Field dependence of state populations in pump-probe pulses

The effects of pulse width, laser wavelength and laser intensity on the state populations of NaI molecule driven by a pump-probe pulse were studied via employing the time-dependent wave packet approach. Wave packet moves periodically with roundtrip time 1000 fs. That the wave packet bifurcates in the crossing region affects state populations. The excitation probability increases and dissociation probability decreases with increasing pulse width. The excitation probability approaches the maximum at the resonance pump wavelength 318 nm, and the dissociation probability decreases with increasing pump wavelength. The excitation probability increases with increasing pump intensity while the dissociation probability does not vary. The probe wavelength and probe intensity have no effect on state populations. The wave packet motion and selective distribution of state populations, excitation and dissociation of molecule can be achieved by adjusting laser parameters. The results can provide some important basis for realizing quantum manipulation of molecules experimentally.