A hollow-core photonic bandgap fiber (HC-PBGF) is an ideal option for realizing an online fiber cavity in integrated optical networks because of its capability of light transmission through the hollow core. In this work, a commercial arc splicer was used for directly splicing an HC-PBGF (HC-800-02) to a single-mode fiber (780-HP), and the effects of several parameters on the fusion quality were analyzed in detail. An HC-PBGF-based low-loss fiber cavity with a length of approximately 1 m was demonstrated, with a total insertion loss of 2.59 dB.

To improve the measurement accuracy and measurement stability of the distributed fiber Raman temperature measurement system, a temperature demodulation method that self-compensates for fiber loss, fiber dispersion, and system fluctuation was presented and experimentally verified. The loss coefficient between the Stokes and Anti-Stokes backscatter signals was calculated in real time by sampling value, and the difference between them was dynamically corrected. This prevents the temperature accuracy from decreasing as the fiber length increases. A linear interpolation algorithm was used to correct the misalignment of the Stokes and anti-Stokes backscatter signals due to the dispersion effect of the optical fiber, eliminating temperature anomaly points caused by dispersion on both sides of the heating point, thus improving temperature measurement accuracy. Finally, the fluctuation of the system was corrected according to the sampling value and the environmental temperature value. Thus, the fluctuation range of the temperature demodulation value was reduced. Experimental results indicated that the error range of temperature measurement decreased from -2.72-7.24% to -0.34-1.04% when the fiber distance was 8 km. Temperature fluctuations were reduced from -0.0128-1.6181 ℃ to -0.8991-0.6476 ℃ across the fiber.

Optical generator to triangular and square waveforms with fundamental frequency and double frequency is proposed by using a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM). With this approach, as the DPMZM1 is driven by an RF signal, and DPMZM2 only performs optical carrier phase shift by direct current (DC) bias without RF signal driven, triangular and square waveforms with fundamental frequency can be obtained following a polarizer and photodetector; as the two DPMZMs are both driven by an RF signal with a 90° phase difference, two waveforms with double frequency can also be generated. The proposed approach was verified by simulation. Triangular and square waveforms with repetition rates of 10 GHz and 20 GHz were generated by changing the phase difference and connection mode of the RF signal. The proposed structure features a single modulator and is filter-free, and demonstrates good tunability and large reconfigurability, which has potential applications in future high-frequency electronic systems.

The indoor visible light communication system under the fluorescence interference is tested experimentally. The time-domain waveform of the received signal under fluorescence interference for the indoor visible light communication system modulated by on-off keying (OOK) modulation is obtained. Then a transmission baseband model and a 5 m×5 m×3 m indoor three-dimensional model are used to obtain the indoor bit error rate distribution. The influence of fluorescence interference on the performance of indoor visible light communication receivers is analyzed. The results show that the fluorescence interference is in the form of additive noise in the received signal, which leads to sinusoidal periodic signal distortion of the received signal. The fluorescence interference spectrum covers a wide range, and signals with a transmission rate of 10-1000 Mbit/s are affected. The signal is denoised by wavelet transform. The results show that the scale flexibility of wavelet transform can eliminate the fluorescence interference.

An optical fiber curvature sensor based on seven-core fiber (SCF) and polarization-maintaining fiber (PMF) structures is proposed. First, a section of SCF is fused with the PMF, and then a common single-mode optical fiber is fused at both ends as the input fiber and output fiber, respectively. Experiments have studied the curvature characteristics of three sensors with SCF lengths of 80, 100, and 120 mm, respectively. The results show that when the curvature increases, the transmission spectrum of the sensor has a significant red shift, and the curvature measurement can be realized by monitoring the shift of the resonant valley wavelength in the transmission spectrum. The curvature sensitivity of the sensor increases with the increasing SCF length. When the length of SCF is 120 mm, the maximum sensitivity is 17.31 nm/m -1. However, the temperature characteristic experiment shows that the sensor with this length has high sensitivity to temperature. Therefore, in order to avoid the influence of temperature on the measurement results, the sensor with the lowest temperature sensitivity and the SCF with a length of 100 mm can be selected for curvature measurement. The maximum curvature sensitivity under this length is 16.79 nm/m -1. Compared with other optical fiber structure sensors, the proposed sensor has the advantages of simple fabrication, low cost, and high extinction ratio, which can be used in civil engineering and other fields.

