Quenching Effect of Microwave to DC Glow Discharge in Gas Lasers

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Role of the Density of Lower Laser Levels in the Control of Generation Parameters of a Copper Vapor Laser

The possibility of controlling the generation parameters of a copper vapor laser (CVL) by varying the density of metastable states of Cu atoms both during pulsed excitation and within interpulse periods is considered. It is shown that control of the CVL generation parameters could be carried out without disruption of laser thermal conditions, and the regime of varying the generation parameters is independent of the means of excitation of the active medium.     

激光烧蚀脉冲放电激发的土壤等离子体电子数密度和温度的研究

以激光烧蚀快脉冲放电激发土壤为例,研究了激光烧蚀快脉冲放电等离子体技术产生的土壤等离子体的电子数密度和温度。根据实验测得的Si原子和离子谱线的强度和萨哈玻尔兹曼方程,计算了等离子体的电子温度,并从分析Si I 250.69nm谱线的斯塔克展宽中导出了等离子体的电子数密度。与使用同样激光能量激发的激光等离子体相比,激光烧蚀快脉冲放电激发等离子体的电子数密度和温度都明显增加,与观察到的光谱信号强度是一致的。     

The Dual Mode Microwave Afterglow Apparatus for Measuring the Electron Temperature Dependence of the Electron‐Ion Recombination

Three dual mode microwave apparatus (one using S ‐band and two using X ‐band) have been developed to determine ambipolar diffusion and electron‐ion recombination rates under conditions such that T_gas = 300K and T_e is varied from 300 K to 6300 K, in the afterglow period of the dc glow discharge. TheTM₀₁₀ cylindrical cavity (in S ‐band) and TM₀₁₁ open cylindrical cavity (X ‐band) are used to determine the electron density during the afterglow period and a non‐resonant waveguide mode is used to apply a constant microwave heating field to the electrons. To test the properties of the apparatus the neon afterglow plasma has been investigated. At T_e = 300 K a value of α (Ne⁺₂) = (1.7± 0.2) × 10^–7cm³/s is obtained which is in good agreement with values of other investigators. Also similar variations of α as T^–0.4_e (S ‐band) and as T^–0.42_e (X ‐band) obeyed over the range 300 ≤ Te ≤ 6300K are in good agreement with some other previous measurements. The simplicity of the X‐band microwave apparatus also allows the measurements of the gas temperature dependency and the study of electron attachment and may be used simultaneously with optical or mass spectrometry investigations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

飞秒脉冲激光作用下金属薄膜的热弹性研究

利用双曲-双温两步热传导和热电子崩力模型,考虑到晶格温度与应变速率的耦合效应,得到了用于描述飞秒激光作用下金属薄膜热力效应的超快热弹性模型。以飞秒脉冲激光辐照金属铜薄膜为例,运用具有人工粘性和自适应步长的有限差分算法,对不同能量密度和脉冲宽度条件下薄膜体内温度场和应力场的变化规律进行了数值模拟,对比分析了电子晶格耦合系数对超快加热过程的影响。结果表明,飞秒脉冲激光辐照早期为明显的非平衡加热过程,电子温度迅速升高,而晶格温度的升高却相对较慢;激光辐照早期的热力耦合效应导致薄膜前表面附近的热应力表现为压应力,随着时间的推移,热应力由压应力转变为张应力,为激光加工和激光对抗提供了理论参考。     

测量飞秒激光脉冲啁啾的方法

介绍了一种能够直接检测飞秒脉冲啁啾大小的方法。采用共轴结构的迈克尔逊干涉自相关二次谐波检测系统对自制碰撞脉冲锁模循环染料激光器输出的最窄脉冲宽度约为200fs的脉冲进行了测量。测得的飞秒脉冲自相关二次谐波曲线表明：实测曲线的下包络两翼明显隆起,包络外形很不整齐,对称性较差,说明光脉冲含有啁啾。通过比较干涉测量曲线和理论曲线的形状与面积的大小,可以直观地反映出光脉冲所含啁啾的大小。实验结果分析表明,利用满足光相关检测所需精度的光学元件和满足光相关探测基本条件的实验装置,能测得含有相位及啁啾信息的快干涉项信号,是一种能够直观检测光脉冲所含啁啾大小的可行方法。     

Pulsed population inversion in recombination of positive metal ions with negative ions of sulfur,selenium, and tellurium

Ion-ion recombination of positive ions of 14 metals with negative ions of sulfur, selenium, and tellurium is considered. The energy levels of metal atoms predominantly populated in the process of ion-ion recombination are estimated. The possibility of creating the population inversion in the afterglow of a pulsed discharge on some atomic transitions is discussed along with realization of noncoherent sources of radiation.     

