The mirrors for the Einstein Observatory represent a substantial advance in the state of the art x-ray optics, and have been tested more thoroughly than previous telescopes. The image is characterized by a narrow, wavelength independent core, and broad energy dependent wings. The width of the core is about that expected from mechanical and visible light measurements taken during fabrication and assembly. The wings of the response function are caused by microscopic surface scattering, but only a qualitative understanding of this process exists. Improvement in surface texture to reduce the wide angle scatter is the most urgent task in the development of large x-ray optics. The mirrors have survived the experiment integration period and launch, and are performing in orbit as they performed upon the ground.

A few years ago, a program for development of space instrumentation for soft X-ray astronomy has been initiated at MPI. It includes the design and fabrication of imaging X-ray telescopes which is done in close cooperation with Carl Zeiss/W.-Germany. After an extensive survey of various materials and polishing techniques applied to flat mirror samples, first paraboloidal mirrors were built each having a frontal diameter of 15 cm and a length of 1 m. A bundle of 12 such mirrors was flown twice on Aries rockets. The next step was the design and production of a Wolter type I telescope compatible with being used on a Skylark or Black Brant rocket. Actually, three of these telescopes were built. The mirror material is aluminium, plated with kanigen and coated with a reflecting gold layer. Each has an aperture diameter of 32 cm and a focal length of 143 cm. They were tested in MPI's short beam X-ray test facility and show nominal reflectivity, on-axis angular resolution of 5 arc sec (FWHM), and extraordinary low surface scattering of 6 I at 1 keV. Currently, a nested 80 cm diameter Wolter type I telescope of 240 cm focal length is being designed. The mirrors will be made from zerodur, a glass ceramic which has excellent thermal properties, low residual mechanical stresses as opposed to aluminium, and the ability to be polished to high surface finish. X-ray tests of the telescope will be performed in MPI's long beam (130 m) facility just under construction.

The following report summarizes our experiences in attempting to make Wolter Type I X-ray telescope mirrors using the diamond-turning facilities at the Oak Ridge Y-12 Laboratory.

A rocket-borne Wolter Type I X-ray telescope having a focal length of 2.3m, an entrance aperture of 66cm and a geometrical area of 380cm2 is nearing completion. The telescope mirrors are formed by diamond turning their figures into forged aluminum substrates of 5083 alloy. These diamond-turned substrates are subsequently plated with a thin coating of electroless nickel and polished to obtain the final X-ray reflecting surfaces. Details of the rocket payload, the X-ray telescope, its calculated reponse and the experience gained in selecting the mirror substrate alloy are discussed and the current status of the telescope is reviewed.

The design, fabrication and performance of two Wolter-Schwarzschild grazing incidence optics are described. Both telescopes have been figured by single point diamond turning and have achieved better than 15 arcsecond on-axis imaging. The telescope for the stellar spectrometer is an f/10 Type II system with an effective area of 225 cm2 at 250 Å and 300 cm2 at 500 X. The primary has a maximum diameter of 38 cm and was fabricated in three elements. The copper-plated aluminum substrate was diamond turned; following nickel plating, the surface was polished and coated with evaporated gold. The performance during a sounding rocket flight is discussed. The prototype telescope for the Extreme Ultraviolet Explorer is an f/1.24 Type I system with an effective field of view of 5.0° diameter. The telescope has a maximum diameter of 40 cm and was fabricated as a single element. The aluminum substrate is to be diamond turned; the nickel plated surface will be polished and electroplated with gold. The design choice and defocussing optimisation aimed at maximizing the field of view and number of image pixels is examined.

