Abstract: The invention relates to a process for the separation of one isotope from a mixture of isotopes, which comprises selectively exciting the desired isotope to an energy level at a distance dE below the ionization continuum by means of laser irradiation, said level dE being at such a distance beneath the ionization continuum that the excited atoms at this level can be ionized by irradiation with an infrared laser, irradiating the excited atoms with an infrared laser so as to ionize them selectively, and separating the ionized atoms by deposition on a desired substrate. According to a modification of the process the desired isotope is excited in two or more steps of laser irradiation to an energy level above the ionization level, the excited atoms are permitted to decay by autoionization so as to form ions of the desired isotope, and these are collected.