We experimentally simulate a parity-time (PT)-symmetric quantum dynamics in a non- Hermitian system using a single-photon interferometer. We measure quantum final state using quantum state tomography. We observe the quantum state evolutions ranging from regions of unbroken to broken PT-symmetry using the single-photon interferometer. We experimentally prove that the eigenvalue of energy changes from real to imaginary corresponding to the non-Hermitian system from the PT-symmetry unbroken region to the PT-symmetry broken region. To the best of our knowledge, this is the first work to intuitively show the exceptional points of PT-symmetry non-unitary quantum dynamics in a single-photon interferometer from the energy perspective.

One of the gases responsible for the greenhouse effect is carbon dioxide (CO2). For climate prediction, human production, and human life, the spatial distribution of CO2 concentrations must be considered. Controlling the spatial and temporal distribution of CO2 worldwide requires an accurate inversion of CO2 concentrations. However, in the near-infrared band, surface reflectance uncertainty affects the inversion of CO2 concentration. The ratio method is introduced to process the satellite ground-to-ground radiation spectrum, and it is verified that the absorption band radiance ratio and CO2 concentration are related; moreover, inverting the CO2 concentration using the relationship is feasible. The data source was the MODTRAN4-simulated radiation spectrum, and the four absorption peaks' spectral radiance ratio and CO2 concentrations were selected for analysis. The results show that the spectral radiance ratio and CO2 concentration have an approximately linear relationship, and the linear relationship is evident at 6310 cm-1, with an error of only 1.15%. The ratio of radiance ratio to concentration is further investigated using various atmospheric and aerosol models. The results show the radiance ratio and concentration are highly correlated in the range of 0.1-0.9 reflectivities, the correlation coefficient is up to 0.98, and the average error is less than 2%. The measured data is subjected to the same processing as the simulation data, and the results are compared with simulated data. The linear relationship at 6334 cm-1 is the best among the four bands, and the linear relationship reaches 0.99. It shows that the spectral radiance ratio and CO2 concentrations have a linear relationship, and this relationship can be effectively applied to the inversion of CO2 concentration, effectively eliminating surface reflectance.

Input with the effects of the ocean's actual atmosphere, such as temperature, humidity, and wind, on the distribution characteristics of transmittance between 3-5 μm and 8-12 μm are quantitatively discussed using the radiative transfer model. The effects of different paths and the cloud type cover on the results of transmittance are also investigated. Results show that the regional and seasonal changes of atmospheric temperature, humidity, and other parameters are obvious, thereby directly affecting the calculation result of radiative transmittance. The establishment of a local atmospheric parameter model plays an important role in the calculation of atmospheric radiative transfer for photoelectric engineering.

By accurately solving the full-dimensional time-dependent Schr?dinger equation (TDSE), the dynamic interference effects in the ionization of atomic hydrogen by chirped laser pulses with different polarizations are numerically studied. The emphasis is put on the influences of the chirp parameters on the dynamic interference patterns of the photoelectron energy spectra. Numerical results show that the increase of the chirp will cause the suppression of dynamic interference pattern in three polarization cases; for any chirp parameter, the interference subpeaks show a rightward shift when the ellipticity of the pulse increases; for any chirp parameter, the dynamic interference pattern will disappear when the laser pulse is up to 30 fs, indicating that the previously reported calculation of one-dimensional TDSE cannot accurately describe the real physical process.

Compared with the mature design in near-infrared band, the lower photon energy in the 3-5 μm wavelength range puts forward higher requirements for the design of broadband optical absorption characteristics of superconducting nanowire single-photon detector (SNSPD). Therefore, a design method of broadband optical absorption characteristics of SNSPD in mid infrared band is proposed. Taking the ultra narrow nanowire structure SNSPD loaded with SiO2/Au reflective cavity as an example, on the basis of realizing impedance matching at two target wavelengths by optimizing the thickness of three dielectric layers in the upper and lower cavities, the ratio of total dielectric layer thickness to resonant wavelength is introduced as an index to evaluate the bandwidth characteristics at each resonant wavelength, so as to better achieve the balance between impedance matching accuracy and bandwidth characteristics, thus, the purpose of double broadband coupling resonance to expand the overall absorption bandwidth is achieved. The numerical results show that the proposed SNSPD can absorb at least 50% of the incident light whose electric field component is parallel to the nanowires in the wavelength range of 2928-4856 nm.

