Subwavelength coherent imaging of periodic samples using a 13.5 nm tabletop high-harmonic light source

Coherent diffractive imaging is unique, being the only route for achieving high spatial resolution in the extreme ultraviolet and X-ray regions, limited only by the wavelength of the light. Recently, advances in coherent short-wavelength light sources, coupled with progress in algorithm development, have significantly enhanced the power of X-ray imaging. However, so far, high-fidelity diffraction imaging of periodic objects has been a challenge because the scattered light is concentrated in isolated peaks. Here, we use tabletop 13.5 nm high-harmonic beams to make two significant advances. First, we demonstrate high-quality imaging of an extended, nearly periodic sample for the first time. Second, we achieve subwavelength spatial resolution (12.6 nm) imaging at short wavelengths, also for the first time. The key to both advances is a novel technique called 'modulus enforced probe', which enables robust and quantitative reconstructions of periodic objects. This work is important for imaging next-generation nano-engineered devices.