The concept of amplitude-wavelength space applied to the development of an x-ray optic provides a means of summarizing and unifying the complex data associated with each stage of its development: the specification; manufacturing tolerances; and metrology. The determination of manufacturing tolerances requires calculation of the image aberrations of perturbed optical systems and is most usefully carried out using a modified asymptotic Debye theory. Its range of applicability and that of other theories is illustrated in amplitude-wavelength space. Subnanometer perturbations are measured by mechanical or optical techniques, and the measuring instruments are calibrated by means of x-ray interferometry in terms of the primary standards of length.

The imaging capability of a thin foil x-ray mirror has been examined with optical light, using a laser beam and a wide optical parallel beam. These measurements reveal that (1) image broadening due to millimeter scale waviness (orange peel) of the aluminum substrate, partly intrinsic to the foil and partly caused during the foil treatment, is 1.2-min of arc half-power diameter (HPD) in two reflections; (2) slope errors due to foil shaping and misalignment cause broadening of 1.6-2.0-min of arc HPD; (3) total broadening is ~3-min of arc HPD, which is consistent with the broadening of 2.6-min of arc HPD measured with x rays.

The ROSAT wide field camera (WFC) is an XUV telescope operating in the 12-250-eV energy band. The mirror system utilizes Wolter-Schwarzschild type I (WSI) grazing incidence optics with a focal length of 525 mm, comprised of three nested aluminum shells with an outermost diameter of 576 mm providing a geometric aperture area of 456 cm2. The reflecting surfaces are electroless nickel plated and coated with gold to enhance their reflectivity in the XUV. The mirrors have undergone full aperture optical testing, narrow beam XUV testing, and full aperture XUV testing. Measurements of the reflectivity are compared to theoretical values derived from the optical constants of gold in the XUV range. Analysis of the focused distribution is used to estimate the surface roughness and figuring errors of the polished surfaces. The results are compared to the mechanical metrology data collected during manufacture of the shells and the power spectral density of the reflecting surfaces is found to have a power-law form.

Although optical systems designed to image extended fields, such as photographic and copying lenses, can tolerate clearly visible degrees of surface contamination and damage, such as dust and scratches, mirrors and lenses required to produce diffraction limited images of point sources require near perfect surfaces. Every particle of contamination and surface defect will create its own diffraction pattern in the image plane, thus transferring information about the surface itself rather than the object under study. This paper reviews techniques currently used for measurement of surface texture and image quality and describes a new approach based on comparing a test mirror with a reference component having known characteristics. The method of operation and the principal design features of this comparator approach are described. If this method is accepted, it may in future be possible to define a code of practice and standards relating to the roughness, flaws and image forming quality of mirrors.

The characterization of the surface of a cylindrical optic requires metrology techniques that are analogous to those for more conventional optics but much different in format. Data on the surface figure can be obtained using interferometry and a fringe scanner. We will describe how fringe scanner data is processed into optical path differences (OPDs) which give the surface profiles along a meridian of the cylinder. We will then describe how multiple meridians are combined with the azimuthal data on the circularity of the cylinder to produce a map that describes the surface figure of the optic. A set of Legendre-Fourier polynomials which are orthogonal over the surface of the cylinder are fit to the data. With the aid of these polynomials, the effects of rigid body motions (misalignments) are identified and removed and the surface figure characteristics relating to optical performance can also be derived. This procedure has been used successfully for doing optical surface metrology of two cylindrical optics which comprise the Technology Mirror Assembly (TMA), a prototype x-ray telescope assembly fabricated by Perkin-Elmer under contract to Marshall Space Flight Center (MSFC). The surface qualities of the two TMA optics are the best of any existing cylindrical optics.

By using Fourier techniques and linear systems theory we have derived an analytic expression for a generalized transfer function for grazing incidence optical systems operating at ultraviolet and x-ray wave-lengths that includes the effects of optical fabrication errors over the entire range of relevant spatial frequencies. The Fourier transform of this transfer function yields the image distribution (or point spread function) from which encircled energy characteristics or other image quality criteria can be obtained. This transfer function characterization of grazing incidence optical systems allows parametric trade studies and sensitivity analyses to be performed as well as the derivation of fabrication tolerances necessary to satisfy a given image quality requirement.

We present the results obtained during the characterization of the mandrels used for the replica of a prototype series of double cone mirrors for the SAX project. In the first part of this paper we will summarize the results concerning the geometry of the mandrels and the metrology involved. We will then give a characterization of the mandrels in terms of their microroughness.

