光阴极微波电子枪中时间抖动对粒子动力学的影响

对光阴极微波电子枪粒子束性能起决定性影响的因素之一就是激光脉冲相对加速微波相位的时间抖动. 对这种时间抖动的测量和反馈控制进行了理论和实验分析, 并对时间抖动对束流品质的影响进行了模拟研究, 得到了利用锁相环回路降低激光脉冲相位噪声的实验经验, 为光阴极微波电子枪中激光与微波相位同步问题提出了解决方法.     

光阴极微波电子枪中激光脉冲的时间抖动测量

 研究了光阴极微波电子枪输出电荷量与驱动激光相对于微波入射相位的关系。通过对光阴极材料在光电子发射时的肖特基效应和电子束团在电子枪内的纵向加速过程分析模拟，得到了电子枪输出电荷量与激光入射相位的一段线性关系，设计了利用此关系测量驱动激光脉冲相对于微波相位的时间抖动的实验方案。结果表明，这种测量方法可以分辨1.15fs的时间抖动，误差为0.23fs。     

汤姆逊硬X射线源中锁模脉冲激光稳频方法

 汤姆逊硬X射线源中，光阴极微波电子枪要求触发激光脉冲与腔中微波场相位的精确时间同步。理论分析了锁模脉冲激光器相位噪声，探讨了对激光脉冲相位探测和控制的方法，并通过实验构建了激光相位抖动测量系统和锁相环稳频回路，用基频鉴相信号驱动压电陶瓷晶体改变谐振腔长，实现了从开环3.42 ps到闭环1.46 ps的均方根相位抖动的测量和控制。     

光阴极注入器的驱动激光器

 光阴极注入器要求驱动激光器的激光时间抖动小、脉冲宽度窄、激光波长短和脉冲功率高。从原理和实验上介绍光阴极注入器的驱动激光器,包括连续波锁模振荡腔、时间同步,激光脉冲功率放大等;该激光器输出激光微脉冲宽度10ps,微脉冲时间抖动小于2ps,宏脉冲宽度2.5 μs, 峰值功率100kW, 已用于光阴极RF腔注入器实验,并获得了很好的结果。     

光阴极RF腔注入器中激光脉冲的时间抖动

 介绍光阴极RF腔注入器中的驱动激光器,采用二极管泵浦的自锁模激光器,通过锁相,使输出激光脉冲的时间抖动小于2ps,实现激光脉冲同微波相位之间的严格同步,在实验上获得流强70A、能量2MeV、亮度4.4×10¹¹A/(m².rad²)的电子束。     

北京大学高平均流强光阴极电子枪驱动激光系统

DC-SC超导光阴极注入器将直流光阴极电子枪和超导加速腔结合在一起,其特点之一是适合于提供高平均流强电子束.文中介绍了直流光阴极电子枪的驱动激光系统的研制.该驱动激光系统的主机为瑞士TBP公司的GE-100-XHP型激光器,是采用可饱和吸收镜技术的被动锁模激光器,其工作晶体为Nd:YVO₄,输出波长为1064nm,脉冲重复频率为81.25MHz,平均功率10W.该驱动激光系统配套的CLX-1100同步控制器可以将激光脉冲与射频参考信号严格锁定,随机抖动不大于1ps.根据使用要求,作者研制了高效的激光倍频器,获得了大于1W的266nm紫外激光.同时,激光到光阴极的传输设计中,采用了傅立叶光学技术,在紫外激光功率650mW左右的条件下,从自行研制的Cs₂Te光阴极上实现了大于500μA的光电流引出     

光阴极微波电子枪驱动激光整形与传输系统

为满足合肥先进光源对高品质注入束流的要求,合肥先进光源预研项目研制了一套光阴极微波电子枪系统作为注入器电子源。为降低空间电荷效应引起的束流发射度增长,对驱动激光整形及传输系统进行了理论和实验研究。通过双折射晶体的脉冲时间整形以及采用光阑高斯截断的空间整形,得到了近似均匀分布的激光脉冲。像传递激光传输光路,实现了光阴极表面激光位置的高稳定性。实验结果显示,光阴极表面的激光位置抖动小于4 μm,激光性能满足实验要求。     

高功率激光系统中的脉冲整形

一台脉冲整形器,完成对调Qns激光脉冲的整形,输出1ns主脉冲,上升和下降时间<400ps.在测试仪器精度极限范围内,主脉冲与诊断短脉冲同步的时间抖动<100ps.     

