High-Resolution Rb Two-Photon Transition Spectroscopy by a Femtosecond Frequency Comb via Pulses Control*

We experimentally observe the high resolution direct frequency comb spectroscopy using counter-propagating broadband femtosecond pulses on two-photon transitions in room-temperature 87Rb atoms. The Doppler broadened background is effectively eliminated with the pulse shaping method and the spectrum modulation technique. The combination of the pulse shaping method and the spectra modulation technique provides a potential approach to reduce background of at least 99%.