Properties Of Free-electron Laser Research Articles

Analysis of the spectral properties of free electron lasers in X-RAY and other bands

Analytical formalism for the description of free electron laser (FEL) spectrum is proposed with account for the electron beam size, divergences, beam energy spread, the off-axis deflection and the periodic harmonic and non-periodic constant magnetic field components in undulators. The exact analytical expressions for the spontaneous undulator radiation (UR) are obtained in terms of generalized Bessel and Airy functions, which describe the spectrum line shape and intensities. The obtained analytical formulae distinguish the effects of each installation and beam parameter on the FEL harmonic radiation. The enhanced phenomenological model is employed for the FEL modeling; it describes the harmonic powers evolution along the undulators and gradual saturation around the saturation length with account for the saturated powers oscillations. With this model, we study the generation of FEL harmonics, including even, in several instances of FEL experiments at LCLS, LEUTL and PAL-XFEL. We analytically demonstrate the even harmonics reasons in the LCLS and LEUTL FEL experiments. The spectrum line split due to the beam size is demonstrated analytically and compared with experimentally measured spectral characteristics. The PAL-XFEL experiment is analyzed and compared with the LCLS experiment; the possibility of high harmonic radiation in it is explored. The modeling results fully agree with the measured values in the studied FELs. The analytical formalism shows physical background for each harmonic in every FEL. It allows the analysis of the radiation and beam alignment in projected, built and working FELs and it can help minimizing losses and correcting magnetic fields as well as projecting experiments with FELs.

On spectral and temporal coherence of x-ray free-electron laser beams.

A model for the coherence properties of free-electron lasers (FELs) in time and frequency domains is introduced within the framework of classical second-order coherence theory of nonstationary light. An iterative phase-retrieval algorithm is applied to construct an ensemble of field realizations in both domains, based on single-pulse spectra measured at the Linac Coherent Light Source (LCLS) in self-amplified spontaneous emission mode. Such an ensemble describes the specific FEL pulse train in a statistically averaged sense. Two-time and two-frequency correlation functions are constructed, demonstrating that the hard X-ray free-electron laser at LCLS in this case behaves as a quasistationary source with low spectral and temporal coherence. We also show that the Gaussian Schell model provides a good description of this FEL.

Time-resolved crystallography and protein design: signalling photoreceptors and optogenetics.

Time-resolved X-ray crystallography and solution scattering have been successfully conducted on proteins on time-scales down to around 100 ps, set by the duration of the hard X-ray pulses emitted by synchrotron sources. The advent of hard X-ray free-electron lasers (FELs), which emit extremely intense, very brief, coherent X-ray pulses, opens the exciting possibility of time-resolved experiments with femtosecond time resolution on macromolecular structure, in both single crystals and solution. The X-ray pulses emitted by an FEL differ greatly in many properties from those emitted by a synchrotron, in ways that at first glance make time-resolved measurements of X-ray scattering with the required accuracy extremely challenging. This opens up several questions which I consider in this brief overview. Are there likely to be chemically and biologically interesting structural changes to be revealed on the femtosecond time-scale? How shall time-resolved experiments best be designed and conducted to exploit the properties of FELs and overcome challenges that they pose? To date, fast time-resolved reactions have been initiated by a brief laser pulse, which obviously requires that the system under study be light-sensitive. Although this is true for proteins of the visual system and for signalling photoreceptors, it is not naturally the case for most interesting biological systems. To generate more biological targets for time-resolved study, can this limitation be overcome by optogenetic, chemical or other means?

Echo enabled harmonic generation free electron laser in a mode-locked configuration

Echo Enabled Harmonic Generation (EEHG) is a method of harmonic up-shifting proposed to extend the temporal coherence properties of Free Electron Lasers (FEL) at shorter wavelengths where coherent laser seed fields are not available. Previous theoretical studies of EEHG have applied periodic boundary conditions to the electron distribution in phase space. It is shown that when these periodic boundary conditions are removed a temporal comb of enhanced electron microbunching is revealed. By matching this comb structure in the electron microbunching to the radiation modes that are generated in a Mode-Locked Optical Klystron (MLOK) FEL configuration, a train of short radiation pulses can be generated.

Quantum statistical properties of free-electron laser with ion-channel guiding

AbstractThe operation of the quantum free-electron lasers (QFELs) with a helical wiggler and in the presence of ion-channel guiding is considered. The quantum Hamiltonian of single particle has been derived in the Bambini-Renieri (BR) frame. Time dependent wave function and three constants of motion are obtained. The Raman-Nath equation (RNE) and its approximation solution have been calculated, and then the resulted solution has been employed to obtain the quantum gain, photon statistics parameter and squeezing parameter. A quantum approach has been used to get quantum statistical properties of the FEL and the photon gain formula for the small signal gain limit. It is found that the ion-channel guiding decreases the squeezing. Also, the conditions for positive (bunching) and negative (antibunching) gain have been studied numerically.

Stability properties of free-electron laser in Raman regime with thermal electron beam

In the context of kinetic theory an expression for the growth rate of a free-electron laser, under the weak resonance instability condition, for full dispersion relation has been obtained. The space-charge potential is included in the analysis and the expression for growth rate reduces to that of the Compton regime under the low density condition. With the assumption of a spread in the longitudinal momentum in the form of a Gaussian distribution function, the effect of the thermal electron beam on the growth rate is studied. The results are compared to another linear theory, a computer simulation, and an experiment.

Short wavelength free electron lasers in 2000

Twenty-three years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs operating in the infrared, visible, UV, and X-ray wavelength regimes are listed and discussed.

Free electron lasers operating with variably polarization undulators

We discuss the properties of Free Electron Lasers (FEL) operating with variably polarizing undulators. We study the characteristics of the electron motion in this type of undulators and analyze the spectral properties of the emitted radiation. We also derive general expressions for the small signal gain coefficient and for the saturation intensity. Finally, we explore the characteristics of FEL operation in the hypothesis of Optical-Klystron configuration with particular reference to devices exploiting undulators with opposite polarizations. Regarding this last point, we show that interference may produce undesidered effects which may reduce rather than increase the small signal gain.

An undulator for FELICITA I

Twenty-three years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs operating in the infrared, visible, UV, and X-ray wavelength regimes are listed and discussed.

Present status of the NIJI-IV free-electron lasers

Twenty-three years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs operating in the infrared, visible, UV, and X-ray wavelength regimes are listed and discussed.

Assessment of free electron lasers

Free electron lasers represent a radical alternative to conventional lasers, being potentially the most flexible, high power and efficient generators of coherent radiation from the ultra-violet to the far infra-red. In this review the properties of free electron lasers are discussed from both a theoretical and an experimental viewpoint, and some likely areas of application for these devices are outlined.