二氯亚砜分子三体解离研究

本文利用飞秒时间分辨的质谱技术,研究了二氯亚砜分子在235 nm泵浦下的超快光解过程.实验记录了母体离子产率随泵浦-探测延迟时间的变化趋势,测得235 nm泵浦下的初始激发态寿命为166 fs.需要注意的是,实验中不仅观察到了二氯亚砜分子逐步解离过程还观察到了协同解离过程.     

二氯亚砜分子三体解离研究（英文）

本文利用飞秒时间分辨的质谱技术,研究了二氯亚砜分子在235 nm泵浦下的超快光解过程.实验记录了母体离子产率随泵浦-探测延迟时间的变化趋势,测得235 nm泵浦下的初始激发态寿命为166 fs.需要注意的是,实验中不仅观察到了二氯亚砜分子逐步解离过程还观察到了协同解离过程.     

飞秒激光参数对非绝热耦合分子态布居的影响

利用含时波包法研究强飞秒泵浦-探测激光场中激光脉宽、波长和场强对非绝热耦合NaI分子各态布居的影响.波包在势能面上做周期性运动,周期约为1 000 fs.延时为200 fs时,波包第一次到达交叉区域分裂成两部分.波包在交叉区域的分裂情况影响各态布居.脉宽增长,NaI分子的激发概率增大,而解离概率减小.泵浦波长为共振波长318 nm时,激发概率最大.泵浦波长增长,NaI分子的解离概率减小.泵浦场强增大,激发概率增大,但解离概率不变.探测激光波长和场强不影响NaI分子各态布居分布.调节激光场参数可实现对波包运动的控制从而控制态布居的选择性分布.研究结果为实验上实现分子的光控制过程提供参考.     

OCS分子在207 nm的光解动力学研究:S(~1D_2)+CO(X~1∑~+)产物通道（英文）

利用直流时间切片离子成像技术对OCS分子在紫外波段207nm的光解产物S(~1D_2)进行了偏振实验研究.通过在两种不同的共振增强多光子电离中间态,~1F_3和~1P_1,以及四种不同的泵浦-探测激光偏振几何构型下探测了光碎片S(~1D_2)的角动量极化特性.使用分子坐标系极化模型和实验室坐标系各向异性模型提取和分析出对应产物CO(X~1∑~+)的角分布.观测到的总平动能释放谱表明解离过程存在三种解离通道,分别对应于低、中、高平动能解离通道.低、中平动能通道的来源与光解波长在较长波长下得到的双峰分布来源一致.高平动能通道是一种新的解离通道,它来自于单重排斥态A(2~1A')的直接解离.     

利用飞秒泵浦-探测技术对分子超快动力学过程研究的新进展

本刊讯 飞秒泵浦-探测技术是一种可以在原子运动时间尺度上实时观测化学反应的有力手段,在飞秒泵浦-探测技术基础上发展起来的分子超快动力学是当前分子反应动力学研究领域的热点和焦点之一。武汉国家光电实验室张冰团队一直从事分子超快动力学方面的研究。最近,该团队利用飞秒泵浦-探测技术与飞行时间质谱和光电子影像技术相结合,对碘甲烷分子的B带预解离超快动力学过程进行了研究并取得重大进展。     

飞秒时间分辨质谱方法研究CF3I光电离动力学

利用飞秒双色泵浦 探测 (pump probe)飞行时间质谱方法研究了CF3 I分子多光子电离动力学 ,所用泵浦光及探测光的中心波长分别为 2 6 5和 398nm .获得了母分子离子CF3 I+ 信号及其碎片离子CF3 + 和I+ 信号的寿命衰减常数分别为 (96± 7)、(198± 13)和 (16 7± 6 )fs.这些离子产生的多光子通道机理不同 :CF3 I来自 (1+2′)跃迁 ,单光子泵浦光与CF3 IA带共振 ;驭光子泵浦光激发CF3 I分子到 5 pπ7sδ(2 Π1/ 2 )里德伯态 ,单光子探测光电离产生的母分子离子解离产生CF3 + ;I+ 来自 (2 +2′)和 (1+1′ +2′)激发过程     

