Sum and difference frequency mixing of molecular vibrations in a polymer under high-density optical excitation

Abstract

Real-time traces of vibrational amplitude detected by the intensity modulation of electronic transition under high-density excitation with sub-5-fs pulse revealed that a combination tone of the C - C and the C = C stretching modes is generated by the exciton-exciton interaction. They were found to be generated in high quantum number vibrational levels in the ground electronic state after internal conversion from higher excited electronic state created by the Auger process. This indicates that the Auger induced highly excited state results in the fusion of vibrational quantum states. At the same time, parametric difference frequency generation of the vibrational modes takes place in the same process.