Author: Ageev, E.I.
Paper Title Page
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).