Measurement of short-term stability of ultra stable oscillators

We present in this paper the progress report of the building of two cryogenic sapphire oscillators (CSO) at LPMO. A description of our original resonator configuration is discussed. The measurement of a short-term frequency instability better than 2middot10^-14 for short integration times is presented. We also demonstrated an exceptional long term frequency stability of better than 5middot10^-14 over one day. We finally report the usefullness of CSO in the characterization of state of the art ultra stable quartz cristal oscillators in a simple way of measurement.