REDUCTION OF THE EFFICIENCY OF PHOTOINDUCED POLYMERIZATION IN C-60 FILMS ON IRRADIATION WITH FEMTOSECOND LASER-PULSES

Photopolymerisation of oxygen-bearing C-60 films by lambda = 459 nm la ser radiation and by 100-fs lambda = 410 nm pulses was compared by vis ual observation of photodarkening spots and by recording the Raman spe ctra, in the range 600-1700 cm(-1), of the irradiated regions. When th e average intensity was 10-20 W cm(-2), the irradiation dose needed fo r photopolymerisation was very different in the cw and pulsed cases. F or 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 attr ibuted to characteristic features of relaxation of the excited molecul es.