Abstract: A Cassegrain optical antenna with parabolic structure is designed. By detailed analysis of Cassegrain optical antenna in partial axis situation，the expression of the area of the receiving spot and the power decline curve are obtained for different deflection angles. The relations between the received antenna gain and the wavelength and deflection angles are discussed in partial axis situation，the curves of gain for partial axis and axis alignment are simulated. The simulation result indicates that the gain of the maximal partial axis decreases by 6.564dB compared with that of axis alignment. Experiments of the optical spot test and the antenna coupling efficiency test are carried out separately for axis alignment and certain partial axis situations. The results show that the antenna coupling efficiency under partial axis situation is 26.97% lower than that of axis alignment. This study will provide a theoretical foundation for the control system to realise perfect alignment of optical axis in inter-satellite optical communications.

Abstract: Understanding the statistical fluctuations of lattice observables over the gauge configurations is important both theoretically and practically. It provides physical insights to tackle the famous signal-to-noise problem and the sign problem, and inspires new thoughts in developing methodologies to improve the signal of lattice calculations. Among many efforts, exploring the connections between the real and imaginary parts of lattice numerical results is a novel way to learn about the lattice signal and error, since both the real and imaginary parts originate from the same sampling of gauge fields and their distributions over the gauge samples are in principle related. Specifically, by analyzing the distributions of the real and imaginary parts of quenched lattice two-point functions with high statistics and non-zero momentum, this work proposes a possible quantitative formula connecting these two distributions as 〈inline-formula〉〈tex-math id="M1"〉\begin{document}$R(x)=\displaystyle\int dy S(y-x) \left[I(y) K(U_y)\right]$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M1.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M1.png"/〉〈/alternatives〉〈/inline-formula〉, where 〈inline-formula〉〈tex-math id="M2"〉\begin{document}$R(x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M2.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M2.png"/〉〈/alternatives〉〈/inline-formula〉 stands for the real-part distribution, 〈inline-formula〉〈tex-math id="M3"〉\begin{document}$I(x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M3.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M3.png"/〉〈/alternatives〉〈/inline-formula〉 the imaginary-part distribution, 〈inline-formula〉〈tex-math id="M4"〉\begin{document}$S(x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M4.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M4.png"/〉〈/alternatives〉〈/inline-formula〉 the underlying signal distribution and 〈inline-formula〉〈tex-math id="M5"〉\begin{document}$K(U_x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M5.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M5.png"/〉〈/alternatives〉〈/inline-formula〉 a kernel function of the gauge field. This theoretical assumption is of general validity since the kernel function contains the gauge field information that determines all the distributions. The formula is numerically verified by calculating the non-trivial statistical correlations of the real parts and the kernel-function-modified imaginary parts with further assumptions on the kernel function. It is found that the most naïve guess of 〈inline-formula〉〈tex-math id="M6"〉\begin{document}$K(U_x)=1$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M6.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M6.png"/〉〈/alternatives〉〈/inline-formula〉 does not work, which leads to no statistically significant correlation. Meanwhile, the assumption that 〈inline-formula〉〈tex-math id="M7"〉\begin{document}$K(U_x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M7.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M7.png"/〉〈/alternatives〉〈/inline-formula〉 is only a sign function works well, giving rise to 〈inline-formula〉〈tex-math id="M8"〉\begin{document}$\sim70\%$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M8.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M8.png"/〉〈/alternatives〉〈/inline-formula〉 correlation. Then, random distortions on the absolute values of the imaginary parts are added with different strength and the results show that even a small distortion, say 1%, would reduce the correlation between the real and imaginary parts down to less than 50%. This essentially proves that the observed 〈inline-formula〉〈tex-math id="M9"〉\begin{document}$\sim70\%$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M9.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M9.png"/〉〈/alternatives〉〈/inline-formula〉 correlation is highly non-trivial and the hypothesis of 〈inline-formula〉〈tex-math id="M10"〉\begin{document}$K(U_x)$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M10.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20230869_M10.png"/〉〈/alternatives〉〈/inline-formula〉 being a sign function captures at least some of the physical mechanisms behind the scenes. Employing this correlation, the variance of lattice results can be improved by around 40%. It is not a significant improvement in practice; however, this study offers an innovative strategy to understand the source of statistical uncertainties in lattice QCD and to improve the signal-to-noise ratios in lattice calculations. Further studies utilizing the power of machine learning on a variety of more precise lattice data will hopefully give better indication and constraint on the form of the kernel function.

