Tailoring spatial entropy in extreme ultraviolet focused beams for multispectral ptychography

Microscopy with coherent extreme-ultraviolet (EUV) and soft-X-ray radiation is a promising diagnostic tool for nanoscience. High-harmonic generation (HHG) sources are becoming a mature table-top source for EUV and soft-X-ray radiation. HHG sources naturally produce broad EUV and soft-X-ray spectra, making them intrinsically suited for spectrally-resolved microscopy. This is particularly interesting because many materials possess unique absorption characteristics in this short-wavelength range. However, focusing and shaping polychromatic EUV radiation for microscopy experiments remains challenging due to the fact that most elements across the periodic table exhibit high absorption and low refractive index contrast, which makes manufacturing good refractive optics such as lenses very difficult. A promising technique capable of simultaneous wavefront sensing and quantitative phase contrast microscopy is ptychography [1] , as the large amount of redundant information available in ptychography allows for polychromatic reconstructions with monochromatic detectors [2] . This is particularly useful for imaging experiments with HHG sources, where polychromatic operation offers largely increased flux. Studies have indicated that a ptychography reconstruction benefits from structured illumination probes [3] – [5] .