Cryogenic sapphire oscillator with improved frequency stability

Extremely high short-term frequency stability has been realized in oscillators based on liquid helium cooled sapphire resonators with a modified mounting structure. These oscillators have exhibited an Allan deviation of about 5.4/spl times/10/sup -16/spl tau/1/2/ for integration time /spl tau/ of 1-4 s and a minimum Allan frequency deviation of 2.4/spl times/10/sup -16/ at 32 s.