With its high torque ratio and stable low-speed operation, the Segmented Arc Permanent Magnet Synchronous Motor provides high-performance drive technology support for large-aperture astronomical telescope observations. Improving the motor’s performance is challenging due to various internal and external interferences during its operation, such as parameter distortion, harmonics, etc. To this end, this paper proposes an integral sliding mode controller based on a new reaching law and a hybrid control strategy that combines an expanded state observer and a load observer, aiming to optimize the traditional sliding mode control and enhance the system’s anti-interference ability. The traditional reaching law has complicated parameters and cannot suppress chattering well. The new reaching law simplifies the parameters and effectively overcomes the system chattering. Second, an expanded state observer is used to estimate the feedback speed. Then, the q-axis current information and the estimated precise speed data are combined as the input of the load torque observer. This further improves the load observation performance and converts the load observation value into current for pre-processing. Feedback compensation is used to improve the moter’s anti-interference performance. Simulation and experimental results show that the proposed dual observer method can accurately observe the motor's speed and load, significantly enhancing the motor’s ability to resist load disturbances. At the same time, the new sliding mode speed controller reduces the motor speed overshoot and suppresses the buffeting of the sliding mode to a certain extent, providing theoretical and experimental support for arc motors in high-precision observation applications of large-aperture astronomical telescopes.

In non-Hermitian systems, controlling the gain or loss of the system can enable the system state to transition from PT-symmetry to broken PT-symmetry. This transition leads to a special point known as the exceptional point, where the system eigenvalues and eigenstates become simultaneously degenerate. When combined with metasurfaces, the exceptional point leads to various intriguing optical phenomena, such as asymmetric transmission, exceptional topological phase, and the non-Hermitian skinning effect. However, active metasurfaces introducing gains are difficult to realize experimentally. Therefore, designing passive metasurfaces using equivalent gains through loss becomes a powerful tool in non-Hermitian research. In this paper, we review the theoretical models, research progress, specific applications, and experimental design in the study of the exceptional point on passive non-Hermitian metasurfaces and look forward to the future direction of this field.

In traditional multi-line laser 3D reconstruction technology, researchers typically use a method that combines binocular epipolar constraints with laser spatial equations. This method first utilizes epipolar constraints to identify multiple potential matching points, and then filters out the correct matching points through the spatial equations of the multi-line laser. The process of 3D reconstruction is then achieved using these matching points. However, due to the inevitable noise affecting the multi-line laser lines, the extracted laser center coordinates often contain certain errors. These errors can lead to the inability to obtain high-precision 3D data when using matching points found based on epipolar constraints for 3D reconstruction directly. To address this issue, this paper proposes a method based on geometric estimation to achieve 3D reconstruction of multi-line lasers. First, by calibrating the quadratic surface equations of the multi-line laser, combined with the binocular epipolar constraint method, the initial matching points of the multi-line laser can be calculated. After finding the correct initial matching points, a geometric distance minimization estimation model is established using the distance constraint from points to epipolar lines. This geometric distance refers to the distance from the laser center points in the left and right images to their corresponding epipolar lines. Through this geometric distance minimization optimization estimation, new matching points that better conform to the epipolar constraints can be recalculated. Finally, these new matching points are used to complete the 3D reconstruction of the multi-line laser. Compared to the traditional method based on epipolar constraints, the algorithm proposed in this paper performs better in terms of matching and accuracy.The accuracy of the final 3D reconstruction can reach about 0.02mm. With this method, the overall accuracy of binocular multi-line laser reconstruction can be significantly improved, thereby obtaining more accurate and reliable 3D data.

Third-order Raman fiber amplifier is used in long-haul unrepeatered optical transmission due to its higher gain and lower noise figure. Third-order Raman fiber amplifier is an advanced technology in Raman amplification, and currently there is very limited research on it in China. The relationship between the pump configuration and performance of the amplifier is not clear yet. Therefore, this paper analyzes the influence of second-order pump seed light on third-order Raman fiber amplifiers through experiments. Firstly, the feasibility of not using second-order pump seed light is qualitatively analyzed. Then it is experimentally verified that in the absence of second-order pump seed light, the third-order Raman fiber amplifier can still achieve signal light gain, but its efficiency will decrease. A 47-channel 200 km wavelength division multiplexing transmission system is constructed, the experimental results show that the third-order Raman fiber amplifier can amplify the signal light without second-order pump seed light, but the introduce of the second-order pump seed light can significantly improve its performance. A second-order pump seed light with only 25 mW can achieve a minimum signal power gain of 3.7 dB, an average gain of 6 dB, and an average signal-to-noise ratio gain of 1.6 dB. Eliminating second-order pump seed light can reduce costs, but introducing a second-order pump seed light brings significant performance improvements to third-order Raman amplifiers.

In order to solve the problem of high-precision surface map testing of coaxial high-order aspherical surface, a null compensation testing method based on CGH is proposed in this paper. Based on the above method, we can effectively realize the separation of the diffraction order in the coaxial aspherical compensation design, and realize the null compensation design of the mirror to be measured. Combined with engineering examples, we have realized null compensation testing design for a coaxial high-order aspherical mirror with 260mm aperture. From the CGH design results, it can be seen that the theoretical design testing residual can reach 0nm RMS value based on our design method described in this paper. At the same time, we also completed the practical testing of the coaxial high order aspherical mirror. In order to further analyze the testing results, we carried out error analysis on the error source in the testing process, so as to verify the reliability and accuracy of the method.

