Observation of Ramsey's Interference Fringes in the Profile of Doppler-Free Two-Photon Resonances

Using two coherent time-delayed short pulses, we have demonstrated that one can obtain, in the profile of Doppler-free two-photon resonances, interference fringes with a splitting $\frac{1}{2T}$ ($T$, delay time between the two pulses) much smaller than the spectral width $\frac{1}{\tau }$ of each pulse ($\tau$ duration of each pulse). This method should lead to a number of important improvements in the presently available techniques of ultrahigh-resolution laser spectroscopy of atoms and molecules.