Observation of coherent effect in undulator radiation

Abstract

The coherent effect in spontaneous emission has been observed in a low-energy, low-gain, waveguide-mode free-electron laser. The intensity of the radiation was more than ${10}^{3}$ times stronger than that of the incoherent radiation. This enhancement is due to coherent radiation emitted by the electron beam, which is randomly modulated by micropulses whose typical pulse width (\ensuremath{\sim}35 ps) is comparable to the radiation wavelength. The measured power tends towards a quadratic dependence on the electron-beam current.