Optical Wiggler Free-Electron X-Ray Laser as a Two-Level Quantum, Generator with Fully Inverted Medium

Recently the possibility was widely discussed of creation of an X-ray free-electron laser (FEL) using a high-power laser pulse as the undulator (optical wiggler FEL) [1]. Optical wiggler FEL is characterized by relatively small energy of the used electrons (ε ~ 1÷10 MeV). In order to achieve high values of the gain for X-rays it is necessary to use rather monoenergetic electron beams (Δγ/γ ~ 10–4) and the wigglers with a large number of periodic elements (N ≥ 104). In such FEL the energy of X-ray quantum can exceed the induced emission Cabsorption) linewidth: ωX > max {εΔγ/γ, ε(4N–1)}. We have shown that in this case the electrons interacting with the fields in FEL behave as two-level particles (the energies of these two levels are defined by energy and momentum conservation laws in an elementary act of stimulated Compton backscattering). The electron beam injected into the region of interaction with the energy close to the energy of the upper level represents a fully inverted medium for the amplified X-ray emission. The possibility is shown of FEL lasing with full extraction of inversion.