Saturated fluorescence method for determination of atomic transition probabilities: Application to the Ar i 430.0-nm (1s4-3p8) transition and the lifetime determination of the upper level

We have developed a new method for determination of atomic transition probabilities based on laser-induced-fluorescence spectroscopy (LIFS). In the method one produces a known population of atoms in the upper level under investigation and relates it to an observed absolute line intensity. We have applied this method to the argon 430.0-nm line (1$s_4$-3$p_8$): In an argon discharge plasma the 1$s_5$-level population and spatial distribution are determined by the self-absorption method combined with LIFS under conditions where the 3$p_8$-level population is much lower than that of the 1$s_5$ level. When intense laser light of 419.1 nm (1$s_5$-3$p_8$) irradiates the plasma and saturates the 3$p_8$-level population, the produced 3$p_8$-level population and its alignment can be determined from the 1$s_5$-level parameters as determined above, by solving the master equation on the basis of broad-line excitation. By comparing the observed absolute fluorescence intensity of the 430.0-nm line with the above population, we have determined the transition probability to be A=(3.94±0.60)×${10}^5$ ${\mathrm{s}}^{\mathrm{-}1}$. We also determined the 3$p_8$-level lifetime by LIFS. Several factors which might affect the measurement are discussed. The result is τ=127±10 ns.