Can chirp enhance cumulative pre-resonant impulsive stimulated Raman excitation?

Simple arguments are presented and numerical calculations are performed which show that frequency chirp increases the amplitude of vibrational motion induced in the ground state of I-2 by optimized sequences of ultrashort, pre-resonant optical pulses. Sequences with a variety of constraints on pulse chirp rates and pulse center frequencies were generated by time local optimization and are compared. A sequence with pulse-by-pulse variable chirp and variable center frequency is shown to be considerably more effective than the most effective sequence with a fixed negative chirp rate and constant pulse center frequency, which is in turn much more effective than a sequence of unchirped fixed-center-frequency pulses considered previously. The best sequence of pulses induces a 0.4 Angstrom circuit in the expectation value of the I-2 stretch from cumulative pre-resonant impulsive stimulated Raman scattering. (C) 1996 American Institute of Physics.