CARS技术中泵浦激光光场相干特性的研究

本文从理论上指出，在分子振动能级的横向弛豫时间远小于激光相干时间的条件下，相干反斯托克斯喇曼散射（ＣＡＲＳ）信号能够反映出激光光场的相干特性，据此可直接了解其相干时间并推算出激光的线宽。实验记录了苯、甲苯的ＣＡＲＳ光信号与激光延时时间的关系，得出了激光的相干时间和线宽。     

High Resolution Laser Transient Spectroscopic Technology under Two-Stage Light Gas-Gun Loading Condition and Stability Study of Shocked BenzeneEI北大核心CSCD

The present paper reports the high resolution transient Raman laser testing technology under two-stage light gas-gun loading experiment, and its application to studying the Raman spectroscopy of shocked benzene. In the experiments, the frequency shift of C-C stretching vibration (992 cm(-1)) and C H stretching vibration peak (3 061 cm(-1)) in the low pressure section (less than 8 GPa) varies linearly with the pressure, and the results agree well with reported data in the literature. The structural changes in liquid benzene about 13 GPa were clarified firstly by the Raman spectral technique; the experimental results show that at a pressure of 9.7 GPa, the structural change of liquid benzene has taken place, not reported in the literature about 13 GPa. But the composition in the production is not clear. The measurement system provides an effective means to study the microstructure changes of transparent and translucent material under dynamic loading experiment.     

High pressure photoinduced ring opening of benzene

The chemical transformation of crystalline benzene into an amorphous solid (a-C:H) was induced at high pressure by employing laser light of suitable wavelengths. The reaction was forced to occur at 16 GPa, well below the pressure value (23 GPa) where the reaction normally occurs. Different laser sources were used to tune the pumping wavelength into the red wing of the first excited singlet state S(1)((1)B(2u)) absorption edge. Here the benzene ring is distorted, presenting a greater flexibility which makes the molecule unstable at high pressure. The selective pumping of the S(1) level, in addition to structural considerations, was of paramount importance to clarify the mechanism of the reaction.     

基于菲涅尔反射的光纤激光器功率测量方法

分析了光纤熔接点处的菲涅尔散射光模型,得出熔接点散射光功率与输出光功率成线性关系的结论。利用该结论设计了kW级光纤激光器的振荡器、泵浦源输出功率检测装置,并安装在某kW级光纤激光器上进行了实验。通过建立线性估计函数,利用最小二乘法对光纤熔接点的散射光功率与光纤激光器的振荡器、泵浦源输出功率的关系进行了拟合。通过实验验证了熔接点散射功率与光纤输出功率的线性关系。实验表明利用熔接点散射光功率间接测量光纤激光器输出功率的方法线性度优于4%。     

Nd：YAG固体脉冲激光器实验研究

介绍了Nd：YAG固体脉冲激光器相关的实验项目：静态和调Q状态的出光阈值、激光脉宽、倍频和激光光束形状等.采用普通相纸、红外相纸和激光能量计检测出不同的激光器静态和调Q出光阈值;采用散射、反射和透射方法研究了静态和调Q输出激光脉冲的宽度,发现用K9玻璃和多层膜镜测试的激光脉冲宽度比散射方法的大;采用激光能量计测试激光器静态和调Q的倍频效率和倍频激光能量与倍频晶体的位置关系;激光光束探测器表征激光器静态和调Q输出光的光斑形状.通过这些实验项目,学生将深入了解和掌握固体脉冲激光器的工作原理、性能参数,以及表征激光器性能参数的仪器设备,并深入地研究解决实验发现的问题,为今后激光相关领域的工作奠定坚实的基础.     

Picosecond pulse generation in a benzene raman generator amplifier system

Picosecond ruby laser pulses generate simultaneously Stokes pulses of the 992 cm^–1 ring breathing mode and of the 3063 cm^–1 CH-stretching mode of benzene in a Raman generator cell by stimulated Raman scattering under self-focusing conditions. The Raman generator light is spectrally filtered, collimated, and amplified in three Raman amplifier cells pumped by ruby laser pulses. Both first Stokes lines have been selectively amplified to short, low divergence, intense light pulses.     

