双爆炸膜内壳层光电离X射线激光实验研究

报道了Pd-NaF,Pd-Cu,Ag-NaF和Ag-Cu耦合双爆炸膜内壳层光电离X射线激光的实验方法和一些实验结果。结果表明,在本实验条件下,激光加热NaF或Cu靶产生的1keV区的光子,可以增强Pd或Ag等离子体中类-Cu离子的3d¹⁰4p-3d⁹4s²软X射线发射的强度,但不足以形成X射线激光的输出。 关键词：     

自动线匹配光泵浦方案的研究

通过对激光驱动Cu等离子体实验的分析,认为对于自动线匹配光泵浦类Ne铜,在适当的条件下能够达到粒子数反转;而能否获得可观的增益,取决于两等离子体的耦合方式及驱动泵浦靶的激光功率密度是否接近最佳值。     

无粒子数反转激光研究的进展

概括地介绍了无粒子数反转光放大与无粒子数反转激光的基本概念和原理，讨论了这种类型激光对激光科学发展的重要意义，叙述了自１９６２年以来科学家们所提出的几种实现无粒子数反转光放大及无粒子数反转激光的主要的理论模型和有关的实验进展，最后介绍了钠原子蒸汽中首次观察到无粒子数反转光放大的实验装置和实验结果。     

碳、氮原子内壳层光电离X射线激光的理论探讨

提出了分析碳、氮原子内壳层光电离X射线激光的解析模型,对C原子K壳层光电离X射线激光的增益进行了理论计算。采用随时间线性增加的X射线抽运速率推导出了激光增益系数随抽运速率的上升速率、原子浓度以衣时间变化的解析表达式,给出了峰值时间和峰值增益。在理论上定量地分析了产生X射线激光所需的激光条件和最佳参数的选取,数值模拟与理论计算的结果是一致的。另外,对N原子K壳层光电离X射线激光作了类似的分析。     

用平均原子模型研究粒子数反转

本文考察了在高度电离的情况下,平均原子模型速率方程与类氢离子速率方程的等效性。着重研究用平均原子模型速率方程计算粒子数反转,给出了用光电离内壳层电子,通过三体复合到外壳层形成粒子数反转所需的条件和一些计算结果。     

9—28keV电子引起的Cu的K壳层电子电离截面

用高分辨的Ｓｔ（Ｌｉ）探测器测量Ｃｕ靶在９—２８ｋｅＶ的电子轰击下产生的Ｋ壳层特征Ｘ射线，以确定其Ｋ壳层电子的电离截面。运用用电子输运双群模型对衬底的反射对电离的贡献进行了修正。测量结果与前人的实验和经验公式计算结果作了比较。     

间接驱动冷冻双壳层点火靶的设计和分析

双壳层靶中,由于燃料被高Z壳层包裹,其点火方式要求燃料整体点火,不同于单壳层中心热斑点火。结合点火条件和对于其中物理过程的认识,设计了间接驱动的冷冻双壳层点火靶。利用冷冻的氘氚(DT)燃料,可适当提高双壳层靶的燃料装量,获得和NIF装置条件下中心热斑点火靶相当的放能。间接驱动下,X射线烧蚀并驱动外壳层碰撞内壳层,把能量传递给内壳层,进而压缩和点燃冷冻的DT燃料。壳层碰撞过程是能量传递的关键,通过调整内外壳层的质量比,提高了碰撞效率,相应地降低了靶丸点火的能量需求。一维数值模拟分析了该点火靶的内爆过程及定性分析了其中的流体力学不稳定性。同时,也指出了泡沫中形成的辐射冲击波对内壳层的预热效应,即辐射冲击波的致稳效应,能够很好地抑制内壳层外界面处的不稳定性发展,进而会减弱高Z内壳层和燃料的混合。     

原子分子真空紫外光吸收和光电离绝对截面的精确测量

介绍了一种精确测量原子分子真空紫外光吸收和光电离绝对截面的实验方法。该方法的主要特点是使用圆筒形多级电极，有效地收集光电离产生的电子和离子，并利用高通量的同步辐射作光源，精确地测量分子（原子）的绝对光吸收、光电离和光离解截面，以及光电离量子产率和光学振子强度分布等。利用该方法获得了Ｘｅ原子和Ｎ２分子的一些实验结果。     

X射线相衬成像中靶丸球壳界面晕区暗区现象

在微聚焦X射线以及等离子体X射线源平台上开展了多层球壳靶丸的相衬成像实验。实验结果表明,通过相衬成像能够获得清晰的多层球壳靶丸图像并观察到球壳内外表面晕区暗区现象。根据光的折射原理解释了该晕区暗区现象产生的物理机制。实验结果与几何模型计算结果符合较好。     

9—46keV电子引起的Ni的K壳层电离截面

用Ｓｉ（Ｌｉ）探测器测量薄Ｎｉ靶在９—４６ＫｃＶ的电子轰击下产生的Ｋ壳层特征Ｘ射线，以确定其Ｋ壳层电子的电离截面。测量结果与前人的实验和理论计算以及经验公式的计算结果作了比较。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.