54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023;
Spokane, Washington
Session N01: Poster Session II (4:00pm-6:00pm, PT)
4:00 PM,
Wednesday, June 7, 2023
Room: Exhibit Hall C
Abstract: N01.00021 : Measurement of Absolute Photoionization Cross Sections from the 7s and 7p Excited States of Atomic Ytterbium*
Abstract
Presenter:
Bilal Shafique
(Department of Physics, University of Azad Jammu & Kashmir)
Authors:
Bilal Shafique
(Department of Physics, University of Azad Jammu & Kashmir)
Raheel Ali
(Quaid-i-Azam University, Islamabad, Pakistan)
New studies of the absolute photoionization cross-sections from the two excited states (6s7s 1S0 and 6s7p 3P2) of neutral ytterbium (Yb I) are reported. The saturation technique has been implemented, in which the intensity of the exciting laser is kept fixed while that of the ionizing laser is varied using neutral density filters. The photo-ion signal from the excited state at and above the threshold region was recorded as a function of ionizing laser intensity. Two Hanna-type dye lasers along with a thermionic diode detector working in the space-charge limited mode were used for the measurements. In the first set of experiments, the population from the ground state (6s2 1S0) was promoted to the 6s7s 1S0 excited state (34350.65 cm-1) via a two-photon transition using the dye laser wavelength tuned at 582.2 nm. The ionization limit above the excited state lies at 50443.08 cm-1 which is accessed via single-photon transition using a 621.4 nm dye laser wavelength. A total of four channels in the continuum at 0.07 eV, 0.11 eV, 0.34 eV, and 1.49 eV excess photoelectron energies above the ionization threshold (I.P.) are accessed. For the former two, dye lasers tuned at 600 nm and 590 nm are used whereas for the later ones, frequency-doubled (532 nm) and –tripled (355 nm) outputs of the Nd:YAG laser is used. The photoionization cross sections at and above the I.P. have been measured using the saturation technique as employed in the first set of experiments. In the third set, photoionization cross sections from the 6s7p 3P2 excited state have been measured at and above the I.P. For the 6s7p 3P2 state (38551.2 cm-1), the I.P. is accessed via 840 nm dye laser wavelength and all the continuum channels are accessed using 720 nm, 590 nm, and 355 nm ionizing wavelengths at 0.25eV, 0.63 eV, 65 and 2.02 eV photoelectron energies, respectively. The measured photoionization cross-sections show a monotonic decrease above the first ionization threshold which is an interesting behavior whereas a higher value of cross-section at the ionization threshold means that the wave functions of the exited state and the continuum channels are strongly overlapped. To the best of our knowledge, all the photoionization cross-section measurements are reported for the first time.
*The authors are grateful to the Higher Education Commission of Pakistan for the financial support.