Phase-stable self-modulation of an electron-beam in a magnetic wiggler

TL;DR

This paper demonstrates a novel self-modulation technique in an electron-beam using coherent radiation from the beam itself, enabling phase-stable energy modulation for generating ultrashort x-ray pulses.

Contribution

It introduces a new infrared source based on electron-beam self-radiation, achieving phase-stable modulation without external lasers in a magnetic wiggler.

Findings

Produced a gigawatt-level CEP-stable infrared field.

Achieved a few MeV phase-stable energy modulation.

Enabled sub-femtosecond x-ray pulse generation.

Abstract

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 gigawatt power. This field creates a few MeV, phase-stable modulation in the electron-beam core. The modulated electron-beam is immediately useful for generating sub-femtosecond x-ray pulses at any machine repetition rate, and the CEP-stable infrared field may find application as an experimental pump or timing diagnostic.