High-Gain Thompson-Scattering X-Ray Free-Electron Laser by Time-Synchronic Laterally Tilted Optical Wave

A novel approach to generating coherent x rays with ${10}^9–{10}^{10}$ photons and femtoseconds duration per laser pulse is proposed. This high intensity x-ray source is realized first by the pulse front tilt of a lateral fed laser to extend the electron-laser synchronic interaction time by several orders, which accomplishes the high-gain free-electron-laser-type exponential growth process and coherent emission with highly microbunched electron beam. Second, two methods are presented to enhance the effective optical undulator strength parameter. One is to invoke lenses to focus two counterpropagating lasers that are at normal incidence to the electron beam as a transverse standing wave; the other is to invent a periodic microstructure that can significantly enhance the center electromagnetic field realized by a resonant standing wave and the quadrupole waveguides. The energy coupling efficiency between the electron beam and laser is therefore greatly improved to generate the high brightness x rays, which is demonstrated by analytical and simulation results.

Figure 1

Time-synchronic interaction of electrons with pulse front tilted lasers: (a) top view; (b) side view.

Figure 2

(a) Equivalence of the tilted pulse and a full rectangular pulse; (b) side view of the flattop laser.

Figure 3

The 3D view of the periodic microstructure for the interaction of electrons and bilaterally fed lasers with pulse front tilt; the vacuum channel width $W_c$, and the height $H_s$ and width $W_s$ for the silicon waveguide.

Figure 4

(a) The complex magnitude field in the quarter of the quadrupole structure. (b) Snapshot of the electric field vector on the central vertical plane. Electron beams fly toward the $+z$ direction.

Figure 5

The normalized complex magnitude of the electric field $E_y/E_m$ along the center line of the Si waveguide in the $x$ direction (bottom, green curve) and along the central line of quadrupole channel in the $z$ direction (upper, red curve) for $W_c=1.3\lambda$, $H_s=0.3\lambda$, $W_s=0.19\lambda$, $L_0=0.42\lambda$, $\Delta \varphi =0.72\pi$. $E_m$ is the peak field in the waveguide.

Figure 6

GENESIS simulation (solid red curve) of a 1 keV FEL together with analytical results (dashed red curve) and that (solid blue curve) of a 6.5 keV FEL together with analytical results (dashed blue curve).