaging scheme is proposed in this study to satisfy the all-weather and all-day remote-sensing application requirements in the fields of battlefield situation awareness, environmental pollution monitoring, and emergency disaster reduction. The proposed system covers visible panchromatic/multispectral, middle-wave and long-wave infrared spectral bands. The spatial resolution of the aforementioned spectral bands can reach 2 m/8 m, 8 m, and 16 m, respectively, and the imaging width exceeds 15 km. The technical parameters of the optical system are analyzed and determined, and the design scheme of the visible/infrared common-aperture modular optical system is proposed. The design and analysis of each module of the optical system and the entire optical system are realized. The design results show that the imaging quality of each module of the optical system and the entire optical system is close to the diffraction limit. Each module can be assembled and tested separately, facilitating the modularization development of the visible light/infrared complex optical system. The complexity and time taken for development of the multispectral, multifocal, integrated optical system can be effectively reduced. Therefore, the visible/infrared common-aperture modular optical system has a significant engineering application value.

Time resolution in the picosecond to nanosecond range is difficult to achieve for a hard X-ray free-electron laser device. To solve this problem, a split-delay optical system design for a hard X-ray free-electron laser device currently under construction in Shanghai is proposed. The design is based on crystal diffraction, the delay time range is calculated, the system throughput is simulated, and a prototype is built and verified. The design can split a single X-ray pulse into two fractions using the spatial division method, and a time delay is introduced between the fractions by using different path lengths. The prototype can operate over a wide and continuous energy range between 7 and 11 keV and provide a delay from -15.4 to 503.3 ps. Throughputs of 33.54% (upper) and 33.64% (lower) for the split-delay optical system were simulated by Shadow, meeting the objective of a 1∶1 ratio. An alignment experiment for the prototype was conducted with a green laser, and the results demonstrate that the prototype can recombine the two beams after spatial division, laying the groundwork for future X-ray verification experiments. The design has the advantages of a small size, wide delay range, and continuously adjustable incident energy and delay time, which can facilitate the development of a split-delay optical system for the Shanghai hard X-ray free-electron laser device.

A surface plasmon polariton (SPP) waveguide structure composed of a straight waveguide with a metal baffle and square cavity is proposed. The magnetic field distribution, Fano resonance, and sensing characteristics are analyzed using the finite element method. The simulation results show that the SPP waveguide structure forms two Fano peaks, and the position of the Fano peaks can be adjusted using structural parameters. In addition, the SPP waveguide structure can be used for refractive index sensing. The maximum refractive index sensitivity and the figure of merit is 2220 nm/RIU (refractive index unit) and 5542, respectively. In glucose concentration detection, the sensitivity reaches 0.264 nm/(g·L-1). The designed SPP waveguide may have potential applications in micro-nano-sensing fields.

A deformable mirror is the core component of an adaptive optics system, its ability to correct is affected by many factors, and its design process is a multidimensional variable optimization problem. The existing design methods for deformable mirrors require repeated iterations over a long period, and the efficiency is low, making it difficult to adapt to the increasing demand for the development efficiency of deformable mirrors. To solve the abovementioned problems, this paper proposes a new design method for deformable mirrors that combines a genetic algorithm and an elastic mechanics influence function analysis model to significantly increase the design efficiency of deformable mirrors and realize rapid design of deformable mirrors. Based on the proposed method, the structural parameters of the defocus and astigmatism-corrected deformed mirror are designed. The results show that the method successfully optimizes the convergence of 11 variables over 100 iterations, significantly reducing the number of individual calculations and allowing for the rapid design of deformable mirrors.

A double-layer petal-structure optical antenna for mid-infrared detection is presented in this paper. The finite-difference time-domain method is used to analyze the effects of structural parameters and polarization direction of incident light on the resonant wavelength of the antenna and intensity of the electric field at the tip of the antenna. Based on the optimization of a single-layer structure, the ratios of the intensity of the electric field at the tip of the upper antenna to the intensity of the incident light are calculated with different incident wavelengths when the gap (h) between the two antennas is 0.1-0.8 μm. To investigate the enhancing mechanism of the lower antenna on the electric field of the upper antenna, the variations of the electric-field intensity ratio of the same measured point with and without the upper antenna are analyzed under fixed incident wavelength and an enlarged gap h (0.1-3.6 μm). The results indicate that the enhancement of the electric field at the tip of the upper antenna is mainly attributed to the coupling effect of the double-layer antenna structure, with h being less than 1 μm. When h is less than 0.2 μm, the electric-field intensity at the tip of the upper antenna reduces with decreasing h. This is because the energy at the tip of upper antenna is transferred to the interlayer region owing to near-field coupling. However, when h exceeds 1 μm, the enhancement of the electric field at the tip of the upper antenna is mainly ascribed to the interference effect of the reflected light from the lower antenna.

