基于激光等离子体加速的自由电子激光研究新进展

激光等离子体加速器能够在cm尺度内产生GeV量级的高品质电子束,为研制台式化自由电子激光提供驱动源。但是受限于激光等离子体加速中的难点和现有技术发展,电子束的品质难以达到自由电子激光的需求,尤其在稳定性、发散角和能散等方面,阻碍了台式化自由电子激光的研制。介绍了基于激光等离子体加速器的自由电子激光的最新进展,整理了目前高增益自由电子激光实验过程中存在的主要挑战和对应的解决方案与实验进展,并展望未来的发展方向。最近的研究结果证明,通过控制和优化激光等离子体加速器的注入和加速过程产生的高品质电子束可以在指数增益区域实现自发辐射放大,产生高增益的辐射,这也推动基于激光等离子体加速器的自由电子激光研究进入了一个新的阶段。     

Simplified small signal gain calculations in free electron lasers

A method proposed recently is used for the evaluation of the small signal gain in various free electron laser configurations. The theory is applied to (a) the wigglerfree free electron laser with a uniform axial guide magnetic field and arbitrary direction of propagation of the amplified radiation and (b) the free electron laser with the axially modulated guide field (lowbitron). It is demonstrated that the new approach simplifies the gain calculation significantly in comparison with the traditional method.     

Effect of betatron oscillations on waveguide free electron laser gain

In this paper we analyse the spontaneous emission and gain spectrum of a waveguide free electron laser with betatron motion included in the analysis. The zero slippage condition and the small signal gain in the waveguide free electron laser is discussed.     

预-主短脉冲激光驱动的高增益类氖氩软X射线激光

 用数值模拟程序计算了脉宽1.5ps预脉冲和主脉冲激光，经1.2ns的时间延迟先后泵浦喷射的密度为6.632×10^-3g/cm³的氩气柱，以获得高增益的类氖离子电子碰撞激发3p-3s跃迁激光的可能性。结果表明：在等离子体中能够形成宽的类氖离子丰度大于50%的区域，并且具有大于10²⁰ cm^-3的自由电子密度。主脉冲到达之后迅速加热自由电子，高密度的自由电子与类氖离子碰撞激发形成具有很高增益系数的增益区，增益区的半高宽度大约100μm，一维理论计算的增益系数为200~300cm^－1，持续时间大约相当于泵浦激光的时间宽度，在1~2ps之间。     

光学速调管结构喇曼自由电子激光器研究

本文提出光学速调管结构喇曼自由电子激光器总体实验设计。采用一维单粒子模型对光学速调管结构目由电子激光器增益和效率的提高进行了研究。 关键词：     

X-ray amplification by laser controlled coherent bremsstrahlung

A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.     

Quantum theory of a free electron laser for strong fields

A quantum mechanical derivation of the gain of the free electron laser is presented which starts from the exact solutions of the Klein-Gordon equation in the presence of the magnetic wiggler field and the stimulating plane wave field. The gain is obtained from the transition amplitude of the electron, which is expressed in terms of the Green's function. For comparatively weak fields the usual small signal gain results, whereas for strong fields saturation behaviour is found.Supported by Deutsche Forschungsgemeinschaft     

A study of the gain mechanism in free electron laser systems

A detailed study of the gain mechanism in low-gain free electron laser systems is presented. The analysis is based on a recently reported analytic solution to the quasi-Bloch equations, which are assumed to govern the evolution of the system.     

The gain-spread relation in a multiphoton picture of the free electron laser

Within the multiphoton picture of the free electron laser we derive a general gain-spread relation which holds for arbitrary tapered wigglers. Corrections to the small signal gain are also indicated.     

Electron trajectories and gain in free electron laser with ionchannel guiding

A detailed analysis of electron trajectories and gain in a helical wiggler free electron laser (FEL) with ion channel focusing using single particle dynamics is presented. Conditions for stability of electron orbit have been obtained and stable regimes have been identified. Gain has been evaluated in the low-gain-per-pass limit with the help of the self-consistent pendulum equation. It is seen that the presence of ion channel leads to significant gain enhancement under appropriate conditions     

Generalized gain-spread expressions for the free electron laser

Starting from a many electron hamiltonian model we derive general expressions for the unsaturated gain and spread of a free electron laser that are valid for arbitrary magnetic field configurations. The general validity of a well known gain-spread relation is demonstrated.     

