This paper presents an novel ultra-wideband thin frequency selective surface (FSS) absorber loaded with lumped resistors. The proposed absorber consists of a single FSS lossy layer with a single resonance structure, and it features thinness, ultra-wide bandwidth and polarization-insensitivity. The absorber is designed with lumped resistors loaded at positions that deviates from the central symmetry axis of the unit cell. It also features the nonuniformly wide metallic strips and the addition of branches with circular tops. All these specific design effectively enhances the bandwidth of the absorber. Both an equivalent circuit model and full wave simulation demonstrate that the proposed absorber achieves over 90% absorption in the frequency range of 6.0-26.77 GHz, with a fractional bandwidth of 126.8%. The thickness of the proposed absorber is 0.086λL (λL is the wavelength at the lowest frequency), which is only 1.09 times the ultimate thickness based on Rozanov’s theory. A prototype of the proposed absorber is fabricated, and good agreements between experimental and simulated results are observed, validating the effectiveness of the design.

This article proposes a phase compensation method for oblique incident electromagnetic wave to improve the angular stability of frequency selective surface (FSS) absorber. By using this method, an ultra-wideband, incident angle-stable FSS absorber-based electromagnetic shield structure is designed to reduce the electromagnetic environment level in enclosed cabins. The proposed single-layer FSS absorber achieves excellent angular stability within an ultrawide band by intentionally using different dielectric layers to compensate for the electromagnetic wave phase at high and low frequency bands respectively, and by designing a novel FSS cross unit cell featuring with gradually width-varying, slotted and top-loaded metallic strips. Simulation results reveal that the proposed absorber achieve over 90% absorption in the frequency range of 3.9-25.8 GHz, with a fractional bandwidth of 147.5%. In the frequency range of 4.7-22.1 GHz (129.9%), the angular stability of two polarizations reaches 30° with 90% absorptivity, and the absorptivity retains over 80% even when the incident angle increases up to 50°. The good agreement between the measurement and simulation results has verified the effectiveness of the design.

The structural models of Si-doped glow discharge polymer (Si-GDP) were established using reactive force field molecular dynamics simulation (ReaxFF MD), and the effects of silicon content, hydrogen content, and density on its hybrid carbon bonding and mechanical properties were investigated. The results show that with the silicon content increasing, the molecules tend to form a silicon-containing macromolecule, and the types and number of small molecules decrease, the silicon content improves the mechanical properties by promoting the binding of carbon and silicon atoms and inhibiting the formation of end-group sp3CH3. Besides, species such as ·C2H3, ·C3H5 and ·Si(CH3)3 were found during the formation of Si-GDP, which were in good agreement with the thin film deposition experiment of glow discharge polymer. The hydrogen content is measured as the atomic ratio of hydrogen to carbon and silicon, as the ratio grows, the number of model molecules did not change significantly, the ratio of sp3C and sp3CH3 increased, and the hydrogen content decreased the mechanical properties mainly by promoting the formation of sp3CH3. With the density increasing, the number of molecular species in the model did not change much, and the proportion of sp2C in the model was significantly increased, while the proportion of sp3C was slightly increased, the mechanical properties of Si-doped hydrogenated amorphous carbon were mainly improved by increasing the proportion of sp2C. This study provides an example for constructing Si-GDP by ReaxFF MD, and may provide a new method and reference for evaluating the structure and mechanical properties of Si-GDP.

Lead cooled fast reactor has obvious advantages in fuel proliferation and nuclear waste treatment. For the Europe Lead-cooled System (ELSY), based on the “two-step method”, Monte Carlo software is used to generate few group component parameters, and after section correction, it is passed to the determining theory program MORPHY for core calculation. The effects of section modification and angle development order on the calculation accuracy were analyzed, and the effective multiplication factor, normalized flux level and control rod value of the ELSY core were quantified and compared. For different examples, transport correction and neutron multiplication effect correction were adopted, and the core calculation was developed with S4 order. The maximum deviation of effective multiplication factor was 38×10-5, the calculation deviation of control rod value was within 45×10-5, the maximum absolute deviation of normalized neutron flux density was 9.73%, and the average absolute deviation was less than 2%. The feasibility of MORPHY program in the physical analysis of lead-cooled fast reactor is preliminarily verified, which is of reference significance for the subsequent development and use of the program.

