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The New Hard X-ray Mission (NHXM) project will be operated by 2017 and is currently undergoing a Phase B study, under the coordination of the Italian Space Agency (ASI). The project is being proposed by an international team in the context of the ESA Call CV M3 as a Small Mission program, with a large Italian participation. It is based on 4 hard X-ray optics modules, each formed by 60 evenly spaced multilayer coated Wolter I mirror shells. An extensible bench is used to reach the 10 m focal length. The Wolter I monolithic substrates with multilayer coating are produced in NiCo by electroforming replication. Three of the mirror modules will host in the focal plane a hybrid a detector system (a soft X-ray Si DEPFET array plus a high energy CdTe detector). The detector of the fourth telescope will be a photoelectric polarimeter with imaging capabilities, operating from 2 up to 35 keV. The total on axis effective area of the three telescopes at 1 keV and 30 kev is of 1500 cm2 and 350 cm2 respectively, with an angular resolution of 20 arcsec HEW at 30 keV. In this paper we report on the design and development of the multilayer coated X-ray mirrors based on NiCo shells.

Focusing X-ray telescopes have been the most important factor in X-ray astronomy’s ascent to equality with optical and radio astronomy. They are the prime tool for studying thermal emission from very high temperature regions, non-thermal synchrotron radiation from very high energy particles in magnetic fields and inverse Compton scattering of lower energy photons into the X-ray band. Four missions with focusing grazing incidence X-ray telescopes based upon the Wolter 1 geometry are currently operating in space within the 0.2 to 10 keV band. Two observatory class missions have been operating since 1999 with both imaging capability and high resolution dispersive spectrometers. They are NASA’s Chandra X-ray Observatory, which has an angular resolution of 0.5 arc seconds and an area of 0.1 m2 and ESA’s XMM-Newton which has 3 co-aligned telescopes with a combined effective area of 0.43 m2 and a resolution of 15 arc seconds. The two others are Japan’s Suzaku with lower spatial resolution and non-dispersive spectroscopy and the XRT of Swift which observes and precisely positions the X-ray afterglows of gamma-ray bursts. New missions include focusing telescopes with much broader bandwidth and telescopes that will perform a new sky survey. NASA, ESA, and Japan’s space agency are collaborating in developing an observatory with very large effective area for very high energy resolution dispersive and non-dispersive spectroscopy. New technologies are required to improve upon the angular resolution of Chandra. Adaptive optics should provide modest improvement. However, orders of magnitude improvement can be achieved only by employing physical optics. Transmitting diffractive-refractive lenses are capable theoretically of achieving sub-milli arc second resolution. X-ray interferometry could in theory achieve 0.1 micro arc second resolution, which is sufficient to image the event horizon of super massive black holes at the center of nearby active galaxies. However, the physical optics systems have focal lengths in the range 103 to 104 km and cannot be realized until the technology for accurately positioned long distance formation flying between optics and detector is developed.

The 0.5 arcsec angular resolution of the Chandra X-ray Observatory is possibly the best that a grazing incidence telescope with substantial collecting area will ever attain. We describe a telescope consisting of a diffractive and refractive doublet that transmits rather than reflects X-rays. Therefore, its angular resolution is relatively insensitive to figure errors and surface roughness, the factors that limit grazing incidence telescopes. When the focal length of the refractive component is minus twice that of the diffractive the chromatic aberration that is inherent in the diffractive and refractive components individually will compensate each other within a limited but not insignificant energy band. We consider a system with a long focal length, about 5000 km, to allow the refractive lens to be thin and transmit X-rays. The long focal length requires very long distance formation flying between an optics spacecraft and a detector spacecraft that must be aligned to better than a few centimeters. Solar orbit is a likely site. We simulate an imaging system where chromatic aberration is corrected to first order at 6 keV. The angular resolution is expected to be better than 0.3 miliarcsec within a 10% bandwidth. The components are lightweight, and can probably be made in a machine shop.

The Max-Planck-Institut fur extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (

The new cosmological frontier will be the study of the very first stars, galaxies and black holes in the early Universe. These objects are invisible to the current generation of X-ray telescopes, such as Chandra. In response, the Generation-X (“Gen-X”) Vision Mission has been proposed as a future X-ray observatory which will be capable of detecting the earliest objects. X-ray imaging and spectroscopy of such faint objects demands a large collecting area and high angular resolution. The Gen-X mission plans 100 m2 collecting area at 1 keV (1000× that of Chandra), and with an angular resolution of 0.1″. The Gen-X mission will operate at Sun–Earth L2, and might involve four 8 m diameter telescopes or even a single 20 m diameter telescope. To achieve the required effective area with reasonable mass, very lightweight grazing incidence X-ray optics must be developed, having an areal density 100× lower than in Chandra, with mirrors as thin as 0.1 mm requiring active on-orbit figure control. The suite of available detectors for Gen-X should include a large-area high resolution imager, a cryogenic imaging spectrometer, and a grating spectrometer. We discuss use of Gen-X to observe the birth of the first black holes, stars and galaxies, and trace their cosmic evolution.

