Optical frequency measurements of 6 s 2 S 1 l 2 - 6 p 2 P 312 transition in a 133 Cs atomic beam using a femtosecond laser frequency comb

Optical frequencies of the hyperfine components of the Dzline in 133CS are determined using high-resolution spectroscopy and a ferntosecond laser frequency comb. A narrow-linewidth probe laser excites the 6s 281/2 (F=3, 4).----+ 6p 2p 3/2 (F=2,3, 4, 5) transition in a highly collimated atomic beam. Fluorescence spectra are taken by scanning the laser frequency over the excited-state hyperfine structure. The laser optical frequency is referenced to a Cs fountain clock via a reference laser and a ferntosecond laser frequency comb. A retroreflectedlaser beam is used to estimate and minimize the Doppler shift due to misaligmnent betweenthe probe laser and the atomic beam. We achieve an angular resolution on the order of 5 X10-6 rad. The final uncertainties (~±5 kHz) in the frequencies of the optical transitions are a factor of 20 better than previous results [T. Udem et aI., Phys. Rev. A 62, 031801 (2000).]. Wefind the centroid of the 6s 28112 ---+ 6p 2p 3/2 transitionto be fm~351 725718.4744(51) MHz.