ObjectiveNanowires (NWs), being one-dimensional (1D) semiconductor materials, hold considerable value due to their distinctive properties in various nanoscale optoelectronic devices. Silicon based optoelectronic technology has high compatibility with microelectronic processes, and the research and development of heteroepitaxial III-V group compounds on silicon are rapidly advancing, enabling the fabrication of silicon photonic chips. Considering the application of doped nanowires in p-n junctions and optoelectronic integrated devices, as well as the rapid development of the micro-optoelectronic industry, the research on Si based doped GaAs nanowires is of great significance. Under the influence of the tide to combine the III-V group compounds with silicon, Zn, Si doped GaAs NWs have been successfully grown on Si/SiO2 substrates using MOCVD technology. In order to explore the Zn, Si doping effects on the optical performance of GaAs NWs, variable temperature and power density photoluminescence (PL) measurement have been conducted on each sample. This manuscript will provide technical reserves and theoretical support for the further research and development of GaAs nanowires.MethodsZn, Si doped and undoped GaAs NWs have been grown via MOCVD technology under some growth conditions. The only distinguishment between three grown samples are the addition of two different dopants, which are SiH4 and DEZn. The growth morphology of three samples were detected through SEM measurement (Fig.1) in order to verify the successful growth of nanowires. The optical performance of Zn, Si doped nanowires was contrasted through low temperature PL spectrum (Fig.2). The luminescence origins of each sample were distinguished through 15 K variable power density PL tests (Fig.3). Subsequently, variable temperature PL tests were performed on each sample to verify the degree of fitting between peak position altering pattern with temperature and theoretical values (Fig.4). In the end, necessary TEM measurement was conducted on Zn doped sample to explore its structure characteristics.Results and DiscussionsThe growth morphology of three samples were detected through SEM measurement. The nanowires were grown via VLS growth mechanism on silicon substrates and the growth direction is random and chaotic (Fig.1). The optical performance of Zn, Si doped nanowires was contrasted through low temperature PL spectrum (Fig.2). The luminescence peak of Zn doped NWs was broaden compared to another samples. The luminescence origin of Zn, Si doped nanowires was investigated through variable temperature and power density PL tests (Fig.3-4). It was found out that, the optical performance of undoped and Si-doped nanowires is better seeing the luminescence origin is free exciton recombination (α＞1). However, the luminescence origin of Zn-doped nanowires is defect or impurity related transitions seeing its characteristic value α ＜ 1. Besides, its peak position is directly proportional to P1/3, indicating the WZ/ZB II type luminescence. Combining with the TEM results, it can be further verified that, Zn-doped nanowires exhibited WZ/ZB mixed structure, which was the main cause of its larger full width at half maxima.ConclusionsThis article used MOCVD technology and VLS growth mechanism to achieve epitaxial growth of silicon-based doped GaAs nanowires. Through SEM measurements, the nanowires were grown using the VLS growth mechanism and the growth direction is relatively disorderly. Through variable temperature and power density PL tests, it was found that the luminescence origin was free exciton recombination. The luminescence origin of Zn doped nanowires was defect or impurity related transitions along with the appearance of WZ/ZB II type luminescence. Based on TEM results, it can be concluded that due to the influence of Zn element, WZ/ZB mixed structure appear in Zn doped GaAs nanowires which complicated the luminescence mechanism of GaAs nanowires and added another radiation recombination. The appearance of WZ/ZB mixed structure caused the broadening of the low-temperature PL peak of Zn doped GaAs nanowires. The luminescence and structural properties of silicon-based doped GaAs nanowires was regulated by changing the doping source.

ObjectiveAtmospheric temperature and humidity profiles are two important parameters for studying the state of the atmosphere, which have important applications in the research of atmospheric science. FY-4A/GIIRS (Geostationary Interferometric Infrared Sounder) has achieved the first geostationary orbit infrared hyperspectral detection, which can continuously obtain high vertical resolution atmospheric temperature and humidity profile information. Currently, when clouds exist in the GIIRS field of view (FOV), the Level 2 operational products only provide temperature profiles above cloud top within the observed field of view, and do not retrieve humidity profiles for the entire field of view. In addition, the commonly used atmospheric temperature and humidity profiles retrieval algorithms, including statistical methods, physical methods, and machine learning algorithms, are only based on a single observation field of view and do not consider the continuity of spatial information (especially horizontal dimensions) and feature transformations between fields of view. Furthermore, there was a lack of methods to retrieve atmospheric temperature and humidity profiles when the observational field of view was affected by clouds. The U-Net convolutional neural network algorithm is used to achieve the GIIRS all-sky atmospheric temperature and humidity profiles retrieval, which can obtain high retrieval accuracy under cloudy field of view.MethodsAll-sky retrieval of atmospheric temperature and humidity profiles, including clear sky and full cloud coverage fields of view, is realized with the U-Net convolutional neural network algorithm based on the GIIRS radiance observations. The algorithm converts the atmospheric temperature and humidity profiles retrieval problem into an image processing problem from the perspective of an image, and considers the image features of multiple neighboring fields of view with different weather conditions to obtain the atmospheric parameter information. This article based on radio sounding observations focuses on the accuracy assessment of the all-sky atmospheric temperature and humidity profiles retrieved by the U-Net machine learning algorithm, especially in cloudy fields of view, and analyzes the effects of different cloud amounts and different cloud optical thicknesses on the retrieval accuracy of the temperature and humidity profiles.Results and DiscussionsFrom Fig.6, it can be shown that the ME (Mean Error) and RMSE (Root Mean Square Error) of clear and all-sky retrieved temperatures by the U-Net algorithm are similar, but the RMSE of retrieval is larger below 800 hPa, especially for the clear sky in winter. From Fig.8, it can be shown that the ME is within ±0.5 g/kg for both winter and summer, all-sky and clear, with negative ME above 600 hPa, and the RMSE of clear sky is slightly smaller than all-sky. In general, the U-Net algorithm has comparable retrieval capabilities for atmospheric temperature and humidity profiles retrieval in clear sky and cloudy fields of view. From Fig.9, it can be shown that the temperature retrieval error increased with increase in cloud amount in winter time. In summer, on the contrary, the retrieval error decreased with the field of view gradually filled with clouds. This indicates that the algorithm has a slightly higher retrieval accuracy in summer compared to winter, and the retrieval accuracy is higher when the field of view has more clouds, and the algorithm is very suitable for the retrieval of atmospheric temperature profiles under cloudy conditions. Figure 10 shows that the RMSE of humidity retrieval increases with increasing cloud amount both in winter and summer. Figure 11 and 12 show that the difference of temperature retrieval error at different cloud optical thicknesses is small, while the humidity retrieval error increases with the increase of cloud optical thickness.ConclusionsThe U-Net retrieval ability of temperature and humidity profiles with cloudy field of view is equivalent to that of clear sky, and the accuracy of temperature retrieval in summer is better than in winter, which is beneficial to the monitoring of disastrous weather in the season of frequent occurrence. In the summer when the cloud system is more active, the retrieval accuracy of the temperature profile becomes gradually higher with the increase of the clouds in the field of view, indicating that the algorithm was applied to retrieve the atmospheric temperature profile under cloudy conditions. And the GIIRS can obtain a good retrieval accuracy for thin clouds. Although the physical significance of the U-Net algorithm is not clear, it can quickly retrieve the all-sky atmospheric temperature and humidity profiles, especially in cloudy conditions, and can obtain higher retrieval accuracy.

ObjectiveThe detectable star magnitude limit, the number of navigation stars in the field of view, the size and weight of the optical system, and etc. are important indicators of optical detection system for all-time star sensor. And the improvement of these indicators is often contradictory and restrictive, which leads to the lack of clear optimization objectives for the parameter design of the optical system. In order to improve the comprehensive performance of the all-time star sensor, the parameter optimization of the optical system is studied in this paper.MethodsAccording to the response characteristics of the short-wave infrared detector, a signal to noise ratio model based on image gray-scale information is established. Based on this model, a parameter optimization scheme of the optical system for the star sensor is proposed aiming at two different navigation modes of tracking and strapdown. The optimization goal of tracking mode is the number of navigation stars in the celestial sphere. The maximum focal length is firstly determined according to the control accuracy of optical axis direction. Then, detectable star magnitude limit with different focal length and diameter is calculated (Fig.2) using the sky background radiation obtained by MODTRAN (Fig.1). A relatively small diameter is chosen to balance the detection ability and the optical system size. After slightly adjusting the cut-off wavelength of the detection band (Fig.3), the focal length is finally determined according to the requirements for detection capability (Fig.4). If the average number of navigation stars in FOV (field of view) is less than 3 for any focal length and diameter, only tracking mode can work (Fig.5). Otherwise, strapdown mode is selected for certain working altitude (Fig.6), and the average number of navigation stars in FOV is the optimization goal. Its change with focal length and diameter is calculated. An appropriate focal length and a relatively smaller diameter are determined when the number of navigation stars meets the requirements and its mean value is greater than 3 (Fig.7). The cut-off wavelength of the detection band is slightly adjusted to improve the average navigation star number in FOV (Fig.8).Results and DiscussionsThe parameters of InGaAs sensor from Sofradir are selected as typical values for simulation, based on which the optical system parameters of the sea-level tracking mode and the high-altitude strapdown mode are designed respectively. Working at sea level, the optimal aperture for daytime star detection is 60 mm, and the cut-off wavelength is between 1.45 μm and 1.6 μm. The focal length is selected according to the requirements of the detectable star magnitude limit. While the optimization results for 20 km is aperture of 125 mm, focal length of 400 mm, and cut-off wavelength between 1.4 μm and 1.5 μm. Besides, the corresponding conversion altitude of the all-time star sensor between tracking and strapdown navigation mode is around 20 km.ConclusionsThe prototype system (Fig.9) has a diameter of 60 mm, a focal length of 515 mm, and a cut-off wavelength of 1.48 μm, which is used to carry out daytime star tracking experiments on the ground. Stars brighter than H-band –0.1 magnitude (Fig.10-11) can be detected around 10:00 am at Hunan, Changsha (altitude of 69 m), which shows that the system has the capability of daytime star detection near the ground. The experiment verifies the validity of the simulation results, indicating that the parameter optimization theory proposed in this paper has high reference value for the optical system design of all-time star sensor.

