Characterization of an All-cryogenic Oscillator as a Stable Frequency Source

摘要

An entirely cryogenic stable oscillator has been constructed and preliminary evaluation is underway. The oscillator consists of a ruby maser stabilized by a superconducting resonator. A unique three-cavity coupling technique isolates the superconducting stabilizer cavity from the biasing magnetic field of the maser while simultaneously providing electromagnetic coupling between these same elements. This general design has been developed into a configuration that is particularly rigid with respect to physical, thermal and electromagnetic distortions. Maser oscillation at 2.69 GHz is developed by a 500 Gauss magnetic field, supplied by a superconducting magnet in persistent mode, and is stimulated by a 13.04 GHz pump signal. The maser operates at very low input power (approx. equal 10(-exp 5) W) with approximately a 2 K noise temperature. The stabilizer cavity consists of a solid sapphire spool onto which a superconducting film has been deposited. This system has been integrated into a He4 cryostat capable of temperatures below 0.9 K. Frequency pulling effects caused by changes in pump amplitude, in pump frequency, in temperature and in magnetic field are being characterized. With a moderate system Q (Q = 10(exp 8)) the stability of the cryogenic oscillator exceeds that of our present rubidium reference oscillator. Using this reference, a stability of sigma y = 3x10(exp -14) in 4000 seconds was measured, a value nearly identical to that obtained when calibrating the reference against a hydrogen maser. Stabilizing resonators with Q > 10(exp 9) have been fabricated.