High spatial resolution X-ray microscopes are being developed for autoradiography of laser fusion reactions and for relay optics, linking an X-ray telescope to focal plane instrumentation such as a photoelectric image detector or a spectrometer. The grazing-incidence optics consist of confocal axisymmetric ellipsoid and hyperboloid pairs. In both fields of application, high spatial resolution is required. The achievement of high spatial resolution involves meeting exacting tolerances on the figure and smoothness of the reflecting surfaces. The performance of a set of optics with 10X magnification has been evaluated in laboratory X-ray testing. The tests consist primarily of imaging various targets illuminated with soft X-rays, and recording the images on photographic film. In this paper we present the first results of the testing which show that resolu-tion of 1-2 Am has been achieved and that the reflection efficiency of the instrument is nearly 100 percent. We include information on the depth of focus and field of view.

The Advanced X-ray Astrophysics Facility (AXAF) is to be a free flying national X-ray observatory that is Shuttle-launched (in mid-1987), maintainable on-orbit, and retrievable. The design lifetime is > 10 years. The AXAF is conceived as an X-ray telescope with 6 nested Wolter type I mirrors (maximum aperture of 1.2m), a focal length of 10m, and interchangeable and replaceable focal plane instruments. The optics will provide 0.5 arcsecond imagery over a several arcminute field and somewhat reduced resolution over 1 degree in the X-ray band from 0.1 to 8 keV. The performance requirements and design of the facility will be discused and comparisons made with present X-ray observatories. The scientific objectives of the AXAF will also be discussed briefly.

The concept of the Large Area Modular Array of Reflectors (LAMAR) is based upon satisfying two important requirements in X-ray astronomy, large collecting area and moderately good or better angular resolution for avoiding source confusion and imaging source fields. An array of identical modules, each consisting of an imaging X-ray telescope of a convenient size and suitable focal length plus an efficient position sensitive detector, are co-aligned only to within ordinary mechanical tolerances to fill any available aperture. The LAMAR provides the same sensitivity and signal to noise in imaging as a single large telescope having the same area and angular resolution but is a great deal less costly to develop, construct, and integrate into a space mission. Furthermore, its modular nature allows for an evolutionary development from a modest size array on Spacelab to a shuttle launched free flyer which the LAMAR is increased in effective area and improved with respect to its angular resolution as funding and technical developments are available. The LAMAR module must provide good angular resolution, be relatively low in cost, and be capable of being produced in substantial numbers at a fast rate of production. At the present time, we can identify three manufacturing methods that show great promise with respect to these requirements, mechanical alignment of slightly curved nested plates of float glass, machining of paraboloid/hyperboid cylinders and replication of highly polished and accurate masters. Detector development has also been encouraging from the standpoint of continually improving spatial and spectral resolution.

An X-ray astronomical observatory called the LAMAR, utilizing multiple grazing incidence X-ray telescopes for high sensitivity observations, is being considered by NASA for a Spacelab facility. A LAMAR utilizing Wolter Type I X-ray optics figured by diamond turning is described and its performance compared with a similar facility involving X-ray optics of Kirkpatrick-Baez design. Effective areas, imaging properties and relative sensitivities of these two LAMAR facilities have been calculated with the aid of computer ray tracing codes. We conclude that the two optical designs provide comparable effective areas. Therefore, the ability to achieve the highest possible angular resolution within cost constraints will be decisive in the choice of X-ray optics for the LAMAR.

A detailed description of x-ray telescopes based on the optical principles of lobster eyes is to be published elsewhere shortly (Angel 1979). We give here a summary of the optical principle and discuss possible applications.

A method of obtaining a parabolic reflecting surface from thin float glass plate is presented including design, analysis, and hardware test results. By applying predetermined moments to each end uniformly along the leading and trailing edges, and controlling the relative end displacement, precise focussing mirrors can be produced inexpensively. The present method is an improvement to the Underwood method to bend a glass strip into a parabolic optical element. Better results are obtained by including the relative end displacement in addition to the two moments in the slope error minimization. Comparison of the results between the improved method and Underwood's are provided. This method has been used to bend a flat plate, with a width comparable to the length, into a parabolic surface. A finite element model based on plate theory is employed to examine the anticlastic effect of a bending plate and the non-uniformity of the applied moments. The design and construction of prototype Kirkpatrick-Baez mirror elements from commercial float glass are described in detail. Correlation of the image resolution between the analytic prediction and the test results is provided. The test results indicate that a mirror system with angular resolution less than one arcminute can be obtained. This method allows production of low cost mirror modules for the LAMAR X-Ray Telescope with improved resolution compared to prior methods.

