Feature-size reduction of photopolymerized structures by femtosecond optical curing of SU-8

The universal scaling of a width of photopolymerized line on the exposure dose was observed in polymerization by direct laser writing using tightly focused femtosecond pulses in SU-8 resist. This scaling can be explained as the photopolymerization by a blackbody-type emission. A spectrally broad thermal emission of electrons heated up to temperatures approximately Te∼103K coincides with an IR-absorption band of SU-8 centered at the 2.9μm and had caused polymerization by a cumulative direct absorption. Three-dimensional photonic crystal templates with approximately twice reduced feature size were fabricated with stop band at the fiber communication wavelength of 1.3μm.