调Q激光光折变自适应光外差探测技术研究

基于光折变晶体中自泵浦与互泵浦相位共轭共存效应,利用新型光折变自适应光外差探测系统进行了调Q脉冲激光的光折变自适应光外差探测技术研究.结果表明,该系统可以用来实现单纵模调Q脉冲激光的自适应光外差探测,并可以通过提高本振光强度有效地提高外差探测灵敏度.进一步的实验和理论分析表明,对于一般的调Q脉冲激光,由于其各个纵模频谱分量之间不相关,难于实现光外差探测.     

飞秒泵浦-探测实验中量子拍频现象的数据处理

应用飞秒时间分辨的泵浦 探测技术结合飞行时间质谱的方法研究1,3 二氯苯分子光解离动力学过 程.对于泵浦 探测数据中的指数衰减过程及量子拍频现象选择合适的模型进行拟合,得到正确的光解动力学信 息.采用图形化编程语言LabVIEW编写程序,其中调用了LabVIEW数学分析程序包中的卷积、去卷积及Leven bergMarquardt最小二乘法拟合子程序等模块,对实验数据进行了处理,得到1,3 二氯苯的第一激发态S1的寿命. 同时也对反映量子相干现象的数据进行拟合,得到量子拍频的频率.     

飞秒时间分辨实验中泵浦-探测交叉相关函数的测量和时间零点的确定

飞秒激光技术的出现使得实时探测与跟踪激发态超快弛豫动力学过程成为可能,并能够给出激发态动力学过程清晰的物理图像。而在飞秒时间分辨实验中,泵浦-探测相关函数和时间零点直接影响实验结果的可靠性和准确性。本文结合飞秒激光在分子激发态超快动力学过程中的应用进展,介绍了根据实验条件和要求,在具体实验过程中泵浦-探测相关函数测量和时间零点确定的几种方法。实验中选择可见光作为泵浦光和探测光时,可以通过测定随泵浦-探测时间延迟变化的泵浦激光与探测激光的和频/差频光强来确定泵浦探测交叉相关函数和时间零点;而选择中心波长在紫外甚至真空紫外的激光脉冲作为泵浦光或探测光时,泵浦-探测交叉相关函数通常采用校正的方法测量。     

飞秒激光脉冲对N2分子非绝热准直的调控

介质内分子在飞秒激光场中的准直会诱导介质内部折射率发生变化并产生光谱调制效应.本文实验上采用泵浦-探测方法测量了N₂中探测光波长偏移量的时间演化,提取了N₂分子的准直度信息;理论上通过求解含时薛定谔方程,计算了分子非绝热准直的时间演化,探究了分子非绝热准直和克尔效应两种机制共同影响所诱导的双折射效应对探测光光谱的调制作用.实验和理论结果符合良好,证实了光谱测量法可以用来表征分子的准直度.进一步采用双脉冲泵浦方式对分子准直进行调控,发现双脉冲泵浦可以有效增强分子的准直度.通过调节双脉冲间的延迟时间,即在分子的一个转动恢复周期及半个转动恢复周期处引入第二束泵浦脉冲,可以分别控制分子准直的增强与消失,起到“准直开关”的作用.双脉冲调控方式同样适用于其他多个分子体系,具有一定的普适性.     

光纤中双宽带抽运SBS慢光及其脉冲展宽减小的理论研究

提出了一种单模光纤中采用双宽带抽运实现宽带受激布罩渊散射(SBS)慢光的方法.给出了双宽带抽运的SBS慢光及其脉冲展宽的理论模型.色散分析发现,两抽运光间存在一个最佳的频率间隔,可有效地减少由于群速度色散所引起的脉冲展宽.理论计算表明,该方案所获得的SBS增益带宽和信号脉冲群延迟分别提高到了相同条件下单宽带抽运的1.7倍和2倍.     

