Strong-field quantum control of 2+1 photon absorption of atomic sodium

We demonstrate ultrafast coherent control of multiphoton absorption in a dynamically shifted energy level structure. In a three-level system that models optical interactions with sodium atoms, we control the quantum interference of sequential 2 + 1 photons and direct three-photon transitions. Dynamic change in energy levels predicts an enormous enhancement of vertical bar 7p >-state excitation in the strong-field regime by a negatively chirped pulse. In addition, the vertical bar 4s >-state excitation is enhanced symmetrically by nonzero linear chirp rates given as a function of laser peak intensity and laser detuning. Experiments performed by ultrafast shaped-pulse excitation of ground-state atomic sodium verifies the various strong-field contributions to vertical bar 3s >-vertical bar 7p > and vertical bar 3s >-vertical bar 4s > transitions. The result suggests that for systems of molecular level understanding adiabatic control approach with analytically shaped pulses becomes a more direct control than feedback-loop black-box approaches. (C) 2011 Optical Society of America