This work addresses the issue of X-ray monitoring for astrophysical applications. The proposed wide-field optical system has not been used in space yet. The proposed novel approach is based on the use of 1D "Lobster eye" optics in combination with Timepix X-ray detector in the energy range 3 - 40 keV. The proposed project includes theoretical study and a functional sample of the Timepix X-ray detector with multifoil wide-field X-ray "Lobster eye" optics. Using optics to focus X-rays on a detector is the only solution in cases the intensity of impinging X-ray radiation is below the sensitivity of the detector, e.g. while monitoring astrophysical objects in space, or phenomena in the Earth's atmosphere. The optical system could be used in a student rocket experiment at University of Colorado. Ideal opportunity is to extend the CubeSat of Pennsylvania State University with the hard X-ray telescope demonstrator consisting of an optical module and Timepix detector.

Several independent astronomical observations in different wavelength bands reveal the existence of much larger quantities of matter than what we would deduce from assuming a solar mass to light ratio. They are very high velocities of individual galaxies within clusters of galaxies, higher than expected rotation rates of stars in the outer regions of galaxies, 21 cm line studies indicative of increasing mass to light ratios with radius in the halos of spiral galaxies, hot gaseous X-ray emitting halos around many elliptical galaxies, and clusters of galaxies requiring a much larger component of unseen mass for the hot gas to be bound. The level of gravitational attraction needed for the spatial distribution of galaxies to evolve from the small perturbations implied by the very slightly anisotropic cosmic microwave background radiation to its current web-like configuration requires much more mass than is observed across the entire electromagnetic spectrum. Distorted shapes of galaxies and other features created by gravitational lensing in the images of many astronomical objects require an amount of dark matter consistent with other estimates. The unambiguous detection of dark matter and more recently evidence for dark energy has positioned astronomy at the frontier of fundamental physics as it was in the 17th century.

We report major element ratios determined for the S-class asteroid 433 Eros using remote- sensing x-ray fluorescence spectroscopy with the near-Earth asteroid rendezvous Shoemaker x-ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended "quiet Sun" periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact-induced volatilization and/or photo- or ion-induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS-rich partial melt. Size-sorting processes could lead to segregation of Fe-Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x-ray spectrometer are not representative of the bulk Eros composition.

The recent discovery of X-ray afterglows of GRBs opens the possibility of analyses of GRBs by their X-ray detections. However, imaging X-ray telescopes in current use mostly have limited field of view. Alternative X-ray optics geometries achieving very large fields of view have been theoretically suggested in the 70ies but not constructed and used so far. We review the geometries and basic properties of the wide-field X-ray optical systems based on one- and two-dimensional lobster-eye geometry and suggest technologies for their development and construction. First results of the development of double replicated X-ray reflecting flats for use in one-dimensional X-ray optics of lobster eye type are presented and discussed. Optimum strategy for locating GRBs upon their X-ray counterparts is also presented and discussed.

The performances of single coating mirrors and supermirrors for hard X-rays are compared. It is found that supermirrors can reflect X-rays at a θ λ ratio more than three times larger than for single coating mirrors. A W Si supermirror is applied to the focusing of a white beam of X-rays and is found to efficiently reflect and focus X-rays for energies up to 69.5 keV. At higher energies the performance is limited by the absorption of W above the absorption edge.

Interest in optics for hard X-ray broad-band application is growing. In this paper, we compare the hard X-ray (20–100 keV) reflectivity obtained with an energy-dispersive reflectometer, of a standard commercial gold thin-film with that of a 600 bilayer W Si X-ray supermirror. The reflectivity of the multilayer is found to agree extraordinarily well with theory (assuming an interface roughness of 4.5 A), while the agreement for the gold film is less. The overall performance of the supermirror is superior to that of gold, extending the band of reflection at least a factor of 2.8 beyond that of the gold. Various other design options are discussed, and we conclude that continued interest in the X-ray supermirror for broad-band hard X-ray applications is warranted.

High resolution spectroscopy is the most favored objective of the next X-ray astronomy mission. A longer term goal is the development of a very large area X-ray telescope whose angular resolution and effective area are superior to the Chandra X-Ray Observatory. Adjustable X-ray optics with thin piezoelectric coatings is a methodology that may be capable of accomplishing that goal. It consists of applying piezoelectric coatings to the rear of a mirror substrate, which will be thermally slumped to the approximate figure. The figure is optimized by applying voltages to the piezoelectric coatings. Near term spectroscopy mission can benefit from higher angular resolution and a Kirkpatrick-Baez telescope should be considered as an alternative to the Wolter telescope. Adjustable X-ray optics technology should be very effective in refining the resolution of a KB telescope. When the thermally slumped mirrors of either the front or rear section are assembled and illuminated by a parallel visible light or X-ray beam line, line images formed by individual mirrors can be isolated by a moveable slit. With the piezoelectric controllers acting in only dimension the figure of each mirror can be optimized sequentially completely under computer control. The front and rear sections can be tuned independently and then joined with rather lenient tolerances. Dispersing along the 45 degree direction between the two orthogonal KB axes reduces the effect of scattering and figure errors similar to what is accomplished by using only part of the azimuth of a Wolter mirror.

