Progress in the building of sapphire-helium clock at LPMO

We report a new high-Q sapphire whispering gallery mode resonator to achieve ultra high frequency stability. We propose to excite a sapphire resonator in an opened cavity to suppress number of low order spurious modes. Providing the azimuthal order of the chosen whispering gallery mode is high enough, Q-factors better than 2.10/sup 8/ have been observed which turns out to be sufficient to reach a high frequency stability. A realization of a 12 GHz WGH sapphire helium oscillator shows a relative frequency instability of 2/spl middot/10/sup -14/ in terms of standard deviation.