Berlin 2012 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 13: Poster II

DF 13.24: Poster

Wednesday, March 28, 2012, 15:00–17:30, Poster E

Adaptive Amplitude Filters for Smaller Feature Sizes in Direct Laser Writing — Erik Waller and •Georg von Freymann — Department of Physics and Research Center OPTIMAS, University of Kaiserslautern

Direct-Laser-Writing is an established technique for the fabrication of almost arbitrary three-dimensional structures in photo resists. These are locally polymerized via two-photon polymerization. The fundamental building block - the so called voxel (volume pixel) - is a volume defined by the iso-intensity surfaces in the focal spot. This voxel is an ellipsoid, defined by the numerical aperture of the microscope objective and the refractive index of the photo resist. The resulting axial elongation is disadvantageous for isotropic features. To overcome this problem, so called shaded-ring filters have been reported. Recently, stimulated-emission-depletion inspired lithography has been demonstrated to yield aspect ratios of one. Corresponding setups require phase masks and an additional laser source. Here, we show that spatial light modulators can be employed to implement shaded-ring filters to decrease the aspect ratio. However, so far shaded-ring filter have to not been able to generate aspect ratios close to one with acceptable side lobe levels. We therefore suggest an adaptive amplitude filter allowing for voxels with an aspect ratio of one, regardless of the scanning direction. This adaptive filter consists of a variable slit with unity transmission imaged onto the entrance pupil of a high numerical aperture objective. We show numerical calculations and experimental data demonstrating the effectiveness of this approach.