Abstract: Rare-earth barium copper oxide (REBCO) as a representative of the second-generation high-temperature superconducting materials possesses superior physical advantages such as high critical magnetic field, elevated critical temperature, and superior current density, which has been applied to many domains. Although the introduction of non-superconducting nanoscale particle dopants, as a critical method, can enhance the magnetic flux pinning capability of REBCO strips, the effect of the doping on the performance change and microstructure evolution of the strips under irradiation is ignored. In this work, undoped and 3.5% BaHfO 〈 sub 〉 3 〈 /sub 〉 (BHO) doped EuBa 〈 sub 〉 2 〈 /sub 〉 Cu 〈 sub 〉 3 〈 /sub 〉 O 〈 sub 〉 7–δ 〈 /sub 〉 strips are investigated in the room-temperature irradiation experiments (1.4 MeV He 〈 sup 〉 + 〈 /sup 〉 ions) with three distinct doses of 5×10 〈 sup 〉 14 〈 /sup 〉 , 5×10 〈 sup 〉 15 〈 /sup 〉 , and 5×10 〈 sup 〉 16 〈 /sup 〉 ions/cm 〈 sup 〉 2 〈 /sup 〉 , respectively. Electrical performance tests reveal that the undoped strips exhibit a slight increase in 〈 i 〉 J 〈 /i 〉 〈 sub 〉 c 〈 /sub 〉 after the low-dose irradiation. However, with dose increasing, 〈 i 〉 J 〈 /i 〉 〈 sub 〉 c 〈 /sub 〉 decreases by over 60%. In contrast, doped strips experience a significantly smaller decline in 〈 i 〉 J 〈 /i 〉 〈 sub 〉 c 〈 /sub 〉 , ranging only between 30% and 40% at high-dose irradiation. Raman spectroscopy and transmission electron microscopy characterizations confirm that the defects induced by He 〈 sup 〉 + 〈 /sup 〉 ion irradiation lead to amorphization and structural disorder within the superconducting layers, which is the primary reason for the decline in the superconducting properties of the strips. The results show that the introduction of localized strain through BHO nanophase in the superconducting layer changes the migration and aggregation behavior of irradiation-induced defects, repairing the damaged superconductor structure. Furthermore, the field dependence and temperature dependence of 〈 i 〉 J 〈 /i 〉 〈 sub 〉 c 〈 /sub 〉 of doped strips are irradiation-resistant due to BHO nanocrystals as strong pinning centers. Additionally, unlike the superconducting properties of the REBCO strips that can be repaired through oxygen annealing after neutron or heavy ion irradiation, the electrical properties of the two types of strips irradiated with high doses of He 〈 sup 〉 + 〈 /sup 〉 ions in this work are further deteriorated after being annealed. It is worth noting that compared with the undoped strip, the localized strain generated by BHO in the doped strip inhibits the size growth of helium defects in the three-dimensional direction at high temperatures, which changes the magnetic flux pinning characteristics and delays the disorder and amorphization of the superconducting layer structure caused by the severe growth of helium bubbles. This study provides a reference for the application of REBCO superconducting strips in the irradiation environment.

