飞秒激光脉冲压缩用啁啾镜新设计方法

对配对啁啾镜传统的优化过程进行了改进,并且尝试了新的多个啁啾镜匹配的方法。理论上实现了在700～1050 nm光谱范围内,两个啁啾镜配对色散总和振荡小于±10 fs2,三个啁啾镜配对色散总和振荡小于±15 fs2。此配对啁啾镜所实现的精确补偿色散,是获得极短光脉冲的基础,可以用于飞秒激光的脉冲压缩。     

一种新型的利用重构等效啁啾超结构光纤光栅消啁啾技术研究

提出了一种利用重构等效啁啾超结构光纤光栅对啁啾光脉冲进行频域消啁啾和时域脉宽压缩的方法.由于重构等效啁啾技术可实现任意物理可实现滤波特性的光纤光栅,因此所提出的新型消啁啾方法可以针对任意啁啾模型的脉冲.仿真结果表明,对于脉宽为20 ps,啁啾系数为-5,啁啾模型为线性、高斯型、洛仑兹型的啁啾高斯脉冲,其被消啁啾后时间带宽积分别由初始的225,265,250下降到0458,0708,0731,脉宽压缩效果明显.针对商业软件给出的增益开关分布反馈半导体激光器输出光脉冲的模型,实际制作相应的重构等效 关键词： 重构等效啁啾 光纤光栅 啁啾 增益开关分布反馈半导体激光器     

高斯脉冲在半导体光放大器中传输的解析表征

采用解析方法,在考虑材料损耗和色散的情况下,详细研究了无啁啾高斯脉冲和啁啾高斯脉冲在半导体光放大器中传输的物理过程,分析了强度增益、脉冲宽度和频率啁啾与线宽增强因子、色散系数、小信号增益特征参数及初始啁啾之间的关系。结果表明:当输入变换极限的高斯脉冲时,色散会引起增益压缩,脉冲展宽和频率啁啾;同样情况下,线宽增强因子越大,脉宽加宽越明显,输出脉冲啁啾越大,且随着线宽增强因子的增大,输出脉冲啁啾极大值向特征参数值较小的一边移动。当输入啁啾高斯脉冲时,初始脉冲啁啾越大,增益压缩越明显,啁啾系数为正时,脉冲单纯展宽,输出啁啾随特征参数的增大而逐渐减小,啁啾系数为负时,初始啁啾与群速度色散导致的啁啾相互竞争,致使脉冲先被压缩后被展宽;脉冲最窄处对应的特征参数随线宽增强因子的增大而先增大后减小,输出啁啾随特征参数的增大而经历振荡后趋于平稳。     

能量啁啾电子束自由电子激光放大啁啾脉冲

 提出采用具有能量啁啾电子束的自由电子激光放大器放大啁啾脉冲,分析说明了它的工作机理和滑移现象对其的影响。采用研制的1维非定态程序GOFEL-P,对能量啁啾自由电子激光放大器放大啁啾脉冲的过程进行了数值模拟和分析,计算了不同啁啾参数的脉冲被放大后的腔外压缩情况。结果表明：与单能电子束时相比,能量啁啾自由电子激光可以放大具有更大啁啾参数的啁啾脉冲,使压缩后的脉冲峰值功率增大至568 GW,脉冲宽度缩短至2.29 fs,大幅增强自由电子激光放大啁啾脉冲以及腔外压缩脉冲的效果。     

用干涉自相关导数谱图明确超短脉冲啁啾方向

提出了新型的确定超短激光脉冲啁啾方向的方法,采用对二次十涉自相关(IAC)中的基频信号求一阶导数,得到干涉自相关导数谱图(D-IAC).利用该导数谱图对啁啾方向有很高灵敏度的特性,通过对高斯型强度分布的线性啁啾、平方啁啾及立方啁啾脉冲进行数值计算与模拟,得到导数谱图的峰与谷分别对应啁啾的负与正.找到了判定啁啾正负的方向因子,即正弦函数因子,并通过实验证实用十涉自相关导数谱图可明确超短激光脉冲啁啾方向,且干涉白相关导数谱图能用丁超短激光脉冲啁啾方向的检测.     

