Stimulated Smith-Purcell radiation

JETP Letters - The design of free-electron lasers (FELs) based on submillimeter-range undulators involves difficulties associated with the fabrication of undulators with a very small period. To do...     

Investigations of ultrafast phenomena in high-energy density physics using X-ray FEL radiation

The advent of highly intense and ultrashort pulses of short-wavelength radiation in the vacuum-ultraviolet to X-ray regime provides for the first time the possibility to study plasmas at the time scale of equilibration or even electron thermalization. The emerging radiation sources are free-electron lasers (FEL) based on high-energy electron accelerators. FELs provide a peak brilliance nine orders of magnitude higher than the best performing X-rays sources today. The FEL radiation parameters will enable the creation of high-energy density states of matter and the development of new diagnostics tools to investigate dense plasmas. As the first of the new sources the VUV-FEL at DESY, Hamburg becomes operational for high-energy density physics experiments during 2005.     

Harmonics Generation in Experiments with Free-Electron Lasers in the X-Ray Wavelength Range: a Theoretical Analysis

Technical Physics - The generation of undulator X-ray radiation harmonics in free-electron lasers (FELs), which has been observed in different experiments, has been given an analytical explanation....     

On Harmonic Generation in X-Ray Free-Electron Lasers with Variable Undulator Deflection Parameter

Technical Physics - X-ray free-electron lasers (FELs) generate ultrashort bursts at wavelengths ~1 –100 Å. The possibility of harmonic generation in the X-ray range in FELs with a...     

Generation of Soft X-Ray Radiation in a Compact Free-Electron Laser with Harmonic Multiplication

Technical Physics - Single-pass free-electron lasers (FELs) with harmonic multiplication in the X-ray range are studied theoretically with the objective of producing intense radiation with the...     

Optimization of a seeded free-electron laser with helical undulators

Seeded single pass free-electron lasers are promising coherent, short-duration, and intense light sources, from the visible to x rays. Operated with adjustable undulators, they are also a unique device for providing fully variable polarized radiation. We report here the first seeding of helical undulators with a variable polarized source. We demonstrate that the adjustment of the seed polarization and focusing allows the free-electron laser radiation to be optimized in terms of intensity and quality.     

Theoretical Analysis of Radiation Properties of X-Ray Free-Electron Lasers

Radiophysics and Quantum Electronics - We perform a comparative analysis of the radiation of X-ray free-electron lasers (FELs) LCLS, PAL-XFEL, SwissFEL, SACLA, FLASH2, and European XFEL, as well as...     

Femtosecond X-ray free-electron lasers: A new tool for studying nanocrystals and single macromolecules

A brief overview of the design of femtosecond X-ray free-electron lasers (XFEL), characteristics of the emitted X-ray pulses, and potentialities of XFEL are presented. A concise analysis of the problems in modeling X-ray scattering patterns produced by ultraintense radiation sources is given.     

X-Ray Free-Electron Lasers with Variable Deflection Parameter of Undulators

Russian Physics Journal - The paper deals with X-ray free-electron lasers (FEL) with the variable deflection parameter of undulators with the electron buncher and harmonic amplifier. The analysis...     

Fully coherent hard X-ray generation by two-stage phase-merging enhanced harmonic generation

Cascading stages of seeded free electron lasers (FELs) is a promising way to produce fully coherent X-ray radiation. We study a new approach to produce coherent hard X-rays by cascading the recently proposed phase-merging enhanced harmonic generation (PEHG) The scheme consists of one dogleg and two PEHG configurations, and may be one of the leading candidates for the extracted undulator branch in future X-ray FEL facilities. FEL physics studies show that such a scheme is feasible within the present technology and can provide high brightness X-ray radiation pulses with narrow bandwidth and full coherence The radiated peak power at 1 Å wavelength converted from an initial 200 nm seed laser is over 2 GW.     

