Energy redistribution from high vibrational levels populated by stimulated emission pumping
Laser pulses with finely controlled amplitude envelopes can selectively invert a portion of a Doppler broadened line, but the extent of inversion varies as the Rabi frequency of the transition changes. Modulation of the phase in addition to the amplitude can compensate for Rabi frequency variations, and pulses can be designed to invert a transition completely over a chosen well-defined frequency range. Using such a pulse, ground-state molecules within a selected range of velocities can be put into an electronically excited state and with a second pulse subsequently transferred to a high vibrational level of the ground electronic state. Excitation of a narrow and well-defined portion of a Doppler profile allows not only vibrational and rotational thermalization of the molecules to be followed but also subtle changes in translational energy of the state. Collisional cross sections of ground-state molecules with many vibrational quanta can be directly compared with cross sections obtained from electronically excited molecules to reveal electronic state contributions to collisional dynamics.