Coherent Diffractive Imaging Near the Spatio-Temporal Limit with High-Harmonic Sources

摘要

This thesis discusses methods for high-resolution static and stroboscopic microscopy using tabletop coherent extreme ultraviolet (EUV) radiation from tabletop high-harmonic generation (HHG) sources. These coherent short wavelength light sources are combined with a lensless, computational, phase and amplitude-contrast technique called ptychographic Coherent Diffractive Imaging (CDI). While ptychographic CDI techniques are currently widespread for visible, EUV and X-ray microscopy, no previous work has been able to achieve at-wavelength resolution of extended samples, especially in a reflection geometry, nor has previous work been able to image periodic samples with high-fidelity. In this work, a combination of experimental methods for high-numerical aperture imaging and novel computational algorithms enabled the highest resolution-to-wavelength demonstrations using any CDI technique. These algorithms include tilted plane correction, which enables high-resolution imaging of surfaces in a reflection geometry, and a powerful technique termed 'modulus enforced probe', which enables both imaging of periodic objects and convergence of the ptychographic CDI algorithm in fewer iterations. Furthermore, the ultrafast pulse duration of the high-harmonic radiation is harnessed to demonstrate proof-of-principle pump-probe imaging of nanostructures, capturing thermal transport processes in nanostructures with an axial resolution of 3 angstroms. Stroboscopic imaging with nanoscale resolution is a critical tool for the investigation of nanoscale heat flow and magnetic switching for the advancement of next generation nano-electronics, data storage, and nano-engineered systems.