Coherent and transient states studied with extreme ultraviolet and X-ray free electron lasers: present and future prospects

The most recent light sources, extreme ultraviolet (EUV) and X-ray free electron lasers (FELs), have extended tabletop laser experiments to shorter wavelengths, adding element and chemical state specificity by exciting and probing electronic transitions from core levels. Through their unique properties, combining femtosecond X-ray pulses with coherence and enormous peak brightness, the FELs have enabled studies of a broad class of dynamic phenomena in matter that crosses many scientific disciplines and have led to major breakthroughs in the last few years. In this article, we review how the advances in the performance of the FELs, with respect to coherence, polarization and multi-color pulse production, have pushed the development of original experimental strategies to study non-equilibrium behavior of matter at the femtosecond–nanometer time–length scales. In this review, the emphasis is placed on the contribution of the EUV and soft X-ray FELs on three important subjects: (i) the new regime of X-ray matter interactions with ultrashort very intense X-ray pulses, (ii) the new potential of coherent imaging and scattering for answering questions about nano dynamics in complex materials and (iii) the unique possibility to stimulate and probe nonlinear phenomena that are at the heart of conversion of light into other forms of energy, relevant to photovoltaics, femtosecond magnetism and phase transitions in correlated materials.     

Multiwavelength anomalous diffraction at high x-ray intensity

The multiwavelength anomalous diffraction (MAD) method is used to determine phase information in x-ray crystallography by employing anomalous scattering from heavy atoms. X-ray free-electron lasers (FELs) show promise for revealing the structure of single molecules or nanocrystals, but the phase problem remains largely unsolved. Because of the ultrabrightness of x-ray FEL, samples experience severe electronic radiation damage, especially to heavy atoms, which hinders direct implementation of MAD with x-ray FELs. Here, we propose a generalized version of MAD phasing at high x-ray intensity. We demonstrate the existence of a Karle-Hendrickson-type equation in the high-intensity regime and calculate relevant coefficients with detailed electronic damage dynamics of heavy atoms. The present method offers a potential for ab initio structural determination in femtosecond x-ray nanocrystallography.     

超快X射线自由电子激光研究进展北大核心CSCD

现代光源的发展不断推动着人们从更深层次上理解物质的基本结构和动力学行为。X射线自由电子激光作为最先进的光源,其超高的峰值功率、超短的脉冲长度和优良的相干性,为人们以原子级时空分辨率探测和操控物质中的超快过程提供了可能。目前全世界已有多个X射线自由电子激光装置建成并投入使用,在原子分子物理、化学、生命科学、材料科学等各学科应用中都显示出了重要价值。同时大量的研究工作也集中于继续提高X射线自由电子激光的性能,包括把脉冲持续时间从fs量级进一步缩短至as量级,这将为超快科学的发展带来新突破。以超快脉冲产生为主线,综述了近年来超快X射线自由电子激光产生方案的研究进展,从产生原理、方案特性、最新成果等方面介绍了各类产生方案,总结对比了各方案的优缺点,最后对超快X射线自由电子激光的未来发展方向进行了展望。     

Single-molecule imaging with x-ray free-electron lasers: dream or reality?

X-ray free-electron lasers (XFEL) are revolutionary photon sources, whose ultrashort, brilliant pulses are expected to allow single-molecule diffraction experiments providing structural information on the atomic length scale of nonperiodic objects. This ultimate goal, however, is currently hampered by several challenging questions basically concerning sample damage, Coulomb explosion, and the role of nonlinearity. By employing an original ab?initio approach, we address these issues showing that XFEL-based single-molecule imaging will be only possible with a few-hundred long attosecond pulses, due to significant radiation damage and the formation of preferred multisoliton clusters which reshape the overall electronic density of the molecular system at the femtosecond scale.     

Unified Analysis for Calculating the Incoherent Spontaneous Emission of Cooperative Radiations

A unified analysis is presented to calculate the incoherent spontaneous power of cooperative radiations based on self-amplified spontaneous emission. Using quantum mechanical tools, we derive analytical expressions for the incoherent spontaneous power of undulator and Cherenkov free-electron lasers(FELs). The undulator and Cherenkov FELs are considered as two different examples for the radiation that accumulate cooperatively. In the case of the undulator FEL, we show an excellent agreement between an expression for the incoherent radiation power derived in the present work and that obtained using a completely different approach [Phys. Rev. E65(2002) 026501] For the Cherenkov radiation,we demonstrate a satisfactory agreement between the incoierent power predicted in our analysis and previous experimental results.     

