Three-dimensional microfabrication with femtosecond laser pulses

摘要

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 nm are discussed. It has recently been demonstrated by several groups 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 μm. 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. ORMOCER~(~R)'s are produced by sol-gel synthesis.