一种实现显微荧光寿命图的测量方法

将脉宽120fs、重复率76MHz激光引入激光扫描显微镜的激发光路,利用其扫描系统对荧光标记样品激发扫描,将激发出的荧光从荧光探测光路引入备用的外部探测口;在探测口接一快速光电倍增管,将光电倍增管的信号送给时间相关单光子计数器,获得时间相关的荧光强度图;最后通过计算机处理获得荧光寿命图。应用此系统对青色荧光蛋白(CFP)、黄色荧光蛋白(YFP)荧光寿命进行了测量,并应用CFP、YFP实现荧光共振能量转移的测量。通过实验看出利用已有的激光扫描显微镜,配合较先进的寿命测量方法,可以很好地实现显微荧光寿命图的测量。     

超短脉冲激光产生等离子体通道寿命研究

利用强飞秒激光在大气中产生等离子体通道内带电粒子的动力学模型,综合考虑二体吸附、三体吸附、离解和复合等因素,分析后续激光退吸附作用对等离子体通道寿命的影响,给出有效延长通道寿命的后续激光控制参量。计算表明,选择不同的激光注入形式和注入时间,对通道寿命的延长有着不同的效果,适当优化的激光可以延长通道寿命达25 s以上。     

超短脉冲激光产生等离子体通道寿命研究

利用强飞秒激光在大气中产生等离子体通道内带电粒子的动力学模型,综合考虑二体吸附、三体吸附、离解和复合等因素,分析后续激光退吸附作用对等离子体通道寿命的影响,给出有效延长通道寿命的后续激光控制参量。计算表明,选择不同的激光注入形式和注入时间,对通道寿命的延长有着不同的效果,适当优化的激光可以延长通道寿命达25 s以上。     

电子在超强激光场中的动力学特性

模拟研究了自由电子在超强激光场中的动力学特性,发现当场强高达Q=eE/m_ecω100时,电子动力学行为将出现全新的现象,其特征为描写激光束的有质动力势模型已完全不再适用,能量较低的电子有可能进入强场区,被光束所俘获,并被剧烈地加速.详细地讨论了这一俘获与加速的规律,指出这一新现象对发展远场激光加速器的意义. 关键词：     

基于不同泵浦波形的荧光寿命测量

该文从理论上分析了不同泵浦波形下的荧光衰减规律,提出了一种在不同泵浦波形下测量荧光寿命的新方法——双脉冲探测法,即利用探测泵浦脉冲与荧光衰减脉冲的方法测量荧光寿命。通过对样品钕玻璃及Cr:ZnSe晶体的荧光寿命测量表明:利用该方法在不同泵浦波形下能够实现可见及近红外到中红外激光介质的荧光寿命测量。因此,利用该测量方法能够方便、有效的避免通过解卷积求样品荧光寿命的繁琐过程,对测量激光介质在不同泵浦波形下的荧光寿命具有参考价值。     

高斯激光场中穿进轨道电子横向动量的阈值

采用数值模拟计算的方法,分析了强激光场中电子的动力学特性,发现穿进轨道电子的入射动量存在一定的阈值.通过研究穿进轨道电子的动力学特征,探讨了电子入射动量的阈值条件,发现与阈值相关的两个因素:激光强度和光束腰宽,推导了阈值的定标关系,结果显示:定标式与数值计算结果基本相符合.     

离子俘获的线性理论及其应用

从线性理论出发,研究了电子束团在储存环里均匀分布和束团串两种情况下离子俘获的条件;在离子系统里引入Twiss参量,推导出电子束团串俘获离子的阈值流强的公式;并以此讨论北京正负电子对撞机(BEPC)在同步辐射专用运行时观察到的电子束流现象,提出采用束团串运行来克服BEPC中的束流寿命下降.     

紧聚焦的超短超强激光脉冲在真空中加速斜入射的相对论电子

研究了紧聚焦的线偏振飞秒超强高斯激光脉冲俘获并剧烈加速斜入射低能相对论电子的效应 ，发现被俘获的电子在激光脉冲纵向有质动力的强大加速作用下，可以获得GeV量级的能量 ，并详细研究了入射电子的初能量、斜入射角、电子与激光脉冲的相对延迟时间和激光脉冲 宽度等条件对电子能量增益的影响，发现当激光脉宽超过10λ时，脉宽对电子能量增益影响 不大. 关键词： 电子加速 有质动力 能量增益 束腰     

空气中激光等离子体通道的荧光探测和声学诊断两种方法的比较实验研究

使用荧光探测和声学诊断两种方法，对超强飞秒激光脉冲在空气中传输形成的等离子体通道同时进行了测量.两种方法都很好地反映了等离子体通道的演化过程.对两种方法的比较研究发现，声学诊断相对于荧光探测方法来说，具有较高的灵敏度和空间分辨能力，实验装置也更简单，更适宜于等离子体通道的常规测量. 关键词： 强飞秒激光等离子体通道 荧光探测 声学诊断     

