基于高能量耗散型脉冲掺铒光纤激光器的实验研究

在正色散掺铒光纤激光器中,利用非线性偏振旋转技术实现自启动锁模,得到了具有极大光谱宽度的高能量、无波分裂耗散型脉冲.该耗散型脉冲的形成是腔内增益、损耗、非线性偏振旋转、正色散和其他非线性效应等共同作用的结果,其形成机理与传统的负色散激光器完全不同.当抽运功率为500 mW时,该类型脉冲的光谱覆盖了1530—1660 nm范围,半高全宽光谱宽度可达42 nm以上.脉冲具有极大的正啁啾,其时间带宽积为483,而单脉冲总能量最大可达34.4 nJ.     

铁磁/反铁磁双层膜中的磁锻炼效应

采用Monte Carlo 方法,研究铁磁/反铁磁双层膜中的磁锻炼效应.结果表明,反铁磁层中冷场诱发的界面净磁化(钉扎效应)的磁弛豫可导致系统中的交换偏置场的磁锻炼效应.进一步研究表明,反铁磁层中掺杂可调控交换偏置场的磁锻炼效应,原因在于反铁磁层中掺杂能有效地改变冷场诱发的净磁化的磁弛豫过程.     

非稳腔主动式直接获取纳秒近似无衍射贝塞尔绿光

通过对基于轴棱锥的贝塞尔谐振腔和贝塞尔-高斯谐振腔的研究,设计了一台腔内倍频Nd:YAG纳秒近似无衍射贝塞尔绿光激光器. 非稳激光器谐振腔由轴棱锥和凸面镜组成. 实验采用单灯脉冲抽运激光增益介质Nd:YAG晶体,倍频晶体选用KTP. 当抽运电压为350 V时,由主动式直接产生纳秒近似零阶贝塞尔绿光,其脉冲宽度为55.1 ns,波长为532 nm,线宽为0.8 nm,近似无衍射零阶贝塞尔绿光的中心光斑直径为192 μm. 利用Fresnel-Kirchhoff 衍射积分和Fox-Li迭代法,通过数值计算得出     

基于磁矩分解的运动舰船磁场模型研究

当前的舰船磁场模型大都是通过其静态特性而构建的，现实适用性较差。围绕运动舰船磁场不同航向、不同航区的适应性模型展开研究。首先分析了舰船磁场建模的等效源方法，接着研究了运动舰船磁场磁矩分解的原理与方法。主要思路是先测量舰船在东、西、南、北 4 个航向上的舰船下方 1 个平面的磁场三分量数据，将这 4 组数据分别作为同一舰船在不同磁化状态下的边界条件，求解出舰船在东、西、南、北 4 种不同磁化状态下的磁矩参数，最后联合求解磁源的固定磁矩和感磁磁矩参数。通过以上过程便可计算出舰船在任意航向、任意航行地点的磁矩，利用磁矩解算磁场得到运动舰船磁场模型。     

电极前置式水下组合磁源磁场研究

随着敌人反潜力量的增强,目前的磁诱饵磁源结构存在着磁模拟耗能大导致诱饵续航不足的问题,越来越无法满足在战役层面的作战需要.针对此问题,基于现有的航行体尾部拖曳后置两电极式磁源结构,提出单电极前置式组合磁源方案,建立其空中磁场分布模型,并进行了仿真分析.结果表明:单电极前置式组合磁源结构能保证较好模拟目标磁场的同时,减小...     

Kerr效应对二项式腔场谱量子干涉的影响

研究了含Kerr介质高Q腔内单个二能级原子与双模二项式光场发生双光子共振相互作用系统的腔场谱,给出了Kerr效应与量子干涉项ΔS(ω)关系的数值计算结果,讨论了Kerr效应对二项式腔场谱量子干涉的影响.结果表明:若初始时刻原子处于激发态而双模光场处于二项式态,随Kerr效应的增强,致使量子干涉项引起谱线强度的改变量呈现出"不规则的周期性衰减振荡"特性,震荡幅度与两模光场的频差密切相关.在Kerr系数χ＜g(g为光场与原子的耦合常数)时,Kerr效应对干涉项的影响比     

对抗航空磁探的磁诱饵模拟指标分析及度量方法

针对航空磁探的威胁,潜艇可通过施放能够模拟其空中磁场特性的装置(磁诱饵)进行对抗，在对磁诱饵进行研究时,需要对其模拟需求进行分析。针对此问题,在对目前常用磁探仪工作原理及优缺点进行分析的基础上建立了基于标量磁探仪的航空磁探潜模型,以所建立的航空磁探潜模型为基础,分析了对抗航空磁探时磁源所需满足的模拟需求,并给出对抗效能评估度量方法及指标:磁场功率比、磁场方向可调性指标及有效面积指标,为潜艇空中磁场模拟方法研究的开展提供了基础。     

