Laser modulation technique for single isotope spectroscopic studies

We demonstrate an atomic-beam approach to obtaining isotope specific driven-atom spectra using samples of arbitrary isotopic composition The method employs modulation of a target isotope ground-state population by an upstream preparation laser. Desired driven-atom signals generated downstream from the preparation laser are isolated using a lock-in amplifier referenced to the preparation laser modulation frequency. In our experiments, an intensity-modulated laser resonant with the barium (6s(2))S-1(o)-(6s6p)P-3(1), 791.1-nm intercombination transition selectively pumps Ba-138 atoms via radiative decays to the (6s5d)D-3(1,2) metastable states. Dressed-atom gain studies using the (6s(2))S-1(o)-(6s6p)P-1(1) 553.5-nm transition demonstrate the efficacy of the method. This technique has general utility for selectively isolating specific isotopic signals in systems possessing optically controllable atomic-beam populations.