Grazing Incidence X-ray Optics Research Articles

Measuring large amplitude surface figure error using coordinate metrology

Advances in optical testing are as important as advances in fabrication because one can make only what one can measure. A high-precision metrology capability is utilized to close the gap between interferometric testing and lower precision metrology, laser radar, or contact-probe-based coordinate measuring machines (CMM) to accurately measure surfaces with large form error. This nearly universal optical testing method employs a precision CMM equipped with a non-contact, confocal probe. This technique was developed to characterize and align a broad spectrum of optical surfaces including ones with high slopes that are nearly impossible to measure using traditional interferometric testing without custom-made optics. Optical components covering a wide range of prescriptions, such as large convex conics, high-sloped aspherics, grazing-incidence x-ray optics, and highly deformed flats, were successfully measured. The resulting data were processed using custom-developed routines to determine the optic’s alignment, the departure from design surface, and the as-built prescription parameters. This information was used to verify and guide the development and fabrication of novel optics.

Enabling precision coordinate metrology for universal optical testing and alignment applications

Optical designs for the next generation space science instruments call for unconventional, aspheric, and freeform (FF), prescriptions with tight tolerances. These advanced surfaces enable superior-performance, compact, and lower cost systems but are more challenging to characterize and, hence, to fabricate and integrate. A method was developed to characterize a wide range of optical surfaces, without requiring custom-made correctors, and to align them to each other for a high-performance optical system. A precision coordinate measuring machine, equipped with a non-contact, chromatic confocal probe, was used to measure numerous optics including large convex conics, high-sloped aspherics, several FF surfaces, and grazing-incidence x-ray optics. The resulting data were successfully reduced using custom-developed, advanced surface fitting analysis tool, to determine the optic’s alignment relative to the global and local coordinate systems, surface departure from design, and the as-built optical prescription. This information guided the modeling and the alignment of the corresponding as-built optical systems, including a flight system composed of a three-mirror anastigmat.

Development and in-orbit performance evaluation of multi-layered nested grazing incidence optics

On November 10, 2016, China launched an X-ray pulsar navigation test satellite (XPNAV-1) to investigate the X-ray pulsar navigation technology, and a lot of scientific observation data have been obtained. The X-ray grazing incidence optics is a critical component of the focusing pulsar telescope. It plays an important role in increasing the effective area and enhancing the sensitivity of the telescope. It is also the first grazing incidence optics verified in orbit in China. According to the characteristic that the times of arrival (TOA) of X-ray photons are measured in pulsar navigation, the grazing incidence focusing optics based on single-reflection paraboloid mirror is designed, and manufacturable mirror design parameters are obtained through theoretical calculation and derivation. The theoretical effective area of the designed optics is 15.6 cm<sup>2</sup> at 1 keV. The designed optics is then simulated to evaluate its focusing performance. It meets the focusing requirement in the full field of view. The electroforming nickel replication process used for manufacturing the mirrors for XMM-Newton and eRosita missions is investigated. A super-smooth mandrel is firstly fabricated and used for follow-up replication. An about-100 nm-thick gold layer is deposited on the mandrel, and serves as the reflection and release layer of the mirror. The nickel substrate of the mirror is electroformed on the gold layer. The mirror is finally obtained by releasing the nickel and gold layer from the mandrel. The patterns and roughness of the mandrel are then replicated onto the inner surface of the mirror. The 4-layered mirror is fabricated for the optics. The reflectivity for each layer of the 4-layered mirror is then measured with a dedicated facility on 4B7B beamline of BSRF. The effective area of the optics based on the above-measured reflectivity is 13.2 cm<sup>2</sup> at 1 keV. Finally, according to the in-orbit observation data, the effective area of the optical system is evaluated to be a typical value of 4.22 cm<sup>2</sup> at 1 keV, which is less than the ground-tested value. The reason for this is analyzed and it turns out to be due to the thermal deformation of mechanical structure and contamination of the mirrors. Therefore, in our future work, we will strictly control the environmental factors and implement space environmental adaptability design, while increasing the accuracy of the optics.

X-ray scattering by the fused silica surface etched by low-energy Ar ions.

