Photopolymerization and Thermal Decomposition of Polymerized Phase in C60crystals Under Strong Laser Illumination

We have investigated the photopolymerization and thermal decomposition of photochemical products with high density excitation (11–480 mW/mm2) by means of time-gated Raman scattering experiments in C60 single crystal. The temperature of laser-illuminated area was measured by Stokes and anti-Stokes Raman scattering of C60 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/mm2 indicating the rapid decrease in C60 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.