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

TitleCoherent Diffractive Imaging Near the Spatio-Temporal Limit with High-Harmonic Sources
Publication TypeThesis
Year of Publication2017
AuthorsGardner, Jr., DFloyd
Academic DepartmentPhysics
Number of Pages153
Date Published2017-01
UniversityUniversity of Colorado
CityBoulder, CO

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 Diractive 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.

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