Numerical modeling of thermal loading of diamond crystal in X-ray FEL oscillators

Due to high reflectivity and high resolution of X-ray pulses, diamond is one of the most popular Bragg crystals serving as the reflecting mirror and mono-chromator in the next generation of free electron lasers(FELs).The energy deposition of X-rays will result in thermal heating, and thus lattice expansion of the diamond crystal,which may degrade the performance of X-ray FELs. In this paper, the thermal loading effect of diamond crystal for X-ray FEL oscillators has been systematically studied by combined simulation with Geant4 and ANSYS, and its dependence on the environmental temperature, crystal size, X-ray pulse repetition rate and pulse energy are presented. Our results show that taking the thermal loading effects into account, X-ray FEL oscillators are still robust and promising with an optimized design.     

Amplification of monochromatic short-wavelength radiation during the stochastic deceleration of a relativistic electron stream in an incoherent pump field

The use of incoherent multiwave pump radiation or randomly varying magnetostatic fields (stochastic undulators) for improving the energy conversion efficiency in free-electron lasers based on stimulated wave scattering and the stimulated undulator emission of relativistic electron beams is proposed. It is shown within the quasilinear approximation that the electronic efficiency increases in proportion to the width of the pump spectrum due to enrichment of the spectrum of combination waves which are synchronous with the electron beam and realization of a mechanism of stochastic particle deceleration when the signal wave is monochromatic. At the same time, the efficiency scarcely depends on the spread of the beam parameters, making the use of the method promising for improving the efficiency of free-electron lasers powered by intense relativistic electron beams. Zh. Tekh. Fiz. 67, 77–81 (July 1997)     

Pumping Systems for Compton Free-Electron Lasers: Microwave Undulators and Powering Sources

Radiophysics and Quantum Electronics - The concept of Compton-type free-electron lasers (FELs) operating in short wavelength ranges with a high efficiency and power level is currently underway at...     

Generation of doublet spectral lines at self-seeded X-ray FELs

Self-seeding schemes, consisting of two undulators with a monochromator in between, aim to reduce the bandwidth of SASE X-ray FELs. We recently proposed to use a new method of monochromatization exploiting a single crystal in Bragg transmission geometry for self-seeding in the hard X-ray range. The obvious and technically possible extension is to use such kind of monochromator setup with two (or more) crystals arranged in a series to spectrally filter the SASE radiation at two (or more) closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet (or multiplet) spectral lines. Exploitations of such mode of operation involve any situation where there is a large change in cross-section over a narrow wavelength range. In this paper we consider the simultaneous operation of the LCLS hard X-ray FEL at two closely spaced wavelengths. We present simulation results for the LCLS baseline, and we show that this method can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band, i.e. within 10 eV. An interesting aspect of the proposed scheme is a way of modulating the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating “mode-beat” component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. Thus, at saturation one obtains FEL-induced modulations of energy loss and energy spread in the electron bunch at optical frequency. These modulations can be converted into density modulation at the same optical frequency with the help of a weak chicane installed behind the baseline undulator. Powerful coherent radiation can then be generated with the help of an optical transition radiation (OTR) station, which have important applications. In this paper we briefly consider how the doublet structure of the XFEL generation spectra can be monitored by an optical spectrometer. Furthermore, the OTR coherent radiation pulse is naturally synchronized with the X-ray pulses, and can be used for timing the XFEL to high power conventional lasers with femtosecond accuracy for pump-probe applications.     

Reshaping of attosecond x-ray pulses in thin crystals

A method for reshaping and control of the duration of attosecond x-ray pulses in thin crystals is proposed. The finite width of the reflection and transmission curves around the Bragg angle allows one to engineer Fabry-Perot-type filters for the generation of a large variety of attosecond pulse shapes. The method considered here can be used to manipulate attosecond pulses produced by high-harmonic generation and also for shorter wavelengths for attosecond pulses from x-ray free-electron lasers. X-ray pulses with controllable amplitude and phase may find useful applications in the newly emerging area of attosecond time-resolved spectroscopy.