Within various x-ray programs there exists a need for a detailed investigation of the surface roughness of mirrored surfaces over a wide spatial wavelength bandwidth, ranging from large scale figure error to microroughness. A number of methods exist to measure the surface roughness. Common to all methods is that they are bandwidth-limited. A crucial point in the analysis of data is, therefore, to specify accurately the wavelength bandwidth limitation and to determine the surface autocorrelation function within this band-width. We present a number of scattering measurements obtained using a triple-axis perfect-crystal x-ray diffractometer and the results of an autocorrelation function analysis. Furthermore, we present some measurements of integrated reflectivity, which we believe provide evidence for microroughness in the range from a few angstroms to tens of microns.

We present comparative measurements of surface roughness on prepared samples. These measurements have been made with both Talystep profilometers and WYKO interferometers. In addition, we have measured scattering distribution from these samples at extreme ultra-violet wavelengths. The utility of the WYKO interferometer and Talystep device for specifying extreme ultraviolet mirror surface quality is discussed.

Electroformed grazing incidence mirrors were tested with x rays and were measured with an optical profiler. Their total effective areas are ⪆70% of the theoretical values both for 1.5- and 6.4-keV x rays. The half-power diameters (HPDs) are ⪅2 min of arc at 1.5 keV. Comparing the x-ray test result with the optical measure-ment, we set requirements of high-frequency roughness <14 Å and a midfrequency roughness <70 Å for a HPD < 1.5 min of arc at 7 keV. We also present a design of the mirror array telescope for high energies (MARTHE) which has a total effective area of ~1000 cm2 for 7-keV x rays.

Surface micro-roughness of grazing incidence optics has long been recognized as a critical parameter in the control of the scattered x-ray intensity and its effects on the point spread function half-energy width. Accurate knowledge of the amplitude of surface micro-roughness is vital to assess optic predicted performance during the final stages of fabrication. This requires not only a knowledge of the spatial bandwidth over which surface features must be measured, but also knowledge of the bandwidth of the measurement instrument. We show that the standard assumption that instruments respond up to their Nyquist limit is an oversimplification which neglects the finite detector size and its bandwidth limiting effects when sampling a real (i.e., two-dimensional) surface.

Surface finish measurements are usually fitted to models of the finish correlation function which are parametrized in terms of root-mean-square roughnesses, σ, and correlation lengths, l. Highly finished optical surfaces, however, are frequently better described by fractal models, which involve inverse power-law spectra and are parametrized by spectral strengths, Kn, and spectral indices, n. Analyzing measurements of fractal surfaces in terms of σ and l gives results which are not intrinsic surface parameters but which depend on the bandwidth parameters of the measurement process used. This paper derives expressions for these pseudo-parameters and discusses the errors involved in using them for the characterization and specification of surface finish.

Grazing incidence optics are a key element of x-ray and extreme ultraviolet astronomy and are becoming increasingly important in aspects of far-ultraviolet astronomy. Metal optics have figured prominently in this work, and machined metal optics offer distinct advantages in some applications. New methods of metrology have combined with innovations in fabrication to produce metal optics of second of arc quality. In this paper we review the fabrication, evaluation, and performance of machined grazing incidence metal optics produced, or in production, for astronomical telescopes.

X-ray astronomy has reached sufficient maturity to demand at least moderate angular resolution light-gathering telescopes to accompany detector development. Keeping the cost of such telescopes within the budget of low-cost flight opportunities such as sounding rockets and SPARTAN missions is a substantial challenge. We have developed a program of precision diamond mirror turning, mechanical polishing, lacquer coating, and metal deposition which produces x-ray telescopes with minute of arc angular resolution at moderate cost. We describe the process and report calibration results for a 80 cm (31.4 in.) diam Wolter I telescope flown aboard an Aries sounding rocket.

