Isotope shift spectroscopy in neutral strontium

Isotope shift spectroscopy provides a sensitive probe into nuclear physics and recent proposals have suggested using the linearity of King plots to put a bound on new physics. The narrow lines and four stable isotopes of strontium are an attractive platform for such an investigation. We present isotope shift measurements, and a King plot analysis on the $^1$S$_0 \rightarrow ^3$P$_0$ clock transition and the $^1$S$_0 \rightarrow ^3$P$_1$ intercombination line in all four stable isotopes of strontium. This work could help resolve discrepancies between measured and theoretical values for the field shift constants from a similar analysis in Ca$^+$. In addition, it paves the way for using the narrow optical transitions of strontium to put limits on new physics.