Basic consideration on high power free-electron lasers

An FEL amplifier to generate a laser power of the order of TW at 4 μm wavelength is investigated for a γ-γ collider. A concept of an amplifier chain consisting of a phase-displacement deceleration FELs is proposed to increase the FEL efficiency and to mitigate the requirement for the beam energy spread. The feasibility of the driving linac for the FEL system is also discussed.