Photoionization cross-section measurements from the 6s5d 1D2 excited state of atomic ytterbium

Abstract

We present new experimental measurements on the photoionization cross-sections from the 6s5d1D2 excited state of ytterbium using a heat pipe-cum-linear thermionic diode ion detector, working in the space-charge limited mode to generate ytterbium vapor. A Nd:YAG laser pumped narrow bandwidth (~ 0.2 cm-1) Hanna-type dye laser, charged with LDS-698 dye and tuned at 722.6 nm, was used to excite atoms via the 6s2 1S0 → 6s5d1D2 two-photon transition from the ground state. The excited state population was then promoted to the ionization threshold at 439.2 nm ionizing laser wavelength and above the ionization threshold at 435 nm, 355 nm, and 266 nm laser wavelengths. The photoionization cross-sections at each of these wavelengths have been determined using the saturation technique. At the first ionization threshold, the photoionization cross-section from the 6s5d1D2 excited state is extracted as 40.5 ± 6.2 Mb, whereas at higher energies in the continuum, the cross-section decreases up to 6.4 Mb at 266 nm, which corresponds to 1.84 eV excess energy.