In inertial confined fusion systems, SiO2 sol-gel antireflective films have been widely used for relief-free planar transmission optical elements. However, owing to the lack of a reliable relief surface coating process, this antireflection method cannot be applied to beam sampling grating (BSG). In this study, meniscus coating and spin coating methods were studied for coating a SiO2 sol-gel antireflective film on the relief surface of BSG. Optical microscopy, optical profilometry, and atomic force microscopy were used to detect the surface morphology of the coated grating. The size and uniformity of the zero-order and negative first-order diffraction efficiency of the grating were tested. Results show that compared with the spin coating method, the grating surface coated using the meniscus coating method is smoother, the consistency of groove filling is better, the retention of the original groove is higher, the repeatability of the process is better, and the film thickness is more uniform. Diffraction efficiency test results show that coating the SiO2 sol-gel antireflective film using the meniscus coating method can effectively improve the zero-order diffraction efficiency of BSG, which increases by 3.8%. Furthermore, the meniscus coating method facilitates a better uniformity of the zero-order and negative first-order diffraction efficiency than the spin coating method.

To replace the existing manual method for measuring the ethanol content in petrol stations and improve the detection efficiency of oil quality at the station end, a new method for the on-site real-time detection of the ethanol content in ethanol gasoline is proposed. The proposed method is based on the refractive index sensitivity of the tilted fiber Bragg grating (TFBG) and can reflect changes in the refractive index of ethanol gasoline attributed to different ethanol contents. The spectral characteristics of the TFBG are analyzed using the couple model theory, and the sensing characteristics of the TFBG for ethanol content detection in ethanol gasoline are investigated. Experimental results show that in the detection of ethanol gasoline with ethanol contents of 8.3%-14.3%, the proposed method achieves a sensitivity of 6.5 nm/RIU (RIU refers to the refractive index unit) and a linear fitting degree of 0.949. The detection accuracy of the E10 ethanol gasoline sample is verified using the wavelength demodulation method, yielding a detection value of the ethanol volume fraction of 10.2% and a relative error of 2%. These findings verify the feasibility of TFBG for ethanol content detection in ethanol gasoline.

The zero-drift compensation of fiber optic gyroscope (FOG) is one of the main methods to improve the working accuracy of FOG. To achieve FOG zero-drift real-time online compensation, an online support vector machine regression (Online-SVR) method based on incremental learning is used to establish the FOG zero-drift real-time compensation scheme. In addition, a real-time temperature change rate acquisition method based on moving average is proposed, which can achieve stable temperature change rate acquisition to meet the requirements of online compensation. The radial basis function neural network, support vector machine regression, and Online-SVR are established by analyzing and preprocessing the measured data of FOG in the range of -15 °C-50 °C. At full temperature, Allan variance is used to analyze the raw and residual zero-drift after compensation of the three models. The results show that the Online-SVR model not only realizes online compensation, but also has better compensation accuracy and stability than the other two models, making it more suitable for online compensation of FOG zero-drift data.

Herein, two refractive index sensors based on exposed-core side-hole fiber Bragg gratings (SH-FBGs) with D-shaped and X-shaped fiber cross sections were proposed and demonstrated. One SH-FBG sensor with the D-shaped fiber cross section was fabricated using the side-polishing technique, in which an air hole of the side-hole fiber (SHF) engraved with the FBG is polished. Another SH-FBG sensor with the X-shaped fiber cross section was developed using the wet chemical etching method, in which two air holes of the SHF engraved with the FBG are etched. The refractive index sensitivities of the first and second sensors are measured to be 24.0 and 15.1 nm/RIU (RIU is the unit refractive index), respectively, for the refractive index of approximately 1.380 and 1.333?1.340, respectively. The 15.1 nm/RIU value can be further optimized using the corrosion scheme. Because the X-shaped SH-FBG sensor shows two polarized reflection peaks owing to birefringence and exhibits different responses to changes in external refractive index yet the same response to temperature variations, it can be used as a temperature-independent refractive index sensor. The air holes of the designed two sensors can be used as microfluidic channels, potentially simultaneously facilitating online detection and drug delivery. Our device is characterized by structural simplification and easy operation and thus is potentially useful for biosensing and medical applications.

At the initial stage of unmanned aerial vehicle formation assembly and networking in air, it is necessary to quickly discover neighbours. According to ultraviolet (UV) characteristics near direct vision communication, this study designs a spherical UV LED communication node model. The longitude at each latitude is changed to reasonably distributed UV LED based on the division of longitude and latitude. In addition, a handshake interaction information frame with random probability is designed to solve the problems of channel conflict and neighbour discovery efficiency in the neighbour discovery process. Random probability is introduced to reduce channel conflict generation, and a token-derived random avoidance neighbour discovery algorithm is proposed. Clock synchronisation information is realised through token dynamic derivation and fusion, reducing channel conflict and improving neighbour detection efficiency. The simulation results show that the spherical UV LED communication node model with a reasonable distribution of nodes can appropriately complete the full coverage of the three-dimensional space. Moreover, the neighbour discovery efficiency is significantly improved using the neighbour discovery algorithm compared with the traditional single token neighbour discovery algorithm. Compared with the multi-token random back off algorithm, the developed better reduces the channel conflict, reduces energy consumption, and achieves a good balance of the signal path conflict and neighbour discovery efficiency.

