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Ultrafast Optical Nonlinearity in Polydiacetylenes Studied by Sub-5-fs Laser
Takayoshi Kobayashi and Mitsuhiro Ikuta

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-of-phase with the C≡C 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 C≡C stretching modes there were determined by singular value decomposition method to be 1472 ±6 cm-1 and 2092 ±6 cm-1, respectively. The double and triple bond stretching frequencies in the ground state which are 1463 ±6 cm-1 and 2083 ±6 cm-1, respectively.

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