In this paper we present the nonlinear quantum theory of X-Ray FEL in a wiggler. We present the solution of the Dirac equation in a space periodic strong magnetic field, which describes the quantum dynamics of a single electron in a wiggler. With the help of obtained wave function of an electron the self-consistent set of the Maxwell and relativistic quantum kinetic equations is obtained. Then, the process of coherent X-ray radiation generation in nonlinear quantum regime, when the photon energy is larger than resonance widths due to energetic/angular spreads of an electron beam and resonance width caused by finite interaction length, is investigated.
We calculate the coherent radiation in an undulator/wiggler with a vacuum chamber of arbitrary cross section. The backward radiation is a coherent and it has wavelengths about twice the period of the undulator/wiggler. Mostly of coherent radiation is going with the wavelengths approximately the bunch length at small angles however.
Electron-beams with a sinusoidal energy modulation have the potential to emit sub-femtosecond x-ray pulses in a free-electron laser. The energy modulation can be generated by overlapping a powerful infrared laser with an electron-beam in a magnetic wiggler. Here we report on a new infrared source for this modulation, coherent radiation from the electron-beam itself. In this self-modulation process, the current spike on the tail of the electron-beam radiates coherently at the resonant wavelength of the wiggler, producing a six-period carrier-envelope-phase (CEP) stable infrared field with gigaw…
We outline the fundamental coherent radiation emission processes from a bunched charged particles beam. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles, a pre-bunched electron beam can emit spontaneously coherent radiation proportional to the number of particles - squared, through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke's). The coherent SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed inje…
We develop a general model of coherent synchrotron radiation (CSR) impedance with shielding provided by two parallel conducting plates. This model allows us to easily reproduce all previously known analytical CSR wakes and to expand the analysis to the situations not explored before. It reduces calculations of the impedance to taking integrals along the trajectory of the beam. New analytical results are derived for the radiation impedance with shielding for the following orbits: a kink, a bending magnet, a wiggler of finite length, and an infinitely long wiggler. All our formulas are benchmark…
NSLS-II x-ray diagnostics will provide continuous online data of electron beam dimensions, which will be used to derive electron beam emittance and energy spread. It will also provide information of electron beam tilt for coupling evaluation. X-ray diagnostics will be based on imaging of bending magnet and three-pole wiggler synchrotron radiation sources. Diagnostics from three-pole wiggler source will be used to derive particles energy spread. Beta and dispersion functions will have to be evaluated for emittance and particles energy spread calculations. Due to small vertical source sizes imag…
Each successive generation of x-ray machines has opened up new frontiers in science, such as the first radiographs and the determination of the structure of DNA. State-of-the-art x-ray sources can now produce coherent high brightness keV x-rays and promise a new revolution in imaging complex systems on nanometre and femtosecond scales. Despite the demand, only a few dedicated synchrotron facilities exist worldwide, partially due the size and cost of conventional (accelerator) technology. Here we demonstrate the use of a recently developed compact laser-plasma accelerator to produce a well-coll…
Phase-Stable Self-Modulation for GHz Continuous-Wave Ultrafast X-Ray Free-Electron Lasers
Shanghai Advanced Research Institute, Chinese Academy of Sciences（中国科学院上海高等研究院）；University of Chinese Academy of Sciences（中国科学院大学）；Zhangjiang Laboratory（张江实验室）
Cascading stages of seeded free electron laser (FEL) is a promising way to produce fully coherent X-ray radiations. 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, which 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 fu…
We propose a new scheme to generate high-brightness and temporal coherent soft x-ray radiation in a seeded free-electron laser. The proposed scheme is based the coherent harmonic generation (CHG) and superradiant principles. A CHG scheme is first used to generate coherent signal at ultra-high harmonics of the seed. This coherent signal is then amplified by a series of chicane-undulator modules via the fresh bunch and superradiant processes in the following radiator. Using a representative of realistic set of parameters, three-dimensional simulations have been carried out and the simulations re…