This paper compares the effects of different physics lists on the dose of proton boron capture therapy (PBCT) in Monte Carlo Geant4 simulation. Geant4 was used to establish PBCT model with three different physics lists (FTFP, QBBC and QGSP). Comparison is made for dose distribution of three physics lists with and without boron using an 80 MeV proton beam, as well as the nuclear reaction product data of a 3 MeV proton beam bombarding pure boron. There is no significant difference in the dose distribution of the three physics lists in the water phantom with and without boron, and the consistency of different physics models’ percentage depth dose (PDD) curves is good. The PBCT nuclear reaction products obtained from FTFP physics list are significantly less than those obtained from QBBC and QGSP physics lists. The yields, mean energies and energy ranges of the alpha particles obtained from the QGSP physics list are more consistent with the actual situation than that of the QBBC physics list. The QGSP physics list in Geant4 is more suitable for MC simulation studies of PBCT, judging by a comprehensive evaluation of the inelastic scattering models used by the three physics lists and the simulated nuclear reaction data.

The high-precision synchronization system is one of the key factors for the accelerator to generate high-quality beams. Based on the existing continuous laser carrier synchronization system of Tsinghua University, this paper analyzes the long-term drift of the reference microwave signal phase difference between different receiving ends, that is, the slow drift of the synchronization system. An electro-optic modulator (EOM) bias voltage control method based on the amplitude of the reference microwave signal at the receiving end was proposed to suppress the slow drift. After adopting this method, the slow drift of the L-band (1300 MHz) synchronization system of Tsinghua University’s VHF band photocathode electron gun test platform was suppressed to 10.45 fs@24 h, and the slow drift of the S-band (2 856 MHz) synchronization system of Tsinghua University’s Thomson Scattering Facility (TTX) was suppressed to 10.53 fs@24 h. Moreover, this method can make the entire synchronization system work in a room temperature environment, effectively improving the adaptability of the synchronization system to the working environment temperature.

Accurate measurement of the intense pulse electron beam is required by upgrade of linear induction accelerator. This is achieved by not only the technology of beam position monitor (BPM) design and assamble, but also the calibration of BPM. This paper describes the research of calibration technology based on the measuring principle of intense pulse electron beam position monitor in linear induction accelerator. Theoretic method is used to calculate calibrated effects in different signal calculation, polynomial fit and calibration. Characteristic plane calibration is provided according to the analytic results. In the system of BPM position calibration, the No.23 RRM (resistive ring monitor) of multi-pulse electron linear induction accelarator is calibrated by different method. The experimental results validate the theoretic results. The calibration method of intense pulse electron beam position monitor is decided according to the results of research.

The Geant4 program was used to simulate the effect of micropore shape on the performance of CsI:Tl X-ray scintillation screen based on silicon microchannel array (SMA). The simulated scintillation screen performance parameters include: scintillation photons, bottom light output, transmission efficiency, percentage of n times total reflection, and modulation transfer function (MTF) versus spatial resolution. The shapes of the micropores were set to be square and circular during the simulation process, and the microchannel array period was the same for both hole shapes, which was 10 μm. The simulation results show that the number of scintillation photons in square micropores is better than that in circular micropores, and the number of fluorescent photons is directly proportional to the cross-sectional area of the micropores; while the thickness is less than 400 μm, the bottom light output of square micropores is better than that of circular micropores, when the thickness is greater than 400 μm, the situation is opposite; The transmission efficiency of circular micropores is better than that of square micropores; For the thickness of 40 and 200 μm, the spatial resolution of the square micropores scintillation screen is better than that of the circular micropores scintillation screen with the same thickness. A square microporous CsI: Tl scintillation screen sample was prepared, and the relationship between its MTF and spatial resolution was measured. When the MTF was 0.1, the spatial resolution was 22.6 lp/mm.

