The Advanced X-ray Astrophysics Facility (AXAF) will soon begin its exploration of the x-ray universe, providing unprecedented angular and spectral resolution. Also unprecedented is the ambitious goal of calibrating the AXAF observatory to an accuracy of a few percent. Toward this end, AXAF science and engineering teams undertook an extensive calibration program at component, subsystem, and system levels. This paper is an overview of the system-level calibration activities, conducted over the past year at the Marshall Space Flight Center (MSFC) X-Ray Calibration Facility (XRCF).

The design and implementation of the high speed imager (HSI) microchannel plate based imaging x-ray detector used for the calibration of the Advanced X-ray Astrophysics Facility (AXAF) high resolution mirror assembly (HRMA) and objective transmission gratings (OTGs) is described. The similarities between the HSI and the AXAF high resolution camera (HRC) are discussed, as well as the modifications to the original HRC- like design needed to operate the detector at count rates up to approximately 2000 Hz used during the HRMA calibration. The imaging performance of the detector that is necessary to achieve the calibration error budget for the HRMA is discussed. Details of the actual performance of the HSI are provided in terms of key parameters such as spatial uniformity and linearity, imaging resolution, and counting rate limitations. The measurement techniques used to verify and calibrate the requisite detector performance are described.

We have completed another full year of reflectance calibrations of AXAF witness mirrors at the National Synchrotron Light Source. At the NSLS, we have used beamlines X8C (5 - 12 keV) and X8A (2 - 6 keV), sponsored by Los Alamos National Laboratory. All of the flats have been calibrated in the 5 - 12 keV range, and approximately 1/4 of all our flats have been calibrated in the 2 - 6.2 keV range. The repeatability in the coating processes reported in Denver has continued with the measurement of additional mirrors. Optical constants from reflectances have been derived for six of the eight AXAF mirror elements, and a degree of spatial uniformity information exists for three of these six. The addition of a semitransparent monitor has markedly increased efficiency of measurements in the 5 - 12 keV range, and efforts are being made to provide such a monitor detector for the lower energy ranges. We report the progress in reflectance data acquisition and optical constant derivations, and discuss implications of the results for the AXAF program.

We discuss calibration of the Advanced X-ray Astrophysics Facility (AXAF) high resolution mirror assembly (HRMA) through the use of surrogate coating process witness flats. Reflectance measurements of representative witness flats have been made at the Advanced Light Source (ALS) Synchrotron Facility over an energy range of 60 - 940 eV. We discuss the procedures used for these measurements and some preliminary results of our studies. The initial results show, for some energy regions, a reduction in reflectance expected from a pure iridium coating layer. The observed decrease in mirror reflectance is believed to be the combined result of the presence of an organic thin film on the mirror surfaces, plus the effects of carbon on the ALS beamline optics. It appears that the tested mirror surfaces have a maximum level of molecular contamination amounting to an effective carbon thickness of from 5 - 10 angstroms. The source of this contamination is not identified, although this amount is not surprising.

We report iridium optical constants fitted from synchrotron reflectance data. Specifically, we have used the NKFIT algorithm of D. L. Windt to derive (delta) (E) and (beta) (E) from 2 - 12 keV reflectance calibrations of AXAF witness mirrors. The model is applied at each energy separately, to fit four to nine data points from reflectance-versus-energy scans at selected grazing angles. The stability of the model in the presence of Gaussian noise has been tested extensively. We report the results of several bias studies, involving the generation and analysis of artificial data. Bias studies have been used to determine the optimal grazing angles to be scanned in the various x-ray energy ranges to condition the optical constants. They have also been used to investigate the effects of individual errant data points on the resulting fits and derived optical constants. The results will aid in eliminating systematic errors in the derived optical constants. We also present results of our investigation of the Debye-Waller and Nevot-Croce roughness correction algorithms as applied to our measurements. The Nevot-Croce method gives a much better representation of the data, however its rigorous justification in this experiment is lacking, and the roughness parameter derived is not constant with energy. A more self- consistent model for roughness correction is sought.

X-ray calibration of the Advanced X-ray Astrophysics Facility (AXAF) observatory at the MSFC X-Ray Calibration Facility (XRCF) made novel use of the x-ray continuum from a conventional electron-impact source. Taking advantage of the good spectral resolution of solid-state detectors, continuum measurements proved advantageous in calibrating the effective area of AXAF's high resolution mirror assembly (HRMA) and in verifying its alignment to the XRCF's optical axis.

The AXAF (Advanced X-ray Astrophysics Facility) high resolution mirror assembly (HRMA) now is complete and has been tested at the NASA Marshall Space Flight Center (MSFC) X-ray Calibration Facility (XRCF). The surface and alignment properties of the mirror were thoroughly measured before the x-ray test, which allowed accurate performance predictions to be performed. The preliminary analysis of the measured x-ray image distributions for all energies tested show excellent agreement with predictions made before the beginning of the test. There is a discrepancy between the measured and predicted effective areas; this typically is less than 5%, and is less than 13% for all energies measured. We present evidence that this discrepancy is due to uncertainties in the calibration of the test instrumentation, and therefore can be expected to be reduced when results from further instrument calibration tests now in progress are incorporated into the analysis. We predict that 65 - 80% (depending upon energy) of the flux from an imaged point source will be contained on a one arc second diameter aperture in flight. We expect the HRMA to more than fulfill the requirements necessary to achieve the AXAF scientific objectives.