A high-precision, numerically controlled, diamond cutting machine has been developed for fabrication of asymmetrical aspheric mirrors, such as toroidal mirrors used in SOR optics. In this machine, a work-piece is securely fixed to a machine base, and its side face is cut by a flying single-point diamond tool. A tool spindle is laid on an X-Y slide, and its position is numerically controlled by using a laser interferometer. It is possible to fabricate a cylindrical surface by having the spindle-axis rotate slightly about an axis perpendicular to the X-Y slide. Furthermore, while the spindle is rotating, cutting-depth can be dynamically controlled by utilizing a piezo-actuator fixed to the diamond tool. The cutting-depth control is synchronized to the current rotation angle of the spindle, and cutting-depth data are numerically programmed as function of X-Y slide position. A suitable combination of these programmable figure parameters allows fabrication of asymmetrical aspheric mirrors. In order to achieve high figure accuracy, accurate straight motion is required with the X-Y slide. Therefore, straightness error compensation control is adopted, which incorporates a ZERODURE straightedge of 1m length and three optical-fiber gap sensors. The machine accepts a work-piece with maximum dimensions of 600mm length and 100mm width. A figure accuracy of 0.1 μm and surface roughness of 0.03μmRmax have been achieved.

Designing optics for photometry in the long-wavelength portion of the EUV spectrum (400-900 Å) poses different problems from those arising for optics, operating shortward of 400 Å. The available filter materials which transmit radiation longward of 400 Å are also highly transparent at wavelengths shortward of 100 Å. Conventional EUV optics, with grazing angles of ⪅10°, have very high throughput in the EUV, which persists to wavelengths shortward of 100 Å. Use of such optics with the longer-wavelength EUV filters thus results in an unacceptably large soft x-ray leak. We have overcome this problem by developing a mirror design with larger graze angles ≥20°, which has high throughput at wavelengths longer than 400 Å but at the same time very little throughput shortward of 100 Å.

A new approach to X-ray optics has been proposed, based on single-step holographic fabrication of highly-efficient X-ray diffraction elements. These elements include holographic gratings and mirrors, slanted (non-Snellian) mirrors, uniform and chirped gratings, holographic optical elements (HOE's), lenses, and beam splitters which effectively demonstrated the proof of concept of POC's holographic technologies. In our approach, the holographic recording of the interference patterns produced by two (or more) coherent electromagnetic waves are used to create the desired transmission and reflection Bragg holographic structures which can perform various non-conventional operations in the XUV region (soft X-ray and EUV, from 1 to 100nm).

The layered synthetic microstructure (LSM) has come into widespread use in VUV and soft x-ray research. Mirrors with large reflectance values (>50%) at normal incidence have been made for wavelengths as short as 160 A. LSMs can also provide large reflectance values at grazing incidence. Reflectance maxima at grazing incidence can have narrow angular half-widths in the soft x-ray region, thus making them useful as dispersing elements. By incor-porating a thick spacer layer, similar to a Fabry-Perot etalon, the angular half-widths can be made even narrower. The location of these spacer layers within the LSM influences the half-width of the maxima. For wavelengths in the soft x-ray region the reflecting maxima do not discriminate between s and p polarization. However, as the wavelength increases, into the VUV, the angular half-widths increase and polarization discrimination does occur. Results of calculations will be presented to illustrate these effects.

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 104 cm2 of effective area will be the largest. A high throughput facility with over 105 cm2 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 design for a mirror array telescope for high energies (MARTHE) with almost 1000 cm2 effective area at 7 keV is described. Briefly, it consists of 36 modules. Each module contains Wolter I mirrors nested 6 deep. The system is small enough to be flown on an Aries rocket. With the current mirrors, the angular resolution at high contrast is 20" and the half power diameter for images is 1.5' at 1.5 keV and 3.5'-4' at 7 keV. Plans to improve upon this performance are discussed.

The scientific instrumentation onboard the Italian satellite for x-ray astronomy (SAX) foresees x-ray imaging concentrators operating in the 0.1-10-keV energy range with a spatial resolution of 1 min of arc. The optics is composed of thirty confocal-nested very thin double-cone mirrors. To achieve good optical quality and to allow the construction of several concentrators at an acceptable cost, a replica technique by electroforming the mirrors from masters is used. This paper presents the results obtained from a set of electroformed mirrors mounted on a concentrator prototype.

High throughput grazing incidence mirrors have been fabricated from float glass using a new inexpensive technique. An array of twelve such mirrors including grazing angles from 3 to 15° has been fabricated and tested. Optical measurement of this array shows a line spread function of 6.3-min of arc FWHM with 90% energy enclosed within 13 min of arc. Three-mirror arrays are used to provide 1-D focusing for a diffuse extreme ultraviolet spectrometer. This paper presents the fabrication techniques and testing procedures used, as well as the mirror performance results.

