MBI Colloquium: Lensless imaging using high-harmonic generation: nanoscale imaging of 3D objects
Wednesday, 25. January 2023 // 14.00 - 15.00
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie
Max Born Hall
Dr. Stefan Witte | Advanced Research Center for Nanolithography (ARCNL) and Vrije Universiteit Amsterdam
Microscopy at extreme ultraviolet (EUV) wavelengths has the potential to transform nanotechnology and materials science, as it may enable non-invasive 3D imaging with a combination of high spatial resolution and element-sensitive contrast. Lensless imaging methods, using algorithm-based image reconstruction from coherent diffraction patterns, are particularly attractive in the EUV range as they do not require imaging optics. Such methods do require coherent illumination, for which table-top high-harmonic generation (HHG) sources seem well suited. The broad spectral bandwidth and high coherence of HHG sources are in principle ideal for coherent imaging, although converting multi-wavelength diffraction data into meaningful images is challenging. We have explored various approaches towards spectrally resolved HHG imaging, through Fourier-transform-based imaging schemes, but also by developing multi-wavelength ptychography algorithms.
I will present our work on lensless imaging with HHG sources for nanoscale imaging applications, including ways towards lensless 3D imaging. Furthermore, I will show how ptychography enables not just imaging, but high-resolution spectrally resolved wavefront sensing as well. Using ptychographic wavefront sensing, we have imaged wavefronts of multiple harmonics at µm-scale spatial resolution. This approach enables reconstruction of the focusing properties of HHG beams, allowing a detailed view of the beam properties at the generation point, and providing insight into possible spatiotemporal couplings of attosecond pulses and chromatic aberrations intrinsic to the HHG process.