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The Zeeman shift plays an important role in the evaluation of optical lattice clocks since a strong bias magnetic field is applied for departing Zeeman sublevels and defining a quantization axis. We demonstrated the frequency correction and uncertainty evaluation due to Zeeman shift in the 87Sr optical lattice clock at the National Time Service Center. The first-order Zeeman shift was almost completely removed by stabilizing the clock laser to the average frequency of the two Zeeman components of mF = ±9/2. The residual first-order Zeeman shift arose from the magnetic field drift between measurements of the two stretched-state center frequencies; the upper bound was inferred as 4(5) × 10−18. The quadratic Zeeman shift coefficient was experimentally determined as −23.0(4) MHz/T2 and the final Zeeman shift was evaluated as 9.20(7) × 10−17. The evaluation of the Zeeman shift is a foundation for overall evaluation of the uncertainty of an optical lattice clock. This measurement can provide more references for the determination of the quadratic coefficient of 87Sr.

In this paper, we report on the active filtering and amplification of a single mode from an optical femtosecond laser comb with mode spacing of 250MHz by optical injection of two external-cavity diode lasers operating in cascade to build a narrow linewidth laser for laser cooling of the strontium atoms in an optical lattice clock. Despite the low injection of individual comb mode of approximately 50 nW, a single comb line at 689 nm could be filtered and amplified to reach as high as 10 mW with 37 dB side mode suppression and a linewidth of 240 Hz. This method could be applied over a broad spectral band to build narrow linewidth lasers for various applications. [ABSTRACT FROM AUTHOR]

We present an experimental determination on the Landé g-factors for the 5s21S0 and 5s5p3P0 states in ultra-cold atomic systems, which is important for evaluating the Zeeman shift of the clock transition in the 87Sr optical lattice clock. The Zeeman shift of the 5s5p 3P0–5s21S0 forbidden transition is measured with the π-polarized and σ±-polarized interrogations at different magnetic field strengths. Moreover, in the g-factor measurement with the σ±-transition spectra, it is unnecessary to calibrate the external magnetic field. By this means, the ground state 5s21S0 g-factor for the 87Sr atom is −1.306(52)×10−4, which is the first experimental determination to the best of our knowledge, and the result matches very well with the theoretical estimation. The differential g-factor δg between the 5s5p 3P0 state and the 5s21S0 state of the 87Sr atoms is measured in the experiment as well, which are −7.67(36) × 10−5with π-transition spectra and −7.72(43) × 10−5with σ±-transition spectra, in good agreement with the previous report [Phys. Rev. A 76 (2007) 022510]. This work can also be used for determining the differential g-factor of the clock states for the optical clocks based on other atoms. [ABSTRACT FROM AUTHOR]

We report a new method for obtaining a stable single-frequency Yb-doped fiber laser by introducing a graphene film into a fiber loop mirror combined with a simple linear cavity. The graphene film acts as a saturable absorber so as to form a dynamic absorbing grating in the 3 dB fiber loop. This grating is like a narrow-band filter for discriminating and selecting longitudinal modes. Moreover, we use a polarization controller in the linear resonator to suppress the spatial hole burning effect. The maximum output power is 16 mW at 1 064 nm with a pump power of 110 mW at 975 nm, the slope efficiency is 15%, and the SNR is about 60 dB. To the best of our knowledge, this is the first demonstration of a 1 064 nm single-frequency laser based on a linear cavity with a graphene-loop mirror filter. [ABSTRACT FROM AUTHOR]