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Physical Review Letters

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

M. M. Salour, Claude N. Cohen-Tannoudji

Published Apr 4, 1977• 173 citations
Publisher

Abstract

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 $\frac{1}{\ensuremath{\tau}}$ of each pulse ($\ensuremath{\tau}$ 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.

DOI
10.1103/physrevlett.38.757

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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 12T\frac{1}{2T}2T1​ (TTT, delay time between the two pulses) much smaller than the spectral width 1\ensuremathτ\frac{1}{\ensuremath{\tau}}\ensuremathτ1​ of each pulse (\ensuremathτ\ensuremath{\tau}\ensuremathτ 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.
We have studied Doppler-free two-photon excitation of atoms with a train of phase-coherent standing-wave light pulses, originating from the same laser pulse. Quantum interference effects produce narrow spectral fringes which have a physical origin similar to that of Ramsey fringes. Linewidths much less than the Fourier-transform limit of an individual light pulse have been observed for the sodium $3S\ensuremath{-}5S$ transition; and a dramatic enhancement of the resonant signal is possible.
Molecular or atomic coherence generated with the irradiation of ultrashort optical pulses should make a significant role for realizing the control of quantum states in a matter. By virtue of the advancement of the ultrashort light sources towards the short wavelength region, the energy range of the quantum states that could be coherently generated reached much more than 15 eV at the present [1] . In particular, Ramsey-type interference fringes observed by scanning the delay between a pair of phase-locked XUV femtosecond pulses unveiled spectral information of the atomic states [2] - [4] . The time ranges of the delay scans in such preceding studies were long enough to finely resolve the spectral features, while the XUV pulse pairs could not temporally overlap because the light sources were split into two before generating the XUV pulses. The near 0 delay control of the XUV pulse pair is important for investigating the dynamics of a cationic system entangled with an ionized continuum electron [5] . In this paper, we performed the delay scan of the XUV pulse pair starting from the complete temporal overlap to show that the optical interference seamlessly continued to the Ramsey-type atomic interference as a prototype of such study.