To study the temperature sensitivity coefficient of the basalt fiber (BFRP) encapsulated long-gauge fiber Bragg grating (FBG) strain sensor, this paper first introduces the temperature sensing principle of the long-gauge FBG strain sensor, and then selects ten fiber packages with different central reflection wavelengths long-gauge FBG strain sensors for ambient temperature test. The temperature sensitivity coefficient of the fiber-encapsulated long-gauge FBG strain sensor is obtained by fitting analysis of the center wavelength change value of the sensor and the temperature change value. The results show that the central reflection wavelength of the long-gauge FBG strain sensor has a better linear fitting relationship with temperature, and the temperature sensitivity of the BFRP packaged long-gauge FBG sensor is about 20% to 50%, which is higher than that of the bare fiber grating sensor. The temperature sensitivity coefficient measured can directly compensate for the temperature of the BFRP packaged long-gauge strain sensor.

This study presents a fiber Bragg grating pressure sensor with a variable cross-section cantilever structure, which meets the needs of surrounding rock-stress measurements in the complex environment of a coal mine. The performances of the designed sensor and a sensor with a constant cross-section cantilever structure are compared, and the relationship between the pressure and fiber grating drift is derived. The cases affecting the sensitivity of different cross-section cantilever beams are analyzed using the finite element method, and the size of the cantilever beam is determined. The effects of different structures and material parameters on the sensitivities of the two cantilever structures are determined through a numerical and finite element analysis. The results are compared with the experimental results of a similar structure. The results showed that the variable cross-section beam should be designed with a relatively thin fixed end and a relatively thick free end. In the final variable cross-section cantilever beam, the thicknesses of the fixed and free ends were 0.5 mm and 2.0 mm, respectively. The sensitivity of the sensor reached 893.45 pm/MPa, which is 294 times that of the bare fiber grating. Even after changing the structure and material parameters, the sensitivity of the variable cross-section cantilever beam was greater than that of the constant cross-section cantilever beam. The sensor structure can meet the needs of coal mine roadway monitoring and exhibits good linearity in the operating range.

Fiber Bragg gratings (FBGs) using femtosecond laser inscription technology exhibit stable thermal ability at approximately 1000 ℃. High temperature sensors based on femtosecond FBGs demonstrate good repeatability and consistency with thin steel tube packages. The temperature measurement accuracy of the sensor reaches ±5 ℃ within 1000 ℃, which indicates that the femtosecond FBG high temperature sensor can measure temperature up to 1000 ℃. Applications of the sensor in quasi-distributed temperature sensing of the top, middle, and bottom parts of an aeroengine using a three FBG sensor array with 15 femtosecond FBGs was conducted. The results reveal that the highest temperature of the top, middle, and bottom parts is 460 ℃, 600 ℃, and 520 ℃, respectively. Moreover, the circumferential temperature distribution is approximately same. This successful application of the femtosecond FBG high temperature sensor in quasi-distributed temperature sensing of the cylindrical parts indicates good performance in accurate temperature measurement and temperature distribution.

In this paper, an optical transmitting antenna is designed using free-form surface design theory, which can generate a uniform rectangular spot to solve the problems of difficult alignment and poor spot uniformity in underwater wireless optical communication systems. The simulation results show that when the distance of the target plane is 10 m, the free-form lens can produce a rectangular spot with 87.3% uniformity and the light energy utilization rate is 93.4%. The free-form lens is applied to the underwater transmitting antenna, when the receiver sensitivity is -?30 dBm and the receiving aperture is 50 mm, the maximum communication distance of the turbid water is 2.3 m, and the maximum communication distance of the pure and clear sea water is greater than 10 m. Compared with the single antenna, the edge uniformity of the spot produced by the 360° omni-directional optical transmitting antenna composed of three sets of the free-form lens increases from 17.4% to 35.2%. The transmitting antenna improves the stability of the underwater optical communication link and provides a new technical idea for solving the alignment problem in underwater wireless optical communication.

