Optical control of electronic state populations via the dynamic Stark effect Original Research Article

Through a synergic combination of theoretical calculations and experimental measurements, we explore the possibility of taking advantage of different AC Stark shifts in different electronic states to populate selected vibrational levels of a molecule that are Condon inaccessible or are otherwise difficult to reach by direct optical excitation. Dynamic Stark shifting of the C 2Πr nC=0 Rydberg vibrational level relative to vibrational levels of the B 2Πr valence state of NO serves as the vehicle for this study. Quantum dynamics calculations of two-photon C 2Πr nC=0←X 2Πr nX=0 intense-laser excitation, Stark shifting of the C 2Πr state and Rydberg-valence state mixing provide a conceptual basis for the proposed test of intense-field optical control, in which the C 2Πr, state acts as a `molecular elevatorʹ, depositing population in B 2Πr nB=7–10 vibrational levels. The viability of this approach is assessed through a combination of spectrally and temporally resolved measurements of B 2Πr NO production. Spectrally resolved B 2Πr nB→X 2Πr nX fluorescence induced by a 100 fs laser field at an intensity of 6.0×1013 W cm−2 and wavelength of 382 nm shows evidence of formation of B 2Πr nB=9, 10 levels via Stark shifting of the optically pumped C 2Πr Rydberg state. In bichromatic pump–probe experiments, an intense, off-resonant Stark field is applied to NO at different times to bring about formation of B 2Πr nB=9, 10 from C 2Πr nC=0 prepared by a spatially overlapping excitation field. These experiments were unable unambiguously to confirm the feasibility for optical control of the B 2Πr nB=9, 10←C 2Πr nC=0←X 2Πr nX=0 pathway suggested by the spectral measurements of the B 2Πr nB→X 2Πr nX band system, and reasons for this are discussed.