Ultrafast Optical Nonlinearity in Polydiacetylenes Studied by Sub-5-fs Laser

Abstract

Molecular vibration of several modes in blue-phase polydiacetylene-3-butoxycarbonylmethylurethane (PDA-3BCMU) was real-time observed by 5-fs pump-probe measurement. The contribution of the vibrational wavepackets in the ground state and in the excited state in the signal were separated by multichannel measurements The C=C stretching mode in the ground state starts to oscillate p-out-ofphase with the CC stretching mode. The structure of PDA-3BCMU in the geometrically relaxed state is not pure butatriene-type but more like acetylene-type. The frequencies of C=C and CC stretching modes there were determined by singular value decomposition method to be 1472 AE 6 cm À1 and 2092 AE 6 cm À1 , respectively. The double and triple bond stretching frequencies in the ground state which are 1463 AE 6 cm À1 and 2083 AE 6 cm À1 , respectively.