We discuss the x-ray measurement of the focus and alignment of the AXAF (Advanced X-ray Astrophysics Facility) x-ray optics. The high resolution mirror assembly (HRMA) consists of four nested Wolter type I x-ray optics. The attainment of the program goals for high resolution imaging requires that the mirror foci be coincident, both axially and laterally; in addition, the relative tilts between optics within each mirror pair must be small. The mirror tilts and the parfocalization were measured at the X-Ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville, Alabama during a series of tests in the winter/spring of 1996/1997. The x-ray measurements are compared to the optical alignment data obtained by Eastman Kodak using the HRMA Alignment and Test System (HATS) during HRMA assembly. From these data a preliminary model for the relative location and rigid-body orientation of the individual mirror elements is developed; this mirror model is a component of the SAO high fidelity HRMA raytrace model.

We discuss the ring focus measurements for the Advanced X-ray Astrophysics Facility (AXAF) x-ray optics -- the high resolution mirror assembly (HRMA). The HRMA is an assembly of four pairs of nested Wolter Type-I grazing incidence mirrors coated with iridium (Ir). The ring focus measurements are an essential part of the AXAF ground calibration carried out at the X-Ray Calibration Facility (XRCF) at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The ring focus measurements reveal aspects of the test system distortions and the mirror surface figures which are difficult or impossible to detect in the focal plane. The measurement results show periodic modulations of the ring width which was caused by gravity and strain in the epoxy bonds that are part of the mechanical support system. The strongest component of the modulation has 12-fold symmetry due to the 12 flexures that support each mirror shell. We discuss the ring focus model and compare it with the test results to understand the test system distortions an the mirror glass imperfection, and to predict the impact for the AXAF mirror on-orbit performance.

We discuss details of the spectral fitting procedures and algorithms used in deriving line count rates for the calibration of AXAF (the Advanced X-ray Astrophysics Facility) during end-to-end testing in the winter and spring of 1996/1997. An approach involving simultaneously fitting both detector and source parameters was implemented within XSPEC, a standard x-ray spectral fitting package (Arnaud 1996). Theoretical and practical difficulties in fitting spectra taken with flow proportional counters (FPC) and solid state detectors (SSD) are discussed, including both effects incorporated into the numerical model, and those which must be estimated outside the model. Sensitivity of the parameter of interest, the counts in a strong line in the spectrum, to changes and errors in the other fit parameters is explored. The impact of uncertainties on the overall absolute AXAF calibration is discussed.

We describe here the computer program for modeling the FPCs and SSDs used in the ground calibration, relative and absolute, of AXAF. The program is called as a subroutine by XSPEC. The design is hierarchical: at the lowest level are models for single electron spectra, upon which are based the computation of moment generating functions (mgfs) for the detector response functions. Any number of discrete lines and a continuum are allowed. The continuum is the source x-ray spectrum as modified by intervening filters. The overall mgf is numerically transformed into the count spectrum via an inverse fast Fourier transform. The component mgfs have unit normalization, and final fitted normalizations give the count rate for each component.

The high-energy transmission grating for AXAF was tested with the AXAF high resolution mirror assembly during December 1996 through April 1997 at NASA's MSFC X-Ray Calibration Facility. This first-use of the HETG confirms sub-assembly measurements and demonstrates the power of this AXAF grating spectrometer. This paper discusses calibration goals, summarizes the pre- XRCF performance predictions, describes the XRCF data taken, and outlines the general approach to their analysis -- concentrating on the HETG contribution to the HETGS effective area. Very preliminary examples of the analysis of the XRCF data are presented. At a crude level (approximately equal to 30%) the data are in agreement with sub-assembly predictions. Future detailed analysis will result in a definitive instrument calibration.

The high-energy transmission grating for AXAF was tested with the AXAF HRMA during December 1996 through April 1997 at NASA's MSFC X-Ray Calibration Facility. This first-use of the complete HETG spectrometer (HETGS) produced some low-level surprises in the line response function (LRF) and indicate that the HETG is meeting or exceeding its resolving-power specifications. This paper reviews the ingredients of the HETGS LRF, describes the pre-XRCF HETG sub-assembly measurements, presents an overview of the XRCF LRF-related measurements and data, and summarizes our knowledge of the HETG contribution to the HETGS line response function. Two low-level effects, grating scatter and grating misalignment, were uncovered in this testing.

The low energy transmission grating spectrometer (LETGS) on board the Advanced X-ray Astrophysics Facility provides high resolution dispersive spectroscopy between 70 eV and more than 7 keV. The LETG contains 180 grating modules, each equipped with 3 grating facets. The freestanding gold gratings have 1008 lines per mm. Early 1997, the AXAF telescope underwent extended calibrations in the long beam X-Ray Calibration Facility at the NASA/Marshall Space Flight Center. As part of the telescope, also the performance of the LETGS with respect of spectral resolving power and effective area was measured. At more than 50 individual energies we have measured the grating efficiency or the effective area of the spectrometer, respectively. All these energies were chosen in order to cover the numerous spectral features due to absorption edges of filters, detector coatings, mirror reflectivities, and grating efficiency variations. Although preliminary, the performance of the gratings is close to the predictions made on the basis of subassembly measurements of individual grating elements. In particular, the first order efficiency is about 15% (both sides including vignetting effects) outside the energy regime of partial transparency of the grating wires; inside the efficiency gains from constructive interference effects. Both first diffraction orders are symmetric within less than 1%. The second order is suppressed by a factor of about 200 relative to the first order.

