Isotope shift in the neon ground state by extreme-ultraviolet laser spectroscopy at 74 nm

Narrow-band extreme-ultraviolet (xuv) radiation in the range 73.5–75.5 nm has been produced in Xe by generating the third harmonic of light from a frequency-doubled, pulsed blue-dye laser. In a one-xuv-photon plus one-uv-photon ionization process both 2${\mathit{p}}^{6\mathrm{-}}$2${\mathit{p}}^5$3s[3/2${]}_1$ and 2${\mathit{p}}^{6\mathrm{-}}$2${\mathit{p}}^5$3s’[1/2${]}_1$ transitions in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ were observed. Frequencies were calibrated using a tellurium absorption spectrum of the fundamental blue light. Frequencies of 134 459.33(5) ${\mathrm{cm}}^{\mathrm{-}1}$ for the 2${\mathit{p}}^{6\mathrm{-}}$2${\mathit{p}}^5$3s[3/2${]}_1$ and 135 888.73(5) ${\mathrm{cm}}^{\mathrm{-}1}$ for the 2${\mathit{p}}^6$-2${\mathit{p}}^5$3s’[1/2${]}_1$ transition in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ are obtained. In both transitions the isotope shift ${(}^{20}$Ne${\mathrm{-}}^{22}$Ne) was measured. The values are -0.014(3) ${\mathrm{cm}}^{\mathrm{-}1}$ and +0.003(3) ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. Combined with existing values for the 3s[3/2${]}_1$ and 3s’[1/2${]}_1$ level shifts, a value for the ground-state specific mass shift of 9.54(15) GHz is deduced, in good agreement with a theoretical value of 10.1 GHz.