Absolute Frequency of Rubidium Optical Clock without Frequency Modulation
Chi-Hsiang Chu, Yu-Jhe Shin, Yi-Ting Lin*, Wang-Yau Cheng
We have measured the clock transition of rubidium. Using the cross-over frequency locking method developed by our team, we have achieved frequency-stabilized and frequency-scanning system only using one 778 nm laser. Moreover, we used a Helmholtz coil to reduce the influence of the Zeeman shift and learned about the coefficient of 87Rb 5S 1/2(F = 2) → 5D 5/2(F = 4) is −48.9 ± 2.6 kHz/G. We also build a vacuum system (~ 〖10〗^(-7) Torr) to measure Rb self-collision shift and found that the linear coefficient is −120±70 Hz/µTorr. Furthermore, the Allan deviation of our system can reach 3×〖10〗^(-13) within 1000 seconds of integration time. Finally, we have measured the rubidium 5S 1/2 (F = 3) → 5D 5/2(F = 1 ∼ 5) transition and only ±5 kHz difference between our results and the suggested value of Certificate in Investment Performance Measurement(CIPM).
Frequency locking and scanning system
(1.)We successfully confirmed by measurements in vacuum Rb chamber that our previous difference in absolute frequency measurements came from frequency shifts caused by gases of different elements
(2.)We use only one 778nm Fiber laser to perform frequency sweep and frequency lock at the same time through the cross-over spectroscopy.
(3) The rubidium atomic optical clock we made has a stability of 5 × 〖10〗^(-12) within 1 second integral time, reaching 3 × 〖10〗^(-13) within 1000 second of integration time.