ABSTRACT
Saturated amplification x-ray lasers using collisional-excitation schemes have been achieved by a laser whose pulse energy contains a few kilojoules in the early stage of the development and then later more than 100 J in a few hundred picosecond pulse duration. Population kinetics of the collisional-excitation laser is in principle rather simple compared to that of a recombining plasma laser. Laser-plasma-based x-ray lasers have been developed worldwide and application experiments have been performed mainly with the electron collisional-excitation scheme. The chapter describes the atomic processes in inner-shell ionization and hollow atom x-ray lasers. It discusses inner-shell ionization and hollow atom x-ray lasers for necessary intensities of x-rays and shows an example of experimental setup. The hollow atom production has been considered to be a fundamental process for inner-shell ionization x-ray lasers. For sufficiently short driving laser pulses, high-order harmonics generated in gases are emitted in a form of a narrow beam with the divergence decreasing with harmonic order.