In order to alleviate the low-resolution issue, a three-dimensional (3D) display simulation method based on frequency domain translation has been proposed. A virtual camera array has been built to collect the light field information of 3D objects to obtain the element array image (EIA). The shifted information of simulation EIA of 3D object can be generated by translation. The simulation EIA has fused with the shifted data. The final 3D display result can be obtained by time division multiplexing. Compared with the traditional methods, the proposed method is relatively simple, which has faster calculation speed and better display quality. And it has great development potential in the prediction and optimization of the light field display.

A reflectance transfer spectrometer can be used to accurately and quickly calculate the spectral reflectance of the ground target from the measured spectral irradiances of the sun and ground, thus achieving the long-term stable-radiation standard transfer on-orbit. In this process, a pinhole aperture is used to largely attenuate sunlight for the direct imaging of the solar disk. The accuracy of the pinhole aperture attenuation factor directly determines the measurement and transfer accuracies of the reflectance. Based on the calibration principle of detector response nonlinearity using a laser, a method that combines the wide dynamic standard light source with a back spectrometer for comparison measurements is proposed for the high-accuracy calibration of the attenuation factor of a front pinhole aperture. Results show that the attenuation factor of the pinhole aperture shows obvious nonuniformity both in terms of the spatial and spectral dimensions. After modifying the experimental outdoor reflectance measurements, the relative difference of the measured spectral reflectance of the white diffusing plate can be reduced from 20% to less than 2%. This finding proves the validity of the laboratory calibration of the aperture attenuation factor and can provide a technical basis for the high-accuracy cross calibration of reflectance transfer spectrometers.

Incoherent laser off-target quantity detection relies on quadrature phase demodulation, and the application of a Kalman low-pass filter can significantly improve the phase discrimination performance of digital quadrature demodulation phasemeters. This paper proposes a solution based on Sage-Husa adaptive filtering, which uses adaptive factors to adjust the state prediction covariance array to effectively reduce the model errors and improve the filtering accuracy, to address the problem that the accuracy of the Kalman low-pass filter decreases when the noise statistics information is unknown. The adaptive Kalman filtering method may substantially improve the phase identification performance of a digital phase-locked demodulator and reduce the decoding error of off-target amount under low signal-to-noise ratio, according to Matlab simulation studies.

The generation of anti-Stokes light based on KGd(WO4)2 (KGW) crystal under the condition of narrow interval pulse train synchronous pump is studied. Using KGW crystal as Raman crystal, pulsed picosecond laser as pump source, the wavelength is 1064 nm, and the pulse repetition rate is 1 kHz. Using flat-flat cavity, plano-convex cavity, and concave-convex cavity as synchronous Raman cavity, the thresholds of anti-Stokes light produced by the three kinds of cavity structures is studied, respectively. Experiments have proved that when the synchronous Raman cavity adopts a plano-convex cavity and a concave-convex cavity structure, it produces a low-threshold output and a high-order anti-Stokes light with a threshold lower than the second-order Stokes light. Light output, where the threshold of high-order anti-Stokes light under the plano-convex cavity structure is lower.

Laser cladding experiments were performed on Ti-C-Nb and Ti-C-Nb-graphene powders. The microstructure, microhardness, and strengthening mechanism of the coatings were analyzed using X-ray diffraction(XRD) and backscattered electron (BSE) imaging. The microstructural and phase analyses of the coating show that the coating is metallurgically bonded to the substrate. Moreover, the microstructure of the coating is composed of γ-Ni, Cr23C6, TiC, and (Ti, Nb) C granular phases. TiC and (Ti, Nb) C particles are dispersed in the γ-Ni grain boundaries and in the grains. The addition of graphene can remarkably refine the grain size and facilitate an evenly distributed particle phase. Furthermore, the microhardness of the coating can be improved remarkably.

Owing to the high melting point of tungsten (W), achieving high-density W and W alloy components is challenging. In this study, different methods were used to study the effects of process parameter adjustment and Re addition conditions on the density, microstructure, and mechanical properties of W-Re alloys. Results show that the density of the W-Re alloy is directly proportional to the laser power and inversely proportional to the scanning speed. When the laser power was 180 W, the scanning speed, scanning interval, and maximum density are 600 mm/s, 0.03 mm, and 96.1%, respectively. The process parameters were optimized to reduce pore formation and achieve fine-grain strength, realizing the maximum hardness of 550 HV. The displacement solution of Re induces a right shift of the diffraction peak of W. At high temperatures, Re can strengthen the solution of W. The density, hardness, crack size, and morphology of the selective laser melted W-Re alloy are better than those of the pure W alloy.