ObjectiveThe registration problem of continuous surfaces with weak features poses a challenge in computer vision and image processing. Automotive glass is a typical example of such a continuous surface with weak features. Due to the unclear characteristics of the Reference Point System (RPS) on automotive glass, it is difficult to accurately register the three-dimensional data obtained from either three-coordinate measurement or optical methods to the RPS coordinate system. To address this issue, the research proposes a low-cost and progressive registration algorithm that does not rely on high-precision fixtures and can still achieve precise registration and dimensional evaluation.MethodsThis method first builds upon the "point to surface" ICP registration, and further proposes a rough matching with boundary penalty function correction to achieve initial alignment between the measurement data and the model, providing good initial values for subsequent registration (Fig.1). Secondly, in order to align with the results of CMM's measurement and meet industrial needs, the distance between non-RPS sampling model points and corresponding measurement data points is directly optimized through CMM's evaluation method, and the measurement point cloud is fine tuned. In order to adjust the overall minimum registration benchmark from the previous step to the RPS benchmark (Fig.2), the distance between the RPS point and the corresponding point in the measurement data was directly optimized using CMM's evaluation method, thereby achieving accurate positioning and surface shape evaluation of the RPS point in the measurement data of weak feature continuous surfaces.Results and DiscussionsThis article validates the effectiveness of the proposed progressive RPS point positioning algorithm through simulation and actual experiments. Combined with (Fig.11), it can be clearly seen that each step of adjusting the measurement data makes the deviation between the measurement data and the model closer to the deviation between the three coordinates and the model. Finally, the surface error between the measurement data and the three coordinates is controlled at the level of -0.06/0.08 mm, as shown in Fig.11, slightly greater than the measurement error of the sensor. The results are basically consistent with the simulation results, as shown in Fig.6, which meets the actual requirements. Because each step of registration is based on sampling points, which are uniformly sampled based on the model, although there are a total of three steps, fast registration of 200 000 measurement point clouds can be achieved in about 10 s using the RPS point coordinate system. And from Fig.11, it can be seen that without any step, the matching error between the measurement data and the three coordinate measurement results is much greater than the deviation between the complete progressive registration measurement data and the three coordinate measurement results. This indicates that each step of the proposed method cannot be ignored.ConclusionsThis article proposes a low-cost progressive registration algorithm to overcome the technical difficulties of optical measurement methods in measuring weak feature surface RPS localization. Experiments have shown that for 40 cm × 40 cm automotive glass, traditional methods based on point-to-point ICP matching or direct matching with models have significant positioning deviations for RPS points, resulting in a significant discrepancy from the evaluation results of the three-coordinate system. However, the deviation between the proposed method and the three-dimensional evaluation is -0.06/0.08 mm, which basically meets the industrial demand, indicating the progressiveness of the proposed method. In addition, the proposed method actually has high computational efficiency. In the future, on the basis of improving the accuracy of automotive glass surface data, it is expected to combine the method proposed in this article to achieve online full inspection of automotive glass.

ObjectiveRail fasteners play a vital role in railway infrastructure by securing rails to sleepers and preventing misalignment. Prolonged usage of these fasteners can lead to different types of defects, including visual defects such as missing, fractured, and misplaced fasteners, as well as structural defects like overly loose or tight fasteners. These defects can range from minor issues affecting passenger comfort to serious risks of derailment, posing significant safety concerns for railway operations. The use of two-dimensional visual imaging techniques allows for quick identification of visual fastener defects, while three-dimensional vision sensors capture color and depth images simultaneously. Implementing multi-modal image fusion methods helps mitigate environmental and illumination effects to improve the accuracy of visual defect detection. Three-dimensional structured light imaging aids in accurately capturing the 3D point cloud of the railway track, enabling the detection of structural defects using the fastener's spatial structure. However, further improvements are needed to enhance the accuracy and reliability of structural defect detection. As a result, a new detection approach for structural defects in railway clip fasteners based on 3D line laser sensors is proposed.MethodsInitially, a 3D line laser sensor is employed to capture the point cloud of the railway track. Subsequently, the point cloud corresponding to the fastener area is swiftly identified based on the fastener's height, and the metal clip point cloud is separated from this region using the PointNet++ network. The clip point cloud is then projected onto a 2D image, from which the clip skeleton is derived. This 2D skeleton is then transformed back into the 3D point cloud to establish the initial clip skeleton, with each point being approximated by a circular cross-section to determine the clip skeleton's center representing the clip's outline and spatial arrangement. Following this, feature points of the clip's 3D skeleton are extracted, aiding in the construction of the fastener's pressing plane and calculation of the clip gap to identify structural defects.Results and DiscussionsThis paper conducts experiments from five aspects to verify the effectiveness of the method: 1) the measurement error of the imaging system ranges between 0.019 mm to 0.054 mm by measuring the standard parts (Fig.12), indicating that the constructed imaging system is capable of accurately capturing the point cloud of track fasteners. 2) The trained PointNet++ network achieves nearly perfect accuracy in segmenting the components of fasteners, thereby providing precise data source for extracting clip skeleton and other point cloud computations (Fig.13). 3) By measuring the clip gap of three types of fasteners, WJ-8, WJ-7, and WJ-2, with different degrees of tightness, the measurement error does not exceed 0.1 mm (Fig.15). Furthermore, showcasing the method's resilience to railway conditions, rust, and contamination on the fasteners (Fig.18-19, Tab.2). 4) For bulk defect detection, with a permissible measurement error of ±0.1 mm, the defect detection accuracy is consistently above 95% (Fig.20-22, Tab.3). 5) Compared with other methods, the proposed method is more precise but is more time-consuming (Tab.5).ConclusionsA visual imaging system has been developed for rail fasteners using 3D line laser sensors. The system accurately captures point cloud data of rail fasteners. The measured clip gap of the fastener using the proposed method shows a measurement error within 0.1 mm when compared with ground-truth data. The proposed approach demonstrates strong resilience against environmental factors such as lighting, rust, and contamination on the fasteners. With a permissible measurement error of ±0.1 mm, the proposed method achieves over 95% accuracy in detecting fastener tightness defects. It is applicable for detecting structural defects in WJ-2, WJ-7, and WJ-8 types of fasteners. The computation time for analyzing a single fastener clip gap is close to 3 s, making the system suitable for offline clip gap analysis and nearly 36 times faster than manual measurement. Future work will involve utilizing point cloud of fastener components segmented with PointNet++ for precise measurements of fastener component, establishing a comprehensive database for "one-pillar-one-file" fastener classification.

ObjectiveGeosynchronous orbit (GEO) satellites are a critical component of global telecommunications and navigation systems, but they are also vulnerable to potential collisions or hostile interactions with other space objects. Therefore, the ability to accurately perceive the approach behavior of these objects is paramount for enhancing the safety and autonomy of GEO spacecraft. This paper proposes a sophisticated and reliable method for detecting the approach behavior of GEO space objects only using line-of-sight measurements of objects derived from optical imaging sensors. Existing methods often rely on distance measurements, which can be challenging to obtain accurately in space environments. Research in this paper aims to overcome this limitation by utilizing only line-of-sight information of objects, which is readily available from optical sensors. By analyzing the temporal variations in azimuth and elevation angles, we aim to identify patterns that are indicative of an approaching object and develop algorithms to accurately perceive the approach behavior of these objects.MethodsTo achieve this objective, a comprehensive analytical framework is presented. First, the effects of illumination conditions and the sensitivity of the optical sensor on the object's visibility are considered (Fig.2). Second, the azimuth and elevation angle variations of a GEO object relative to a mission spacecraft are analyzed to identify patterns that are indicative of an approaching object (Fig.4). As the object approaches, the magnitude of variations in the tangent of the azimuth angle increases over time (Fig.5), providing a potential signature for perception. By leveraging the orbital periodicity of the space object and the consistency of its visible arcs, the proposed method correlates multiple observation segments (Fig.7), fits the temporal trend of the azimuth angle tangent, predicts extreme values, and monitors the pattern of these extremes to accurately perceive the object's approach behavior.Results and DiscussionsSimulations were conducted to evaluate the performance of the proposed method (Fig.8). The results demonstrate that the method is capable of accurately detecting the approach of GEO objects using only line-of-sight measurements from optical imaging sensors. Specifically, the method achieved an accuracy rate of over 96% in identifying approaching objects using only three orbital periods of data, with each orbital period containing effective segments greater than 30 minutes (Tab.2). This high accuracy indicates that the method can provide valuable information for spacecraft self-defense systems, enabling them to detect potential threats at an early stage. Furthermore, the method exhibits several advantages over traditional methods that rely on distance measurements. First, it does not require additional sensors or instrumentation for distance measurements, thus reducing the complexity and cost of the overall system (Fig.10). Second, it is robust to variations in illumination conditions and sensor sensitivity, ensuring reliable performance in a range of environmental conditions. Finally, the method's simplicity and efficiency make it suitable for real-time implementation on spacecraft with limited computational resources.ConclusionsA method for detecting the approach behavior of GEO space objects only using line-of-sight measurements of objects derived from optical imaging sensors is designed, by leveraging the unique patterns in the temporal variations of azimuth and elevation angles. This method represents a significant advancement in the field of space safety and security, as it overcomes the limitations of traditional distance-based methods and provides a reliable means for autonomous threat detection. The simplicity and efficiency of the proposed method make it suitable for real-time implementation on spacecraft, enabling them to detect potential threats at an early stage. In summary, this research has laid the foundation for a new paradigm in space object perception and trackin, leveraging line-of-sight information from optical sensors to provide enhanced capabilities for spacecraft self-defense and situational awareness.

