Author: Nakajima, T.
Paper Title Page
TUP063
 Observation of Time-Resolved Phase Change in Polymer Films using a Mid-Infrared FEL  
 
  • T. Nakajima, E.I. Ageev, T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  
  The op­er­a­tion wave­length of FEL at Kyoto Uni­ver­sity is 5-20μm with a macropulse du­ra­tion of 1.5μs, mi­cropulse du­ra­tion of 0.6ps, and wave­length sta­bil­ity of <1.3% [1]. Using fre­quency con­ver­sion we can ob­tain the sin­gle-shot spec­tra of mid-IR FEL [2]. To­ward the time-re­solved (TR) study we have in­stalled the plasma mir­ror to shorten the macropulse du­ra­tion from μs to ns [3]. Poly­mers are in­ter­est­ing can­di­dates for the TR study in the mid-IR re­gion. Some of the well-known poly­mers are poly­styrene (PS), poly­eth­yl­ene (PE), etc. PS ex­ists only in an amor­phous phase, while PE ex­ists in both amor­phous and crys­tal phases. In this study we un­der­take the TR study of PE films. We melt the PE film with ns laser pulses at 532 nm, and probe the fol­low­ing dy­nam­ics using the mid-IR FEL. To in­crease the ab­sorp­tion ef­fi­ciency at 532 nm, we fab­ri­cate the PE film doped with gold nanopar­ti­cles. As a re­sult of melt­ing the sharp ab­sorp­tion peaks of PE turns to the broad peak, in­di­cat­ing the phase change from crys­tal to amor­phous. This way, we can ob­serve the phase change of PE films in a TR man­ner with the mid-IR FEL, which is not pos­si­ble with other com­monly used de­vices such as FTIR.
[1] Qin et al., Opt. Lett. 38, 1068 (2013).
[2] Wang, Nakajima, Zen, Kii, Ohgaki, Opt. Lett. 37, 5148 (2012).
[3] Wang, Nakajima, Zen, Kii, Ohgaki, Appl. Phys. Lett. 103, 191105 (2013).