Key Techniques Of Cold Ytterbium Atomic Clocks

The fractional frequency uncertainty of the optical clocks has gone beyond that of the current cesium fountain atomic clock. It means that the optical frequency standards may become the next generation of frequency standards. The optical clocks have a great impetμs for the physical study, scientific measurement and high technology research. The key techniques of optical clocks will have important applications in varioμs research fields, such as global positioning system, high-speed communications and deep space exploration.We present the key techniques of a cold ytterbium atomic clock in this thesis. Firstly, an efficient and simple frequency-locking schemeμsing the modulation transfer spectroscopy technique combined with a hollow cathode lamp for ytterbium atoms is introduced. It is insensitive to the background absorption and directly provides a dispersion-like signal with a zero-crossing at line center which isμsed to lock a laser to a well-defined frequency reference with high sensitivity and high resolution. The optimum parameters for maximizing the MTS signal are presented. Combined with the Doppler-free spectroscopy in a collimated atomic beam, the isotope shifts and hyperfine splittings of all ytterbium isotopes at 399nm transition are precisely measured. Later, by optimization of two-dimensional optical molasses, magneto-optical trap and careful designment of Zeeman slower, we finally observed the cold ytterbium atomic cloud in the magneto-optical trap. The temperature of the cold atoms is about two milli-Kelvins calculatedμsing the time-of-flight method; the number is about 10', which is calculatedμsing the release and recapture method. Secondly, the frequency stabilization of 556nm laser for the second-stage Doppler cooling is introduced, here we chose the method of the frequency modulation combined with the fluorescence detection spectroscopy. By optimization of the MOT alignment, polarization and so on, we ultimately observed the loading of the 556nm atomic cloud at the center of the magneto-optical trap with a temperature of about thirty micro-Kelvins. Thirdly, a brief introduction of the three-dimensional optical lattice was presented. We introduced the frequency locking method for the lattice laser and made a theoretical analysis of the one-dimensional optical lattice potential. By carefully alignment of the lattice laser, we finally observed the loading signal of the optical lattice. Lastly, the Pound-Drever-Hall techniqueμsed to lock the clock laser frequency and fiber phase noise cancellation technique are introduced, hoping to obtain the clock transition spectroscopy in the optical lattice. In addition, we make a comprehensive analysis of the systematic frequency shifts of the clock transition.