High aspect ratio gratings can be made by perpendicularly cutting in the growth direction of multilayers. X-ray exposure technique using a sectioned multilayer grating based on Talbot effect is a new type of nano patterning method. Although 300 nanometer gratings through the experiment are completed, some phenomena in the experiments cannot be satisfactorily explained and the factors influencing the nano pattern quality have not been fully understood yet. Here we use a rigorous coupled-wave theory to discuss several important factors, including grating thickness, the fraction of material thickness and multilayer period, which is the first time as far as we know for Talbot self-imaging in X-ray range. Simulation results show that the grating thickness affects both X-ray transmission efficiency and fringe contrast, while the fraction of material thickness determines the quality of fringes. And the position deviation of the best image plane in near field is related to both the thickness of the grating and the multilayer period. Moreover, the multilayer gratings with smaller periods can achieve higher resolution, indicating that the Talbot effect can be used to fabricate a more detailed structure.

We propose a vector beam generation method based on the spatial light modulator composed of twisted nematic liquid crystal. According to the relation between the rotation angle and the applied voltage on the spatial light modulator, a common optical system for generating a variety of vector beams is designed in experiments. By using this common optical system, a variety of vector beams in axisymmetric phases as well as the complex vector beams are generated, and their polarization characteristics are observed and measured experimentally, where a tight focusing field is obtained, and this may be applied in optical tweezers and lithography. In addition, the device structure is simple and easy to operate, its efficiency of producing vector beam is very high and the laser spectral characteristics are not changed in the proposed generation of vector beams. Therefore, the method we proposed can find important potential applications in strong laser of vector beams interacting with matter, and laser acceleration, etc.

This paper studies the equivalent refractive index method and other methods to measure the liquid diffusion coefficient. Based on this, a quick method to measure the liquid diffusion coefficient is proposed, i.e. using a specially designed asymmetric liquid-core cylindrical lens as both diffusive pool and imaging element. By means of this system with the liquid-core cylindrical lens to measure the diffusion coefficient, we can eliminate the spherical aberration and improve the accuracy in refractive index measurement. Based on the spatially resolving ability of the cylindrical lens in measuring the refractive index, only one instantaneous diffusive picture is required. Depending on the correspondence between the image width and the refractive index, we thus can quickly calculate the diffusion coefficient D by the Fick’s second law. Then the diffusive process of ethylene glycol in water at 25℃ is investigated by this method. We calculate the diffusion coefficient between 660-3000 s with the method to analyse an instantaneous diffusion picture. At the beginning, injection will cause the liquid turbulent, and thus create a larger diffusion coefficient. In the course of diffusion, the influence of turbulence on the diffusion coefficient gradually decreases, but the image narrowing can make inaccurate results. Therefore, this method is required to be used at an appropriate time and an appropriate position to reduce experimental errors. After repeated experiments we can conclude that, between 1500-2700 s we may select the appropriate measurement of location for measuring liquid diffusion coefficient by the method to analyze an instantaneous diffusive picture. This not only can avoid the effect of turbulence but also avoid the effect of fewer sampling points. Compared with other methods reported in the literature, the results show that this method is characterized by short time (~20 ms) in data acquisition, faster measurement (< 1 s), high-accuracy (relative error < 3%), and easy operation, thus providing a new method for measuring the diffusion coefficient of liquids rapidly.

Based on terahertz time domain spectroscopy, a false-color imaging system is demonstrated by experiments. Three frequency ranges are defined as color ranges for three primary colors (red, green and blue). The mixture of the spectral integral values in each color range presents the final color of each pixel on the false-color THz image. Since the absorption frequencies of different materials are different, the spectral integral values in defined ranges are different, leading to different color on the false-color THz image. The false-color THz images of two kinds of white powder which are lactose and 4-aminobenzonic acid are obtained from the imaging system with two different definitions of color ranges. From the first color range definition, the absorption frequency of lactose lies in the green range, so only the green light is absorbed, and the color of lactose is magenta. In the meanwhile, there are two absorption frequencies for 4-aminobenzonic acid lying in the green and blue ranges, so both green and blue light are absorbed, and the color of 4-aminobenzonic acid is red. They can be told easily by different colors on the false-color THz image. From the second color range definition, the colors of two kinds of powder are more different. Both false-color THz images can present the cuvette and two kinds of powder clearly. By comparing the THz imaging with grayscale images, false-color THz imaging can display different materials by different colors in one image, instead of the requirement of many grayscale images. It is no need to generate grayscale images at each frequency, making false-color THz imaging consume less time. The false-color imaging is clearer and more efficient, which is more suitable for recognition in a rapid security check. In the situation of complex materials, more false-color THz images can be generated by different color range definitions to assist the detection. The spatial resolution of the imaging system is also investigated. The resolution of imaging system is investigated by imaging home-made standard sample plate. For the frequency range that is higher than 0.3 THz, the resolution can reach 0.4 mm, which is larger than enough for most practical applications.