The AXAF-payload consisting of a high resolution telescope, two different transmission gratings and two imaging detection systems, has been extensively tested between mid December 1996 and the end of April 1997. In this paper we report a few preliminary results on the resolution of the low energy transmission grating spectrometer. The measurements reported here utilize different x-ray sources and different detector systems. The resolving power at long wavelength ((Delta) (lambda) at 130 angstrom) equals 0.074 angstrom.

We present the development status of the normal incidence XUV multilayer mirrors for XUV Doppler telescope, which observes coronal velocity fields of the whole sun. The telescope has two narrow band-pass multilayer mirrors tuned to slightly longer and shorter wavelengths around the Fe XIV line at 211.3 Angstrom. From the intensity difference of the images taken with these two bands, we can obtain Dopplergram of 1.8 MK plasma of the whole sun. It is required that the multilayer has high wavelength-resolution ((lambda) /(Delta) (lambda) approximately 30 per mirror), anti-reflection coating for intense He II 304 angstrom emission line and high d-spacing uniformity of approximately 1%.

The performance of multilayer structures as x-ray, soft x-ray and extreme ultraviolet optics is dependent on the nature of the interfaces between constituent layers. Interfacial structure and the interaction between atoms at interfaces has also been demonstrated to have significant impact on the physical properties of multilayer materials in general and thus on their performance in other applied areas. A short summary of the approaches to characterization of interfaces in multilayer structures is presented as background. Two new techniques for the experimental evaluation of interfacial structure and interfacial structure effects are then considered and examples presented. The paper is concluded with review of these results and an assessment of their implications relative to multilayer development.

We describe a bending magnet beamline for the characterization of optical elements (mirrors, gratings, multilayers, detectors, etc.) in the energy range 50 - 1000 eV. Although it was designed primarily for precision reflectometry of multilayer reflecting optics for EUV projection lithography, it has capabilities for a wide range of measurements. The optics consist of a monochromator, a reflectometer, a 3-mirror order suppressor, and focusing mirrors to provide a small spot on the sample. The monochromator is a very compact entrance slitless, varied line spacing plane grating design in which the mechanically ruled grating operates in the converging light from a spherical mirror working at high demagnification. Aberrations of the mirror are corrected by the line spacing variation, so that the spectral resolving power (lambda) /(Delta) (lambda) is limited by the ALS source size to about 7000. Wavelength is scanned by simple rotation of the grating with a fixed exit slit. The reflectometer has the capability of positioning the sample to 10 micrometer and setting its angular position to 0.002 degrees. LABVIEW^TM based software provides a convenient interface to the user. The reflectometer is separated from the beamline by a differential pump, and can be pumped down in 1/2 hour. Auxiliary experimental stations can be mounted behind the reflectometer. Results are shown which demonstrate the performance and operational convenience of the beamline.

Sum rule tests demonstrate that there are deficiencies in the available optical data for materials important in multi-layer mirror applications, such as Si and Mo, leading to errors in the estimation of the real and imaginary parts of the refractive index n equals 1 - (delta) + i(beta) ((delta) , (beta) are also known as 'optical constants'). The refractive index of Si is investigated in the region 50 - 180 eV using angle dependent reflectance measurements. It is shown that the reflectance method has limited efficiency in certain energy regions. Transmission measurements for the refractive index of Mo are performed in the energy range 60 - 930 eV. The new experimental results are used in order to form an improved, self-consistent database for the real and the imaginary part of n for Si and Mo and they are compared to the values in the 1993 atomic tables. The normal incidence reflectivities of Mo/Si and Mo/Be multilayer mirrors are calculated using the new results.

We present the spectroscopic techniques for studying imaging, spectral, and polarizing properties of multilayer optics intended for solar astronomy and laboratory applications. The measurements were performed using line or quasicontinuous radiation (15 - 400 angstrom) of a point-like source driven by 0.15-J, 5-ns laser pulses at 0.54 micrometer. The imaging quality of focusing normal-incidence multilayer mirrors (MMs) in the subarcsecond resolution range was evaluated from small- source imaging tests employing a high-resolution photographic film. The spectral properties of focusing and plane MMs were measured using the configuration of a transmission grating spectrograph with a medium dispersion, the plate scale typically lying in the range 10 - 30 angstroms/mm. This technique allowed us to measure: (1) the resonance wavelengths versus MM aperture (evaluation of lateral uniformity of the d- spacing); (2) the spectral shape of the primary resonance reflection peak; (3) outside-resonance reflection and higher- order reflection maxima revealed under irradiation by a broad spectrum; (4) for plane MMs, the reflectivities at arbitrary angles of incidence. In the evaluation of plane MMs, the function of focusing radiation was transferred to grazing- incidence toroidal mirrors. About 40 MMs ranging in resonance wavelength from 45 to 310 angstroms, synthesized in different laboratories, were studied using these techniques. A broadband spectrograph comprising a grazing-incidence toroidal mirror and a transmission grating proved to be inherently suited for characterizing the laser-plasma source itself. Two versions of tungsten-coated toroidal mirrors were used, which operated at grazing angles of 7.6 degrees and 4 degrees and had the respective practical short-wave cutoffs at about 40 and 15 angstroms. A source of collimated polarized quasimonochromatic radiation in the 170 to 180 angstrom band was implemented around MMs and our laser-plasma source. The peak polarizance of plane Mo-Si MMs with a d-spacing of 120 angstroms, measured around 175 angstroms at 41 degrees off normal, proved to be 98.2%, which was consistent with the calculated value (98.75%). Two high-resolution high-throughput stigmatic spectrographs were implemented, each comprising a couple of identical concave normal-incidence MMs and a plane grating at grazing incidence. Space-resolved line spectra of laser- produced plasma were obtained and analyzed. The spectrograph for the 130 - 140 angstrom range had a practical resolving power of at least 4000, a plate scale of 0.7 angstroms/mm, and measured 0.6 m. These parameters for the 170 - 190 angstrom range instrument were respectively 24,000, 0.35 angstrom/mm, and 1.1 m. A highly dispersive spectroheliograph was put to a test using a laser-plasma source; the configuration was closely related to that of the spectrograph but involved a reversed ray propagation.