激发态质子转移分子2-(2''-羟基苯基)苯并噻唑溶液的全光开关效应

研究了激发态质子转移(ESPT)分子2-(2'-羟基苯基)苯并噻唑(HBT)在不同极性溶剂中的光开关行为,探讨了溶剂极性对HBT分子光开光效应的影响.揭示了光开关脉冲信号的形成原因,建立了基于光诱导HBT分子激发态非线性折射效应的皮秒全光开关的理论模型.根据对时间响应函数的理论计算和实验结果分析,确定了光开关脉冲信号下降前沿和上升后沿的形成机理以及影响因素,并提出了增强光开关信号下降前沿的关断深度,提升上升后沿的恢复速度的有效途径和方法.本文工作为制成皮秒量级关断,微秒甚至纳秒量级重新打开的快速全光开关器     

均匀磁化球体的磁力线方程

基于磁力线定义和均匀磁化球体周围的磁场分布,通过解算微分方程,推导出一个简单的磁力线簇公式,便于在地磁场研究中绘制均匀磁化球体的磁力线。     

光致原子解吸附对冷原子磁光阱装载的动力学研究

在获得光致原子解吸附(light-induced atom desorption,LIAD)效应的基础上,从理论和实验方面分析了LIAD对铯原子磁光阱装载的动力学过程的影响,特别是背景原子对磁光阱的影响.通过实验获得了不同光强和照射时间下关闭解吸附光后磁光阱中铯原子的衰减过程,理论模型定量地描述了背景铯原子造成压强的变化及其对最终平衡态下真空度的影响.该研究对中性原子的长时间俘获,有效控制磁光阱中原子的装载过程具有重要意义.     

NPB/Alq3 界面激子拆分研究

采用瞬态光电压技术研究了NPB和Alq₃界面激子拆分过程和拆分机理.对NPB和Alq₃组成双层结构的样品,在脉冲355nm激光照射下,测量样品的瞬态光电压信号,通过对不同结构的和有界面激子阻挡层的样品的瞬态光电压分析,并排除了ITO/有机外界面对激子拆分的影响,得出了NPB/ Alq₃界面激子拆分机理是向Alq₃ 注入电子,向NPB注入空穴.     

影响磁性pn结自旋极化输运特性的因素

利用漂移扩散理论研究了磁性pn结中自旋的输运特性.探讨了外加电压、平衡自旋极化率、外加自旋注入和自旋寿命对磁性pn结电流密度和电阻的影响,讨论了磁性pn结自旋伏特效应与pn结宽度的关系.发现平衡自旋极化率使得不同自旋方向电子具有不同的势垒高度从而能有效调制电流;而外加自旋注入则为磁性pn结提供了非平衡自旋极化电子从而达到对电流的调制作用,同时发现自旋伏特电流随准中性p区宽度减小而增大.     

数值模拟飞秒激光加热金属的热电子发射

研究了超短超强激光脉冲与薄膜靶相互作用中产生的电子热发射.当超短激光脉冲与薄膜靶相互作用时,首先入射超短脉冲激光对吸收深度内的自由电子进行热激发;接下来热激发电子将能量传递到附近的晶格,再通过电子和晶格二体系的热传导,以及电子晶格间的热耦合,将能量传递到材料的内部.因此,电子在皮秒级甚至更短的时间内不能与晶格进行能量耦合,使电子温度超出晶格温度很多,电子热发射就变得非常明显了.用双温方程联合Richardson-Dushman方程的方法对飞秒脉冲激光照射金属靶的电子热发射进行了研究,结果发现电子热发射对飞     

Diagenetic magnetic enhancement of sapropels from the eastern Mediterranean Sea

Diagenetic dissolution of magnetic minerals has been widely observed in organic-rich sediments from many environments. Organic-rich sediments from the eastern Mediterranean Sea (sapropels), recovered during Leg 160 of the Ocean Drilling Program, reveal a surprising catalogue of magnetic properties. Sapropels, from all sites studied across the eastern Mediterranean Sea, are strongly magnetic and the magnetization is directly proportional to the organic carbon content. The magnetization of the sapropels is dominated by a low-coercivity, probably single domain magnetic mineral (with an inverse magnetic fabric) that exhibits a clear decay in magnetic properties when exposed to air. During heating, the magnetic particles irreversibly break down between 360 and 400°C. The contrast between the magnetic properties of sapropels and surrounding sediments is marked, with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments. The contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non-steady-state diagenesis: sulphate-reducing conditions dominated during sapropel deposition, while overlying sediments were deposited under oxic conditions. The mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate-reducing conditions that existed during times of sapropel formation. Attempts to identify this mineral have been unsuccessful, but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase. The influence of diagenesis on the magnetic properties of cyclically-deposited eastern Mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments.     

