  In order to effectively improve the output quality of X-ray free electron
laser (XFEL), we theoretically propose an XFEL scheme seeded by atomic
inner-shell laser. As well known, an atomic inner-shell laser based on neutral
atoms and pumped by an XFEL has been experimentally demonstrated, which
produced sub-femtosecond X-ray pulses with increased temporal coherence. It
shows that, by using the inner-shell laser as a seed to modulate the electron
bunch, very stable and almost fully-coherent short-wavelength XFEL pulses can
be generated. The proposed scheme holds promising prospects in X-ray
wavelengths, and even shorter.
