Comment on `On quantum effects in spontaneous emission by a relativistic electron beam in an undulator' by G. Geloni, V. Kocharyan and E. Saldin (arXiv:1202.0691)

In arXiv:1202.0691, Geloni et al. criticise our recent work describing the spontaneous emission by a relativistic, undulating electron beam. In particular they claim that our prediction of a quantum regime in which evolution of the electron momentum distribution occurs as a sequential population of discrete momentum groups rather than in terms of a drift-diffusion process is unphysical and artificial. We show that the criticism of our model contained in arXiv:1202.0691 is unfounded.