Scanning interference field exposure (SBIL) is an effective way to fabricate monomeric large-area high-precision gratings. Using dual-frequency laser interferometer feedback table position to splicing interference fringes accurately, the measurement error will inevitably introduce grating engraving error and reduce the diffraction wavefront quality of grating. The intrinsic error caused by the structure of laser interferometer is analyzed, and the evaluation method of the intrinsic error index of laser interferometer in complex environment is proposed. The theoretical models of dead path error and measuring optical path variation error combined with actual working conditions and empirical formulas are established. By constructing translation and rotation operators, the coupling relationship between rotation and displacement of any point of the table is deduced, and the measurement errors under different table attitude roll angles are simulated. The displacement error experiment and grating scanning exposure experiment are carried out. The experimental results show that the displacement error is consistent with the theoretical calculation results. The diffraction wavefront of the 200 mm×200 mm grating is 0.278λ@632.8nm. The analytical method in this paper connects the transmission link between the grating diffraction wavefront and the measurement error, and lays a theoretical and experimental foundation for the fabrication of meter-size nano-precision holographic gratings.

Granulation is a common internal disease of citrus fruits, and it is difficult to identify the fruits with this disease from their external features. In this study, an acoustic vibration experimental setup was constructed using a micro-laser Doppler vibrometer (micro-LDV) and a resonance speaker. This was used to collect vibration response signals of ‘Aiyuan 38’ jelly orange. The one-dimensional vibration response signals were converted into vibration multi-domain images, and a Resnet-Transformer network (ResT) was constructed to extract deeper features from the vibration multi-domain images for identifying granulation disease in jelly oranges. In this paper, the ResT, Resnet50, and Vision Transformer (ViT) models were trained using vibration multi-domain images, and their performances were compared. Then, partial least squares discriminant analysis (PLS-DA) and support vector machine (SVM) models were trained using vibration multi-domain image texture features or vibration spectrum features, and the performance was compared with the ResT model. The results show that the ResT model trained using vibration multi-domain images can achieve accurate identification of jelly orange granulation disease with 98.61% detection accuracy, 0.986 F1, 0.986 precision, and 0.986 recall. The proposed method can accurately identify granulated jelly oranges with simplicity, speed, and low cost.

The electrowetting triple-liquid lens has excellent zoom performance, but its structural complexity and design difficulty are relatively high. Therefore, we propose a method for optimizing the structural parameters of the electrowetting triple-liquid lens based on joint simulation. To design a triple-liquid lens, Comsol and Zemax software are used to establish triple-liquid lens simulation models under different structural parameters, and its focal lengths under different voltages are obtained. The effects of height and taper on zoom range and initial focal length are analyzed, and a set of structural parameters with the maximum zoom range and the longest initial focal length is determined. To verify the methods reliability, we prepare the triple-liquid lens models with different heights and tapers, and conduct zoom experiments. The simulation and experimental results show that the initial focal length of the triple-liquid lens correlates positively with height and taper; the zoom range correlates positively with taper, but height is the main influencing factor. When the height is 12 mm and the taper is 20°, the lens has the most extensive zoom range and the longest initial focal length. When the taper is less than 15°, the simulation and experimental results are highly consistent.

There is nonradiative recombination in waveguide region owing to carrier leakage, which in turn reduces output power and wall-plug efficiency. In this paper, we designed a novel epitaxial structure, which suppresses carrier leakage by inserting n-Ga_0.55In_0.45P and p-GaAs_0.6P_0.4 between barriers and waveguide layers, respectively, to modulate the energy band structure and to increase the height of barriers. The results showed that leakage current density reduced by 87.71%, compared to traditional structure. The nonradiative recombination current density of novel structure reduced to 37.411 A/cm², and output power reached 12.80 W with wall-plug efficiency of 78.24% at an injection current density 5 A/cm² at room temperature. In addition, temperature drift coefficient of center wavelength was 0.206 nm/°C at the temperature range from 5 to 65 °C, and the slope of fitted straight line of threshold current with temperature variation was 0.00113. The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.

In order to enhance the control performance of piezo-positioning system, the influence of hysteresis characteristics and its compensation method are studied. Hammerstein model is used to model the dynamic hysteresis nonlinear characteristics of piezo-positioning actuator. The static nonlinear part and dynamic linear part of the Hammerstein model are represented by models obtained through the Prandtl-Ishlinskii (P-I) model and Hankel matrix system identification method, respectively. This model demonstrates good generalization capability for typical input frequencies below 200 Hz. A sliding mode inverse compensation tracking control strategy based on P-I inverse model and integral augmentation is proposed. Experimental results show that compared with PID inverse compensation control and sliding mode control without inverse compensation, the sliding mode inverse compensation control has a more ideal step response, no overshoot and the settling time is only 6.2 ms. In the frequency domain, the system closed-loop tracking bandwidth reaches 119.9 Hz, and the disturbance rejection bandwidth reaches 86.2 Hz. The proposed control strategy can effectively compensate the hysteresis nonlinearity, and improve the tracking accuracy and anti-disturbance capability of piezo-positioning system.

