Photopolymerization and thermal decomposition of polymerized phase in C60 crystals under strong laser illumination

We have investigated the photopolymerization and thermal decomposition of photochemical products with high density excitation (11-480 mW/mm(2)) by means of time-gated Raman scattering experiments in C-60 single crystal. The temperature of laser-illuminated area was measured by Stokes and anti-Stokes Raman scattering of C-60 Hg(1) mode, which shows the local temperature rise with increase of laser power density. The Raman intensity of Ag(2) mode rapidly decreases with irradiation time for I < 170 mW/mm(2) indicating the rapid decrease in C-60 monomer density due to photopolymerization. For higher power densities, however, the Raman intensity increases after showing a minimum, which suggests a dissociation of photopolymers. The results are well explained by the rate equation model taking into account photochemical generation and thermal decomposition of photo-produced dimers. These results indicate the strong laser illumination simultaneously induces the photopolymerization and thermal decomposition.