A Mach-Zehnder-structured CO sensor based on Co-tetrakis(4-carboxy- phenyl) porphyrin (Co-TCPP) metal-organic framework is proposed in this study. In the sensing structure, a thick taper is fused between two sections of thin-core optical fiber and between the thin-core fiber and the single-mode fiber, and Co-TCPP is coated on the thin-core fiber's surface. The nanosheet-like morphology and porous microstructure of Co-TCPP make the sensor not only easy to adhere to the fiber but also have a strong adsorption capacity for CO. The structure, morphology, and properties of the sensitive material Co-TCPP are characterized and analyzed by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis. The findings demonstrate that the sensor's sensitivity to CO mass fraction is 0.0497 dB/10-6, the fitting degree to mass fraction-light intensity is as high as 0.99148, and the response time is around 120 s when the CO mass fraction is 40 × 10-6, and it has good selectivity and time stability to CO.

The integration of communication and sensing (ICAS) in optical networks is an effective design based on optical cable resources, and is in line with the development trend of communication system resource integration. The use of this integrated system will not only facilitate the intelligent operation and maintenance of optical networks and improve network quality, but will also expedite intensive acquisition of sensor data and innovation of new applications, effectively revitalizing the optical fiber assets of operators. In this paper, the key technologies of optical-network ICAS system are described. Sensing technologies based on the principles of Rayleigh, Raman, and Brillouin scattering are compared and analyzed. Combined with relevant research, several potential application scenarios of optical-network ICAS technology are discussed, thus providing ideas for the popularization and application of this technology.

Distributed feedback fiber laser hydrophones are small in size, high in sensitivity, easy to be reused into arrays and recycled, which has become an important technical path in the field of fiber optic hydrophones. In this paper, the probe package structures and application of distributed feedback fiber laser hydrophones are reviewed. According to the characteristics of package structures, three main package structures and their array applications are introduced, which are bending beam type, side compression type and axial tension or compression type. By analyzing the research indexes of main research institutions at home and abroad, the advantages and disadvantages of different package structures of distributed feedback fiber laser hydrophones are compared, and the future development of distributed feedback fiber laser hydrophones array is prospected.

Ultra-high-speed laser cladding is an emerging surface coating technology. Through the optimal coupling of powder and laser, the cladding efficiency can be substantially enhanced, surface quality can be made better than that of traditional laser cladding coating, and damage to the substrate can be minimized. The principle and technical benefits of ultra-high-speed laser cladding are introduced in this study. The influence of laser power, scanning rate, powder feeding speed, and overlap rate on the cladding layer formation is summarized by comparing with the characteristics of traditional laser cladding technology. In addition, investigation status of the major properties of ultra-high-speed laser cladding coating, such as hardness, wear resistance, and corrosion resistance, is introduced in detail, and the industrial application status of ultra-high-speed laser cladding technology at home and abroad is listed. Finally, based on the current investigation progress, it is pointed out that there is a gap in the study on the interface bonding state of the ultra-high-speed laser cladding coating and the mechanics of the coating component, and prospects for the development of this technology are presented. It is predicted to offer theoretical support for the extensive application of ultra-high-speed laser cladding technology.

If the electric field intensity in the detection area of the capillary cell is non-uniform, a slight change in the detection position will result in a large change in the electric field intensity, which in turn will reduce the accuracy of the zeta potential measurement results. In order to improve the accuracy and repeatability of the zeta potential measurement results, an electric field simulation was carried out for capillary cells with different electrode sizes and cell structures. By analyzing the effect of electrode size and capillary cell structure on electric field intensity uniformity, the optimal capillary cell structure was obtained.

Based on the principle of dynamic light scattering, this paper develops a set of dynamic light scattering apparatus which can measure the thermal diffusivity. The experimental system includes scattering light path, pressure vessel, temperature control system, and data acquisition system. The optical fiber is introduced into the dynamic light scattering system as a probe, which reduces the experimental system to 1/3 of the similar system. In this paper, the reference fluid n-hexane was used to test the accuracy of the experimental system. The thermal diffusivity obtained from the experiment was fitted into a polynomial equation with a maximum deviation of 0.19%, an average absolute deviation of 0.11%, and the maximum deviation between experimental and literature values was 3%. After uncertainty analysis, the uncertainty of liquid thermal diffusivity measured by the newly developed dynamic light scattering experimental system is 2% (k=2).