Anomalously high x-ray scattering at a wavelength of 0.154 nm by super-polished substrates of fused silica, which were etched by the argon ions with the energy of 300 eV, is detected. The scattering intensity increases monotonically with increasing of the etching depth. The effect is explained by the scattering on the volume inhomogeneities with the lateral size greater than 0.5 μm of the subsurface "damaged" layer. The concentration of volume inhomogeneities increases with the increase of the fluence of argon ions, but the concentration of implanted argon atoms in the layer quickly reaches the maximum value and then begins a trend of going down. The thickness of the "damaged" layer is approximately equal to the penetration depth of the Ar atoms and can be directly determined from the x-ray specular reflection. It is shown that the presence of volume inhomogeneities of the subsurface "damaged" layer does not affect the geometric roughness of the surface. The observed effect imposes limitations on the usage of grazing incidence x-ray optics without reflective coatings and of the diffuse x-ray scattering (DXRS) method for studying the substrate roughness. A new method that potentially enables to evaluate the applicability of the DXRS method in practice is proposed.

Full-shell x-ray optics development at NASA Marshall Space Flight Center.

NASA's Marshall Space Flight Center (MSFC) maintains an active research program toward the development of high-resolution, lightweight, grazing-incidence x-ray optics to serve the needs of future x-ray astronomy missions such as Lynx. MSFC development efforts include both direct fabrication (diamond turning and deterministic computer-controlled polishing) of mirror shells and replication of mirror shells (from figured, polished mandrels). Both techniques produce full-circumference monolithic (primary + secondary) shells that share the advantages of inherent stability, ease of assembly, and low production cost. However, to achieve high-angular resolution, MSFC is exploring significant technology advances needed to control sources of figure error including fabrication- and coating-induced stresses and mounting-induced distortions.

Optics for Nano-Satellite X-Ray Monitor

Abstract The Schmidt lobster eye design for a grazing incidence X-ray optics provides a field of view of the order of many degrees, for this reason it can be a convenient approach for the construction of space X-ray monitors. It is possible to assemble Schmidt lobster eye telescopes with the dimensions and focal lengths acceptable for nano-class satellites. In this paper, a draft of nano-class space mission providing monitoring of specific sky areas is presented. A preliminary optical design study for such mission is performed. Two of possible optical designs are presented, for which the field of view, the effective input area and other basic optical parameters are calculated. Examples of the observed images are also presented.

Fluence thresholds for grazing incidence hard x-ray mirrors

X-ray Free Electron Lasers (XFELs) have the potential to contribute to many fields of science and to enable many new avenues of research, in large part due to their orders of magnitude higher peak brilliance than existing and future synchrotrons. To best exploit this peak brilliance, these XFEL beams need to be focused to appropriate spot sizes. However, the survivability of X-ray optical components in these intense, femtosecond radiation conditions is not guaranteed. As mirror optics are routinely used at XFEL facilities, a physical understanding of the interaction between intense X-ray pulses and grazing incidence X-ray optics is desirable. We conducted single shot damage threshold fluence measurements on grazing incidence X-ray optics, with coatings of ruthenium and boron carbide, at the SPring-8 Angstrom compact free electron laser facility using 7 and 12 keV photon energies. The damage threshold dose limits were found to be orders of magnitude higher than would naively be expected. The incorporation of energy transport and dissipation via keV level energetic photoelectrons accounts for the observed damage threshold.

Calibration of the High Energy Replicated Optics to Explore the Sun (HEROES) Hard X-ray Telescope

On 2013 September 21–22, the High Energy Replicated Optics to Explore the Sun (HEROES) hard X-ray telescope flew as a balloon payload from Ft. Sumner, NM. HEROES observed the Sun, the black hole binary GRS 1915+105, and the Crab Nebula during its 27 h flight. In this paper, we describe laboratory calibration measurements of the HEROES detectors using line and continuum sources and applications of these measurements to define channel to energy (gain) corrections for observed events and to define detector response matrices. We characterize the HEROES X-ray grazing incidence optics using measurements taken in the Stray Light Facility (SLF) in Huntsville, AL, and using ray traces. We describe the application of our calibration measurements to in-flight observations of the Crab Nebula.

