Technology Readiness of the Cryogenic Sapphire Oscillator.

Abstract

International audienceThe cryogenic sapphire oscillator (CSO) delivers a reference signal exhibiting the lowest frequency fluctuations. For<br&gtthe best units, the Allan deviation (ADEV) is σy(τ ) &lt; 10−15 for integration time between 1 and 104 s, with a drift &lt; 10−14 in one day. The oscillator is based on a sapphire monocrystal resonating at 10 GHz in a whispering-gallery mode, cooled at 6 K for highest Q-factor and zero thermal coefficient. We report on the progress accomplished implementing eleven CSOs in about 10 years starting with the first sample delivered to the ESA station&nbsp; Argentina. Short- term stability is improved by a factor of 3-10, depending on τ, and the refrigerators electric power is reduced to 3 kW. Frequency stability and overall performances are reproducible, with unattended operation between scheduled maintenance every two years. The CSO is suitable to scientific applications requiring extreme frequency stability with reliable long-term operation. For example, flywheel for primary frequency standards, ground segment of GNSS, astrometry, VLBI, and radio astronomy stations. The CSO technology developed at the FEMTO-ST Institute is now mature for deployment in real very demanding application