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

TL;DR

This study presents highly precise isotope shift measurements of calcium isotopes in the D2 transition, revealing a relativistic effect on the field shift factor through a King-plot analysis.

Contribution

It provides improved isotope shift data for calcium isotopes and demonstrates the relativistic influence on the field shift factor between D1 and D2 transitions.

Findings

Isotope shift measurements improved by a factor of 5-10.

The field shift factor in D2 is about 1.8% larger than in D1.

Relativistic effects influence the wave function contributions to isotope shifts.

Abstract

We report on improved isotope shift measurements of the isotopes $^{40,42,44,48}$Ca in the $4s\,^2 \rm{S}_{\frac{1}{2}} \rightarrow 4p\,^2\rm{P}_{\frac{3}{2}}$ (D2) transition using collinear laser spectroscopy. Accurately known isotope shifts in the $4s\,^2 \rm{S}_{\frac{1}{2}} \rightarrow 4p\,^2\rm{P}_{\frac{1}{2}}$ (D1) transition were used to calibrate the ion beam energy with an uncertainty of $\Delta U \approx \pm 0.25$ 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.