基于自适应陷波器的电子能量损失谱能量漂移的消除方法

电子能量损失谱是透射电子显微术中一种重要的分析手段,它可以帮助人们从纳米尺度上认识材料的电子结构等信息。但电子能量损失谱仪特别容易受到周围环境因素的影响,比如说固定工频干扰,而产生电子能量损失谱能量的漂移。本文结合串行快响应能谱探测器和自适应陷波器手段,提出了一种消除电子能量损失谱中能量漂移的方法,实验结果表明这种方法能够有效消除电子能量损失谱中由于固定工频干扰所造成的能量漂移。     

电子能量损失谱的数据采集和谱图处理及在3 d过渡族元素谱图中的应用

本工作以有序Ni3Fe样品的电子能量损失谱EELS（electron energy loss spectroscopy）的采集、处理和分析为例,叙述了内置（Ω型）与后置能量过滤器在采集和处理电子能量损失谱的工作原理、处理步骤及注意要点.实验结果表明：在采集谱图过程中,内置Ω型能量过滤器零峰非常稳定,后置GIF（gatan image filter）能量过滤器可以节约采集过程中处理谱图的时间.在处理谱图时发现,利用Ω型能量过滤器采集的电子能量损失谱中谱图的背底曲线与理论拟合结果偏差很大;本文提出了通过数据处理给出的校正因子可以很好地弥补这一偏差.由于Ω型能量过滤器的物距较小,在零峰附近常伴随有衍射点,所以无论样品厚度如何,由Ω型能量过滤器采集的电子能量损失谱必须扣除多重散射的影响.     

能量回收电路的功耗优化方法

能量回收电路的非绝热损失正比于CLΔV2,文中提出了两种方法降低CL和ΔV因子.HEERL(high efficient energy recovery logic)电路利用自举效应减小了回收节点的残留电压ΔV,IERL(improved energy recovery logic)电路增加了回收的通路,在控制回收通路的小电容节点产生了CAΔV2的非绝热损失,从而使大电容输出节点电荷被充分回收,降低了电路的整体功耗.降低非绝热损失两个因子CL和ΔV的能量回收电路与其它能量回收电路相比,电路面积增加很小(2个NMOS管),而功耗可降低50%以上.     

能量回收电路的功耗优化方法

能量回收电路的非绝热损失正比于CLΔV2,文中提出了两种方法降低CL和ΔV因子.HEERL(high efficient energy recovery logic)电路利用自举效应减小了回收节点的残留电压ΔV,IERL(improved energy recovery logic)电路增加了回收的通路,在控制回收通路的小电容节点产生了CAΔV2的非绝热损失,从而使大电容输出节点电荷被充分回收,降低了电路的整体功耗.降低非绝热损失两个因子CL和ΔV的能量回收电路与其它能量回收电路相比,电路面积增加很小(2个NMOS管),而功耗可降低50%以上.     

高温超导体Bi2Sr2CaCu2O8电子能量损失谱研究

自从发现高温超导体以来,对它的导电机理及电子结构研究引起了人们广泛的兴趣。本文用电子能量损失谱(EELS)研究了Bi_2Sr_2CaCu_2O_8超导体的价电子结构,能量损失函数及介电函数,计算了其它各种光学常数。实验过程为将烧结超导样品在盛有CCl_4的玛璃研钵中研碎,然后将其滴于由铜网支持的微孔碳膜上。实验在装备有GATAN-666同时检测电子能量损失谱仪     

利用电子能量损失谱对二氧化铀电子结构的研究

锕系元素因具有复杂的5f电子结构,其显示出神秘而又独特的物理、化学特性.为了加深对锕系金属、合金和化合物的特异行为的理解,对其电子结构精确表征的重要性日益凸显.电子显微技术与电子能量损失谱技术的结合在锕系元素原子结构和电子结构研究中发挥了至关重要的作用.本文采用电子能量损失谱研究二氧化铀的5f电子结构,并讨论了铀5f电子的相互作用特性.     