Digital micro holography offers an in-situ, non-contact and three-dimensional way to explore the microscopic world. However, as it is difficult to focalize the whole object in one single reconstructed image, the application of digital micro holography to cases with a large longitudinal object volume is limited by the microscope’s depth of field. By extending the depth of field in reconstructed micro holograms in the wavelet domain, this paper fully takes advantage of numerical reconstruction algorithms to solve this problem. First, a recorded hologram is rebuilt using the wavelet transform approach by setting up an appropriate longitudinal interval to obtain a series of reconstructed hologram planes. Then each plane is decomposed with wavelet into its sub-images of both high and low frequencies. Furthermore, the local variance of the maximum intensity gradients of the high- and low-frequency coefficients is calculated and utilized as the focus criterion. Finally, the image planes are fused into a single one with the depth of field extended to a large extent. The feasibility and robustness of this reconstruction procedure for both continuum and particle fields are investigated. One of the demonstrations is made in an experiment of a tilted continuum:carbon fiber. It is different from most of the previous applications where the interrogated is the particles and where the area involved is parallel to the CCD. The carbon fiber gets successfully reconstructed in three dimensions, and the measurement errors of its diameter are presented together with the reconstruction distances. Another is an experiment of a dispersed particle field:micro transparent particles are generated by an ultrasonic atomizer, for which the reconstruction procedure achieves an extended depth of field. In addition, a numerical model based on generalized Lorenz-Mie theory is used to simulate the holograms of both opaque and transparent particles of 1-15 μm in diameter. Variations of the longitudinal location errors with the Fraunhofer number are analyzed, and comparisons are made between the results of opaque and transparent particles. Both the experimental and simulation outcomes show that this reconstruction procedure is a reliable one to acquire an extended-depth-of-field hologram for both the continuum and the dispersed particle fields, and then to accurately measure the objects.

This paper analyzes theoretically and numerically the refraction phenomenon of detonation wave at the explosive-metal interface, motivated by the problem that there exist large discrepancies between the experimental results and the classical shock polar theory. After pointing out the major defects of the classical shock polar theory based on CJ model of detonation, an improved shock polar theory based on ZND model of detonation is presented to give the styles of the refraction of detonation wave and the pressure values at the interaction point between the refracted shock wave and the incident shock wave, to show the pressure values at free-surface of copper remarkably lower than the ones at the shock interaction point due to the attenuation effects from the chemical reaction expansion and the following Taylor rarefaction. A second-order cell-centered Lagrangian hydrodynamics method with high resolution based on the subcharacteristics theory is develped to solve the reactive flow equations of detonation in condensed explosive, and then to numerically simulate a representative refraction experiment about T2 explosive interacting with copper. The simulated pressure values at the interaction point agree well with the ones from the improved shock polar theory, and the simulated pressure values at free-surface of copper agree well with the experimental values, meanwhile, the refraction styles predicted by the improved shock polar theory are confirmed by the numerically simulated flowfield images. From the theoretical and numerical results, there exist three kinds of refraction styles of detonation waves at explosive-metal interface:i) the regular refraction with reflecting shock wave, ii) the irregular refraction with Mach reflection, and iii) the regular refraction without any reflecting wave; in particular, the regular refraction with no reflecting wave is a kind of refraction style unable to be predicted by the classical shock polar theory, meanwhile, the pressure values at the free-surface and the interaction point inside the shocked metal both monotonically decrease with the increase of the incident angle.

The discovery of superconductivity in iron-based superconductors by Professor Hosono in Japan in 2008 has triggered off an enormous group of researches the world wide. The iron-based superconductors are regarded as another kind of high-T_c superconductors, which possess lots of merits, such as very high upper critical field (H_c2), high critical current density (J_c), and small crystal anisotropy (γ), are promising for high field applications. Ba_1-xK_xFe₂As₂, as a typical FeAs-122 superconductor, is focused on by both theoretical physicists and material scientists since its discovery. In this paper, we first successfully fabricate Ba_1-xK_xFe₂As₂ single crystal. It has an onset transition temperature up to 38.5 K, while its zero resistivity temperature reaches 37.2 K. Both the R-T and M-T data of it show very sharp superconducting transition, and its critical current density at 5 K and self field is over 10⁶ A·cm^-2 and almost field independent. The flux pinning force and the relative pinning mechanisms in Ba_1-xK_xFe₂As₂ are discussed by analyzing the data obtained from the measurements about the R-T and M-H under different conditions. Results indicate that the Ba_{1- x}K_xFe₂As₂ superconductors have very strong intrinsic vortex pinning force, and the vortex potentials (U₀) under 9 T field are 5800 K and 8100 K for the H//c and H//ab, respectively. Furthermore, the vortex pinning mechanism is also investigated by analyzing the relationship J_c-B. According to the present results, the flux pinning mechanism should be δ(l) pinning because of the change of mean free path for electrons induced by nano-size crystallographic defects in Ba_1-xK_xFe₂As₂.