The adder topology solid state modulator is a device that uses insulated gate bipolar transistors (IGBTs) to discharge the stored energy of capacitors to generate high voltage pulses. Compared with pulse forming network (PFN) type modulator, it has lots of advantages such as modularity, good stability, and long lifespan. However, the normal operation of IGBT requires the use of gate drive circuit to amplify the control signal, and the performance of the drive circuit directly affects the switching characteristics of the IGBT, ultimately affects the quality of pulse voltage, especially the turn-on jitter index of the drive circuit, which is one of the key factors affecting the pulse voltage repetition precision. Based on the operating characteristics of IGBT in the adder topology solid state modulator, the drive circuit was studied with the goal of improving pulse voltage repetition precision. The impact of turn-on jitter on voltage repetition precision was analyzed, the design principle was introduced, the drive circuit board was developed, and its working performance was experimentally tested using a discharge module. The test results indicate that the turn-on jitter of the drive circuit is 300 ps, which is three times better than commercial driving circuits. At the charging voltage of 1 kV, the discharge module discharges on a 0.5 Ω load, forming a pulse voltage with the rise time of 500 ns and the peak-to-peak value of turn-on jitter below 5 ns. When the desaturation fault occurs, the drive circuit can turn off the IGBT within 4 µs. This drive circuit meets the working requirements of high pulse repetition precision solid state modulators.

The classical Jiles-Atherton (J-A) equation has been modified through theoretical analysis, which enhances its adaptability under pulsed conditions. Hysteresis loops of Fe-based nanocrystalline cores are measured at different magnetization rates by using an experimental platform for pulsed magnetization properties. The genetic algorithm (GA) is used for J-A parameter identification under pulsed excitation, and the validity of the modified J-A equations is verified by fitting the algorithmically simulated hysteresis loops to the experimentally tested hysteresis loop dataset. Finally, the J-A parameter obtained by GA optimization are applied to the definition of magnetic core parameters in the field-circuit coupling model of the pulse transformer, the simulation and experimental errors when the primary voltage of the pulse transformer is 1.5 kV are analyzed. The results show that the pulse front error of the output waveform is 3.33% and the amplitude error is 2.91%, which is more accurate than the conventional nonlinear solving method of J-A parameter. This indicates that the optimized J-A parameter can be better applied to the modeling and simulation of magnetic-containing components in pulsed power systems.

Large-scale coherent beam combining is one of the effective techniques to break through the limit of a single laser, and obtain laser with extreme characteristics such as ultra-high peak/average power, ultra-high pulse energy, ultra-high spatial/spectral brightness, and the key to large-scale coherent beam combining is active phase control. Active phase control technology can control the phase of each beam actively, compensate for coherence degradation and efficiency reduction caused by phase noise, and realize high-quality combined laser. Since the proposal of coherent beam combining technology, researchers have developed a variety of active phase control methods for phase correction, among which active phase control methods suitable for large-scale coherent laser beam combining have developed rapidly. In this paper, active phase control methods for large-scale coherent laser beam combining are systematically reviewed, and the principles, characteristics, application scenarios and expansibilities of different methods are analyzed; the latest progress and landmark achievements of coherent beam combining achieved by various active phase control methods are introduced, and the breakthrough result of 6 μs closed-loop locking time for 19-channel coherent beam combining is reported; the future development trend of large-scale active phase control methods is predicted.

