Dynamic Alignment of D2 Enhanced by Two Few-cycle Pulses

利用数值方法求解D2分子刚性转子模型在超短飞秒激光脉冲作用下的薛定谔方程,计算了双原子分子D2在两束固定强度的飞秒激光脉冲作用下,延迟时间对于分子取向的影响.结果表明,只要选取合适的延迟时间,就能很好改善分子取向;保持两束激光强度不变,通过调整两束脉冲的宽度,选择合适的延迟时间能够进一步有效提高D2分子的取向程度.     

1064nm纳秒激光脉冲激发的外腔式PbWO4拉曼激光器

研究了外腔式PbWO4拉曼激光器在纳秒脉冲抽运下的输出特性。利用主动调Q的Nd:YAG激光器产生的脉冲宽度为31.4ns,最大输出能量为200mJ的1064nm激光作为抽运源。拉曼激光谐振腔采用的是平凹腔设计。测量了输出的拉曼光脉宽与抽运能量的关系,分析了输出的拉曼光脉冲波形图和光谱图,测量了输出的拉曼光脉冲能量与抽运能量的关系,计算了转换效率与抽运能量的关系。当注入抽运光能量达到42mJ时,得到了一阶斯托克斯光脉冲的最大能量和转换效率分别为10mJ和24%,获得外腔式PbWO4拉曼激光器的一阶斯托克斯光脉冲波长为1177.6nm,典型的一阶斯托克斯光脉冲脉宽为20ns。     

超短强激光脉冲与H2＋相互作用研究：经典与量子计算的比较

用经典动力学和量子力学方法分别研究了Ｈ２＋在超短强激光场中的电离、离解和残存行为，得到了相似的结果：即在超短强激光脉冲作用下，Ｈ２＋的电离占优，但有限的量子计算低估了Ｈ２＋的离解几率；而经典处理则没有显示Ｈ２＋在超强场中的稳定化。另外，经典计算表明当核间距Ｒ伸展到一定范围时，Ｈ２＋的电离率最大。这符合量子计算中发现的电荷谐振增强电离（ＣＲＥＩ）现象。     

Laser-induced Alignment and Coulomb Explosion of CO2

实验研究了CO₂分子在飞秒强激光脉冲作用下的动力学过程,包括分子取向,隧穿电离和库仑爆炸,激光强度从1×10¹³W/cm²变化到6×10¹⁴W/cm². 当激光强度小于分子的电离阈值时,CO₂分子的非绝热转动激发形成一个相干转动波包,波包演化导致分子沿激光电场方向取向. 激光脉冲结束后,分子取向可以周期性地再现,利用另一束激光可以对取向结构进一步进行修饰. 当激光强度大于分子     

Simulation of Ultrashort Laser Pulse Propagation in Silica Fibre by FDTD+

The finite-difference time-domain algorithm is extended to solving the Maxwell's equations with nonlinear terms which include all exact Sellmeier-fitting values in this paper. The results obtained by the presented method are in good agreement with those from experiments, and this method is even better than solving the generalized nonlinear Schrödinger equation by split-step Fourier method. The spectral phase of propagated pulses is also obtained by the presented method, which is important for investigation of single-cycle optical pulse generation via phase compensation of the nonlinear-chirped in silica fibers.     

Microscopic Dynamics of Nonsequential Double Ionization by Elliptically Polarized Few-Cycle Laser Pulses

With the classical ensemble model, we investigate nonsequential double ionization (NSDI) of xenon atoms using 780 nm, 0.25 PW/cm2elliptically polarized few-cycle laser pulses. The momentum distribution of correlated electron along the long axis of the laser polarization plane shows an obvious V-like structure locating at the third quadrant, and the momentum along the short axis of the laser polarization plane are mainly distributed in the second and fourth quadrants. Moreover, we demonstrate that the Coulomb repulsion interaction plays a decisive role to the above results.By back analyzing the classical trajectories of NSDI, we find that there are two kinds of recollision trajectories mainly contribute to NSDI, and the different microscopic dynamics for the two kinds of trajectories are clearly explored.     