In this paper, polycrystalline BaFe_4-xTi_2+xO₁₁ (x=0, 0.25, 0.5, 0.75, 1) samples have been synthesized by the conventional solid-state reaction method. X-ray diffraction (XRD) patterns of all the samples show that the diffraction peaks correspond to that of an R-type hexagonal ferrite structure, and no trace of second phase is detected. Measurement of X-ray photoelectron spectroscopy (XPS) reveals that most of the Fe ions in BaFe₄Ti₂O₁₁ are trivalent and the fitting of two peaks in Fe 2p spectrum corresponding to different Fe ion sites, while the amount of Fe²⁺ ions increases with the increase of Ti ions in BaFe_4-xTi_2+xO₁₁. The spectroscopy of Ti ions confirms that the valence of Ti in BaFe_4-xTi_2+xO₁₁ are tetravalent. Magnetic susceptibility of BaFe_4-xTi_2+xO₁₁ (x= 0, 0.25, 0.5, 0.75, 1) reveals two magnetic transitions at T₁～250 K and T₂～83 K, which indicate a complex magnetic order driven by competing interactions on a frustrated lattice with a noncentrosymmetric structure. For all the samples, the magnetic susceptibility obeys Curie-Weiss law above T₁, and M-H curves exhibit a linear variation with magnetic field in this temperature range, which is consistent with the paramagnetic behavior. A decrease of the effective magnetic moment is due to the increase of Fe²⁺ ions with the increase of Ti content in BaFe_4-xTi_2+xO₁₁. Below T₁, the magnetization curve as a function of temperature (M-T) and the magnetization versus magnetic field (M-H) at different temperatures imply its characteristic of a typical canted antiferromagnetic or ferrimagnetic state. Meanwhile, the transition temperature T₂ drops gradually with the increase in Ti content, which might be related to the change of occupying of Fe ions in the kagome layers.

With the rapid development of satellite, manned space flight and deep space exploration technology, semiconductor devices are used in extreme environments, especially in radiation and low temperature environment. SiGe HBT is a potential candidate for space applications because of its inherent robustness to total ionizing dose (TID) radiation. However, due primarily to charge collection through the collector-substrate (CS) junction and the relatively low substrate doping., SiGe HBTs are vulnerable to single event effects (SEEs) because of new features of process and structure. Thus, the SEE becomes a key factor in restricting space applications of SiGe HBTs. This paper presents an SEE hardening approach that uses a dummy collector to reduce charge collection in the SiGe HBT. The dummy collector is obtained by using the silicon space between adjacent HBTs. It is obtained without any process modification or area penalty. At first, we build simulation models for both normal and hardened SiGe HBTs, and then carry out SEE simulations respectively. The charge collection mechanism is obtained by analyzing the transient current and charge collection changes at different ion incident positions. Unlike the normal HBT, we can see that charge is continuously collected by the dummy CS junction. This causes more charges diffuse outward and the charges available for collector terminal to be reduced. For all ion incident positions, in the case of hardening, the drift components of charge collection are approximately the same, while the diffusion charge collection components are nearly completely compressed. During SEE, the CS junction either directly collects the deposited charges through drift within the potential funnel or indirectly collects charges after they have arrived at the junction after diffusion. The diffusion length of the carriers is on the order of tens of microns or more. Hence a dummy CS junction should be able to reduce the quantity of diffusive charges collected by the HBT collector. The actual charges collected by the collector are effectively reduced. The emitter and base charge collection also decrease by the dummy collector to different extents. Dummy-collector effectively mitigates the SEE of SiGe HBT. The SEE sensitive area of SiGe HBT is also effectively reduced by half. This work is carried out for the SiGe HBT circuit level radiation hardening design of single event effects

Experimental nuclear charge radii for 885 nuclei with N≥8 and Z≥8 have been systematically investigated. Results show that the formula for single parameter Z^1/3 law is superior to that for the A^1/3 law in describing nuclear charge radii. For two-parameter and three-parameter formulae, the Z^1/3 law is as good as the A^1/3 law. Considering the importance of shell effect and deformations for nuclear charge radii, we add a term including the Casten factor P into the conventional three-parameter formula and thus obtain very good results. The corresponding root-mean-square deviation falls to σ=0.0273 fm, i.e. reduced by about 50% when compared with the result obtained with the old three-parameter formula. Shell effect can be well reproduced for some elements by adding the Casten factor term. It is shown that the Casten factor plays a key role for nuclear charge radii. The odd-even staggering is a common phenomenon in many nuclear fields. This phenomenon can be observed with nuclear charge radii for most elements. For this reason, we add a δ term into the formula (10) in this paper. The root-mean-square deviation falls to σ=0.0266 fm. A five-parameter formula can well reproduce the variation of the nuclear charge radii for most elements. Calculated results are well consistent with the experimental data available. The differences between the experimental nuclear charge radii and the results calculated using the conventional three-parameter formula and the present five-parameter formula for the 885 selected nuclei are presented. A comparison of the formulae mentioned in this paper is given. The present five-parameter formula including the Casten factor P and the odd-even staggering is the best formula to fit available R_C data and gives the smallest root-mean-square deviation σ. Our calculated results may be useful for future experiments.