Abstract
Current progress with tunable lasers has made possible the selective excitation of practically any single quantum state of an atom or a molecule with excitation energy in the range 0.1 to 10 eV. Already we can obtain coherent radiation with sufficient intensity to excite a significant fraction of an atomic or molecular sample into chosen quantum states in the wavelength range 2000 Å to 20 microns. Systematic studies of the effect of selective laser radiation on matter have been under way since around 1969 and 1970, when substantial progress in the art of quantum electronics made the experiments possible.