In order to study the polarization characteristics of typical airport ground materials, this paper provides a theoretical model. This model is required for the development of polarization imaging instruments. Based on the P-G model, it first analyzes serious shadow masking effects. These effects occur when light is incident at a large angle. It then optimizes the shadow masking function using the spherical trigonometry formula. This optimization equates the specular reflection point to a three-dimensional sphere. Due to the unique dispersion characteristics of different targets, a new bidirectional polarization distribution function (BPDF) model is introduced. This model replaces the traditional BRDF parameter affected by wavelength and body scattering. The new BPDF model integrates diffuse reflection and body scattering. In the experimental stage, the accuracy of line polarization degree is calibrated. The line polarization degree of typical airport ground material is fitted with model parameters. This fitting is based on the dynamic TS algorithm through multi-angle BRDF experiments. The fitting model's six parameters are used to obtain the root mean square roughness parameter. This process verifies the validity of the modified BPDF model. In the simulation stage, the root mean square error (RMSE) is used as the accuracy index. The modified BPDF model, control model, and experimental results are compared. This comparison analyzes the effects of detection angle, azimuth angle, and incidence angle on polarization characteristics. The accuracies of four experimental targets improved by 4.39%, 4.00%, 4.17%, and 5.26%. This is compared with the control model. The root mean square error is less than 0.05 for large detection angles. This allows the modified model to study polarization characteristics of rough materials like airport ground targets. Finally, the effect of fitting parameters on polarization characteristics is simulated. Results show that line polarization is positively related to the refractive index. It is inversely related to surface roughness. The accuracy of the modified BPDF model is thus proved. This provides ideas for studying polarization characteristics of airport ground targets.

To identify orbital angular momentum (OAM) with imbalanced label, a derived model based on global cost SMOTE and deep extreme learning machine (DELM) has been proposed. Different from typical machine learning methods, the proposed model can obtain the analytical expression of the mapping model. It will avoid the repeated parameter optimization process, thus building a suitable model for time-varying engineering applications. In the data generation stage, the inverse matrix of covariance is used to remove the dimension influence, and the differences of the same sample set are measured effectively. In the model selection stage, considering the transmission characteristics of light signal in atmosphere turbulence, the DELM is adopted to quantify the mapping relationship between light spots and labels. Then the FISTA algorithm helps to calculate the analytical expression of the model. Experiments are carried out on different intensity atmospheric turbulence data sets. The representative comparative methods include WELM and K-nearest neighbor. Experimental results show that the root mean square error(RMSE) of the proposed method achieve 0.2049 and 0.0894, which are superior to the comparison method under different turbulence intensities. It is proved that the proposed method can fully explore the characteristics of OAM spot collection and has better recognition effect.

This paper presents a topological load difference detection technique for the orbital angular momentum of vortex beams. Two vortex beams with different topological charges obtained the periodic intensity distribution. The orbital angular momentum of the vortex beam to be measured can be quickly and accurately calculated by reading the number of spots in one period. The traditional interference and diffraction methods need to receive the complete vortex beam. In contrast, the topological charge difference method only needs to receive a small amount of vortex beam to measure. This has great advantages in the measurement of high-order and large-scale vortex beams. It has potential applications in long-distance free-space optical communication of vortex beams.

To realize effective co-phasing adjustment in large-aperture sparse-aperture telescopes, a multichannel stripe tracking approach is employed, allowing simultaneous interferometric measurements of multiple optical paths and circumventing the need for pairwise measurements along the mirror boundaries in traditional interferometric methods. This approach enhances detection efficiency and reduces system complexity. Here, the principles of the multibeam interference process and construction of a co-phasing detection module based on direct optical fiber connections were analyzed using wavefront optics theory. Error analysis was conducted on the system surface obtained through multipath interference. Potential applications of the interferometric method were explored. Finally, the principles of the multipath interference process were experimentally revealed. Evidently, flat-field calibration and incoherent digital synthesis enhanced the fringe contrast to more than 0.4, with the dynamic range exceeding 10 times the working center wavelength (1550 nm). Moreover, a resolution better than one-tenth of the working center wavelength (1550 nm) was achieved. Simultaneous three-beam interference can be achieved, leading to a 50% improvement in detection efficiency. This method can effectively enhance the efficiency of sparse aperture telescope co-phasing, meeting the requirements for observations of 8–10 m telescopes. This study provides a technological foundation for observing distant and faint celestial objects.

Fast steering mirror (FSM) typically operates in harsh environments, susceptible to vibrations, temperature fluctuations, and other factors, which can lead to malfunctions. Focusing on the most prevalent constant bias fault, this paper proposes an LMI-based fault observer design method, aiming to enhance the reliability of fault detection and strengthen the stability and anti-interference capabilities of the FSM. Firstly, the model identification method based on Hankel matrix is employed to identify the two-axis fast steering mirror model including the coupling effect. Then, the fault model of the fast steering mirror system is established, and the fault observer of the fast steering mirror is designed by using the LMI-based method. Finally, the proposed method is verified through simulations and experiments. The results indicate that when both axes of the fast steering mirror have constant bias faults in the actuators and sensors, the Riccati-based fault observer can only detect the fault in one axis, while the LMI-based fault observer can detect faults within 0.1 seconds after the fault of the X-axis occurs, and detect faults within 0.06 seconds after the fault of the Y-axis occurs. Therefore, the fault observer designed by the LMI method proposed in this paper can improve the fault detection performance of the fast steering mirror.

