Multi-photon polymerization by means of Nanoscribe’s direct laser writing systems allows for the fabrication of complex and replicable 2.5D structures. Polymer micro-optics can be used as moulds for replication or masters for pattern transfer. The key advantage compared to 2.5D gray scale lithography or 2D UV-exposure and subsequent reflow techniques is clear: arbitrary complex shapes can be fabricated in one single step. These can be refractive optics such as arrays of aspheres, diffractive optics such as Fresnel lenses or even stacked micro-lenses.
In addition, negative-tone resists may be used which are less sensitive to the development process compared to positive-tone resists - thus allowing for high reproducibility of the complete process chain. Furthermore, micro-optics of up to several 100 µm height can be fabricated with optimal resolution. A sub-category of 2.5D structures are freeform surfaces. Here, arbitrarily complex surfaces can be written by two-photon polymerization - including closed surfaces with undercuts, micro-optics of complex shape and calibration samples.