With the development of adaptive optics (AO) technology in laser field, a variety of improvement measures based on software monitoring and hardware protection have been added to the classical AO system to ensure stable and continuous light output of laser AO system. Facing the reliability challenge brought by the increase of structural complexity, how to build a system failure model to evaluate the reliability of laser AO system has become an important part of the development of laser AO system. In this paper, a dynamic fault tree (DFT) method is proposed to evaluate the reliability of laser AO system, and the dynamic fault tree is established according to the dynamic relationship between the equipment. The bottom event failure rate is estimated by combining the manufacturer information, fatigue life test and historical data. The reliability parameters of DFT are obtained by using binary decision graph and Markov model. Using DFT to analyse the reliable running time of the AO system with the improvement measures, the result shows more than ten times improvement relative to the basic fault tree. In the actual system joint commissioning, no self-induced failure occurred during the expected reliable running time, which is consistent with the DFT estimate. It is proved that the reliability evaluation of laser AO system with improvement measures is more accurate by using DFT method.

When a vortex beam propagates in a turbulent medium, the phase will be distorted by the influence of turbulent motion. In this paper, a point pixel phase extraction method based on heterodyne interference is proposed. By collecting the relative phase of each point's interference fringes in a period, the phase distribution of a vortex beam is reconstructed after its turbulent transmission under water. The random phase screen is generated by the power spectrum inversion method, and the transmission simulation of the vortex beams under different turbulence is completed. The result shows that the distortion increases with the increase of turbulence intensity. An experimental device was built to realize the phase measurement of vortex beams in underwater environments. The experimental results show that when a vortex beam is transmitted in turbulent water, its complex amplitude distribution undergoes a relatively complicated transmission process, and its intensity distribution and phase are distorted. The method proposed in this paper can accurately measure the complex phase distribution of a vortex beam and effectively identify its topological charges.

Due to factors such as geographical position, sun and atmospheric environment, it is impossible to obtain the real images of space targets under various postures and illumination conditions, let alone under the interaction between laser, sun and background light. In this paper, a real-time target image generation method under multi-light source irradiation is proposed. This method is based on the modern graphics card programming technique and frame caching object advantages. At the GPU (Graphics Processing Unit) side, shader language is used to efficiently calculate target brightness values and enhance realism under the influence of multi-light source. The open-source 3D graphics engine named OSG (Open Scene Graph) helps support 3D model files of various formats and improve the compatibility with the domestic Kirin operating system as well as common battlefield situation display software. Simulation experiments demonstrate the effectiveness and superiority of the proposed method.

The Tm3+ gain medium with high doping concentration can improve the quantum efficiency of the laser through the cross relaxation process, but it also increases the energy loss caused by energy up-conversion and limits the improvement of laser efficiency. The fluorescence characteristics and laser performance of Tm:SrF2 crystal are studied. Under laser-diode (LD) end-pumping, a continuous-wave laser with a maximum output power of 2.99 W and a slope efficiency of up to 82.1% is realized. The pump threshold of the laser is 0.81 W, and the center wavelength is 1851 nm. Electro-optic Q-switching of the Tm:SrF2 laser is demonstrated. At the repetition rate of 500 Hz, a maximum pulse energy of 1.02 mJ and a minimum pulse width of 45 ns are achieved, resulting in a peak power of 22.67 kW. The experimental results indicate that the Tm:SrF2 laser based on LD pumping has very high efficiency and is expected to be an ideal pump source for optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs).

The RbTiOPO4 crystal Raman emission at high-order Stokes with 271 cm-1 shift driven by an end-pumped passively Q-switched laser was demonstrated. The Nd:YAG and Cr4+:YAG bonding design was used to reduce the intracavity loss and make the laser system compact, so as to raise the intracavity photon density, which proved helpful for the conversion of Raman shift to high-order Stokes light. The first-Stokes laser with different Raman shifts is designed to oscillate in different cavities, and the first-Stokes laser with 687 cm-1 shift is suppressed by using the difference in cavity mode matching with the fundamental laser, and the fifth-order Stokes laser with 271 cm-1 shift is obtained. Under the pump power of 8.1 W, a 1 244 nm wavelength laser with an average output power of 230 mW was obtained, and the corresponding pulse width and pulse frequency repetition were 2.9 ns and 11.7 kHz, respectively. The 1 244 nm laser wavelength perfectly matched the OH-1 absorption peak in water, which could have significant applications in fields such as surface vegetation and planetary water detection.

