Selective control of vibrational modes with sequential femtosecond-scale laser pulses

For nonresonant femtosecond-scale laser pulses, we showed earlier that the optimum FWHM pulse duration is 0.42 T if one wishes to achieve maximum relative excitation of a specific vibrational mode with period T. Here we show that much greater enhancement of a specific mode can be achieved with a sequence of laser pulses which have both this optimized duration and optimized delays between pulses. One can thus enhance a selected set of modes that are particularly useful in identifying or characterizing a chemical system, to lift them out of the background of less informative modes.