Ultra-high resolution spectroscopy in the infrared region using a supersonic beam of SF/sub 6/

Summary form only given. We have developed a Doppler-free two-photon Ramsey fringes experiment with a supersonic beam of SF/sub 6/. We first separated the two interaction zones by 8 cm, and recorded some fringes with a periodicity of 2.3 kHz. Then, with a He beam seeded with SF/sub 6/ and a 20 cm separation we decreased the periodicity to 1.5 kHz, which corresponds to a 375 Hz linewidth. This is comparable with the highest resolution achieved at 10 /spl mu/m but the signal to noise ratio is currently better. Our last result, with such a large separation, demonstrates the experimental advantage of a two-photon configuration. Concerning the metrological features, we estimated that the systematic effects are either very small or can be easily and precisely measured or calculated. We have now improved the collimation of our experimental apparatus by adding an intermediate chamber and have the opportunity to increase the interzone distance as well as the resolution by one order of magnitude. This Ramsey method seems very promising for ultra-high resolution spectroscopy, and our set-up is a very serious candidate for a novel frequency standard in the infrared region with a potential accuracy in the 10/sup -14/-10/sup -5/ range.