Abstract
Present shortest wavelength of the atomic resonant laser reaches to be 1.5A. This length is beyond the
lattice constant of many condensed matter and the photon energy exceed up to 8 keV, which is
photoionization energy of the first transition metal. Here, the development of this inner shell excitation
Kα laser is mentioned with fundamental model to consider the threshold condition of this laser
oscillation. In addition, new mode selection method in hard x-ray laser is introduced. The present
research activities related to such ultra-high intense x-ray filed becomes high and we consider it is good
opportunity to consider future science with these new lasers.
