This PDF file contains the front matter associated with SPIE Proceedings Volume 11110, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

There is a large performance gap between conventional, electron-impact X-ray sources and synchrotron radiation sources. Electron-impact X-ray sources are compact, low to moderate cost, widely available and can have high total flux, but have limited tunability (broad spectrum bremsstrahlung plus fixed characteristic lines) and low brightness. By contrast, synchrotron radiation sources provide extremely high brightness (coherent flux), are tunable and can be monochromatized to a very high degree. However, they are very large and expensive, and typically operated as national user facilities with limited access. An Inverse Compton Scattering (ICS) X-ray source can bridge this gap by providing a narrow-band, high flux and tunable X-ray source that fits into a laboratory at a cost of a few percent of a large synchrotron facility. It works by colliding a high-power laser beam with a relativistic electron beam, in which case the backscattered photons have an energy in the X-ray regime. This paper will describe the working principle of the Lyncean Compact Light Source, a storage-ring based ICS source, its unique beam properties and recent developments that are expected to increase flux and brightness by an order of magnitude compared to earlier versions. Furthermore, it will illustrate how such an X-ray source can be the cornerstone of a local X-ray facility serving applications from diffraction and imaging to scattering and spectroscopy. An overview of demonstrated and potential applications will be provided.

ThomX is a new generation Compact Compton Source. It is under installation in the Laboratory of Linear Accelerator at Orsay. The first beams is expected at the end of 2019. The aim of ThomX is to demonstrate the feasibility of an intense and Compact (lab-size) X-ray Source based on the Compton Scattering. The performances are mostly driven by the laser optical system which is above the state of the art of the stored laser power. Firstly, this article present the machine status. Then, the issues and limits of the laser system are discussed. Finally, the expected performances for the next years and the possible experiments that can be made with this new machine are detailed.

There is a strong demand for small foot-print high-flux hard X-rays machines in order to enable a large variety of science activities and serve a multidisciplinary user community. For this purpose, two compact Inverse Compton Sources (ICSs) are currently being developed in Italy. The most recent one is the Bright and Compact X-ray Source (BriXS) which has recently been proposed to produce very energetic X-rays (up to 180 keV) and high photon flux (up to 10¹³ photons/s with expected bandwidth of 1-10%). BriXS will be installed in Milan and it will enable advanced large area radiological imaging applications to be conducted with mono-chromatic X-rays, as well as allowing basic fundamental science of matter and health sciences at both pre- and clinical levels. Based on an energy-recovery linac (ERL) scheme and superconducting technology, BriXS will operate in CW regime with an unprecedented electron beam repetition rate of 100 MHz. The second Italian ICS light source is the Southern Europe Thomson back-scattering source for Applied Research (STAR) which is currently installed at the University of Calabria (UniCal). STAR is a compact machine that has been designed to produce monochromatic and tunable, ps-long, polarized X-ray beams in the range 40-140 keV with a photon flux up to 10¹⁰ photons/s and energy bandwidth below 10%. The electron beam injector is based on normal-conducting technology in S-Band with a repetition rate up to 100 Hz.

The short-wavelength FEL is a revolutionary instrument, which for the first time has permitted the structure of atomic and molecular matter to be interrogated at the spatial and temporal scales relevant to electron rearrangement – Å and fsec, respectively. This frontier tool has produced a paradigm shift in imaging, but suffers from limited access, as the $1B-class instruments needed for both photon science and exploring the attosecond world of the FEL are located at a few national labs worldwide. Due to this expense, access to coherent X-rays for iterative experimentation by the optimal width of the photon science community is suppressed. Further, R&D aimed at cutting edge FEL physics and in the US, has extremely limited resources, thus dimming the prospects for a new, approach to FELs in which the cost and scale of the machine is consistent with university financial and space budgets. The scientific and technological environment of the free-electron laser and related next generation instruments is complex, embracing a wide range of cutting edge fields which are undergoing rapid maturation. This infrastructure is intended to address both scientific and educational roadblocks in the current FEL and photon science communities, by pursuing a vision of an FEL that is an extension of current techniques, pushed to the limits of current performance. This vision entails an approach based on progress in three areas: very high brightness electron beam production; compact, high gradient acceleration; advanced beam manipulations aimed a current enhancement without phase space dilution; and new techniques in realizing very short period undulators. UCLA has played a lead role in high brightness beam production for several decades. It has recently, with support of the NSF through the Center for Bright Beams (CBB), brought a new concept towards fruition, a cryogenic RF photoinjector capable of operations at very high field, and achieving an order of magnitude improvement in electron beam brightness. This beam can be accelerated to GeV energies with the same technical approach, recently shown in proof-of-principle experiments by a Stanford and UCLA. These beams can, further, be compressed by optical bunching techniques, as has been studie successfully at SLAC and UCLA in recent years. Finally, one can utilize a new generation of undulators with periodicity in the mm-scale, exploiting MEMS-based research in this area. In combination, this approach may produce an Angstrom X-ray FEL with fluxes up to ~5% of the LCLS, yet costing an estimated $20M and occupying a footprint of a few tens of meters. This new class of coherent light source will be exploited UCLA and collaborating scientists to explore a new model for both advanced FEL and photon science experimentation. UCLA and its direct collaborators in universities, national labs worldwide, and industry are leaders in these fields, the expertise needed to push thiss state-of-the-art concept is available.