ObjectiveTerahertz radiation, which lies between microwaves and infrared in the electromagnetic spectrum, combines the penetration ability of microwaves with the high resolution of optical waves. This unique spectral position endows terahertz radiation with enormous potential for applications across various fields such as biomedical imaging, national security surveillance, next-generation wireless communication and non-destructive testing. The terahertz detector is the core component of a terahertz detection system, responsible for transforming terahertz radiation into electrical signals. Existing terahertz detection technologies suffer from high costs, slow response times, dependency on low-temperature conditions and high power consumption. To overcome these challenges, the development of a room-temperature terahertz detector that is highly sensitive, rapidly responsive and energy-efficient has become imperative. The study presented introduces a heterostructure terahertz detector based on a novel topological magnetic insulator, MnBi2Te4, and graphene. By exploiting the photothermoelectric effect, the detector achieves high sensitivity, swift response, and low power consumption at room temperature.MethodsUltraviolet lithography was first employed to create electrode structures on an intrinsic silicon substrate (ρ>10000 Ω·cm), followed by the deposition of 10 nm of titanium (Ti) and 50 nm of gold (Au) via electron beam evaporation. After the metal electrodes were fabricated using a lift-off process, graphene and MnBi2Te4 flakes were exfoliated by mechanical exfoliation and subsequently transferred onto the metal electrodes in sequence through a dry transfer method. In this design, the metal electrodes functioned both as conduits for electric current and as antennas for the efficient coupling of terahertz waves. When terahertz radiation was incident on the bow-tie antenna, a significant enhancement in the light absorption efficiency within the device channel was observed. For this reason, the geometric parameters of the bow-tie antenna were simulated and optimized for a terahertz source with a central frequency of 0.12 THz using the finite-difference time-domain method. After the fabrication was completed, the photovoltaic response of the heterostructure device was tested under room temperature and atmospheric conditions. The terahertz response current was amplified by a preamplifier and finally read out with a lock-in amplifier.Results and DiscussionsAt room temperature, the terahertz detector based on graphene and the magnetic topological insulator MnBi2Te4 demonstrated an ultrafast photoelectric response time of 16 μs (as seen in Fig.2(c)) at frequencies of 0.04 THz and 0.12 THz, with responsivities reaching up to 0.43 mA/W and 14.37 mA/W (as shown in Fig.3), along with a comparatively low noise-equivalent power. The detector operates on the principle of thermally exciting the carriers within the graphene-MnBi2Te4 heterojunction due to incident terahertz radiation. The differences in thermal conductivity, light absorption, and the Seebeck coefficient between the two materials create a temperature gradient that drives the carriers to move, forming a thermoelectric potential difference and effectively converting terahertz radiation into an electrical signal. The imaging results obtained from the terahertz imaging system constructed in the laboratory (as shown in Fig.5(c)) validate the performance of the detector when integrated into the system.ConclusionsIn this study, a heterostructure of graphene and MnBi2Te4 was designed to harness the synergistic effects arising from the combination of these two materials. Based on the photothermoelectric effect, the detector exhibited exceptional terahertz detection capabilities in a self-driven mode without the need for an external bias. At room temperature, the device demonstrated high responsivity, ultra-short photoresponse times, and lower noise-equivalent power at frequencies of 0.04 THz and 0.12 THz. These findings suggest that the heterojunction devices composed of the magnetic topological insulator MnBi2Te4 and graphene hold significant potential for development in the field of terahertz detection.

ObjectiveDiatomic/polyatomic molecules in rocket exhaust plumes emit specific bands of infrared radiation during high-temperature vibrational transitions, making them crucial radiation sources of concern in the measurement field. Usually, afterburning occurs when rocket exhaust plumes mix with air, releasing a large amount of heat and significantly raising the temperature level and infrared radiation of the plumes. Therefore, afterburning is a crucial step in accurately calculating the reacting flow field parameters and infrared radiation of rocket exhaust plumes. Using computational fluid dynamics (CFD) methods to predict the reaction flow field of rocket exhaust plumes and evaluate the degree of afterburning has become a feasible technical approach. This underscores the importance of constructing an accurate chemical reaction kinetics model to predict afterburning in rocket exhaust plumes. A highly accurate flow field structure is essential, as different chemical reaction dynamics models can lead to significant differences in the composition, content, and distribution of the flow field of rocket exhaust plumes. However, the infrared radiation characteristics of rocket exhaust plumes are extremely sensitive to the flow field temperature, component content and distribution. To improve the accuracy of infrared radiation calculation for rocket exhaust plumes, higher requirements are placed on the chemical reaction dynamics model for accurate flow field parameters of rocket exhaust plumes.MethodsWith solid rocket engines as the research focus, the central difference scheme method is employed to solve the three-dimensional Navier-Stokes (N-S) equations with chemical reaction sources. Based on the finite rate chemical reaction model expressed in the Arrhenius formula, a 10-step gas-phase chemical reaction kinetics model is developed for the CO/H2 reaction system. The gas radiation physical properties parameters are computed using the statistical narrow spectral band model, and the radiation transport equation is solved using the apparent light method. Through fitting of experimental data using the three-parameter Arrhenius formula, a chemical reaction kinetics model is structured to closely match the experimental data.Results and Discussions There is little difference in the plume structure calculated by different chemistry models (Fig.4), and a maximum temperature difference of 200 K exists in the area where afterburning occurs (Fig.6). The influence of chemical reaction kinetics on the unstable product CO is most significant (Fig.9(b)). The maximum difference in CO2 reaches nearly 50% (Fig.9(a)), mainly occurring in high-content regions, and the impact on low mole fraction components varies by 2-3 orders of magnitude (Fig.10). The impact of different chemical reactions on the peak intensity of spectral radiation varies by nearly 40% in the 2.7 μm and 4.3 μm bands (Fig.11), and the difference in integrated spectral band intensity within different bands reaches about 40% (Fig.13). Based on the proposed CO/H2 reaction system with 9 components and 10 steps, the difference between the calculated spectral intensity of BEM-II plumes' infrared radiation and the measured data is less than 6% (Tab.4).Conclusions Different chemical reaction kinetics models have a relatively small impact on the structure of the rocket exhaust plume flow field but have a significant effect on temperature, component generation, and infrared radiation characteristics. For different chemical reaction models, the collision frequency, temperature correlation index and activation energy parameters corresponding to each chemical reaction kinetic equation are different. Under the same operating conditions, the reaction rate and heat release (absorption) between components are different, which affects the temperature, component content, and distribution of the reaction flow field. A chemical reaction kinetics model with small errors was constructed by combining the trend of positive reaction rate curves corresponding to each reaction kinetics equation and experimental data. This study can provide high-fidelity chemical reaction models for accurately predicting the reaction flow field and infrared radiation of rocket exhaust plumes.

ObjectiveSingle photon avalanche diode (SPAD) is extensively applied in low-light detection scenarios, such as LIDAR, quantum communication and fluorescence spectroscopy, owing to its attributes of rapid response, strong anti-interference capabilities, compact form factor and low power consumption. In these applications, operation in Geiger Mode (GM) involves applying a reverse bias voltage surpassing the intrinsic avalanche breakdown voltage, endowing the SPAD with single-photon detection sensitivity. The ensuing avalanche current triggered by a single-photon signal necessitates immediate quenching to prevent sensor overcurrent damage. Achieving this quenching, coupled with prompt detector reset a standby state, is facilitated by the quenching circuit. The rapid quenching time of this circuit assumes critical importance in ensuring SPAD reliability and sustaining a high photon detection rate. The resistor $ R\mathrm{~~S} $ can quickly sense avalanche current and also play a role in quenching. However, the resistance $ R\mathrm{~~S} $ will lead to an RC delay in the passive quenching stage, which will slow down the quenching speed. Therefore, it is necessary to obtain the optimal value range of induction resistance. For this purpose, through mathematical model analyzing, a quenching circuit is designed in this paper.MethodsA fast active-passive mixed quenching circuit structure is designed in this paper (Fig.9). The value of the inductive resistance $ R\mathrm{~~S} $ is optimized to improve the relevant performance of the quenching circuit. The improvement of delay performance when the resistance increases can be combined with the overhead of layout area to draw the corresponding “cost performance” curve. When the block resistance value is constant, the increase of resistance value is linear with the consumption of area. Even if there are some differences in the intrinsic parameters of the detector due to the non-uniformity of the array, the values of the inductive resistance in the interface circuit have approximately the same best “cost performance” value.Results and DiscussionsThrough mathematical model analyzing, the inductive resistance value $ R\mathrm{~~S} $ is set to20 kΩ. The layout of the proposed quenching circuit is designed in TSMC 0.35 μm CMOS technology. The main function and performance of the circuit are tested. The delay caused by parasitic capacitance carried by the probe is taken into account. The chip test results show that the quenching time of the circuit is about 2.9 ns and the resetting time is about 1.75 ns (Fig.11). Considering that the circuit designed in this paper not only integrates the avalanche quenching circuit, but also integrates the circuit of wide range dead-time adjustment, therefore, the circuit designed in this paper using the optimized fast quenching structure has a high "cost performance"(Tab.1).ConclusionsBased on the detection and imaging application of SPAD in Geiger mode, a rapid quenching circuit is designed in this paper. The circuit adopts a fast active-passive mixed quenching structure, and the quenching time performance of the circuit is optimized. Combined with the layout area, the best value of induction resistance when the detector parameters change in a certain range is obtained. In addition, the circuit layout design and tape-out are completed based on TSMC 0.35 μm CMOS process. The chip test results show that the quenching time of the circuit is about 2.9 ns and the resetting time is about 1.75 ns.

