Direct frequency comb of two-photon transition spectroscopy in a cesium vapor

A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 6²S_1/2-6²P_1/2,3/2-8²S_1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an originate way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.