A Mach-Zehnder interferometer based on fiber core mismatch and core-offset splicing is proposed and experimentally tested for the simultaneous measurement of refractive index and temperature. The sensor structure consists of a multi-mode fiber segment with an up-taper structure and a core-offset joint as two coupled units. The up-taper increases the light energy propagating in the fiber cladding, which improves the fringe visibility. Wavelength shifts were recorded for two transmission dips, associated with variations in the temperature and refractive index, respectively, to build up a sensing matrix for the device. The experimental results show that the sensitivities to changes in the refractive index and temperature are -25.682 nm/RIU and 0.073 nm/℃ within the refractive-index range 1.3449-1.3797 and temperature range 25-65 ℃. The proposed sensor is easy to fabricate and has low cost, so we believe that it has application prospects for various types of multi-parameter detection, including temperature, refractive index, etc.

Combined with the data delivery mechanism and queuing model of bundle protocol/Licklider transmission protocol (BP/LTP) in delay tolerant network (DTN), the more accurate retransmission round number is calculated, and the average length model of the custody queue of the relay node memory space is constructed. The model is used to measure the change trend of node memory space, and the joint optimization scheme is proposed based on the number of protocol data unit bundles and the length of Licklider transmission protocol (LTP) data segments. Theoretical analysis and simulation results show that, without affecting the normal data transmission, this optimization scheme can minimize the memory queue length of the node memory space, that is the smallest memory space. Under the premise that the arrival rate of bundle and channel bit error rate change, the optimized queue length reduces by 70.9% and 61.8%.

In this paper, the physical layer security of quantum-noise randomized cipher (QNRC) system based on quadrature phase shift keying (QPSK) is analyzed quantitatively with the secrecy capacity as the evaluation index. The key and data eavesdropping channel models are established, respectively. The expressions of key system and data secrecy capacity are derived, and the maximum security rate of the system is obtained. The effects of key parameters (scale number, internal optical amplifier gain and mesoscopic coherent state power) on the key and data security of QPSK-QNRC system are evaluated and compared with phase shift keying (PSK)-QNRC system in the same frame. The results show that the key system parameters have the same effect on the security of the two systems. Compared with the PSK-QNRC system, the QPSK-QNRC system has higher key security and maximum achievable security rate, lower data security, and stronger mesoscopic power level. At the same time, the maximum achievable security rate of the PSK-QNRC system is mainly limited by the security of key, while the maximum achievable security rate of the QPSK-QNRC system is mainly limited by the security of data.

Herein, a phase error correction method based on a multi-level fringe order correction was proposed to address the issue of the easy generation of the phase-jump error in the multi-frequency heterodyne phase unwrapping method. First, the initial rough correction was performed on the synthetic fringe orders according to the phase period of the synthetic fringe, which can effectively avoid further accumulation and transmission of the phase-jump error caused by the Gamma effect and flooring function. Thereafter, the secondary fine correction was performed on the initial fringe orders by optimizing the flooring function and using the absolute phase of the error. Finally, a more accurate target absolute phase was calculated based on the corrected fringe orders. Experimental results showed that the three-dimensional reconstruction model corrected by the proposed method exhibited a smooth surface, clear details without obvious spots or color patches, which can significantly suppress the phase-jump error and enhance the robustness of the structural light three-dimensional measurement system.