It is shown that compact designs of multifocus, conical approximations to highly nested Wolter I telescopes, as well as single reflection concentrators, employing realistic graded period W/Si or Ni/C multilayer coatings, allow one to obtain more than 1000 cm2 of on-axis effective area at 40 keV and up to 200 cm2 at 100 keV. The degree of concentration is defined by a focusing factor i.e., the effective area divided by the half power focal area. For the cases studied, this is 400 at 40 keV and 200 at 100 keV for a 2 arcmin imaging resolution. This result is quite insensitive to the specifics of the telescope configuration provided that mirrors can be coated to an inner radius of 3 cm. Specifically we find that a change of focal length from 5 to 12 m affects the effective area by less than 10%. In addition the result is insensitive to the thickness of the individual mirror shell provided that it is smaller than roughly 1 mm. The design can be realized with foils as thin (≤0.4 mm) as used for ASCA and SODART or with closed, slightly thicker (∼1.0 mm) mirror shells as used for JET-X and XMM. The effect of an increase of the inner radius is quantified on the effective area for multilayered mirrors up to 9 cm. The calculated Field of View (full width at half maximum), ranges from 9 arcmin at 1 keV to ≥ 5 arcmin at 60 keV. Finally, the continuum sensitivity of the design assuming a signal to noise ratio of 5 and a 10% energy bandwidth has been calculated. For a balloon flight observation of 104 sec. with a telescope having 2 arcmin imaging resolution the point source sensitivity is ~3 • 10.6 photons/cm2/s/keV up to 70 keV for a W/Si coated telescope and up to -100 keV for a Ni/C coated telescope. For a satellite observation time of 105 sec and an imaging resolution of 1 arcmin the sensitivity is ~10.7 photons/cm2/s/keV which demonstrates the great potential of this hard X-ray imaging telescope in the energy range up to 100 keV.

Classical X-ray mirror optics usually has a limited Field of View (FoV) of ∼ 1°. Wide-field imaging can be achieved by lobster-eye type reflecting X-ray optics. We summarise several different approaches and suggest an innovative technology for the production of X-ray reflecting flats and cells necessary to develop one- or two-dimensional wide-field X-ray optics. The technology is based on double-sided, replicated reflecting foils produced by electroforming and CF/composite technologies.

Nanometer scale structures such as multilayers, gratings and natural crystals are playing an increasing role in spectroscopic applications for X-ray astrophysics. A few examples are briefly described as an introduction to current and planned applications pursued at the Danish Space Research Institute in collaboration with the FOM Institute for Plasma Physics, Nieuwegein, the Max-Planck-Institut fur Extratemestrische Physik, Aussenstelle Berlin, the Space Research Institute, Russian Academy of Sciences, the Smithsonian Astrophysical Observatory, Ovonics Synthetic Materials Company and Lawrence Livermore National Laboratory

As a platform for x-ray astronomy, the surface of the Moon is outstanding for its stability, the availability of unlimited space for large instruments, and the ability to observe any object continuously for as much as 14 days. There is likely to be three phases of lunar based investigations. The first would be the soft landing of simple, self-contained instruments sent from Earth in their operating configuration, that require no assistance to begin functioning. The range of possible instruments is limited by the availability of power for survival during lunar night. One candidate instrument is a very wide field camera system for detecting and positioning bursts, flares, and transients and monitoring the interesting temporal variations shown by virtually all point-like sources. Another candidate for early deployment is a transit telescope that would perform a partial sky survey with better angular resolution, better energy resolution, and at higher energy than the one recently completed by ROSAT. The second stage would consist of the assembly of more complex telescopes, and all-sky monitors with human or robot assistance from components sent from Earth. The third, or ultimate stage would be the robotic fabrication of large telescopes from lunar materials.

X-ray astronomy grazing incidence telescopes use the principle of nested shells to maximize the collecting area. Some of the more recent missions, such as XMM-Newton [1], have used an electroformed nickel replication (ENR) process [2] to fabricate the mirror shells. Upcoming missions, such as Spectrum-Rontgen-Gamma [3] and Focusing Optics X-ray Solar Imager [4] , also use the electroforming process to fabricate nested shell grazing incidence X-ray telescopes. We present recent results on fabrication of replicas with multilayer coatings from Wolter-1 mandrels using a new hardcoat release material to simplify and improve this electroforming process.

The soft X-ray band hosts a larger, more diverse range of variable sources than any other region of the electromagnetic spectrum. They are stars, compact binaries, SMBH's, the X-ray components of Gamma-Ray Bursts, their X-ray afterglows, and soft X-ray flares from supernova. We describe a concept for a very wide field (~ 4 ster) modular hybrid X-ray telescope system that can measure positions of bursts and fast transients with as good as arc second accuracy, the precision required to identify fainter and increasingly more distant events. The dimensions and materials of all telescope modules are identical. All but two are part of a cylindrical lobster-eye telescope with flat double sided mirrors that focus in one dimension and utilize a coded mask for resolution in the other. Their positioning accuracy is about an arc minute. The two remaining modules are made from the same materials but configured as a Kirkpatrick-Baez telescope with longer focal length that focuses in two dimensions. When pointed it refines the hybrid telescope's arc minute positions to an arc second and provides larger effective area for spectral and temporal measurements. Above 10 keV the mirrors act as an imaging collimator with positioning capability. For short duration events this hybrid focusing/coded mask system is more sensitive and versatile than either a 2D coded mask or a 2D lobster-eye telescope. Very wide field X-ray telescopes have become feasible as the ability to fabricate large area arrays of CCD and CMOS detectors has improved. This instrument's function in the soft X-ray band is similar to that of Swift in hard X-ray band and there are a greater variety of fast transients in the soft X-ray band. An instrument with considerably more sensitivity than current wide field X-ray detectors would be compatible with a modest NASA Explorer mission., Comment: 15 pages, 5 figures, To be presented at SPIE Conference 8147 "Optics for EUV, X-Ray, and Gamma-Ray Astronomy V", Aug.21-25, 2011