Spectroscopic Study on the Pyrolytic Products of Amines

Abstract

From the early days of alchemy, heating has been a primary method to promote chemical reaction and to obtain new materials. Organic and inorganic compounds, such as benzene and sulfuric acid, were being prepared pyrolytically by the early 19th century. The use of light, particularly the advent of the laser in this century, added another tool for chemical reaction. The ease of regulation and superior selectivity of laser frequencies are advantages over the thermal reaction. State-to-state chemistry in combination with the laser is highly developed at the present time. On the other hand, although some of the black-box character of thermal reactions makes it difficult to rigorously study reaction mechanisms, most of the new compounds are still created by the effects of heating.     

Orientation of benzene in supersonic expansions, probed by IR-laser absorption and by molecular beam scattering

This work represents the first experimental demonstration that planar molecules tend to travel as a "frisbee" when a gaseous mixture with lighter carriers expands into a vacuum, the orientation being due to collisions. The molecule is benzene, the prototype of aromatic chemistry. The demonstration is via two complementary experiments: interrogating benzene by IR-laser light and controlling its orientation by selective scattering on rare gas targets. The results cast new light on the microscopic mechanisms of collisional alignment and suggest a useful way to produce intense beams of aligned molecules, permitting studies of steric effects in gas-phase processes and in surface catalysis.     

0.351μm激光辐照Au盘靶吸收、散射规律的实验研究

在“星光Ⅱ”激光装置上，利用80只分立式探测器研究了约0.8ns，0.351μm激光辐照Au盘靶的吸收、散射．结果表明，强度约为5×10¹⁴W/cm²的激光以10°角入射，吸收可达90%以上；但是，以45°角入射，吸收仅为75%左右，散射高达25%．散射主要来自未被等离子体充分吸收的激光在弯曲临界面上的反射，同时伴随少量受激布里渊散射．吸收的理论计算与实验结果进行了比较，两者符合较好． 关键词：     

用质谱和光电子能谱研究飞秒强场中的电离动力学

报导了用自制飞秒激光器通过飞秒多光子电离质谱和光电子能谱对飞秒强激光场与分子（氨、苯）相互作用的研究,飞秒激光脉宽约１００ｆｓ,二倍频中心波长４０７．５ｎｍ,聚焦后脉冲功率密度达到１０＾１２Ｗ／ｃｍ＾２,氨的光电子能谱显示了（２＋２）ＲＥＭＰＩ和（２＋２）＋１ＡＴＩ、（２＋２）＋２ＡＴＩ三组电子峰,每组峰又包括伸缩振动ｖ１的带系,ＡＴＩ峰的振动布居出现反转,随着光强增加,谱峰加宽而且振动能级出现平     

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S₁-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S₁-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.     

激光诱导荧光聚焦纹影系统及超声速燃烧流场应用

纹影是一种常用的流动显示技术，广泛应用于可压缩流动显示及超声速燃烧流场实验.然而，在变Mach数超声速燃烧实验中，燃烧室总温随来流Mach数变化.受准稳态/非定常温度变化影响，光学玻璃窗口的折射率发生显著改变，影响基于密度梯度的纹影成像质量.同时，普通纹影为光程体积沿程积分，难以同二维燃烧场成像信息进行直接比较以开展燃烧与流动耦合研究.聚焦纹影技术可抑制燃烧室内高温引起的玻璃窗口折射率变化，并实现毫米级的急剧聚焦深度，获得二维流场结构，同时配合纳秒级脉宽Nd:YAG激光光源可冻结高超声速流场.在传统聚焦纹影系统基础上发展了激光诱导荧光聚焦纹影系统并应用于变Mach数超声速燃烧实验，创新点在于使用激光诱导荧光染料，以荧光作为光源消除原本激光光源中的相干噪声，同时发展了边缘增强图像处理方法.实验结果表明激光诱导荧光聚焦纹影系统及边缘增强图像处理方法能够有效消除激光光源相干噪声，捕捉二维超声速燃烧流场结构.      

Enhanced spatiotemporal laser-beam smoothing in gas-jet plasmas

Spatiotemporal smoothing of large-scale laser intensity fluctuations is observed for a laser beam focused into underdense helium plasmas. This smoothing is found to be severely enhanced when focusing the laser beam into a helium gas jet. In contrast to other experiments with preformed plasmas, the average and the peak laser intensities are well below the threshold for ponderomotive self-focusing. The coherence characteristics of the transmitted light are measured for various electron densities, and the smoothing effect is explained by multiple scattering of laser light on self-induced density perturbations.     