ObjectiveLaser range-gated 3D imaging is a new type of 3D imaging technology for long-distance detection. Fog, rain, snow and other severe weather conditions have been regarded as one of the technical challenges that hinder the landing of autonomous driving in recent years. This technology has the characteristics of suppressing backscattering and increasing the effective distance. At the same time, it can achieve 3D imaging of the target with millions of pixels, showing great potential for long-distance detection in severe weather such as fog, rain, and snow. Traditional gated 3D imaging methods have problems such as high system complexity, dependence on hardware characteristics, poor system flexibility, and difficulty in balancing accuracy and real-time performance. The existing visual guidance method does not consider the visual characteristics of the gated slice image, resulting in limited accuracy. Affected by the rear radiation, the traditional RGB camera effectively detects very low in the dense fog and strong light environment. Although scanning laser radar can obtain accurate distance information, it is limited by mechanical scanning angle, resulting in low space resolution of long -distance detection timing; They are difficult to meet the long -distance detection and perception needs of autonomous driving under bad weather conditions.MethodsWe proposed a vision-guided range-gated 3D imaging method that integrates an attention mechanism. Starting from the visual level, this method focuses on calculating regional weights for object contours, areas with weak textures, and other areas to improve regional prediction accuracy. A lidar depth completion algorithm is combined with the true value used for model supervision to obtain a dense depth truth image, thereby further improving the model's depth estimation accuracy.Results and DiscussionsThe results are shown in Fig.6. In the figure, it can be seen from the rectangular box area that the proposed method has made a clear qualitative comparison with other methods. The first line is an enlarged display of the rectangular box content. The proposed method has higher detection accuracy and precision for objects at a longer distance, such as cars, traffic signs, and trees at night, while keeping the edge details of the target clearer. From the figure, it can be seen that the imaging effect of the SGM model is poor, there are regional imaging errors, low imaging accuracy, and many image noise points. The results of the methods compared with the AdaBins model, Monodepth model, and PackNet model have been improved. The imaging effect is better at a distance, but the details around the object are omitted. Overall, the imaging effect of the target is still poor. In contrast, the Gated2depth model provides a clearer imaging effect, better imaging accuracy for the target, but there are erroneous imaging of the target edge, and low imaging accuracy for the distant area. Compared with other methods, the proposed method has higher imaging accuracy in the target contour, and good imaging effect in the open area and weak texture area in the distant area. It can be seen from the comparison around the vehicle in the enlarged area that the proposed method effectively reduces the interference of noise, making the overall imaging accuracy higher. The results of the comparative test evaluation indicators are shown in Tab.1-2 below, where G2d represents the abbreviation of Gated2depth.Conclusions The result has higher depth prediction accuracy than existing methods. The experimental results show that it has higher accuracy in object contours. Through comparative experiments in bad weather (rain and snow), it is more resistant to interference than other methods, and has better range-gated imaging effects. It has the ability to suppress noise in the image and has strong processing capabilities for weak textures, obtaining clearer target edges and retaining more details. The MAE in night data increased by 6.3%, and the effectiveness of the proposed method was verified by experiments. In the future, it is necessary to further improve the network based on the optical characteristics of the gated image to improve the accuracy of depth estimation.

ObjectiveDetection of underwater obstacles represents a significant area of interest within marine detection technologies. Airborne LiDAR, an active detection modality, has found extensive application in domains including terrain surveying and underwater obstacle detection. The streak tube camera, by splitting laser light, considerably reduces the energy of emitted laser pulses for each channel. In contrast, single beam LiDAR detection capitalizes on the full energy of the emission pulse, facilitating deeper detection capabilities. LiDAR is particularly effective for detecting underwater obstacles in turbid water conditions. Considering the data characteristics of line scanning airborne LiDAR and the detection requirements, this study introduces an image processing approach inspired by the streak tube imaging system. The method involves splicing echo waveform data from each point on a scanning line to create a two-dimensional profile that directly illustrates the spatial distribution of echo energy, from which obstacle information is subsequently extracted and analyzed. An automated obstacle identification criterion is developed and validated. This research contributes to the refinement of data processing methods for underwater obstacle detection and identification using airborne LiDAR systems.MethodsA sequence of LiDAR echo data strips is chronologically assembled; Each column corresponds to an echo waveform, with gray values representing the echo energy at each point. Rows, ordered from top to bottom, depict the amplitude at respective sampling moments. To address horizontal plane deformation due to scanning angle variations, the water surface slope distance is initially extracted from the waveform using the Linear Leading Edge Approximation (LLE) method. A model representing the emission angle of the laser light is then developed, based on the scanning architecture of the ocean LiDAR system. These components are integrated to pinpoint water surface points, facilitating the calculation of the discrepancy between the laser slope distance and the actual height at specific angles, thereby correcting water surface deformation and enabling accurate obstacle contour restoration. In the subsequent image processing phase, the Canny edge detection operator is employed to identify edges with high echo energy in images generated by adjacent scan lines. This analysis includes evaluating the depth position consistency via the centroid of edge pixels and comparing contour shapes using Hu moments. Ultimately, an automatic obstacle identification criterion is established and validated using 20 sample images to assess its efficacy.Results and DiscussionsThe integration of angular modeling with Linear Leading Edge (LLE) extraction for slope distance demonstrates notable corrective effects. Energy profiles pre- and post-correction are illustrated in Fig.7(a) and 7(b), respectively. Prior to correction, the water surface height exhibits significant undulation, characterized by an increase in slope distance at larger scanning angles. Post-correction, the water surface along a scanning line appears flatter, aligning with experimental observations on a calm lake, as seen in Fig.8. Post-correction, the water surface height fluctuates around 0.45 m. Concerning obstacle morphology, the results post-correction, as shown in Fig.9, markedly improve over those in Fig.4. A high degree of similarity exists between obstacle contours extracted from adjacent scan lines through image processing, detailed in Tab.1. The maximum depth difference across six images is 0.092 4 m, indicating that the variation in depth for the center of gravity of the extracted obstacle contours remains below the system's vertical detection resolution. Automatic identification successfully detects obstacles in 17 out of 19 images, achieving a detection success rate of 89.5%, with representative samples depicted in Fig.12.ConclusionsLiDAR echo data are integrated into two-dimensional images, followed by angular correction to restore the morphology of underwater obstacles. Contours are subsequently extracted using advanced image processing techniques. The algorithm's effectiveness is evaluated through comprehensive correlation analysis, leading to the establishment of a recognition criterion for validating automatic detection. This approach provides a valuable reference for the development of data processing methods in underwater obstacle detection and recognition using airborne LiDAR systems.

ObjectiveFemtosecond laser-induced periodic surface structure (LIPSS) is the most common surface morphology on almost any material after irradiation by a linearly polarized laser, which has been widely studied by researchers. However, research on inducing LIPSS on magnetic thin films using high femtosecond lasers is still relatively limited. The authors used femtosecond laser with central wavelength of 1 030 nm, pulse width of 300 fs, and repetition rate of 100 kHz to induce the formation of LIPSS on 100 nm nickel film. The optical microscope and scanning electron microscope images show that affected by the thermal effect of the high repetition femtosecond laser, the measured period of LIPSS stripes is about 989 nm. Through the analysis of experimental data measured by the X-ray diffractometer and SQUID, it was proved that the material atomic recombination caused by the formation process of LIPSS did not change the particle size or composition of the nickel film. The saturation magnetization of the laser-induced magnetic material is also basically consistent with the reference sample, but the coercivity changes significantly. The authors consider that it is due to the pinning effect generated by the little amount of anti-ferromagnetic nickel oxide particles splashed out during the processing.MethodsThis study used a galvanometer-based femtosecond laser processing system (Fig.1) to produce two grating samples with different periods of LIPSS (Fig.2-3). The period was measured based on the diagrams of the scanning electron microscope (Fig.4), and the X-ray diffraction spectra of the samples were measured by XRD (Fig.5). The hysteresis loops were measured by SQUID (Fig.6, Tab.1), and the calibrated saturation magnetization was calculated (Tab.2).Results and DiscussionsThe SEM measurement shows that the period of LIPSS is about 989 nm, which is caused by the thermal effect of high repetition femtosecond laser. The XRD results show that the particle size and composition of the grating samples is basically the same with the reference sample. The SQUID data show that the saturation magnetization of the grating samples with period of 40 μm and 24 μm is 97% and 91% of the reference sample after calibration, respectively. The sample with period of 24 μm has a little amount of damage, so the ratio of the calibrated saturation magnetization should be slightly higher than the value of 91%. Therefore, the authors consider that the recombination of the atoms in LIPSS did not significantly alter the saturation magnetization of the material. The coercivity of the grating sample has undergone significant changes, which may be due to the pinning effect of anti-ferromagnetic nickel oxide nanoparticles splashed out during the laser-induced processing on ferromagnetic nickel materials.ConclusionsThis article used high repetition femtosecond laser to induce LIPSS on the surface of nickel film. Its period is close to the center wavelength of the laser pulse under the influence of thermal effect brought by the high repetition femtosecond laser. The average value measured by SEM is 989 nm. The grating samples with different periods were fabricated by a galvanometer-based femtosecond laser scanning system. Through the analysis of X-ray diffraction spectra and hysteresis loops, the authors consider that although the process of generating LIPSS is a process of material recombination, it has no significant impact on the particle size, composition, and saturation magnetization of the material. However, this process significantly changes the coercivity of the material. On the one hand, it is due to the atomic recombination of the material in the LIPSS zone, resulting in a change in internal stress. On the other hand, it is due to the pinning effect of anti-ferromagnetic nickel oxide nanoparticles splashed out during the laser-induced processing on ferromagnetic nickel particles. The experimental results show that high repetition femtosecond laser can be a powerful tool for rapid processing of micro patterns on magnetic thin film.