Abstract: In this paper, the DV-X method of ab-initio calculations and the effective Hamiltonian model are introduced to calculate the crystal-field and spin-orbit parameters of rare earth ions doped in various crystals, especially for the crystal with low-symmetry. For the low-symmetry crystal, the number of parameters is more than that of energy levels, thus experimental energy levels fitting cannot determine all parameters, while ab-initio calculations can determine all crystal-field and spin-orbit parameters accurately. Firstly, the crystal-field and spin-orbit parameters of Yb3+ doped in GdTaO4 crystal are calculated by this model, and then the energy level structure of Yb3+:GdTaO4 is given and the continuous emission band of Yb3+:GdTaO4 emission spectrum is analyzed, which is conducive to the laser tunable and laser mode-locking output, so Yb3+:GdTaO4 is a potential laser medium for high efficiency laser operation and new ultrashort pulse output. Also, the crystal-field and spin-orbit parameters of Yb3+ doped in YTaO4 and ScTaO4 are calculated by this model, and the energy level structures of Yb3+:YTaO4 and Yb3+ :ScTaO4 are given, which leads to a conclusion similar to that drawn from the Yb3+:GdTaO4 crystal.

Abstract: 〈sec〉Recently, helicon plasma sources have aroused the great interest particularly in plasma-material interaction under fusion conditions. In this paper, the helicon wave antenna in helicon physics prototype experiment (HPPX) is optimized. To reveal the effect of the radial density configuration on wave field and energy flow, Maxwell's equations for a radially nonuniform plasma with standard cold-plasma dielectric tensor are solved. Helicon wave coupling and power deposition are studied under different types of antennas, different antenna lengths and driving frequencies by using HELIC. Through the numerical simulation, the optimal antenna structure and size are obtained, that is, half helix antenna, which works at 13.56 MHz and has a length of 0.4 m, can generate nonaxisymmetric radio frequency energy coupling to excite higher electron density.〈/sec〉〈sec〉The influences of different static magnetic fields and axis plasma densities on power deposition are also analyzed. It is found that the absorbed power of the plasma to the helicon wave has different peak power points in a multiple static magnetic field and axial plasma densities, and the overall coupling trend increases with static magnetic field increasing, but decreases with axis plasma density increasing. According to the simulation results, the ionization mechanism of helicon plasma is discussed. In order to further study the coupling of helicon wave with plasma in HPPX, the induced electromagnetic field and current density distribution are given when the plasma discharges. Under parabolic density distribution, the field intensity of the induced electric field at the edge is large, while neither the induced magnetic field nor current density changes much along the radial direction, the energy is distributed evenly in the whole plasma. Under the Gaussian density distribution, the induced electric field intensity is higher at the edge, while the induced magnetic field and current density in the center are much higher than at the edge. 〈/sec〉〈sec〉In this paper studied are the structure and size of helicon wave antenna, the influences of static magnetic field and axial plasma density on plasma power deposition and the distribution of induced electromagnetic field and current density during plasma discharge under different density distributions. This work will provide important theoretical basis for helicon wave antena design and relevant physical experiments on HPPX.〈/sec〉

Abstract: A synthesis method for a few hundred megawatt level power microwave is presented in this paper. Based on the coupling wave theory and the polarized wave orthogonal theory, the pulse series of one gigawatt level power microwave and one hundred megawatt level power microwave can be put in two separate ports and put out from one common port. The synthesizer is unitized by two cylindrical waveguides which are back to back combined; the cylindrical waveguide which is joined with the output port is named main channel, and the other cylindrical waveguide is called associate channel. The main channel transmits horizontally polarized TE011 mode microwave, and the operation frequency band is only limited to the barrier frequency c. The associate channel transmits vertical polarized TE011 mode microwave, and the operation frequency band can reach up to several hundred mega hertz. High power experiment indicates that the transmission energy efficiency of the main channel is nearly 100% and the coupling energy efficiency of the associate channel is above 87%, the power capacity of the main channel is more than 1GW and that of the associate channel is about 300 MW.

Abstract: The dispersive character of ?ffner stretcher was studied, and a concise expression of output pulse duration was presented. An ?ffner stretcher was setup experimentally, which could stretch a 19fs seed pulse to 605 ps after 4 passes in it free of aberration.