基于吸收光谱原理的高温水汽浓度测量方法研究

可调谐半导体激光吸收光谱(tunable diode laser absorption spectroscopy,简称为TDLAS)技术具有高灵敏度、快速响应、非接触式、环境适应性强等优点,能够实现燃烧温度、组分浓度、速度等参量的实时动态在线测量。为准确测量高温下的水汽浓度,采用窄带半导体激光器作为光源,结合实验室的高温测量系统,记录了常压下1.39μm附近水汽在773~1 273K温度范围内的吸收光谱,利用多线组合非线性最小二乘法拟合得到高温吸收光谱的吸光度,找出了两条适合高温水汽浓度测量的吸收线7 154.35和7 157.73cm-1,首次提出高温水汽浓度测量的模型求解方法,该方法测得的高温下水汽浓度符合理论推理,浓度测量的标准误差低于0.2%,相对误差低于6%。通过实验验证了该测量方法的可行性。     

Recent Developments in Modulation Spectroscopy for Trace Gas Detection Using Tunable Diode Lasers

Abstract

The need for higher sensitive detection technology for trace gas samples, either in the laboratory setup or in the atmospheric remote sensing has been a goal for several decades. The development of the tunable diode laser has propelled the progress of trace detection technology, and modulation technology enables the improvement of the detection sensitivity. As a result, the detection of 10^?7 or 10^?8 absorbance is possible for some applications, and modulation technology has been applied to the ultraviolet as well as mid-infra red wavelength range. In this review, recent progress of tunable diode lasers and diode laser-based modulation technologies are presented. Wavelength modulation, frequency modulation, and two-tone frequency modulation techniques are mainly described along with the actual application of the techniques. In addition, the state-of-the-art of diode laser development which can be adopted for the trace detection is presented.     

利用激光感应瞬态光栅技术测量超短激光脉冲宽度

描述了利用激光感应瞬态光栅技术测量超短脉冲激光的脉冲宽度和相干时间的方法，来自同一光源的两束激光在非线性介质中相干形成积分光栅，测量光栅自衍射强度与两束光脉冲之间的延迟时间关系，利用相干光束的四阶相干函数关系，可以求出光源的脉冲宽度和相干时间。     

光调制技术测量半导体激光器固有高频响应

采用一种新的全光纤连接的半导体激光器光调制技术,实现了对高速半导体激光器同有响应的直接测量。利用速率方程能够对光调制的动态响应过程进行准确的描述。基于对抽运源和探测器的频率响应对光调制数据准确性影响的分析．通过将网络分析仪校正到同轴端．然后用直接扣除法和相互扣除法,在网络分析仪外部对测量数据进行了修正。两种修正方法得到了一致的结果．并且同已有的理论和实验结果相符合。改进后的光调制技术和两种修正数据的方法不但提高了数据的精确性,而且扩展了测量的频率范围。     

Electron Density of Polymeric Nanoparticles Determined by Image Processing of Transmission Electron Micrographs: Insights into Heavy Metal Staining Processes

A crucial parameter for the investigation of in particular low electron scattering materials by transmission electron microscopy is their ability to attenuate the electron beam and by this to generate appropriate contrast. Surprisingly little attempts have been devoted to at least qualitatively judge on this property of materials. Here an automated imaging analysis algorithm is introduced for the determination of a characteristic electron attenuation factor for homo‐ and (co)polymer nanoparticles which provides a means to access a measure for the contrast in a systematic study of the inherent contrast as well as of the contrast of the nanoparticles after staining procedures. The determination is based on similar imaging conditions for different nanoparticle systems, which enables a comparative approach. Additionally, based on the importance and versatility of osmium tetroxide staining, experiments are conducted elucidating the staining process of model nanoparticle systems bearing olefinic groups. The binding of osmium tetroxide in the environment of the nanoparticle is investigated by means of high‐resolution electrospray mass spectrometry.     