In phase-shifting profilometry, the non-standard phase-shifting profilometry combined with the temporal phase unwrapping algorithm requires fewer fringe patterns, thereby achieving higher measurement efficiency. Given that fringe frequency has a significant effect on measurement accuracy, this paper analyzes phase errors in the temporal phase unwrapping of the non-standard phase-shifting profilometry and further evaluates its reliability. It is found that the reliability of phase unwrapping is closely related to the allocation of fringe frequencies. Consequently, an optimal fringe frequency allocation strategy is proposed. Based on this strategy, this paper conducts comparative experiments on different frequency combinations of non-standard phase-shifting profilometry, and the experimental results show that compared with the non-optimal frequency combinations of the 3f_h1+2f_h2+2f_h3 heterodyne algorithm, the average error rate of the frequency combination proposed in this paper is reduced by 62.96%; compared with the non-optimal frequency combinations of the 2f_h+2f_m+3f_l hierarchical algorithm, the average error rate of the frequency combination proposed in this paper is reduced by 49.23%.

Due to the constraints of volume and weight in spacecraft, it is challenging to simultaneously obtain large aperture, high resolution and hyperspectral information in satellite remote sensing systems. This paper proposes a novel hyperspectral imaging system that utilizes a shared primary and secondary mirror design, along with a coaxial five-mirror optical path for multi-channel separation. By integrating Offner convex grating spectroscopy, the system enables hyperspectral detection from the visible to the long-wave infrared spectrum. Design results indicate that with a primary mirror diameter of 1000 mm at an altitude of 500 km, the spatial resolution in the visible and short-wave bands exceed 2 m, in the mid-wave band exceed 3 m, in the long-wave band exceed 6m, and the panchromatic resolution is better than 1 m. The system achieves a full field of view of 2.3°, accommodating a swath width of 20 km for detection.To enhance the system's capabilities for aberration and distortion correction, high-order aspheric elements are incorporated to create a telecentric optical path, ensuring optimal matching between the telescope and the spectrometer. Furthermore, we propose housing the spectrometer module in a cooling chamber to effectively mitigate the impact of background radiation from the optical structure on image quality.The final design demonstrates excellent imaging quality, a simple layout, and a compact structure, enabling the simultaneous acquisition of high spectral information across the entire spectrum. This system has broad applications in satellite-based earth observation and imaging.

CMOS image sensor is one of the most widely used sensors, widely used in aerospace, medical imaging, industrial detection, military reconnaissance and other fields.The laser interference and damage of CMOS image sensor has also become a research hotspot in related fields at home and abroad. To investigate the impact of pulsed laser on back-illuminated CMOS image sensors, this paper selects the Sony IMX178 back-illuminated CMOS image sensor as the target material. Based on the heat conduction equation, the finite element simulation software COMSOL Multiphysics is used to compare and calculate the temperature distribution of the CMOS image sensor under the irradiation of single-pulse lasers with different parameters.The calculation results indicate that the point damage thresholds of the sensor under the effects of single-pulse lasers at 532 nm (1 ns), 1064 nm (1 ns), 532 nm (30 ps), and 1064 nm (30 ps) are respectively 61.12 mJ/cm², 75.76 mJ/cm², 31.83 mJ/cm², and 37.43 mJ/cm².Subsequently, an experimental study on the laser irradiation effects of back-illuminated CMOS image sensors was conducted.The experimental results demonstrate that the image sensor exhibits a lower damage threshold under the influence of 532 nm pulsed lasers compared to 1064 nm pulsed lasers; picosecond pulsed lasers, with higher peak power compared to nanosecond pulsed lasers, are more prone to causing point damage; the calculated point damage thresholds are in good agreement with the experimental results.

In order to explore the effect of titanium dioxide (TiO₂)/poly(sodium 4-styrenesulfonate) (PSS) nanofilms on the Kretschmann-type surface plasmon resonance sensor, the spectral changes of the sensor after depositing TiO₂/PSS nanofilms of different thicknesses were systematically studied. The reasons for the spectral changes were further explained and discussed theoretically. First, TiO₂/PSS multilayer films were deposited in situ on the surface of the glass chip sputtered with a gold layer via electrostatic layer-by-layer self-assembly technology, and the corresponding reflection spectra of the sensor were recorded in real time. Then, the original reflectance spectrum data was processed to make the spectral curve clearer and more visible. Finally, the experimental results were simulated and analyzed using MATLAB software programming. The results show that as the number of TiO₂/PSS bilayers increased, four different types of reflection peaks successively appeared in the sensor’s spectra in the 450−900 nm wavelength range. The four types of reflection peaks correspond to the surface plasmon resonance mode, the first-order mode, the second-order mode, and the third-order mode of the transverse magnetic mode of the sensor, respectively. This indicates that the Kretschmann-type sensor’s sensing mode and reflection spectrum type can be modulated by controlling the thickness of TiO₂/PSS thin films.

Aiming at the problems in existing infrared and visible image fusion methods, such as the difficulty in fully extracting and preserving the source image details, contrast, and blurred texture details, this paper proposes an infrared and visible image fusion method guided by cross-domain interactive attention and contrastive learning. First, a dual-branch skip connection detail enhancement network was designed to separately extract and enhance detail information from infrared and visible images, using skip connections to prevent information loss and generate enhanced detail images. Next, a fusion network combining a dual-branch encoder and cross-domain interactive attention module was constructed to ensure sufficient feature interaction during fusion, and the decoder was used to reconstruct the final fused image. Then, a contrastive learning network was introduced, performing shallow and deep attribute and content contrastive learning from the contrastive learning block, optimizing feature representation, and further improving the performance of the fusion network. Finally, to constrain network training and retain the inherent features of the source images, a contrast-based loss function was designed to assist in preserving source image information during fusion. The proposed method is qualitatively and quantitatively compared with current state-of-the-art fusion methods. Experimental results show that the eight objective evaluation metrics of the proposed method significantly outperform the comparison methods on the TNO, MSRS, and RoadSence datasets. The fused images produced by the proposed method have rich detail textures, enhanced sharpness, and contrast, effectively improving target recognition and environmental perception in real-world applications such as road traffic and security surveillance.