Abstract: In the process of eliminating the residual pump light and high-order laser light, the cladding power stripper (CPS) generates abundant heat, which can affect the performance of the fiber laser system due to the photothermal conversion. Hence the efficient dissipation of thermal energy becomes a current research focus. In this paper, the five kinds of existing CPSs are simulated and compared with the results in the literature. It is found that the surface-volume ratio between the heat source and the heat transfer medium can be effectively increased by changing the shape of the polymer filling hole when the CPS is made by the high refractive index polymer method, thus reducing the temperature peak and valley value of the CPS. Besides, the heat distribution uniformity of CPS can be improved by combining the high refractive index polymer method with the acid corrosion method to prepare the two-section fiber cladding structure with uneven thickness. According to the above results, a novel CPS structure is proposed and its thermal effect is studied. The results show that when the cladding light power is 150 W, the temperature peak value of the CPS is 298 K, the temperature valley value is 293 K, and the temperature difference is 5 K. Comparing with the above five CPSs, the peak temperature is reduced by up to 11.3%, and the valley temperature is reduced by up to 8.4%, the temperature difference is reduced by up to 87.5%, which proves that the novel CPS structure can effectively suppress the temperature rising and have excellent heat distribution uniformity.

Abstract: Analogous to graphite, hexagonal boron nitride (h-BN) has a layered structure composed of boron and nitrogen atoms that are alternatively bond to each other in a honeycomb array. As the layers are held together by weak van der Waals forces, h-BN thin films can be grown on surfaces of various metal crystals in a layer-by-layer manner, which is again similar to graphene sheets and thus attracts a lot of research interests. In this work, scanning tunneling microscope and spectroscope (STM and STS) were applied to the study of an h-BN thin film with a thickness of about 10 nm grown on Cu foil by means of chemical vapor deposition. X-ray diffraction from the Cu foil shows only one strong peak of Cu(200) in the angle range of 40-60, indicating that the Cu foil is mainly Cu(100). After sufficient annealing in an UHV chamber, the h-BN film sample is transferred to a cooling stage (77 K) for STM/STS measurement. Its high quality is confirmed by a large-scale STM scan that shows an atomically flat topography. A series of dI/dV data taken within varied energy windows all exhibit similar U shapes but with different bottom widths that monotonously decrease with the sweeping energy window. The dI/dV curve taken in the energy window of [-1 V, +1 V] even shows no energy gap in spite that h-BN film is insulating with a quite large energy gap of around 6 eV, as observed in a large-energy-window dI/dV curve (from -5 V to +5 V). These results indicate that the STM images reflect the spatial distribution of tunneling barriers between Cu(100) substrate and STM tip, rather than the local density of states of the h-BN surface. At high sample biases (from 4 V to 1 V), STM images exhibit an electronic modulation pattern with short range order. The modulation pattern displays a substructure in low-bias STM images (less than 100 mV), which finally turns to the (11) lattice of h-BN surface when the sample bias is extremely lowered to 3 mV. It is found that the electronic modulation pattern cannot be fully reproduced by superimposing hexagonal BN lattice on tetragonal Cu(100) lattice, no matter what their relative in-plane crystal orientation is. This implies that the electronic modulation pattern in the STM images is not a Mori pattern due to lattice mismatch. We speculate that it may originate from spatial distribution of tunneling barrier induced by adsorption of H, B and/or N atoms on the Cu(100) surface in the CVD growth process.

Abstract: High power microwave (HPM) pulse compression is a main method to obtain high power microwave with non-relativistic devices. The mature HPM pulse compression systems are nearly all based on rectangular resonant cavity, and the pulse compression systems based on cylindrical resonant cavity are in progress. A new type pulse compression system based on cylindrical resonant cavity is proposed in this paper, and the structure of the system is different from those of all other HPM pulse compression systems ever reported. The structure and the numerical simulation results of the key parts are presented, and a preliminary analysis of the power capability of the system and the quality factor of the resonant cavity is also given. For a pulse compression system, the power capacity is a key factor for the output microwave pulse power, and the quality factor of the resonant cavity has a close relationship with the system energy efficiency. According to the experimental results, the pulse capacity of the pulse compression system based on cylindrical resonant cavity can be 10 times higher than that of the systems based on the rectangular resonant cavity, and the quality factor of the resonant cavity can be improved by a factor of 5.