The X-ray emission from hollow atoms produced by collisions of multiply charged ions accelerated by a short pulse laser with a solid or foil is studied theoretically. The possibility of obtaining a high conversion efficiency X-ray source in an ultrafast atomic process (∼1 fs) is demonstrated using the multistep-capture-and-loss (MSCL) model. Such an X-ray source has a clear advantage for the spectral range around a few kiloelectron volts over the conventional Kα X-ray source. Namely, the number of X-ray photons increases as the laser energy becomes larger and could reach 3 × 1011 photons for a laser energy of about 10 J.