Shanghai Coherent Light Facility (SCLF) is a quasi-CW hard X-ray free electron laser user facility which is recently proposed. Due to the high repetition rate, high quality electron beams, it is straightforward to consider an X-ray free electron laser oscillator (XFELO) operation for SCLF. The main processes for XFELO design, and parameters optimization of the undulator, X-ray cavity and electron beam are described. The first three-dimensional X-ray crystal Bragg diffraction code, named BRIGHT is built, which collaborates closely with GENESIS and OPC for numerical simulations of XFELO. The XFE…
Synchrotron radiation emitted by electrons passing through an undulator placed in a storage ring is decomposed in coherent modes. The case of ultimate storage rings where the electron emittance is comparable to the emittance of the photon fan is analyzed by means of the cross spectral density and the coherent mode spectrum. The proposed method permits naturally the statistical analysis and propagation of the cross spectral density along the beamline optics. The coherence properties of the X-ray beam at any point of the beamline are completely given in terms of the eigenvalues and coherent mode…
We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source base…
In this paper, we propose a scheme to generate tunable coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulator, a laser chirper and two bunch compressors to generate a prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. The initial modulation energy wavelength can be compressed by a factor of $1+h_b R_{56}^a$ in phase space, where $h_b$ is the energy bunch length chirp introduced by the laser chirper, $R_{56}^a$ is the momentum compaction factor of the first bunch compressor…
X-ray free-electron laser oscillator (XFELO) is expected to be a cutting edge tool for fully coherent X-ray laser generation, and undulator taper technique is well-known for considerably increasing the efficiency of free-electron lasers (FELs). In order to combine the advantages of these two schemes, FEL amplifier seeded by XFELO is proposed by simply using a chirped electron beam. With the right choice of the beam parameters, the bunch tail is within the gain bandwidth of XFELO, and lase to saturation, which will be served as a seeding for further amplification. Meanwhile, the bunch head whic…
We theoretically investigate the use of the intense transverse field created by a relativistic electron bunch to drive strong-field processes. Such bunches can be easily implemented from beam shaping in existing electron accelerators. We focus on the process of strong-field driven high harmonic generation and calculate the single-atom dipole response to the space-charge field of relativistic tilted electron beam. We compare the emitted radiation spectrum of the space-charge field to that of a few-cycle laser pulse and show that the space-charge field creates a spectrum which extends much furth…
In this paper, we propose a scheme to generate tunable multi-color attosecond coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulators, a laser chirper and two bunch compressors to generate a multi-spike prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. Such an electron beam transports through a series of undulator radiators and bunch compressors to generate multi-color coherent X-ray radiation. As an illustration, we present an example to generate two attosecond pulses wi…
The evolution from 3rd to 4th generation synchrotron radiation (SR) sources significantly enhanced their coherence, making coherent scattering techniques such as coherent X-ray diffraction imaging (CXDI) and X-ray photon correlation spectroscopy (XPCS) more accessible. We take advantage of a coherent modes decomposition and propagation model to carry out coherence analysis and simulations of CXDI experiments for the coherent Hard X-ray Coherent Scattering (HXCS) beamline at High Energy Photon Source.
The successful operation of the hard x-ray self-seeding experiment at the LCLS opens the era of fully coherent hard x-ray free electron lasers (FELs). However, the shot-to-shot radiation fluctuation is still a serious issue. In this paper, high-gain, single-pass x-ray FEL schemes seeded by the narrow bandwidth radiation signal from an x-ray FEL oscillator were proposed and investigated, which are expected to generate high brightness, fully coherent and stable x-ray pulse. A simple model has been developed to figure out the temporal and the spectral structures of the output pulses in x-ray FEL …
The propagation of hard X ray beam from partially coherent synchrotron source is simulated by using the novel method based on the coherent mode decomposition of Gaussian Schell model and wave front propagation. We investigate how the coherency properties and intensity distributions of the beam are changed by propagation through optical elements. Here, we simulate and analyze the propagation of the partially coherent radiation transmitted through an ideal slit. We present the first simulations for focusing partially coherent synchrotron hard X ray beams using this novel method. And when compare…