Comment on determination of electron temperature from Langmuir probe data in tokamak edge plasma

Langmuir probe measurements of electron temperature in a plasma in the limiter shadow of a tokamak are presented together with a method of probe data analysis which takes into account the influence of the ion current vs voltage dependence in the determination of electron temperature, The method is based on the transformation of a single into a double probe characteristic. Values of the electron temperature calculated using this method are compared with the values estimated from single probe characteristic data.     

Fano profile in a novel double cavity optomechanical system with harmonically bound mirrors

We investigate a double cavity optomechanical system generating single and double Fano resonance (multi-Fano). By altering a single parameter, the tunnelling rate g of the middle mirror, we are able to switch between single and double Fano line shapes. The first spectral line shape is stronger in the case of multi-Fano than in the case of single Fano. Also the behaviour of the steady state value of the displacement of the middle mirror, with respect to g, heavily influences the behaviour of double Fano lines in our scheme. This tunability along with using a single pump and signal/probe laser has an added advantage in situations where only low power consumption is available.     

Pump-probe optical response of an asymmetric double quantum dot molecule

We study the interaction of an asymmetric double semiconductor quantum dot molecule with a weak probe field and a strong pump field. We show that the optical properties of the system are controlled by a gate voltage and the pump field. For example, we find that the application of the pump field leads to controlled probe absorption, optical transparency, and gain for weak tunneling rates, while for stronger tunneling rates optical gain disappears and absorption spectra with double peaks are formed.     

A Method for the Ion Density Estimation from the Double Probe Data at Medium and Higher Pressures

In this article a method of estimation of the positive ion density from the double probe data is developed. In the presented method we suggest to use the single probe collisional model developed in [10]. The method itself can, however, use any ion/electron collection model and the pressure range of applicability of the method will then depend on the range of pressures within which the used particle collection model is valid. The application of the developed method is demonstrated on a sample of experimental double probe data and the ion density determined from these data is compared to the electron density estimated independently using the microwave diagnostic technique.     

Proposal for the measuring molecular velocity vector with single-pulse coherent Raman spectroscopy

Methods for simultaneous measurements of more than one flow velocity component using coherent Raman spectroscopy are proposed. It is demonstrated that using a kilowatt broad-band probe pulse (3–30 GHz) along with a megawatt narrow-band pump pulse (～100 MHz), coherent Raman signal resulting from a single laser pulse is sufficient to produce a high-resolution Raman spectrum for a velocity measurement.     

Transient Intersubband Optical Absorption in Double Quantum Well Structure

The microscopic equations of motion including many-body effects are derived to study the intersubband polarization in the double quantum well structure induced by an ultrafast pumping infrared light. Based on the self-consistent field theory, the transient probe absorption coefficient is calculated. These calculations are beyond the previous steady-state assumption. Transient probe absorption spectra are calculated under different pumping intensity and various pump probe delay.     

Diffractive heavy flavour production at the Tevatron and the LHC

We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading-order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant Q₂ dependence. We give numerical predictions for single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor.     

Femtosecond time-resolved absorption processes in lithium niobate crystals

Femtosecond pump pulses are strongly attenuated in lithium niobate owing to two-photon absorption; the relevant nonlinear coefficient beta(p) ranges from approximately 3.5 cm/GW for lambda(p) = 388 nm to approximately 0.1 cm/GW for 514 nm. In collinear pump-probe experiments the probe transmission at the double pump wavelength 2lambda(p) = 776 nm is controlled by two different processes: A direct absorption process involving pump and probe photons (beta (r) = 0.9 cm/GW) leads to a pronounced short-duration transmission dip, whereas the probe absorption by pump-excited charge carriers results in a long-duration plateau. Coherent pump-probe interactions are of no importance. Hot-carrier relaxation occurs on the time scale of < or approximately equal to 0.1 ps.