Transverse effects in the production of x rays with a free-electron laser based on an optical undulator

Abstract

The interaction between high-brilliance electron beams and counterpropagating laser pulses produces x rays via Thomson backscattering. If the laser source is long and intense enough, the electrons of the beam can bunch on the scale of the emitted x-ray wavelength and a regime of collective effects can establish. In this case of dominating collective effects, the FEL instability can develop and the system behaves like a free-electron laser based on an optical undulator. Coherent x rays can be irradiated, with a bandwidth very much thinner than that of the corresponding incoherent emission. The emittance of the electron beam and the distribution nonuniformity of the laser energy are the principal quantities that limit the growth of the x-ray signal. In this work we analyze with a 3D code the transverse effects in the emission produced by a relativistic electron beam when it is under the action of an optical laser pulse and the x-ray spectra obtained. The scalings typical of the optical wiggler, characterized by very short gain lengths and overall time durations of the process, make possible considerable emission also in violation of the Pellegrini criterion for static wigglers. A generalized form of this criterion is validated on the basis of the numerical evidence.

Plasma Undulator Based on Laser Excitation of Wakefields in a Plasma Channel

“…Undulators with periods less than or on the order of a millimeter, often referred to as micro-undulators, are, therefore, of great interest. Several micro-undulator ideas have been proposed including electro-static undulators [3,4], crystalline undulators [5], RF-based [6], laser-plasma-based [7][8][9], and optical undulators [10][11][12][13][14][15][16][17]. In this Letter we propose a micro-undulator based on controlling the transverse forces experienced by an electron beam inside a laserexcited plasma channel.…”

Experimental requirements for X-ray compact free electron lasers with a laser wiggler

“…1 Ref. [21] contains some incorrect and misleading results, which can generate confusion in the scientific community: (a) As it is well known, the spectrum of the SASE radiation is affected by random spikes when the electron beam contains many cooperation lengths [5]. Up to now, this spiking behavior has been confirmed by all the numerical simulations [12][13][14] and experiments [6][7][8].…”

“…We remark that the values of R and s cannot be arbitrarily chosen, but must be deduced consistently by the independent parameters of the system (see also the scaling laws given in Appendix A). A different but less accurate approach to the classical case with similar parameters has been recently published [21]. 1 Ref.…”

Dual color x-rays from Thomson or Compton sources

“…Considering negligible the correlations between the electrons that could give rise to collective effects [47,48], and in a linear or moderately nonlinear regime [49,50] generalization to an ensemble of electrons can be made by summing over the whole beam the contributions of the single particles. As regards the interacting field, Gaussian functions describe correctly the profiles, with the normalized electric field A L given by the expression…”