This paper presents the designs and simulations of twin Wolter mirrors for focusing and imaging experiments with soft Xray free electron lasers. Wave-optical simulations at a photon energy of 100 eV indicate that the designed focusing Wolter mirror focuses soft X-ray beams to a 300 nm × 200 nm spot with an acceptable rotational error of 1.7 mrad × 1.4 mrad and that the objective Wolter mirror, which receives the beam that passes through the focusing Wolter mirror and a sample, forms bright-field images with a spatial resolution of 140 nm × 140 nm. The focusing Wolter mirror enables long-term experiments with high stability, and the objective Wolter mirror is applicable to imaging-before-destruction.
In synchrotron radiation facilities, soft X-ray nanofocusing with mirrors remains a hurdle due to difficulties in mirror fabrication. We have been researching the use of ellipsoidal mirrors for soft X-ray nanofocusing. Information on the wavefront errors of focused beams is helpful for improving the focusing system. This study presents ptychographic wavefront measurements for a nanofocusing system with an ellipsoidal mirror. We developed a ptychography program and performed several simulations at 300 eV to investigate the theoretical accuracy of the wavefront measurements. The simulation results indicate that wavefront measurements with high accuracy are possible.