The preparation of Tb3Al5O12 (TAG) phosphors was fabricated by the sol-gel method. Thermal analysis data confirm that an increase in the H3BO3 molar ratio correlates with a reduction in the transition temperature of the final phase. Concurrently, scanning electron microscopy revealed that an elevated H3BO3 molar ratio results in larger phosphor particle sizes. Under the excitation wavelength of 275 nm, the emission spectrum manifests multiple peaks within the 480-650 nm range, originating from the 5d→4f transitions of Tb3+ ions. Subsequently, the phosphor@SiO2 aerogel composite luminescent material was successfully synthesized through a combination of physical doping and a supercritical drying process. This composite luminescent material exhibited a substantial increase in the internal quantum yield, reaching 63.64% compared to the standalone phosphor. Excited by a 355 nm laser source, the phosphor@SiO2 aerogel composite luminescent material demonstrated the capability for wire-free, long-distance luminescence with commendable uniformity. These findings demonstrate the potential application prospects of the phosphor@SiO2 aerogel composite luminescent material in the domain of laser emergency lighting.

To address the low ignition efficiency and reliance on electricity in traditional solid-state pyrotechnic pumped lasers, we designed a system based on the principle of adiabatic compression, utilizing entirely non-electric compressed air to ignite the pyrotechnic materials in an Nd:YAG laser medium. This design improves ignition synchronicity and pyrotechnic material combustion efficiency, achieving a laser output threshold of 10 mg pyrotechnic agent and utilizing 30 mg KClO4/Zr agent, resulting in a laser energy of 30.2 mJ with a pulse width of 10 ms. This advancement provides a new implementation pathway for small-scale non-electric high-energy lasers.

To estimate the aircraft pose in complex situation, this paper proposes a new method of aircraft pose estimation based on neural network line extraction. This method uses 3D model to render images, and forms dataset through adding backgrounds. The dataset is enhanced to make the algorithm robust. The line extraction model uses convolutional neural network to extract deep features, and uses heatmap to obtain aircraft feature lines. The target pose is solved by combining the aircraft feature line, the aircraft 3D model and the perspective-n-line method. The accuracy of the line extraction model is 91% in complex background. The accuracy is 84% after addingall sorts of noises. The aircraft pose is solved by using EPnL algorithm and nonlinear optimization. The average angle error is about 0.57°, and the average translation error is about 0.47% when the target is in a complex background. After addingall sorts of noises to the image, the average angle error is about 2.11°, and the average translation error is about 0.93%. The aircraft pose estimation method proposed in this article can accurately predict the aircraft pose under complex backgrounds and various types of noise, and its application scenarios are more extensive.

The far-field phase inversion exhibits degeneracy states, leading to the problem of encountering multiple solutions when recovering the wavefront. In comparison to traditional iterative algorithms, the combination of phase modulation and deep learning in the phase inversion method not only significantly reduces computational complexity but also effectively solves multi-solution problems. This method possesses strong real-time capabilities and a simple structure, showcasing its unique advantages. In this paper, different Walsh functions are used to modulate the phase, and a deep learning approach is taken to train a convolutional neural network to obtain the 4th-30th order Zernike coefficients from the modulated single-frame far-field intensity maps so as to recover the original wavefront, which solves the problem of multiple solutions of phase inversion. For the residual wavefront of the turbulent aberration of 3-15 cm atmospheric coherence length, the ratio of its RMS to the RMS of the original wavefront can reach 7.8%. In addition, this paper also deeply investigates the effects of various factors such as Zernike order, random noise, occlusion, and intensity map resolution on the wavefront recovery accuracy. The results show that this deep learning-based phase inversion method exhibits good robustness in complex environment.