HfO2/SiO2薄膜的激光预处理作用研究

对电子束蒸发方式镀制的HfO2/SiO2反射膜采用大口径激光进行辐照,采用激光量热计测量了激光辐射前后的弱吸收值。实验发现HfO2/SiO2反射膜在分别采用1 064 nm和532 nm的激光辐照前后薄膜吸收分别从5.4%和1.7%降低到1.4和1.2%。采用聚焦离子束技术分析了激光辐照后薄膜的损伤形态并探究了损伤原因,发现：薄膜在激光辐照下存在节瘤的地方容易出现薄膜损伤,具体表现为熔融、部分喷发、完全脱落3种形态,节瘤缺陷种子来源的差异是导致其损伤机理也存在着巨大差异的主要原因。同时这些节瘤缺陷种子来源也影响着激光预处理作用效果,激光预处理技术对于祛除位于基底上种子形成的节瘤是有效的,原因是激光辐射过后该节瘤进行了预喷发而不会对后续激光产生影响;而激光预处理技术对位于膜层中间的可能是镀膜过程中材料飞溅引起的缺陷是无效的,需要通过飞秒激光手段对该类节瘤进行祛除。     

激光冲击陶瓷中反射拉伸波破坏的预防

激光冲击过程中,反射拉伸波一直都是造成材料失效的主要破坏模式。为了进一步分析陶瓷材料的冲击性能,控制拉伸波对材料造成的破坏,从而最终达到改善其脆性的目的,使用高功率钕玻璃脉冲激光器对Al2O3陶瓷进行了冲击试验。通过在Al2O3试样背表面粘贴胶带,发现陶瓷表现出与无粘贴状态下完全不同的破裂模式。使用扫描电子显微技术观察其断口形貌并结合理论分析,发现粘贴胶带以后,对背表面的反射拉伸波能量有相当程度的衰减,大幅减少了拉应力的作用。通过计算表明,这种背面粘贴的胶带可降低冲击波能量到反射前的40％左右,这样就可以通过降低反射波能量来大幅减少拉伸波造成的灾难性脆断。     

连续CO2激光脉冲制作长周期光纤光栅的研究

利用耦合模理论分析了均匀长周期光纤光栅中的模式耦合, 描述了连续CO₂激光脉冲逐点写入长周期光纤光栅技术的实验研究情况, 实验中观测到模式耦合强度随光栅区域长度发生周期性变化.     

飞秒激光诱导的Mn2+掺杂锗酸盐玻璃上转换发光

研究了室温下的飞秒激光诱导过渡金属Mn2+掺杂锗酸盐玻璃的上转换发光现象。样品的激发光谱与发射光谱表明,激发过程是能级6A(6S)→4E(4G)/4A1(4G)的跃迁,该过程源于Mn2+离子的4T1(4G)→6 A1(6 S)跃迁。由409 nm单色光激发样品得到的发射光谱与800 nm飞秒激光激发的光谱相一致。通过分析飞秒激光泵浦功率密度与荧光强度的依赖关系以及飞秒激光辐照样品前后的吸收谱,认为该上转换过程为双光子同时吸收过程。随着Mn2+浓度的提高,上转换发光的中心波长发生红移。     

Different crystallization processes of as-deposited amorphous Ge2Sb2Te5 films on nano- and picosecond single laser pulse irradiation

The crystallization dynamics of as-deposited amorphous Ge₂Sb₂Te₅ films induced by nano- and picosecond single laser pulse irradiation is studied using in situ reflectivity measurements. Compared with nanosecond laser pulse, the typical recalescence phenomenon did not appear during the picosecond laser pulse-induced crystallization processes when the pulse fluence gradually increased from crystallization to ablation threshold. The absence of melting and recalescence phenomenon significantly decreased the crystallization time from hundreds to a few tens of nanoseconds. The role of pulse duration time scale on the crystallization process is qualitatively analyzed.     

TEA-CO2激光辐照HgCdTe图像传感器的实验研究

利用TEA-CO₂激光对碲铬汞(HgCdTe)图像传感器的干扰和损伤现象进行了实验研究,分析了干扰和损伤机理。探测器上激光能量密度小于255 mJ/cm2时,饱和像素仅出现在光斑区域,激光能量密度为425.8 mJ/cm2时,像素被损伤,观察到了弥散斑和暗环等现象。建立了探测器的激光辐照模型,计算了探测器的温升,讨论了温升与载流子浓度、迁移率的关系。分析认为,弥散斑的出现是探测器升温产生的热激发载流子浓度扩散所致,暗环的出现是迁移率与载流子浓度扩散共同作用的结果,像素的损伤则是因为温升导致汞的析出。     

三态K2分子飞秒含时光电子能谱的理论研究

利用三态模型和含时波包法, 研究了K₂分子在强飞秒抽运-探测激光场中延时、脉宽以及抽运波长对光电子能谱和波包动力学过程的影响. 研究结果表明, 激光场强较弱或者脉宽较短都可能不发生Autler-Townes分裂, 光电子能谱呈现出单峰结构; 延时和抽运波长的改变影响能峰结构、位置和相对峰高; 对于不同的抽运波长, 波包的振动周期是相同的, 波包振荡幅度随脉宽增大而减小; 光电子能谱反映了波包动力学信息. 研究结果可以为实验上实现分子的光控制以及量子调控过程提供一定的参考, 并为进一步研究K₂分子的动力学性质提供有用的信息.     

Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm

A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles.     

Line profile study from diode laser spectroscopy in the CH4 2ν3 band perturbed by N2, O2, Ar, and He

We present a line profile study for two lines in the 2ν₃ band of CH₄ recorded with a frequency stabilized tunable diode laser spectrometer. The broadening and narrowing (Dicke effect) parameters of the R(0) line perturbed by N₂, O₂, and He are derived from a simultaneous fitting of spectra at pressures from 20 to 300 Torr by using the soft and hard collision models. These parameters are determined for the A and F components of the unresolved R(3) manifold perturbed by N₂, Ar, and He from the line profile analysis of spectra at pressures between 50 and 500 Torr. The line mixing effect between the two F components is also taken into account and the absorber speed dependent effect on broadening is estimated for N₂ and Ar.     

正交双色场中氢分子非次序双电离的研究

利用经典系综模型,研究了正交双色场作用下氢分子非次序双电离中双电离电子的相关特性.结果表明,双电离电子相关动量谱强烈地依赖于正交双色场的相对相位.通过改变正交双色场的相对相位,相关动量可以从反相关模式转变为相关模式.向后分析表明,相关电子动量谱对双色场相对相位的依赖关系起源于碰撞过程中碰撞电子碰撞角和碰撞动量对相对相位...     

532 nm HfO2/SiO2高反膜的激光预处理效应

采用单台阶能量光栅扫描以及R-on-1测试两种不同预处理方式研究了激光预处理技术对532 nm HfO2/SiO2高反膜的阈值提升效果。用Nd:YAG二倍频激光对电子束蒸发制备的532 nm HfO2/SiO2高反膜进行1-on-1损伤阈值测试,然后分别进行单台阶能量光栅扫描以及R-on-1测试。通过对损伤概率以及损伤形貌的分析,发现激光预处理能够去除薄膜内低阈值缺陷,达到提高损伤阈值的目的,损伤阈值分别提高38%和30%。     

脉冲CO2激光器峰值功率的增益饱和现象

 从理论和实验的角度分析了在腔损耗调制状态下,当调制速度与CO₂激光转动能级间的弛豫速度相当时,激光器输出脉冲峰值功率与增益系数间存在的非线性特性：峰值功率随增益系数的增加,存在饱和现象。这种特性是CO² B-类激光器的特点,实验和理论模拟结果一致。     

脉冲CO2激光烧蚀锡靶等离子体的数值研究

使用一维辐射流体力学程序MULTI模拟了脉冲CO2激光烧蚀平面锡靶的过程,研究了脉冲宽度、峰值功率密度、靶材初始密度对锡等离子体电子密度、电子温度的时空分布的影响,并结合统计分析得到最有利于产生13.5 nm 极紫外光的激光脉冲宽度。模拟结果表明,脉冲宽度为100~200 ns的长脉冲激光产生的等离子体有利于实现极紫外输出的最佳条件,通过分析等离子体的电子密度、电子温度的分布对这一结论进行了解释。临界电子密度区域有效吸收了脉冲能量,而低密度的羽辉对激光与极紫外辐射的吸收很少。采用长脉冲激光,使得辐射极紫外等离子体持续时间更长,是提高极紫外辐射效率的有效手段。同时模拟还发现,靶材初始密度对等离子体参数的影响不大。     

O_2（~1△_g）二聚物的兰色激光振荡

通过微波（２．４５０ＧＨｚ）激励高纯氧产生Ｏ２（１△ｇ）二聚物，利用放大自发辐射法首次测得了Ｏ２（１△ｇ）二聚物在４８６ｎｍ处的小信号增益系数。采用平凹稳定谐振腔观察到了４８６ｎｍ的兰色激光振荡，最大激光输出功率为１３０μＷ，发散角为２８ｍｒａｄ。