少周期强激光脉冲下氩原子的再碰撞激发电离

文章利用库仑修正的量子轨迹方法（Coulomb-corrected quantum-trajectories, CCQT）研究了氩（Ar）原子在少周期激光脉冲中的再碰撞激发电离（recollision excitation with subsequent ionization,RESI）过程。研究发现，随着光强的增大，Ar原子的动量关联分布逐渐由第二四象限向第一三象限转变，与实验结果吻合。分析表明，电子关联的转变主要是由于第一个电子返回时所携带的能量随光强变化造成的。     

高频强激光场中氢原子基态电离特性研究

本文采用相空间平均法详细研究了氢原子H的基态(1s)在外加高频强激光脉冲作用下的电离率及光电子角分布情况.侧重探讨了激光频率、偏振、脉冲长度和位相对原子电离的影响.研究发现,对超短脉冲,电离对激光场的位相非常敏感.根据激光脉冲上升沿和下降沿陡峭程度,提出了"位相模糊区"的概念,对基态氢原子电离特性的位相依赖给予了很好的区分和解释.     

联合双原子高次谐波发射的动力学研究

首先从经典理论出发,分析了一维普薛耳-特勒势(P-T势)模型原子在激光场作用下的动力学行为。进而设定联合双原子模型的核间距。然后利用一束特殊设定的双色激光脉冲辐照该模型,在保证原子有适当的电离和较大的复合效率的前提下,获得了截止位置远达Ip 8Up且效率高达10-9的高次谐波发射。最后给出了电离电子空间波包随时间的演化行为,并从波包动力学出发对谐波发射功率谱的形成机制给出了合理的解释。     

激光光斑面积对多光子电离离子产量的影响

研究了在激光脉冲能量和激光脉冲宽度一定时激光光斑面积对多光子电离离子产量的影响。得到了离子产量最高的条件即最佳探测条件，同时还讨论了激光光斑面积对探测中常用的多光子电离的离子产量影响的程度。结果表明，激光光斑面积对离子产量的影响与光强指数在l附近变化快慢有关，光强指数变化越快，激光光斑面积对离子产量的影响越大。     

反向旋转圆偏振双色激光场驱动下氩原子非顺序双电离研究

在经典系综模型下,研究了氩(Argon, Ar)原子在800 nm和400 nm反向旋转圆偏振双色(Counterrotating Circularly Polarized Two-Color, CRTC)激光场驱动下的非顺序双电离(Non-Sequential Double Ionization, NSDI)过程.理论分析了激光强度、双色场强度比、脉冲相对相位,以及激光脉冲宽度等光场参数对非顺序双电离机制及其量子产率的影响,得到了双电子能量的时间演化谱;发现并分析了两种不同的非顺序双电离机制;讨论了电子返回碰撞能对不同非顺序双电离过程的影响.     

钴原子激发态光电离的实验研究

文章报道了在300-310nm波长范围内3d过渡金属Co原子共振增强多光子电离(REMPI)的实验研究结果.实验中采用激光烧蚀和高压脉冲超声分子束相结合的技术制备等离子体,获得的等离子体与探测激光作用形成光电离产物,由飞行时间质谱仪对光电离产物进行甄别.通过分析光电离产物产额随探测激光强度的变化关系,得到了Co原子激发态的绝对光电离截面.     

激光光斑面积对多光子电离离子产量的影响

研究了在激光脉冲能量和激光脉冲宽度一定时激光光斑面积对多光子电离离子产量的影响。得到了离子产量最高的条件即最佳探测条件 ,同时还讨论了激光光斑面积对探测中常用的多光子电离的离子产量影响的程度。结果表明 ,激光光斑面积对离子产量的影响与光强指数在 1附近变化快慢有关 ,光强指数变化越快 ,激光光斑面积对离子产量的影响越大     

钙原子二步三光子与三步三光子共振电离研究

激光共振电离光谱技术是痕量分析中的重要手段之一。本以速率方程理论为基础，对钙原子的激光共振电离过程进行了分析，通过编程对该原子的二步单色三光子和三步三色三光子非饱和激发电离过程进行模拟，得到了相应的电离效率与激光的能量、作用时间之间的关系曲线，并对这2种电离方案进行了比较。     

kHz 脉冲分子束的产生及其在强场原子分子物理实验中的应用

采用悬臂压电脉冲阀, 制备出最高重复频率达到3 kHz 的脉冲分子束。通过测量氮气分子束在飞秒激光作用下隧道电离生成的N2 +(B-X)荧光光谱, 对脉冲阀的性能做了表征。这种kHz 脉冲分子束搭配kHz 飞秒激光器, 将推动飞秒强激光驱动的原子分子动力学实验研究。     