Extremely broadband grazing-incidence multilayers for hard-x-ray reflection can be obtained by a gradual change of the layer thicknesses down through the structure. Existing approaches for designing similar neutron optics, called supermirrors, are shown to provide respectable performance when applied to x-ray multilayers. However, none of these approaches consider the effects of imperfect layer interfaces and absorption in the overlying layers. Adaptations of neutron designs that take these effects into account are presented, and a thorough analysis of two specific applications (a single hard-x-ray reflector and a hard-x-ray telescope) shows that an improved performance can be obtained. A multilayer whose bilayer thicknesses are given by a power law expression is found to provide the best solution; however, it is only slightly better than some of the adapted neutron designs.

Generation-X is required to be an X-ray observatory with 50 m2 effective collecting area and 0.1 arcsec half-power diameter (HPD) angular resolution at 1 keV. It is conceived that a launch vehicle such as that studied for the Ares V will carry a monolithic 16-m-diameter mirror to the earth-sun L2 point. Even with such a vehicle, the reflectors comprising the ≈ 250 nested shells must be extremely light-weight. Therefore their figure and alignment cannot be achieved on the ground, and likely could not be maintained through the launch environment. We will present a conceptual solution to those constraints: adjustable X-ray optics, as a case of "adaptive" optics where the stability once in orbit should require adjustments no more frequently than yearly. The figure would be adjusted via thin-film actuators deposited directly to the back (non-reflecting) side of each element. This bi-morph configuration would impart in-plane strains via the piezoelectric or electrostrictive effect. Requirements of the adjustment are to the order of a few nanometer precision. Each shell, and each module, must also be aligned, to tolerances of about 0.1 micrometer. We conceive that on-orbit data would be acquired by a built-in Hartmann system for the alignment adjustments and low-order figure, and by ring profile measurements of a very bright celestial X-ray source to correct figure errors up to the mid-frequency range of several hundredths cycles mm −1 .

The New Hard X-ray Mission (NHXM) project will be operated by 2016 and is currently undergoing the Phase B study. It is based on 4 hard X-ray optics modules, each formed by 60 evenly spaced multilayer coated Wolter I mirror shells. An extensible bench is used to reach the 10 m focal length. The Wolter I monolithic substrates with multilayer coating are produced in NiCo by electroforming replication. Three of the mirror modules will host in the focal plane a hybrid a detector system (a soft X-ray Si DEPFET array plus a high energy CdTe detector). The detector of the fourth telescope will be a photoelectric polarimeter with imaging capabilities, operating from 2 up to 35 keV. The total on axis effective area of the three telescopes at 1 keV and 30 kev is of 1500 cm 2 and 350 cm 2 respectively, with an angular resolution of 20 arcsec HEW at 30 keV. In this paper we report on the design and development of the multilayer optics of the mission, based on thin replicated Ni mirror shells.

Platinum is being explored as an alternative to the sprayed boron nitride mandrel release coating under study at GSFC for the International X-ray Observatory (IXO). Two and three inch diameter, polished (PFS) and superpolished (SPFS) fused silica flat mandrels, were used for these tests. Pt was applied to the mandrels by DC magnetron sputtering. The substrate material was 400 micron thick D263 glass, the material which has been proposed for the IXO segmented optics. These substrates were placed on the mandrels and thermally cycled with the same thermal profile being used at GSFC in the development of the BN slumping for IXO. After the thermal cycle was complete, the D263 substrates were removed; new D263 substrates were placed on the mandrels and the process was repeated. Four thermal cycles have been completed to date. After initially coating the mandrels with Pt, no further conditioning was applied to the mandrels before or during the thermal cycles. The microroughness of the mandrels and of the D263 substrates was measured before and after thermal cycling. Atomic force microscopy (AFM) and 8 keV X-ray reflectivity data are presented.

Several x-ray astronomy missions of the 1990s will contain focusing telescopes with significantly more collecting power than the Einstein Observatory. There is increasing emphasis on spectroscopy. ESA's XMM with 10(4) cm(2) of effective area will be the largest. A high throughput facility with over 10(5) cm(2) of effective area and 20-sec of arc angular resolution is needed ultimately for various scientific studies such as high resolution spectroscopic observations of QSOs. At least one of the following techniques currently being developed for fabricating x-ray telescopes including automated figuring of flats as parabolic reflectors, replication of cylindrical shells, and the alignment of thin lacquer-coated conical foils is likely to permit the construction of modular arrays of telescopes with the area and angular resolution required.

A grazing incidence x-ray mirror in the Kirkpatrick-Baez geometry was constructed and tested. Its geometric aperture measures 20 by 30 cm and its length is 100 cm. The focal length is 3.4 m measured from the front to the focal plane. It is the first of eight mirrors to be built for the LAMAR experiment of the Shuttle High Energy Astrophysics Laboratory. Its angular resolution was measured at 1.5 and 6.4 keV in a quasiparallel x-ray beam at the Marshall Space Flight Center. The half-power width (HPW) of the resolution function projected along a horizontal axis is 31 sec of arc at both energies and in visible light. With the addition of small isolation pads the mirror is able to withstand the vibration and acceleration levels of a Space Shuttle launch. The resolution remains under 35-sec of arc HPW for changes in temperature of 9.5 degrees C and when a modest temperature gradient is imposed on the mirror.