紫外新激光染料IBOP的研究

本文介绍一种新合成的化合物IBOP.经在多种染料激光器上测试表明,其激光转换效率高,光化学稳定性好,能溶于多种溶剂.性能优于DPS等相同波段的常用激光染料.IBOP在各种溶剂中的激光调谐范围为388～428nm,激光峰值波长在400nm左右.本文给出了IBOP的荧光光谱、吸收光谱、激光特性、溶剂效应和浓度效应等数据,并作了讨论.     

强泵浦下掺Yb3+双包层光纤激光器输出特性数值分析和实验研究

对强泵浦下线形腔掺Yb3+双包层光纤激光器输出特性进行了理论和实验研究。通过数值模拟,分析了泵浦光及激光在光纤中的分布、输出功率与泵浦功率的关系、光纤长度及腔镜反射率对激光输出功率的影响。在实验中,利用D型掺Yb3+双包层光纤获得了输出功率10 6W的光纤激光输出,斜率效率达86%。测量了在不同输出耦合条件下的输出功率、阈值泵浦功率和斜率效率,理论分析与实验结果基本一致,为进一步提高光纤激光器功率提供了理论和实验依据。     

激光二极管反馈干涉的实验观测

利用LabView软件虚拟示波器和信号源,观测了激光二极管反馈干涉实验现象．实验证明反馈回激光二极管的光的入射方向和入射光强以及信号处理电路的带宽,对反馈干涉信号有很大的影响．     

Laser-plasma interaction in the context of inertial fusion: experiments and modeling

Many nonlinear processes may affect the laser beam propagation and the laser energy deposition in the underdense plasma surrounding the pellet. These processes, associated with anomalous and nonlinear absorption mechanisms, are fundamental issues in the context of Inertial Confinement Fusion. The work presented in this article refers to laser-plasma interaction experiments which were conducted under well-controlled conditions, and to their theoretical and numerical modeling. Thanks to important diagnostics improvements, the plasma and laser parameters were sufficiently characterized in these experiments to make it possible to carry out numerical simulations modeling the laser plasma interaction in which the hydrodynamics conditions were very close to the experimental ones. Two sets of experiments were carried out with the LULI 2000 and the six beam LULI laser facilities. In the first series of experiments, the interaction between two single hot spots was studied as a function of their distance, intensity and light polarization. In the second series, the intensity distribution of stimulated Brillouin scattering (SBS) inside the plasma was studied by means of a new temporally resolved imaging system. Two-dimensional (2D) simulations were carried out with our code Harmony2D in order to model these experiments. For both series of experiments, the numerical results show a very good agreement with the experimental ones for what concerns the main SBS features, namely the spatial and temporal behavior of the SBS-driven acoustic waves, as well as the average SBS reflectivities. Thus, these well diagnosed experiments, carried out with well defined conditions, make it possible to benchmark our theoretical and numerical modelings and, hence, to improve our predictive capabilities for future experiments.     

激光激发荧光谱的双光路多道分析方法研究

使用双光路相关方法有效的克服了激光激发荧光谱分析中激发激光波动对荧光光谱分析的影响 ,显著降低了分析误差。在对若丹明 6G荧光和对十二烷基硫酸钠 (SDS)对R6G的荧光增强的测量中 ,相关系数大于 0 9。和采样平均法比较表明 ,在激发光波动较大时 ,此方法有明显优势。     

Fluctuations of second harmonic generated light

We calculate the statistical properties of light, arising by second harmonic generation from stationary quasimonochromatic light fields as thermal and single-mode laser light. After a derivation of the correlationfunctions we draw conclusions about spectral densities and the expected results for photon-counting experiments for the converted light.     

空芯带隙型光子晶体光纤整体空气孔包层导光特性研究

 传统光纤包层中仅存在泄漏的倏逝波,能量较小,不利于包层传感的应用。增大包层中的能量,实现整体包层导光是提高光纤传感灵敏度的有效途径。从理论上分析了利用空芯带隙型光子晶体光纤(HC-PCF)包层进行导光的机理。在实验上选用带隙外的冷光源和激光对一种典型结构的HC-PCF进行了空气孔包层的导光实验,并利用折射率引导型光子晶体光纤和单模光纤进行对比实验。结果表明,带隙范围外光波在HC-PCF中传输时将不受禁带效应的约束泄露至包层中重新分布。包层中SiO2与空气孔的周期型结构将光波约束在高折射率介质中,实现HC-PCF整体空气孔包层中光波的稳定传输。PBG-PCF包层的整体导光在传感上有提高灵敏度的潜在价值。