信号直接调制色泵噪声的单模激光光强涨落

应用线性化近似方法计算了信号直接调制方式下由具有色关联的色泵噪声和色量子噪声驱动的单模激光增益模型的光强相对涨落，分析了噪声和调制信号等参量对光强相对涨落的影响，结果表明，泵噪声自相关时间与量子噪声自相关时间及其比值对光强相对涨落起到重要的作用．     

双电极对TEACO2激光器解码系统设计

双电极对脉冲TEACO2激光器具有增益高，输出能量大等特点，特别是在不需要高真空条件下可获得时间间隔连续可调的2个高强度光脉冲对。利用电光普克尔盒对双光束脉冲对进行脉冲编码，使其产生交替的左旋及右旋偏振光，在此基础上，设计双光束解码系统。该系统在目标识别、大气环境监测、激光冷却原子等应用中具有重要的价值.     

Attosecond control of electrons emitted from a nanoscale metal tip

Attosecond science is based on steering electrons with the electric field of well controlled femtosecond laser pulses. It has led to the generation of extreme-ultraviolet pulses with a duration of less than 100 attoseconds (ref. 3; 1 as = 10(-18) s), to the measurement of intramolecular dynamics (by diffraction of an electron taken from the molecule under scrutiny) and to ultrafast electron holography. All these effects have been observed with atoms or molecules in the gas phase. Electrons liberated from solids by few-cycle laser pulses are also predicted to show a strong light-phase sensitivity, but only very small effects have been observed. Here we report that the spectra of electrons undergoing photoemission from a nanometre-scale tungsten tip show a dependence on the carrier-envelope phase of the laser, with a current modulation of up to 100 per cent. Depending on the carrier-envelope phase, electrons are emitted either from a single sub-500-attosecond interval of the 6-femtosecond laser pulse, or from two such intervals; the latter case leads to spectral interference. We also show that coherent elastic re-scattering of liberated electrons takes place at the metal surface. Owing to field enhancement at the tip, a simple laser oscillator reaches the peak electric field strengths required for attosecond experiments at 100-megahertz repetition rates, rendering complex amplified laser systems dispensable. Practically, this work represents a simple, extremely sensitive carrier-envelope phase sensor, which could be shrunk in volume to about one cubic centimetre. Our results indicate that the attosecond techniques developed with (and for) atoms and molecules can also be used with solids. In particular, we foresee subfemtosecond, subnanometre probing of collective electron dynamics (such as plasmon polaritons) in solid-state systems ranging in scale from mesoscopic solids to clusters and to single protruding atoms.     

Observation of coherent optical information storage in an atomic medium using halted light pulses

Electromagnetically induced transparency is a quantum interference effect that permits the propagation of light through an otherwise opaque atomic medium; a 'coupling' laser is used to create the interference necessary to allow the transmission of resonant pulses from a 'probe' laser. This technique has been used to slow and spatially compress light pulses by seven orders of magnitude, resulting in their complete localization and containment within an atomic cloud. Here we use electromagnetically induced transparency to bring laser pulses to a complete stop in a magnetically trapped, cold cloud of sodium atoms. Within the spatially localized pulse region, the atoms are in a superposition state determined by the amplitudes and phases of the coupling and probe laser fields. Upon sudden turn-off of the coupling laser, the compressed probe pulse is effectively stopped; coherent information initially contained in the laser fields is 'frozen' in the atomic medium for up to 1 ms. The coupling laser is turned back on at a later time and the probe pulse is regenerated: the stored coherence is read out and transferred back into the radiation field. We present a theoretical model that reveals that the system is self-adjusting to minimize dissipative loss during the 'read' and 'write' operations. We anticipate applications of this phenomenon for quantum information processing.     