Multilayers used at grazing incidence offer likely the only real opportunity for extending imaging techniques in x-ray astronomy to tens of keV, or well beyond the usual upper bound when using single material reflecting surfaces. There are several reasons why conical foils are particularly suited for multilayer applications. For one thing, many of the arguments made in the past in favor of foil reflectors still hold, since multilayers do not eliminate the need of extreme oblique incidence. We show, additionally, that foil reflectors offer other important advantages which are likely to be essential toward the realization of wide band x-ray mirrors. Successful multilayer depositions on segments of our epoxy replicated foil reflectors have already been reported. In this paper we review our own efforts at multilayer deposition on replicated surface foils, addressing in detail such relevant issues as consistency, quality and uniformity of the deposits, boundary roughness and potential, stress-induced foil shape distortions. Finally, we present detailed mirror design and modeling aimed at future wide-band astronomical research.

We are engaged in a program to develop focusing hard x-ray telescopes in a double conical or Wolter 1 geometry that function up to 100 keV by employing small graze angles and multilayer coatings. Directly polished substrates are not an option because they are too thick to be nested efficiently. The only alternative is to fabricate the very thin substrates by replication. Our objective is the production of integral cylindrical substrates because they should result in better angular resolution than segmented foil geometries. In addition, integral cylinders would be more resistant to possible stress from deep multilayer coatings than segmented ones. Both electroforming of nickel (method of SAX, JET-X, and XMM) and epoxy replication are under consideration. Both processes can utilize the same types of mandrels and separation agents. While electroforming can produce substrates that are thin, the high density of the nickel may result in high weight optics for some missions. For convenience, experimentation with replication and coating is being carried out initially on flats. Our replication studies include trials with gold and carbon separation agents. This paper reports on our efforts with epoxy replicated optics.

The influence of varying the Ar-pressure in the process of depositing Ni/C multilayers by dc-magnetron sputtering has been studied, and atomic force microscopy (AFM) measurements, x-ray characterization results and transmission electron microscopy (TEM) results are presented. Single Ni and C films and Ni/C multilayers were deposited at Ar-pressures of 1.5, 3, 5 and 7 mTorr. The one-dimensional power spectral density data from the AFM measurements clearly indicate that the best densities and thin film qualities for both materials are obtained at lower Ar-pressure, i.e. 1.5 mTorr.

The development of x-ray optics for astrophysical investigations in the 40 - 100 keV energy range is extremely important. In this energy range, a focusing system is necessary to resolve crowded regions, to improve sensitivity, and to provide the deep sky images necessary to make the next great step forward in this field. Such a step was ably demonstrated by the Einstein and ROSAT observatories. These systems used grazing incidence optics, and, as is well known, the critical angle of reflectivity decreases linearly with energy for ordinary metal surfaces which adversely impacts on the design of a focusing system for higher energy x rays. At least 3 parameters are negatively affected: (1) the field of view is decreased; (2) the projected area of an individual mirror element is decreased; and, (3) the focal length for a fixed diameter system is increased. In order to counter these effects, mirrors coated with multilayers have been designed. It is theoretically possible to increase the grazing angle by coating the mirror surface with a graded d-spacing. The ability to produce a coated mirror with close to theoretical performance is, however, technically challenging. We describe our approach to the fabrication of a system designed for the 40 - 100 keV range that is based on electroforming technology. We also describe some of the general considerations that must be taken into account when fabricating a viable mirror.

Bragg diffraction with mosaic crystals is one of the techniques proposed to realize focusing telescopes for hard x- ray (greater than 10 keV) photons. The best candidate material for this application is pyrolytic graphite. Indeed, this crystal is characterized by a very high reflection efficiency, even if it is produced on a very limited scale. In this paper we investigate the possible use of other materials, with a larger commercial availability. In particular we propose the use of polymeric crystalline films. These materials are extremely attractive not only for their lower costs than pyrolytic graphite, but also because they are well suited for good mechanical processing. Here we discuss perspectives and problems related to the construction of Bragg telescopes based on polymeric fibers.