标准金属量器液位图像识别装置的研制

在使用标准金属量器对液体进行计量过程中,传统的人工读取液位的方法测量效率和准确度都比较低。提出了一种高精度的标准量器液位图像识别装置,该装置主要由水平调整和图像处理两部分组成,选用S3C2440 ARM芯片和Linux嵌入式系统作为硬、软件平台。水平调整是通过SCA100T双轴倾角传感器测量量器的倾角并控制步进电机自动调整;对采集的液位图像,由OpenCV进行灰度化、滤波、边缘检测、液位提取,再经过标定计算转换成实际液位高度。实验结果表明该方法能快速测量液位,精度高,应用于燃油加油机计量检定装置上,有较好的推广价值。     

热喷雾蒸气发生原子吸收法测定生物样品中的镉

文章采用热喷雾技术,将样品和硼氢化钾引入喷雾器,并在喷嘴处混合发生热雾相反应。生成的蒸气态物质经去溶装置冷却后直接进入T形石英管中用原子吸收法测定。该方法的灵敏度和稳定性较传统气动雾化法有了较大提高,检测限为18 ng·L-1,相对标准偏差为2.1%。用于烟草中镉的测定,回收率为94%～103%。     

Studies of the Longitudinal Electrophoresis Dynamics in Pulse-Periodic Discharges

The establishing in time of the axial distribution of metal vapors is studied on injecting them electrophoretically into a pulse-periodic discharge. In particular, the time-dependent solution of the diffusion equation for the metal vapor concentration is obtained averaged through a number of pulses. The axial distributions of vapors for various instants of time are calculated. The homogeneity criteria for these distributions are determined. The settling times of the homogeneous distribution in conditions typical for the pulse-periodic metal vapor lasers are found. These times are rather short (about 1 s). The results obtained show promise for using electrophoresis in pulse-periodic metal vapor lasers to form homogeneous active media.     

高重复率脉冲放电金属蒸气激光中电泳对金属蒸气分布的影响

建立了一个理论模型描述了高重复率脉冲放电金属蒸气激光中的电泳动力学过程.得到了稳态和瞬态时金属蒸气密度扩散方程的解析表达式.分别计算了高重复率脉冲放电的He-Sr⁺和He-Cd⁺激光在不同时刻金属蒸气密度的轴向分布过程.结果表明，在放电开始后约2s内即可在阴极区建立起相当均匀的轴向金属蒸气密度分布，从而确保了电泳式金属蒸气激光的稳定输出特性. 关键词： 电泳 高重复率脉冲放电 轴向金属蒸气分布 金属蒸气激光     

常压化学气相沉积法在Ag/Si(111)模板上生长ZnO薄膜及其性能研究

在Si衬底上利用磁控溅射的方法沉积1.5 nm厚度的Ag膜用以阻挡Si衬底被氧化。采用常压金属有机化学气相沉积法(MOVCD),在Ag/Si(111)衬底上成功地生长出马赛克结构的ZnO薄膜。用光学显微镜观察表面形貌,结果显示有带晶向特征的微裂纹,裂纹密度为100 cm-1。依据X射线晶体衍射的结果,薄膜结晶质量良好,呈C轴高度择优取向。用双晶X射线衍射得到(002)面的ω扫描半峰宽为1.37°。温度10 K时光致发光谱(PL)观察到自由激子、束缚激子发射及它们的声子伴线。结果表明,金属有机化学气相沉积法方法在Si(111)衬底上制备ZnO薄膜时,Ag是一种有效的缓冲层。     

金属有机化学气相沉积生长Zn1-xMnxSe薄膜的发光和磁光性质

利用金属有机化学气相沉积(MOCVD)方法在GaAs衬底上生长了不同组分的Zn_1-xMn_xSe薄膜。X射线衍射和X射线摇摆曲线证明样品具有较好的结晶质量。在低温、强磁场下对样品的发光进行了研究,在带边附近观察到两个发光峰的相对强度随着磁场增强发生了变化。通过变温光谱探讨了这两个发光峰的来源,并被分别归因于自由激子跃迁和与Mn有关的束缚态激子跃迁。同时随着磁场的增强,ZnMnSe带隙发光红移是由于类S带和类P带电子与Mn离子的3d⁵电子的自旋交换作用。