ObjectiveHaze is extremely common in our daily lives and is a common natural phenomenon. In recent years, the presence of atmospheric haze has had a serious impact on our production and life, making our daily travel extremely inconvenient and limiting people's outdoor activities. For vision-based intelligent machines, the presence of haze seriously reduces the quality of images captured by intelligent devices. In recent years, a variety of haze removal methods have appeared, such as image enhancement, image restoration, deep learning based haze removal methods, but the use of the above haze removal methods in the image of the bright areas of the processing effect is not ideal, prone to distortion. Meanwhile, the use of the above haze removal methods to remove the haze of the image obtained after the PSNR performance is generally lower, indicating that after the removal of the haze of the image of the presence of the corresponding noise, and has not been reasonably removed. The mainstream defogging methods can not solve the above two problems at the same time. Therefore, it is necessary to deeply process the haze present in the image.MethodsConsidering the shortcomings of the current defogging methods, based on the atmospheric scattering model and combined with the dark channel prior theory, we propose an image defogging algorithm with transmittance prior and luminance perception (Fig.1). The algorithm first constructs a module for solving the atmospheric light value, which transforms this type of problem into a problem of overcoming the influence of interference factors and reducing the solution error; Secondly, it introduces a Gaussian filtering noise reduction module, which is embedded into the image de-fogging model in order to improve the anti-noise performance of the de-fogged image; Finally, it proposes a transmittance a priori method in order to correct the transmittance of the bright region, and designs the image luminance sensing model (Fig.2-3) to enhance the visualization effect of the image, and the image visualization effect is enhanced. Results and DiscussionsThe experiments are carried out under three datasets: the synthetic foggy dataset, the SOTS dataset, and the HSTS outdoor dataset, in order to verify the effectiveness of the proposed method. According to the performance evaluation results of this method and the mainstream algorithms on the synthetic dataset (Fig.7), the degree of distortion and the degree of color shift of the de-fogged image obtained by this algorithm is lower than that obtained by other algorithms, and more important information in the image can be retained. The average PSNR value of the image obtained by the algorithm in this paper is 39.579 9 dB, which has a significant advantage over other defogging algorithms, indicating that the image has a better anti-noise performance and lower noise content. From the results of image SSIM evaluation, the defogging performance obtained by using the algorithm in this paper reaches 82.54%, indicating that the defogging results obtained by using the algorithm in this paper are comparatively more similar to the original image, and can maximize the retention of important information in the image. According to the performance evaluation results of the performance evaluation on the SOTS dataset (outdoor), it can be seen (Fig.8) that the average value of the image PSNR obtained by applying the algorithm of this paper is 39.601 8 dB and the average value of the SSIM reaches 82.84%. According to the performance evaluation results of the performance evaluation on the HSTS dataset (Fig.9), the average value of image PSNR obtained by using this paper's algorithm is 40.770 1 dB, and the average value of image SSIM reaches 88.78%. The experimental results under the three foggy datasets all show that the algorithm in this paper has a significant advantage over other mainstream de-fogging algorithms, which not only can effectively deal with bright regions such as the sky, but also can remove the noise content, which verifies the effectiveness of the proposed algorithm.ConclusionsAs can be seen from the experimental results (Tab.7), the use of Ref.[22] algorithm to get a corresponding good de-fogging effect, but also consumes a relatively large amount of de-fogging time, the time cost is larger, in the requirements of the de-fogging efficiency of the scene can not be well applied. The use of Ref.[23] algorithm to get the de-fogging effect is more ideal, but comprehensively, in the de-fogging performance and de-fogging efficiency is slightly weaker than the algorithm proposed in this paper; The use of Ref.[12] algorithm for the de-fogging processing of the time cost is small, but the de-fogging effect is not ideal. Comprehensively, the use of the algorithm proposed in this paper in the fogging effect and time cost have good performance.

SignificanceInfrared thermography is a typical representative of non-destructive testing technologies. According to the external excitation source, infrared thermography can be roughly divided into passive thermography and active thermography two categories. Among them, passive thermography uses the difference between the temperature of the measured target and the surrounding environment to realize infrared detection of the target in the heat exchange process between the measured target and the environment, and can detect the health status of the equipment and components in operation without the need to impose an external excitation source. Unlike passive thermography, active thermography requires external excitation source to stimulate the object to be measured and generate thermal contrast, which is more suitable for defects detection. Compared to other external excitation, active thermography with laser as excitation source has been widely used in recent years because of its advantages of stable output power, uniform energy distribution and strong controllability.ProgressThe basic principle of laser thermography non-destructive testing and the composition of laser thermography non-destructive testing system are introduced at first. The laser thermography non-destructive testing system is generally composed of laser driver, an infrared thermal imager, an image acquisition unit, an image processing unit, and a motion control device to improve the detection efficiency. Then the laser thermography is classified from two perspectives of excitation mode and heating mode. There are three excitation modes of laser thermography, which include laser point, line and surface. While laser thermography can be divided into laser pulsed thermography, laser lock-in thermography and laser pulsed phase thermography three categories according to the heating mode. Different excitation and heating modes have their applicable application scenarios. Since laser thermography was first proposed in the 1960s by Kubiak, the main research focus on improving the performance of laser thermography non-destructive testing. To overcome insufficient precision, low efficiency and limited detection objects, researchers from different countries have continuously optimized and innovated the laser thermography non-destructive testing technology from various aspects such as excitation and heating mode, detection conditions, image processing, and put forward a series of improved methods and strategies. Because of the advantages of laser thermography, countries have successfully carried out a number of studies to detect defects. The application scenarios have been gradually expanded, no longer limited to the defect detection of metal material and composite materials. It has been applied to the defect detection of chips, inductors, ceramic materials, as well as the measurement of thermal properties of materials and even artworks. The end of this paper surveys on prospects of laser thermography non-destructive testing, which intends to provide reference to the development and research of laser-based thermography technology.Conclusions and Prospects At present, there are still few studies focusing on the improvement of laser thermography heating uniformity and the reduction of the noise influence from the perspective of improving the excitation mode. Most studies still need complex image post-processing methods to improve the image quality. At the same time, the deeper applications such as three-dimensional defect measurement are less considered in defect detection. The level of intelligence in the quantification and automatic identification of defects also needs to be improved. Limited by the detection system, laser thermography still has a lot of room for improvement in large components and field applications. With the development of a new generation of information technology and the improvement of detection technology accuracy requirements, laser thermography non-destructive testing has expanded from surface defects such as cracks to internal defects including delamination and debonding, from qualitative defect analysis to quantitative defect calculation, and from two-dimensional defect identification to three-dimensional defect reconstruction. Based on the detailed analysis of the existing research, it is considered that 3D quantitative defect detection combined with intelligent algorithm is a future development direction of laser thermal imaging. And the development of high performance small portable laser can also expand the application field of laser thermography non-destructive testing.

SignificanceThe mid-infrared (MIR) spectral range generally spans from 2 μm to 20 μm (500-5 000 cm-1), which includes numerous vibrational absorption lines of various atoms and molecules, and encompasses several atmospheric windows. Therefore, MIR lasers hold significant application value and potential in the fields such as remote sensing communication, spectroscopic detection, medical applications, and military uses. Miniaturized on-chip integrated devices, which offer substantial advantages in size, power consumption, and large-scale production deployment, are particularly important. Thus, leveraging these characteristics to achieve miniaturized MIR photonic integrated devices is of outstanding significance. In recent years, MIR photonic integrated chips, which possess enormous potential in spectral measurement and biosensing, have become a research hotspot in integrated optics. Various MIR photonic integrated systems, which have been realized using materials such as silicon, germanium, indium phosphide (InP), and chalcogenide glass, demonstrate this potential. Among these systems, MIR light sources, which are crucial components, make the realization of on-chip integrated MIR lasers one of the pressing issues in MIR photonic integration.ProgressDespite recent significant breakthroughs in the direct generation of broadband MIR pulses in quantum cascade lasers (QCL), their performance remains incompatible with some high-power applications, and the spectral bandwidth of these QCL combs is still quite narrow. Therefore, nonlinear frequency conversion techniques, which can achieve ultra-broadband spectra and ultrashort pulse outputs, are considered one of the most promising solutions for realizing miniaturized MIR lasers aside from QCL. Based on the order of nonlinear effects, they can mainly be divided into second-order nonlinear and third-order nonlinear effects. Second-order nonlinear effects include optical parametric generation (OPG), optical parametric amplification (OPA), difference frequency generation (DFG), and optical parametric oscillation (OPO). Third-order nonlinear effects primarily include stimulated Raman-Scattering (SRS), four-wave mixing (FWM), optical frequency comb generation (FC), and supercontinuum generation (SCG). Based on this classification, this paper first introduces the research status of on-chip MIR lasers based on second-order nonlinear effects. It then elaborates on the research progress of four main third-order nonlinear on-chip MIR lasers, summarizing their latest research achievements. Based on second-order nonlinear effects, the waveguide materials for on-chip mid-infrared (MIR) lasers mainly include PPLN (periodically poled lithium niobate), OP-GaAs (orientation-patterned gallium arsenide), and ZGP (zinc germanium phosphide). In PPLN waveguides, on-chip gains exceeding 100 dB/cm have been achieved over a bandwidth of 600 nm centered at a wavelength of 2 μm, with experimental reports of OPO (optical parametric oscillation) at a repetition rate of 10 GHz. However, the narrow transparency range of PPLN limits its applications at longer wavelengths. OP-GaAs waveguides have demonstrated continuous output from 4 μm to 9 μm, with mid-infrared outputs extending up to 12 μm. While suitable for longer wavelengths, OP-GaAs waveguides require further efficiency optimization and involve complex manufacturing processes. ZGP waveguides have achieved low-threshold and high-efficiency mid-infrared generation covering a spectrum from 5 μm to 11 μm. However, due to two-photon absorption effects, they still require pump wavelengths greater than 2 μm. These different waveguide materials in on-chip mid-infrared laser research highlight their respective advantages and limitations, offering diverse options for achieving high-efficiency mid-infrared lasers suitable for broader applications. SRS (Stimulated Raman-Scattering) does not require phase matching and dispersion control, but its output wavelength is typically shorter, usually less than 5 μm. FWM (Four-Wave Mixing) requires precise phase matching and dispersion management, suitable for broadband conversion. Both FC (Frequency Comb) and SCG (Supercontinuum Generation) can generate broadband mid-infrared outputs, but FC can use continuous-wave pumping without relying on high-power ultrafast pulses as pump sources. Currently, research on on-chip nonlinear mid-infrared lasers mainly focuses on third-order nonlinear waveguide platforms based on materials such as silicon and germanium. These platforms often require complex and precise waveguide dispersion control and high-quality factor microresonators to achieve efficient mid-infrared laser outputs. Therefore, developing a simple and efficient on-chip mid-infrared laser generation based on nonlinear frequency conversion remains a pressing technological challenge.Conclusions and ProspectsThe mid-infrared (MIR) spectral range finds critical applications in biomedical, environmental monitoring, and strong-field physics, among many other fields. Miniaturized and efficient MIR lasers have been a focal point in recent years, holding significant research significance for applications such as MIR spectroscopic detection and real-time environmental monitoring. While quantum cascade lasers (QCLs) can directly generate MIR outputs, they are limited by radiation bandwidth and mode-locking mechanisms. Therefore, nonlinear frequency conversion technologies remain the preferred approach for on-chip broadband ultrafast MIR pulse generation. On-chip MIR lasers based on nonlinear frequency conversion offer advantages such as compact structure, wide tunable spectral range, and high stability, leading to rapid development and widespread applications in recent years. This paper first introduces the current research status of on-chip MIR lasers based on second-order nonlinear frequency conversion. It then provides a comprehensive review of four main on-chip third-order nonlinear MIR lasers, including Stimulated Raman-Scattering (SRS), Four-Wave Mixing (FWM), Frequency Comb (FC), and Supercontinuum Generation (SCG). The emergence of mid-infrared waveguides based on ZGP (zinc germanium phosphide) birefringent phase-matching crystals provides a new approach for realizing on-chip mid-infrared nonlinear lasers. Currently, this approach relies on femtosecond laser direct writing to fabricate nonlinear waveguides, which still have significant limitations in roughness and flexibility. Professor Ya Cheng's research group at East China Normal University has developed a technique combining chemical mechanical polishing with femtosecond laser direct writing to fabricate high-quality lithium niobate microresonators. Additionally, Professor Yuanlin Zheng's research group at Shanghai Jiao Tong University has used semiconductor-compatible UV lithography and deep dry etching techniques to fabricate high-quality PPLN (periodically poled lithium niobate) waveguides. These advancements provide new pathways to enhance the fabrication processes of birefringent phase-matching mid-infrared nonlinear on-chip lasers. It is expected that utilizing various birefringent phase-matching nonlinear crystal systems will enable the realization of diverse functional mid-infrared nonlinear on-chip devices.

