[1] Horton J W, Marrison W A. Precision determination of frequency[J]. Proceedings of the Institute of Radio Engineers, 16, 137-154(1928).
[2] Feng J J, Su H, Gao J, Ge C X. Summary of International Metrology Conferences (Continued)[J]. China Metrology, 45-48(2007).
[3] Wang Y Q, Wang Q J, Fu J S et al[M]. Principles of quantum frequency(1989).
[4] Huang Y, Guan H, Zeng M Y et al. 40Ca+ ion optical clock with micromotion-induced shifts below 1 × 10-18[J]. Physical Review A, 99, 011401(2019).
[5] Chou C W, Hume D B, Koelemeij J C J et al. Frequency comparison of two high-accuracy Al+ optical clocks[J]. Physical Review Letters, 104, 070802(2010).
[6] Fürst H, Yeh C H, Kalincev D et al. Coherent excitation of the highly forbidden electric octupole transition in 172Yb+[J]. Physical Review Letters, 125, 163001(2020).
[7] Ohtsubo N, Li Y, Nemitz N et al. Frequency ratio of an 115In+ ion clock and a 87Sr optical lattice clock[J]. Optics Letters, 45, 5950-5953(2020).
[8] Wang P, Zhang K S, Wei Z Y et al. Preface of “advanced laser technology and application”[J]. Chinese Journal of Lasers, 48, 0501000(2021).
[9] Yao B, Chen Q F, Chen Y J et al. 280 MHz linewidth DBR fiber laser based on PDH frequency stabilization with ultrastable cavity[J]. Chinese Journal of Lasers, 48, 0501014(2021).
[10] Rosenband T, Schmidt P O, Hume D B et al. Observation of the 1S0→3P0 clock transition in 27Al+[J]. Physical Review Letters, 98, 220801(2007).
[11] Wei L J, Cao J, Zhang Q M et al. Frequency doubling of fiber laser based on narrow linewidth grating[J]. Laser & Optoelectronics Progress, 58, 1914010(2021).
[12] Black E D. An introduction to Pound-Drever-Hall laser frequency stabilization[J]. American Journal of Physics, 69, 79-87(2001).