Based on the coupling characteristics of waveguide and microcavity in two-dimensional photonic crystals, an all-optical 4×2 encoder is proposed. The encoder realizes a high-contrast fast encoding function by introducing a microcavity into the Y-shaped waveguide. The performance of the proposed 4×2 encoder is studied by using plane wave method (PWM) and finite-difference time-domain (FDTD) method. The results show that the proposed encoder has a contrast ratio up to 24.55 dB, a response time not exceeding 1.11 ps, a data transmission rate not less than 0.90 Tbit/s, and a size of about 147.45 μm2 at a working wavelength of 1.55 μm. The proposed encoder has simple structure, high contrast, fast response speed, and easy integration, which is expected to play an important role in the fields of optical communications and integrated optical circuits.

Scanning silicon surface with a picosecond laser with pulse width of 10 ps, frequency of 200 kHz and wavelength of 1064 nm will self-form microhole structure. By changing pulse energy density, scanning speed and scanning times, the evolution law of microhole is studied experimentally. The results show that the influence of different parameters on microholes can be summarized as pulse energy density and effective pulse number per unit area. With the increase of pulse energy density, the microholes gradually move to both sides of the groove, from the initial random arrangement to the one-dimensional linear uniform arrangement. With the increase of effective pulse number per unit area, the number of microholes on both sides of the edge changes from less to more, and the size changes from small to large, and finally microholes disappear. By simulating the temperature field, the change of phase transition and surface tension of materials at different temperatures was analyzed. It was found that liquid silicon solidified under the drive of surface tension to form protrusions, which led to uneven deposition of laser energy and finally formed microholes. This indicates that the physical mechanism of microhole self-forming is the combined action of laser-induced material phase transformation and Marangoni effect.

The effects of scanning speed on the remelting layer depth, microhardness, surface roughness, and tensile and fracture behaviors of high energy density laser surface remelting CuCr50 alloy were investigated. The results show that with the increase of scanning speed from 2000 mm/min to 8000 mm/min, the average depth of remelting layer decreases from (486.2±32.8) μm to (26.8±13.4) μm and the average microhardness increases from 203 HV to 250 HV, which is about three times of the substrate microhardness (85 HV). The surface roughness increases with the decrease of scanning speed. The yield strength of CuCr50 alloy after laser remelting treatment on one side surface is 16.5%‒28.0% higher than that of untreated alloy. The fracture morphology of the remelting layer is equiaxed dimple, showing the ductile fracture. The fracture morphology of the substrate is mainly intergranular fracture extending along the grain boundary, showing the brittle facture. Thus, mechanical properties including microhardness and yield strength of the modified CuCr50 alloy are greatly improved. By modulating the scanning speed, laser surface modified alloy with better comprehensive performance can be obtained.

This work examines the effect of linear and volumetric energy densities on the printing of TC4 titanium alloy using selective laser melting. With an increased linear energy density, the width of the molten pool increased rapidly at first and gradually converged to a maximum value of 122 μm. Meanwhile, the height difference of the melted track decreased from 27 μm to 18 μm and then increased to 28 μm. Owing to the apparent and forming densities, the given powder thickness of 30 μm cannot represent the real powder thickness, which was re-evaluated to be 55 μm by the numerical model in this work. The re-evaluated powder thickness was then applied to calculate the volumetric energy density quantitatively. By comparing the relationship between the linear and volumetric energy densities with the surface roughness and efficiency of space filling of cube samples, it was observed that volumetric energy density can be used as a process parameter to evaluate three-dimensional printing quality.

Laser radar is widely used in unmanned driving, surveying, and mapping, etc. In order to reduce power consumption, cost, and volume, pulsed semiconductor laser has become the first choice of laser drive circuit. Under this background, an optimal design of narrow pulse and large current semiconductor laser drive circuit is completed with inductor as energy storage element. Based on the working principle of the driving circuit in detail, the influence relationship between the value of the energy storage inductor and the power consumption of the circuit is emphatically studied. The driving circuit simulation model was established by using ORCAD PSPICE simulation software, and the main factors affecting the pulse width, peak value, and wave oscillation of the pulse current were summarized. The test results show that the power loss of the energy storage inductor is 59 mW, the pulse width of the driving circuit is 3.8 ns, the rising edge is 3.5 ns, the falling edge is 3.7 ns, the peak current is 132 A, and the peak optical power of the laser output is about 326 W at 10 kHz.