Significance Deep space exploration is the cornerstone of humanity to explore and understand the universe, and it is one of the frontier fields of scientific research. Deep space communication serves as the information bridge that establishes contact between deep space detectors and Earth, acting as a spatial link to ensure the successful completion of deep space exploration missions. The communication system that uses lasers as carrier, characterized by high communication rates, small size, and light weight, has become the main direction for the future development of deep space communication and has also become an international research hotspot in recent years.Progress The article summarizes the characteristics of deep space optical communication technology. Deep space laser communication has the following features: long link distance, significant space loss, extended transmission delay, non-cooperative pointing acquisition and tracking, high relative velocity, large point ahead angle, substantial Doppler frequency shift, and long mission duration. Using examples such as LLCD, DSOC, O2O, LunaNet, OPTEL-D, and DOCS, the article provides a detailed overview of the development trends, latest research progress, and future plans in deep space laser communication technology across the United States, Europe, and China. In the future, deep space laser communication will continue to evolve towards longer communication distances, network integration, terminal miniaturization, integration and type serialization. Key areas of focus include ultra-long-distance PAT, high photon utilization modulation and coding, high-power optical emission, terrestrial large-aperture optical antenna, and ultra-sensitive single-photon reception. The article concludes with a summary and prospects, offering valuable insights for the development of deep space laser communication and interstellar laser communication networks in China.Conclusions and Prospects Both the United States and Europe have been pioneers in deep space laser communication technology research. They have conducted in-orbit technology verification for lunar-to-Earth laser communication and achieved breakthroughs in several key technologies related to deep space laser communication. In contrast, domestic deep space laser communication in China is still in its early stages. Laser communication is an inevitable choice for the future development of deep space communication and is a crucial component of space exploration activities. The moon is the closest celestial body to the earth, carrying out the moon - earth laser communication will provide a more efficient means of data transmission for lunar exploration. Additionally, this effort contributes to building a solid technological foundation for more distant deep space laser communication, marking the first step in China’s research on deep space laser communication technology. Simultaneously, China has initiated planetary exploration projects, and future plans include launching missions to more distant targets such as asteroids and Mars sample return missions. To ensure the successful completion of these long-distance exploration tasks, establishing a matching deep space communication capability is of paramount importance. As laser communication technology continues to evolve, deep space laser communication will become a critical component of the interstellar internet. It will play essential roles in interstellar backbone networks, extension networks, and planetary networks. Furthermore, the development of deep space laser communication complements space optical communication network technologies, mutually reinforcing each other. Ultimately, this progress will lead to the establishment of a near-Earth laser communication network based on ground stations and near-Earth orbit satellites, which will serve as the foundation for an interstellar laser communication network.

ObjectiveThe existing FBG vibration sensor has a wide operating frequency band, but it has low sensitivity compared to high-sensitivity vibration sensor. Additionally, the sensor's intrinsic frequency is not high, and there are mutual constraints on the relationship between the working frequency band of the FBG vibration sensor and the measurement sensitivity. Consequently, the extension of the sensor's operating frequency spectrum has significant research value in order to guarantee the high sensitivity of the vibration sensor simultaneously.MethodsThe proposed FBG vibration sensor is made up of two FBGs, two integrally molded sensing units, and front and rear end caps (Fig.2), each of which has a tower-shaped mass block, an L-shaped base, and a circular flexible hinge (Fig.1). First, structural mechanics modeling research was used to determine the elements influencing the sensing unit's sensitivity and inherent frequency. To enhance the sensitivity, the mass block was shaped like a rectangle. The sensitivity of the sensing unit was determined by measuring the distance between the FBG and the hinge center. The mass block is designed as a tower to increase the intrinsic frequency by lowering the mass block's center of mass, which expands the operating band of a single sensing unit. The intrinsic frequency of the sensor unit is related to the mass block's moment of inertia, which is related to the distance from the mass block's center of mass to the center of the hinge. The sensing unit is skeletonized with such a way that the resonance peak and the "working area" sensing units complement one another and work together to broaden the working frequency band. Subsequently, the dimensional parameters of the sensor are optimized and expedited by the combined simulation of ANSYS and SolidWorks. To finish the packaging and characterization investigations of the sensor, the packaging system (Fig.6) and the performance test system (Fig.9) were constructed.Results and DiscussionsThe intrinsic frequency of the sensing units 1 and 2 are 650 Hz and 925 Hz, respectively (Fig.10). The sensor operates in the frequency range of 0 to 1500 Hz (Fig.11), with a sensitivity of better than 410.4 pm/g (Fig.12) and a measurement resolution of 0.16 mg (Fig.13).ConclusionsThis article proposes a method of design for a high-sensitivity wide-band FBG vibration sensor based on a hinge complementary structure, providing an innovative approach to the current problem of mutual limits on the operating frequency range and sensitivity of vibration sensors. With its wide working frequency range and outstanding sensitivity, the developed sensor provides a unique technical method for micro-vibration monitoring.

ObjectiveWith the development of technology and the requirement of industrial manufacturing, the automatic measurement of key dimensions of products in the production process has gradually replaced the traditional manual measurement. As a non-contact measuring instrument, line laser triangulation instrument has the advantages of simple structure, small size and wide application. However, the uncertainty of measurement for this instrument is physically limited by the speckle, which are formed when the measured surface is illuminated by the laser. Fortunately, this uncertainty can be improved by reducing the laser wavelength or increasing the numerical aperture of the optical system. Lasers with a short wavelength of 405 nm are already widely used in triangulation instruments, and increasing the numerical aperture of the optical system is another one method to further reduce the measurement uncertainty. However, the further increase of numerical aperture brings great difficulties to the design of optical systems while keeping the field of view unchanged.MethodsTo improve the measurement uncertainty of the line laser triangulation measurement instrument, this paper designs a bi-telecentric system with large numerical aperture with the two-dimensional Q-type polynomial freeform surface. Firstly, the working principle of the triangulation measurement instrument is introduced. Based on the principle and the specifications of the line laser triangulation measurement instrument, the parameters of the imaging optical system are analyzed. Then, the optical system based on double-Gauss optical layout is designed and the optical stop is placed on the focal plane of front group and back group. The position and number of freeform surfaces in the imaging optical system are determined by using the aberration sensitivity analysis and the freeform surface aberration characteristics. Finally, the optical system is optimized with optical design software to achieve the best performance.Results and DiscussionsTwo-dimensional Q-type polynomial freeform surfaces are set to each surface, and the RMS radius of the system point diagram was used as the error function to determine the contribution degree of each surface to aberration optimization. The final choice is to set the surfaces S2, S6, S9, and S14 as two-dimensional Q-type polynomial free surfaces. After optimization, the optical system is consisted of seven lenses, four of which are based on two-dimensional Q-type polynomial freeform. The designed system has a numerical aperture of 0.2, and an field of view of 10 mm×14 mm. The design results of this system are evaluated using RMS radius of the spot diagram, modulation transfer function (MTF) distortion and telecentricity. The MTF of the system is better than 0.6, the maximum distortion is 0.21%, and the telecentricity is less than 0.3° for the objective and image sides.ConclusionsLine laser triangulation measurement instrument is a high-precision, small-size and widely used measuring instrument. It can meet the demand for high-speed measurement of product dimensions in industrial production. A large numerical aperture telecentric Scheimpflug imaging optical system for line laser triangulation is designed using a two-dimensional Q-type polynomial free-form surface. Compared with the spherical system, the imaging quality of the system is improved without increasing the number of lenses and the system size. The designed optical system has the advantages of large numerical aperture, double telecentricity and high imaging quality, which can effectively improve the measurement uncertainty of the instrument. It has important application in triangulation instruments with high measurement accuracy.