We present new results in the development of high throughput hard x-ray telescopes with multilayer supermirror coatings. Basic techniques to make the supermirror are at first developed in deposition of constant d spacing multilayers. The reflector of multilayer on the float glass achieves high reflectivity, limited by the surface roughness of substrate, while, we need more improvement in getting comparable reflectivity of multilayers on the replica foil. We put the mask just in front of sample, it reduced the nonuniformity of the thickness less than 2%. In order to maximize the effective area and field of view, we have optimized the supermirror parameters; d spacing, number of layer pairs, and thickness ratio of heavy and light element. Multiblock method is introduced to design the supermirror, and it gives high reflectivity of approximately 30% in the 25 - 40 keV band. A test supermirror sputtered on a glass sample exhibits reasonable reflectivities of about 20 - 30%. We designed a telescope system with 45 cm diameter, 20 cm mirror length in two stage, and focal length of 8 m. The effective area of four such telescopes is 320 cm² for the x rays between 25 and 40 keV. We plan the application of this type of telescope to the balloon experiment named InFOC(mu) S to reveal hard x-ray images of clusters of galaxies or supernova remnants.

The on- and off-axis imaging properties and effective area of the two SODART flight telescopes have been measured using the expanded beam x-ray facility at the Daresbury synchrotron. From on-axis measurements the encircled power distribution and the point spread function at three energies 6.627 keV, 8.837 keV and 11.046 keV have been measured using a one-dimensional position sensitive detector. We found that the point spread function can be presented well by a function which is a sum of a Gaussian divided by the radius and two exponential terms where the first has a 1/e value close to 2 arcmin and the other a 1/e value of ca. 15 arcmin. The data have been used to calculate the half power diameter (HPD) for three different SODART focal plane detectors, the high energy proportional counter (HEPC) with a field of view (FOV) of 65 arcmin, the low energy proportional counter (LEPC) with a FOV of 33 arcmin and the 19 element solid state detector array (SIXA) with a FOV of 18 arcmin. We found that the HPD decreases with increasing energy due to poorer figure of the outermost mirrors. The HPD falls in the range from 2.4 to 3.8 arcmin depending on energy and FOV. Data have also been obtained on the on- and off-axis effective area at all three energies and compared to that obtained from a raytracing of an ideal telescope configuration. We found that the measured on-axis effective area integrated over a FOV of 105 arcmin is ca. 65% of the area predicted from an ideal geometry. Finally the one- dimensional detector data has been used to obtain the radial dependence of the on-axis HPD and the on-axis effective area and the data from the two-dimensional position sensitive detector has been used to obtain the azimuthal dependence of the on-axis HPD and the on-axis effective area.

The SODART x-ray telescope includes an objective crystal spectrometer (OXS) providing an energy resolving power around 1000 by Bragg reflection upon crystals. A program to calculate the SODART-OXS response function is described. It includes the simulation of the arrangement of the LiF, Si, and RAP crystals on the Bragg panel, the angle-dependent projection of the infalling x rays onto the mirrors, and the partial shadowing of the panel by the entrance door. The response function depends also on the parameters of the crystals (reflectivity and rocking curve width), using calculated and measured values in their energy dependence. The effective area of the mirror shells and the detector efficiencies are included, too. The energy dependences of the individual factors are shown and used to define an optimal crystal layout taking simulated and measured x-ray source lines (within the XANADU package) to find the most important Bragg-angle regions. It turns out that the optimal Si-RAP crystal distribution on the panel is asymmetric, thus favoring high-energy Si and low-energy RAP line regions. The response functions are displayed and used for the calculation of count rates for line and continuum registration.

The European Space Agency (ESA) X-Ray Mirror Module (XMM) telescope is a set of three multiple shell grazing incidence Wolter Type I telescopes that will study astronomical x-ray sources from Earth orbit. There are a total of 58 nested mirror shells within each telescope. Each shell consists of a paraboloid primary and hyperboloid secondary that together focus x rays that are incident at grazing incidence onto a detector, known as the EPIC. Two of the telescopes also have grazing incidence diffraction gratings that disperse a portion of the focused x rays across a second detector, known as the RFC. The complex geometry of XMM makes stray light design and analysis of this telescope a unique and difficult challenge. The fundamental problem is that the detectors collecting the x-rays are also sensitive to visible and near-infrared radiation from outside sources such as the Sun and the Earth. This paper is an overview of the approach used to perform a stray light analysis of this visible radiation, and a presentation of four of the stray light problems that are unique to XMM and related grazing incidence telescopes. For each problem, a summary of the technique that was used to calculate the magnitude of the stray light is given.

Nowadays the most used technology to obtain thin and light mirror shells for x-ray optics is the replica technique by nickel electroforming. This technology has been successfully employed for projects like SAX, JET-X and XMM. Nevertheless, the high density of the nickel poses some limitations to the possibility of extending the use of this technology for the future x-ray missions demanding high collecting area, good angular resolution and low weight of the optics. In the paper we analyze which are the present limits of the nickel electroforming technology and we underline the potentiality of using SiC and other ceramic materials for the manufacture of large and light x-ray optics. Possible manufacturing process are proposed and preliminary results of prototypes of ceramic mirror shells are presented.