Electromagnetic radiation in the soft x-ray spectral range ($1-100~\rm{nm}$ wavelengths or $0.01-1~\rm{keV}$ photon energies) is rapidly gaining importance in both fundamental research and industrial applications. At present the degree of coherence and the average photon flux required by advanced applications is only available at large-scale synchrotron facilities and Free Electron Lasers (FELs), severely limiting the range of applications. We propose a fully coherent soft x-ray source, based on Inverse Compton Scattering (ICS) of electron bunches created by photoionization of a laser-cooled a…
We simulate the focusing of a partially-coherent X-ray beam emitted by an undulator in a fourth-generation storage ring performing coherent mode decomposition and wave optics propagation. The focus position is shifted, and its size is enlarged when an entrance slit crops the beam. This is the usual case when a slit is used to select the coherent fraction. The pairing of two focusing elements (mirrors, lenses or transfocators) to ensure a fixed focal position is also analyzed. Our results show that the image of a partially coherent source, such an undulator in a low-emittance storage ring, is a…
Fine time-resolved analysis of matter - i.e. spectroscopy and photon scattering - in the linear response regime requires a fs-scale pulsed, high repetition rate, fully coherent X-ray source. A seeded Free-Electron Laser (FEL) driven by a Super-Conducting Linac, generating $10^{8}$-$10^{10}$ coherent photons at 2-5 keV with abou 0.5 MHz of repetition rate, can address this need. The seeding scheme proposed is the Echo-Enabled Harmonic Generation, alimented by a FEL Oscillator working at 13.6 nm with a cavity based on Mo-Si mirrors. The whole chain of the X-ray generation is here described by me…
The fluctuations of the longitudinal coherence length expected from the world's first hard X-ray Free Electron Laser, the Linac Coherent Light Source, are investigated. We analyze, on a shot-to-shot basis, series of power spectra generated from 1D-FEL simulations. We evaluate how the intrinsic noise in the spectral profile of the X-ray beam reflects on its longitudinal coherence length. We show that the spectral stability of the LCLS beam will allow coherent X-ray experiments with a reasonable acquisition time. We also propose a scheme to deliver single-mode X-ray radiation using a narrow band…
The most promising way to increase the output power of an X-ray FEL (XFEL) is by tapering the magnetic field of the undulator. Also, significant increase in power is achievable by starting the FEL process from a monochromatic seed rather than from noise. This report proposes to make use of a cascade self-seeding scheme with wake monochromators in a tunable-gap baseline undulator at the European XFEL to create a source capable of delivering coherent radiation of unprecedented characteristics at hard X-ray wavelengths. Compared with SASE X-ray FEL parameters, the radiation from the new source ha…
Population of the 8 eV $^{229m}$Th isomer via the second nuclear excited state at 29.19 keV by means of coherent x-ray pulses is investigated theoretically. We focus on two nuclear coherent population transfer schemes using partially overlapping x-ray pulses known from quantum optics: stimulated Raman adiabatic passage (STIRAP), and successive $π$ pulses. Numerical results are presented for three possible experimental setups. Our results identify the Gamma Factory as the most promising scenario, where two ultraviolet pulses combined with relativistically accelerated ions deliver the required i…
We present a study of direct laser driven electron acceleration and scaling of attosecond bunch compression in unbound vacuum. Simple analytical expressions and detailed three-dimensional numerical calculations including space charge reveal the conditions for compression to attosecond electron sheets. Intermediate emittance minima suitable for brilliant x-ray generation via coherent inverse Compton scattering (ICS) are predicted. We verify the coherent emission properties of the resulting x-ray fields and demonstrate feasability for realistic laser parameters.
Compact coherent x-ray sources have been the focus of extensive research efforts over the past decades. As a result, several novel schemes like optical and nano-undulators for generating x-ray emissions in "table-top" setups are proposed, developed, and assessed. Despite the extensive efforts in the past decades, there exists no operational FEL based on optical or electromagnetic undulators. By combining the particle confinement capability of optical cavities with wiggling motion inside an optical undulator, this paper proposes a new concept for making a compact coherent x-ray source. The full…
A coherent x-ray or gamma ray can be created from a dense electron beam propagating through an intense laser undulator. It is analyzed by using the Landau damping theory which suits better than the conventional linear analysis for the free electron laser, as the electron beam energy spread is high. The analysis suggests that the currently available physical parameters would enable the generation of the coherent gamma ray of up to 100 keV. The electron quantum diffraction suppresses the FEL action, by which the maximum radiation energy to be generated is limited.