ObjectiveThe goal of designing the imaging optical system is to image the object to be observed clearly to the image plane, and to realize the mapping relationship between object and image of the observation scene. According to the requirement of similarity between object and image, the pinhole imaging model is generally used, with rectilinear projection, which satisfies the f-tanθ mapping relationship. With the increase of the field of views (FOVs), an equidistant projection is produced, which satisfies the f-θ mapping relationship, and a variety of projections such as stereographic, equisolid, and orthographic are then derived. There are also more complex observation scenarios that generate more personalized mapping relationship requirements. As the scenes for imaging optical system is becoming more complex, the image heights for different FOV need to be carefully constrained when utilizing conventional design method to realize complex mapping relationship between object and image, which requires a large amount of calculations based on ray tracing. Therefore, it is necessary to propose a method that exhibits flexible constrain ability for mapping relationships and satisfies a lot of complex imaging scenes. For this purpose, an optical system design method for complex mapping relationship between object and image based on field-dependent parameters is proposed in this paper.MethodsThe essence of the mapping relationship between object and image is to describe the incremental change of image height with the change of the FOV. Due to the multi-type target scene observation requirements, the focusing ability and resolution of the optical system, complex requirements are put forward, and the local parameters related to the FOV can be more intuitive and accurate to characterize these requirements. If the full FOV is divided into multiple sub-fields, and the respective central reference is established in each sub-field of view, then each FOV has its focal length. Like the local focal length, the entrance pupil that changes with the FOV is defined as the local entrance pupil. Further, according to the traditional definition of F-numbers, local F-numbers are generated. Therefore, this paper proposes to use the local focal length and local parameters related to the FOV as the optimization control target to realize the precise control of multi-type mapping relationship and resolution. By assigning different local focal length targets to the center and marginal FOVs, a variety of mappings and a variety of angular resolution distributions are realized. By controlling the same local F-number, a high relative illuminance is achieved.Results and DiscussionsThree wide-angle lenses all with 120° FOVs but different mapping relationships by utilizing the proposed design method are presented. The first case provides f-tanθ rectilinear projection in the central -20°-20° FOVs and f-θ equidistant projection in the marginal ±20°-±60° FOVs. The second and third cases both provide uniform distributions of the instantaneous field of view (IFOV) across -16°-16° and ±28°-±60°, and the IFOV in the central is 1.5 and 0.667 times the IFOV in the marginal for the second and third cases respectively.ConclusionsA design method based on field-dependent parameters is proposed in this manuscript, in which the local focal length and local F-number are both utilized for mapping relationship and resolution constraint, and the improvement of relative illumination is simultaneously achieved. The full FOV of the optical system is divided into several sub-fields, and the central reference is found in each sub-field. The first-order parameters such as focal length, entrance pupil and F-numbers, which describe the characteristics of the optical system, can be extended from central FOV to any FOV, and the field-dependent local parameters describing the focusing and resolution characteristics of any FOV of the optical system are formed. Three cases are designed to achieve different mapping relationships and high relative illuminance in the full FOV. The proposed method has the characteristics of flexibility, directness and precision for the regulation of imaging characteristics, and can adapt to the observation requirements of different scenes.

Objective With the rapid development of infrared imaging systems, target recognition of infrared images can achieve the determination of ultra long range targets and the guidance of long-range weapons. To accurately analyze the performance of infrared systems, it is necessary to improve the simulation ability of the infrared simulator itself to match high-resolution and high dynamic range infrared images. The research on domestic infrared dynamic scene simulators mainly focuses on small field of view, short exit pupil distance, and the projection system adopts a one-time imaging method, which can meet the requirements of low resolution MTF. The DMD type infrared simulator requires a light source for illumination as the DMD is a radiation modulation device. The illumination method mainly uses Kohler illumination, where the filament of the light source is imaged at the entrance of the optical system through a condenser and a variable aperture. Although it can improve the uniformity of the system, the lens composition and the system are more complex. The lighting system adopts TIR splitter prisms, which require complex splitter prism design and reduce energy utilization efficiency; Adopting an off-axis system can avoid interference and occlusion between the projection system and the lighting system. However, due to the characteristics of DMD itself, it requires a large aperture angle, resulting in a large size of the lighting system. Based on the current development status of DMD type infrared simulators, the optical mechanical system design of compact infrared simulators is carried out, which effectively reduces the size of the simulator, improves energy utilization efficiency, and improves lighting uniformity.Methods Due to the large exit pupil and field of view angle of the system, the infrared projection system in this article adopts the telecentric optical path method of secondary imaging (Fig.3); The splitting method did not adopt the design of splitting prisms and off-axis, but adopted the critical illumination method of blackbody combination mirrors for design. In the selection of light sources, a high-accuracy surface source blackbody with adjustable temperature and wide range was selected as the system's light source (Fig.8). On the premise of ensuring high resolution, two reflective mirrors are added to the optical path to compress the overall volume of the system (Fig.8). Due to the overall reduction of the system, the mechanical structure of the system has also been designed and analyzed to ensure that it can provide stable mid-wave infrared simulation (Fig.12-16).Results and Discussions This article designed a compact telecentric optical path projection system and a critical illumination method using a blackbody combination mirror, effectively compressing the overall size of the system and improving its uniformity. Using ZEMAX for optical path analysis, the design results show that the MTF of the projection system is better than 0.5 at 36 lp/mm (Fig.4), the wavefront aberration is less than 0.076 7$ \lambda $ (Fig.5), and the distortion is less than 1% (Fig.7). The uniformity of the lighting system is greater than 98% (Fig.9). Using ANSYS for mechanical analysis, it was found that the first-order modal frequency is 212 Hz (Fig.12), the maximum deformation of the radial X-direction medium wave simulator is 0.054 mm (Fig.13), and the maximum stress is 17.116 MPa (Fig.14). The maximum deformation of the radial Y-direction medium wave simulator is 0.028 mm (Fig.15), and the maximum stress is 5.27 MPa (Fig.16), which meets the requirements for use. Finally, an infrared simulator system was established, with a volume of less than 400 mm × 300 mm × 400 mm. By inputting images and using a thermal image for testing, it was shown that the overall design of the system is compact, the imaging quality is high, and stable infrared image simulation can be provided in the medium wave band.Conclusions This article designs the optomechanical system of a compact infrared simulator. Through analysis of current infrared simulators, in order to make the system more compact, reduce system size, and improve system uniformity, while ensuring high resolution, a compact telecentric optical path projection system is designed. The critical illumination method of a blackbody combination mirror is adopted, effectively reducing the volume of the system. Finally, an infrared simulator system was established, with a volume of less than 400 mm×300 mm×400 mm. By inputting images and using a thermal image for testing, it was shown that the overall design of the system is compact, the imaging quality is high, and stable infrared image simulation can be provided in the medium wave band.

ObjectiveUtilizing magnetic compound fluid (MCF) polishing technology, a comprehensive study was conducted on the polishing process of fused quartz components. The aim was to compare the removal characteristics of fused quartz materials when subjected to traditional MCF and ultrasound-assisted MCF (UMCF) polishing. This comparison aimed to assess the impact of both MCF and UMCF polishing on the removal amount/removal rate of fused quartz materials and surface roughness across various polishing durations. A material removal rate model was formulated, incorporating the effects of polishing stress and duration.Methods The polishing characteristics of MCF and UMCF at different times were investigated by five-axis polishing and processing machine tool equipment (Fig.1), the polishing spot cross-section profile test was analyzed on the polished optical components using a surface profiler (Fig.3), and the surface morphology of the processed components was analyzed using a metallurgical microscope and roughness tester (Fig.6).Results and DiscussionsThe findings of the study reveal that UMCF significantly outperforms traditional MCF in terms of material removal rate enhancement and surface roughness reduction. Both polishing methods operate on the principle of elastoplastic removal. Notably, UMCF achieved a remarkable 68.88% improvement in surface roughness compared to MCF. Attributed to the synergistic effect of hydrodynamic pressure and ultrasonic vibration pressure, the material removal rate of UMCF reaches an impressive 5.74×10-3 mm3/min, surpassing MCF by a factor of 3.04. Furthermore, the material removal rates of both MCF and UMCF exhibit a power function relationship with polishing stress and duration. Notably, the influence of polishing stress on the removal rate is more pronounced in UMCF compared to MCF.ConclusionsWith the same polishing time, UMCF polishing rather than MCF polishing can be obtained by the greater length, width and depth of the polishing spot. And with the increase in polishing time, MCF polishing material removal rate MRR showed a slow increase in the trend, while the UMCF polishing removal rate showed a rapid decline in the trend of the UMCF polishing in 5 min, MRR can reach a maximum of 5.74 × 10-3 mm3/min, 4.04 times that of the MCF polishing at the same time. With the prolongation of MCF polishing time, a certain polishing track will appear on the surface of the component, resulting in poor surface roughness of the component. UMCF polishing did not show obvious polishing track, and the surface roughness Ra decreased to 0.108 μm at 15 min of polishing, which was optimized by 68.88% compared with MCF polishing at the same time; The dynamic pressure of the polishing fluid showed an inverted "W" distribution, which coincided with the spatial geometry of the polishing spot, and the UMCF polishing increased the ultrasonic pressure effect compared to MCF polishing, so the material removal rate of UMCF was high compared to MCF polishing, and the material removal mechanism of MCF and UMCF polishing in this study was elastic-plastic removal; The material removal rate modeling showed that the material removal rate of MCF and UMCF polishing showed power function correlation with both polishing stress and polishing time, and the effect of polishing stress on the removal rate was more weighted in UMCF polishing than in MCF polishing.