To investigate the surface quality and mechanical properties of parts produced by powder feeding laser additive and milling subtractive hybrid manufacturing technology, using 316L stainless steel as the research object, we manufactured the samples by the alternate "additive-subtractive-additive-subtractive" cycle and tested the surface roughness, microhardness, and mechanical properties of the samples. The findings demonstrate that the surface roughness of the samples produced by the powder feeding laser additive and milling subtractive hybrid manufacturing decreases with increasing milling speed and increases with increasing feed per tooth. The powder feeding laser additive and milling subtractive hybrid-manufactured samples have lower surface roughness than the substrate sample prepared by the traditional process and have higher microhardness than additive-manufactured and forged parts. The tensile and yield strengths of powder feeding laser additive and milling subtractive hybrid-manufactured samples increase by 5% and 60.5%, respectively, compared with the additive-manufactured sample. However, their elongation rate after breaking reduces. The powder feeding laser additive and milling subtractive hybrid manufacturing technology can produce parts with high surface quality and good mechanical properties and can be directly applied to manufacture parts, such as 316L stainless steel tire molds. This method combines the features of additive manufacturing's high material utilization and degree of freedom with subtractive manufacturing's high precision and surface quality to produce parts with complex structures as well as high shape accuracy and surface quality.

Alumina ceramics have high thermal conductivity, good heat dissipation, and a small dielectric constant. It is a common substrate material used in mobile communication and integrated electronics; however, its high hardness and brittleness make it crack easily during conventional machining. In this study, we utilized a nanosecond ultraviolet laser to study the blind cutting process of an ultra-thin ceramic plate. Moreover, we analyzed the slit width and depth variations by controlling the three main processing parameters of the nanosecond laser, which were laser repetition frequency, scanning speed, and repetition times. The experimental results show that as the laser repetition frequency increases, the slit width increases and remains unchanged, and the slit depth first increases and then decreases. As the scanning speed decreases and the number of repetition times increases, the slit depth first increases and then decreases, and the slit width slightly fluctuates. With the slit depth-width ratio as the index, we obtain the following conclusions through an orthogonal experiment: the maximum depth-width ratio of single-pass multiple scanning in the blind cutting process of the ultra-thin ceramic substrate is 4.0137, and the optimal laser parameter combination is 40 kHz laser frequency, 0.07 m/s scanning speed, and 25 repetition times.

In this study, we have achieved novel continuous and passive Q-switched mode-locked operation in a Tm‍‍∶‍ZBLAN laser using a special crystal design. When the laser is in continuous operation, the maximum output power of 254, 296, and 230 mW is obtained using 1.5%, 3%, and 5% output mirrors, respectively. We use a 1.5% output mirror and transmission-type GaAs-SESAM as a mode-locking element to achieve a mode-locking operation. The absorbed pump threshold is as low as 131 mW. When the absorption pump power is greater than 1.09 W, a stable Q-switched mode-locking operation is achieved. The maximum output power is 98 mW, the pulse width of the Q-switched envelope is 6 μs, the repetition frequency is 19.23 kHz, the repetition frequency of the pulse under the Q-switched envelope is 102 MHz, and the pulse width is about 800 ps. The maximum single-pulse energy is 0.96 nJ.

In this study, the influences of different process parameters, such as the laser power, scanning speed, overlap rate, and distance from the cladding head to the substrate, on the morphological characteristics of the cladding layer, such as the average height of the cladding layer, average substrate melt depth, average dilution rate, and average surface height difference, were explored. Moreover, the prediction of the coating morphology was achieved. An entire factor experiment was designed and the mathematical model between the coating morphology and process parameters was constructed based on the response surface analysis method. The predicted results were compared with the experimental data. Results show that the scanning speed, laser power, distance between the cladding head to the substrate most significantly affect the average height of the cladding layer, average substrate melt depth, and average dilution rate, respectively. Furthermore, the average surface height difference is mostly affected by the scanning speed. The average relative errors of the average height of the cladding layer, average substrate melt depth, average dilution rate, and average surface height difference are 10.09%, 4.96%, 8.83%, and 8.34%, with the Radjust2 (goodness of fit) of 0.8971, 0.9251, 0.9240, and 0.8545, respectively.

We introduced the attenuation of rays in the absorbing medium. The proposed model was used to analyze the radial position change in the lens focus due to the optical element's heat absorption in the semiconductor processing process through simulation calculations, such as ray power, lens surface temperature distribution, thermodynamic property, deposition power, and lens refractive index change. The radial focus position deviation of the ultraviolet laser fine processing equipment with a laser source power of 20 W was calculated to be 14 μm; the simulation analysis results were verified by laser processing experiments, laser confocal microscope observation, and step meter measurement. Problems commonly overlooked in the semiconductor industry were analyzed and demonstrated in this article.