Gas-solid two-phase flow is widely used in the transportation of materials in industrial production. The electrostatic method is widely used in the measurement of two-phase flow due to its disadvantages of low cost, easy detection, and strong adaptability. Based on the principle of electrostatic induction, the structure parameters (thickness of tube wall, electrode width, charge, position, etc.) of the sensor are set by finite element analysis method. The spatial sensitivity of the sensor is studied under different electrode width. The amplitude frequency characteristics of the sensor are studied and analyzed according to the static and dynamic characteristics of the electrostatic sensor. Simulation results show that: the electrostatic sensor has low-pass filtering characteristics in the spatial frequency domain; the closer the particles pass through the pipeline, the narrower the spatial frequency band; the faster the speed of those particles in the pipeline, the wider the frequency band of the sensor; the longer the axial length of the electrode, the greater the amplitude of the signal. When the electrode width is determined, the best sensing range of the electrode in the pipeline can be obtained.

In order to measure the width of stiffener in service, fast, contactless and non-destructive, a laser ultrasonic C-scan measurement method is proposed in this work. First, the ultrasonic wave field induced by a pulsed laser excited at a 2 mm-thick 304 stainless steel plate is studied by modelling and theoretical calculation. Then, the ultrasonic field distribution in the 304 stainless steel plate is obtained by laser ultrasonic experiments, and the results are compared with theoretical calculation. Finally, the laser ultrasonic C-scan is used to measure the width of the stiffeners, and the images are processed by the wavelet denoising and image averaging filtering methods. Experimental results show that the amplitude of the reflected transverse wave excited by the pulsed laser on the 304 stainless steel plate is higher than that of the longitudinal wave when the receiving point is 4 mm away from the exciting point. Using the reflected transverse wave amplitude as the characteristic signal, the laser ultrasonic C-scan measurement is performed on the stiffeners on the 304 stainless steel plate, and the absolute error between the width of stiffener obtained from the image and the actual width is less than 0.05 mm, which meets the error requirements of engineering inspection.

A light stripe extraction algorithm based on double-Gaussian fitting is proposed to solve the influence of high-reflective light on a light stripe extraction when the line laser measurement system measures the metal surface. First, the multipeak distribution rule of light stripe gray level is determined by analyzing the gray level of the light stripe section. Second, the reflection model of light is deduced, and the generation principle and energy distribution model of high-reflective light on metal surface are studied. Then, a double-Gaussian fitting model is established based on the distribution model, and a light strip extraction algorithm is designed. The effectiveness of the proposed algorithm is verified using examples. Finally, a comparative experiment is performed to analyze the extraction effect of the double-Gaussian fitting method and the traditional light stripe extraction algorithm and to evaluate and analyze the confidence of the results. The results show that the double-Gaussian fitting method can effectively suppress the influence of high-reflective light in the light stripe image, accurately extract the center of the light stripe, and its confidence evaluation performance is better than that of the traditional algorithm.

To improve the angle measurement accuracy of a circular grating encoder and meet the accuracy measurement requirements of arc-second and even sub-arc-second levels, this paper analyzes the error sources that affect the accuracy of the angle measurement and proposes the compensation method of the multi-reading head reading averaging method to control the error sources. According to the principle of the circular grating angle measurement, the error sources, such as the grating system engraving error, reading head interpolation error, grating installation eccentricity error, installation deformation error, and shaft shaking error, are analyzed, and each error spectrum is analyzed from the perspective of frequency domain. According to the error source analysis, the compensation method of multi-reading head reading averaging method can be used. Experimental results show that under the condition that the eccentricity error is about 15″ and the grating deformation error is about 1.5″, the measured angle error is better than 0.8″ by the four-reading head averaging method, which greatly improves the angular measurement accuracy of the circular grating.

