Optical pumping to the 6s5d states in atomic barium.

Using a flow apparatus the time dependence of 6s(2) (1)S(0)- 6s6p (1)P(1) (553.5nm) resonance fluorescence in atomic barium has been studied following switch-on of cw laser excitation. It was found that the fluorescence decays with rates as great as 1.3x10(6)s(-1). Assuming this can be ascribed to the pumping of atoms to the 6s5d (1)D and (3)D metastable levels we obtain a value for the sum of the spontaneous decay rates A(6s6p (1)P(1)-6s5d (1)D, (3)D) = (2.1+-0.4)x10(-6)s(-1), significantly larger than other recent measurements and theoretical estimates.