介电函数及其在电子能量损失谱低能区分析的应用

一、前言:电子能量损失谱学(EELS或ELS)是研究电子激发的一次过程。一幅电子能量损失谱大致可分为三个区域:零损失区、低能损失区(5～50eV)和高能损失区(>50eV)。对各谱区进行细致的分析研究、可获得与样品化学成分或电子结构有关的信息。利用电子能量损失谱低能区研究固体的电子结构、引起物理和电子显微学界的关注。因为它不仅能提供固体的电子结构信息、还能在同一台仪器上研究固体的微区晶体结构、成分和形貌。但在电子能量损失谱5～50eV的低能区很难直接确定有关电子结构方面的信息。这是由于在该区等离子激发占主导地位、而外     

电子能量损失谱在类金刚石碳膜结构表征中的应用

本文先介绍了类金刚石碳膜的结构特点及电子能量损失谱的原理和分类;然后着重评述了近年来电子能量损失谱在类金刚石碳膜(及有些金刚石膜)结构表征中的应用;同时也讨论了类金刚石碳膜经某些后处理后其能量损失谱的变化特征。     

钴硅化合物的理论电子能量损失谱

本文采用扩展平面波加局域轨道方法和广义梯度近似对钴硅系中Co2Si，CoSi和CoSi：三种不同硅化物的电子结构以及电子能量损失近边结构（ELNEs）进行了理论计算。结果表明计算得到的硅化物中Co的ELNES很好反映了Co在费米能级以上d的未占据态密度分布，其中Co2Si和CoSi2具有金属性质；而CoSi呈现出半金属性质。计算还表明电子能量损失谱仪应具有足够高的能量分辨率（0．2ev），电子能量损失近边结构才能正确反映出钴硅化合物的电子结构特征。     

Mo和Ta的有效电子能量损失函数

在用Monte Carlo方法模拟电子与物质相互作用过程时，常用Mott截面描述电子与原子的弹性碰撞，而用介电函数理论描述电子的非弹性散射。Penn利用光学能量损失函数Im{-1／ε（q=0，ω）}外推法获得了描述动量转移不为零的能量损失函数Im{-1／ε（q，ω）}。该介电函数主要描述由于体激发而引起的能量损失，但当入射电子能量降低，或电子掠入、出射时，电子在表面区域会引起较强的表面电子激发模式，在电子能量损失谱中对应特征的能量损失，如表面等离子体激元峰，故常用的光学能量损失函数不适于描述电子的表面激发行为。     

Schmidt modes and entanglement in continuous-variable quantum systems

The extraction of Schmidt modes for continuous-variable systems is considered. An algorithm based on the singular-value decomposition of a matrix is proposed. It is applied to the entanglement in (i) an atom—photon system with spontaneous emission and (ii) a system of biphotons with spontaneous parametric downconversion (SPDC) of type II. For the atom—photon system, the evolution of entangled states is found to be governed by a parameter approximately equal to the fine-structure constant times the atom-to-electron mass ratio. An analysis is made of the dynamics of atom—photon entanglement on the assumption that the system’s evolution is determined by the superposition of an initial and a final state. It is shown that in the course of emission the entanglement entropy first rises on a timescale of order the excited-state lifetime and then falls, approaching asymptotically a residual level due to the initial energy spread of the atomic packet (momentum spread squared). SPDC of type II is analyzed by means of the polarization density matrix and a newly introduced coherence parameter for two spatially separated modes. The loss of intermodal coherence is addressed that results from the difference in behavior between ordinary-and extraordinary-ray photons in a nonlinear crystal. The degree of intermodal coherence is investigated as a function of the product of crystal length and pump bandwidth.     

Calculated spontaneous emission factor for double-heterostructure injection lasers with gain-induced waveguiding

The fraction of spontaneous emission going into an oscillating laser mode has been calculated. It is shown that this fraction strongly depends on the strength of astigmatism in the laser output beam. Therefore the spontaneous emission factor in planar stripe lasers with narrow stripe is in the order of 10^-4and by one order of magnitude larger than in injection lasers with a comparable active layer volume and with a built-in index waveguide. It is shown that the spontaneous emission factor is approximately proportional to the solid angle of laser radiation and nearly independent of the transverse active layer dimensions. Owing to the large spontaneous emission factor, the spectral width of narrow planar stripe lasers is significantly broader compared to narrow stripe lasers with a built-in index waveguide. In addition the large spontaneous emission coefficient also yields a much stronger damping of relaxation oscillations.     

