High-sensitivity detection of two-photon Ramsey fringes at 30 THz by frequency-comb assisted stimulated emission

Spectacular improvements in both resolution and signal-to-noise ratio of two-photon Ramsey fringes obtained at 30 THz have been achieved by implementing a new detection scheme. A molecular beam of SF₆, after passing through the Ramsey regions, is interrogated by a separate laser beam which makes optimal use of the entire Doppler profile by generating a comb of frequencies within a compensated high-finesse cavity. Resulting molecular spectra have the highest resolution ever obtained with CO₂ lasers and, as a standard, the system will soon outperform the best currently available.