飞秒时间分辨实验中相关函数和时间零点的确定

结合飞秒激光在研究分子激发态弛豫动力学中的应用,介绍了几种飞秒时间分辨实验中确定泵浦激光脉冲与探测激光脉冲的相关函数和时间零点的方法.对于波长在可见波段的泵浦和探测激光脉冲,我们可以利用非线性光学的技术手段,探测泵浦光与探测光的和频光的强度随二者间的时间延迟的变化来确定相关函数和时间零点;对于波长在紫外甚至更短的波段的泵浦和探测激光脉冲,由于单脉冲能量比较低,目前还很难利用技术手段来测定泵浦激光与探测激光的相关函数及时间零点,可以利用某些原子气体(如Xe)或某些具有短寿命态的分子作平行实验进行间接测量.     

Laser stabilitron

We consider a new method for producing intensity stabilization of cw lasers. This method incorporates negative feedback from a nonlinear saturable absorber to provide wideband noise-reduction and may produce an output beam for which shot noise is below the quantum limit. This new method can be used with a large variety of cw lasers and is particularly applicable to frequency-stabilized lasers which are locked to absorption lines.Permanent address: Institute of Laser Physics, Novosibirsk 630090, Russia     

Laser applications in nuclear physics: Present and future

The use of lasers for nuclear physics research is widespread and growing rapidly. The major impact in nuclear structure research has come from nuclear size and shape determinations for nuclei far from stability via high resolution isotope shift measurements. In addition, systematic data on nuclear magnetic and quadrupole moments have been obtained via the hyperfine splitting resolved in laser fluorescence studies of atomic spectra in both stable and unstable systems. The tunability, high intensity and inherent polarization of laser light can be used to polarize atomic nuclei for nuclear reaction studies. The rapid efficient polarization of unstable nuclei with lasers also presents opportunities for new research in nuclear physics. In this paper the physics of the laser interaction for the studies indicated will be introduced. Some examples of work completed and in progress will be presented primarily from on-line laser studies at charged particle accelerators. Extensions of current research, particularly with respect to possible studies of short-lived nuclei, are discussed and the synergistic effects of certain advances in quantum electronics and nuclear physics described.     

Emission spectra of terahertz quantum cascade laser

We calculated energy levels, wave functions, and energies of radiative transitions in terahertz quantum cascade lasers based on GaAs/Al_0.15Ga_0.85As heterostructures. Current-voltage characteristics and current dependences of laser radiation intensity were measured, and the maximum operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade lasers were measured for different temperatures, and the effect of intensity “pumping” from low-frequency modes to high-frequency modes was found to happen in the case of an increase in the current and time delay of the signal capture, which is explained by heating of the sample during a pulse of the current. Application of the lasers for registration of impurity photoconductivity signals in semiconductor heterostructures was demonstrated.     

Dose estimation and shielding calculation for X-ray hazard at high intensity laser facilities

An ionizing radiation hazard produced from the interaction between high intensity lasers and solid targets has been observed. Laser-plasma interactions create "hot" electrons, which generate bremsstrahlung X-rays when they interact with ions in the target. However, up to now only limited studies have been conducted on this laser-induced radiological protection issue. In this paper, the physical process and characteristics of the interaction between high intensity lasers and solid targets are analyzed. The parameters of the radiation sources are discussed, including the energy conversion efficiency from laser to hot electrons, hot electron energy spectrum and electron temperature, and the bremsstrahlung X-ray energy spectrum produced by hot electrons. Based on this information, the X-ray dose generated with high-Z targets for laser intensities between 10¹⁴ and 10²⁰ W/cm² is estimated. The shielding effects of common shielding items such as the glass view port, aluminum chamber wall and concrete wall are also studied using the FLUKA Monte Carlo code. This study provides a reference for the dose estimation and the shielding design of high intensity laser facilities.     

Electron Acceleration by a radially polarised cosh-Gaussian laser beam in vacuum

In this paper, a radially polarised cosh-Gaussian laser beam(CGLB) is used to study the electron acceleration produced in vacuum. A highly energetic electron beam can be achieved by a CGLB,even with comparatively low-powered lasers. The properties of a CGLB cause it to focus earlier,over a shorter duration than a Gaussian laser beam, which makes it suitable for obtaining high energies over small durations. It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile. It is also observed that for a fixed value of energy gain, if the decentering parameter is increased, then the intensity of the laser field decreases. The dependence of the energy gained by electrons on the laser intensity and the laserspot size is also studied.     

