Resonant Laser Ablation of Lanthanides: Eu and Lu Resonances in the 450−470 nm Region

Abstract

Resonant laser ablation (RLA) of solids with a pulsed dye laser achieves wavelength-specific enhancements in yields of particular metal ions (M+) by resonant photoionization or photoexcitation of atoms in the ablation plume. In the present study, RLA was performed for λ = 450−470 nm on solids comprising selected lanthanide elements. Enhancements in yields of Eu+ and Lu+ occurred at wavelengths corresponding to one-photon resonant absorptions for the neutral atoms: Ln + hν → Ln*. The excited Ln* were subsequently preferentially ionized by the quasi-thermal collisional processes normally operative in the ablation plume: Ln* + kT → Ln+ + e-. The excessive atomic absorption line widths of up to 40 cm-1 (fwhm) were attributed primarily to collisional and Stark broadening in the dense plume. The strongest Eu+ resonances correspond to transitions from ground Eu (4f76s2 8S7/20) to 4f76s6p 8PJ levels at 21 445 (J = 5/2), 21 605 (J = 7/2), and 21 761 cm-1 (J = 9/2). Primary Lu+ resonances were for excitation from...