Generating carrier-envelope-phase stabilized few-cycle pulses from a free-electron laser oscillator

We propose a scheme to generate carrier-envelope-phase (CEP) stabilized few-cycle optical pulses from a free-electron laser oscillator. The CEP stabilization is realized by continuous injection of CEP-stabilized seed pulses from an external laser to the FEL oscillator whose cavity length is perfectly synchronized to the electron bunch repetition. Such CEP-stabilized few-cycle FEL pulses will be an efficient driver for exploring high-harmonic generation at energies 1-10~keV for attosecond and zeptosecond science, broad-band x-ray optical frequency combs and coherent control of chemical reaction.