Echo-enabled谐波放大自由电子激光参数

通过数值模拟,结合解析计算分析,研究了Echo-enabled谐波放大自由电子激光对装置参数和主要束流参数变化的独立敏感性,给出了谐波聚束因子和饱和功率随参数变化的数值模拟结果;对色散段由相干同步辐射效应引起的能散和发射度增长进行了估算和数值模拟。结果表明:相干同步辐射效应引起的切片能散和切片发射度增长在5%以内,对最后辐射影响不大。     

Ultra-high order harmonic generation via a free electron laser mechanism

In this paper,by using the"frequency up-conversion"principle with a high gain harmonic generation free electron laser and an external seed laser,we consider the possibility of modulating a relativistic electron beam on the attosecond scale,so that it can produce coherent spontaneous radiation from the deep ultraviolet to the hard X-ray spectral region with a very short radiator.Analytical estimation and three-dimensional numerical modeling show the great potential to reach ultra-high harmonics up to several thousand.For an electron bunch with the typical quality as in the free electron laser scheme and a seed laser with 800 nm wavelength,0.8 nm attosecond trains with alterable duration and GW scale peak power are modeled.The output radiation exhibits good shot-to-shot stability,full coherence and perfect tuning ability between the discrete harmonics of the seed frequency.     

Operating the SDUV-FEL with the echo-enabled harmonic generation scheme

Using the recently proposed echo-enabled harmonic generation (EEHG) free-electron laser (FEL) scheme, it is shown that operating the Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is very promising, with higher frequency up-conversion efficiency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.     

A proposed method to characterize high harmonic microbunching in EEHG operation of SDUV-FEL

The echo-enabled harmonic generation （EEHG） scheme offers remarkable efficiency for generating high harmonic microbunching with a relatively small energy modulation. A proof of principle experiment of the EEHG scheme has been proposed at the Shanghai deep ultraviolet （SDUV） free electron laser （FEL） facility, where the 4th harmonic of the seed laser is amplified in the 9 m long radiator. To explore the advantages of the EEHG scheme, in this paper, a method of measuring the coherent high harmonic radiation of the radiator is proposed to investigate the electron beam microbunching corresponding to the 10th-20th harmonics of the seed laser. The principle of the proposed method, comparisons with existing methods and the simulation results are presented and discussed.     

Operating the SDUV-FEL with the echo-enabled harmonic generation scheme

Using the recently proposed echo-enabled harmonic generation （EEHG） free-electron laser （FEL） scheme, it is shown that operating the Shanghai deep ultraviolet FEL （SDUV-FEL） with single-stage to higher harmonics is very promising, with higher frequency up-conversion effciency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.     

相干谐波储存环自由电子激光

相干谐波自由电子激光不用光学谐振腔及反射镜,可望工作在紫外和真空紫外光波段,是第四代同步辐射光源的可能途径之一。由于对束流品质要求很高,相干谐波自由电子激光首先是以储存环作为驱动器而发展起来的。由于光阴极微波电子枪的发展和直线加速器技术的进步,目前,已开始有直线加速器驱动的高增益相干谐波自由电子激光的建议。文章介绍了相干谐波储存环自由电子激光的原理、现状及展望。     

Three dimensional study of harmonic operation at the Shanghai deep ultraviolet free electron laser

With the right choice of parameters in the free electron laser (FEL) scheme, the undulator can be primarily operated at high order harmonic modes and the harmonic radiation is expected to be significantly enhanced. Recently, the possibility of proof-of-principle harmonic operation experiments on the basis of the Shanghai deep ultraviolet (SDUV) FEL test facility has been studied. In this paper, the principle of harmonic operation, three dimensional numerical approaches, and detailed performances of proposed harmonic operation at SDUV FEL are presented.     

Three dimensional study of harmonic operation at the Shanghai deep ultraviolet free electron laser

With the right choice of parameters in the free electron laser （FEL） scheme, the undulator can be primarily operated at high order harmonic modes and the harmonic radiation is expected to be significantly enhanced. Recently, the possibility of proof-of-principle harmonic operation experiments on the basis of the Shanghai deep ultraviolet （SDUV） FEL test facility has been studied. In this paper, the principle of harmonic operation, three dimensional numerical approaches, and detailed performances of proposed harmonic operation at SDUV FEL are presented.     

回声谐波放大型自由电子激光相干涡旋X射线产生方案

外种子型自由电子激光具有全相干、频谱稳定、极高亮度的优点,可以实现在超小空间和超快时间尺度下对物质结构的研究。具有特殊横向相位模式的光特别是具有螺旋相位的带轨道角动量的涡旋光已经在众多科学领域有了应用,基于自由电子激光原理产生的辐射横向模式基本上为简单的高斯模式,为产生具有横向螺旋相位的相干涡旋X射线,对基于回声谐波放大型(EEHG)自由电子激光产生涡旋光方案进行了深入研究,并且根据上海软X射线自由电子激光装置(SXFEL)的参数,进行了相关方案设计和模拟研究。三维模拟结果表明,外种子型EEHG自由电子激光可以产生峰值功率可达到GW量级的相干涡旋软X射线。     

Preliminary study of EEHG-based superradiant undulator radiation at the HLS-Ⅱ storage ring

We investigate storage ring-based Echo-Enabled Harmonic Generation(EEHG) superradiant undulator radiation as a possible scheme to obtain shorter wavelengths at the HLS-Ⅱ(Hefei Light Source-Ⅱ) storage ring. In this paper we give the designation of the storage ring based EEHG up to the 26 th harmonic, where 31 nm vacuum ultraviolet light is radiated from an 800 nm seeded laser. The novelty of our design is that both the two dispersion sections of EEHG are realized by the storage ring's own magnet structure. In particular, the whole ring is used as the first dispersion section, and two modulators of the traditional EEHG can be done with the same undulator. These two dispersion sections are realized by changing the superperiod of the present lattice structure, and more precisely by changing the focusing strengths of the present structure. Since no additional magnets and chicanes are used,the beam circulates around the storage ring repeatedly, and thus this storage ring-based EEHG can have a higher repetition rate than a linac-based EEHG.     

