METHOD TO MEASURE EXCITED-LEVEL-TO-EXCITED-LEVEL BRANCHING RATIOS ANDATOMIC TRANSITION-PROBABILITIES BY TIME-RESOLVED LASER PHOTOIONIZATION SPECTROSCOPY

An established photoionization branching-ratio measurement method, in which an excited level of an atom is populated by a pulsed laser from the ground level and repopulation of the ground level is measured by a second laser or lasers, is extended to the case with a finite lower-l evel lifetime. Two pulsed dye lasers populate the upper and the lower levels of the transition of interest. A third pulsed dye laser probes the time evolution of the lower level by a photoionization process. Th is measurement, coupled with the upper- and the lower-level lifetimes, permits the determination of the branching ratio and transition proba bility. Cerium branching ratios obtained are compared with those that we determined from the emission spectrum of cerium. The method is test ed for the difficult case in which the lifetimes of the transition lev els are nearly equivalent. The effects of magnetic sublevels are inves tigated in ytterbium.