高功率钕玻璃啁啾脉冲放大系统光谱整形

增益窄化效应限制了啁啾脉冲放大系统输出的最短脉冲宽度,需要对注入放大系统的种子啁啾脉冲进行光谱整形,以保证放大后的啁啾脉冲光具有足够的带宽并满足特定的光谱分布.理论上假定放大后啁啾脉冲的光谱分布为高斯分布或超高斯分布,对"百焦耳级钕玻璃啁啾脉冲放大系统"进行逆运算.研究发现,所需种子啁啾光的能量、带宽以及压缩后脉冲的信噪比都与该分布密切相关.通过光谱整形,使放大后的啁啾脉冲光的光谱分布为二阶超高斯分布.能够获得小于400 fs高信噪比的超短脉冲输出,此时所需种子啁啾脉冲能量仅为33μJ,带宽14 nm,在装置前级注入能力的范围之内.为百焦耳装置光谱整形实验的开展提供了理论指导.     

负五阶非线性下预啁啾高斯光脉冲的啁啾和频谱

为探究光纤负五阶非线性和光脉冲预啁啾对高斯光脉冲频率啁啾和频谱的综合影响,在忽略光纤色散的情况下,利用包含三五阶非线性的扩展非线性薛定谔方程,计算和分析了啁啾高斯脉冲的频谱和总啁啾。结果表明,脉冲无预啁啾时,负五阶非线性的存在可使脉冲频率啁啾的形状由单“S”形变为双“S”形,并使脉冲的中心附近由正啁啾变为负啁啾。此外,负五阶非线性的存在使预啁啾对脉冲频谱的影响发生了较大的变化。预啁啾与非线性所致啁啾叠加后对脉冲频谱的谱峰数目影响较小,而对能量在各个谱峰上的分布影响较大,在某些最大非线性相移下,甚至会出现总啁啾减小使谱峰值数目增加的情况。该研究对光开关、光脉冲压缩以及光纤通信系统等领域的深入发展具有一定的指导意义。     

500 nm带宽啁啾镜对的设计与应用

设计了中心波长在825 nm、有效带宽在600 nm～1100 nm的超宽带啁啾镜对,色散补偿量目标值为-100 fs2。配对设计的啁啾镜对有效抑制了单个啁啾镜的色散振荡,啁啾镜对色散振荡幅度的最大值为50 fs2,用设计制作的啁啾镜对进行色散补偿,用频率分辨光学开关测量装置对脉冲进行测量。将10.3 fs的超短脉冲通过0.5 mm厚的LBO晶体,色散效应导致脉冲展宽,半峰值处的全宽度为39.6 fs,实验结果表明,经过啁啾镜对一次色散补偿后的脉冲形状,半峰值处得全宽度为11.6 fs;脉冲经过2次补偿后,脉冲被压缩到10.7 fs。     

脉冲啁啾对于阿秒脉冲的影响

采用单电子近似和软核势模型, 通过数值求解一维含时薛定谔方程, 理论研究了当脉冲分别带有正、负啁啾的情况下所产生的阿秒脉冲.分析了不同脉冲啁啾特性对阿秒脉冲的强度和宽度的影响. 研究结果表明, 无论是正啁啾还是负啁啾, 随着啁啾量的增加, 都将使激光脉冲由产生单个阿秒脉冲趋向于产生阿秒脉冲链. 正啁啾和负啁啾对于阿秒脉冲宽度的影响是不同的, 负啁啾对于阿秒脉冲宽度影响很小, 适当的负啁啾有利于缩小阿秒脉冲的宽度; 而正啁啾脉冲产生的阿秒脉冲较无啁啾时展宽, 且随着啁啾量的增加, 其阿秒脉冲宽度迅速增大.     