双色高频激光作用下原子低阶次谐波的理论研究

通过数值求解含时薛定谔方程,研究了高频双色激光脉冲与原子相互作用产生的光辐射.研究表明,光辐射谱中既有基频光的谐波,又可观测到谐波能量附近的多个频率的光辐射产生,且辐射的峰值强度随着入射激光强度的提高呈指数增强,相邻辐射频率差值为入射的两束激光脉冲频率差.     

储存环自由电子激光相干谐波实验的同步系统

 为了获得短波长自由电子激光(FEL),可以使储存环中的相对论性电子与外加强激光脉冲在光学速调管中充分耦合,从而产生高次谐波的相干辐射。为使耦合充分,必须使电子束团与激光脉冲在时间和空间上完全同步。其中空间上的同步可通过调节外激光的光路来实现,给出了实现时间上同步的一种方案。     

Generating optical orbital angular momentum in a high-gain free-electron laser at the first harmonic

A scheme to generate intense coherent light that carries orbital angular momentum (OAM) at the fundamental wavelength of an x-ray free-electron laser (FEL) is described. The OAM light is emitted as the dominant mode of the system until saturation provided that the helical microbunching imposed on the electron beam is larger than the shot-noise bunching that leads to self-amplified emission. Operating at the fundamental, this scheme is more efficient than alternate schemes that rely on harmonic emission, and can be applied to x-ray FELs without using external optical mode conversion elements.     

附加谐波脉冲生成强的39阿秒孤立脉冲

采用多周期800 nm激光组合它的27次谐波脉冲生成超短、宽频的孤立阿秒脉冲.研究表明,脉宽为1 fs的27次谐波脉冲可以有效地控制电子动力学过程.将其加入到单色激光场的特定时域,可以控制电离概率在半个光学周期内迅速提升,使得谐波的转化效率相对于单色场情形增强4个数量级,并实现单一的短量子路径选择,出现频宽为108 eV的超连续辐射谱,叠加该连续谱140次到210次谐波获得了脉宽为39as的强、短孤立脉冲.与文献[7]中采用5 fs/800 nm激光附加紫外阿秒脉冲的方法相比,该方案生成的连续谱频带增宽一 关键词： 组合激光脉冲 连续辐射谱 阿秒脉冲     

上海软X射线自由电子激光外种子运行模式的模拟研究

上海软X射线自由电子激光用户装置（SXFEL）是我国首台可以运行在水窗波段的自由电子激光装置,未来可以为5个实验线站供光,其主要运行模式为自放大自发辐射模式以及外种子模式。本文就SXFEL的外种子模式进行了从头到尾的模拟研究,主要包括EEHG-HGHG混合级联与单级EEHG两种方案。模拟结果表明,虽然EEHG-HGHG混合级联模式较为复杂,但能够产生更高功率的高次谐波辐射。除此之外,我们还研究了各种三维效应对EEHG的影响。模拟和分析结果表明,通过上述两种方案,采用紫外波段的种子激光,用户可以得到全相干、窄带宽、短脉冲的水窗波段自由电子激光。     

合肥储存环相干谐波自由电子激光研究方法的改进

 根据简单的计算模型,导出辐射能量谱形状因子和相干谐波辐射表达式,用此表达式讨论了不对称光学速调管的相干谐波辐射;对于合肥储存环相干谐波自由电子激光,提出了一个不对称光学速调管相干谐波辐射的研究方案,并且作了详细的计算,结果表明在较高的电子束能量下,调整光学速调管和外激光参数,使辐射段波荡器的辐射基波与外激光的二次谐波共振,进行相干谐波产生实验,能获得10⁹量级相干加强因子。     

Enhanced betatron radiation by a modulating laser pulse in laser wakefield acceleration

We propose a new idea to enhance and control the betatron radiation by using a modulating laser pulse in laser wakefield acceleration. In this scheme, a high-power laser pulse is used for self-trapping and acceleration of the plasma electrons and the accelerated electron beam is modulated by a separately-propagating laser pulse for large amplitude betatron oscillations and microbunching. In this way, the relatively low power modulating laser pulse can enhance the X-ray photon flux and energy significantly. We performed two-dimensional particle-in-cell simulations to demonstrate the idea and the results show that a sub-TW laser pulse is enough for electron beam modulation and it can generate easily-controllable fs X-ray pulses with a wide range of photon energies from soft X-rays to hard X-rays.     

Harmonic operation of high gain harmonic generation free electron laser

In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL. Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy.     

上海深紫外自由电子激光装置中激光与束流的精确同步

介绍了一种基于相干辐射测量的激光-电子束同步方法,描述了实现空间及时间同步的基本原理、步骤和细节,并利用这种方法在上海深紫外自由电子激光装置（SDUV-FEL）上实现了电子束与激光之间亚ps量级的精确同步,为基于外种子激光的高增益高次谐波产生（HGHG）、回声型谐波产生（EEHG）和级联HGHG自由电子激光实验奠定了坚实的基础。还利用这种手段对不同条件下的电子束纵向特性进行了测量和分析。     

提高相干谐波输出的一种新方法

本文利用自由电子激光(FEL)纵模统一理论讨论了光学速调管自由电子激光相干谐波的输出情况。从物理上分析了非对称光学速调管的设计,得出了采用非对称的光学速调管可使FEL的相干谐波输出提高近30％。