大型激光装置精密同步系统总体技术研究

提出了一种用于大型激光装置的精密同步系统总体架构技术。该技术采用时钟及数据恢复、光级联技术成功地实现了多数量、多种类同步触发信号的有序组合,保证了同步触发信号的精度,获得的ps级精密同步触发信号的时间间隔抖动为:峰峰抖动小于100ps,均方根值小于10ps。     

DC-SC光阴极注入器的束载实验的调试进展

 北京大学射频超导实验室设计了新型超导光电子枪——DC-SC光阴极注入器，目标是为自由电子激光平台提供能量在2~3MeV，脉宽小于10ps，脉冲重复频率为81.25MHz，平均流强约为1mA的低发射度电子束。现在已经建成了DC-SC光阴极注入器实验平台，包括激光驱动光阴极系统，Pierce直流高压加速结构，1.3GHz 1＋1/2纯铌超导腔，恒温器低温系统，4.5kW连续波微波系统，1/16分频与同步控制系统，束流诊断系统和能量分析系统等。并且完成了超导腔的静态实验，直流加速结构也经过了100μA低电流测试。实验结果符合设计要求，整体调试后即可以进行束载实验。     

脉宽对超快激光平衡光学互相关测距影响的研究

采用基于平衡光学互相关的超快激光绝对距离测量方法对大气中一段15m的空间距离进行了测量。仿真了不同脉冲宽度、不同光强损耗对平衡互相关信号的影响,理论分析表明脉宽展宽对平衡互相关信号影响较大。采用中心波长为1037nm、重复频率为260MHz的超快激光器光源,搭建了测距系统。实验验证了在脉宽分别为1.44ps、132fs时,对平衡互相关信号的影响,实验结果符合理论分析。研究了不同脉冲宽度对测量分辨力的影响,结果显示,采样时间为5ms,脉宽为1.44ps,测量分辨力不低于50μm;而当脉宽为132fs时,测量分辨力优于5μm。     

Ultrafast mode-locked dual-wavelength thulium-doped fiber laser using a Mach-Zehnder interferometric filter

A simple and robust method to generate a dual-wavelength mode-locked laser using a tunable Mach-Zehnder filter (TMZF) and a single-wall carbon nanotube (SWCNT) based saturable absorber (SA) is proposed and demonstrated. The proposed laser uses a thulium-doped fiber for lasing in the two-micron region and exploits the interferometric spectrum of the TMZF to produce dual peaks with nearly equal magnitude. SWCNT based SA enables mode-locking at a threshold value of 150.4?mW with distinct dual-wavelength peaks at 1919.2?nm and 1963.7?nm. The peaks have a calculated pulse width of 1.8?ps and 1.6?ps, respectively with a repetition rate of 9.1?MHz with a relatively high optical-signal-to-noise ratio value of 59.1?dB. The output is also observed to remain unchanged over time, indicating high stability. The proposed laser has a promising application, particularly in ultrafast gas molecular spectroscopy and sensing.     

Bunch length measurement using a traveling wave RF deflector

RF deflectors can be used for bunch length measurement with high resolution. This paper describes a completed S-band traveling wave RF deflector and the bunch length measurement of the electron beam produced by the photocathode RF gun of the Shanghai DUV-FEL facility. This is the first time that such a transverse RF deflector has been developed and used to measure the bunch length of picosecond order in China. The deflector's VSWR is 1.06, the whole attenuation 0.5 dB, and the bandwidth 4.77 MHz for VSWR less than 1.1. With a laser pulse width of 8.5 ps, beam energy of 4.2 MeV, and bunch charge of 0.64 nC, the bunch lengths for different RF input power into the deflector were measured, and an averaged rms bunch length of 5.25 ps was obtained. A YAG crystal is used as a screen downstream of the deflector, with the calibrated value of 1 pix = 136 μm.     

