基于外差法的光纤激光器相干合成

采用波长1064 nm,功率为1 W的种子激光实现了两路光纤激光的相干合成,采用了两只保偏光纤准直器接收两路光干涉信号,与利用透镜直接把干涉信号会聚在探测器上相比,这种耦合方式得到的光干涉信号的条纹对比度更高。对相位噪声以及相位噪声的带宽进行了研究,结果表明,相位噪声由电信号串扰以及环境扰动产生。通过人为拨动光纤来增加相位噪声带宽,当相位噪声带宽增加时,相位控制精度下降。提出了提高相位控制精度的方法,实验获得了桶中功率为21.3%、斯特列尔比为79%、相位控制精度为0.008的相干合成效果。     

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.     

基于多元高斯声束模型的圆柱体超声检测声场仿真

为了提高圆柱体缺陷检测的准确性,需了解其超声声场分布。针对圆柱体实际检测的要求,本文采用超声水浸检测法。通过多元高斯声束模型分别模拟了实心圆柱体及空心圆柱体中的辐射声场,计算仿真了垂直入射与倾斜入射至圆柱体时的声场,实现了检测声场的可视化。通过计算得出仿真结构与实际理论相符,表明本论文的方法能够应用在圆柱体结构超声声场仿真中。     

基于无模型方法的混沌系统自适应控制

传统的混沌控制方法大多需要获知混沌系统的模型知识, 但是工业实际中系统的参数经常是未知的,与此同时系统建模过程当中经常会不可避免地存在未建模的动态不确定性, 这种情况下常规的混沌控制方法不能取得优化的控制性能指标．为解决此问题, 提出了一类基于无模型方法的混沌系统自适应控制算法．该算法基于数据驱动, 无需混沌系统的先验知识, 无需训练过程, 在线调整参数较少, 是一种低成本的控制器．数学证明了该控制系统的稳定性, 仿真结果说明了这种理论的有效性． 关键词： 混沌控制 自适应 无模型 数据驱动     

基于光外差技术的超宽带频率响应测量系统

介绍了一种利用光外差技术测量光电探测器超宽带频率响应的测试方法。将一个可调谐外腔激光器和一个固定波长的分布反馈激光器（DFB-LD’s）产生的激光输入到光电探测器进行混频。通过对可调激光器腔长的控制,可以在光电探测器产生从DC到上百GHz的拍频信号,在无需额外校准光源的情况下就可以进行光电探测器超宽带频率响应特性的测试,这是该方法最突出的优点。实验证明该方法比较准确、简便、易于操作。在实验中,对两个不同的InGaAs p-i—n探测器进行测量,得到器件的3dB带宽分别为14．4GHz和40GHz。该测量方法对同类实验的研究和应用都具有实用意义。     

Enhanced NIR emission in Ce^3＋/Er^3＋-doped YAG induced by Bi^3＋ doping

Ce^3＋/Er^3＋/Bi^3＋ triply-doped yttrium aluminum garnet （YAG） is synthesized using co-precipitation method. The Bi^3＋ concentration-dependent near-infrared （NIR） emission behavior is systemically in- vestigated. The NIR emission of Er^3＋ ions at 1531 nm is enhanced threefold by the addition of 7 mol% Bi^3＋. Bi^3＋doping results in the formation of exciton in YAG and the variation in the local environment of the doped rare-earth ions. The enhancement in NIR luminescence is ascribed to the combined effects of the sensitization of exciton→Ce^3＋ →Er^3＋ and the Bi^3＋ doping-induced adjustment of the local environment for Ce^3＋ and Er^3＋ ions.     

螺吡喃光响应的汞、铬、银离子探针及相互作用光谱

合成并表征了1-羟乙基-3,3-二甲基-6′,8′-二叔丁基吲哚啉苯并螺吡喃配体1及其衍生物配体2。由于苯并螺吡喃6′,8′-二叔丁基斥电子基团的电子效应,开环体部花菁酚氧负离子上的负电荷难以分散,使其结构不稳定,配体1在紫外光照射下不直接开环,只有在极性较强的甲醇溶剂中受适当金属离子诱导才能形成有色开环体部花菁结构形式。配体1能较好地选择识别Hg2+,Cr3+和Ag+。当其相互作用时,不但紫外可见光谱及荧光光谱有明显“turn-on”变化,而且体系颜色明显地由无色变成黄色,目视识别效果直观明显。其他金属离子的存在对Ag+,Cr3+和Hg2+的识别几乎没有干扰。配体1与Ag+,Cr3+和Hg2+络合的化学计量比均为1∶1,检出限分别是：7.435 8×10-6, 6.126 8×10-6, 3.452 4×10-6 mol·L-1。通过配体2进一步证明了配体1和金属离子识别的结合模式。即螺吡喃结构中N1位取代侧链上的羟基,和其开环体酚氧负离子相互协调并与金属离子结合。     

网纹红土中铁矿物与粘土矿物赋存关系的X射线衍射证据

高纯度的粘土矿物样品是粘土矿物学重建古气候的关键,然而,土壤中的铁矿物(如针铁矿和赤铁矿等)和有机质的存在导致粘土矿物与非粘土矿物相互包裹,使富集的粘土矿物样品常含有其他矿物杂质。土壤沉积物中有机质去除的研究已较为充分,但铁矿物在土壤沉积物中的赋存状态倍受争议,制约了高纯度粘土矿物样品的制备。该研究将以长江中下游九江网纹红土作为研究对象,通过逐级分离试验对网纹红土中铁矿物与粘土矿物的赋存关系进行研究,为土壤沉积物中铁矿物的去除提供一定的启示。试验结果表明,针铁矿和赤铁矿等铁矿物可能主要呈现被膜状吸附在羟基间层蒙脱石和伊利石的表面,也有部分被高岭石吸附。     

A novel method to measure dielectric properties of materials in terahertz spectroscopy

We present a simple method to obtain the optical and dielectric properties of samples without reference measurement in the reflection-type terahertz time-domain spectroscopy. The dielectric properties of the samples of silicon and gallium arsenide were examined. The optical and dielectric properties of the samples were measured through only simple configuration, without the misplacement error. The obtained dielectric functions of the samples in reflection geometry are in good agreement with that predicated by the theory. The main advantage of this method over other methods is its simplicity and accuracy and ease for application of the reflection systems with different incident angle.     

Theoretical and experimental investigations on the structures of purified clay and acid-activated clay

The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH₃-TPD, molecular NH₃ desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na⁺ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH₃ on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al³⁺ for tetrahedral Si will be favorable to NH₃ adsorption.