Measurements of oscillator strengths for the principal series of calcium 4${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$→4snp ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ (11≤n≤25) are reported. The data were acquired using the magneto-optical spectroscopic technique, utilizing the linearly polarized light emitted by the 2.5-GeV electron accelerator, a 7-T superconducting magnet, and a 3-m-high dispersion spectrograph with photographic detection. A quantum-defect plot of the density of the oscillator strengths of discrete transitions yields the photoionization cross section at threshold as 2.04±0.20 Mb, in agreement with earlier measurements.

• Received 18 October 1993

DOI:https://doi.org/10.1103/PhysRevA.49.3419