Doppler-free two-photon spectroscopy of neon

Doppler-free two-photon transition between the $3s$, $J=2$ metastable state and the 4d^'(5/2), $J=3$ excited state of neon has been performed with a monomode cw dye laser. We have measured the hyperfine constants of the 4d^'(5/2), $J=3$ state of ²¹Ne to be A=-235.9±0.6 MHz and B=11±9 MHz. The isotopic shifts for this two-photon transition are E(²²Ne)-E(²⁰Ne)=2780.0±2.5 MHz and E(²¹Ne)-E(²⁰Ne)=1452±6 MHz. From these results, the possibility of a slight departure from the mass formula cannot be rejected.