Single-shot measurement of free-electron laser polarization at SDUV-FEL

In this paper, a division-of-amplitude photopolarimeter(DOAP) for measuring the polarization state of a free-electron laser(FEL) pulse is described. The incident FEL beam is divided into four separate beams, and four Stokes parameters can be measured in a single-shot. In the crossed-planar undulators experiment at the Shanghai deep ultraviolet FEL test facility, this DOAP instrument constructed in house responsed accurately and timely while the polarization-state of fully coherent FEL pulses were switched, which is helpful for confirming the crossed-planar undulators technique for short-wavelength FELs.     

自由电子激光放大啁啾脉冲的数值模拟

 利用1维非定态程序对单程自由电子激光(FEL)放大器放大线性啁啾脉冲的过程进行了数值模拟,得到了不同啁啾参数的脉冲通过FEL放大器的增益曲线,计算了不同啁啾参数的脉冲被单程FEL放大器放大后的腔外压缩情况。通过对数值模拟结果的定性分析得出：影响输出脉冲宽度和峰值功率的主要因素是FEL放大器的增益线宽和啁啾参数,并以此说明,通过先使用FEL放大器放大啁啾脉冲、然后再将其在腔外压缩的方法产生超短脉冲FEL是可行的。     

自由电子激光辐射频谱测量

文章描述了在环形电子束和实心电子束自由电子激光(FEL)研究中,测量辐射频谱使用的两种方法——波导色散线和带通滤波器谱仪。介绍了测量系统的组成和特点,给出了测量结果:环形束FEL试验。辐射频率在27—38GHz内可调:实心束FEL试验,辐射频谱带宽～1.2GHz。     

CAEP远红外100 μm FEL自发辐射谱的实验研究

在FEL实验中,电子束通过摇摆器,一方面由于周期性磁场作用,电子束轨迹要周期性的摆动,另一方面还要辐射同FEL辐射波长一致的自发辐射,该辐射谱反映电子束、摇摆器集成后的参数。在CAEP(Institute of China Academic Engineering Physics)远红外100 μm FEL实验中,自发辐射谱通过Ge∶Ga低温探头和远红外100 μm光栅谱仪测量。文章侧重从实际摇摆器磁场分析了远红外100 μm FEL的自发辐射谱。     

孔耦合自由电子激光振荡器光场横向结构特性

 孔耦合输出对自由电子激光(FEL)振荡器腔内光场的横向结构有很大的影响, 在输出镜上横模之间发生很复杂的耦合转换。基于中物院远红外自由电子激光振荡器, 研究了 孔输出波导 FEL的数值模拟, 对孔耦合及其引起的腔内光场的变化给以特别的注意, 依据数 值结果, 分析了孔耦合FEL光场横向结构的特性。     

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％。     

短波自由电子激光放大器数值模拟

介绍在理论上研究自由电子激光(FEL)的MICFEL程序。MICEFL是以单粒子理论为基础的二维放大器程序。利用MICFEL计算的Paladin实验结果与FRED程序计算结果以及25米Paladin实验结果相比均基本符合。理论计算的结果显示了FEL增益光导的特性。     

利用Compton散射对自由电子激光器的研究

通过坐标变换的方法，利用康普顿散射对自由电子激光器(FEL)的自发辐射进行了研究，精确地推导了FEL的自发辐射的波长公式，其近似式就是经典散射理论推导的自发辐射波长公式；对自发辐射的辐射功率也进行了近似推导，结果与经典散射理论公式一致。     

远红外FEL摇摆器的改进及调试

摇摆器是相对论性电子束与光场相互作用的区域，在FEL研究中起着至关重要的作用。在电子束品质(能散、发射度、流强等)一定的情况下，摇摆器的性能参数，如峰值场强、峰峰值误差、好场区大小等就基本决定了FEL增益。中物院远红外。FEL摇摆器由于受使用寿命及国内加工水平不够等因素影响，其整体性能在使用3年后发生了较大变化，已不能再满足下一阶段FEL受激辐射研究的需要。概括起来有以下5点：峰值场强的设计值为0．3000T，研制完成时的实际值约为0．2900T，现已下降至0．27T。峰值场强的下降不但会引起总体设计波长的漂移，而且会导致FEL小信号增益的下降；研制完成时的峰峰值误差为1．4％，现在的最好状态为2．5％。峰峰值误差过大将导致FEL谱线展宽，     

Simulation studies on laser pulse stability for Dalian coherent light source

Dalian Coherent Light Source will use a 300 MeV LINAC to produce fully coherent photon pulses in the wavelength range between 150–50 nm by high gain harmonic generation free electron laser(FEL)scheme.To generate stable FEL pulses,a stringent tolerance budget is required for the LINAC output parameters,such as the mean beam energy stability,electron bunch arrival time jitter,peak current variation and the transverse beam position ofset.In order to provide guidance for the design of the Dalian Coherent Light Source,in this paper,the sensitivity of FEL pulse energy fluctuation to various error sources of the electron bunch was performed using intensive start-to-end FEL simulations.     

