Beam shaping effects in two photon polymerization of hybrid material systems

Two-photon polymerization (2PP) is now an established technique for nanofabrication. Conventional fabrication processes using laser 2PP commonly use a single point beam delivery system in order to write artifacts in the volume of a resin. Complex shapes such as micro-models, woodpile photonic structures and spiral structures have been realized in several material systems including, sol-gels, organically modified ceramics and resins. One area of current interest in 2PP micro fabrication is the introduction of more complex beam delivery systems, aimed at introducing a degree of parallel processing to the writing method. In this paper we describe two alternative parallel processing approaches to beam delivery that demonstrate the use of diffractive and refractive optics to shape the laser before focusing. Firstly a Fraunhofer diffractive optical element to generate a linear array of 4 spots of equal intensity thus writing four structures simultaneously. Secondly an axicon lens is used to form an annulus in the focal plane of the focusing element. This enables complete three dimensional annular structure fabrication without the use of scanning stages. For all experiments, a Ti:sapphire laser was used to initiate 2PP microfabrication. The materials system used was a Zr/PMMA hybrid prepared by the sol-gel method on a glass substrate.