Due to too many coupling parameters involve in laser arc hybrid welding, in order to obtain a good hybrid welding, a lot of parameter optimization work is usually required to obtain a relatively stable process parameter window. To shorten the experimental period and find out the inherent mechanism of unstable state, in this work, the experimental design method was used to study the surface forming and process stability of the distance laser-arc, welding voltage, laser power, and laser+pulse melting gas metal arc hybrid welding (GMAW). Though high speed photography and electrical signal system, the reasons for the difference of forming law were explained. The results show that higher voltage and smaller distance laser-arc will lead to instability of welding process. The reason for this phenomenon is that the force mode and size of droplet change, and finally the droplet drop point deviates from the moving direction of the welding gun.

The pure Ni samples were formed by selective laser melting technology. The influences of linear energy density on the density, microstructure, mechanical properties, and electrochemical properties of nickel solid were investigated under a certain layer thickness and hatch distance. The results indicated that under the linear laser energy density of 244.8 J/m, the comprehensive performance of formed part was the best. Under this condition, the surface of the formed parts was smooth, the surface roughness was 10.5 μm, the density was 99.7%, the microhardness was 165.4 HV0.2, the tensile strength reached 420 MPa, the yield strength was 321 MPa, the elongation was 23.2%, and the fracture was ductile. In the solution with mass fraction ω (NaOH)=20%, the self-corrosion potential of hydrogen evolution reaction was -1.5×10 -6 mA·cm -2, and the polarization passivation region was from -1.038 V to 0.442 V.

To investigate the influence of the laser-cladding scanning path on the distortions of a thin plate, a displacement sensor was used to measure dynamic distortions during the cladding process. In addition, all the distortions of the thin plate were measured after cladding using three different scanning paths. The three scanning paths all produced concave distortions at measurement point P2. In the cladding stage, the distortions accumulate and stack continuously, taking the form of periodic expansions and contractions. Spiral scanning produced the maximum bending distortion. The cladding area of single-direction scanning and reciprocating scanning experienced concave distortions, while the upper edge of the thin plate underwent convex distortions. During spiral scanning, the center of the spiral-scanning cladding layer and the edges of both ends of the thin plate experienced convex distortions. The sectional distortion transverse to the centerline was of the “W” type, and it produced small torsional distortions. Among the three types of scanning paths, single-direction scanning effectively reduced the distortions of the thin plate, and the formed quality of the cladding area was better.

In this paper, a trajectory planning method for laser cladding of robot surface based on spot control technology is proposed. The energy density of laser input surface is controlled by the change threshold of spot projection area. The influence of defocus and attitude on the cladding quality is analyzed by changing the geometrical shape of laser beam projection spot on the surface trajectory interpolation point. The results show that the cladding effect is better when the defocusing amount is 5 mm, the cracks appear when the space angle is 23.4°; the inclusions and cavities appear when the space angle is more than 30°; the thickness of the cladding decreases with the increase of the space angle and the overall hardness is higher than that of the substrate. The trajectory interpolation points are verified by the change of spot area, and then the attitude change is controlled to achieve high-quality cladding on the laser surface.

In order to improve the geometrical features of the cladding layer and to explore the distribution law of residual stress after laser cladding, we use dilution ratio and width-height ratio as the evaluation indexes. Based on the response surface method, a composite design matrix test with 4 factors (laser power, scanning speed, powder feeding rate and defocusing amount) and 5 horizontal centers is established. The influence laws of cladding parameters on each response value under the interaction of single factor and multiple factors are explored. The research results show that scanning speed and defocusing amount have the most significant influence on width-height ratio, defocusing amount and laser power have the most significant influence on dilution rate, and the interaction between laser power and scanning speed has certain influence on dilution rate. Finally, the correctness of the predictive model is verified by experiments. The optimized morphology and process parameters of the cladding layer are selected for numerical simulation, and it is found that the maximum residual tensile stress in the x direction is 532 MPa and occurs at the end of the cladding layer. In the longitudinal section of the cladding layer, the tensile stress mainly appears in the cladding layer and the heat-affected zone. As the depth increases, the tensile stress gradually decreases and is converted into the compressive stress at the bottom of the cladding layer. However, in the y direction, due to the deformation of the formed parts, the bottom surface of the substrate is subjected to tensile stress.