Inverse Compton scattering of infrared photons from relativistic electrons generates brilliant quasi-monochromatic X-rays with an electron accelerator with dimensions of only a few meters, e.g. at the storage ring based inverse Compton scattering X-ray source employed at the Munich Compact Light Source. Availability of synchrotron light in a laboratory comes along with broader access to synchrotron techniques, especially in - but not limited to - clinical imaging and pre-clinical biomedical applications. We have been exploring the latter in daily user operation since commissioning of the MuCLS. So far, the focus has been on dynamic in vivo small-animal respiratory imaging, grating-based phase-contrast imaging, e.g. for quantitative material decomposition, and spectroscopic imaging, e.g. for angiography.

Radiation sources based on Compton interaction that are being developed or operated are often composed of either a LINAC and an optical circulator or a storage ring and a Fabry-Perot optical resonator. A path towards cost and footprint reduction and increased easiness of operation while preserving performances would consist in coupling a normal conducting LINAC to a burst-mode optical Fabry-Perot resonator. This arrangement would thus profit from a high-quality electron beam and a high optical power with optimized performances. This presentation will describe a numerical optimization of a burst-mode Fabry-Perot cavity in this context.

We provide a pathway to compact ultrabright light sources, based on ultrabright, high energy electron beams emerging from a combination of plasma Wakefield acceleration and plasma photocathodes. While plasma acceleration is known to produce accelerating fields three or four orders of magnitude larger than conventional accelerators, the plasma photocathode allows production of electron beams three or four orders of magnitude brighter than conventional, and thus is suitable to unleash the full potential of plasma accelerators. In particular, this is the case for various types of light sources, which profit enormously from an increased electron beam brightness. Building on the recent first experimental demonstration of the plasma photocathode, in this work we discuss the prospects of plasma photocathodes for key photon source approaches such as x-ray free-electron lasers, betatron radiation, ion-channel lasers and inverse Compton scattering.

The generation of X-rays and γ-rays based on synchrotron radiation from free electrons, emitted in magnet arrays such as undulators, forms the basis of much of modern X-ray science. This approach has the drawback of requiring very high energy electron beams, and km scale facilities to obtain the required photon energy. Compact, less costly, monochromatic X-ray sources may enable diverse, paradigm-changing X-ray applications ranging from novel X-ray therapy techniques to active interrogation of sensitive materials, by making them accessible in energy reach, cost and size. The Inverse Compton Scattering (ICS) interaction can be used as the source for generating high-brightness, monochromatic, and ultra-short X-ray pulses in a facility on the scale of university laboratories. A moderately energetic beam of relativistic electrons can up-scatter infrared wavelength laser photons to X-rays. Recent experimental advances in ICS will be reviewed. The coupling of an advanced accelerator with an ICS interaction point has been demonstrated by the collaboration of UCLA and BNL. In an effort to increase the total throughput of an ICS source, RadiaBeam Technologies and BNL have demonstrated a recirculated system, in which the energy of a TW laser pulse is recycled, driving multiple ICS interactions. These experiments and the demand for a high-quality X-rays pave the way for the development of a stand-alone commercial system at RadiaBeam Technologies.

