The laser cooling of ytterbium (Yb) atoms needs a 399-nm laser which operates on the strong 1S0 -1P1 transition and can be locked at the desired frequencies for different Yb isotopes. We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference. For unresolved fluorescence peaks, we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations; the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references. A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest, and a frequency stability of 304 kHz is achieved. This frequency-locked laser enables us to realize stable blue magneto-optic-traps (MOT) for all abundant Yb isotopes.

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1S0-3P1 intercombination transition of ytterbium (Yb) atoms. A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm. A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed. The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity. A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system. The laser can be stably locked for more than 5 h. This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.

We build a Zeeman slower with consecutive coils and use it to load an Yb magneto-optical trap (MOTs). Cooling efficiency is measured by the fluorescence intensity of the atomic cloud trapped by the MOT. An optimized magnetic field profile can acquire the maximum cooling efficiency, corresponding to a good compromise between the smaller magnetic field mismatch and the high capture velocity. Our studies provide useful information on how the performance of the Zeeman slower can be improved.