光阴极RF腔注入器

 光阴极RF腔注入器是一种强流、窄脉冲(ps量级)、低发射度的电子束源。文章给出了CAEP光阴极RF腔注入器的结构和实验结果,结构主要包括驱动激光器、Cs₂Te阴极制备室、2.5个RF腔、高功率微波源和测量仪器等,其中驱动激光器的参数是影响注入器电子束质量的重要因素;实验上,该光阴极RF腔注入器可稳定输出能量2MeV、流强70A、发射度～4mm.mrad的高亮度电子束流。     

Self-starting passive harmonic mode-locked femtosecond Yb3+-doped fiber laser at 1030 nm

We demonstrate, for the first time to our knowledge, a self-starting passive harmonic mode-locked femtosecond Yb3+-doped fiber laser with a scalable repetition rate of up to 585 MHz and >45 dB of supermode suppression. Pulse-to-pulse jitter of approximately 14 ps is measured by optical cross correlation at the ninth harmonic, and radiofrequency (RF) spectrum measurements show that certain correlations exist between pulses in harmonic mode. Our results suggest that one of the proposed passive harmonic mode-locking mechanisms may be dominant for this laser.     

Nd:YVO₄ amplifier for ultrafast low-power lasers

An Nd:YVO₄ amplifier consisting of two modules end pumped at 808?nm at 30?W total absorbed power has been designed for efficient, diffraction-limited amplification of ultrafast pulses from low-power seeders. We investigated amplification with a 50?mW, 7?ps Nd:YVO₄ oscillator, a 2?mW, 15?ps Yb fiber laser, and a 30?mW, 300?fs Nd:glass laser. Output power as high as 9.5?W with 8?ps pulses was achieved with the 250?MHz vanadate seeder, whereas the 20?MHz fiber laser was amplified to 6?W. The femtosecond seeder allowed extracting Fourier-limited 4?ps pulses at 7?W output power. To our knowledge, these are the shortest pulses from any Nd:YVO₄ laser device with at least 7?W output power. This suggests a novel approach to exploit the gain bandwidth of vanadate amplifiers with high output power levels. Such amplifier technology promises to offer an interesting alternative to high-power thin disk oscillators at few picoseconds duration, as well as to regenerative amplifiers with low-repetition-rate fiber seeders.     

Picosecond pulse generation in a mono-layer MoS_2 mode-locked Ytterbium-doped thin disk laser

A mode-locked(ML)picosecond ytterbium-doped thin disk laser using a monolayer Mo S2as the saturable absorber(SA)is demonstrated.The monolayer MoS_2 is fabricated through the method of low-pressure chemical vapor deposition.The laser directly produces stable ML picosecond pulses at a slope efficiency of 9.71%.The maximum output power is approximately 890 mW,while the corresponding repetition,pulse energy,and pulse duration are 48.6 MHz,18.3 nJ,and 13.1 ps,respectively.Results suggest that the monolayer MoS_2 is a promising SA for ultrafast lasers system.     

钛宝石激光抽运的被动锁模Tm:YAG陶瓷激光实验研究

本文采用连续钛宝石激光作抽运,掺杂浓度为6 at.%、长度为2.7 mm的Tm:YAG陶瓷作增益介质,通过引入半导体饱和吸收体获得了稳定的被动锁模运转.实验中获得的激光锁模功率为116.5 mW,中心波长为2007 nm,重复频率为109 MHz,通过自行搭建的腔外非共线强度自相关测量得到的脉冲宽度是55 ps.     

Photo-triggered pulsed cavity compressor for bright electron bunches in ultrafast electron diffraction

Temporally resolved observation of microscopic structural dynamics of solids with ultrafast electron diffraction (UED) requires extremely short pulsed, highly charged, monoenergetic electron beams with sufficient transverse coherence length of several unit cells of the investigated samples. However, Coulomb repulsion defeats these parameters in free propagation of an electron pulse initially bright on the photo cathode. We demonstrate a new electron pulse compressor design based on a simple and compact RF structure incorporating a pair of gallium arsenide photoconductive semiconductor switches that are triggered by femtosecond laser pulses, thereby providing a longitudinal voltage gradient of up to 20?V/ps. Our proof of principle experiment achieved compression of bunches containing 26,000 electrons to a duration of below 750?fs and a beam diameter of 300???m in the temporal and spatial focus of the device while maintaining the good beam collimation required for time resolved electron diffraction experiments. The simplicity of the compressor provides a strong incentive for its further development toward practical implementation in sub-relativistic UED experiments requiring the highest possible source brightness.