In order to solve the problem of RF discharge impedance matching of high-power fast axial flow CO₂ lasers, an impedance matching network with low reflectivity and high dynamic matching range was designed to realize the efficient utilization of RF excited fast axial flow CO₂ lasers under different discharge structures. Based on the impedance matching theory of RF circuits, a multi-electrode equivalent circuit model was constructed, a method of introducing tunable high-voltage ceramic capacitors into the matching network was proposed, and a dynamic L-type matching network suitable for high-power RF excited fast axial flow CO₂ lasers was designed. The simulated dynamic L-type matching network can inject 60 kW RF power into 16 discharge tubes and achieve a reflectivity of less than 1% in the range of total load impedance of 12.81 Ω~49.94 Ω. A single-tube RF discharge experimental device was built, and the reflectivity of the dynamic L-type matching network was measured as less than 1% at 4 kW injection power, which was consistent with the simulation results. It is proved that the dynamic L-type matching network with adjustable high-voltage ceramic capacitors can achieve impedance matching in the high dynamic range, which meets the design requirements of high-power RF excited fast axial flow CO₂ laser matching circuits.

In this paper, a coal pyrolysis HCN gas concentration detection system based on thermogravimetry-tunable diode laser absorption spectroscopy (TG-TDLAS) was successfully constructed, and the stability and sensitivity of the system were further improved by combining wavelength modulation technology. Taking advantage of the characteristics of HCN with high absorption intensity at wavelength 1531 nm and less interference by common gases in the atmosphere, the HCN concentration information was obtained by second harmonic signal processing. A high-precision flow controller is used to obtain HCN from 5×10^-6 mol/mol to 20×10^-6 mol/mol using a 99% standard nitrogen dilution ratio, and the measurement data is calibrated. The experimental results show that the linear correlation coefficient R2 of HCN reaches 0.9978. Then, the effects of different coal types, heating rate, and coal particle size on pyrolysis were discussed, as well as the relationship between the coal samples’ weight loss rate and the amount of HCN concentration released. The release characteristics of HCN and the nonisothermal pyrolysis kinetics in the volatile matter of three coal types with different coalification degrees were analyzed. A pyrolysis kinetic model was established by dividing the pyrolysis temperature stages, and the activation energy and frequency factors of varying coal types at different heating rates were calculated. The results show that the HCN emission is closely related to the degree of coalification and nitrogen content of coal types. The lower the degree of coalification, the higher the nitrogen content and the more HCN emitted. Under the fixed pyrolysis final temperature, an increase in the heating rate will increase the amount of HCN released. With the decrease in coal particle size, the time of HCN release from the pyrolysis reaction will be delayed, and the HCN concentration will decrease. There was a different correspondence between the release of HCN concentration and the coal samples’ weight loss rate in different pyrolysis stages. The more intense the pyrolysis reaction, the greater the proportion of HCN concentration released to the coal samples’ weight loss rate. This study provides an important experimental basis for further evaluation of the toxicity of HCN during coal pyrolysis reactions.

Microdefects in cavity mirrors utilized in cavity ring-down spectroscopy (CRDS) adversely affect measurement accuracy. This paper establishes a microdefect scattering model grounded in Bobbert and Vlieger's Bidirectional Reflectance Distribution Function (BRDF) theory to analyze the characteristics of scattered light from microdefects under varying wavelengths, incident angles, defect sizes, types, densities, and substrate coatings. Studying the cavity mirror microdefect scattering model shows that defects in the micrometer to submicron range (100 um to 0.1 um) affect the ring-down absorption accuracy. Aiming at detecting microdefects of this order, this paper’s authors constructed analytical models of microdefect scattering and dark field detection of microdefects in cavity mirrors. Establishing and analyzing the scattering light model of CRDS mirror microdefects is critical to realizing the high-precision detection of CRDS mirror microdefects and recovering CRDS measurement accuracy.

Rapid determination of rare earth elements (REEs) in liquid-phase samples is of great significance in the fields of ion-adsorption rare earth resource exploration and exploitation, quality control of extraction processes, recycling of rare earth resources, and nuclear industry wastewater monitoring. In order to reduce the detection limit of REEs in liquid samples by laser-induced breakdown spectroscopy (LIBS), superhydrophobic array-assisted spark-enhanced laser-induced breakdown spectroscopy (SHA-SD-LIBS) was used in this study to determine the REEs in liquid-phase samples. Optimal experimental conditions were chosen to measure the REEs with the parameters of La II 394.91 nm, Er 402.051 nm, Ce II 418.66 nm, Nd II 424.738 nm, Gd II 443.063 nm, and Pr 492.46 nm as the characteristic spectral lines, and the calibration curves were established for the quantitative analysis of the solutions of six rare earth elements (La, Er, Ce, Nd, Gd and Pr) with different concentrations. The results show that the fit coefficients R² of the calibration curves were above 0.99. The corresponding detection limits were 0.007 μg/mL, 0.045 μg/mL, 0.011 μg/mL, 0.019 μg/mL, 0.041 μg/mL, and 0.008 μg/mL. The proposed method is a simple, low-cost, and highly efficient way to improve the quality of the liquid-phase sample. Compared with the conventional LIBS method, the proposed method can significantly reduce the detection limit of REEs in liquid phase samples with simple sample preparation and low cost. It can serve as a basis for new rapid and accurate methods of measuring rare earth element types and contents in liquid phase samples.

