Development of 171 Yb optical lattice clock at KRISS Chang Yong Park*, Dai-Hyuk Yu, Won-Kyu Lee, Sang Eon Park, Taeg Yong Kwon, Sang-Bum Lee, and Jongchul Mun Center for Time and Frequency, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejeon 305-340, Korea *cypark@kriss.re.kr ABSTRACT — We developed an 171 Yb optical lattice clock and measured the absolute frequency of the optical clock transition 1 S 0 (F = 1/2) – 3 P 0 (F = 1/2). The frequency was determined at 518 295 836 590 865.7 (9.2). The uncertainty is equivalent to 1.8×10 -14 relatively. The magic wavelength of lattice laser was founded at 394 798.18(79) Hz. Index Terms — Optical clock, optical lattice clock, clock transition of 171 Yb atoms, precision measurements, magic wavelength, I. INTRODUCTION Since the first demonstration of optical lattice clock [1], the idea has been extensively tested in various ways globally for the past decade. As the result some of laboratories have reported optical clock operation surpassing the best microwave clock in stability and uncertainty [2]. There have been obstacles like collisional shift and lattice induced shift for all types of optical lattice clock for long time, however recent progresses show that they can be overcome under 10 -17 level [3, 4]. The black body radiation shift is also possible to be reduced under 10 -17 level in room temperature by a recent precise measuring the static polarizabillity of ytterbium atoms, and similar research are in progress for other atoms [5]. It is believed that the systematic uncertainty of several optical lattice clocks will reach 10 -17 level in near future. Currently ytterbium atom is one of most popular species studied for optical lattice clock, as is strontium atoms. Until now two groups [6, 7] were reported the absolute frequency of the clock transition of 171 Yb. We recently measured the frequency of 171 Yb trapped in one-dimensional optical lattice potential, which is the third independent measurement for 171 Yb atom. Our results are in good agreement with the previous measurements and will contribute to reduce the total uncertainty of the clock transition frequency of 171 Yb atoms. II. EXPERIMENT AND SYSTEMATIC SHIFTS In Fig. 1, the clock transition and other relevant energy levels of 171 Yb are depicted. About 10 8 atoms were trapped by using 1 S 0 - 1 P 1 transition resonant to 399 nm light which provides strong friction force in magneto optical trap (blue- MOT) and Zeeman slower. The trapped atoms were transferred to deep cooling MOT (green-MOT) prepared by using 1 S 0 - 3 P 1 transition resonant to 556 nm light with which atoms could be cooled down to 30 µK during 50 ms. After turnoff the 556 nm trapping laser, about 10 4~5 the atoms depending on loading time of bule-MOT were easily loaded into an 1-D optical lattice potential formed by an 1 W of 759 nm laser beam with a beam waist of 25 µm. In next step, 100 nW of 578 nm clock laser was shined on the trapped atoms during 20 ms for exciting atoms in ground state to the excited state of clock transition. The probability of the excitation was measured by detecting fluorescence of 399 nm light from the atoms remained in ground state (signal A) with a photo multiplying tube (PMT). Number fluctuation of trapped atoms in optical lattice was about 30%, which was canceled by normalization process. For the normalization, the excited atoms were optically pumped to the ground state by using 649 nm and 770 nm laser resonant to 6s6p 3 P 0 - 6s6p 3 S 1 and 6s6p 3 P 2 - 6s6p 3 S 1 respectively. 399 nm laser shines again on the optically pumped atoms into ground state. This second fluorescence (signal B) was detected with the same PMT. The value of signal B divided by the sum of signal A and B was taken as the normalized signal. Fig.1. Relevant energy levels of ytterbium atoms and lasers. The clock laser of 578 nm obtained by using sum-frequency generation of 1030 nm and 1319 nm laser. Two laser beams were quasi-phase matched in a ridge wave-guided periodically poled Li:Niobate. A super-cavity of finesse 400,000 was used for narrowing the linewidth of 578 nm laser by using Pound- Drever-Hall technique, with which clock laser linewidth was narrowed to 80 Hz. The frequency of the laser was scanned near the resonant frequency of the clock transition, giving the spectrum like in Fig.2. The spectrum linewidth (200 Hz) was much broader than that of the clock laser (80 Hz) because of