Three-dimensional microfabrication with femtosecond laser pulses

Investigations on two-photon polymerization of inorganic-organic hybrid materials initiated by femtosecond Ti:sapphire laser pulses are performed. The applied resins are designed for ultraviolet photo-lithography and contain photo-initiators sensitive to 390 nm radiation. These resins exhibit exceptionally good mechanical, optical, and chemical properties and can be microstructured by laser-enforced transition from liquid to solid state. These materials are transparent in the infrared, therefore, by tightly focusing femtosecond laser pulses into the volume of a liquid resin, two-photon polymerization can be initiated in a small focal region inside the liquid. First applications of this technique for the fabrication of three-dimensional microstructures and photonic crystals in inorganic-organic hybrid polymers with a structure size down to 200 nm and a periodicity of 450 run are discussed. It has recently been demonstrated by several groups [1-5] that two-photon-polymerization (2PP) of photosensitive materials allows the fabrication of complicated three-dimensional microstructures. When tightly focused into the volume of a liquid resin (which is transparent in the infrared), femtosecond laser pulses can initiate two-photon polymerization and produce structures with a resolution better than 0.2 mum. Compared to conventional photolithography which is a planar processing, 2PP is a real three-dimensional volume microfabrication technique. At present, materials can be viewed as the playground for photonics where it is still impossible to foresee a winner. There is a strong demand for cheap and reliable materials which can be photo-chemically patterned in two and three. dimensions. Very promising materials for photonics are multi-functional inorganic-organic hybrid polymers (like ORMOCER(R)'s, used in this work) whose properties can be tuned from those that are characteristic for organic polymers to those that are similar to inorganic glasses. ORMOCERO's are produced by sol-gel synthesis [6,7].