Reduction of the efficiency of photoinduced polymerisation in C60 films on irradiation with femtosecond laser pulses

Photopolymerisation of oxygen-bearing C60 films by λ =459 nm laser radiation and by 100-fs λ=410 nm pulses was compared by visual observation of photodarkening spots and by recording the Raman spectra, in the range 600 - 1700 cm-1, of the irradiated regions. When the average intensity was 10 - 20 W cm-2, the irradiation dose needed for photopolymerisation was very different in the cw and pulsed cases. For the cw radiation, it was close to the dose for oxygen-free samples, amounting to 20 kJ cm-2. For the femtosecond pulses, the threshold radiation dose was two orders of magnitude higher, which could be attributed to characteristic features of relaxation of the excited molecules. (interaction of laser radiation with matter)