Montel mirror coated by laterally graded multilayer is a key two-dimensional collimating optics for x-ray analysis instrument. To provide guidance for the fabrication, the collimation property of a W/Si multilayer Montel mirror with parabolic shape is simulated systematically by a ray-tracing program. The influence of different source sizes, multilayer reflection bandwidth, mirror-detector distance, figure errors, and the assembly errors on the collimation performance is simulated. The mechanism for the change of divergence angle, collimation efficiency, beam uniformity, and so on is analyzed. Based on the results, the optimum mirror structure and the tolerance for fabrication and assembly errors were estimated for a high-performance x-ray Montel mirror.
In many single-pulse experiments of X-ray free electron lasers, the spectrum and intensity distribution of the self-amplifying spontaneous radiation beams fluctuate significantly. It is necessary to perform accurate spectral characterization of each pulse. In this paper, we present an in-line spectrometer that can observe the distribution of energy and incident intensity of single pulse X-ray photons in real time. The X-ray diffraction is achieved by using a high precision transmission crystal bending to fixed pressure bending, and the spectrum is recorded by a spatial resolution detector. At the same time, most of the incident flux is transmitted to the downstream experiment. In this paper, based on the X-ray crystal diffraction theory, geometric optical path designs were carried out, high-precision transmission curved-crystal with fixed bending was developed, the optical path of in-line transmission spectrometer was built, and the copper Kα1 and Kα2 obtained by the test were used for spectral calibration. The experimental results show that each pixel on the detector corresponds to 0.43eV, and the half-width of Kα1 is 3.44 eV. The Single-pulse spectrometer can be used for hard x-ray free electron lasers spectroscopy experiments.
In X-ray laser plasma diagnostics, fast and accurate integrated alignment is essential, yet existing methods are not only limited in accuracy but also time inefficient. An integrated alignment method of X-ray diagnostic systems with accurate, rapid and repeatable characteristics was proposed in this paper. First, the method establishes precise object-image relationship of X-ray diagnostic system based on laboratory X-ray imaging experiments, and then the relationship is indicated by the ball pointer and the image indication module. To achieve high resetting accuracy, the ball pointer and image indication module are coupled to the X-ray diagnostic system by linear guides. Finally, the X-ray diagnostic system is directly switched to the online environment at the laser facility by the indication of the ball pointer and image indication module. The paper presents the optical design, mechanism structure and experimental result of the integrated alignment method taking HOPG spectrometer for copper emission spectrum as an example. The method has been applied in the adjustments of X-ray diagnostics systems for several physics experiments in multiple laser facilities.
Precise X-ray Imaging diagnostics to acquire the plasma state and its evolution plays an important role in basic researches such as inertial confinement fusion (ICF), high energy density physics (HEDP), and another ultrafast phenomenon. The plasma signals with the characteristics of small scale, rapid evolution and complex spectrum requires the X-ray diagnostics optics to have high spatial resolution and collection efficiency, as well as certain spectral resolution. The multilayer Kirkpatrick–Baez (KB) microscope is a common X-ray optics to obtain high spatial, collecting efficiency or spectral resolution. Coupling multichannel KB microscope with the framing camera, the temporal evolution behavior of the ultrafast plasma can be recorded. The paper mainly presents our latest research on two-energy sixteen-channel multilayer KB microscope for double-cone ignition (DCI) experiments, including its optical and multilayer design. By high-resolution backlighting and self-emission imaging using two-energy multichannel KB microscope, plasma information related to density and temperature can be realized simultaneously.
The Hot Universe Baryon Surveyor (HUBS) mission is proposed to study “missing” baryons in the universe. Unlike dark matter, baryonic matter is made of elements in the periodic table, and can be directly observed through the electromagnetic signals that it produces. Stars contain only a tiny fraction of the baryonic matter known to be present in the universe. Additional baryons are found to be in diffuse (gaseous) form, in or between galaxies, but a significant fraction has not yet been seen. The latter (“missing” baryons) are thought to be hiding in low-density warm-hot ionized medium (WHIM), based on results from theoretical studies and recent observations, and be distributed in the vicinity of galaxies (i.e., circumgalactic medium) and between galaxies (i.e., intergalactic medium). Such gas would radiate mainly in the soft X-ray band and the emission would be very weak, due to its very low density. HUBS is optimized to detect the X-ray emission from the hot baryons in the circumgalactic medium, and thus fill a void in observational astronomy. The goal is not only to detect the “missing” baryons, but to characterize their physical and chemical properties, as well as to measure their spatial distribution. The results would establish the boundary conditions for understanding galaxy evolution. Though highly challenging, detecting “missing” baryons in the intergalactic medium could be attempted, perhaps in the outskirts of galaxy clusters, and could shed significant light on the large-scale structures of the universe. The current design of HUBS will be presented, along with the status of technology development.