A grazing incidence telescope has been developed for the x-ray astronomy satellite ROSAT including a verification model and a flight model. The telescope consists of a fourfold nested Wolter type I mirror assembly of 84-cm front aperture and 240-cm focal length. The verification model has been built and fully assembled to a telescope. Full aperture x-ray measurements performed in our 130-m long-beam facility are pesented and successfully compared with model predictions based on mirror metrology data. An energy independent angular resolution of 4-sec of arc half-energy width for the encircled point spread function and a mirror surface microroughness of <3 Å have been achieved. Metrology of the actual flight mirrors (although not yet assembled to a telescope) indicates an even better performance.

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°C and when a modest temperature gradient is imposed on the mirror.

Some simple formulas are derived to calculate the maximum effective area that can be obtained by Kirkpatrick-Baez, Wolter, and conical x-ray telescopes in those cases for which that area is limited by the focal length. Electroforming and epoxy replication techniques are reviewed, and the design and production technology chosen for the high throughput telescopes to be flown on the European X-Ray Spectroscopy Mission are presented.

For the past decade, we have been developing at Goddard conical grazing incidence mirrors in an effort to increase the sensitivity and resolution of astronomical observations in the iron K spectral band around 7 keV. Tightly packed conical foils give us the option of trading some imaging capability for light weight, large throughput, and low cost, all crucial requirements at the higher energies where grazing angles become very small. Nearing the completion of the broad band x-ray telescope for NASA's SHEAL II mission, we have decided important design and fabrication issues including reflector substrate material and supports and most techniques for reflector preparation, mirror assembly, and alignment. We will review the design, fabrication, status, and performance of our present mirrors. Future applications along with prospects for improved spatial resolution for these mirrors will be discussed.

High throughput X-ray telescopes require thin mirrors with super-smooth surfaces, typically with rms surface roughnesses of 5 A. The simple and inexpensive process of coating a suitable substrate with an acrylic lacquer to achieve a high quality surface finish is discussed. The surface roughnesses of several candidate materials, including rolled aluminium foil, polyester sheet, and diamond turned flats have been investigated. The surfaces, both before and after coating, have been examined by X-ray scattering measurements. Surface roughness in the spatial frequency range 2 - 70 mm-1 is attenuated by up to a factor of 7. Below 2 mm-1 the lacquer is unable to reduce the roughness and actually degrades the surface quality. The polyester surface has a roughness of 11 A rms in the spatial frequency range 18 - 70 mm-1 but suffers from large profile errors probably introduced by mounting the sample.

Replica technology was developed for manufacturing numerous low-cost grazing incidence x-ray mirrors for both laboratory and astrophysical experiments. About forty mirrors with apertures between 1.7 and 24 cm have so far been made. The results of tests both at optical and x-ray wavelengths indicate that replica optics is well suited for space and laboratory uses.

The major telescopes in this program are the one flown on the Einstein or HEAO-B satellite in 1978 and the one planned for the AXAF which should be launched in late 1995. The x-ray performance of the Einstein mirror is reviewed briefly, and its surface properties are inferred from a combination of its x-ray properties and the information available from the limited fabrication metrology of that era. The improvements necessary for satisfying the AXAF specification are summarized. Much of this technology already has been demonstrated in the TMA program, and this progress is reviewed.

We describe a rocket-borne X-ray Objective Grating Spectrograph designed to measure the spectra of cosmic sources in the 8 Å to 60 Å region with a spectral resolution of 100. Experience gained in fabricating the payload is discussed and preliminary performance data obtained in the laboratory and at the Marshall Space Flight Center are presented.

At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beam lines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally-induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the NSLS) and the effects of these figure errors on two classes of soft x-ray beam lines are presented.

New platinum-coated grazing incidence mirrors with low surface roughnesses have been developed to focus bending magnet radiation from the SSRL/SLAC SPEAR storage ring on the entrance slits of two Beam Line VIII grating monochromators. The first mirror in the toroidal grating monochromator (TGM) branch is a cooled SiC cylinder capable of absorbing synchrotron radiation power levels of up to 260 watts without excessive distortion. This mirror deflects the beam vertically through a 12° angle and focuses it sagitally on the TGM entrance slit plane. The second TGM optical element is a fused-silica spherical mirror with a large radius of curvature that deflects the beam vertically through an additional 12° and focuses it tangentially with 3/1 demagnification. The first mirror in our spherical grating branch is a 5°-vertically deflecting, cooled SiC toroid designed to focus tangentially on the monochromator entrance slits and sagitally on the exit slits. A 4°- deflecting fused silica mirror is used after the exit slits in each beam line to refocus on to the sample. For this application a thin cylinder is bent to approximate an ellipsoid. The mirrors are now installed at SSRL and performance measurements are planned. Qualitatively the focus of the TGM optics at the entrance slit plane appears very good. In this paper we discuss considerations leading to the choice of SiC for each of the two first mirrors. We present highlights of the development of these mirrors with some emphasis on SiC polishing techniques. In addition, the specialized metrology developed to produce the more difficult figure of the toroid will be described. Measured surface roughness and figure results will be presented.

