基于可调谐静电啁啾镜的电子脉冲压缩技术

分析了基于双级反射静电系统的电子脉冲压缩技术方法。类比于光子脉冲压缩用多层介质啁啾镜, 将该静电系统称为可调谐静电啁啾镜：根据静电啁啾镜电气结构参数的设置, 入射电子脉冲在系统中U形反射运动飞行时间与其初始轴向能量具有相应不同的色散关系, 也即正负啁啾特性。讨论了该啁啾镜正负啁啾属性的可调谐性及脉冲压缩技术细节, 并给出了计算实例。     

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。     

基于高非线性微结构光纤环镜的脉冲压缩与基座抑制

提出了利用一种高非线性微结构光纤构成非线性光纤环镜（NOLM）进行脉冲压缩和基座抑制的方案.所提出的微结构光纤具有高非线性系数和大反常色散.理论研究了基于这种微结构光纤的NOLM对脉冲的压缩效应,并分析了压缩的机制.数值结果表明,这种NOLM采用较短的光纤长度就能有效地压缩脉冲并明显抑制了基座.对于给定的输入脉冲,存在一个最优的环路长度,可以获得高质量的压缩脉冲.通过适当选择耦合比和环路长度,则可以完全消除脉冲的基座.     

基于非线性啁啾光纤光栅实现的色散可调谐

从原理上证明了一种基于非线性啁啾光纤光栅以及光纤光栅的温度特性的色散可调谐方案.实验证明在25.5℃的温度变化范围内,光纤光栅对1550.43nm波长的色散补偿量从759.1ps/nm上升到1659.9ps/nm,色散调谐范围达到900ps/nm,这个方案具有对补偿波长和特定补偿波长所需要的色散补偿量同时进行调谐的特点.     

基于半导体光放大器的光脉冲压缩方案的研究

对一种基于半导体光放大器(SOA)和普通单模光纤的光脉冲压缩方案进行了理论分析和实验验证.建立了该方案的理论分析模型,并在此基础上数值模拟了光脉冲的传播过程.计算结果表明,通过合理选取单模光纤的长度,可使50 ps光脉冲压缩到5 ps.实验表明利用普通单模光纤群速度色散导致的脉冲啁啾抵消SOA自相位调制引起的脉冲啁啾,实现了色散补偿及脉冲压缩.     

利用色散渐减光纤获得线性啁啾抛物线脉冲的研究

以利用双曲渐减的正常色散渐减光纤(ND-DDF)获得啁啾抛物线脉冲为基础,进一步利用对称分布傅立叶的数值方法,研究了其它色散渐减的ND-DDF获得啁啾抛物线脉冲的情况.数值研究的结果表明:在采用不同的色散渐减时,如线性、指数、高斯、余弦、双曲等,最终输出的脉冲均具有较好的线性啁啾,且基本符合抛物线形状,这说明在利用ND-DDF获得啁啾抛物线脉冲时色散渐减方式可灵活选择;同时结果还显示,色散渐减的方式导致所得脉冲的啁啾强度、以及脉冲宽度和峰值功率会有所差异;文章最后给出了不同情况下抛物线脉冲经啁啾补偿后的输出脉冲形状和压缩因子.     

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。     

基于啁啾镜色散补偿技术的超宽带飞秒激光脉冲

在精确计算包括空气在内的钛蓝宝石激光器腔内色散的基础上，通过合理选取啁啾反射镜，直接用简单的四镜腔结构获得了光谱覆盖540—1030nm波段的超连续激光光谱.进一步探讨分析了实现超过一个倍频程光谱宽度的有关物理与技术. 关键词： 超连续 啁啾镜 飞秒     

基于脉冲形成线充电的脉冲压缩技术

利用脉冲压缩技术,将具有一定初始电压的高阻抗长脉冲形成线对低阻抗短脉冲形成线充电到一定值时,其输出开关导通,在其后的传输线上可以产生高功率短脉冲。给出了脉冲压缩理论分析;前级脉冲驱动源采用GW级纳秒脉冲形成线,其特性阻抗为40 、电长度为3.9 ns,输出脉冲宽度约8 ns;研制了与前级脉冲驱动源匹配的脉冲压缩装置和变阻抗传输线,考虑到脉冲压缩装置低阻抗形成线绝缘击穿和开关导通限制,选取脉压装置形成线特性阻抗6.5 、电长度0.5 ns。利用GW级纳秒脉冲驱动源开展了脉冲压缩实验,得到了输出功率增益达4倍左右的脉宽1.5 ns高功率短脉冲,输出脉冲功率增益与理论值基本相符。     

