Resonant Excitation of Coherent Optic Phonons by Femtosecond Multiple-Pulse Impulsive Stimulated Raman Scattering

Abstract

Generation of coherent optic phonons through impulsive stimulated Raman scattering (ISRS) can occur whenever a sufficiently short optical pulse passes through a Raman-active medium [1–3]. In this paper we report the application of specially shaped femtosecond pulse trains to achieve improved control over coherent vibrational motion. In particular, we demonstrate “multiple-pulse” ISRS, in which terahertz-rate trains of fsec pulses are used for repetitive impulsive excitation of optic phonons. By matching the pulse repetition rate to a particular phonon frequency, we are able to select and amplify individual vibrational modes [4]. Each successive pulse in the sequence arrives at the sample in phase to amplify the coherent vibrational motion, analogous to repetitively pushing a child on a swing.