# High Resolution Imaging Using Micro-Objectives Fabricated by 2-Photon-Polymerization
## 5 Conclusions  
In conclusion, we demonstrated the fabrication of shape-fidelity optical micro structures using 2 PP for high resolution near-field microscopy. A challenge here are the small dimensions of the typically used optical micro structures with aperture and radii of curvature of less then 20 \(\upmu\)m. In order to demonstrate the potential of fabricating optical micro structures for this field of application, we compared the imaging properties with those of conventionally fabricated micro spheres. This comparison shows that micro structures fabricated using 2 PP lithography are an alternative to the typically used micro spheres and open up additional degrees of freedom in the design of the used micro structures. To highlight these new degrees of freedom, for the first time we demonstrated imaging below the resolution limit using a biconvex micro lens in near-field microscopy. The FRISP simulation method [19] was extended to include the properties of the object illumination and the imaging properties of the microscope objective used for imaging, thus demonstrating a possibility for the computing time-optimized improvement of refractive  
Figure 6: Comparison of the imaging properties of the central imaging element of the micro-objectives in Figures 4 and 5 with simulated intensity distributions. (**a**) Simulated intensity distribution in the image plane of a micro sphere with a diameter of 10 \(\upmu\)m and (**b**) the corresponding experimentally measured intensity distribution. the star-shaped bright areas in (**a**) are artifacts from the simulation. (**c**) Simulated intensity distribution in the image plane of the micro lens with a radius of curvature of 12.5 \(\upmu\)m, an aperture diameter of 20 \(\upmu\)m and (**d**) the corresponding experimentally measured intensity distribution. micro structures for use in high-resolution near-field microscopy. The simulation enabled the prediction of the magnification caused by the optical micro structures on the object surface and thus the achievable resolution. Furthermore, the simulation gives a correct prediction of the position of the image plane relative to the object plane. Due to the accordance with the experimental data, FRISP is a valid alternative to the classically used FDTD simulations. In addition, we demonstrated that the 2 PP process allows a high degree of flexibility and additional degrees of freedom, enabling an individual adaptation of the dimensions and geometries of the micro structures. This adaptability was demonstrated by the fabrication of complex microsystems, such as the micro-objectives shown in Figures 1 and 5. Furthermore, for the first time, an adapted geometry for high-resolution imaging using 2 PP lithography was fabricated with a biconvex micro lens and proven to be applicable. This opens up new possibilities for the fabrication of complex microsystems with advanced optical designs tailored to specific high-resolution imaging applications. Conceptualization, F.T., M.A. and C.F. ; methodology, F.T. and M.A. ; software, F.T. ; validation, F.T. and C.F. ; formal analysis, F.T. and C.F. ; investigation, F.T. and M.A. ; resources, F.T. ; data curation, F.T. ; writing--original draft preparation, F.T. and M.A. ; writing--review and editing, F.T., M.A., C.F. and R.B.B. ; visualization, F.T. and M.A. ; supervision, R.B.B. and C.F. ; project administration, F.T. ; funding acquisition, R.B.B. All authors have read and agreed to the published version of the manuscript. The authors gratefully acknowledge the support of the Deutsche Forschungsgemeinschaft (DFG) for funding this work under the project \"Hochauflosende optische Mikroskopie mittels transmissiver Mikrostrukturen--HOMiTrans\", grant no. 431605610. Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request.