Wavelength dependence four-wave mixing spectroscopy in a micrometric atomic vapour

This paper presents a theoretical study of wavelength dependence four-wave-mixing (FWM) spectroscopy in a micrometric thin atomic vapour. It compares three cases termed as mismatched case I, matched case and mismatched case II for the probe wavelength less, equal and greater than the pump wavelength respectively. It finds that Dicke-narrowing can overcome width broadening induced by Doppler effects and polarisation interference of thermal atoms, and high resolution FWM spectra can be achieved both in matched and mismatched wavelength for many cases. It also finds that the magnitude of the FWM signal can be dramatically modified to be suppressed or to be enhanced in comparison with that of matched wavelength in mismatched case I or II. The width narrowing and the magnitude suppression or enhancement can be demonstrated by considering enhanced contribution of slow atoms induced by atom-wall collision and transient effect of atom-light interaction in a micrometric thin vapour.     

东菲律宾海柱样沉积物的磁性特征

对东菲律宾海帕里西维拉海盆西侧F090102柱样进行了系统的古地磁和岩石磁学研究,测量了天然剩磁倾角、磁化率、饱和等温剩磁、非磁滞剩磁、-T曲线等磁学参数,进行了磁性地层的划分对比,识别出松山反极性时内的贾拉米洛和奥都维正极性亚时。对磁学参数及其有关比值的研究发现,岩心磁性矿物以低矫顽力磁铁矿为主,可能含有一定的钛磁铁矿。磁性矿物主要是陆源碎屑成因,岩心底段受到海底火山作用的影响。根据磁学参数随深度的变化将岩心分为3段,各段反映了沉积环境和古气候的变化。     

单层正三角锯齿型石墨烯量子点的电子结构和磁性

采用基于密度泛函理论的广义梯度近似(GGA),对不同尺寸(N=2—11)的单层正三角锯齿型石墨烯量子点(Z _{N -GNDs)的结构进行优化,得到与实验数据较好符合的晶格常数,进一步计算得到不同尺寸下体系的自旋多重度、磁矩、电子态密度以及自旋电子密度.结果表明:所有体系都呈现金属性,在尺寸较小的体系中量子尺寸效应对电子结构的影响比较明显;与单层石墨烯片一样,sp²杂化作用和非键态电子在量子点中仍起到非常重要的作用;费米能级上有自旋向上的电子分布,体系的自旋多重度}     

Serpentinized peridotites as a possible source for oceanic magnetic anomalies

New data acquired on the slow spreading Mid-Atlantic Ridge during several Legs of the Ocean Drilling Programme (ODP) give evidence that, in many places, serpentinized peridotites constitute the upper oceanic crust in the vicinity of rift valley. This discovery contradicts the classical view on the formation of oceanic crust at the ridge axis, which postulates that only basalts constitute the upper oceanic crust.The magnetic properties of 57 samples of such serpentinized peridotites, collected at five ODP sites in the Atlantic Ocean, have been analyzed in order to examine the origin and evolution of their natural remanent magnetization (NRM). All samples are characterized by NRM (average value about 3.5 A/M) comparable with NRM of altered oceanic basalts. Average Q-ratio (NRM to induced magnetization ratio) was about 2.The results reported here give evidence that serpentinization is a complex and irregular process. The local concentration of magnetite is determined by magnetostatic interaction between magnetic grains rather than volume concentration of magnetite. This local concentration, which represents the degree of serpentinization, affects the NRM value. The domain structure of magnetite grains developed during serpentinization is controlled by the degree of serpentinization.Experimental data show that original remanence of serpentinites exposed in the upper oceanic crust may contribute to the oceanic magnetic anomalies. In particular, serpentinites with magnetite of pseudodomain size represent a very probable source for magnetic anomalies. It is however unlikely that such ODP serpentinites systematically contribute to the oceanic magnetic lineations.     

冲绳海槽中部火山事件的环境磁学记录

对冲绳海槽中部DH180岩心沉积物进行了AMS14C测年、磁化率、非磁滞剩余磁化强度和饱和等温剩余磁化强度等试验,在含火山物质高的两段层位各磁学参数发生了异常变化。在57.5~82.5和212.5~252.5 cm深度处磁化率、非磁滞剩余磁化强度和饱和等温剩余磁化强度表现出增大的变化趋势,饱和度则出现相对减小的变化趋势。根据磁学参数异常变化的位置和测年数据,对所记录的两次火山事件发生年代进行了计算,它们分别为距今约12.6和6.2 ka,最近一次火山喷发的年代与K-Ah火山喷发的年代基本一致。