Significance Near space covers the stratosphere, mesosphere and part of the thermosphere regions of the atmosphere and is a complex transition region between the Earth's atmosphere and space. The detection of its wind and temperature fields is of great engineering and scientific significance for space weather warning and climate change modeling. By monitoring and analyzing atmospheric wind temperature information in the near space, it is possible to gain insight into the dynamical mechanisms of atmospheric circulation, atmospheric chemical processes, and the transport and transformation of various constituents. In addition, the use of atmospheric wind temperature data in the near space makes it possible to optimize satellite orbit design, predict space weather conditions, plan space mission trajectories and ensure the safe operation of satellites and space vehicles. However, due to the limitations of engineering and technical capabilities, global atmospheric wind temperature information in the near space region is very scarce, and remote sensing of atmospheric wind temperature in the near space at the global scale has become a research hotspot in the field of international atmospheric physics and space science.Progress Satellite remote sensing technology is an important means of obtaining atmospheric wind temperature information. In comparison, the development of satellite remote sensing technology for atmospheric temperature field information is more mature, while the vertical detection of the atmospheric wind field, as well as the simultaneous detection of the wind field and temperature field profile, are both difficult and hot spots in the field of satellite remote sensing in the international arena. According to different means of obtaining information, satellite remote sensing technology can be categorized into active and passive detection methods. The active detection method, represented by satellite-based LiDAR, mainly acquires wind field information in the low-altitude region below 30 km. Passive detection, represented by the Atomic Airglow Spectral Imaging Satellite Interferometer (AASIS), acquires wind temperature information in the region above 90 km altitude. For the near space region of 20-100 km, the detection capability of atmospheric wind temperature remote sensing satellite payloads currently operating in orbit is very limited. In view of this, this paper provides a systematic review of the research progress of satellite-based wind temperature detection in near space, aiming to provide reference and inspiration for the research in related fields. First, the current status of atmospheric wind temperature satellite remote sensing technology is introduced, and the detection principles and performance of representative international payloads are summarized. Secondly, starting from three different detection bands, namely near-infrared, long-wave infrared and mid-wave infrared, the target source characteristics, instrument development and detection capability of three types of typical remote sensing technologies for atmospheric wind temperature in near space are discussed in detail, and the applicability and reliability of the three technological solutions under different conditions are summarized through the analysis of the spatial and temporal coverage and the measurement accuracy, which provide important references for the subsequent research. Finally, the future development of satellite remote sensing technology for atmospheric wind and temperature fields in the near space is envisioned.Conclusions and Prospects In summary, satellite-based remote sensing of wind temperatures in near space has developed to some extent over the past decades, but is still insufficient to reach the level of operational detection. Looking forward to the future development trend of satellite-borne wind temperature remote sensing technology in near space, focusing on the spatial coverage capability, time continuity and detection accuracy of atmospheric wind temperature remote sensing payloads, and discussing the engineering difficulty of payload development, it is possible to provide an effective idea for the research and development and application of wind temperature remote sensing satellites in near space. This will provide effective technical means and scientific support for the in-depth study of changes in the atmospheric environment, the improvement of the accuracy of weather forecasts and the optimization of aerospace mission planning, and will make an important contribution to the filling of proximity spatial data and the advancement of meteorological science.

ObjectiveModern spectroscopic analysis technology has developed into a discipline that studies the absorption, emission or scattering spectra of substances, and has played a key role in many fields. In the field of spectroscopy, spectral scanning is performed by adjusting slits in spectroscopic instruments, but there are problems such as wavelength drift and frequency instability caused by mechanical movement. The stability of mechanical movement and the performance of spectroscopic elements gradually limit the development of spectrometers. In the field of gas detection, with the development of laser technology, gas detection lidar based on optical frequency comb locking can achieve high-resolution remote sensing of various gas spectra. The optical frequency comb reference locking scheme has the advantages of high stability and wide tuning range, but it also faces the problems of complex system and long tuning process. In summary, whether it is adjusting the slit or the laser cavity, the current spectrum analysis technology operates and detects the spectrum in the optical frequency.MethodsThis paper proposes a spectral analysis technology based on time dispersion gating to achieve fast and high-resolution spectral analysis without locking. First, a large amount of dispersion is introduced through time stretching technology to stretch femtosecond laser pulses to nanosecond pulses, and achieve one-to-one mapping between spectrum and time. Secondly, picosecond pulses are used in the time to modulate the time stretched ns pulses to achieve selective passage of light frequency, similar to the role of slits in spatial dispersion spectrometers. Finally, spectrum scanning is achieved by adjusting the delay of the ps pulse. Since the ps pulse is generated by electronic devices and loaded into the modulator, the ps pulse width and delay are controlled by the electrical signal generator. Its one-to-one corresponding spectral resolution and scanning speed can break through the limits of traditional spectral analysis technology, without mechanical scanning making this spectral analysis technology inherently frequency stable.Results and DiscussionsThrough the time dispersion gating experiment, it can be obtained that the spectral signal and time signal of the gas-free absorption line composed of ps pulses under different delays (Fig.4). The time and frequency information of the time pulse vertex and the corresponding frequency spectrum vertex are obtained, the coordinates of (time, frequency) form and fitting is performed to obtain the time-frequency mapping equation (Fig.5). The experimentally obtained ps pulse time signals containing gas absorption lines at different delays can be mapped through the above time-frequency mapping equation to obtain the corresponding spectral data. The error of the spectral data obtained by time-frequency mapping inversion is compared with the actual spectrum (Fig.6). The standard deviation of the available error is only 0.006 5. Only one of the 51 points collected is not within the ideal range, and the maximum deviation ratio is only 1.54%. The probability of up to 98% proves that the spectral inversion results are consistent with the actual results. This shows that the HCN gas absorption spectrum retrieved from this experiment is in good agreement with the measured data, and further proves that high-speed, lock-free spectral scanning can be achieved in the time.ConclusionsThis paper proposes a spectral analysis technology based on time- dispersion gating to achieve a lock-free, fast, high-resolution spectral analysis method in the time, and experimentally verifies its feasibility in the field of gas spectrum remote sensing. This paper designed a time- dispersion gating experiment and calculated the time-frequency mapping equation. Through the time-frequency mapping equation, it can be concluded that the spectral resolution under this method is 6.2 GHz and the spectral scanning interval is 1.5 GHz. Based on this mapping relationship, the time data passing through the gas cavity can be collected to invert the optical frequency data to achieve spectral analysis. The spectrum analysis experiment based on time- dispersion gating adopts an all-fiber system design scheme, which has a streamlined and stable structure. In order to expand the practical application of this method, the team will build a system with shorter modulation pulse width and faster scanning speed in the future, and amplify the gated pulses and emit them into the atmosphere for remote sensing of atmospheric gas spectra.

ObjectiveTo obtain the infrared radiation characteristics of the high-emissivity blackbody coating in wide temperature range, the spectral emissivity of two blackbody coatings which are applicable in various temperature scenarios were measured based on two devices. The temperature measurement range of JSC-3 coating spans from room temperature to 1 000 ℃, while the temperature measurement range of GR coating extends from room temperature to 150 ℃. The relationship between the spectral emissivity and the temperature of the JSC-3 and GR coating was shown respectively, and the investigation delved into variations in directional spectral emissivity across different angles. Experimental findings indicated that the spectral emissivity of JSC-3 and GR coatings at 8-14 μm exceeds 0.96 and 0.97, respectively. The spectral emissivity of the two coatings remains stable in the wide temperature region, and the variation is separately less than 0.01 and 0.003. Both coatings demonstrate excellent directional spectral emissivity consistency within 0°-30°, exhibiting minimal variations of less than 0.005. Finally, the spectral emissivity of JSC-3 and GR coatings in the range of 3 μm to 14 μm at room temperature was measured by integrating sphere reflectance method, which successfully obtained comprehensive spectral emissivity data coverage across a wide temperature range and broad wavelength band for two coatings.MethodsBased on the different emissivity measuring devices, the spectral emissivity characteristics of two blackbody coatings in wide temperature region were studied (Fig.1-2). The variation of the spectral emissivity of the coating with temperature and angle was discussed, and the difference of the spectral emissivity at various temperature and angles of two blackbody coatings was shown concretely.Results and DiscussionsThe spectral emissivity of JSC-3 and GR coating is respectively better than 0.96 and 0.97 (Fig.5, Fig.8), The variation of the spectral emissivity of two coatings is separately less than 0.01 and 0.005. There is a slight decrease within 0.005 in directional spectral emissivity for both JSC-3 and GR coatings as angle increases within 30° (Fig.6, Fig.9), and the maximum reduction of JSC-3 is 0.05 in the range of 0°-60° (Fig.6). The spectral emissivity of the GR coating exhibits a higher sensitivity to angle variations at elevated temperatures (Fig.9). The continuous spectral emissivity data of the two coatings in the range of 3 μm to 14 μm were obtained using the integrating sphere reflection method at room temperature, enabling broad coverage of their spectral emissivity data across a wide temperature range.ConclusionsTwo blackbody coatings have excellent spectral emissivity performance at the operating temperature, and the average spectral emissivity of JSC-3 and GR coatings at 8-14 μm is better than 0.96 and 0.97, respectively (Fig.5, Fig.8). The difference of average spectral emissivity of JSC-3 from room temperature to1000 ℃ is less than 0.01, while the difference of GR from room temperature to 150 ℃ is less than 0.003. The temperature stability exhibited by all of them was commendable. When the angles are ranging from 0° to 30°, there is a slight decrease within 0.005 in directional spectral emissivity for both JSC-3 and GR coatings as angle increases, the spectral emissivity in the direction of 30° remains consistent. The continuous spectral emissivity data of the two coatings were acquired at room temperature in range of 3-14 μm measured by integrating sphere reflectance method, and the spectral emissivity data coverage of the two coatings is achieved across a wide temperature range and a broad spectrum. The experimental results provide robust evidence supporting the simulation and design of blackbodies across various temperature ranges and spectral bands.