Ferromagnetism in ZnO with（Mn,Li） codoping

First-principles calculations were performed to investigate the magnetic properties of Zn(Mn,Li)O based on the Perdew-Burke-Ernzerhof form of generalized gradient approximation. Antiferromagnetic (AFM) ordering is the ground state in Mn-doped ZnO system without the codopant of Li, while seven different geometrical configurations of Zn(Mn,Li)O prefer stable ferromagnetic (FM) ordering. We found that dopant Li can effectively change the magnetic coupling in the ZnMnO system. The Curie temperature (T_C) of FM ordering depends on the geometric configuration, and the highest T_C is about 1388 K. The FM stabilization is greatly affected by Mn-Mn distance rather than by the position of dopant Li. We propose that dopant Li mediates FM coupling through a double exchange interaction or an RKKY interaction when Li is located, respectively, near or far from Mn ions.     

利用低频场控制轨道直接产生低于50阿秒的单个脉冲

提出一种直接得到脉宽小于50as的单个脉冲的新方法.利用波长为800nm脉宽为5fs的超短脉冲叠加上波长为10μm,强度为超短脉冲强度的10％且脉宽足够长的低频场脉冲驱动氦原子,谐波谱可以拓展到I_p+8.2U_p,同时,高于4.2U_p的谐波几乎是连续的.如果继续调节超短脉冲的载波包络相位,超连续谱可以继续拓宽,从而可以得到低于50as的单个脉冲. 关键词： 阿秒脉冲 超连续谱     

Nucleon Mass Splitting at Finite Isospin Chemical Potential

We investigate nucleon mass splitting at finite isospin chemical potential in the frame of the two-flavour Nambu-Jona-Lasinio model. It is analytically proven that in the phase with explicit isospin symmetry breaking, the proton mass decreases and the neutron mass increases linearly in the isospin chemical potential.     

Monte Carlo Simulation of Cooling Induced by Parametric Resonance

We demonstrate that the parametric resonance in a magnetic quadrupole trap can be exploited to cool atoms by using Bird＇s method. In our programme the parametric resonance was realized by anisotropically modulating the trap potential. The modulation frequency dependences of temperature and fraction of the trapped atoms are explored. Furthermore, the temperature after the modulation as functions of the modulation amplitude and the mean elastic collision time are also studied. These results are valuable for the experiment of parametric resonance in a quadrupole trap.     

Scattering Noise Properties of Holographic Photopolymers by Means of Real-Time Transmittance Analysis

We propose a simplified model to analyse the temporary behaviour of transmittance for holographic photopolyreefs, based on the existing first-harmonic diffusion theory, with assumptions of constant polymerization coefficient and negligible diffusion effect for noise gratings. By applying this model to measure real-fime transmittance of our novel blue-sensitized photopolymer, the bleaching time constant of dye and polymerization rate are extracted, and the effect of the material composite on the noise property is revealed. This provides a prompt method to assess the performances of holographic photopolymers.     

利用调制的偏振态门控制阿秒脉冲的产生

提出一种利用多光周期驱动脉冲获得极紫外宽带超连续谱的新方法.利用波长为1600nm的基频场组成的偏振态门增强高次谐波产生效率对椭扁率的依赖,并叠加上波长为800nm的倍频场来调制电离比率.计算结果表明,采用脉冲宽度为6个光周期(32.4fs)的基频脉冲就能够将高次谐波辐射限制在0.5个光周期内,获得了带宽为280eV的超连续谱,这个谱宽支持傅里叶极限为10as的单个脉冲输出.直接选取超连续谱上的一段,可以获得100as的脉冲输出.此外,在调制的偏振态门中可以使用相对延迟较小的两束基频光组成偏振态门,提高了 关键词： 阿秒脉冲 超连续谱 偏振态门     

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I--V (current--voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.     

乙二胺和聚乙二醇在纳米介孔氧化铝制备中的协同导向作用

以无机铝盐Al(NO₃)₃为原料, 以乙二胺和聚乙二醇为协同模板导向剂, 与氨水反应, 经过“沉淀-超声-煅烧”等过程, 制得介孔纳米氧化铝. 用TEM, XRD, N₂吸附-脱附等测试技术对样品进行了测试和表征. 研究结果表明, 所得样品具有相当高的比表面积(510 m²•g^－1)、较大孔容(1.13 cm³•g^－1)和较为集中的孔径(5.8 nm)分布. 根据乙二胺和氧化铝表面的溶液化学反应及在不同pH条件下的溶液组分分布, 探讨了它们在介孔氧化铝制备过程中的协同模板作用机理.     

基于少模长周期光纤叠栅的模式转换器

本文提出一种在同一段少模光纤上写入两个不同周期Λ1和Λ2的长周期光纤光栅构成叠栅的方法,实现了纤芯基模LP_(01)向高阶纤芯模LP_(11)模式转换的宽带宽的新型的全光纤模式转换器.利用有限元法和耦合模理论建立了模式转换器的理论分析模型.数值仿真分析了叠栅中两个子光栅周期间隔、光栅长度、耦合系数等光栅参数对模式转换器的影响.仿真分析和实验结果表明,通过改变两个子光栅的周期间隔来改变两个损耗峰的位置,形成一个损耗峰,从而可以实现宽带宽的模式转换器,其10dB带宽约是单栅的2倍.与传统的模式转换器相比,该转换器带宽宽、转换效率高,尺寸小、抗干扰能力强,可以在模分复用系统和光通信中得到广泛的应用.     

光纤环形谐振腔的频率锁定及其特性

基于可调分束比的光纤分束器,制作了光纤环形谐振腔并通过调节分束比实现了对光纤环形谐振腔的欠耦合、临界耦合和过耦合的状态控制.实验测量了腔最小反射率与腔损耗之间的关系,获得光纤环形谐振腔的腔内衰减率为κ_0=2π×(1.60±0.03) MHz ,品质因子为Q=(1.10±0.02)×10.8.在此基础上,结合了压电陶瓷拉伸光纤以控制腔长和Pound-Drever-Hall锁频两大技术优势,克服了之前温度反馈控制等方法的反馈带宽窄、噪声大和稳定性差等问题,实现了对光纤环形谐振腔共振频率的快速、灵敏的控制和锁定.结果表明,锁频过程中相位调制功率与相位调制引起腔反射光的强度调制之间的关系为线性关系,进而通过降低相位调制信号的功率以减小相位调制对腔反射光强度调制的影响.当调制功率设定最低为–9 dBm时,光纤环形谐振腔仍能被稳定锁定.该光纤环形谐振腔为其与原子、金刚石色心等发光粒子相互作用的腔量子电动力学实验研究奠定了坚实的基础.