Proposal to Generate an Isolated Monocycle X-Ray Pulse by Counteracting the Slippage Effect in Free-Electron Lasers

A novel scheme is proposed to generate an isolated monocycle x-ray pulse in free-electron lasers, which is based on coherent emission from a chirped microbunch passing through a strongly tapered undulator. In this scheme, the pulse lengthening by optical slippage, being intrinsic to the lasing process of free-electron lasers, can be effectively suppressed through destructive interference of electromagnetic waves emitted at individual undulator periods. Calculations show that an isolated monocycle x-ray pulse with a wavelength of 8.6 nm and a peak power of 1.2 GW can be generated if this scheme is applied to a 2-GeV and 2-kA electron beam.

Figure 1

Mechanism to generate a monocycle pulse from the chirped microbunch.

Figure 2

Layout of the undulators and chicanes for the MCHG scheme.

Figure 3

Schematic illustration of the current profiles ($j$) and electric field distributions ($E$) at the borders between different sections.

Figure 4

Simulation results for $n=7$ (8.6 nm), ${\sigma }_{\gamma }/\gamma =5\times {10}^{-5}$, and $\mathrm{\Delta }K/K=0.5$.

Figure 5

(a),(c) Peak power and (b),(d) pulse length plotted as a function of $m$ for different values of ${\sigma }_{\gamma }/\gamma$.