High-energy astrophysics is a relatively young scientific field, made possible by space-borne telescopes. During the half-century history of x-ray astronomy, the sensitivity of focusing x-ray telescopes-through finer angular resolution and increased effective area-has improved by a factor of a 100 million. This technological advance has enabled numerous exciting discoveries and increasingly detailed study of the high-energy universe-including accreting (stellar-mass and super-massive) black holes, accreting and isolated neutron stars, pulsar-wind nebulae, shocked plasma in supernova remnants, and hot thermal plasma in clusters of galaxies. As the largest structures in the universe, galaxy clusters constitute a unique laboratory for measuring the gravitational effects of dark matter and of dark energy. Here, we review the history of high-resolution x-ray telescopes and highlight some of the scientific results enabled by these telescopes. Next, we describe the planned next-generation x-ray-astronomy facility-the International X-ray Observatory (IXO). We conclude with an overview of a concept for the next next-generation facility-Generation X. The scientific objectives of such a mission will require very large areas (about 10000 m2) of highly-nested lightweight grazing-incidence mirrors with exceptional (about 0.1-arcsecond) angular resolution. Achieving this angular resolution with lightweight mirrors will likely require on-orbit adjustment of alignment and figure., Comment: 19 pages, 11 figures, SPIE Conference 7803 "Adaptive X-ray Optics", part of SPIE Optics+Photonics 2010, San Diego CA, 2010 August 2-5

The use of depth-graded multilayer coatings is foreseen in several future X-ray telescopes (e.g. Hexit-Sat/NHXT, NuSTAR, IXO, NeXT), in order to extend to higher energies (up to 80 keV) the focusing capabilities of present day telescopes, like Chandra and XMM/Newton, that are operative in the soft X-ray band (0.1-10 keV). The deposition of multilayer coatings is a difficult process, in which a good control of the individual layer thickness is required. The process must also be stable for the long time needed (several hours). The main issues are the accuracy of the film (stability of the process), interfacial and surface roughness, the lateral homogeneity and the long-term stability of the film. Physical properties of the film, like the density or the crystallicity are also important. The analysis of reflectivity measurements is an important tool to study the structure of multilayer samples, investigating in a non-destructive way the whole properties of the film down to the deepest layers. Nevertheless the analysis of data is not easy, neither standardized. Two samples were realized using different materials (Pt/C and W/Si). The film structures were designed to be representative of broad angular/energy band multilayer coatings foreseen in hard X-ray focusing telescopes. Their reflectivity was measured for several energies in the 40-130 keV range as a function of the reflection angle. The High energy reflectivity data are compared with the theoretical expectations derived from low-energy (8.04 keV) measures acquired after the deposition.

X-ray astronomy grazing incidence telescopes use the principle of nested shells to maximize the collecting area. Some of the more recent missions, such as XMM-Newton, have used an electroformed nickel replication process to fabricate the mirror shells. We have been developing coatings to simplify and improve this electroforming process. This paper discusses our most recent results from studies using TiN as a mandrel hardcoat in the electroforming process of fabricating nickel shell optics. The results indicate that nickel replicas separate easily from the TiN coated mandrel, and little (if any) degradation of the mandrel occurs after more than 20 replications. AFM characterization of the mandrel and replica surfaces is shown. Preliminary results are also included from studies which use this same process to replicate multilayer coatings; these results indicate no change in the multilayer stack after separation from the mandrel.

The angular resolution of Chandra is close to the practical limit of grazing incidence telescopes due to the difficulty of imparting an accurate figure and smooth surface to mirror substrates whose physical area is over two orders of magnitude larger than their effective area. However, important scientific objectives lie beyond the reach of Chandra and all future missions being planned by the space agencies. By transmitting X-rays diffractive and refractive optics are not subject to the same limitations and have a superior diffraction limit. A Fresnel zone plate can be paired with a refractive lens such that their intrinsic chromatic aberrations cancel to 1st order at a specific energy. The result is a limited but significant energy band where the resolution is a milli arc second or better, for example, at 6 keV. Chromatic aberration can be corrected to 2nd order by separating the diffractive and refractive elements. This configuration allows a resolution of a few micro arc seconds. The optics are very light weight but have extremely long focal lengths resulting in a requirement for very long distance formation flying between optics and detector spacecraft, and small fields of view. Opacity of the refractive element imposes a lower limit upon the X-ray energy of about a few keV.

MASSIM, the Milli-Arc-Second Structure Imager, is a mission that has been proposed for study within the context of NASA's Astrophysics Strategic Mission Concept Studies program. It uses a set of achromatic diffractive-refractive Fresnel lenses on an optics spacecraft to focus 5-11 keV X-rays onto detectors on a second spacecraft flying in formation 1000 km away. It will have a point-source sensitivity comparable with that of the current generation of major X-ray observatories (Chandra, XMM-Newton) but an angular resolution some three orders of magnitude better. MASSIM is optimized for the study of jets and other phenomena that occur in the immediate vicinity of black holes and neutron stars. It can also be used for studying other astrophysical phenomena on the milli-arc-second scale, such as those involving proto-stars, the surfaces and surroundings of nearby active stars and interacting winds. We describe the MASSIM mission concept, scientific objectives and the trade-offs within the X-ray optics design. The anticipated performance of the mission and possible future developments using the diffractive-refractive optics approach to imaging at X-ray and gamma-ray energies are discussed.