The production of future high throughput x-ray telescopes optics using a replication method foresees the use of a high number of mandrels and a tight control of their shape. The proposed ion beam polishing of the mandrels is a technique that is either cost effective and offers accurate shape control. The aluminum-kanigen coated mandrels are initially diamond turned, superpolished to the required microroughness and then figured with ion beam polishing. An ion beam facility has been built to test the concept. After the characterization of the source, samples of superpolished electroless nickel have been ion polished. The behavior of the material and the degradation of its microroughness after the etching have been investigated and the results are here reported.

Danish Space Research Institute is supplying the high throughput x-ray concentrators, the so called SODART telescopes, to be flown on the Spectrum Rontgen-Gamma (SRG) satellite. We have completed the process of the developing, building, testing and calibrating the two flight units and one spare unit. Their design is based on the principle of multiple, concentrically nested foil mirrors constituting a conical approximation of the Wolter I geometry. We describe some aspects of the mechanical design, alignment and production process. The optical characteristics of the thin foil telescopes are partly determined by the optical characteristics of the foil mirrors and partly by the assembly and alignment tolerances. The influence of the mirror manufacture processes on some aspects of its optical characteristics is discussed. The concept and the steps of the assembly and alignment procedure are given. The process of obtaining the required accuracy involves a number of technological processes that need optimization in order to reduce the mechanical errors. The overall alignment was tested and improved by optical methods. The experience gained during the development and building of the SODART telescopes shows the potential for improvements in the utilization of the foil mirrors optical characteristics and in future thin foil telescope design and manufacture.

Fresnel hard x-ray zone plate was manufactured by sputter- sliced technology to work on 2.29 A wavelength. Cu and Cr were used to create opaque and transparent zones. The experimental setup was prepared to investigate optical properties of obtained zone plate. The focusing effect was observed. The numerical methods and software were developed to simulate imaging properties of Fresnel zone plate. Experimental data was compared with calculations.

During the last several years we have seen intense development of the capillary optics. This fact is connected with improvement of the capillary optics technology. One of the important last achievements in this development is the use of capillary lenses for receiving intense polarized x-ray beams. This experiment was carried out at the Institute for Roentgen Optics (IRO). The new x-ray florescent analyzer was constructed by IRO. We have received minimal detection limit 10^-13g using portable small power x-ray tube (approximately 1 - 2 W) and the capillary lens. On the basis of new technology, which was made for the first time in our Institute, we had success in the imaging of thick samples with micron level resolution. Last year, in collaboration with scientists from Europe, we carried out the experiments in focusing of neutron beams in atomic reactors. These experiments demonstrated that capillary optics provide record concentration of neutron beams.

Polycapillary X-ray optics, which is comprised of bundles of tens of thousands to millions of hollow glass capillary tubes, can be used as concentrators of astronomical X-rays for spectroscopic studies. Measurements have been performed of transmission efficiency of straight polycapillary fibers in the range of 10-80 keV. A geometrical optics simulation has been developed which accurately models experimental results and includes the effects of surface roughness and profile error. An optic designed for 8-keV photons has been tested as a concentrator for parallel beam synchrotron radiation. The results, a factor of 65 in intensity gain, are in good agreement with optics simulation. A prototype optic designed for 10-50 keV is currently under construction with a predicted gain of more than 100. Design requirements for higher energy photons are considered. By using a small or position sensitive detector, improvements of two orders of magnitude at 80 keV are expected from the use of this type of collector.

Source lateral displacement is analyzed by computer simulation and its influence on Kumakhov optics work is discussed. The displacement influences focal spot forming and angular distribution of quasiparallel beams at the output of Roentgen optical systems.

The scientific instrumentation on board the x-ray astronomy satellite BeppoSAX, launched at the end of April 1996, includes four identical mirror units, each composed of 30 nested grazing incidence mirrors. The focal plane detectors are 3 identical position sensitive medium energy gas scintillation proportional counters, operating in the energy range 1.3 - 10 keV and 1 low energy gas scintillation proportional counter in the range 0.1 - 10 keV. During the science verification phase (July-November 96) a selected number of x-ray targets has been observed in order to have an in-flight calibration of the instrument. This paper describes some results with particular emphasis to the on axis and off axis behavior of the optical systems.

The variations of the intensity and spectral distribution of the EUV and x-ray solar fluxes from the whole disk in the wavelength range 0.1 - 134 nm are the main reason of changes in all upper atmospheric and ionospheric parameters and one of the principal factors in the solar-terrestrial relation changes. However the permanent monitoring of the solar EUV and soft x-ray radiation (0.8 - 120 nm) is absent at present. In this paper the recent advances in the elaboration of the topical-electronic apparatus complex for the permanent space patrol of EUV and soft x-ray solar radiation are discussed and optical schemes of solar spectrometers of grazing and normal incidence with diffraction gratings and also their energetic characteristics are presented.

We present an overview of a sounding-rocket experiment that is scheduled to be launched by the Institute of Space and Astronautical Science (ISAS) in January 1998, the rising phase of the 11-year activity cycle of the sun. The purpose of this experiment is (1) to obtain whole-sun images taken in an XUV emission line, Fe XIV 211 A, using the normal incidence multilayer optics with a high spectral resolution of about 40, and (2) to carry out the velocity-field measurement with a detection limit as high as 100 km/s.