Fabrication and testing of aspheric surfaces has always been a challenge for the optical industry. A mirror that is part of an ellipsoid is particularly difficult to manufacture when the axis of rotation does not intersect the surface and the radii change in two directions. Another difficulty in fabrication is the stringent specifications imposed by the nature of the application of the mirror. The physical requirements are for a 50 mm thick piece of fused silica with a 400 x 100 mm surface area platinum coated for use at grazing incidence. The mirror is used to image energy from a synchroton radiation source at one focus. The tolerances require a high figure accuracy, small slope deviations, and a minimum of surface roughness. The purpose of this paper is to present the methods used to fabricate and test such an elliptical mirror as described.

Following three X-ray astronomical satellites, HAKUCHO(1979), TENMA(1983), and GINGA(1987), we, Japanese X-ray astronomers, are planning an X-ray telescope mission called SXO in early 1990's. Main project is the X-ray spectroscopy with E/ΔE >20 at 6 keV and with spatial resolution of about 1 arc min. A thin foil mirror is considered to cover the energy range up to 10 keV with high throughput (>500 cm2 at 6 keV). A position sensitive gas scintillation proportional counter and some types of solid state detector are studied as the focal plane instruments.

Spacef light, stellar pointing telescopes require baffle systems to define the field of view and protect this observational area from stray and scattered light. In the case of near normal incidence telescope systems, the problem consists in controlling the stray/scattered radiation reaching the image plane when circular platesl, the primary and secondary mirrors, are the imaging elements. The case addressed in this paper is quite different in that it involves baffling two conical surfaces, i.e., the primary and secondary mirrors of a Wolter Type II telescope. A strategy is described for systematically moving through the telescope system and establishing criteria for placement of baffles. Calculations are given which determine the size and number of permitted baffles as a function of practical physical parameters. Clear options are given for the design of minimum baffle lengths to meet packaging constraints.

In Wolter type I grazing incidence telescopes, ghost images result whenever unreflected x rays or singly reflected x rays pass through the telescope and impinge on the focal plane. These ghost images degrade image quality and can be eliminated by appropriately positioned stops and baffles. However, conflicting demands can be placed on an aperture design by requirements for field of view, vignetting, and ghost image control. These problems are particularly severe for high energy x-ray telescopes which require very small grazing angles of incidence. We have developed and used analytical and numerical tools to perform parametric analyses of ghost image behavior and to obtain an aperture plate design capability that can be utilized to satisfy specific ghost image requirements.

The wavefront aberration polynomial and transverse ray aberration expansions will be derived for grazing incidence two-mirror Wolter telescopes including all paraboloid-hyperboloid and paraboloid-ellipsoid combinations. The reference sphere is determined with the help of the principal surface of the telescope, and the aberration polynomials will be given as functions of the coordinates of the ray intersection with the reference sphere. Third, and some of the fifth- and seventh-order aberration terms will be analyzed. Also, the well-known relationship between wavefront aberration polynomial and transverse ray aberration polynomials will be verified.

A preliminary interferometric procedure is described showing potential for obtaining surface figure error maps of grazing incidence optics at normal incidence. The latter are found in some laser resonator configurations, and in Wolter type X-ray optics. The procedure makes use of cylindrical wavefronts and error subtraction techniques over subapertures. The surface error maps obtained will provide critical information to opticians in the fabrication process.

An interferometric fringe scanner was used for the Technology Mirror Assembly (TMA) x-ray telescope, built by Perkin-Elmer as a technology demonstration for the Advanced X-Ray Astrophysics Facility (AXAF). We discuss advanced data processing features, implemented during a follow-on project to improve the mirror's midfrequency errors still further. Data processing techniques include interleaving of multiple scans, and optimal smoothing and interpolation of the interleaved data onto a uniform grid. We discuss the underlying mathematics behind the processes, the motivation in terms of recovering the highest possible spatial frequencies from the data, and some sample results.

