带轴向引导磁场自由电子激光的单粒子哈密顿理论

在Ｂａｍｂｉｎｉ－Ｒｅｎｉｅｒｉ坐标系中给出了带轴向引导磁场自由电子激光的单粒子哈密顿形式．得到了轴向场对器件增益放大系数的表达式，并讨论了对轴向场取值的一些限制条件．

Application of Laser Dispersion Method in Apparatus Combining H Atom Rydberg Tagging Time-of-Flight Technique with Vacuum Ultraviolet Free Electron Laser

Photodissociation of H2S in the VUV region plays an important role in the atmospheric chemistry and interstellar chemistry.To date,however,few studies have been focused on this topic.In this article,we have described a laser dispersion method applied in the apparatus combining the high-n H atom Rydberg tagging time-of-flight technique with the vacuum ultraviolet free electron laser(VUV FEL).The Lyman-αlaser beam(121.6 nm)used in the H-atom detection was generated by the difference frequency four-wave mixing schemes in a Kr/Ar gas cell.After passing through an off-axis biconvex LiF lens,the 121.6 nm beam was dispersed from the 212.6 nm and 845 nm beams due to the different deflection angles experienced by these laser beams at the surfaces of the biconvex lens.This method can eliminate the background signal from the 212.6 nm photolysis.Combined with the VUV FEL,photodissociation of H2S at 122.95 nm was studied successfully.The TOF spectrum was measured and the derived total kinetic energy release spectrum was displayed.The results suggest that the experimental setup is a powerful tool for investigating photodissociation dynamics of molecules in the VUV region which involves the H-atom elimination processes.

Infrared Spectroscopy of Neutral Clusters Based on a Vacuum Ultraviolet Free Electron Laseri

Spectroscopic characterization of clusters is crucial to understanding the structures and reaction mechanisms at the microscopic level,but it has been proven to be a grand challenge for neutral clusters because the absence of a charge makes it di伍cult for the size selection and detection.Infrared(IR)spectroscopy based on threshold photoionization using a tunable vacuum ultraviolet free electron laser(VUV-FEL)has recently been developed in the lab.The IR-VUV depletion and IR+VUV enhancement spectroscopic techniques open new avenues for size-selected IR spectroscopies of a large variety of neutral clusters without confinement(i.e.,an ultraviolet chromophore,a messenger tag,or a host matrix).The spectroscopic principles have been demonstrated by investigations of some neutral water clusters and some metal carbonyls.Here,the spectroscopic principles and their applications for neutral clusters are reviewed.

Multi-objective Genetic Optimization for LCLS-II X-ray FEL

The LCLS-II （linac coherent light source II） will build on the success of the world＇s most powerful X-ray laser： the LCLS （linac coherent light source）. It will add two new X-ray laser beams and room for additional new instruments, thus greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, MOGA （multi-objective genetic algorithm） is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance.

Numerical Investigations of Transverse Gradient Undulator Based on Novel Light Sources

With the stat-of-the-art laser technique, the quality of electron beam generated from LPA （laser-plasma accelerator） is now becoming much better. The natural merits of electron beam from LPA, e.g., high peak current, ultra-low emittance and ultra-short bunch length, etc., pave the way to the novel light sources, especially in the realm of developing much more compact x-ray light sources, e.g., table-top XFEL （x-ray free-electron laser）. However, the radiation power is limited by the rather larger energy spread than conventional radio-frequency electron LINAC （linear accelerator）. Luckily, much more power could be extracted by using the undulator with transverse gradient when energy spread effect could be compensated. In this paper, we introduce a novel soit x-ray light source driven by LPA together with TGU （transverse gradient undulator） technique, meanwhile we present a simple idea on how to achieve much higher rep-rate （e.g., -100 kHz） FELs （free-electron lasers） boosted by TGU based on storage rings.

A single stage EEHG at SXFEL for narrow-bandwidth soft X-ray generation

The echo-enabled harmonic generation （EEHG） scheme holds promising prospects for efficiently generat- ing intense coherent radiation at very high harmonics of the initial seed laser. In this paper, we study the feasibility of operating the Shanghai X-ray free-electron laser test facility with a single stage EEHG setup. With a combina- tion of existing numerical codes, start-to-end simulations considering various three-dimensional effects have been carried out to show the possible performance of the EEHG FEL. Simulation results demonstrate that a single stage EEHG can generate high power soft X-ray radiation pulses with narrow bandwidth directly from UV seed lasers. With the help of the harmonic lasing technique or upgraded linac, we also show the possibility of generating coherent soft X-ray radiation in the ＂water window＂ with a single stage EEHG.