For segmented detectors, surface flatness is critical as it directly influences both energy resolution and image clarity. Additionally, the limited adjustment range of the segmented detectors necessitates precise benchmark construction. This paper proposes an architecture for detecting detector flatness based on optical fiber interconnection. By measuring the dispersion fringes for coplanar adjustment, the final adjustment residual is improved to better than 300 nm. This result validates the feasibility of the proposed technology and provides significant technical support for the development of next-generation large-aperture sky survey equipment.

To detect gravitational waves in space, the telescope and optical platform require high stability and reliability. However, the cantilevered design presents challenges, especially in the glass-metal hetero-bonding process. This study focuses on the analysis and experimental research of the bonding layer in the integrated structure. By optimizing the structural configuration and selecting suitable bonding processes, the reliability of the telescope system is enhanced. The research indicates that the use of J-133 adhesive achieves the best performance, with a bonding layer thickness of 0.30 mm and a metal substrate surface roughness of Ra 0.8. These findings significantly enhance the reliability of the optical system while minimizing potential risks.

As an advanced technology for observing atmospheric winds, the spaceborne Doppler Asymmetric Spatial Heterodyne (DASH) interferometer also encounters challenges associated with phase distortion, particularly in limb sounding scenarios. This paper discusses interferogram modeling and phase distortion correction techniques for spaceborne DASH interferometers. The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted, and the effectiveness of the analytical expression was verified through numerical simulation. The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms. In contrast, the phase distortion correction algorithm can achieve effective correction. This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer, providing a feasible solution to enhance its measurement accuracy.

Owing to the low p-type doping efficiency of GaN-based ultraviolet (UV) vertical-cavity surface-emitting laser (VCSEL) hole injection layers (HILs), effective hole injection in multi-quantum wells (MQW) is not achieved, significantly limiting the photoelectric performance of UV VCSELs. By improving hole injection efficiency, the hole concentration in the HIL is increased, and the hole barrier at the electron barrier layer (EBL)/HIL interface is decreased. This minimises the hindering effect of hole injection. In this study, we developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs. A mathematical model of this structure was established using a commercial software, photonic integrated circuit simulator in three-dimension (PICS3D). We conducted simulations and theoretical analyses of the band structure and carrier concentration. Introducing polarisation doping through the Al composition gradient in the HIL enhanced the hole concentration, thereby improving the hole injection efficiency. Furthermore, modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface, smoothing the valence band. This improved the stimulated radiative recombination rate in the MQW, increasing the laser power. Therefore, the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.

This paper describes what is thought to be the first generation of a continuous wave deep ultraviolet laser at 275 nm by efficient frequency doubling of a blue-diode-pumped Pr:YLF laser at 550 nm. A TEM₀₀ mode deep UV laser radiation at 275 nm with an output power of 351 mW was obtained through the use of novel methods of coating and LD collimating. The authors could not find any prior reports on a Pr:YLF laser operating at 275 nm and believe this paper is the first.

In order to simulate dynamic scenes with high accuracy and high reliability, a short-wave infrared (SWIR) and mid-wave infrared (MWIR) multiband catadioptric common-aperture optical system is designed. The system combines the advantages of reflection, refraction and common-aperture optical path, and is independently designed into the main optical system, short-wave optical system and mid-wave optical system. The initial structure of the optical system is obtained according to theoretical calculation, and the optical parameters are further detailed by optical design software. Finally, according to the principle of pupil matching, the sub-systems are combined. The image quality of the system is further optimized and the rationality of the system design is verified by the simulation of modulation transfer function (MTF) and distortion. The designed short-wave optical system has a field angle of ±0.107°, a focal length of 2500mm, an entry pupil size of 300mm, MTF reaches the diffraction limit, and the distortion is less than 0.3%. The field angle of the mid-wave optical system is ±0.65°, the focal length is 750mm, the entry pupil size is 300mm, the MTF is close to the diffraction limit, and the distortion is less than 1%. The system has good image quality, small size and strong practicability, and has great application potential in the field of photoelectric tracking and space detection.

Precise timing plays a vital roel in national economic development, scientific and technological progress, national defense and military security. The optical frequency standard based on two-photon transition is expected to become a practical miniaturized optical frequency standard due to its significant advantages such as high stability, good reproducibility and easy miniaturization. In this paper, the basic principle of two-photon transition is briefly described, and the research status and progress of rubidium atomic optical frequency standards based on two-photon transition at home and abroad are introduced. Finally, it is concluded that the future development trends of rubidium atomic optical frequency standards based on two-photon transition is system miniaturization, performance improvement, integrated application and engineering.