As the spectrum of each pulse from XFEL (X-ray free electron lasers, XFEL) undulator (often referred as pink X-ray) varied between each other, it is necessary to measure the intensity and spectrum of each pulse. The major parameters of the spectrometer are the facet of bent crystal, the Bragg angle, the transmittance (related to the material, its thickness and transmission angle), energy range and energy resolution. An ultrathin Si wafer was put above a concave lens and under a convex lens. Bending was achieved by applying the pressure, then the Si wafer with 25μm thickness would be regularly bent onto the concave profile until the convex substrate, Si wafer and the concave lens were overlap. The cylindrical substrates were provided with holes to let the FEL beam through the crystal, and the radius of curvature could be varied from 0.2m to 1m. The crystal orientation and miscut angle were measured by a high resolution X-ray diffractometer. Finally, the energy dispersion spectra were measured by a spectrometer built in laboratory.
With the rapid development of extreme ultraviolet (EUV) light sources, such as plasma-based light source and Free Electron Laser (FEL), it provides unprecedented powerful ultra-short EUV radiations. These extremely high intense ultra-short pulses of radiation bring great challenges to the optical components utilized for steering these light beams, especially the radiation damage issues. However, more studies on the EUV damage mechanisms on optical materials are still quite desired because of limited beamtime provided by FEL facilities. In this study, we present a table-top focused EUV optical system built at the Institute of Precision Optical Engineering (IPOE) for performing EUV damage tests on optical materials. This setup consists of a laser-plasma light source, a modified Schwarzschild objective and an EUV energy attenuator. With a large numerical aperture of 0.44 and a demagnification of 11, the Schwarzschild objective is composed of two annular spherical mirrors coated with Mo/Si multilayers. By using the Zirconium filter and Mo/Si multilayers, this setup can generate the focused radiation with an energy density of 2.27 J/cm2 at the wavelength of 13.5 nm on the image plane of the objective with ~8.3 ns pulse duration. The EUV energy can be changed using a gas attenuator by varying the gas pressure of Helium or Nitrogen inside the chamber. The performance and potentials of this setup are demonstrated by the single-shot or multi-shot damage tests on some samples, such as Au thin film, CaF2 and Mo/Si multilayer mirror. The damage thresholds were determined and the possible damage mechanisms are discussed together with available experimental results.
A table-top soft x-ray polarimetry setup has been developed at the Institute of Precision Optical Engineering for characterizing the polarization properties of mirrors designed for the lightweight asymmetry and magnetism probe project. Based on a Co/C multilayer polarizer mirror, linearly polarized soft x-rays were generated at a wavelength of 4.48 nm, which could be rotated around the beam-propagation direction by using a differentially pumped rotary feedthrough. The setup design and the alignment method are described in detail. The capabilities of this spectrometer were demonstrated through a polarization test on a twin Co/C multilayer polarizer sample, and the results agree well with the expected sine wave.
Monochromatic energy multilayer Kirkpatrick-Baez microscope is one of key diagnostic tools for researches on inertial confinement fusion. It is composed by two orthogonal concave spherical mirrors with small curvature and aperture, and produce the image of an object by collecting X-rays in each orthogonal direction, independently. Accurate measurement of radius of curvature of concave spherical mirrors is very important to achieve its design optical properties including imaging quality, optical throughput and energy resolution. However, it is difficult to measure the radius of curvature of spherical optical surfaces with small curvature and aperture by conventional methods, for the produced reflective intensity of glass is too low to correctly test. In this paper, we propose an improved measuring method of optical profiler to accomplish accurate measurement of radius of curvature of spherical optical surfaces with small curvature and aperture used in the monochromatic energy multilayer Kirkpatrick-Baez microscope. Firstly, we use a standard super-smooth optical flat to calibrate reference mirror before each experiment. Following, deviation of central position between measurement area and interference pattern is corrected by the theory of Newton’s rings, and the zero-order fringe position is derived from the principle of interference in which surface roughness has minimum values in the position of zero light path difference. Measured results by optical profiler show the low relative errors and high repeatability. Eventually, an imaging experiment of monochromatic energy multilayer Kirkpatrick-Baez microscope determines the measurement accuracy of radius of curvature.
A large-field high-resolution x-ray microscope was developed for multi-keV time-resolved x-ray imaging diagnostics of laser plasma at the Shenguang-III prototype facility. The microscope consists of Kirkpatrick–Baez amélioré (KBA) bimirrors and a KB single mirror corresponding to the imaging and temporal directions of a streak camera, respectively. KBA bimirrors coated with an Ir single layer were used to obtain high spatial resolutions within the millimeter-range field of view, and a KB mirror coated with Cr/C multilayers was used to obtain a specific spectral resolution around 4.3 keV. This study describes details of the microscope with regard to its optical design, mirror coatings, and assembly method. The experimental imaging results of the grid with 3 to 5 μm spatial resolution are also shown.
The degradation of image quality of the nested conical Wolter-I X-ray telescope mainly results from mirror-position tolerance, alignment-bar tolerance and surface-figure tolerance. The analytical approach of the three kinds of tolerance was presented in this paper. Based on the predetermined initial structure, we analyzed and compared image qualities with different tolerances. Furthermore, we simulated the distribution of the spot diagrams and calculated the spatial resolution of the entire system. Shift along the optical axis (Z axis) and rotation around it have no effects on the image quality for position tolerances. However, shift along X, Y directions and rotation around X, Y axes change the distribution of spot diagrams and decrease the spatial resolution. For higher resolution, we should control the alignment-bar tolerance by placing a displacement sensor at the end of the alignment bar. The angular resolution increases from 1' to 13'' as the alignment-bar tolerance decreased from ±15um to ±3um. With respect to surface-figure tolerance, we simulated image qualities by inserting Zernike polynomial to the surface.
