Comparison experiments of neon and helium buffer gases cooling in trapped ~(199)Hg~+ ions linear trap

The influences of different buffer gas, neon and helium, on199Hg+clock transition are compared in trapped199Hg+linear trap. By the technique of time domain’s Ramsey separated oscillatory fields, the buffer gas pressure frequency shifts of199Hg+clock transition are measured to be(d f /dPNe)(1/ f) = 1.8 × 10-8Torr-1for neon and(d f /dPHe)(1/ f) = 9.1 × 10-8Torr-1for helium. Meanwhile, the line-width of199Hg+clock transition spectrum with the buffer gas neon is narrower than that with helium at the same pressure. These experimental results show that neon is a more suitable buffer gas than helium in199Hg+ions microwave frequency standards because of the199Hg+clock transition is less sensitive to neon variations and the better cooling effect of neon. The optimum operating pressure for neon is found to be about 1.0 × 10-5Torr in our linear ion trap system.     

Evaluation of the frequency instability limited by Dick effect in the microwave ~(199)Hg~+ trapped-ion clock

In the microwave ~(199)Hg~+ trapped-ion clock, the frequency instability degradation caused by the Dick effect is unavoidable because of the periodical interrogating field. In this paper, the general expression of the sensitivity function g(t)to the frequency fluctuation of the interrogating field with Nπ-pulse(N is odd) is derived. According to the measured phase noise of the 40.5-GHz microwave synthesizer, the Dick-effect limited Allan deviation of our ~(199)Hg~+ trapped-ion clock is worked out. The results indicate that the limited Allan deviations are about 1.75 × 10~(-13)τ~(1/2) and 3.03 × 10~(-13)τ~(1/2) respectively in the linear ion trap and in the two-segment extended linear ion trap under our present experimental parameters.