A program of solar X-ray astronomy using grazing incidence optics has culminated in X-ray images of the corona having one arc second spatial resolution. These images have demonstrated that in general X-ray optics can be fabricated to their specifications and can provide the level of resolution for which they are designed. Several aspects of these programs relating to the performance of X-ray optics in regard to resolution, including the point response function, the variation of resolution with off-axis position and the recognition that nearly all solar X-ray images have been film limited, are discussed. By extending the experience gained on this and other programs it is clearly possible to design and fabricate X-ray optics with sub-arc second resolution. The performance required to meet the scientific objective s for the remainder of the century are discussed in relation to AXIO, an Advanced X-Ray Imaging Observatory for solar observations which is proposed for flight on the space shuttle. Several configurations of AXIO are described, each of which would be a major step in the quest for ultra-high resolution observations.

Important stages in the production of X-ray telescope mirrors are the selection of the mirror material and the blank manufacturing method, the machining of the blank to form, the overcoating of some metal substrates with more polishable materials such as electroless nickel and the lapping and polishing. Measurements of surface figure and quality are necessary at the various fabrication stages to ensure that the mirror will be made to the specified tolerances. Production costs rise sharply the higher the specification so that the X-ray optical design theory Must be sufficiently well developed to enable manufacturing tolerances to be calculated to ensure both that the specified tolerances can be met and that they are not more stringent than necessary.

Improvements in vacuum deposition technology have made it possible to produce structures in whichotwo materials are arranged in alternating layers of uniform thickness. These layers may be as thin as 5A. Such structures act as Bragg diffractors or "artificial crystals" for x-rays - alternatively they may be viewed as multilayer interference coatings. These devices have many potential applications in x-ray and euv astronomy. Through the use of a dynamical theory, we show how the properties of LSM's depend on the layer materials and thicknesses and how these properties may be "tailored" for specific applications. Laboratory results at various x-ray wavelengths are presented. Finally, specific x-ray astronomy applications in the areas of spectroscopy, imaging, polarimetry and laboratory calibration are discussed.

The X-Ray Telescope High Resolution Mirror Assembly (HRMA) designed by American Science and Engineering (AS&E) and Smithsonian Institution Astrophysical Observatory (SAO) was developed, manufactured, assembled, and tested by Perkin-Elmer under contract to AS&E. This paper describes each phase of its fabrication and testing except for the surface roughness measurement and the optical coating which are discussed in separate papers. Particular emphasis is placed on the achievement of the circumferential variation in slope, A (A R), and its measurement during the loose-abrasive grinding operations. Also discussed, at length, are the optical figuring, surface smoothing via submerged polishing, and figure measurement using a semi-automated fringe scanner and modular interferogram analysis computer programs. The optical testing used during the assembly operation is reviewed and the test equipment and test methods are described. The pertinent specifications of the High Resolution Mirror Assembly and achievements of the program are summarized.

Analysis of the Wolter type substrates in terms of optical coating parameters is discussed. This analysis shows that, in general, the variations in coating thickness can be reduced to negligible proportions by properly using aperture masks and by rotating and translating Wolter type substrates. Results achieved in coating the optical elements of the HEAO-2 X-ray telescope are discussed in view of the analysis.

X-ray reflectivity and surface scattering measurements between 8.34 Å and 44.8 Å have been performed on three geometrically identical 32 cm diameter Wolter type I telescopes of high surface finish. The telescopes are made from aluminium, plated with kanigen and coated with a reflecting gold layer. Based on the results from three telescopes, a tendency for a correlation between reflectivity and surface scattering level is observed. The reflectivity data are compared and found to agree with theoretically expected values.

