Ultrafast optical response of IR-treated polyacrylonitrile films

✍ Scribed by Tatyana S. Zhuravleva; Sergey A. Kovalenko; Yuri E. Lozovik; Yuri A. Matveets; Vadim M. Farztdinov; Alexander L. Dobryakov; Andrey V. Nazarenko; Lev M. Zemtsov; Vladimir V. Kozlov; Galina P. Karpacheva; Gerd Marowsky

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 207 KB
• Volume: 9
• Category: Article
• ISSN: 1042-7147
• DOI: 10.1002/(sici)1099-1581(1998100)9:10/11<613::aid-pat825>3.0.co;2-j

✦ Synopsis

An ultrafast photoinduced optical response of infrared (heat) treated polyacrylonitrile films (PAN-IR) was studied by a femtosecond pump±supercontinuum probe technique in the energy region of 1.6 ± 3.2 eV. Two types of films were used corresponding to 600°C (1st) and to 700°C (2nd) heating. The samples were excited by optical pulses with a duration of 50 fsec and energy of h Å 3 pump = 2.34 eV. The temporal evolution of the photoinduced response is characterized by two relaxation times t 1 and t 2 . For the 1st film type, the spectral dependence of the ultrafast relaxation time shows nonmonotonous behavior, it decreases from t 1 % 170 fsec to 70 fsec at 1.6 h Å 3 probe 1.9 eV and increases from t 1 % 80 fsec to 140 fsec at 1.9 h Å 3 probe 3.2 eV. The spectral region 1.6±1.95 eV corresponds to photoinduced darkening while the region 1.95±3.2 eV corresponds to photoinduced bleaching. For the 2nd film type, only photo-induced bleaching is observed, and the ultrafast relaxation time decreases monotonously from t 1 % 200 fsec to t 1 % 70 fsec. The second relaxation time t 2 is of $1 psec for both types of films.