Improved Absolute Frequency Measurement of the 171Yb Optical Lattice Clock towards a Candidate for the Redefinition of the Second

We demonstrate an improved absolute frequency measurement of the S-1(0)-P-3(0) clock transition at 578nm in Yb-171 atoms in a one-dimensional optical lattice. The clock laser linewidth is reduced to approximate to 2 Hz by phase-locking the laser to an ultrastable neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 1064 nm through an optical frequency comb with an intracavity electrooptic modulator to achieve a high servo bandwidth. The absolute frequency is determined as 518 295 836 590 863.1(2.0) Hz relative to the SI second, and will be reported to the International Committee for Weights and Measures. (C) 2012 The Japan Society of Applied Physics