Isotope shift of ${}^{40,42,44,48}$Ca in the $4s{}^2{\mathrm{S}}_{\frac{1}{2}}\to 4p{}^2{\mathrm{P}}_{\frac{3}{2}}$ transition

Abstract

We report on improved isotope shift measurements of the isotopes ${}^{40,42,44,48}$Ca in the $4s{}^2{\mathrm{S}}_{\frac{1}{2}}\to 4p{}^2{\mathrm{P}}_{\frac{3}{2}}$ (D2) transition using collinear laser spectroscopy. Accurately known isotope shifts in the $4s{}^2{\mathrm{S}}_{\frac{1}{2}}\to 4p{}^2{\mathrm{P}}_{\frac{1}{2}}$ (D1) transition were used to calibrate the ion beam energy with an uncertainty of $\hat{I}”U\approx \pm 0.25$ V. The accuracy in the D2 transition was improved by a factor of $5-10$. A King-plot analysis of the two transitions revealed that the field shift factor in the D2 line is about 1.8(13) % larger than in the D1 transition which is ascribed to relativistic contributions of the $4p_{1/2}$ wave function.