三五阶非线性下啁啾超高斯脉冲的啁啾和频谱

利用三五阶非线性效应下的扩展非线性薛定谔方程,在忽略光纤色散的情况下,计算模拟了以二阶情形为例的啁啾超高斯光脉冲的啁啾和频谱。结果表明,脉冲无预啁啾时,正五阶非线性增大啁啾量,负五阶非线性在减小啁啾量的同时还改变啁啾曲线的形状。当预啁啾与五阶非线性系数同(异)号时,总啁啾增加(减小)。随着超高斯脉冲阶次的增大,总啁啾量增大,脉冲中心附近无啁啾的范围变宽,整个有啁啾的范围变小,总啁啾中预啁啾所占比重增大。脉冲无预啁啾时,正负五阶非线性分别可以增大和减小频谱展宽。预啁啾若增强非线性所致啁啾,则可能使频谱峰值结构加强,谱峰数目增多。当超高斯光脉冲的阶次或最大非线性相移增大时,在某些宽大的频谱峰上还可能出现许多精细谱峰。     

Double-mode electrostatic dispersing prism for electron pulse time-domain compression

The generalized theory of double-mode electrostatic dispersing prism for time-domain compressing electron pulse is presented. The fundamental difference between the two modes of o mode and e mode lies in the dispersive dependence of electron's time of flight on its initial kinetic energy at prism entrance: the electrons with higher initial axial energy definitely have longer time of flight for o mode, while not the case for e mode, which results from the electron pulse's U-shaped motion in the prism. The dispersive dependence of time of flight constitutes the mechanism of electron pulse compression for each mode. An example is given to demonstrate the issue of parameter choosing for the prism and to verify its tunable performance of compression.     

两电极静电同心球系统的近轴电子光学及其空间-时间像差

将从近轴解出发研究两电极静电同心球系统的空-时轨迹及其像差.由近轴轨迹方程和近轴运动方程出发,先求解两电极静电同心球系统中自光阴极逸出的运动电子的近轴空间-时间轨迹,然后讨论此系统的静动态电子光学及其空间-时间像差,揭示近轴光学系统成像的一般规律.文中定义和推导了各级近轴空间像差和近轴时间像差,得到了与关于近轴空间-时间像差同样的结论,表明完全可以直接由近轴轨迹方程和近轴运动方程出发来研究理想成像及其空间-时间像差.     

两电极静电同心球系统的成像电子光学及其空间-时间像差

基于实际轨迹方程和电子运动方程对两电极静电同心球系统求解由光阴极逸出的运动电子的空间和时间轨迹,推导成像位置和电子飞行时间的精确和近似表达式,并由空间和时间轨迹的解析解出发讨论系统的空间-时间特性.对空间像差和时间像差给出统一的定义,即横向像差可视为近轴横向像差和几何横向像差的合成,时间像差可视为近轴时间像差和几何时间像差的合成,并导出了所有相应的像差表示式.     

Static and dynamic imaging electron optics and spatial-temporal aberrations in a bi-electrode spherical concentric system with electrostatic focusing

In imaging electron optics, for a concentric spherical system composed of two spherical electrodes with electrostatic focusing, the electrostatic potential distribution and the spatial-temporal trajectory of electron motion can be expressed by analytical forms. It is naturally to take such system as an ideal model to investigate the imaging properties, as well as the spatial-temporal aberrations, to analyze its particularity and to find the clue of universalities and regularities. Research on this problem has important significance, which can afford theoretical foundation not only in studying static electron optics for the night vision devices, but also in studying dynamic electron optics for high-speed image converter tubes.In the present paper, based on the practical electron ray equation and electron motion equation for a bi-electrode concentric spherical system with electrostatic focusing, the spatial-temporal trajectories of moving electrons emitted from the photocathode have been solved, the exact and approximate formulae for image position and flight time of electrons, have been deduced. Start from solutions of spatial-temporal trajectories, the electron optical spatial-temporal properties of this system are then discussed. According to the definitions of spatial-temporal aberrations, the paraxial and geometrical lateral aberrations, as well as the paraxial and geometrical temporal aberrations, have been deduced, that are classified by the order of and .     

Opto-Mechanical Effects in Superradiant Light Scattering by Bose-Einstein Condensate in an Optical Cavity

We investigate the effects of a movable mirror (cantilever) of an optical cavity on the superradiant light scattering from a Bose-Einstein condensate (BEC) in an optical lattice. We show that the mirror motion has a dynamic dispersive effect on the cavity-pump detuning. Varying the intensity of the pump beam, one can switch between the pure superradiant regime and the Bragg scattering regime. The mechanical frequency of the mirror strongly influences the time interval between two Bragg peaks. We find that when the system is in the resolved side band regime for mirror cooling, the superradiant scattering is enhanced due to coherent energy transfer from the mechanical mirror mode to the cavity field mode.     