Inertial navigation has the advantages of strong autonomy, good concealment, all-weather and all-time work, so it becomes an indispensable core navigation mode in strategic and tactical weapons, which in turn puts forward high precision requirements for inertial devices. The optical-trap-force-based atomic accelerometer adopts the closed-loop system and the influence of the friction damping of elastic support elements on the measurement results is small because there is no mechanical connection in the structure, and thus it possesses the advantages of strong anti-interference ability and high precision, which is effective to realize the miniaturization of a high precision accelerometer. According to the Rayleigh scattering model, we establish the mechanical model of the single-axis double-beam accelerometer and conduct the numerical simulation. In addition, we analyze and simulate the influence of laser wavelength, focusing degree and other optical-trap parameters on optical-trap force. Through the sensitivity analysis of the accelerometer, the parameters are optimized to obtain the measurement sensibility of 10 -7g·nm -1(g=10 m·s -2). The research results show that the optical-trap-force-based atomic accelerometer has a relatively high measurement precision.

It is difficult to directly measure the effective wind speed at the hub of large wind turbines. Traditional wind speed estimation methods have hysteresis. The Taylor frozen turbulence assumption ignores the changes in the wind field structure from the lidar measurement point to the hub, which affects the accuracy of the measurement data. Aiming at the above problems, the auto-regressive moving average and external input (Armax) model were used to model the wind evolution process. The particle swarm optimization algorithm is used to estimate the model parameters, and the inertia weight of the conventional particle swarm algorithm is improved to avoid falling into a local minimum. In order to ensure the real-time and fast control action of the wind power system, the effective wind speed at the hub is predicted one step in advance according to the established model. Using Fast and Matlab/Simulink software, the joint simulation is carried out with an average wind speed of 7 m/s and a turbulence level A as an example. The simulation results show that the proposed method has higher real-time performance and accuracy and is more effective than traditional method of wind speed estimation.

To improve the high-temperature oxidation characteristics of the Al2O3/CoNiCrAlY coatings, they are prepared on the surface of the K438 alloy via laser cladding. In addition, the effects of different energy densities on the microstructure and high-temperature oxidation behavior of materials are studied. The experimental results indicate that the Al2O3/CoNiCrAlY coatings comprise α-Co, γ-Ni/Cr, Al2O3, Ni3Al, and Ni2Cr3. The coating will exhibit an appropriate microstructure after the addition of Al2O3. Further, the coating is oxidized at 1100 ℃ to obtain AlN at the grain boundary. The oxide films form on the coating surface comprise an inner layer of α-Al2O3 oxide and an outer layer of Cr2O3 and (Co,Ni)(Al,Cr)2O4 mixed oxide. All the kinetic curves of the high-temperature oxidation of the coating under different energy densities conform to the parabolic law. The coating exhibits optimal high-temperature oxidation resistance when the energy density is 64.97 J/mm 3.

In this paper, a multiband filter with notch function based on spoof surface plasmon polaritons (SSPPs) is designed. First, a gradualy slot unit structure is introduced into the waveguide structure to obtain better dispersion characteristics, and a low-pass filter with a cut-off frequency of 7.1 GHz is built on this basis. Then, the multiband filter is formed though exciting the stuffing wave by loading an E-shaped resonator. When the odd and even resonance modes are excited at the same time, two low-pass filters with insertion loss of 3 dB and cut-off frequency of 2.83 GHz and two band-pass filters with insertion loss of 3 dB and bandwidth of 2.94-4.37 GHz and 4.40-7.10 GHz are formed. When the resonance degradation disappears in even mode, a low-pass filter with 3 dB insertion loss and 2.83 GHz cut-pass frequency, and a band-pass filter with insertion loss of 3 dB and bandwidth of 2.94-7.10 GHz are formed. It is proved that the structure of multiband filter based on E-shaped resonator is of great significance to the development of SSPPs in microwave field in the microwave field.

