Measurements of photoionization cross section of the 4p levels and oscillator strength of the 4p→nd 2D3/2,5/2 transitions of potassium

•New measurements of the photoionization cross sections from 4p-level of potassium.•New data on oscillator strengths of the 4p–nd transitions.•Two-step laser excitation and ionization.

We have carried out measurements of absolute photoionization cross sections of the 4p excited levels and oscillator strengths of the 4p→nd Rydberg transitions in potassium using a two-step photo-excitation and ionization technique in conjunction with a thermionic diode ion detector. The measurements were conducted using the linearly polarized laser light and the absolute values of the cross sections from the 4p 2P3/2 and 2P1/2 excited levels have been determined at the ionization threshold as (6.3±0.9) Mb and (5.4±0.8) Mb respectively. In addition, photoionization cross sections have been determined at various ionizing wavelengths above the first ionization threshold to explore different energy regions of the continuum. The oscillator strengths for the 4p 2P1/2→nd 2D3/2 and 4p 2P3/2→nd 2D3/2,5/2 Rydberg transitions have been deduced by using the measured cross sections of the 4p 2P1/2 and 2P3/2 levels at the ionization threshold. The new results are in good agreement with the available theoretical and experimental data.