影响AlGaN/GaN量子级联激光器性能的因素研究

在已有理论基础之上,采用严格的计算方法对激光器实现太赫兹(THz)波的辐射进行了可能性分析。利用传递矩阵法,通过Matlab软件计算了基于AlGaN/GaN材料体系的三能级量子级联激光器导带子能级与电子波函数的分布,详细分析了由该材料特有的极化效应所产生的极化场,得出了在近共振条件下偶极跃迁元、外加电场、垒层Al组分及导带子能级能级差之间的关系,并研究了它们对激光器性能的影响。分析结果表明,实现受激辐射的条件非常严格,Al组分取0.15或0.16时较为适宜,同时外加电场需大于63kV/cm,但不能过大,这样才能满足近共振条件,实现粒子数反转达到太赫兹量子级联激射。在Al组分为0.15,外加电场为69.0kV/cm时激光器的偶极跃迁元最大,表明跃迁几率也最大,对激光器的性能有利,可以为量子级联激光器构造较好的有源区。     

具有时间分辨能力的强流电子束束剖面测量系统

 高能强流电子束的束参数测量是加速器研制过程中重要的一项测量工作,由于光学渡越辐射具有时间响应快、分辨率高等特点而被用于测量电子束的具有时间分辨能力的束剖面、发散角、能量等多个参数;通过电子束束参数的时间分辨测量则能够了解电子束产生、输运中的问题,非常有利于加速器的研究与调试。一种具有时间分辨能力的、利用光学渡越辐射进行高能强流电子束束斑测量的系统在中国工程物理研究院被建立起来,并在12 MeV LIA的电子束束斑的测量中用于电子束传输研究,该系统拍摄图像的间隔时间最小为10 ns,最小的曝光时间为3 ns,具有一次可以拍摄8幅图像的能力,并获得了12 MeV LIA约100 ns内相应的时间分辨的束斑变化情况,观察到了一些过去未观察到的现象,为加速器的研究提供了又一个新测试方法。     

Surface photovoltage in semiconductors under sub-band-gap illumination: continuous distribution of surface states

Surface photovoltage spectra in semiconductors are analyzed when the sub-band-gap illumination induces the electron transitions from surface states to the conduction band under the assumption that distribution of surface states is continuous. From analysis performed it follows that the fictitious densities of surface states can be induced due to the wavelength dependence of the photoionization capture cross-section of surface states for electrons and by the electron recombination capture cross-section of surface states which depends on the energy position of surface states in the energy gap. The high illumination intensity (laser illumination), which makes completely empty the surface states, can eliminate the fictious surface states when the density of surface states is not very large, the temperature of measurements is low, and the surface potential barrier is high. Received: 24 June 1998 / Accepted: 29 March 1999 / Published online: 14 June 1999     

Process in high energy heavy ion acceleration

A review of processes that occur in high energy heavy ion acceleration by synchrotrons and colliders and that are essential for the accelerator performance is presented. Interactions of ions with the residual gas molecules/atoms and with stripping foils that deliberately intercept the ion trajectories are described in details. These interactions limit both the beam intensity and the beam quality. The processes of electron loss and capture lie at the root of heavy ion charge exchange injection. The review pays special attention to the ion induced vacuum pressure instability which is one of the main factors limiting the beam intensity. The intrabeam scattering phenomena which restricts the average luminosity of ion colliders is discussed. Some processes in nuclear interactions of ultra-relativistic heavy ions that could be dangerous for the performance of ion colliders are represented in the last chapter. The text was submitted by the author in English.     

I. Synchrotron radiation from the large electron-positron storage ring LEP

The properties of synchrotron radiation from LEP are investigated. This radiation from LEP are investigated. This radiation is assumed to be in a parasitic mode without changing any of the operating parameters. At 86 GeV the radiation from the normal bending magnet has a critical energy of 0.4 MeV and a power of ～500 W/m, and is probably of limited interest. High photon energies (10–20 MeV) of high intensity can be obtained from normal and superconducting wiggler magnets. Undulators can give quasi-monochromatic radiation of high brightness with photon energies of up to 5 MeV. New magnet developments might increase this energy range. Quasi-monochromatic γ-rays of ～100 MeV can be created with soft Compton back scattering without disturbing the electron bean. This relies on future free electron lasers in the submillimetre range. The natural collimation, the polarization and the time structure make all these photon beams unique tools for research in nuclear physics. The synchrotron rediation can be used to produced photoneutrons with intensities of up to 10¹⁴ neutrons/s. It is foreseen that LEP will be equipped with superconducting cavities in later stage and that is energy will be increased to ～130 GeV. This will approximately double the photon energies obtained from wigglers and undulators.