Abstract

The possibility of a neutral atom-based "ultimate" frequency standard in the optical domain has improved dramatically with the discovery of sub-Doppler cooling mechanisms. Unfortunately, the atoms with clock transitions of order 1 Hz that have been identified will be extremely difficult to laser cool. We have identified a two-photon transition in metastable xenon (³P₂→³P₀) at 2.19 microns with a calculated linewidth of 2 Hz. Metastable xenon can be laser-cooled with a cycling transition at 882 nm, convenient for Ti:sapphire lasers, with cooling parameters almost identical to cesium. Expected temperatures should be about 3 microkelvin, which will allow a fountain to be constructed that has little loss of signal due to spatial spreading of the atoms. After making the 2-photon clock transition, the atoms that are in the ³P₀ metastable state can be detected with high efficiency with a metastable detector. Atoms in the lower metastable state can be completely removed by applying small amounts of diode laser light at 828 nm to drive atoms into the ground state, allowing high efficiency, essentially background-free detection. Two-photon transition rates and AC stark shifts have been calculated and will be presented. Possible laser sources for the clock transition will be discussed, as well as a connection from this optical frequency to the microwave.

© 1990 Optical Society of America