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|Title:||Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator|
|Citation:||IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2014; 61(9):1463-1469|
|Publisher:||IEEE-Institute of Electrical and Electronics Engineers|
|Akifumi Takamizawa, Shinya Yanagimachi, Takehiko Tanabe, Ken Hagimoto, Iku Hirano, Ken-ichi Watabe, Takeshi Ikegami, and John G. Hartnett|
|Abstract:||The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.|
|Rights:||© 2014 IEEE|
|Appears in Collections:||IPAS publications|
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