Singleshot polychromatic coherent diffractive imaging with a high-order harmonic source

© 2020 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.Singleshot polychromatic coherent diffractive imaging is performed with a high-intensity high-order harmonic generation source. The coherence properties are analyzed and several reconstructions show the shot-to-shot fluctuations of the incident beam wavefront. The method is based on a multi-step approach. First, the spectrum is extracted from double-slit diffraction data. The spectrum is used as input to extract the monochromatic sample diffraction pattern, then phase retrieval is performed on the quasi-monochromatic data to obtain the sample’s exit surface wave. Reconstructions based on guided error reduction (ER) and alternating direction method of multipliers (ADMM) are compared. ADMM allows additional penalty terms to be included in the cost functional to promote sparsity within the reconstruction

Mapping Atomic Motions with Electrons: Toward the Quantum Limit to Imaging Chemistry

Recent advances in ultrafast electron and X-ray diffraction have pushed imaging of structural dynamics into the femtosecond time domain, that is, the fundamental time scale of atomic motion. New physics can be reached beyond the scope of traditional diffraction or reciprocal space imaging. By exploiting the high time resolution, it has been possible to directly observe the collapse of nearly innumerable possible nuclear motions to a few key reaction modes that direct chemistry. It is this reduction in dimensionality in the transition state region that makes chemistry a transferable concept, with the same class of reactions being applicable to synthetic strategies to nearly arbitrary levels of complexity. The ability to image the underlying key reaction modes has been achieved with resolution to relative changes in atomic positions to better than 0.01 Å, that is, comparable to thermal motions. We have effectively reached the fundamental space-time limit with respect to the reaction energetics and imaging the acting forces. In the process of ensemble measured structural changes, we have missed the quantum aspects of chemistry. This perspective reviews the current state of the art in imaging chemistry in action and poses the challenge to access quantum information on the dynamics. There is the possibility with the present ultrabright electron and X-ray sources, at least in principle, to do tomographic reconstruction of quantum states in the form of a Wigner function and density matrix for the vibrational, rotational, and electronic degrees of freedom. Accessing this quantum information constitutes the ultimate demand on the spatial and temporal resolution of reciprocal space imaging of chemistry. Given the much shorter wavelength and corresponding intrinsically higher spatial resolution of current electron sources over X-rays, this Perspective will focus on electrons to provide an overview of the challenge on both the theory and the experimental fronts to extract the quantum aspects of molecular dynamics

Quantitative diffraction imaging using attosecond pulses

We have proposed and developed a method to utilize attosecond pulses in diffraction imaging techniques applied to complex samples. In this study, the effects of the broadband properties of the wavefield owing to attosecond pulses are considered in the reconstruction of images through the decomposition of the broad spectrum into multi-spectral components. This method successfully reconstructs the multi-spectral information of complex samples, probes, and spectral bandwidths using broadband diffraction intensities generated from computational scanning experiments. The results obtained in this research open the opportunities to perform quantitative ultrafast imaging using the attosecond pulses.Comment: 17 page

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

Coherent diffractive imaging is unique as the only route for achieving diffraction-limited 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, to date, high-fidelity diffraction imaging of periodic objects has been a challenge because the scattered light is concentrated in isolated peaks. Here, we use tabletop 13.5nm 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 sub-wavelength spatial resolution (12.6nm) 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, quantitative, reconstructions of periodic objects. This work is important for imaging next generation nano-engineered devices.Comment: 15 pages, 5 figure

Roadmap on label-free super-resolution imaging

Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label-free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field

Nanoscale EUV Microscopy on a Tabletop: A General Transmission and Reflection Mode Microscope Based on Coherent Diffractive Imaging with High Harmonic Illumination

A new scientific frontier exists at the intersection of the nanoscale and the ultrafast. In order to explore this frontier, new tools with unique capabilities for imaging with nanometer spatial and femtosecond temporal resolution are critical. This thesis describes the development of such a tool, combining coherent diffractive imaging (CDI) with an extreme ultraviolet (EUV) high harmonic generation (HHG) light source to produce a compact, accessible, high-resolution microscope. Here, this microscope is used to demonstrate 22 nm resolution in transmission, a record for any full-field tabletop light-based microscope. Further, this microscope is used to demonstrate the most general reflection mode implementation of CDI to date, enabling image reconstruction at any angle of incidence. Chapter 2 describes the optimization of the HHG source for use with CDI. A pulse shaper is implemented to produce transform-limited pulses at 800 nm for increased HHG conversion efficiency. Furthermore, the long-term stability of the HHG source is improved by an order of magnitude through the pointing stabilization of the kHz driving laser. Chapter 3 develops the ideas necessary for the data processing techniques that enable general reflection mode CDI. Chapter 4 describes enhancements to the microscope to produce images with record 22 nm resolution in addition to extension of the microscope to image more complex, transmissive samples. Chapter 5 presents the most general implementation of reflection mode CDI to date. In chapter 6, the route towards dynamic femtosecond imaging of complex nanosystems is outlined, which includes potential for simultaneous hyperspectral EUV imaging across multiple absorption edges

A High-Flux Compact X-ray Free-Electron Laser for Next-Generation Chip Metrology Needs

Recently, considerable work has been directed at the development of an ultracompact X-ray free-electron laser (UCXFEL) based on emerging techniques in high-field cryogenic acceleration, with attendant dramatic improvements in electron beam brightness and state-of-the-art concepts in beam dynamics, magnetic undulators, and X-ray optics. A full conceptual design of a 1 nm (1.24 keV) UCXFEL with a length and cost over an order of magnitude below current X-ray free-electron lasers (XFELs) has resulted from this effort. This instrument has been developed with an emphasis on permitting exploratory scientific research in a wide variety of fields in a university setting. Concurrently, compact FELs are being vigorously developed for use as instruments to enable next-generation chip manufacturing through use as a high-flux, few nm lithography source. This new role suggests consideration of XFELs to urgently address emerging demands in the semiconductor device sector, as identified by recent national need studies, for new radiation sources aimed at chip manufacturing. Indeed, it has been shown that one may use coherent X-rays to perform 10–20 nm class resolution surveys of macroscopic, cm scale structures such as chips, using ptychographic laminography techniques. As the XFEL is a very promising candidate for realizing such methods, we present here an analysis of the issues and likely solutions associated with extending the UCXFEL to harder X-rays (above 7 keV), much higher fluxes, and increased levels of coherence, as well as methods of applying such a source for ptychographic laminography to microelectronic device measurements. We discuss the development path to move the concept to rapid realization of a transformative XFEL-based application, outlining both FEL and metrology system challenges

Structured High-Harmonic Light Sources for Enhanced Extreme Ultraviolet Microscopy

Lensless imaging techniques such as ptychography have revolutionized short-wavelength metrology by enabling photon-efficient, diffraction limited, robust phase-contrast imaging of nanostructured samples. At the same time, light sources based on the extreme nonlinear optical process of high harmonic generation have enabled these and other short-wavelength metrology techniques to be carried out on a tabletop. However, due to the lack of refractive optics for manipulating extreme ultraviolet and X-ray light, short-wavelength imaging currently lacks the vast flexibility of visible light microscopy, which in part is made possible by the many optical elements available for tailoring the illumination. This thesis aims to fill this gap by integrating amplitude, phase, and polarization structured light into the high harmonic generation process to produce a great deal of flexibility in the light source at its generation, and giving initial demonstrations of how using such tailored light sources can expand the capabilities of tabletop EUV microscopy techniques.</p