Aiming at the mixed transmission of quantum signals and classical signals in the network, and through the analysis of the characteristics of the PM protocol, we proposes a hybrid quantum-classical optical network scheme based on PM protocol to improve the key generation rate, secure transmission distance, and so on. In addition, the QKD performance of the far-band isolation scheme is simulated. The numerical results show that not only the key generation rate of the PM protocol is high and the secure transmission distance is long, but also the key generation rate decreases slowly with the increase of transmission distance. For a small hybrid optical network, the PM protocol has the longest secure transmission distance and the highest key generation rate for long-distance transmission. For a medium-sized network, the PM and BB84 protocols still have their advantages, but the performance of the MDI protocol is the worst. For a large network, the performance of the BB84 protocol is the best, that of the PM protocol is the second, and that of the MDI protocol is the worst.

In the process of quantum satellite communication, the satellite link between the quantum satellite and the ground receiver is inevitably affected by the natural factors such as rain, snow, dust, haze, and ionosphere, which results in a decrease in communication quality. However, the research on the switching strategy of quantum satellite satellite-ground links is still few in the context of dust storms. In order to reduce the effect of dust storm on the switching of satellite-ground links, we propose a switching strategy of dual-satellite satellite-ground links based on optimal entanglement. By establishing the relationship between the parameters of sandstorm and the entanglement degree of satellite-ground links, the effects of dust diffusion mode index, dust particle radius, observation height, and sand disaster coefficient on the entanglement of links are analyzed. According to the entanglement of satellite-ground links in the context of sandstorm, a new switching strategy is proposed, that is, in the case that the current dual-satellite serves a ground user, one satellite with the largest entanglement degree is selected from the multiple candidate satellites as the optimal target satellite to be switched by the link. The simulation results show that the sand dust diffusion mode index, sand particle radius, observation height, and dust disaster coefficient can lead to the significant change of entanglement degree of links. The proposed optimal entanglement-based switching strategy of dual-satellite satellite-ground links can not only reduce the impact of sandstorm on the entanglement degree, but also make link interruption disappear during the switching process. Thus the switching strategy based on the optimal entanglement degree of satellite-ground link can effectively improve the communication quality of links.

Recently, how to eliminate the influence of collective noise in quantum communication has become an urgent problem. To solve the problem of low qubit efficiency of the current quantum key agreement protocols under collective noise, we propose two improved quantum key agreement protocols immune to collective phase noise and collective rotation noise, respectively. These two protocols mainly make use of the correlation among logical quantum states, delay measurement technology, unitary operation, and multi-particle entangled states to ensure that the communication parties can fairly establish a shared key. The qubit efficiency of the protocols is up to 27.27%, which effectively improves the existing quantum key agreement protocols immune to collective noise.

Resultsshow that the proposed method exhibits high accuracy and strong adaptability.

The rapid development of the satellite remote sensing technology provides important technical support for land utilization change detection. To further improve the accuracy of land utilization change detection, this paper proposes a land utilization change detection method combining AlexNet and support vector machine (SVM). This method involves the use of the GF-1 satellite remote sensing images in Nanchang City, Jiangxi Province, China, from 2013 to 2017 in order to generate the land utilization change map of the area in the five years. In addition, an analysis of the land utilization change characteristics is also conducted. The results reveal that the land types in the study area are mainly vegetation, water, bare land, and building. In the past five years, the vegetation area has changed the most, which decreased by 54.74 km 2; the water area has increased by 22.12 km 2, the building area has increased by 19.45 km 2, and the bare land area has decreased by 5.17 km 2.

