Wed, 25.01.2023  |  14:00 - 15:00
Room: Max Born Hall
MBI Colloquium

Lensless imaging using high-harmonic generation: nanoscale imaging of 3D objects (and the HHG source itself)

Dr. Stefan Witte | Advanced Research Center for Nanolithography (ARCNL) and Vrije Universiteit Amsterdam

talks about

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.