Isotope shifts and hyperfine structure of the laser cooling Fe I 358-nm line

Abstract

We report on the measurement of the isotope shifts of the $3d^74s \,\, a \, {}^5\!F_5 - 3d^74p \,\, z \, {}^5\!G^o_6$ Fe~I line at 358~nm between all four stable isotopes ${}^{54}$Fe, ${}^{56}$Fe, ${}^{57}$Fe and ${}^{58}$Fe, as well as the hyperfine structure of that line for ${}^{57}$Fe, the only stable isotope having a nonzero nuclear spin. This line is of primary importance for laser cooling applications. In addition, an experimental value of the field and specific mass shift coefficients of the transition is reported as well as the hyperfine structure magnetic dipole coupling constant $A$ of the transition excited state in $^{57}$Fe, namely $A(3d^74p \,\, z \, {}^5\!G^o_6)=31.241(48)$ MHz. The measurements were carried out by means of laser-induced fluorescence spectroscopy performed on an isotope-enriched iron atomic beam. All measured frequency shifts are reported with uncertainties below the third percent level.