Characterization of 60 GHz Multi Quantum well passively mode-locked laser under optical self-injection locking

The quality and pulse compression of the 60 GHz millimeter wave signals generated by 750 μm long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self-injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24 mA to 90 mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61 GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self-injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900 kHz to 24 kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self-injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.     

Prism reflectors for high power lasers

A new type of laser reflector is described in which the laser beam is split by frustrated total internal reflection and the components combined again. It has the properties of high reflectivity, high damage resistance, wide bandwidth and variable reflectivity. The design of two particular reflectors is discussed and their performance evaluated. One of these reflectors has the property of lateral inversion of the reflected beam, which is found to aid transverse mode selection in a ruby laser. As an application of the reflectors, a damage free, single transverse mode, mode-locked ruby laser is described.     

基于单透镜的空间光-单模光纤耦合方法

将自由空间光耦合进单模光纤产生超连续谱的实验中,空间光与单模光纤的耦合效率是其中的一个关键问题。常采用的单透镜或显微物镜进行耦合存在耦合效率低、调整难度大、端面易损伤等问题。提出了先将自由空间的光耦合进纤芯尺寸较大的单模光纤,然后将纤芯较大的单模光纤和纤芯较小的单模光纤进行熔接。实验结果表明,改进的耦合系统耦合效率大大提高,达到60%以上,且调整难度降低,光纤端面的损伤概率降低,大大提高了超连续谱产生的效率。     

Analysis of the radiation pattern of laser diode radiation based on experimental data

It is shown that the radiation pattern of laser diode radiation can quantitatively be analyzed without labor-intensive and expensive measurements of the radiation intensity distribution in the near-field zone. Formulas are obtained in the explicit form, which analytically describe the radiation pattern of laser diode radiation in free space, and a simple algorithm is developed for determining the fundamental lasing mode.     

On the determination of the stored optical energy of an atomic iodine laser amplifier from the energy measured in the free running mode

An exact determination of the stored optical energy of an amplifier from the energy measured in the free running mode has been difficult for the iodine laser because of the influence of the recombination of ground state iodine atoms with radicals to the parent molecule on the population of the lower laser level. A formula is derived relating the stored optical energy to the one measured in the free running mode with due consideration of this effect.     

基于组合模理论设计的激光二极管阵列外腔

针对激光二极管阵列提出了"组合模"概念,计算了组合模的远场分布.每个组合模在远场的空间分布呈双瓣结构.基于激光二极管阵列组合模的远场分布特征,设计了离轴外腔反馈的激光二极管阵列.运用此装置所获得激光二极管阵列的远场分布有了明显变化.与自由运转的激光二极管阵列相比,离轴外腔反馈的激光二极管阵列远场宽度减少了4.3倍.在抽运电流为16 A时,测得输出激光的功率1.82 W,这相当于相同电流下自由运转激光器输出功率的79%.组合模理论不仅可以用来指导设计一维离轴外腔反馈激光二极管阵列,而且也可以用于设计二维离轴外腔反馈激光二极管阵列.二维离轴外腔反馈激光二极管阵列可以产生高功率,高光束质量输出的激光.     

激光照射下铝靶表面汽化压力的测量

 本文分析了会聚自由振荡钕玻璃脉冲激光束辐照平面铝靶的汽化特性。在激光功率密度约10 MW/cm²下，由拍摄激光与靶相互作用产生射流发光的时间积分照片测得靶面的汽化压力约3.6 GPa。把时间积分照片与高速分幅照片比较，证明在激光与靶相互作用一段时间后确实存在着马赫盘。     

Dispersion effects in a highly birefringent fiber laser sensor with fiber Bragg grating reflectors

The effects of dispersion in the highly birefringent fiber Bragg grating reflectors of a polarimetric elliptical-core fiber laser sensor are experimentally and theoretically investigated. The laser sensor is designed to measure fluid pressure. It is experimentally and theoretically shown that the wavelength-dependent phase shifts in the gratings can be employed to remove the near degeneracy of the polarization mode beat frequencies of a given order, which substantially improves the resolution of the sensor. A resolution of a few parts in 10(6) of the free spectral range of the laser is demonstrated.     

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。