Development of high spatial resolution detector for characterization of X-ray optics

Technological innovations in grazing incidence X-ray optics have been crucial to the advancement of the field of X-ray astronomy. Improvements in X-ray focusing optics translate to higher sensitivity for X-ray telescopes operating in the energy range above 10 keV. Full characterization of the X-ray optics involves measurement of the point spread function, scattering, and reflectivity properties of substrate coatings. This requires a very high spatial resolution, high sensitivity, photon counting and energy discriminating large area detector. In this paper we describe the construction of a detector that is well suited to meet these requirements. A prototype version of this camera was used to calibrate the X-ray focusing optics for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission. Analysis of the data obtained during the ground calibration of the NuSTAR telescopes demonstrated the advantages of such a high resolution 2D detector for hard X-rays (30+ keV); however it showed some limitations for medium energy X-rays (8–30 keV). We present here, alternative methods under investigation to improve performance of the detector for medium energy X-rays such as changing the morphology of the CsI:Tl scintillator, improving light transport from scintillator to EMCCD and using a novel bright scintillator, Ba2CsI5:Eu.

Differential deposition technique for figure corrections in grazing-incidence x-ray optics

A differential deposition technique was investigated as a way to minimize axial figure errors in full-shell, grazing-incidence, reflective x-ray optics. These types of optics use a combination of off-axis conic segments-hyperbolic, parabolic, and/or elliptical, to reflect and image x-rays. Several such mirrors or "shells" of decreasing diameter are typically concentrically nested to form a single focusing unit. Individual mirrors are currently produced at Marshall Space Flight Center using an electroforming technique, in which the shells are replicated off figured and superpolished mandrels. Several factors in this fabrication process lead to low- and mid-spatial frequency deviations in the surface profile of the shell that degrade the imaging quality of the optics. A differential deposition technique, discussed in this paper, seeks to improve the achievable resolution of the optics by correcting the surface profile deviations of the shells after fabrication. As a proof of concept, the technique was implemented on small-animal radionuclide-imaging x-ray optics being considered for medical applications. This paper discusses the deposition technique, its implementation, and the experimental results obtained to date.

Tests of lobster eye optics for small space X-ray telescope

The Lobster eye design for a grazing incidence X-ray optics provides wide field of view of the order of many degrees, for this reason it can be a convenient approach for the construction of space all-sky X-ray monitors. We present preliminary results of tests of prototype lobster eye X-ray optics in quasi parallel beam full imaging mode conducted using the 35 m long X-ray beam-line of INAF-OAPA in Palermo (Italy). X-ray images at the focal plane have been taken with a microchannel plate (MCP) detector at several energy values from 0.3 to 8 keV. The gain, the field of view and the angular resolution have been measured and compared with theoretical values.

An investigation of differential deposition for figure corrections in full-shell grazing-incidence X-ray optics

We are investigating differential deposition as a way of correcting small figure errors inside full-shell grazing-incidence X-ray optics. The optics in our study are fabricated using the electroformed-nickel-replication technique, and the figure errors arise from fabrication errors in the mandrel, from which the shells are replicated, as well as errors induced during the electroforming and mounting process. Combining, these give sub-micron-scale figure deviations which limit the angular resolution of the optics to 10–15 arcsec. Sub-micron figure errors can be corrected by selectively depositing (physical vapor deposition) material inside the shell. The requirements for this filler material are that it must not degrade the ultra-smooth surface finish necessary for efficient X-ray reflection (∼5 A rms), and must not be highly stressed. In addition, a technique must be found to produce well controlled and defined beams within highly constrained geometries, as some of our mirror shells are less than 3 cm in diameter. We report on our efforts to date to implement this technique.

Grazing Incidence X-ray Optics for Wavelength Dispersive Spectrometers in Micro-Analysis

Grazing Incidence X-ray Optics for Wavelength Dispersive Spectrometers in Micro-Analysis

Microcomb design and fabrication for high accuracy optical assembly

There are two popular optic designs for x-ray space telescopes: the traditional monolithic design, which has demonstrated subarcsecond resolution but at enormous weight and cost per collecting area, and the foil design, which has achieved far greater collecting area per weight and cost, but with resolution limited to the arcminute level, in part due to foil assembly inaccuracy. In this article, we present the design and the fabrication of a novel micromechanical device, the so-called microcomb, which is used to assemble high-accuracy foil x-ray optics. To achieve submicron foil alignment accuracy, two types of microcombs have been fabricated via microelectromechanical systems technology. Reference combs provide highly accurate single-point contacts against which foils are registered, and spring combs provide the mechanical actuation needed to properly position and shape the foils. Briefly, we introduce some basic concepts regarding grazing-incidence x-ray optics. We then present a theoretical model that has given rise to the unique shape of the spring microcomb. Finally, the fabrication process used to produce the microcombs is discussed.

