Search

Laser plasma interaction (LPI) is an important content in laser plasma related research, and it is one of the key issues related to the success or failure of inertial confinement fusion ignition, and has received extensive attention. In order to suppress the relevant LPI process as much as possible, the major laboratories around the world have developed a variety of beam smoothing methods through decades of research. However, the current understanding and suppression of LPI are still far from enough, and further in-depth studies are still needed. Generally, the research of LPI is based on nanosecond laser driving, and focuses mainly on the effects of the related LPI process caused by nanosecond lasers. However, the LPI processes, such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), etc., occur and develop on a time scale of picoseconds.The comprehensive effect can be studied only on a longer scale of nanosecond. For highly nonlinear LPI processes, the comprehensive effect may be difficult to reflect the real physical laws. The emergence of the picosecond laser has made it possible to study the LPI process in more detail and on a more appropriate time scale. The present research tries to gain an understanding of LPI from a more refined perspective. The experimental research of picosecond laser driving LPI is carried out on the Shenguang-Ⅱ upgrade and picosecond laser facilities. First, a nanosecond laser is used to irradiate a target to generate a large-scale plasma, and a few nanoseconds later, the picosecond laser is injected as an interaction beam to drive the LPI scattering such as SBS and SRS. The spectral signal of backscatter light is measured experimentally by using the method of diffuse reflector. From the research results it is found that the backward signals of the band near the laser wavelength contain, in addition to the true backward SBS component, a large number of interference signals introduced by picosecond laser and nanosecond laser. The interference signal introduced by nanosecond laser can be eliminated by using specific measures, but the interference signal introduced by picosecond laser cannot be eliminated experimentally, which will affect the estimation of the true share of the backward SBS. The comprehensive results show that under different experimental conditions, the backward scatter energy of SBS may be less than half that of the total recorded signals. This result is helpful in further understanding and re-recognizing previous relevant experimental data.

This paper studies the optimal operating strategy of high-speed trains to reduce the total energy consumption in fixed time. Optimization of train running trajectory and efficient utilization of regenerative energy are two effective methods for energy-efficient operation. Based on the analysis of dynamic model of high-speed trains, this paper proposes a Genetic Algorithm-Particle Swarm Optimization(GA-PSO) fusion algorithm in the pursuit of a sequence of speed codes at each end of subsection, which shares the same geographical data, to minimize the energy consumption. First, we formulate a two-objective dynamic model with energy consumption and operating time. Second, we design a combined algorithm with real number encoding to obtain the optimal solution. Then, we conduct the proposed optimization method under an actual route condition to verify the effectiveness. The simulation results show that the proposed operating strategy saves 22.81% more than the minimum time strategy and 4.22% than the global optimization on energy consumption. Finally, the situation involving interval speed limit is simulated with proposed method. The results demonstrate that optimal train trajectory saves 6.76% more than the normal train control strategy.

Thermal properties of CdSiP2 polycrystalline were studied by differential thermal analysis (DTA) technique with a quartz capillary column. It is found that the melting point and crystallization temperature of CdSiP2 are 1139 and 1126 °C, respectively, and the supercooling degree of CdSiP2 melt is evaluated to be 13 °C. According to the results of DTA, the structure of a furnace and the temperature profile of the crystal growth for CdSiP2 were optimized. A crack-free CdSiP2 crystal with 15 mm in diameter and 40 mm in length was grown by the modified vertical Bridgman (VB) method. The X-ray diffractionmeter (XRD), X-ray energy dispersive microanalysis (EDX) and infrared spectrophotometer (IR) were employed to characterize the properties of as-grown crystal. A new cleavage face of (112) was identified in XRD spectrum. The results of EDX indicate that the crystal is of good stoichiometry. The infrared transmission is up to 55% in the infrared region from 7000 to 1500 cm−1. All the characterization results show that the obtained crystal is integrated in structure and good in optical quality which can be used in devices fabrication.

