Nanofocused hard x-ray beams are an essential tool at modern synchrotron radiation facilities. Tightly focused probe beams are mandatory to reach highest resolution in various x-ray microscopy schemes mapping the local elemental composition, chemical state, or atomic structure. Achievable spatial resolution is typically limited by the probe size itself and the applied dose. Both parameters are strongly dependent on the focusing quality and efficiency of x-ray optics used. This thesis focuses on the improvement of refractive hard x-ray optics. A new lens design is introduced that facilitates the use of coating techniques to fabricate lenses. This enables one to exploit x-ray optically favorable materials like aluminum oxide that were inaccessible beforehand. Experimental results proof the working principle of this new lens design and demonstrate the feasibility of aluminum oxide as a suitable material for refractive x-ray optics.In addition an aberration correction scheme based on a corrective phase plate, applicable to various x-rayoptics, is presented. On the example of beryllium lenses spherical aberrations are characterized by meansof ptychography. Based on this knowledge a corrective phase plate was designed and matched exactlyto the specific optical element. It consists of fused silica and is machined by laser ablation. Experimentson different synchrotron radiation facilities are performed, demonstrating a reduction in the strength ofspherical aberrations by an order of magnitude. The corrected optical element performs nearly at thediffraction limit, eliminating disadvantageous side lobes and increasing the peak intensity in the focalplane simultaneously. Benefits and possible new application fields for this aberration free, radiationhard, and efficient refractive hard x-ray optics are outlined