Arguments leading to the tentative conclusion that production and measurement techniques developed for low scatter optical surfaces should be directly applicable to low scatter x-ray optics are briefly reviewed, and some of the more useful methods for making and testing high quality optical surfaces are discussed.

The measuring equipment has been designed and constructed for testing the directrix of Wolter-type telescope mirrors. Due to the high accuracy required its design is based on the principles of industrial metrology and has been adapted to the specific problems encountered with the Wolter-type tlescope. Measurement is carried out by an inductive probe which, as a result of its low contact pressure, can also be used on polished surfaces. The meridian curve is compared with a test glass of optimum spherical surface so that deviations in the order of 1/100 Tim can be detected. A digital scale is used to localize the contact points measured in mirror axis direction. In the final version, the two measured values obtained are fed into a calculator for nominal/actual comparision. The differences obtained between directrix and test glass are compared with the nominal values already stored in the calculator and the resulting deviations then recorded on an analog recorder.

An interferometer is described which allows in situ assessment and alignment of any image forming grazing incidence optic. The fringes are localized in the exit pupil of the X-ray telescope or microscope (either under manufacture or during use) and mark out in units of one wavelength the departure of an actual convergent image forming wavefront from the Gaussian reference sphere. In one variation of the principle the interferometer is comprised of one grazing incidence reflecting surface only. Visible interferograms are shown for two current applications.

A method of measuring the surface roughness of aspheric surfaces has been developed. This method combines surface replication techniques and FECO (fringes of equal chromatic order) interferometry to avoid many of the practical ligtitations of the more conventional techniques. A series of measurements was taken of a 30A calibration sample ovpr a long period of time and gave an average measured surface roughness by replication of 33A ±8A.

The European X-ray observatory EXOSAT, to be launched in 1981, will carry two Wolter I type X-ray telescopes, each having a geometric area of about 100 cm2. Due to severe mass constraint of only 7 kg per mirror assembly, imposed by the spacecraft, an epoxy replication technique has been used for the mirror fabrication. A description is given of the manuacturing techniques employed to produce the glass master, the beryllium substrate and the final replica mirror shells. Special measurement and control techniques were used during the replica optics manufacturing. These techniques and same of the results are discussed. Finally a description of the integration and alignment procedure and performance figures in optical light are also given.

A research programme, with the objective to manufacture optical surfaces with a very low X-ray scattering level by means of the epoxy replica technique, has been carried out. X-ray scattering measurements at 44, 13.3 and 8.3 X on a variety of optical surfaces down to a r.m.s. roughness of about 2.0 X, have been performed and results are presented. The dependence of the measured X-ray scattering level on various replica production parameters, i.e.: master surface roughness, epoxy curing temperature, epoxy thickness and substrate surface roughness are discussed.

This paper discusses the relationship between x-ray mirror scattering and surface topography using vector electromagnetic scattering theory. The results relate the angular distribution of the scattered intensity to various surface-finish parameters which can, in principle, be determined independently; for example, by x-ray scattering in other geometries, visible-light scattering, or stylus measurements. The key role of spatial band-width limits in such parameters is emphasized. General results are described and illustrated by a discussion of the scattering from isotropically rough surfaces, measured in both a point-detector and in a line-detector geometry. Recent experimental results are then interpreted in terms of the surface-tension model of surface roughness, which predicts a hyperbolic scattering in the line-detector geometry. The present results are offered as a subject for further experimental investigation, a mechanism for predicting the scattering from a given surface, and as a rationale for specifying surface finish in terms of system performance.

Very high spatial frequency irregularities with small amplitude on a polished surface that usually cause wide-angle scattering in conventional optical systems produce narrow-angle scattering in X-ray systems. Yet, even this small amount of scattering degrades the imaging properties of X-ray systems. Statistical surface perturbations and their effects on X-ray image quality are discussed. A model of surface roughness that is reasonably consistent with surface-profile measurements and visible-scatter-profile measurement is discussed. This model is then used to evaluate the image profile of an X-ray system.

