A New Dynamics Expansion Mechanism for Plasma during Pulsed Laser Deposition

The dynamics expansion mechanisms for plasma plume generated by pulsed laser radiation are studied in detail, taking account of plasma ionization effect. Based on the consideration of local conservations of mass, momentum, collected as the assumption that plasma can be viewed as compressible ideal fluid and high temperature-high pressure ideal gas, we develop a new dynamics expansion mechanism for plasma produced by pulsed laser radiation. Using the analytical method, the space number density and pressure evolvement of plasma in cylindrical coordinate are obtained, the dynamics evolvement equations are also derived. The results from the present model indicate that the plasma dynamic expansion behaviour can be evidently influenced by the ionization fraction η. Its effect is similar to a new dynamic source for plasma expansion and increases the expansion acceleration in all directions. The predictions of the expansion of the plasma is affected by the temperature, the average atoms mass and the ionization degree of the plasma are consistent with the experimental results.     

Optical Properties of Co-BaTiO3/Mg（100） Nano-Composite Films Grown by Pulsed Laser Deposition Method

Co nanoparticles embedded in a BaTiO3 matrix, namely Co-BaTiO3 nano-composite films are grown on Mg（100） single crystal substrates by the pulsed laser deposition （PLD） method at 650℃. Optical properties of the CoBaTiO3 nano-composite films are examined by absorption spectra （AS） and photoluminescence （PL） spectra. The results indicate that the concentration of Co nano-particles strongly influences the electron transition of the Co BaTiO3 nano-composite films. The PL emission band ranging from 1.9 to 2.2eV is reported. The AS and PL spectra suggest that the band gap is in the range of 3.28-3.7eV.     

Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica

We carry out the numerical simulations of femtosecond laser propagation with TEMoo mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEM00 mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEM00 mode under the same focusing conditions.     

Temperature Controlled Filamentation in Argon Gas

Temperature controlled filamentation is experimentally demonstrated in a temperature gradient gas-filled tube. The proper position of the tube is heated by a furnace and two ends of the tube are cooled by air. The experimental results show that multiple filaments are shrunken into a single filament or no filament only by increasing the temperature at the beginning of the filament. This technique offers another degree of freedom of controlling the filamentation and opens a new way for intense monocycle pulse generation through gradient temperature in a noble gas.     

MgB2超导薄膜制备方法对比研究

文章结合MgB2超导薄膜在电子器件中的应用,简介了混合物理化学气相沉积法、脉冲激光沉积法、磁控溅射法、分子束外延法和电子束蒸发法等MgB2超导薄膜制备方法和研究进展,并对主要的MgB2超导薄膜制备方法进行了比较,提出了改进意见.对MgB2超导薄膜的应用前景作了展望.     

脉冲电晕氢等离子体370～1100nm发射光谱分析

用CCD (Charge Coupled Device)光谱仪记录并标识了脉冲电晕氢等离子体370～1100nm的发射光谱.通过与非相对论修正的氢原子能级理论计算值和标准数据库比较,巴耳末系测得5条,帕邢系测得14条.其中包括帕邢系的821.334nm(ni=99),821.838nm(nI=77),823.651nm(nI=49),826.709nm(nI=35)和834.655nm(nI=23)等.通过发射光谱线相对光强比较,656.318nm处激发最强,其次为486.050nm和844.524nm,激发最弱的为397.133nm.     

时域飞秒散斑的特性与测量

阐述了飞秒激光脉冲在随机介质传播过程中产生时域散斑的原理,并对时域飞秒散斑进行了测量. 时域飞秒散斑的产生是飞秒脉冲在随机介质中经历多重散射形成的随机干涉现象在时域的体现. 初步讨论了时域散斑的统计特性并给出了相应的实验结果. 关键词： 时域散斑 飞秒脉冲 随机介质     

信号光的调制对基于光纤光参量放大光脉冲源的改善

在理论上从四波混频的强度耦合方程出发,给出了基于光纤光参量放大(FOPA)光脉冲的光场表达式,并进一步分析了信号光被相位调制或强度调制后,光脉冲的频率啁啾和强度演化.结论指出：若信号光被强度调制,对所生成脉冲宽度无明显的影响,但可以提高消光比;若信号光被相位调制,所生成的脉冲具有更大的线性正啁啾,可以在相同的抽运功率条件下得到比无相位调制时更窄的脉冲.实验上给出了10 GHz工作速率下的结果,其结果与理论分析符合得很好.通过信号光的相位调制,在05 W平均抽运功率条件下得到了消光比22 dB,脉宽为5 关键词： 光纤参量放大 四波混频 光脉冲源 频率啁啾     

高阶色散效应常系数Ginzburg-Landau方程自相似脉冲演化的解析分析

采用自相似分析方法,基于常系数高阶色散的Ginzburg-Landau方程,通过分离变量法得出了高阶色散效应自相似脉冲演化的解析解,给出了自相似脉冲的振幅、相位、啁啾以及脉冲宽度的一般表达式.研究表明,在增益光纤的二阶正常色散区域,同时考虑高阶色散和增益色散双重效应影响下演化的自相似孤子脉冲仍然保持线性啁啾;振幅解析解的三阶色散效应显著.这与数值计算的结果非常一致. 关键词： 三阶色散 Ginzburg-Landau方程 自相似脉冲 二阶正常色散     

6H碳化硅衬底上硅碳锗薄膜的生长特性研究

采用低压热壁化学气相沉积法,在6H-SiC衬底(0001)面上生长了不同温度(1100—1250℃),不同GeH₄流量比(6.3%—25%)的SiCGe薄膜样品,研究了SiCGe薄膜的表面形貌、生长特性以及样品中Ge组分含量的变化. 扫描电镜测试结果表明,SiCGe薄膜在低温下倾向于岛状生长模式,随着生长温度提高,岛状生长逐渐过渡到层状生长模式,同时伴有岛形状和密度的变化. X射线光电子能谱测试得出SiCGe样品中的Ge含量约为0.15％—0.62％,在其他参数不变的情况下,样品的G 关键词： 碳化硅 化学气相沉积 反相边界 岛状生长