Effect of the photoinitiator presence and exposure conditions on laser-induced damage threshold of ORMOSIL (SZ2080)

Abstract

The optical resistance of the hybrid inorganic–organic photopolymer ORMOSIL (SZ2080) was investigated by means of laser-induced damage threshold. The chosen material is widely used in direct laser writing 3D lithography and the study was performed with Nd:YAG and Yb:KGW laser systems representing nanosecond and femtosecond pulse durations. Refractive index and extinction coefficient of pure and photosensitized SZ2080 over a whole visible range was measured by ellipsometric technique. The effect of the photoinitiator on the damage threshold has been studied at the fundamental (1064 and 1030nm) and second (532 and 515nm) harmonics. It is both qualitatively and quantitatively shown that the photosensitization of the polymer leads to the reduction of the damage threshold at the second harmonics. A model of incubation being responsible for the damage threshold decrease at multipulse regime is considered. Damage morphology after laser irradiation was investigated by optical and scanning electron microscopies. Obtained data was used for the discussion of the polymers optical breakdown mechanism. The experimental results showed sufficiently high optical resistance of the polymers in the ns pulse mode (at the order of tens J/cm2) while in fs pulse mode typical values were lower by order of magnitude.