Experimental Study On Frequency Stabilization System Of The Lattice Laser In Ytterbium Clock

Optical lattice clock based on neutral ytterbium(Yb)atoms has achieved an instability of 10-18 level(1000s averaging time),and it has been determined to be a candidate of SI secondary representation of the definition of second.The idea of optical lattice applied to optical atomic clock is a milestone contribution,it can effectively improve the signal to noise ratio and suppress the interaction among the atoms simultaneously.Due to the concept of the magic wavelength,that is,there exists a particular frequency for the clock transition,the upper and lower level of the clock transition suffer the same amount of energy shift in optical lattice field.The wavelength is vital important toward the higher stability and precision of the lattice clock.Accurate control of the linewidth and frequency stability for the lattice laser is a key technique for optical lattice clock.Concerning on this topic,I have designed and built a frequency stabilization system based on optical transfer cavity technology,and succeed realizing the control of the linewidth and long term frequency drift of 759nm lattice laser during the graduate student period.My main results are summarized as follows:1)A modulation transfer spectroscopy(MTS)based locking system has been built to provide a 780nm pre-stabilized laser as reference laser.The beat signal between two individual systems shows the system can provide an Allan deviation below 1kHz for 1s averaging time.2)An optical transfer cavity made of Invar alloy has been built,error signal from PDH method is as the feedback signal to the PZT of the transfer cavity to realize the cavity lock to the 780nm reference laser.Experimental results show the free spectral range is 375MHz,and the finesse corresponding to 780nm and 759nm is 236 and 341 respectively;3)Several feedback loops for reducing the residual amplitude modulation(RAM)effect have been built.By controlling the temperature of electro-optic modulators(EOM)used in the locking stages,frequency fluctuation induced by RAM is suppressed.Experimental results show the RAM noise from the 759nm PDH loops is below 2.3kHz in the worst situation.RAM noise in the open loop is effectively reduced after the transfer cavity is locked at frequency range below 0.1 Hz and there is almost no relation with the locking status of the transfer cavity at frequency range above 0.1 Hz.4)By locking the transfer cavity,the linewidth and the long term frequency drifts of 759nm lattice laser are effectively controlled.The lattice laser can be steadily locked for more than 10 hours without mode hop.Beat note with an optical comb shows the Allan deviation of the lattice laser is 6kHz for 1s averaging time,as well as a maximum long-term drift of 261kHz for 200s averaging time.In conclusion,during my graduate student study,I have succeeded designing and developing a frequency stabilization system based on transfer cavity technique for 759nm lattice laser.With the system,lattice laser can be scanned with a 600kHz step,which paves the way for the following determination and control of accurate value of the magic wavelength for Yb lattice clock.Also,the long term drifts of the frequency stabilization system ensure the instability of the Yb lattice clock below 10-17 level.