With the development of high precision optical clock and its various applications, higher and higher precision is needed for time-frequency transmission technology. Time-frequency transmission technology based on optical fiber has been relatively mature, while the time-frequency transmission technology based on free-space laser can be applied to the fields of inconvenient laying of optical fiber, fast maneuvering, and time-frequency transmission between the satellite and the Earth and between satellites. This paper introduces the research status of near-earth space and time-frequency transmission between the satellite and the Earth, and the development trend is also prospected. In the future, free-space laser time-frequency transmission will develop towards higher transmission accuracy, time-frequency transmission, ranging, communication integration, and time-frequency space networking.

Curing cancer has been one of the greatest conundrums in the modern medical field. Because of side-effects associated with radiotherapy and chemotherapy, photothermal therapy ( PTT) utilizing photothermal therapeutic agents (PTA)—accumulate in tumor tissues by intravenous injection—to further generate sufficient heat under near-infrared (NIR) light irradiation for solid tumor ablation has attracted extensive attention of researchers. The method allows the local treatment process to be performed in a non-invasive direct and accurate manner due to the easy focusing and tunable properties of the incident light. In this review, we first summarize the major advances in PTA based on photothermal conversion nanomaterials in the study of ablation of solid tumors in recent years. Second, we summarize the different strategies to improve therapeutic efficacy. Finally, the limitations and challenges in the clinical application of photothermal tumor therapy based on photothermal conversion nanomaterials are discussed.

In this study, high-performance liquid chromatography and terahertz time-domain spectroscopy were used to experimentally detect metronidazole analytical pure and oral metronidazole. Based on various exchange-correlation function models of density functional theory, the molecular vibration frequencies of metronidazole in the terahertz band were calculated, and the characteristic absorption peaks of metronidazole were identified. The experimental results show that the results of terahertz time-domain spectroscopy are in good agreement with those of high-performance liquid chromatography, and terahertz time-domain spectroscopy can quickly detect drug residuals. The positions of the characteristic absorption peaks of metronidazole obtained via terahertz time-domain spectroscopy are very close to the calculated values, which indicates that the metronidazole molecular vibration frequency is in the measurable range of the system, and the formation mechanism of the characteristic absorption frequency is similar to the vibration mode of the molecular group. This research has important reference value for the applications of rapid detection of antibiotic drugs and the identification of active ingredients in compounds.

Terahertz time-domain spectroscopy technology was applied to detect fluororubber materials with different degrees of thermal damages to acquire the time-domain spectrum, frequency-domain spectrum and absorption spectrum of each sample in 0.4-1 THz band. The experimental results showed that the terahertz spectrum of fluororubber materials was between -382 ps and -376 ps. Further comparison and fitting analysis of the maximum value, peak-to-peak value, and absorption coefficient of terahertz characteristic spectrum of different degrees of thermal damage samples indicated that these values had good linear relationships with the temperature of the thermal damage, in which the correlation coefficient could reach 0.9614. The results could provide a reference for terahertz nondestructive identification and quantitative detection of thermal damage for fluororubber materials.

The effects of different substrate materials on the focusing performance of the collecting mirror in the extreme ultraviolet (EUV) radiation-damage-test system including fused silica, SiC and AlSi are simulated and analyzed. Compared with ceramic substrates such as fused silica and SiC, the thermal conductivity of AlSi-based collector mirrors is higher, but in the EUV irradiation damage research system, the maximum temperature rise of the surface of the collector on the AlSi substrate is 1.39 ℃ when the power of 10 W is applied to the 300 mm diameter collector. Although AlSi has larger expansion coefficient than that of fused silica and SiC, the maximum structural deformation of the reflector is 3.51 μm, and the wavefront aberration is increased by 8.071λ and the root mean square radius of the spot is increased by 0.028 μm compared with the ideal non-deformation collector, but the AlSi based collectors can be used in non-imaging systems or systems with low requirements for imaging quality, it has obvious advantage for collectors with large aperture and complex surface.