The study of atmospheric refraction is an ancient subject that has been explored by scholars since the latter half of the 20th century and remains a challenging and significant area of study. This paper presents various aspects related to atmospheric refraction to gain insight into the advances in this field. It divides the effects of atmospheric refraction into two categories: the visible to infrared bands, which are used in research fields such as optical imaging, laser transmission, and optoelectronic tracking, as well as the radio bands, in radar measurements and satellite detection. The calculation formulas for these two bands are different in their practical treatment. According to the history of the development of refractive index formulas, this paper points out the limitations of each formula. The current best choice for the former formula is the one summarized by Rüeger scholars, while for the latter it is recommended to choose the radio refractive index formula in the Rec. ITU-R P.453-14. In addition, the relationship between the refractive index of the Earth's surface and altitude, reference data for the refractive index on a global scale, and statistical distributions for the calculation of the refractive index gradient are given in the recommendation. Finally, traditional calculation methods for obtaining atmospheric refraction and optical observation methods are presented, with the former study being based on the modeling of atmospheric patterns or meteorological data, formulae for refractive indices in specific regions, or model fitting to satisfy accuracy in a single environment or on an average scale. The optical measurement method does not need the atmospheric model as the basis, not to mention relying on meteorological parameters, and the measurement results of the data in real-time, more representative of the path, can make up for some of the shortcomings of the traditional way, more in line with the development trend of the future.

In this paper, a high-sensitivity temperature and pressure sensor is designed. The sensor structure is based on the double-hinged lever structure and diaphragm to transfer pressure, adopting fiber Bragg grating (FBG1) as the strain sensor to realize the measurement of pressure. The introduction of the double-hinged lever effectively improves the pressure measurement sensitivity of the sensor. The measuring range of sensor is 0−18 MPa and the sensitivity is 453.16 pm/MPa. At the same time, another fiber Bragg grating (FBG2) is pasted on the lever to eliminate the temperature influence in the process of pressure measurement and realize the simultaneous measurement of temperature and pressure. The temperature sensitivity of the sensor is 10.41 pm/°C in the range of 25−65 °C. Due to the anti-electromagnetic interference characteristics of optical fiber sensors, they are usually used to measure temperature and pressure in harsh environment.

In response to the current problem of difficulty in achieving extremely short total length and low sensitivity in medium wave infrared zoom systems under conditions of large zoom ratio and long focal length, this paper adopts a reasonable allocation of aspherical and diffractive surfaces, as well as a low sensitivity design method for independent components. By reducing the aberration of each component, the goal of reducing system tolerance sensitivity is achieved, achieving system simplification and miniaturization, and improving the feasibility of engineering applications. Design a low sensitivity medium wave infrared zoom optical system with a total length of only 337mm and no need for folding optical paths. The system achieves a 30x zoom ratio and continuous zoom with a long focal length of 30-900mm. The system has advantages such as large zoom ratio, long focal length zoom, extremely short total length, low sensitivity, and good image quality within the full focal length range. It has significant application advantages for military applications such as target recognition, tracking, and detection in narrow spaces.

As an important component informatization database, infrared data has been extensive used territories such as night investigation, weapon navigation and long-range early warning, etc. Ship-borne infrared radiation characteristic measuring system works in the marine environment, the variation of temperature and humidity is huge. In view of the variation of environment’s temperature affects bias a lot but gain for the measuring system, this paper presents an united calibration method internally and externally based on environment temperature self-adaption amendment and amend temperature influence by means of self-adaption interpolation, thus accomplishes the valid measuring system assessment for sensibility and responsive characteristic of external target. Radiant calibration in different infrared waveband has completed by the measuring system, serial temperature have been set in each integrating time to calibrate and fit, and determined the effectiveness of the method by error statistics. In the meanwhile, the radiant characteristic of high-precision black-body and aquatic target are inversed. As a result, the obtained minimum error of 6.82%, the maximum error of 10.21% for black-body measuring precision and high confidence coefficient for measured radiant inversion value verify the effectiveness and application prospect of the calibration method presented in this paper, ulteriorly.

In order to achieve low complexity balancing of nonlinear damage at the receiver of short-range fiber optic data communication systems, we propose an equalization structure named Decision Feedback Neural Network which introduce the Decision Feedback Structure into the Fully Connected Neural Network. The nonlinear distortion is introduced by using a photodetector with a linear working area that does not match the experimental system. The experimental system is built based on a 56 Gbit/s PAM4 with a C-band direct-modulated laser, and we compare the equalization performance of decision feedback neural network with other equalization schemes. Experimental results show that compared with the fully connected neural network, the improved scheme achieves a sensitivity improvement of 2 dB at 20 km transmission, and the equalization performance is close to the convolutional neural network with lower complexity. This paper has great significance for the rate and capacity upgrade of short-distance optical fiber communication system, and can be used as a reference for further scientific research and industrial application.

The complex reflective properties of highly reflective surface bring overexposure and underexposure problems to surface structured light technology. In order to reconstruct the measured surface completely and accurately, a multiple exposure method is proposed, which can predict the exposure time according to the reflective intensity of the measured surface. Firstly, the camera response curve of the imaging system is obtained by projecting a series of uniform gray images at different exposure times, and at the same time, the irradiance image which can reflect the reflection intensity of the measured surface is calculated. Then, the fuzzy C-means clustering method is used to adaptively segment different irradiance regions of the target and obtain the central irradiance of each region, and the optimal exposure time is predicted for different reflection regions based on the camera response curve. Finally, the 3D reconstruction of the highly reflective surface is realized by combining the multiple exposure fusion algorithm. The experimental results show that the proposed method can simultaneously reconstruct the strongly reflective area and the excessively dark area of the aluminum alloy surface, with the reconstruction error less than 0.5mm, the maximum deviation reduced by 74.78% and the standard deviation reduced by 48.96%. The proposed method can correctly predict the exposure time according to the regional reflection characteristics, effectively overcome the problems of phase loss and phase distortion caused by regional overexposure and regional darkness, and completely and accurately reconstruct different reflection regions of the highly reflective surface.