Filters fabricated from metalized polyimide have been specified for a number of x-ray astronomy missions, including the Advanced X-ray Astrophysics Facility (AXAF), the x-ray spectrometer (XRS) on Astro-E, the Advanced Composition Explorer (ACE), and the Geostationary Operational Environmental Satellite (GOES). Polyimide offers greater strength, improved temperature stability, and effectiveness in blocking unwanted ultraviolet radiation compared to polymeric films previously employed. This paper reviews the various x- ray astronomy missions and the particular challenges that were met with polyimide filters. The paper also reviews the development of free standing thin foils of polyimide with mechanical properties optimized for x-ray astronomy and other applications, such as synchrotron research.

We report on a continuing program to develop and test reflecting coatings suitable for use in Fabry-Perot etalons operating in the far ultraviolet region of the spectrum. UV etalons are of particular interest for solar studies as they have the potential to enable one to make wide-field high resolution diagnostic images such as spectroheliograms, dopplergrams, and density maps in isolated spectral lines formed in the upper chromosphere, transition region and lower corona. The performance of the high-efficiency coatings required by a UV etalon is limited both by the availability of suitable materials, and by the uniformity and accuracy of the deposition process. The lack of UV transmitting materials with a wide range of refractive index is especially troublesome. The latter problem may be partially overcome by using a vacuum-spaced etalon design. A vacuum-spaced etalon with cultured quartz plates was successfully operated at 160 nm in a previous study. In this study, we investigated a family of coating designs based on the fluoride salts of magnesium and lanthanum, finding that usable etalon performance may be achievable at wavelengths as short as 120 nm. Results of theoretical predictions and the performance of test coatings are presented. This work was supported by NASA under contract NASW-5007.

Optical schemes of spectrometers with concave diffraction grating are considered herewith to register Sun radiation in a range of 1.8 - 120 nm. The optimization of normal and grazing incidence monochromators is represented hereinafter. In both cases slitless and classical spectrometers are offered. Classical schemes are preferable in terms of spectral resolution, while slitless ones are better in terms of energy.

The Danish Space Research Institute is supplying high- throughput x-ray mirror modules (MM) for the SODART telescopes to be flown on the Russian Spectrum-X-Gamma mission. We have finished the process of building two flight units and one spare unit. We have measured 5500 flight quality single mirrors using laser scanning. Edge deformations have been found to be a persistent phenomenon giving rise to reduced effective area and alignment accuracy. The degree of foil straightness is a function of the radius of curvature. Detailed optical measurements of the MMs is a control of the mechanical alignment achieved by repeated adjustments between the stages of assembly. The results of these investigations are discussed and compared with x-ray calibration measurements. A combination of the optical results and x ray results is fed into a raytracing code resulting in a reliable prediction of the imaging capabilities of the SODART telescopes.

Reflectivity at (lambda) equals 0.154 nm and mechanical stress in the bulk thin films of tungsten and silicon and single d- spacing multilayers on their basis with d approximately equals 2.8 nm deposited by the magnetron sputtering technique on flat thin substrates of Si wafer (approximately 0.2 mm), glass (approximately 0.3 mm), and epoxy gold replicated aluminum foil (approximately 0.3 mm) have been studied. The interfacial roughness of the multilayers has been calculated from the x- ray reflectivity curves as the following: on Si wafer (sigma) approximately equals 0.31 nm, on glass (sigma) approximately equals 0.32 nm, and on foil (sigma) approximately equals 0.34 nm. There was not observed a significant dependence on the stress in the Si film with change in rf power, Ar gas pressure and biasing. For the W films an increase of dc power results in an increase of stress. A similar relationship is also evident for W films deposited by rf power, but this dependence is less pronounced. The influence of low temperature (up to 200 degrees Celsius) annealing on x-ray reflectivity and stress in the multilayers has been investigated. There was not found an appreciable changes in the absolute value of reflectivity or in d-spacing with annealing temperature. The stress in the coatings changes with annealing temperature from compressive to tensile. There was observed a temperature of annealing at which the stress is no longer present in the film. The absolute value of this temperature measured for W/Si multilayer is approximately 120 degrees Celsius.

It is shown that the x-ray mirrors which have been made on the verge of potentialities of the modern technology, give rise to deterioration of the coherent properties of the beam delivered by the third generation synchrotron radiation sources. In other words mirrors produce speckle structure in the reflected x-ray beam. The theoretical analysis of partially coherent x- ray beam scattered by moderately rough mirror surface under the total reflection condition is presented and the estimates for the intensity contrast as a function of the surface parameters are given. The observed speckle structure was experimentally recorded by means of high resolution photo film. It is shown that the polishing process must be significantly improved in the case of the long mirrors (approximately 1 m) used as the standard optical elements at the beamlines, while small mirrors (less than 0.2 m) are in a better state and may be applied to various imaging techniques exploiting coherent x-ray properties.

The use of x-ray optics in x-ray instrumentation for dispersing, collecting, focusing and imaging x rays is expected to become increasingly important. In recent years clear trends towards the more efficient use of laboratory sources and improved focal properties using different kinds of x-ray optics are observed. In the present work we have performed an experimental characterization of a polycapillary device. The energy dependent transmission and lateral resolution have been assessed. Next to this, ray-tracing calculations were performed to verify our experimental results. Our preliminary results on the size of the beam waist are indicative for the applicability of these focusing devices in laterally resolved x-ray experiments. Quantitative results are presented in conjunction with our ray-tracing simulations.