高功率可调谐超短激光脉冲

用高重复频率的准分子(Xecl)激光器泵浦染料可调谐激光器的腔倒空输出,进行二级超短脉冲放大。染料可调谐激光器是由锁模氩离子激光器泵浦,得到了峰值功率为8.5Mw,脉冲重复频率100Hz,波长从5780(?)到6150(?)可连续调谐,脉宽为微微秒的激光输出。     

利用动力学去耦合脉冲增大和调节量子相干性和三体纠缠

本文研究了动力学去耦合脉冲对腔量子电动力学系统中量子相干性, 量子失谐和量子纠缠的影响, 发现动力学去耦合脉冲不仅能够增大系统中两原子之间的量子相干性, 同时也能增大它们之间非经典关联（量子失谐和量子纠缠）. 同时, 凭借迹距离的方法, 探讨了动力学去耦合脉冲增大两原子之间量子相干性的原因, 通过探究可以看出动力学去耦合脉冲能够控制和加速量子信息从其他子系统回流到两个原子中去, 并减少两原子子系统和其他子系统之间的量子信息流动, 从而增加两原子间的量子相干性和非经典关联. 最后, 利用保真度的方法研究了系统中三体纠缠出现的情况, 结果显示在不同的时间, 系统中会出现三体纠缠, 特别值得指出的是, 可以通过动力学去耦合脉冲来调节和增加系统中三体纠缠出现的时间.     

脉冲对激发的上能级布局振荡

引入时间演化算符，证明均匀增宽二能级体系在飞秒激光脉冲对作用下上能级激发态布居是周期性变化的，它以飞秒脉冲对之间的延时为时间轴，以该原子能级之间的跃迁频率为振荡频率。     

Atomic transient recorder

In Bohr's model of the hydrogen atom, the electron takes about 150 attoseconds (1 as = 10(-18) s) to orbit around the proton, defining the characteristic timescale for dynamics in the electronic shell of atoms. Recording atomic transients in real time requires excitation and probing on this scale. The recent observation of single sub-femtosecond (1 fs = 10(-15) s) extreme ultraviolet (XUV) light pulses has stimulated the extension of techniques of femtochemistry into the attosecond regime. Here we demonstrate the generation and measurement of single 250-attosecond XUV pulses. We use these pulses to excite atoms, which in turn emit electrons. An intense, waveform-controlled, few cycle laser pulse obtains 'tomographic images' of the time-momentum distribution of the ejected electrons. Tomographic images of primary (photo)electrons yield accurate information of the duration and frequency sweep of the excitation pulse, whereas the same measurements on secondary (Auger) electrons will provide insight into the relaxation dynamics of the electronic shell following excitation. With the current approximately 750-nm laser probe and approximately 100-eV excitation, our transient recorder is capable of resolving atomic electron dynamics within the Bohr orbit time.     

Direct observation of electron dynamics in the attosecond domain

Dynamical processes are commonly investigated using laser pump-probe experiments, with a pump pulse exciting the system of interest and a second probe pulse tracking its temporal evolution as a function of the delay between the pulses. Because the time resolution attainable in such experiments depends on the temporal definition of the laser pulses, pulse compression to 200 attoseconds (1 as = 10(-18) s) is a promising recent development. These ultrafast pulses have been fully characterized, and used to directly measure light waves and electronic relaxation in free atoms. But attosecond pulses can only be realized in the extreme ultraviolet and X-ray regime; in contrast, the optical laser pulses typically used for experiments on complex systems last several femtoseconds (1 fs = 10(-15) s). Here we monitor the dynamics of ultrafast electron transfer--a process important in photo- and electrochemistry and used in solid-state solar cells, molecular electronics and single-electron devices--on attosecond timescales using core-hole spectroscopy. We push the method, which uses the lifetime of a core electron hole as an internal reference clock for following dynamic processes, into the attosecond regime by focusing on short-lived holes with initial and final states in the same electronic shell. This allows us to show that electron transfer from an adsorbed sulphur atom to a ruthenium surface proceeds in about 320 as.     

激光脉宽对椭偏光驱动的原子次序双电离的影响

利用经典模型,研究了激光脉宽对椭偏光驱动的Ar原子次序双电离(SDI)的影响.结果发现,二价离子动量分布强烈地依赖于激光脉宽.随激光脉宽增加,离子动量分布从二带结构变为四带结构,然后又变为六带结构.向后分析双电离轨迹既显示了椭偏光驱动的原子次序双电离中的亚周期电子出射现象,又表明带状结构随激光脉宽的演化取决于第二个电子电离时间随激光脉宽的变化.     

里德堡钾原子在超高斯脉冲激光场中的量子跃迁

用含时多态展开方法,计算了超高斯脉冲激光场中里德堡钾原子两个Stark态21 s与19 f之间的量子跃迁情况.结果表明这两个Stark态之间的跃迁几率与超高斯激光场的初始振幅、脉冲形状参数m和脉冲半宽度有关;在m等于3和m等于4时,当激光场初始振幅和半宽度取合适值时,可以实现这两个Stark态之间布居数的较大跃迁,并实现终态囚禁.