The SIMBOL-X formation-flight X-ray mission will be operated by ASI and CNES in 2014, with a large participation of the French and Italian high energy astrophysics scientific community. Also German and US Institutions are contributing in the implementation of the scientific payload. Thanks to the formation-flight architecture, it will be possible to operate a long (20 m) focal length grazing incidence mirror module, formed by 100 confocal multilayer-coated Wolter I shells. This system will allow us to focus X-rays over a very broad energy band, from 0.5 keV up to 80 keV and beyond, with more than two orders of magnitude improvement in angular resolution (20 arcsec HEW) and sensitivity (0.5 µCrab on axis @30 keV) compared to non focusing detectors used so far. The X-ray mirrors will be realized by Ni electroforming replication, already successfully used for BeppoSAX, XMM-Newton, and JET-X/SWIFT; the thickness trend will be about two times less than for XMM, in order to save mass. Multilayer reflecting coatings will be implemented, in order to improve the reflectivity beyond 10 keV and to increase the field of view 812 arcmin at 30 keV). In this paper, the SIMBOL-X optics design, technology and implementation challenges will be discussed; it will be also reported on recent results obtained in the context of the SIMBOL-X optics development activities.

Gamma ray bursts have become as important as supernova in astrophysics and cosmology and they should be studied with the same amount of diligence and continuity. Most of the types of telescopes and detectors needed already exist and in fact have already been in space. The addition of a very wide field, high angular resolution X-ray telescope would open a much larger window to bursts whose spectra are soft, either intrinsically or as a result of high redshift. Sensitivity in the X-ray band also benefits from the large number of photons of the X-ray afterglow. To fill that role we describe a telescope that is a lobster-eye optic in one dimension and a coded aperture in the other. It has larger area and bandwidth than a two-dimensional lobster-eye optic but is subject to more background. A permanent site that can accommodate a complete set of instruments that covers the entire energy range from soft X-ray to gamma ray would be preferable to the current practice of launching new spacecraft periodically with instruments that cover only part of the range. Astronomers generally favor free space, over the Moon as an observatory site. However, the architecture of a gamma ray burst observatory is more compatible with a lunar base than is the typical observatory. The instruments can be delivered gradually and perhaps at lower cost to the astrophysics budget through an Earth-Moon transportation system that is supported by the Exploration program.

The 0.5 arcsec angular resolution of the Chandra X-Ray Observatory is likely to be the best that a grazing incidence telescope with substantial collecting area will ever attain. We describe a concept for a telescope composed of diffractive and refractive components that transmit rather than reflect X-rays. Therefore, its angular resolution would be relatively insensitive to figure errors and surface roughness. With appropriately selected values for the two focal lengths the chromatic aberration that is inherent in both the diffractive and refractive components individually would compensate each other within a limited but not insignificant energy band. The system has a focal length of about 10 4 km because the refractive component is rather weak. The long focal length requires a very demanding type of formation flying between an optics spacecraft and a detector spacecraft. We simulate the simplest diffractive/refractive imaging system where chromatic aberration is corrected to first order at 6 keV. The angular resolution is expected to be better than a miliarcsec within a 10 % bandwidth. The energy band could be broadened either by employing an array of smaller systems with the same total area or by modifying the diffractive component in situ. The components are lightweight, not difficult to fabricate and can probably be made in a machine shop. We also consider possible sites for the system.

Large collecting area x-ray telescopes are designed to study the early Universe, trace the evolution of black holes, starsand galaxies, study the chemical evolution of the Universe, and study matter in extreme environments. TheConstellation-X mission (Con-X), planned for launch in 2016, will provide ~ 10 4 cm 2 collecting area with 15 arc-secresolution, with a goal of 5 arc-sec. Future missions require larger coll ecting area and finer resolution. Generation-X(Gen-X), a NASA Visions Missio n, will achieve 100 m 2 effective area at 1 keV and angular resolution of 0.1 arc-sec, half power diameter. We briefly describe the Con-X flowdown of imaging requ irements to reflector figure error. Tomeet requirements beyond Con-X, Gen-X optics will be thinner and more accurately shaped than has ever beenaccomplished. To meet these challenging goals, we incorporate for the first time active figure control with grazing incidence optics. Piezoelectric material will be deposited in discrete cells directly on the back surface of the optical segments, with the strain directions oriented parallel to the surface. Differential strain between the two layers of the mirror causes localized bending in two directions, enablin g local figure control. Adjusting figure on-orbit eases fabrication and metrology. The ability to make changes to mirro r figure adds margin by mitigating risk due to launch-induced deformations and/or on-orbit degradation. We flow down the Gen-X requirements to mirror figure and fourtelescope designs, and discuss various trades between the designs.Keywords: x-ray optics, active optics, adjustable optics, Con-X, Gen-X

The Beyond Einstein Program in NASA's Office of Space Science Structure and Evolution of the Universe theme spells out the top level scientific requirements for a Black Hole Imager in its strategic plan. The MAXIM mission will provide better than one tenth of a microarcsecond imaging in the X-ray band in order to satisfy these requirements. We will overview the driving requirements to achieve these goals and ultimately resolve the event horizon of a supermassive black hole. We will present the current status of this effort that includes a study of a baseline design as well as two alternative approaches