Over the last years, the liquid-metal-jet technology has developed from prototypes into fully operational and stable X-ray tubes running in many labs over the world. Key applications include X-ray diffraction and scattering, but recently several publications. We will show very impressive computed tomography and X-ray microscopy results using the liquid-metal-jet anode technology, especially in phase contrast imaging and also show its applicability to industrial applications. Phase-contrast imaging achieves a significant improvement on the contrast and resolution of soft-issue with hard X-rays, however, the imaging quality, has been compromised by the low flux and brilliance using traditional microfocus tubes or adding optical elements. Therefore, the high brilliance liquid-metal-jet technology paves the way for the development of laboratory-scale phase-contrast imaging, especially its biomedical applications, by enabling shorter exposure time, higher imaging resolution and contrast. Besides, the high stability of the source at its top performance perfectly matches the requirement of the associated phase-contrast imaging techniques. Sharp characteristic line of Gallium, one of the main components in the liquid metal alloy, MetalJet fits well in the optics-based, i.e. X-ray zone plate, X-ray microscopy, while at the same time, reducing the exposure time and maintaining the ultimate resolution. Several application examples will be given during the conference, illustrating the capability of Metaljet in commercial or in-house built X-ray microscopy system. The Kα line of gallium, which is just above the absorption edge of copper, makes MetalJet beneficial for imaging copper with high contrast. Therefore, its advantage in electronic imaging, i.e., imaging copper in obsolete silicon materials. Besides the high brightness microfocus Metaljet tube, based on the advanced electron beam technology, a new nanofocus x-ray tube, with tungsten-coated diamond-transmission target, has been published and reached an extreme resolution of 150 nm line-spacing. Additionally, the unique features of the nanofocus tube also consists in the internal calibration of the current focal spot size before each scan and the high stability for long-time, comparative investigations. The extreme small, true round focal spot of the Nanotube can be used for non-destructive, sub-µm resolution 2-D and 3-D imaging investigation.

Both laboratory and synchrotron-based microanalytical techniques (e.g. microXRF, microXRD, x-ray microscopy, SAXS, etc.) have made substantial advances in the past decades, including improved algorithms and faster, higher sensitivity detectors. However, laboratory performance remains comparatively limited in performance (e.g. sensitivity and resolution), primarily due to limited laboratory x-ray source brightness and narrow selection of usable x-ray optics. Here we present our patented x-ray source concept. Coupled with our proprietary high efficiency x-ray optics, the system provides over 50X brightness over a conventional x-ray illumination beam system comprised of a microfocus source and polycapillary optic. The brightness is enabled by the design of the x-ray targets, which are comprised of microstructured x-ray emitters in thermal contact with a diamond substrate. Utilization of a diamond substrate enables highly localized and large thermal gradients that rapidly cool the metal as x-rays and heat are generated under the bombardment of electrons. In addition to brightness, the spectral output of the x-ray source, particularly the characteristic lines, is sometimes indeed more important than brightness alone. For example, fluorescence cross-sections can vary by several orders of magnitude depending on the characteristic energy employed. Throughput and contrast of x-ray imaging and microscopy are also highly dependent on x-ray energy. Because characteristic lines can be the dominant spectral output for some metals, the ability to select and change metal types within an x-ray source provides substantial performance advantages. Sigray’s x-ray source incorporates several choices of metals on its x-ray target for push-button energy selectability within the x-ray source. A turret of Sigray’s interchangeable x-ray optics that are optimized for highest efficiencies at these energies can be coupled to provide the optimal flux and spectrum for each application.

The construction of BEaTriX, the Beam Expander Testing X-ray facility, is underway at INAF-OAB (Osservatorio Astronomico di Brera). This laboratory-based X-ray source was designed to generate a broad (170 mm x 60 mm), uniform, and collimated X-ray beam, with a residual divergence of 1.5 arcsec HEW at either 1.49 keV and 4.51 keV. The main scientific driver for BEaTriX is represented by the opportunity to routinely calibrate the modular elements of the ATHENA (ESA) X-ray telescope, based on the silicon pore optics (SPO) technology. Nevertheless, the application domain of BEaTriX is potentially much wider (e.g., X-ray tomography). BEaTriX comprises a microfocus source of X-rays, followed by an optical chain including a collimating mirror, crystal monochromators, and an asymmetric beam expander. The final beam collimation and homogeneity relies on the optical quality of the optical components (X-ray source dimension, mirror polishing, crystal lattice regularity) and on their mutual alignment. In order to determine the most critical parameters, focus the development efforts, and establish specifications, a set of optical simulations has been built. Our paper describes the simulation tool we developed to this specific aim, and discusses the results achieved in terms of manufacturing and alignment tolerances.