Microbeam generation with capillary optics (invited)

Grazing incidence x-ray optics for microbeam generation can be classified into five types: ellipsoidal mirror, Wolter mirror, monocapillary concentrator, microchannel array, and polycapillary concentrator. These components each have their own properties, yet they are closely related. Each optical component is at a different stage of development. Ellipsoidal mirrors are based on a mature technology and at 1/10 magnification should yield 10-μm-diam beams. Optics based on replicate Wolter mirrors are capable of producing beams on a 1–10 μm scale with high gain. Monocapillary concentrators are producing beam sizes of less than 0.1 μm. On a larger scale, polycapillary concentrators, and microchannel arrays are promising microbeam components. Ray tracing programs exist in different forms for some of these components. Prototype capillary optics have been tested, but as a whole, the manufacturing methods could be significantly improved with further investments in time and effort. All of these optical designs show great promise for intensifying a beam in a small area if they can be adequately perfected. This is the great challenge before us.

X-ray focusing using microchannel plates

We present measurements of the x-ray focusing properties of square-pore microchannel plates (MCP's). Square-pore MCP's contain large numbers of closely packed optical surfaces, as required for grazing incidence x-ray optics. The surface of individual MCP channels has been measured and found to have high microroughness transverse to the channel axis and low microroughness parallel to the axis. The high frequency transverse roughness, on length scales greater than 400 nm, has a rms value of 5.9 nm and a Gaussian autocorrelation function with correlation length of 1.41 microm. We find that the geometric misalignments of the surfaces of different channels limit the angular resolution obtainable with current samples of MCP's to 7.1 arcmin.

Wölter x-ray microscope characterization facility (abstract)

The capability for making ongoing characterization measurements of the spatial resolution and spectral reflectance of the Wölter x-ray optics used at Nova is essential for the interpretation of data taken with these imaging diagnostics. Equally important is an assessment of the long-term performance of grazing incidence x-ray optics used in the harsh environment of an ICF target chamber. We have designed and are currently building an off-line facility for such a characterization. The facility will consist of an x-ray source with specially designed pinhole-target foil array, the Wölter optics housing, monitoring and measuring detectors, a data acquisition system, and an in situ alignment system for rapid periodical verification. Each component of this lab will be discussed, along with possible initial results. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

Test facility for astronomical x-ray optics

Grazing incidence x-ray optics for x-ray astronomical applications are used outside the earth's atmosphere. These devices require a large collection aperture and the imaging of an x-ray source that is essentially placed at infinity. The ideal testing system for these optical elements has to approximate that encountered under working conditions; however, the testing of these optical elements is notoriously difficult with conventional x-ray generators. Synchrotron radiation (SR) sources are sufficiently brilliant to produce a nearly perfect parallel beam over a large area while still retaining a flux considerably higher than that available from conventional x-ray generators. A facility designed for the testing of x-ray optics, particularly in connection with x-ray telescopes, is described. It is proposed that this facility will be accommodated at the Synchrotron Radiation Source at the Daresbury Laboratory in the United Kingdom.

Review of grazing incidence optics fabrication techniques for x-ray astronomy

This paper covers the various techniques that are currently being used and developed to fabricate grazing incidence x-ray optics for the energy range from about 0.2 to 20 keV. Techniques covered will include diamond turning, thin foils, epoxy/carbon-fiber replication, electroforming replication, and float glass/Kirkpatrick-Baez techniques.

Wide-band x-ray optics with a large angular aperture

Grazing-incidence x-ray optics is briefly reviewed and shown to have several interesting properties. Capillary focusing systems which make use of multiple reflection of x rays are described. This optics is of interest in surface research, medicine, etc.