To characterize the elastic modulus of laser cladding coating, a nondestructive evaluation method based on laser ultrasonic surface wave is proposed. First, we establish a theoretical model of surface wave propagation in two-layer structures, namely, the coating and substrate. Then, we obtain the theoretical dispersion curves by solving the wave equation. Afterward, we excite and receive the surface wave signals on different areas of the laser cladding coating using laser ultrasonic equipment and obtain the experimental dispersion curves of the surface wave using two-dimensional Fourier transform. To solve the inverse problem of the surface wave, the elastic modulus of different coating regions is determined by minimizing the difference between theoretical and experimental dispersion curves. According to the elastic modulus on different areas of coating, we conclude that the coating material prepared using laser cladding technology is nonuniform. The laser ultrasonic surface wave method is useful for testing the elastic modulus of laser cladding coating and improving the laser cladding technology.

In this study, line defects and point defects are introduced in a complete two-dimensional triangular lattice silicon. Using waveguide coupling and linear interference, an all-optical half-adder structure based on photonic crystal is proposed. The half-adder consists of waveguide beam splitters, an all-optical logic AND gate and an all-optical logic XOR gate. Using Rsoft software, combined with the plane-wave-expansion method and the finite-difference time-domain method, the proposed half-adder is simulated. Results show that the contrast ratios of the "carry" and "sum" ports of the proposed half-adder are 4.67 dB and 10.77 dB when the input-light wavelength is 1530 nm, and the response time is about 2.67 ps. In order to improve the contrast ratio of the "carry" port, the structure of the half-adder is optimized. The contrast ratios of the "carry" and "sum" ports of the optimized half-adder are 8.26 dB and 15.34 dB, respectively, and the response time is 3.67 ps. Theoretically, it can reach a data transmission rate of 0.273 Tbps. The proposed half-adder with optimized structure has the characteristic of high contrast ratio, and plays an important role in all-optical signal processing systems and integrated optical circuits.

Aiming at the application requirements of natural objects false targets in laser angle deception jamming, based on the analysis of the energy transmission of jamming and the relationship between the weapon threat angle, ground object inclination, incident angle and reflection angle in the jamming process, the energy distribution model of natural object false target established. According to the established model, the simulation study on the disturbance energy distribution of sand and gravel and building features is carried out. The simulation results show that under the same conditions, the sand and gravel features have better interference effect than the building features. The interference energy reflected from the same ground object increases with the increase of the angle of the ground object. For the building false target with better diffuse reflection characteristics, when the ground object inclination is constant, the reflection energy is the largest when the threat angle roughly coexists with the ground object inclination. For sand and gravel targets, there is a mirror reflection component with the change of the inclination angle of the object, which makes the threat angle and the residual angle of the inclination angle of the object deviate, and the deviation angle is approximately a Gaussian distribution. The research results have certain guiding significance for the application of false target of natural objects.

In order to study the propagation characteristics of vortex Airy beams through electromagnetically induced transparency medium, the analytical expression is obtained for vortex Airy beams passing through the electromagnetically induced transparency medium based on the ABCD matrix optics theory. The propagation properties of vortex Airy beams passing through the electromagnetically induced transparency medium are obtained by using the formula. The results show that the center lobe is distorted due to the superimposition of the Airy beam and the vortex. The center lobe is reconstructed and the revival of the vortex after a long distance. In addition, it is feasible to controlling the intensity and the location of vortex Airy beams via manipulation Rabi frequency of the electromagnetically induced transparency medium.

At present, measurement systems for measuring diameter and roundness of steel-ball-type spherical parts have significant drawbacks, such as complexity and high cost. To overcome these challenges, we propose a method based on the Fresnel diffraction. It is found that the diameter and roundness error of a steel ball can be measured according to the light intensity distribution curve, based on the relation between the peak point and projection edge of spherical Fresnel diffraction, which is calibrated using the dot calibration plate. Experimental results show that the measurement uncertainty of the diameter and roundness error of a millimeter steel ball is less than 0.0031 mm (confidence level is 95%) and 0.0046 mm (confidence level is 95%), respectively, without considering the diffuse reflection and scattering of the steel ball surface. Our proposed system is easy to realize, cost effective, and does not need an additional optical system.

