Spacing and width of Coulomb blockade peaks in a silicon quantum dot

We present an experimental study of the fluctuations of Coulomb blockade peak positions of a quantum dot. The dot is defined by patterning the two-dimensional electron gas of a silicon MOSFET structure using stacked gates. The ratio of charging energy to single-particle energy is considerably larger than in comparable GaAs/AlGaAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb blockade regime was found to be unimodal and does not follow the Wigner surmise. The fluctuations of the spacings are much larger than the typical single-particle level spacing and thus clearly contradict the expectation of random matrix theory. Measurements of the natural line width of a set of several adjacent conductance peaks suggest that all of the peaks in the set are dominated by electrons being transported through a single-broad energy level.     

聚酰胺富集双波长光度法同时测定金和银

本文研究了聚酰胺树脂的吸附性能，发现Ａｕ和Ａｇ蝗形成稳定的硫氰酸络阴离子。在稀硝酸介质中吸附于聚酰胺树脂进行富集并与大部分贱金属元素分离。采用Ｎａ２ＳＯ３作为解脱剂，可以定量解脱树脂上的Ａｕ和Ａｇ而树脂不被破坏可以反复使用。     

基于半导体纳米线和金属脊的混合表面等离子体波导模式特性分析

波长可开关光纤激光器可以选择多波长光纤激光器中的一个或多个波长输出,支持光网络中多个波长的动态分配,适应现代光纤通信系统信道数越来越多的波分复用和密集波分复用的发展方向.本文提出并实现了一种自激发多波长可开关掺铒光纤激光器.该激光器通过一个980 nm泵浦进行抽运,使用掺铒光纤作为增益介质,产生1 550 nm光谱,并通过一个环形结构返回,从而实现自激发的过程,降低了实验成本.实验使用一个含有两段保偏光纤的Sagnac环作为滤波器.通过调整Sagnac环形滤波器内偏振控制器的角度,改变Sagnac环形滤波器的腔内增益,可以让光纤光栅反射出来的波长选择性通过,从而实现波长的开关功能.实验证明,通过调整Sagnac滤波器的腔内增益而让多波长选择性通过,是一种有效的实现波长可开关功能的方法.     

嵌入式粒子群-遗传算法的水质COD检测特征波长优化算法

基于紫外-可见光谱法的水质测量中,光谱信号易受到系统噪声干扰、悬浮物散射干扰,且存在信息冗余、多重共线性等特征,导致水质COD测量中特征波长的选取产生较大偏差。因此,提出了基于嵌入式粒子群-遗传（EPSO_GA）算法的水质COD检测特征波长优化算法,以提高波长选择精度。为验证检测特征波长优化算法的可行性,采集了某高校池塘水样、生活污水和排水沟水样的光谱数据,利用EPSO_GA算法对预处理后的光谱数据选取特征波长。EPSO_GA算法采用实数编码方法实现了粒子群（PSO）优化算法和遗传（GA）优化算法的统一编码,在PSO算法中更新粒子时嵌入GA算法的选择、交叉、变异等操作,改善了这两种算法各自在光谱波长特征选取问题上的局限性。将EPSO_GA算法选取的特征波长结合偏最小二乘法（PLS）构建了EPSO_GA_PLS的水质COD预测模型,并且与传统的PSO算法、GA算法选取特征波长建立的PSO_PLS、GA_PLS和全光谱构建的PLS水质COD预测模型做了对比。结果表明：与PSO_PLS,GA_PLS和全光谱构建的PLS水质COD预测模型相比,EPSO_GA改善了PSO算法和GA算法在光谱特征波长选择中早熟和收敛速度慢的问题,降低了全光谱构建PLS水质COD预测模型的复杂度,提高了模型的预测精度。基于EPSO_GA算法建立的EPSO_GA_PLS水质COD预测模型,均方根误差降到了0.212 3,预测精度增加到0.999 3,可以快速定量检测水质COD,为紫外-可见光谱法测COD提供了更好的预测模型。     