基于脉冲形成线充电的脉冲压缩技术

利用脉冲压缩技术,将具有一定初始电压的高阻抗长脉冲形成线对低阻抗短脉冲形成线充电到一定值时,其输出开关导通,在其后的传输线上可以产生高功率短脉冲。给出了脉冲压缩理论分析;前级脉冲驱动源采用GW级纳秒脉冲形成线,其特性阻抗为40Ω、电长度为3.9ns,输出脉冲宽度约8ns;研制了与前级脉冲驱动源匹配的脉冲压缩装置和变阻抗传输线,考虑到脉冲压缩装置低阻抗形成线绝缘击穿和开关导通限制,选取脉压装置形成线特性阻抗6.5Ω、电长度0.5ns。利用GW级纳秒脉冲驱动源开展了脉冲压缩实验,得到了输出功率增益达4倍左右的脉宽1.5ns高功率短脉冲,输出脉冲功率增益与理论值基本相符。     

Compressing ultrafast electron pulse by radio frequency cavity

An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10~5 can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.     

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.     

Sensitive ultrashort pulse chirp measurement

The chirp of an ultrashort laser pulse can be extracted with high accuracy from a modified spectrum auto-interferometric correlation waveform by using a new time domain algorithm that allows signal averaging. We display results revealing high sensitivity to chirp even with signal-to-noise levels approaching unity. Correction algorithms have been developed to accommodate signal distortion arising from bandwidth limitations, interferometer misalignment, and nonquadratic detector response.     

Normal-incidence electrostatic Rydberg atom mirror

A Rydberg atom mirror has been designed and its operational principle tested experimentally. A supersonic expansion containing H atoms moving with a velocity of 720 m/s initially propagates toward a quadrupolar electrostatic mirror. The H atoms are then photoexcited to n=27 Rydberg states with a positive Stark shift and move in a rapidly increasing electric field. The H atom beam is stopped in 4.8 micros, only 1.9 mm away from the photoexcitation spot, and is then reflected back. The reflection process is monitored by pulsed field ionization and imaging.     

多电极静电拉伸薄膜反射镜的光学检测

利用研制的φ300 mm口径多电极薄膜反射镜原理样机,开展了光学检测实验工作.利用高斯光学原理对薄膜反射镜的基本光学参数进行了检测,获得了随电压变化的薄膜反射镜曲率丰径和最大变形值曲线,趋势与理论计算结果一致.对薄膜反射镜的面形特性和面形检测方法进行了分析,采用激光干涉仪测试了无电压时中心区域的平面面形,RMS值为1....     

Self-compression controlled by the chirp of the input pulse

Self-compressed (SC) pulses have been achieved through the filamentation process in air without any additional dispersion compensation, using the input pulse chirp as the control parameter. For any studied input pulse energy (3-5 mJ), we have found two opposite sign input group-delay dispersion values for which SC pulses can be achieved systematically. In addition, we have observed that the energy coupled into the inner core of the filament is always of the order of 20% of the total input pulse energy, which opens the way to a scalable technique to obtain intense short pulses directly from the filamentation process.     

Generation of 40-as few-cycle pulse through chirp manipulation

We discuss theoretically how supercontinuum spectra produced from high-order harmonic generation processes in a synthesized same-color laser field is optimized by adjusting the chirp parameter of the controlling pulse. Furthermore, a 40-attosecond isolated pulse with an effective bandwidth of 121 orders is obtained from He+ ion when the chirp rate ratio of pulses has a small value. The numerical results show that the efficiency of single as pulse generation is enhanced, and the quantum paths are controlled successfully. Our simulation shows that the produced pulses with high signal-to-noise ratio are obtained straightforwardly without any phase compensation. These results are explained using the classical approach.     

周期性啁啾脉冲色散衍射实现近场强度匀滑

 对惯性约束聚变（ICF）激光驱动器中的周期性啁啾脉冲光谱色散后的自由空间衍射传输和近场强度匀滑特性进行了理论分析和数值模拟,并计算了色循环数对两者的影响。计算结果表明：远场光斑随色循环数增加而变大,强度调制加剧;近场强度匀滑效果随色循环数和传输距离增加而增强,但空间形状变化加剧。通过匀滑效果对比发现,基于周期性啁啾脉冲的光谱色散平滑系统的近场强度匀滑效果优于传统的正弦调频光束。     

Relativistic effects in the calibration of electrostatic electron analyzers. II. Parallel plate and cylindrical mirror analyzers

Relativistic correction terms up to the second order are derived for the kinetic energy of an electron travelling along the central trajectory, which crosses the non-relativistic foci of electrostatic parallel plate and cylindrical mirror analyzers. The effects of fringing fields and source geometry are neglected. In both cases the magnitude of relativistic corrections depends on the geometry of the analyzer, but generally it is smaller than for the toroidal family of analyzers.