Laser-interferometric measurements, possessing the ultra-high sensitivity, have been widely applied to fundamental scientific research and practical technological developments. However, low-frequency classic noise (less than 1 Hz) dominates exclusively in the interferometer system and measurement of sub-Hertz physical signals beyond the shot noise limit is still facing great challenges. Using the degree of freedom of laser polarization as the separation channel of light energy in the interferometer and the sub-Hertz low-frequency physical signal as the detection target, the key problem of difficult acquisition of local oscillator light in the readout scheme of the laser interference signal is solved. A dual-frequency working laser is used to convert the low-frequency displacement signal into high-frequency AC photoelectric signal at the system output to naturally avoid the technical problems of 1-Hz band electronic noise, thereby providing important theoretical guidance and experimental support for quantum noise limit ultra-low-frequency laser interference and interference signal readout method. It is expected to provide a reference path and scheme for upgrading ground gravitational wave antenna.

In recent years, topological photonic crystals have attracted growing interest for their unique propagation characteristics. With the development of theoretical models in topological photonics, numerous novel applications have emerged. Topological edge states formed by topological photonic crystals can realize optical enhancement and unidirectional transmission in optoelectronic devices. Such optoelectronic devices can have distinct characteristics such as immunity to local defects and high transmission efficiency, offering enormous potential benefits to chip development, biosensor, military communication, and other applications. This study summarizes and analyzes a range of optical devices based on theoretical models of edge states formed by topological photonics in different dimensions: topological lasers, optical waveguides, unidirectional conduction devices, and optical modulators. The presented examples demonstrate the huge potential of topological photonic crystals in structural design and material selection. Finally, the current research progress of topological photonic crystals is clarified and the defects and optimization direction of topological photonic devices in the design process are evaluated and prospected.

In recent years, vortex beams have been widely used in optical communication, optical manipulation, imaging, sensing quantum information, and other fields owing to their unique phase structure and the characteristic of carrying orbital angular momentum (OAM). However, these applications must rely on the generation of high-quality vortex beams so that the optical microcavity occupies a very important position in the modern optoelectronic device manufacturing because of its compact structure, high quality factor, small element size, and other advantages. The developed new integrated optical device can emit high-quality vortex beam. The principle, research progress, design schemes, and experimental generation of optical microcavities to generate OAM beams are discussed in this paper. Simultaneously, the performance of existing OAM lasers is analyzed. Finally, the challenges faced by the applications of integrated optical devices and the directions for further improvement are considered.

Using the photomultiplication (PM) effect to enhance the external quantum efficiency of the device is a significant way to realize high-sensitivity organic photodetectors. This review introduces the research progress of PM-type organic photodetectors in recent years based on charge accumulation-type PM. The strategies for achieving PM and the corresponding PM mechanisms are clarified in detail from the perspective of the methods of implementing charge accumulation. Furthermore, the future research of the PM-type organic photodetectors is prospected.

Thulium-doped lasers are an ideal choice for biological tissue ablation and lithotripsy applications due to the advantage of efficient absorption by water molecules. They have great application prospects in the field of biomedicine. This paper briefly describes the principle of thulium-doped lasers and biological action, introduces the latest research results for thulium-doped lasers at home and abroad and their application in tissue ablation and lithotripsy surgery, and summarizes different laser parameters, including working mode and power. The effects of the irradiation time, spot area, and pulse frequency, among others, on tissue ablation and lithotripsy surgery reveal that the thulium-doped fiber lasers are an important development direction for medical lasers in the future. In addition, suggestions are made for the development of domestic thulium-doped lasers in the biomedical field.

Continuous variable squeezed light plays an important role in quantum information processing, and the most effective generation tool known is the optical parametric oscillator. At present, most research focus on the fundamental mode, however, the intensity and phase distribution of higher-order mode are more complicated. In addition, based on the characteristics of different order modes and their orthogonal characteristics, high-order mode squeezed light brings more choices and applications for quantum communication and quantum precision measurement. This review introduces the experimental research progress of the continuous variable higher-order mode squeezed light based on the optical parametric oscillator, and expounds two common methods for generating high-order mode squeezed light field, including operation in high-order mode OPO and fundamental mode squeezed light combined mode shaping device.

Based on ultraviolet-visible spectroscopy technology, a system that can be used for real-time online detection of water quality parameters dissolved oxygen (COD) was designed, and the measurement principle and overall structure (light path and circuit) design of the system were introduced. By detecting the COD of the water body, the spectral data of the COD solution was measured, the partial least squares regression (PLS) algorithm prediction model and the voltage solution model were established using the spectral data, and the prediction accuracy of the two models was compared. At the same time, considering the environmental interference factors in the water body, the impact of turbidity and temperature on the COD measurement results was analyzed, and the constructed model was compensated and corrected, which improved the detection accuracy of the system. The experimental results show that, compared with the traditional water quality COD detection method, the system achieves the purpose of fast, high-precision and real-time online detection.