Beam arrays have great application value in free-space optical communication. The light intensity evolution and the on-axis scintillation index of radial Gaussian vortex beam array propagating through atmospheric turbulence are analyzed based on multi-phase screen simulation. The effect of initial beam parameters on the scintillation properties of radial Gaussian vortex beam array is studied, and the variation of the on-axis scintillation index values of radial Gaussian vortex beam array and a Gaussian vortex beam is compared. The results indicate that in the weak fluctuation regime, the on-axis scintillation index of Gaussian vortex beams remains within a numerical range of less than 1, while the on-axis scintillation index of radial Gaussian vortex beam arrays is around 1. In the medium fluctuation regime, the on-axis scintillation index of the radial Gaussian vortex beam array is smaller than that of a single Gaussian vortex beam. And the on-axis scintillation index of radial Gaussian vortex beam array decreases with the decrease of orbital angular momentum and the increase of radial array radius. The research results have certain theoretical significance and application value for vortex optical communication in turbulent atmospheric environments.

Liquid crystal optical phased array (LC OPA) is widely used in lidar, laser communication and laser weapons to scan and control laser beams. In order to realize the optimal design of LC OPA and high-precision control of laser beam, this paper focuses on the influence of working wavelength, number of pixels, pixel size and effective grey levels on beam pointing accuracy. Firstly, according to the principle of liquid crystal phase modulation, the effective scanning angle and diffraction efficiency of the period grating and the variable period grating methods are simulated and analyzed. Secondly, assuming the phase modulation is equally divided by the driving voltage, the variation law of the pointing error with the working wavelength, the number of pixels, the pixel size and the effective grey levels is simulated and analyzed, and the multivariable universal formula is derived. Thirdly, the pointing accuracy of the nonuniform phase modulation is simulated, analyzed, and compared with the results of the uniform phase modulation. Finally, the relationship between the effective grey levels and the pointing error is verified by experiments, and the validity of the empirical formula is preliminarily confirmed. The research results can provide a theoretical basis for the design of LC OPA.

In order to meet the needs of broad band, high diffraction efficiency and polarization independent, a double-layer trapezoidal polarization independent beam grating is proposed in this paper. Firstly, based on the strict coupled wave theory, a design model of polarimetric independent combined beam grating based on particle swarm optimization algorithm is established, and the efficiency characteristics are optimized by randomly generating characteristic wavelengths. Then, the effects of slot depth, width ratio, side Angle and other structural parameters on the diffraction efficiency and bandwidth of single-layer and double-layer trapezoidal grating are analyzed in detail. Finally, the electric field enhancement characteristics of the two structures are analyzed and discussed. The results show that the double-layer trapezoidal polarimetric beam independent grating achieves a theoretical diffraction efficiency of more than 99% in the bandwidth range of 51 nm (1038 nm−1089 nm), and has a larger process tolerance than the traditional single-layer trapezoidal structure, which meets the bandwidth of 30 nm and the high diffraction efficiency of 98% in the tolerance range, and has lower near-field enhancement of the grating. Can have a stronger resistance to laser damage. The proposed double-layer trapezoidal grating with wide band and high diffraction efficiency can improve the output power of laser system, and has great application value in the field of laser beam combination.

Long-period fiber gratings have the advantages of small size, corrosion resistance, anti-electromagnetic interference, and high sensitivity, making them widely used in biomedicine, the power industry, and aerospace. This paper proposes a long-period fiber grating sensor based on periodic microchannels. First, a series of linear structures were etched in the cladding of a single-mode fiber by femtosecond laser micromachining. Then, the laser-modified region was selectively eroded by selective chemical etching to obtain the periodic microchannel structure. Finally, the channels were filled with polydimethylsiloxane (PDMS) to improve the spectral quality. The experimental results show that the sensor has good sensitivity in the measurement of various parameters such as temperature, stress, refractive index, and bending: it has a temperature sensitivity of −55.19 pm/°C, a strain sensitivity of −3.19 pm/με, a maximum refractive index sensitivity of 540.28 nm/RIU, and a bending sensitivity of 2.65 dB/m⁻¹. All of the measurement parameters show good linear responses. The sensor has strong application prospects in the field of precision measurement and sensing.

Laser communication utilizes light waves as the transmission medium. It offers many advantages, including high data rates, expansive bandwidth, compactness, robust interference resistance, and superior confidentiality. It has the critical capability to enable high-speed transmission and secure operation of space information networks. Prominent research institutions have committed to studying a series of challenges that need to be solved in the process of networking laser communication technology, including point-to-multipoint simultaneous laser communication, all-optical switching and forwarding of multi-channel signals within nodes, node dynamic random access, and network topology design. Numerous demonstration and verification experiments have been conducted, with a subset of these research results finding practical applications. Based on the analysis and discussion of space laser communication networking technology, this paper summarizes the development of laser communication networking technology both domestically and internationally, focusing on the application of laser communication networking technology in the fields of satellite constellations, satellite relays, and aviation networks; furthermore, it presents a review of pertinent domestic research methodologies, experimental validations, and technical solutions; finally, it predicts the development trend of laser communication networking technology and applications.

The Terahertz wave possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the airy disk radius. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.