Nanoscale coherent diffractive imaging using high-harmonic XUV sources
Imaging using sources in the XUV and X-ray spectral range combines high resolution with longer penetration depth (compared to electron/ion microscopy) and found applications in many areas of science and technology. Coherent diffractive imaging (CDI) techniques, in addition, lift the performance limitation of conventional XUV/X-ray microscopes imposed by image forming optics and enable diffraction limited resolutions. Until recently, CDI techniques were mainly confined to large scale facilities e.g. synchrotrons and X-ray free electron lasers due to unavailability of suitable table-top XUV/X-ray sources. Table-top sources based on high-order harmonic generation (HHG) nowadays offer high and coherent photon flux which widened the accessibility of CDI techniques. So far, table-top CDI systems were not able to resolve sub-100 nm features using performance metrics that can qualify these systems for real world applications. In this work, CDI experiments with the highest resolutions in different modalities using a high flux fiber laser driven HHG source are presented. In conventional CDI, a record-high resolution of 13 nm is demonstrated together with the possibility of high speed acquisition with sub-30 nm resolution. In a holographic implementation of CDI, features with a half-distance of 23 nm are resolved which are the smallest features to ever be resolved with a table-top XUV/X-ray imaging system. Ptychographic imaging of extended samples is also performed using a reliable Rayleigh-like resolution metric and resolving of features as small as 2.5 wavelengths is demonstrated. These systems can find applications in material and biological sciences, study of ultrafast dynamics, imaging of semiconductor structures and EUV lithographic mask inspection.