engleski

Velocity selective optical pumping of Rb hyperfine lines induced by a train of femtosecond pulses

In our work we have been observed the velocity selective optical pumping of the 87, 85Rb(5 2S1/2) ground state hyperfine levels induced by the femtosecond pulse train excitation. Due to the smaller fs laser repetition period than the atomic relaxation times, the resonances of the laser field with the atomic system are determined by the laser frequency comb. We developed a modified direct frequency comb spectroscopy (DFCS) based on the fixed frequency comb and a weak cw scanning probe laser. The probe laser monitors the 85, 87Rb(5 2S1/2) hyperfine level populations via 5 2S1/2→ 5 2P3/2 absorption. The 5 2S1/2→ 5 2P1/2 fs pulse train excitation of a Doppler broadened Rb four-level atomic vapor is investigated theoretically in the context of the density matrix formalism. The calculations show the velocity dependent population transfer between 5 2S1/2 hyperfine ground levels with a unique oscillatory structure corresponding to the comb frequency spectrum. Excellent agreement of the calculated velocity dependent 5 2S1/2 hyperfine ground level populations with the experimentally observed modulations in the 5 2S1/2→ 5 2P3/2 hyperfine absorption line profiles is obtained.

optical pumping; femtosecond pulse train

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