The new frontier in astrophysics is the study of the very first stars, galaxies and black holes in the early Universe. These objects are beyond the grasp of the current generation of X-ray telescopes such as Chandra, and so the Generation-X Vision Mission has been proposed as an X-ray observatory which will be capable of detecting these earliest objects. Xray imaging and spectroscopy of such distant objects will require an X-ray telescope with large collecting area and high angular resolution. The Generation-X concept has 100 m2 collecting area at 1 keV (1000 times larger than Chandra) and 0.1 arcsecond angular resolution (several times better than Chandra and 50 times better than the resolution goal for Constellation-X). The baseline mission involves four 8 m diameter telescopes operating at Sun-Earth L2. Such large telescopes will require either robotic or human-assisted in-flight assembly. To achieve the required effective area with launchable mass, very lightweight grazing incidence X-ray optics must be developed, having an areal density 100 times lower than in Chandra, with perhaps 0.1 mm thick mirrors requiring on-orbit figure control. The suite of available detectors for Generation-X should include a large-area high resolution imager, a cryogenic imaging spectrometer and a grating spectrometer.

No future X-ray telescope is likely ever to have angular resolution significantly superior to the Chandra X-Ray Observatory without adopting a new technology. We consider focusing systems based upon diffraction and refraction rather than grazing incidence reflection. The elements are Fresnel zone plates and refractive lenses in configurations where chromatic aberration is corrected over a finite bandwidth. This technique is likely to be especially effective in the intermediate regime between the 0.5 arcsec capability of the Chandra telescope and the one-tenth microarcsec resolution required for the NASA "Vision Mission" entitled the "Black Hole Imager." Diffractive/refractive systems can also be configured as high throughput flux concentrators for third generation X-ray timing studies and non-dispersive spectroscopy. They may also have an important role in very high resolution spectroscopy. Because these elements focus by transmitting X-rays at normal incidence they can be extremely lightweight compared to grazing incidence telescopes. Furthermore the figure accuracy and surface smoothness are much less critical. On the other hand diffractive/refractive optics are characterized by chromatic aberration, which can be corrected only in small wavelength bands. Focal lengths range up to 105 km making the application of diffractive/refractive X-ray optics to astronomy dependent upon the development of technology for formation flying of very widely separated spacecraft.

The next generation X‐ray timing observatory will be a more powerful and versatile facility if it is based upon focusing optics rather than large area detectors. With X‐ray CCDs or active pixel detectors (or possibly even microcalorimeters) in the focal plane(s) the spectral resolution will be significantly superior to the RXTE PCA making it possible to study the dynamics of the gravitationally redshifted Fe line in great detail. With orders of magnitude reduction of background the ability to study temporal variations of fainter sources in external galaxies will be much greater than with large area counters of the same collecting area. Furthermore, source confusion will not be an issue as it may be when large area detectors observe sources near the galactic center or in other galaxies. Focusing detectors do require larger open apertures than counters and their bandwidth is smaller. However, they are not necessarily heavier and in fact one candidate optic would be much lighter.

Fresnel lenses allow almost perfect imaging in widely different circumstances, but their focus is perfect only for a single wavelength. Wang et al. have shown how the effective bandpass may be widened for X-ray microscopy by using a compound diffractive/refractive lens near to an absorption edge. A compound lens has also been proposed for high-energy astronomy, working well above all absorption edges. Although the scale is very different, we point out here that the principle is the same. Ever since Galileo constructed an astronomical telescope that he was able to reconfigure to study fleas and gnats, astronomy and microscopy have relied on optics that are closely related, but different in detail.

The NASA's Constellation X-Ray Mission consists of a Soft X-Ray Telescope (SXT) based on large collecting area optics plus a focusing Hard X-Ray Telescope (HXT) operating between 8 and 70 keV and possibly at even higher energy. The Con-X HXT will have a focal length of 10 m and graze angles are small (0.25 - 0.1 deg). The substrates will be coated with multilayers to enhance the reflectivity but single heavy element coatings are an alternative for the small diameter substrates of the set. Twelve copies of the HXT are distributed evenly among the four Con-X spacecrafts. With multiple telescopes it is appropriate to consider electroforming, the replication process used successfully by Beppo-SAX, JET-X/SWIFT, and XMM-Newton, to produce their substrates. The important feature of the technique is that for mirrors with aperture diameters less than 40 cm also with thin substrates it is possible to achieve good angular resolution, which is important for obtaining high signal-to-noise ratios in deep observations and imaging extended sources. We review the main results of our development study devoted to proving the feasibility of the process for the Con-X/HXT, with particular stress on demonstrating, not only by theoretical considerations but also presenting an important experimental proof, that we can satisfy the severe mass constraints of the mission still maintaining good imaging capabilities.