The effects of misalignment and surface deformations on the image quality of a grazing incidence telescope with six nested subsystems are investigated. The axial rms-spot size serves as a measure for the image quality. The surface deformations are simulated by ellipsoidal and sinusoidal deviations from the ideal surface. Misalignments are tilts, decenters, and despaces of the individual elements. The effects of each type of defect are analyzed in a single two-element system. The full nested system is then analyzed in the presence of all possible defects on all 12 elements, whereby the magnitude of the defects is randomized within a given upper limit.

A two-mirror grazing-incidence telescope having a non-parabolic primary, and designed to be free of spherical aberration has been investigated. A method for determining the second surface equation is described, when the surface equation for one mirror is given. Application to grazing incidence systems such as used in X-ray and planned for EUV astronomy is discussed. Of special interest is the design of a secondary mirror when the hyperboloid of a conventional Wolter type I system is taken as the primary.

We have examined the claim that grazing incidence telescopes having surfaces described by generalized equations have image characteristics superior to those of the paraboloid-hyperboloid and Wolter-Schwarzschild configurations. With emphasis on specific applications in solar and cosmic X-ray/EUV astronomy, raytracing has shown that in many cases there is no advantage in the polynomial design, and in those cases where advantages are theoretically to be expected, the advantages are outweighed by practical considerations.

Prior to the development of imaging X-ray optics at MPI two short beam X-ray test facilities have been set up and are operational since 1976. They consist of high power X-ray sources, 15 m and 10 m, respectively, long vacuum tubes and instrument chambers equipped with an optical bench and high precision manipulator systems for positioning of the test specimen. By means of the facilities various investigations have been performed comprising measurements of X-ray surface scattering from polished flat mirror samples and imaging telescopes, testing of imaging X-ray detectors and efficiency measurements of X-ray transmission gratings. For testing and calibrating an 80 cm diameter Wolter telescope currently under development at MPI the 15 m facility will be extended to 130 m beginning its operation by the beginning of 1980.

A position-sensitive proportional counter capable of imaging X-rays (0.1-3 keV) over a 10 cm x 10 cm aperture has been constructed. Positioning is obtained by sensing the sig-nals induced by an X-ray event on the two orthogonal sets of cathode wires. Each cathode is divided into a series of cathode strips, each 0.5 cm wide. An X-ray event induces signals on several adjacent strips. Signals from each cathode strip are amplified separately and then added in an equally weighted and an unequally weighted summing amplifier. The position in each direction is obtained by dividing the output of the unequally weighted summer by that of the equally weighted summer. At 0.94 keV, the accuracy of the position sensing is 190 1.1m. At the same energy, the energy resolution is -65% (FWHM). The proportional counter system is currently being incorporated into a sounding rocket payload having metal mirror optics, which is being constructed by the X-ray astronomy group at the California Institute of Technology.

Future shuttle launched telescopes for X-ray astronomy will require a wide range of instruments to exploit the potential scientific return. A Charge Coupled Device (CCD) offers the unique possibility of simultaneously fulfilling requirements for high angular resolution (1/4 arcsec -- 12 µm), high quantum efficiency (> 50% from 1 to 7 keV), and moderate spectral resolution (E/A E > 5 E). We have verified detection and localization of single X-ray photons. Our studies have established many of the requirements for application to the Advanced X-ray Astronomy Facility (AXAF) telescope: the device must be cooled, must be readout in no more than 0.3 sec, and must have a thickness of at least 50 p.m both to detect 7 keV X-rays efficiently and to provide a clear discriminant against cosmic rays and charged particles. We use an algorithm to recognize event existence and then sum charge from several adjacent pixels to obtain the position centroid location and to optimize the energy resolution. With some technological advances, CCD's might also replace separate low angular resolution instruments currently used to obtain a wide energy range (0.1-10 keV) and a large field of view (1°).

