We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P_{ 3/2} state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D_{ 2} lines. This scheme allows for a velocity selective spectroscopy in a large spectral range including the 5D_{ 3/2} and 5D_{ 5/2} states. The results are well described in a simplified frequency domain picture, considering the interaction of each velocity group with the cw laser and a single mode of the frequency comb.
Categories: physics.atom-ph physics.optics