Photoselective adaptive femtosecond quantum control in the liquid phase

Coherent light sources can be used to manipulate the outcome of light-matte r interactions by exploiting interference phenomena in the time and frequen cy domain. A powerful tool in this emerging field of 'quantum control'(1-6) is the adaptive shaping of femtosecond laser pulses(7-10), resulting, for instance, in selective molecular excitation. The basis of this method is th at the quantum system under investigation itself guides an automated search , via iteration loops, for coherent light fields best suited for achieving a control task designed by the experimenter(11). The method is therefore id eal for the control of complex experiments(7,12-20). To date, all demonstra tions of this technique on molecular systems have focused on controlling th e outcome of photo-induced reactions in identical molecules, and little att ention has been paid to selectively controlling mixtures of different molec ules. Here we report simultaneous but selective multi-photon excitation of two distinct electronically and structurally complex dye molecules in solut ion. Despite the failure of single parameter variations (wavelength, intens ity, or linear chirp control), adaptive femtosecond pulse shaping can revea l complex laser fields to achieve chemically selective molecular excitation . Furthermore, our results prove that phase coherences of the solute molecu le persist for more than 100 fs in the solvent environment.