The program of solar physics missions for the 1980's will include earth-orbiting and solar-orbiting free flying satellites as well as Shuttle sorties carrying large facility instruments and smaller PI-class investigations. Individual missions will have specific, unifying objectives in contrast to the exploratory nature of missions of the 1960's and 70's. The Solar Maximum Mission will study solar flares in 1980 and 1981. The International Solar Polar Mission will swing past Jupiter and traverse the Sun's polar caps in 1986, measuring the high-latitude solar wind. Three of the early Shuttle flights will carry PI-class solar experiments, and the Solar Optical Telescope, to fly in about 1984, will provide extremely high spatial resolution of solar features. Possible future missions include the Solar Cycle and Dynamics Mission to study the Sun's magnetic cycle, and the Solar Probe, which will pass within 4 solar radii of the Sun's surface.

The objectives of the UVSP experiment are to study solar ultraviolet radiations, particularly from flares and active regions, and to measure constituents in the terrestrial atmosphere by the extinction of sunlight at satellite dawn and dusk. The instrument is designed to observe the Sun at a variety of spectral and spatial resolutions in the range from 1150 to 3600 Å. A Gregorian telescope with effective focal length of 1.8 m is used to feed a 1 m Ebert-Fastie spectrometer. A polarimeter containing rotatable magnesium fluoride waveplates is included behind the spectrometer entrance slit and will allow all four Stokes parameters to be determined. Velocities on the Sun can also be measured. The instrument is controlled by a computer which can interact with the data stream to modify the observing program. The observing modes, including rasters, spectral scans, velocity measurements, and polarimetry, are also Aescribed along with plans for mission operations, data handling, and analysis of the observations.

We describe a new sounding rocket payload that has been developed for X-ray spectro-scopic studies of the Solar Corona. The instrument incorporates a grazing incidence Row-land mounted grating spectrograph and an extreme off axis paraboloic sector feed system to isolate regions of the sun of order 1 x 10 arc seconds in size. The focal surface of the spectrograph is shared by photographic and photoelectric detection systems, with the latter serving as a part of the rocket pointing system control loop. Fabrication and alignment of the optical system is based on high precision machining and mechanical metrology techniques. The spectrograph covers the 10 to 50 Angstrom interval and has a resolution of 16 milliangstroms in the current version. Modifications planned for future flights will improve the resolution to around 5 milliangstroms, permitting line widths to be measured. The instrument has been developed under the NASA Contract NAS2-9181 and the Lockheed Independent Research Program.

The telescope mirror for the X-Ray Spectrograph Spectrometer Telescope System is a sixty degree sector of an extreme off-axis paraboloid of revolution. It was designed fo focus a coronal region 1 by 10 arc seconds in size on the entrance slit of the spectrometer after reflection from the gold surface at a glancing angle of about 2.9 degrees. This paper discusses the design, manufacture, and metrology of the mirror, the methods of precision mechanical metrology used to focus the system, the mounting system which serves to locate the mirror and has proven itself through several vibration tests, and the results of reflection efficiency measurements at 8 and 44 Angstroms, and alignment tolerances and ray trace analysis of the effects of misalignment. The mirror was developed under NASA Contract NAS2-9181.

The CRLS-229 Solar X-ray Spectrometer/Spectroheliograph payload was launched in the solar pointed section of the U. S. Air Force Space Test Program P78-1 satellite on 24 February 1979. The payload consists of two instruments furnished by The Aerospace Corporation, known as SOLEX and MONEX, and two instruments furnished by the Naval Research Laboratory. Thp SOLEX instrument provides maps of the sun in individual x-ray spectral lines and also obtains spectra in the 3 to 25 Å wavelength interval while pointed at a specific solar region. The basic SOLEX hardware consists of two multigrid collimators with 20 arc sec and 60 arc sec spatial resolution, RAP and ADP scanning high resolution Bragg crystals, and a proportional counter and an array of channel electron multipliers as detectors. The MONEX experiment, consisting of two proportional counters, provides full disk solar x-ray intensity with moderate spectral resolution and excellent temporal resolution in the 1 to 140 keV energy interval. Examples of data from the Spectrometer/Spectroheliograph are presented.