Application Of The Er-fiber Frequency Comb In Ytterbium Optical Lattice Clocks

Cold ytterbium atom clock became a hotspot in the field of atomic frequency standard research in recent years. To detect the clock-transition spectrum, ytterbium atoms need to go through the first stage 399nm laser cooling and the second stage 556nm laser cooling, and then loaded to an optical lattice for probing. In order to increase the first stage cooling efficiency and implement a normalized detection scheme, we have to repump the atoms out of the 3Po and 3P2 state by using 649nm&770nm repumping lasers through 3S1 state, which then return to the ground state. Since repumping lasers play a vital role in ytterbium atom clock system, the high performance of their frequency stabilization scheme is indispensable.Frequency comb provides highly accurate and stable frequency standard, which can be used to phase-lock both 649nm&770nm repumping lasers. In this paper, we begin with the basic principle of mode-locking mechanism, introducing the technics of active and passive mode-locked fiber lasers, and then stable mode-locked Er-fiber lasers operated in different dispersion regimes have been realized with nonlinear polarization rotation effect. We change the intra-cavity birefringence index through polarization controller to obtain the multi-wavelength fiber laser operation in the near-zero dispersion regime, within 3dB bandwidth,50 lines lasing has been achieved. Under the stretched-pulse mode-locked circumstance, we design an electronic system to lock its repetition frequency 64.399MHz to the commercial crystal oscillator. The 3.4mW seed laser has been amplified to 210mW by chirped pulse amplification(CPA) and bidirectional pump technics; in addition, the pulse is stretched to 1.94ps and compressed to around 200fs. We use this laser source delivered to the spliced HNLF for supercontinuum generation(SC). Furthermore, we use GNLSE to analyze the impact of group velocity dispersion(GVD) and third-order dispersion(TOD) of the HNLF on supercontinuum generation, and this results may lay a foundation for the subsequent development of the offset frequency fo detection scheme and locking system, all of this would eventually lead us to simultaneously locking the repumping lasers(649nm&770nm) to a stable Er-fiber frequency comb.