Periodic multilayer KB microscopes have widely implemented in x-ray diagnostic experiments of ICF, especially at relatively high x-ray energies (8keV or higher). But the obvious disadvantage, due to narrow bandwidth of periodic multilayer, is the ununiformity of x-ray image brightness and the limited field of view. The literature describes the characterization of a high-energy KB microscope with aperiodic multilayer configured to achieve larger effective field of
view than existing periodic multilayer KB microscopes. The microscope, working on 8keV with grazing angles of 1.1330° and 1.1837°, is capable of 5μm resolution over ±200μm object field. Design of the multilayer and experimental results with a Cu x-ray tube will be shown.
A Schwarzschild microscope at 18.2 nm for ultra-fast laser plasma diagnostics has been developed.
Based on the third-order aberration the microscope is designed for numerical aperture of 0.1 and
magnification of 10. Spatial resolution of the objective can achieve 1250 lp/mm within the field of ±1
mm. Mo/Si multilayer films with peak throughout at 18.2 nm is designed and deposited by magnetron
sputtering, and the measured reflectivity of optical elements is 45%. The 600 lp/inch copper grid
backlit by laser produced plasma is imaging via Schwarzschild microscope on CCD. The spatial
resolution is measured as 3 μm approximately in the field of 1.2 mm.
To study the action of shock wave in CH target, one-dimensional grazing incidence
KBA microscope for 4.75keV energy was set up. Because of strong absorption in air, 4.75keV
energy microscope can just work in vacuum. Accordingly, the alignment and assemblage will be
very complicated and difficult. A special multilayer method, using double periodic multilayer, was
proposed to solve this problem. This multilayer has high reflectivity not only for 4.75keV x-rays
but also for 8keV x-rays at the same grazing incidence angle. It means 1D-KBA microscope has
the same light trace for different working energies. Therefore, we can implement the alignment
and assembly of 4.75keV system by the help of 8keV x-rays. Because 8keV x-rays is very easy
produced by x-ray tube and has strong transmittability in air, the alignment and assemblage
process became relatively easy. By now, we have finished the alignment experiment at 8keV and
obtained imaging results. The performance is about 2-3μm resolution in 250μm field of view. It is
coincide with the calculation.
An auxiliary visible imaging method was introduced to solve the axial and pointing
alignment of x-ray Kirkpatrick-Baez optics. Through ZEMAX simulation and x-ray imaging
experiments, the axial and pointing alignment accuracy were determined to be ±300μm and
±20μm respectively. The numerical aperture of x-ray Kirkpatrick-Baez optics is rather small, so
it's impossible to adjust Kirkpatrick-Baez system by visible imaging directly. An auxiliary visible
lens was designed, which was equivalent to x-ray Kirkpatrick-Baez optics on conjugate
relationship and accuracy control. The comparative experiments of visible imaging and x-ray
imaging indicate that this auxiliary system could meet the alignment accuracy of Kirkpatrick-Baez
optics.
A double-periodic multilayer method was proposed to test KBA system of 4.75keV
using 8keV source. Alignment of angle is the key for most of grazing incidence systems in x-ray
range. But for soft x-ray, strong absorption makes the alignment have to be operated in vacuum,
which is difficult enough. A double-periodic multilayer was used to experiment at 8keV in air
replacing 4.75keV in vacuum. This multilayer includes two parts, the top and the bottom. The top
is W/B4C multilayer with four bilayers and 6.93nm periods. The bottom is W/B4C multilayer with
10 bilayers and 3.95nm periods. For 8keV energy, x-ray will penetrate through the top and
reflected by the bottom. While for 4.75keV, x-ray will be reflected by the top directly. The full
width of half maximum is 0.1° at 8keV and 0.3° at 4.75keV, so it is accurate enough for 4.75keV
to experiment at 8keV, which was also verified by the 1-D KBA experiment. This double-periodic
multilayer provides a valid solution for alignment in soft x-ray range.
A hard x-ray (8 keV, Kα line of Cu) Kirkpatrick-Baez (KB) microscope was designed for the diagnostics of inertial confinement fusion (ICF). Three main parts including optical design, fabrication of multilayers, and alignment method were discussed in this paper. According to the deduced equation of aberration in whole field, an optical system was designed, which gives attention to not only spatial resolution but also the collection efficiency. Tungsten (W) and boron carbide (B4C) were chosen as multilayer materials and the non-periodic multilayer with 40 layers was deposited. The measured reflectivity by XRD is better than 18% in the bandwidth range of about 0.3%. Super accurately alignment is another difficulty in the application of KB microscope. To meet the requirements of pointing and co-focusing, a binocular laser pointer which is flexible enough was designed. Finally, an 8keV x-ray tube was used as source in x-ray imaging experiment and images with magnification of 2× were obtained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.