We have developed a math model relating the measured parameters of the Technology Mirror Assembly (TMA) to its final performance. This scalar scattering model is valid for large and small amplitude features. It allows the user to specify power spectral densities and/or autocovariance functions within any spatial bandwidth, including microroughness. We present new TMA data in the bandwidth of ~0.1-1000 mm-1, predicting performance and comparing them with x-ray test data. We also account for assembly, alignment, and particulate contamination. Finally, we comment on improved performance expected after repolishing.

In the context of developing high reflectivity coatings for X ray telescopes highly polished Zerodur and BK 7 glass flats have been coated with either gold or iridium. Grazing incidence reflectivity measurements at various X-ray energies are reported and compared with standard theory prediction.

We report measurements of the extreme ultraviolet reflectivity of gold from 44 to 920Å at grazing incidence. Gold was deposited using vacuum evaporation and electroplating on substrates of glass and polished nickel respectively. We also present measurements of the extreme ultraviolet reflectivity of electroless nickel in the same wavelength region, where one of the polished nickel substrates was used as a sample. Derived optical constants for evaporated and electroplated gold and electroless nickel are presented. Additional studies of the effects of various contaminants on the EUV reflectivity are also reported. The variations of the optical constants are discussed in terms of density variations, surface roughness and contamination effects. These results are reported as part of studies for the Extreme Ultraviolet Explorer satellite program to determine acceptance criteria for the EUV optics, contamination budgets and calibration plans.

The grazing incidence reflectance of silicon carbide films produced by plasma-assisted chemical vapor deposition has been evaluated in the spectral region from 256 to 1216 Å. The results show that reflectivities higher than conventional coatings can be obtained on coatings deposited both on silicon wafers and quartz substrates. Potential application of silicon carbide films for EUV astronomical instruments will be discussed.

The prospects for imaging x rays at energies from 10 to 40 keV with grazing incidence optics are explored. The scientific rationale and existing laboratory measurements are reviewed. Measurements of reflectivity using possible mirror materials are described. Iridium-coated float glass gives an improved performance over gold by the factor predicted by theory but both had a lower absolute level. This may be due to a lower density of the thin metal layer caused by the deposition method. The reflectivity of a sample of iridium-coated float glass was measured at small grazing angles (25-5 min of arc) at energies of 8, 17, and 26 keV. High reflectivity (>50%) was seen out to angles of 33, 16, and 11 min of arc, respectively. These are close to the theoretical values. A design for a high energy imaging telescope of the Explorer class is described.

We have performed in situ oxide contamination and XUV reflectance vs angle of incidence studies on fresh aluminum and silicon films evaporated in an ultrahigh vacuum system (base pressure 2 X 10-10 Torr). Our ellipsometric measurements indicate that a surface monolayer of oxide forms on aluminum (1 h at 2 X 10-8-Torr oxygen) and silicon (1 h at 10-7-Torr oxygen). The monolayer formation time is inversely proportional to oxygen pressure. Our reflectance vs angle of incidence measurements at 58.4-nm wavelength indicate that unoxidized aluminum and silicon coatings can be used as multifacet retroreflectors with net retroreflectances in excess of 75% for aluminum and 50% for silicon.

Contamination assessment for space optical systems requires an understanding of the sensitivity of component performance, e.g. mirror reflectance, to materials deposited on the mirror surface. In a previous study, the sensitivity of typical normal incidence mirror coatings to surface deposits of generic hydrocarbons was reported. Recent activity in the development of grazing incidence telescopes for extreme ultraviolet space astronomy has stimulated the need for a similar assessment in the spectral region extending from approximately 100Å to 1000Å . The model used for analysis treats the contamination layer as a continuous thin film deposited on the mirror surface. The mirror surfaces selected for this study are opaque vacuum deposited gold and the uncoated and polished Zerodur. Scatter caused by film irregularities or particulates are not included in this assessment. Parametric evaluations at 100Å , 500Å, and 1000Å determine the sensitivity of mirror reflectance to a range of optical constants selected for the generic contaminants. This sensitivity analysis combined with the limited amount of optical data in the EUV for hydrocarbons, is used to select representative optical constants for the three wavelength regions. Reflectance versus contamination layer thickness curves are then calculated and used to determine critical thickness limits based on allowable reflectance change. Initial observations indicate that thickness limits will be highly dependent on the real part of the complex index of refraction of the contaminant film being < 1.0. Preliminary laboratory measurements of samples contaminated with some commonly encountered hydrocarbons confirm trends indicated in the analytical studies.