This study establishes a quick way to test lipsticks. Twenty-eight lipstick samples were classified using Raman and X-ray fluorescence spectroscopy. Using Raman spectroscopy technology to analyze and test samples, the samples can be effectively classified according to the difference in Raman characteristic peaks. A principal component analysis was used to process the data. The classification based on Raman characteristic peaks was scientifically validated when combined with Pearson correlation analysis. When combined with X-ray fluorescence spectroscopy, two types of groups were obtained, and the groups were distinguished based on Ca-Ti. The result shows that this method is simple and fast to operate and does not require special pretreatment. This study will provide a new idea for public security organs to investigate and solve cases and has broad application prospects in public security practice.

To improve the detecting precision and robustness in the determination of water pH value using visible near-infrared (Vis-NIR) spectroscopy, a multivariate calibration model is constructed based on successive projections algorithm (SPA) and particle swarm optimization-least squares support vector machine (PSO-LSSVM). The Vis-NIR spectra data of 60 water samples with different pH values are collected, and the original spectral data are preprocessed by Savitzky-Golay smoothing and standard normal variate. Based on the characteristic wavelength of SPA screening and PSO algorithm, the modeling parameters of LSSVM are automatically optimized and a multivariate nonlinear calibration model is established. The results show that the SPA-PSO-LSSVM model has higher accuracy and stability than the comparison models. For the verification set, the root mean square error is 0.67, the coefficient of determination is 0.91, and the residual predictive deviation is 3.10.

Bacterial Raman spectrum is characterized by a weak signal, high similarity, and susceptibility to noise. Its classification using traditional machine learning approaches requires complex spectral preprocessing, and the efficiency is low. In this study, to enhance the accuracy and efficiency of bacterial Raman spectral classification, a one-dimensional convolutional neural network model Raman-net based on dense connection is suggested, which could efficiently complete spectral classification without additional spectral preprocessing. The experimental findings demonstrate that the classification accuracy of Raman-net for 30 bacterial low-signal-to-noise ratios Raman spectra in the Bacteria-ID public data set is 84.26%, which is substantially higher than that of traditional machine learning approaches and comparison approaches. Raman-net attained a classification accuracy of 99.16% for surface-enhanced Raman spectroscopy of 2 Klebsiella pneumoniae susceptible and resistant to carbapenems. This demonstrates that Raman-net can attain remarkable classification findings for ordinary Raman spectroscopy and surface-improved Raman spectroscopy of bacteria without spectral preprocessing, and offers a fast and efficient approach for Raman spectroscopy identification of pathogenic bacteria.

To achieve the quick nondestructive detection of hazelnut protein, a near infrared spectroscopy and interval random frog algorithm-based hazelnut protein detection model is proposed in this paper. After extracting the near infrared spectral data of hazelnut, first-order derivative and standard normal variable transformation preprocessing on the hazelnut spectral data is performed. Considering the uncertainty of the initial subset of the random frog algorithm and the final band number threshold's uncertainty, an interval random frog algorithm is utilized to extract the characteristic band, competitive adaptive reweighted sampling algorithm, and successive projections algorithm, and the original random frog algorithm are compared. Furthermore, a partial least squares regression model is developed based on the extracted feature bands. The experimental findings depict that the interval random frog algorithm had the best performance and the developed model is more stable when compared with other algorithms. The regression coefficient and root mean square error of the interval random frog algorithm for the cross-validation set are 0.9082 and 0.0178, respectively, and the regression coefficient and root mean square error for the test set are 0.8999 and 0.0372, respectively.

Sunscreen is a common semi-fluid substance, and it is difficult to obtain better results by direct ablation and detection by laser-induced breakdown spectroscopy (LIBS). The effects of film thickness and substrate material types on spectral signals were discussed, and the optimal experimental conditions for LIBS detection were determined. Under optimal conditions, the detection limit of Cd element was calculated by linear fitting to be 2.17 μg·g-1, which has reached the national standard. The results prove that LIBS technology can be used for the quantitative analysis of heavy metal elements in sunscreen, which provides a basis for the detection of heavy metal elements in cosmetics.