ZnGeP 2 (ZGP) single crystal with size of 24 mm in diameter and 70 mm in length was grown by a modified vertical Bridgman (VB) method in a three-zone furnace. The crystal was annealed in ZnGeP 2 powder at 600 °C for 500 h. X-ray diffraction (XRD), X-ray fluorescence (XRF) and Fourier transform infrared spectrophotometry (FTIR) were employed to characterize its properties. A ZGP optical parametric oscillator (ZGP-OPO) device was fabricated from the annealed sample. Laser experiment was carried out on the device. Tunable mid-infrared laser in the range of 3∼5 μm was realized on the ZGP-OPO pumped by 2.1 μm, 7 kHz laser. All the results indicate that our grown crystal is in good quality and can be used for nonlinear optical applications.

An integral CdGeAs 2 (CGA) single crystal with the size of Φ15 mm×45 mm was obtained by the modified Bridgman method. For the reasonable application of the CGA crystal, different polishing techniques have been employed in this work. The as-grown ingot was cut and wafers with (101) plane were mechanically polished by means of metallographic abrasive papers. Then the surface element composition and valences of (101) plane on the CGA crystal were analyzed by the X-ray photoelectron spectroscopy (XPS). Finally, the wafers were chemically polished by a bromine-methanol corrosive solution. The samples chemically polished for different time were studied by X-ray diffraction (XRD) and optical microscopy. It is found that after etching by bromine-methanol solution for 50 s at room temperature, the CdGeAs 2 wafer has no scratch marks, and possesses a narrow full width at half maximum (FWHM). Meanwhile, the thickness of the surface damage layer of CdGeAs 2 wafer was also calculated.

Materials can be experimentally characterized up to terapascal pressures by sending a laser-induced shock wave through a sample that is pre-compressed inside a diamond-anvil cell. Pre-compression expands the ability to control the initial condition, allowing access to thermodynamic states from the principal Hugoniot and enter into the 10 TPa to 100 TPa (0.1-1 Gbar) pressure range that is relevant to planetary science. We demonstrate here a laser-driven shock wave in a water sample that is pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P-T phase diagram of fluid water to high density. According to the loading characteristics of the SG-Ⅱ high-power laser, the traditional diamond anvil cell is improved and optimized, and a new diamond anvil cell target adapting to high power laser loading is developed. In order to adapt to laser shock, the diamond window should be thin (100 μm) enough so that the shock can propagate to the sample before the side rarefaction erodes too much the shock planarity. With a thickness of 100 mm over an aperture of 600 μm diameter, a pre-compressed water sample at 0.5 GPa can be obtained. The water is pre-compressed to 0.5 GPa by using the diamond anvil cell. Hugoniot curve is partially followed starting from pre-compression at a pressure of 0.5 GPa. Pressure, density, and temperature data for pre-compressed water are obtained in a pressure range from 150 GPa to 350 GPa by using the laser-driven shock compression technique. Our P-ρ-T data totally agree with the results from the model based on quantum molecular dynamics calculations. These facts indicate that this water model can be used as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range and should improve our understanding of these types of planets.

采用WinTA 100热膨胀仪研究了四方黄铜矿CdGeAs 2 晶体在320~620 K温度范围内的热膨胀行为, 探索了CdGeAs 2 晶体热膨胀各向异性的物理机制。测定晶体a轴和c轴方向的热膨胀系数 α a 和 α c 发现, α a >> α c >0, 表现出强烈的各向异性热膨胀特性。利用最小二乘法, 拟合出CdGeAs 2 晶体的晶格常数( a , c )与温度( T )的函数关系式, 与文献报道值吻合。分别计算出不同温度下的四方畸变因子 δ =2– c / a , Cd-As 键长( l Cd-As )和 Ge-As 键长( l Ge-As )以及相应的热膨胀系数 α Cd-As 和 α Ge-As 。结果表明, a 、 c 、 δ 、 l Cd-As 、 l Ge-As 和 α Cd-As 均随着温度的升高而增大, c / a 和 α Ge-As 则随着温度的升高而减小。当 T =360 K时, α Cd-As 是 α Ge-As 的6.36倍, 是造成CdGeAs 2 晶体强烈热膨胀各向异性的主要原因。