One-body electron dynamics in a free electron laser

The free electron laser is analyzed by solving the one-body classical Lorentz force equation in the presence of periodic magnetic field and a plane electromagnetic wave. Phase space paths for electrons are related to those of a simple pendulum and describe laser gain, saturation, and coherent electron beam modulation.     

紧聚焦的超短超强激光脉冲在真空中加速斜入射的相对论电子

研究了紧聚焦的线偏振飞秒超强高斯激光脉冲俘获并剧烈加速斜入射低能相对论电子的效应 ，发现被俘获的电子在激光脉冲纵向有质动力的强大加速作用下，可以获得GeV量级的能量 ，并详细研究了入射电子的初能量、斜入射角、电子与激光脉冲的相对延迟时间和激光脉冲 宽度等条件对电子能量增益的影响，发现当激光脉宽超过10λ时，脉宽对电子能量增益影响 不大. 关键词： 电子加速 有质动力 能量增益 束腰     

Gain enhancement in two-stream free electron laser with a planar wiggler and an axial guide magnetic field

The theory for a two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

Three dimensional gain analysis of free electron laser with focusing permanent magnet wiggler

A three dimensional simulation software system developed to estimate a free electron laser (FEL) gain has been applied to FEL using a standard plane polarized wiggler and an alternately shifted magnet wiggler. It is seen for the latter wiggler that a large filling factor could be selected and each maximum gain corresponding to each orbit of electron beam concentrates at a certain frequency region of FEL radiation. It is, therefore, implied that a proper shift between the adjacent magnets in the wiggler produces the improvement of the FEL gain.     

Interaction of a relativistic dense electron beam with a laser wiggler in a vacuum: self‐field effects on the electron orbits and free‐electron laser gain

Employing laser wigglers and accelerators provides the potential to dramatically cut the size and cost of X‐ray light sources. Owing to recent technological developments in the production of high‐brilliance electron beams and high‐power laser pulses, it is now conceivable to make steps toward the practical realisation of laser‐pumped X‐ray free‐electron lasers (FELs). In this regard, here the head‐on collision of a relativistic dense electron beam with a linearly polarized laser pulse as a wiggler is studied, in which the laser wiggler can be realised using a conventional quantum laser. In addition, an external guide magnetic field is employed to confine the electron beam against self‐fields, therefore improving the FEL operation. Conditions allowing such an operating regime are presented and its relevant validity checked using a set of general scaling formulae. Rigorous analytical solutions of the dynamic equations are provided. These solutions are verified by performing calculations using the derived solutions and well known Runge–Kutta procedure to simulate the electron trajectories. The effects of self‐fields on the FEL gain in this configuration are estimated. Numerical calculations indicate that in the presence of self‐fields the sensitivity of the gain increases in the vicinity of resonance regions. Besides, diamagnetic and paramagnetic effects of the wiggler‐induced self‐magnetic field cause gain decrement and enhancement for different electron orbits, while these diamagnetic and paramagnetic effects increase with increasing beam density. The results are compared with findings of planar magnetostatic wiggler FELs.     

Gain enhancement in two-stream free electron laser with planar wiggler and axial guide magnetic field

The theory for the two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

Posibilities of Channelling Radiation as γ-Laser

In this paper the electron axial channeling radiation has been compared with a free electron laser (FEL),and the possibility of reforming this type of radiation as γ–laser has been discussed.introducing equivalent magnetic field to describe ~electron’s motion,the pendulum equation and energy gain of the electron longitudial motion have been obtained using interaction of the electron with the radiation field. it shows that the channeling radiation is very similar to fel, if there exists standing wave field in the crystal.     

Design of cascading two stages of high gain harmonic generation scheme based on Shanghai deep ultraviolet free electron laser

Cascading stages of high gain harmonic generation free electron laser (FEL) seem to be a feasible way to generate short wavelength radiation. With help of the analytical estimates, we design a two-stage cascading scheme to achieve 131 nm DUV radiation on the basis of the Shanghai deep ultraviolet free electron laser test facility. Detailed studies on the FEL performance, the stability and the sensitivity of the output power to parameter variation have been achieved by GENESIS1.3, and design of the lattice structure is presented.