Oscillator strength measurements of the 3p ↦ nd Rydberg transitions of sodium

We report new measurements of the oscillator strengths of the 3p 2P3/2 ↦nd 2D5/2, 3/2 and 3p 2P1/2 ↦ nd 2D3/2 Rydberg transitions of sodium using a thermionic diode ion detector in conjunction with the Nd:YAG pumped dye lasers. The ns 2S1/2 and nd 2D5/2,3/2 Rydberg series have been recorded via two-step excitation, from the 3p 2P3/2 and 3p 2P1/2 intermediate states. Employing the saturation technique, the photoionization cross sections from the 3p 2P3/2 and 3p 2P1/2 intermediate states at the first ionization threshold are determined as 7.9(1.3) Mb and 6.7(1.1) Mb respectively. The f-values of the Rydberg transitions are calibrated with the photoionization cross section measured at the first ionization threshold and compared with the earlier data