Design of a mirror aberration corrector and a beam separator for LEEM

A SPLEEM (spin polarized low energy electron microscope) has been designed with a numerical simulation of electrostatic and magnetic field distributions and electron ray trajectories. Highly (more than 90%) spin polarized electron source has been used. A Wien type spin manipulator and a magnetic lens type spin rotator are used to align spin direction. A magnetic field free objective lens is designed to observe magnetic domain structure of magnetic materials. High or low magnification mode can be selected by using a combined electrostatic and magnetic objective lens for a high spatial resolution and a wide imaging area observation. An electrostatic mirror aberration corrector is installed after the image forming objective lens. A double deflection 45° beam separator is used to bend the direction of electrons from the source to the objective lens and from the objective lens to the mirror aberration corrector.     

Opto-Mechanical Effects in Superradiant Light Scattering by Bose-Einstein Condensate in an Optical Cavity

We investigate the effects of a movable mirror (cantilever) of an optical cavity on the superradiant light scattering from a Bose-Einstein condensate (BEC) in an optical lattice. We show that the mirror motion has a dynamic dispersive effect on the cavity-pump detuning. Varying the intensity of the pump beam, one can switch between the pure superradiant regime and the Bragg scattering regime. The mechanical frequency of the mirror strongly influences the time interval between two Bragg peaks. We find that when the system is in the resolved side band regime for mirror cooling, the superradiant scattering is enhanced due to coherent energy transfer from the mechanical mirror mode to the cavity field mode.     

Optical “visualization” of Pythagorean triples and electrostatic multipoles in quantum dash

The problem of the features of the electron energy spectrum in a quantum parallelepiped has been considered. The family of triply degenerate energy levels has been found for the chosen model of the quantum parallelepiped. The optical transitions in this system has been investigated. It has been established that primitive Pythagorean triples are in the basis of every family of triply degenerate levels and this fact is directly reflected on the optical properties of the quantum dashes. In particular, due to the selection rules for the electronic transitions, it is possible to "visualize" Pythagorean triples theoretically. The dependence of absorption coefficient on the incident photon energy of quantum dash ensemble has been studied. The dipole, quadrupole moments and the electrostatic field created by the electron localized in a quantum dash have been investigated.     

Pulse compression of a high-order harmonic

The fifth harmonic pulses of an intense femtosecond Ti:sapphire laser were experimentally shown to be negatively chirped by using an LiF plate as a positive dispersive medium. The chirp of the harmonic pulse originates from the intensity-dependent atomic dipole phase, which is estimated to be proportional to 25 U_p, where U_p is the ponderomotive energy. Consequently, we have succeeded in compressing the chirped pulses to 13 fs by compensating the intrinsic negative chirp. Chirp effects of the fundamental laser on the pulse width of the fifth harmonic were consistent with the negative chirp of the fifth harmonic.     

Ionisation of Rydberg hydrogen atom near a metal surface by short pulse laser

In the ionisation of Rydberg hydrogen atoms near a metal surface,the electron will escape from the nucleus and arrive at the detector in a time sequence.This probability flux train relies on the initial electron wave packet irradiated by the laser pulse.For simplicity,the laser pulse is usually simplified to a delta function in energy domain,resulting in a sharp initial arrival time with an exponentially decaying tail at the detector.Actually and semiclassically,the initial outgoing wave should be modeled as an ensemble of trajectories propagating away from the atomic core in all directions with a range of launch times and a range of energies.In this case,each pulse in the pulse train is averaged out rather than a sharp profile.We examine how energy and time averaging of the electron wave packet affects the resolution of escaping electron pulses and study the energy dependence of the arrival time for each pulse in the ionisation train.An optimization condition for the laser pulse shape to generate narrow ionisation electron pulse in the train is obtained.The ionisation rates with various excitation energy are calculated also,which show the excitation to higher N Rydberg states will narrow the electron pulse as well.