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HL: Fachverband Halbleiterphysik

HL 44: Photonic crystals

HL 44.4: Vortrag

Dienstag, 12. März 2013, 15:45–16:00, H3

Active focal volume modification for two-photon polymerization process studies — •Erik Waller, Michael Renner, and Georg von Freymann — Department of Physics and Research Center OPTIMAS, University of Kaiserslautern

Direct-Laser-Writing (DLW) is used for the fabrication of almost arbitrary three-dimensional structures by focusing an intense laser beam into photo resists. In standard DLW systems the iso-intensity surfaces of the focal volume and therefore the obtainable feature sizes are defined by the numerical aperture of the focusing optics. The resolution is additionally limited by the proximity effect caused by accumulated intensity in the photo resist. Here, we spatially structure the incoming laser beam with a spatial light modulator to modify the focal volume. Polymer template structures written with these shaped focuses give insight in the formation of the proximity effect.

To evaluate the effect of the accumulated intensity we introduce shaded-ring filters (SRF) which reduce the axial elongation of the focal volume but cause sidelobes. Using SRFs with different sidelobe height and feedback from high resolution three-dimensional structures we find an acceptable sidelobe level for the serial writing process. The evolution of the proximity effect with time is tested using phase patterns that generate highly uniform high-resolution multi-focuses along a line in a parallel writing approach. The resulting obtainable resolution is compared to the obtainable resolution of a two-dimensional grating written in a serial process. The accumulated intensity is deduced from point-spread-function scans, the writing speed and the spot distance.