Doppler-free two-photon spectroscopy of neon

Doppler-free two-photon transition between the 3s, J=2 metastable state and the 4d^' (52), J=3 excited state of neon has been performed with a monomode cw dye laser. We have measured the hyperfine constants of the 4d^' (52), J=3 state of ^21Ne to be A=-235. 90. 6 MHz and B=119 MHz. The isotopic shifts for this two-photon transition are E (^22Ne) -E (^20Ne) =2780. 02. 5 MHz and E (^21Ne) -E (^20Ne) =14526 MHz. From these results, the possibility of a slight departure from the mass formula cannot be rejected.