Laser plasma sources of soft X-rays and extreme ultraviolet (EUV) have been developed for application in various fields of science and technology. The sources are based on a gas puff target irradiated with a nanosecond laser pulse. The targets are created using an electromagnetic valve system equipped with a double-nozzle. The valve system, which is supplied with two different gases, produces a double-stream gas puff target which consists of an elongated stream of high-Z gas surrounded by a stream of low-Z gas. The double-stream gas puff target approach secures high conversion efficiency of laser energy into soft X-ray and EUV energy without degradation of the nozzle. The targets are irradiated with laser pulses produced by commercial Nd:YAG lasers (EKSPLA) with a duration of 1 ns to 10 ns, energy in the pulse from 0.5 J to 10 J with a repetition of 10 Hz. The sources have been applied in various fields, including metrology, processing of materials, nanoimaging, radiography and tomography, photoionized plasma studies, and radiobiology. In this paper the recent results on application of the sources in X-ray absorption spectroscopy and optical coherence tomography (OCT) are presented. The use of the source in laboratory systems for the near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is demonstrated. The NEXAFS system was applied for 2-D elemental mapping of EUV-modified polymer samples. A single-shot exposure NEXAFS spectroscopy is presented. Application of the source in X-ray optical coherence tomography (XCT) has been also demonstrated. The preliminary results on XCT imaging of Mo/Si multilayers with 2 nm axial resolution, using broad-band soft X-ray emission, are presented.

The sensitivity of soft X-ray instrumentation for use in spectroscopy and monochromatization in the Hettrick-Underwood (HU) configuration can be significantly enhanced by replacing the common one-dimensional (1-D) variable line space grating by a two-dimensional (2-D), point-focusing reflection zone plate (RZP). To demonstrate the gain in the performance, we present examples of a flat-field spectrometer for the TiO2 fluorescence between about 390 eV and 530 eV and a femtosecond (fs) monochromator for an energy as low as 38.5 eV. In this context, the application to laser-based high harmonic generation (HHG) sources is discussed.

About one third of all deaths worldwide can be traced back to some form of cardiovascular disease. The gold standard for the diagnosis and interventional treatment of blood vessels is digital subtraction angiography (DSA). An alternative to DSA is K-edge subtraction (KES) imaging, which has been shown to be advantageous for moving organs and to eliminate image artifacts caused by patient movement. As highly brilliant, monochromatic X-rays are required for this method, it has been limited to synchrotron facilities so far, restraining the applicability in clinical routine. Over the past decades, compact synchrotron X-ray sources based on inverse Compton scattering have been evolving, which provide X-rays with sufficient brilliance and that meet spatial and financial requirements affordable in laboratory settings or for university hospitals. In this study, we demonstrate a proofof-principle KES imaging experiment using the Munich Compact Light Source (MuCLS), the first user-dedicated installation of a compact synchrotron X-ray source worldwide. It is shown that the proposed filter-based KES method allows for iodine-contrast agent and calcium to be clearly separated, thereby providing X-ray images only showing one of the two materials. The results show that the quasi-monochromatic spectrum of the MuCLS enables filter-based K-edge subtraction imaging and can become an important tool in pre-clinical research and possible future clinical diagnostics.

The brightness and coherence of modern light sources is pushing the limits of X-ray beamline design. The open source Synchrotron Radiation Workshop (SRW) provides physical optics based algorithms for correctly simulating such beamlines.¹ We present new SRW capabilities to calculate source brightness and related quantites for undulators. The Sirepo cloud computing framework^{2, 3} includes a browser-based GUI for SRW.^4–6 In addition to high-accuracy wavefront simulations, the Sirepo interface now supports analytical calculations for flux, photon beam size, divergence and photon brightness. We have included the effects of detuning from resonance and electron beam energy spread, which can be important in realistic operational conditions. We compare our results to features previously available in the Igor Pro interface to SRW, to analytical formulae available in the literature, and also to the results of simulated wavefront propagation. Differences between the various approaches are explained in detail, so that all the assumptions, conventions and ranges of validity can be better understood.

Femtosecond laser microfabrication allows for precise dimension control and reduced thermal stress of the machined materials. It can be applied to a wide range of materials from copper to diamond. Combined with secondary operations like polishing laser microfabrication can be utilized in various state of the art components required for X-Ray community. In this presentation we will review several applications of laser microfabrication in refractive optics.