Isotopically selective excitation from plural excited states

An isotope separation process is described for selectively producing transitions in particles of one first isotope type in an environment of a material having plural isotopes. The process includes the steps of: (1) producing a first transition in the particles of the first isotope type in the environment from a first highly populated energy state to a substantially higher energy condition therefore; 2) controlling the transition to selectively produce the first transition in the particles of the first isotope type without corresponding excitation of the other particles of the environment; 3) producing a second transition in further particles of the environment from one or more other populated states to a higher energy condition therefore; and 4) controlling the second transition to selectively produce the second transition in the particles of the one or more other populated states to the substantially higher energy condition without correspondingly exciting other particles of the environment. (author)