We have been able to utilize silicon monoxide (SiO) as a refractory coating to improve on the replicated figure of composite optics made from carbon fiber reinforced plastic (CFRP) sandwich panels. We apply an evaporative coating of SiO to the surface of the mirror and polish that coating to obtain the desired figure for the complete mirror. We have developed this technique to allow the use of CFRP optics which are both stable and have a low areal density. This represents a novel use of thin film vacuum coating to produce an optical substrate rather than a simple reflective or protective overcoating and represents an advance in producing thick SiO coatings (10 - 40 micrometers) over large areas (25 - 60 cm).

The first measurements are reported of non-specular scattering of EUV radiation normally incident on a multilayer mirror. The scattering from a Mo/Si multilayer mirror has been measured as a function of angle and wavelength. A peak in the angular distribution of scattered light is observed which is due to the correlation of the roughness of different interfaces. The scattering from correlated roughness can be described by a simple kinematic theory of scattering. In the region of the Bragg reflectivity peak dynamical effects lead to a reduction in the scattering from the simple kinematic theory. The total integrated scatter (TIS) has been measured and is found to peak on the short wavelength side of the Bragg peak. The TIS is less than 1% of the incident intensity.

We present a small investigation of the possibility of improving the bandwidth and associated integrated reflectivity of multilayers at 8 keV. We investigate two multilayer material combinations: Ni/C and W/Si, and 3 different types of multilayer designs: periodic, linearly graded, and a-periodic. The optimizations are performed using a simulated annealing routine and we find that improvements of up to 42% may be obtained in the case where one considers a 10% bandwidth, and only 10% for a 5% bandwidth.

A proposal for an x-ray optics test facility based at a synchrotron radiation source is presented. The facility would incorporate a clean preparation area, and a large evacuable test area. The advantages of using a synchrotron as the source of the test radiation are discussed. These include the ability to produce a highly parallel beam of monochromatic x rays ranging from 200 eV to around 70 keV.

The prelaunch calibration of AXAF encompasses many aspects of the telescope. In principle, all that is needed is the complete point response function. This is, however, a function of energy, off-axis angle of the source, and operating mode of the facility. No single measurement would yield the entire result. Also, any calibration made prior to launch will be affected by changes in conditions after launch, such as the change from one g to zero g. The reflectivity of the mirror and perhaps even the detectors can change as well, for example by addition or removal of small amounts of material deposited on their surfaces. In this paper, we give a broad view of the issues in performing such a calibration, and discuss how they are being addressed in prelaunch preparation of AXAF. As our title indicates, we concentrate here on the total throughput of the observatory. This can be thought of as the integral of the point response function, i.e. the encircled energy, out to the largest practical solid angle for an observation. Since there is no standard x-ray source in the sky whose flux is well known to the approximately 1% accuracy we are trying to achieve, we must do this calibration on the ground. We also must provide a means for monitoring any possible changes in this calibration from prelaunch until on-orbit operation can transfer the calibration to a celestial x-ray source whose emission is stable. In the paper, we analyze the elements of the absolute throughput calibration, which we call the effective area. We review the requirements for calibrations of components or subsystems of the AXAF facility, including the mirror, detectors, and gratings. We show how it is necessary to have an absolute calibrated detection system available during the prelaunch calibrations to measure the flux in the x-ray beam used for calibrating AXAF. We show how it is necessary to calibrate this ground-based detection system at standard man-made x-ray sources, such as electron storage rings. We present the status of all these calibrations, with indications of the measurements remaining to be done, even though the measurements on the AXAF flight optics and detectors will have been completed by the time this paper is presented. We evaluate progress toward the goal of making 1% measurements of the absolute x-ray flux from astrophysical sources, so that comparisons can be made with their emission at other wavelengths, in support of observations such as the Sunyaev-Zeldovitch effect, which can give absolute distance measurements independent of the traditional distance measuring techniques in astronomy.

The design, performance, and calibration of the seven flow proportional counters (FPCs) used during AXAF ground calibration are described. Five of the FPCs served as beam normalization detectors (BNDs), and two were used in the telescope focal plane in combination with a set of apertures to measure the point response functions and effective areas of the AXAF mirrors and transmission gratings. The BNDs also provide standards for determining the effective areas of the several telescope/grating/flight-detector combinations. With useful energy resolution and quantum efficiency over the entire 100-eV to 10 keV AXAF energy band, the FPCs provided most of the data acquired during AXAF calibration. Although the principles of proportional counter operation are relatively simple, AXAF's stringent calibration goals require detailed calibration and modeling of such effects as window- support-wire obscuration, window deformation between the support wires, electron diffusion and avalanche processes, gain nonuniformities, and gas pressure and temperature variations. Detector aperture areas and signal processing deadtime must also be precisely determined, and detector degradation during the many months of AXAF calibration must be prevented. The FPC calibration program is based on measurement of individual components (such as window transmission and aperture size) and the relative quantum efficiencies of complete detector systems, as well as absolute QE calibration of selected detectors at the BESSY synchrotron, an x-ray source of precisely known intensity.