Abstract
Three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers has been demonstrated. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d(5)4s5s f(6)S(5/2) level at 49 415.35 cm(-1), while Rydberg transitions were reached from the 3d(5)4s4d e D-6(9/2,7/2,5/2) levels at around 47 210 cm(-1). Analyses of the strong Rydberg transitions associated with the 3d(5)4s4d e D-6(7/2) lower level indicate that they belong to the dipole-allowed 4d -> nf(6)F degrees(9/2,7/2,5/2) series converging to the 3d(5)4s S-7(3) ground state of Mn II. From this series, an ionization potential of 59 959.56 +/- 0.01 cm(-1) is obtained for Mn. At high ion source temperatures the semi-forbidden 4d -> nf(8)F degrees(9/2,7/2,5/2) series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.