Limits on amplification of picosecond pulses by using semiconductorlaser traveling-wave amplifiers

The limiting factors in picosecond pulse amplification by semiconductor traveling-wave laser amplifiers are investigated, including the effects of the spontaneous emission. For the amplifier with a negligible amount of spontaneous emission, amplification is limited by the energy saturation for low-repetition-rate pulses, while the power saturation is the limiting factor for high-repetition-rate pulses. The spontaneous emission decreases both the signal gain of the amplifier and the signal-to-noise ratio considerably. The effective gain recovery time and the effective saturation energy are strong functions of the input pulse energy, and the amount of the spontaneous emission     

Finite-temperature effects in free-electron lasers

The effect of energy spread on the gain of a dense-beam free-electron laser amplifier is analyzed. The formalism includes collective effects and allows for the use of an arbitrary distribution function. The dispersion relation is solved numerically. Besides broadening of the spectrum and decrease in gain, lowering of the central emission frequency with energy spread is observed. An initial-value problem is formulated and numerically solved, with power computed as a function of distance. The relative contributions of the different modes when temperature changes are analyzed. In particular, the competing effects of a decrease in coupling loss with temperature together with Landau damping are investigated.     

Transfer matrix analysis of the amplified spontaneous emission ofDFB semiconductor laser amplifiers

Analytical expressions are derived for the amplified spontaneous emission of a DFB (distributed-feedback) semiconductor laser amplifier with reflective cavity ends. The analysis is extended to a multisection DFB structure including a phase-shifted DFB semiconductor laser amplifier. It is shown that the spontaneous emission power per unit frequency bandwidth emitted from one facet is proportional to the transmission gain and to a quantity which at threshold becomes the inverse of the differential quantum efficiency of the other facet. The analysis is applied to two practical cases: (1) calculation of emission spectra of a DFB semiconductor laser biased below the threshold, and (2) assessment of the signal-to-noise ratio performance of DFB semiconductor laser amplifiers     

Quantum Dots Decorated with Magnetic Bionanoparticles

A new class of water‐soluble, fluorescent, magnetic quantum dots––magnetoferritin bioconjugate––is prepared. The nanostructures are patterned mainly as dimer particles as characterized by high‐angle annular dark‐field scanning transmission electron microscopy and electron energy loss spectroscopy. Magnetic (high spontaneous magnetization values, superparamagnetism) and fluorescent (narrow emission peaks, uniform brightness) properties of both nanoblocks are maintained in the final nanostructure.     

Effect of random secondary delay times and emission velocities inelectron multipactors

Traditionally, the modeling of rf driven electron cascades (multipactors) has employed a constant emission velocity and zero delay time for all secondaries. This paper introduces the effects from the random secondary emission velocities, as well as the random delay time in the secondary emission. By combining the emission related random phase kicks with the focusing rf action it is shown that the electron impact phase, though wandering erratically, nevertheless stays in the vicinity of a stable phase-locked multipactor phase; the rms phase deviation from phase locking is bounded and directly proportional to the rms fluctuation in the secondary emission. The random phase wandering around the locked phase reduces the nominal secondary emission coefficient δ to an effective value δ* between δ>δ*⩾δ/2 and depending not only on the impact energy of the primary but also on the thermal spread of the secondaries. Multipactor quenching from secondary spreads may occur through the reduction in δ*. For sufficiently small fluctuations, the modeling of a “cold” multipactor with zero thermal spreads is sufficient to determine the actual multipactor behavior in terms of only two control parameters; the normalized rf and magnetic field strengths     

Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the RMS timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the mode-locker driver phase noise will dominate unless high-stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning     

EAM-DFB集成光源典型参数特性的电路级分析

针对电吸收型调制器和分布反馈激光器集成光源(EAM-DFB)的光电混合特征,建立了包含自发辐射、俄歇复合、寄生效应以及隔离电阻的等效电路模型。分析了在不同驱动电流和自发辐射因子下,该模块的输出、调制及噪声特性,并与直接调制DFB作了对比。结果表明,EAM-DFB可生成超短脉冲(小于25 ps);随着驱动电流的增加,输出功率增大、脉冲展宽,噪声增强且峰值点向高频移动;减小自发辐射因子和增加驱动电流均使其调制带宽增加;与DFB相比,EAM-DFB增加了少量噪声,但具有更陡峭的功率-电流特性和更大的调制带宽。     

Direct observation of the spatial hole burning and the saturation of the spontaneous emission in InGaAsP/InP lasers

The saturation behavior of the spontaneous emission intensity from a diffused-stripe InGaAsP/InP laser is studied. In InGaAsP/ InP DH lasers, a spontaneous emission can be observed through the InP substrate without any optical loss. The spatial distribution and the spectrum of the emission were directly observed from the substrate surface. The spatial hole burning was observed in the wider stripe lasers but in the case of narrow stripe lasers, the spontaneous emission almost uniformly saturates. The spectrum of the emission from the center of the narrow stripe lasers was analyzed and it was confirmed that, above the threshold current, the spectra in the lasing region saturated over the entire spectral region.