纳秒激光电离分子团簇产生高离化离子的激光波长效应

 利用脉冲分子束-激光电离-飞行时间质谱仪,在10⁹～10¹² W·cm^-2激光功率密度条件下,考察了Nd：YAG激光器输出的1 064,532,266 nm波长的激光与苯、氨、硫化氢等团簇的相互作用。发现1 064 nm的激光可以电离分子束产生高离化态的C⁴⁺,N⁵⁺,S⁶⁺等离子;波长为532 nm的激光则电离产生价态较低的C³⁺,C²⁺,N³⁺,N²⁺, S⁴⁺,S³⁺以及S²⁺ 等离子;在266 nm波长条件下进行实验,没有产生任何高价离子。提出了一个“多光子电离引发-逆轫致吸收加热-电子碰撞电离”模型来解释高价离子的产生。激光场下电子在团簇内部的逆轫致加热是整个过程的关键步骤,电子被加热的速度正比于激光波长的平方。这可以解释为何长波长的激光有利于更高价态离子的产生。     

一种新型主动锁模光纤激光器腔长稳定技术研究

提出了一种全新的主动锁模光纤激光器的腔长稳定方案,通过波长的变化检测腔长的漂移,使用波长锁定器得到偏移误差信号补偿腔长变化.实验得到了脉宽为7.6 ps的近变换极限锁模脉冲,其超模抑制比达到60 dB,并且在近2 h的工作时间内工作稳定,波长漂移小于0.01 nm.与已有的方案相比较,不但输出脉冲质量高、并可长时间稳定工作,而且由于采用了低成本的稳定方案,更易于实现.     

飞秒受激拉曼光谱线形:基于泵浦及探测脉冲光的共振条件研究

Resonance enhancement has been increasingly employed in the emergent femtosecond stimulated Raman spectroscopy (FSRS) to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint efforts by the technique-and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. During spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Raman pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodamine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by different resonance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence (HL) pathways. Meanwhile, on-resonance conditions of the Raman pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.     

基于能量重分配的波长偏移校正方法

针对原子光谱分析中波长偏移问题,提出了一种基于能量重分配原理实现波长偏移校正的方法.用抛物线插值法对能量密度分布进行反演,以谱图相似度为判断指标,通过三分法确定最佳偏移量,并根据最佳偏移量与能量密度分布对光谱强度进行重新计算,实现了亚像素级别的波长校正.对微型光纤光谱仪与单道扫描光谱仪获得的谱图进行了算法验证,使Eu元素的背景噪音平均降低了48%,Mo元素的信号稳定度由20%改善至约5%.该方法对具有结构化特征的谱图具有较好的适用性,且无须寻峰算法配合使用,有助于提高光谱分析精确度.     

Parameter optimization and characteristic analysis of a polymer microring resonant wavelength multiplexer

Novel formulas of transmission functions are presented, some parameters are optimized, and transmission characteristics are analyzed for a polymer microring resonant wavelength multiplexer around the central wavelength of 1.55 μm with the wavelength spacing of 5.6 nm and with eight vertical output channels. The computed results show that the designed device possesses some excellent features including the 3 dB bandwidth of 0.25 μm, weaker background light of 3.8×10⁻⁴, smaller inserted loss of less than 0.6 dB, and lower crosstalk below −20 dB for every vertical output channel.     

Distributed control based routing and wavelength assignment strategy for WDM optical networks

Wavelength-division-multiplexing (WDM) is emerging as the dominant technology for the next generation optical networks. The control strategy can be either centralized or distributed. In centralized control, there is a central controller to keep track of the state of the network. It is also responsible for selecting the path for data transmission. Most of the work done in this field is based on centralized control. For large networks, distributed control is preferred over centralized control because of low control overhead. Distributed control strategy requires exchange of control messages among nodes. The distributed control generally results in the possibility of resource reservation conflicts among simultaneous path establishments and poor resource utilization. In this paper, we have proposed one distributed control based routing and wavelength assignment strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources.