Spatial control of XUV solid-state high harmonics

Short wavelength high-harmonic sources are undergoing intense development for applications in spectroscopy and microscopy. Despite recent progress in peak and average power, spatial control over coherent extreme ultraviolet (XUV) beams remains a formidable challenge due to the lack of suitable optical elements for beam shaping and control. In this work, we demonstrate a robust and precise approach that structures XUV high-order harmonics in space as they are emitted from a nanostructured MgO crystal. Our demonstration paves the way for bridging the numerous applications of shaped light beams from the visible to the short wavelengths, with potential uses for applications in (nonlinear) microscopy with chemical and elemental specificity, direct nanoscale laser writing, and for sub-cellular mass-spectroscopy of biological tissue (nano-imaging mass cytometry).

To achieve structured XUV beams we developed a fabrication method to etch grooves and other patterns in a crystalline MgO surface. Intense infrared pulses shone on the structure acquire the phase shift imposed by the pattern and encode it (multiplied) to the high-order harmonics generated from the crystal itself. The multiplied phase modulation reaches up to a half-wavelength of the XUV radiation, thereby resulting is very efficient diffraction, as seen in the figure below (diffraction from a 2-dimensional grating).

Korobenko, A., et al. “Generation of structured coherent extreme ultraviolet beams from an MgO crystal.” Optics Express 29.15 (2021): 24161-24168. https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-15-24161&id=453311