The high rate at which importatn results are emanating formthe Chandra X-ray Observatory heightens our appreciation of the significance of high angular resolution telescopes in x-ray astronomy. However, the Chandra telescope is probably the last member of a line of high resolution telescopes with a conventional architecture. Qualitative improvement upon Chandra's resolution requires a new technology. We discuss a promising approach that is capable potentially of achieving microarcsecond resolution, possibly the highest angular resolution in astronomy of any wavelength band. It is based upon x-ray optics that focus by transmission at normal incidence rather than by reflection at grazing incidence. Its components are refractive lenses and Fresnel zone plantes. Extreme chromatic aberration is intrinsic to these devices but it can be overcome in small wavelength intervals above 2 keV with a technique described by Van Speybroech and by other methods. Like x-ray interferometry these systems have extremely long focal lengths and require 'formation flying' consisting of precise positioning between the optics and detector that be aboard separate spacecraft spaced far apart. However, it is less demanding of accuracy in formation flying than x-ray interferometery. These systems have much lower mass than grazing incidence telescopes with comparable collecting area.

There is broad interest in a next generation timing mission to succeed the PCA of RXTE which will provide more effective area than its 0.6 square meters and much better energy resolution. Currently prospective missions are, like the PCA, based upon large area detectors. Serious consideration should also be given to a focusing system. The focusing system would be a modular array of relatively small diameter imaging telescopes or concentrators with solid state detectors in their focal planes. For areas exceeding a square meter a focusing system could actually be less complex, more reliable, and for one particular optical design perhaps not much more massive. The total detector area would be only a few percent of the telescope aperture, which makes the acquisition of detectors much less challenging. Today it is possible to obtain commercially a sufficient number of detectors with good energy resolution for all the focal planes of the focusing array. They require only modest cooling and that could be accomplished passively in space. Several optical designs are possible. The disadvantages of an optical system are larger mass, more difficultly obtaining broad bandwidth, smaller field of view, and larger volume to accommodate the focal length distance and a larger diameter. On the other hand, the focusing system is more sensitive to fainter sources, is much more efficient below 2 keV, is less sensitive to background and is likely to be less costly overall than an array of solid state area detectors with equally good energy resolution.

We report the results obtained during the second phase of a program which consists of comparing the performance of different multilayer material combinations. These coatings will be used to extend the bandpass of current hard X-ray optics toward 100 keV, an order of magnitude higher than present technology. The materials studied here are W/Si, Pt/C, and W/C. A comparison of the performance of depth graded multilayers of these different materials at energies 30-80 keV was undertaken. Specular reflectivity data were acquired at 30-80 keV using the X17B1 beamline of the National Synchrotron Light Source. Reflectivity versus energy plots showed a high enough reflectivity for the bandpass of interest at grazing angles typical for hard x-ray telescope mirror shells. The next phase of our program will continue with similar high-energy pencil beam measurements on multilayer coated telescope prototype shells.

We present the results of a study of the influence of the deposition process parameters on the X-ray reflectivity of multilayer mirrors for applications at energies above 10 keV. The coating process used is DC magnetron sputtering and we have begun an optimization analysis for two material combinations: W/Si and Pt/C. The following process parameters were considered: argon pressure, distance between cathodes and substrate, and sputtering cathode currents. The samples are coated on 2' polished silicon wafers and their X-ray reflectivity is measured by performing a specular scan with an 8.05 keV (Cu K-alpha) X-ray beam. The reflectivity scans were analyzed with the IMD software and the fitted interface roughness values were correlated with the deposition parameters. The analysis of variance (ANOVA) statistical treatment of the data allows the determination of the contribution of each process parameter to the reflectivity and establishes which of the parameters need tighter control.

Multilayer structures with depth-graded spacing can show a high reflectivity in a broad energy passband for hard X-rays if the interface roughness/diffuseness is controlled and minimized. We present a study of several multilayer systems deposited by DC magnetron sputtering on silicon wafers and superpolished fused silica substrates. The material combinations discussed are W/Si, WSi2/Si, W/C, Pt/C, Ni/C, Ni/B4C, and Mo/Si. The deposition method used was DC magnetron sputtering at low argon pressures (1.5 to 5 mT). The characterization methods used were: Atomic Force Microscopy in tapping mode, stylus profilometry, Rutherford backscattering, cross sectional TEM, and specular X-ray reflectivity (XRR) scans at 8.05 keV. Different process parameters were varied in order to optimize the interface roughness/diffuseness (sigma) that was measured by XRR scans.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The recently available first prototypes of innovative very wide field X-ray telescopes of Lobster-Eye type confirm the feasibility to develop such flight instruments in a near future. These devices are expected to allow very wide field (more than 1000 square degrees) monitoring of the sky in X-rays (up to 10 keV and perhaps even more) with faint limits. We will discuss the recent status of the development of very wide field X-ray telescopes as well as related scientific questions including expected major contributions such as monitoring and study of X-ray afterglows of Gamma Ray Bursts.

Estimates of background in CZT detectorsi indicate that even with the beneficial concentration of a focussing telescope measurements in the 20 to 100 keV band of the Constellation X-ray Mission's HXT will become background limited after several thousand seconds of observing. This time is less than the expected exposure of most measurements. Consequently the sensitivity of most if not all observations of the HXT will be background limited. Therefore, the angular resolution should be as good as possible as long as the effective area remains high. We are pursuing a method for fabricating telescopes for thetwelve units of HXT that consists of electroforming integral shell substrates, a process that has been highly developed for XMM. We are attempting to adapt this method to higher energy X-rays by employing multilayer coatings, and smaller graze angles, and also reduce the mass of the telescopes from the XMM prescription by employing stronger, lighter alloys. The resolution that XMM has achieved, 15" HPW is an indication of the resolution we can expect.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.