Results of a battery of X-ray tests on the AXAF Verification Engineering Test Article (VETA) X-ray optics which were performed shortly after their fabrication are presented. The optics, a paraboloid, and a hyperboloid in the classic Wolter-1 configuration are the outer mirrors of what is now the AXAF-I mission. The optical elements are each about 1.2 m in diameter and 0.8 m long. The principal proof that the optics met their specification was to demonstrate that the angular resolution was at least 0.5 arcsec. The final result was an angular resolution smaller than 0.25 arcsec.

The design of the mount for the outer pair of Advanced X-ray Astrophysics Facility (AXAF) optics for the Verification Engineering Test Article-I (VETA-I) hardware for initial performance test was a challenging task. Extensive analysis of mirror strains induced by the mounting hardware during assembly was required to ensure that the imaging tests at Marshall Space Flight Center would be successful. This paper describes the techniques used to design the mirror cell to insure that the x-ray tests would accurately represent the quality of the mirror surfaces and minimize errors due to the effects of mounting and gravity. The measures taken to compensate for the large gravity effects during testing are discussed in detail.

The Verification Engineering Test Article-I (VETA-I) was an assembly which held the largest pair of Advanced X-ray Astrophysics Facility (AXAF) mirror elements (1.2 meter diameter). The X-ray performance of this mirror pair, as held in the VETA-I, was tested in September 1991 at the Marshall Space Flight Center (MSFC) X-ray Calibration Facility (XRCF). Alignment of the optical elements to each other, and to the test facility axis, was required in order to execute the test. This paper will describe the VETA-I, its alignment requirements, and the hardware and procedures used to bring it into alignment.

Intensity distribution measurements of the X-ray source for the AXAF VETA-I mirror test are reported. During the VETA-I test, microscope pictures were taken for each used anode immediately after it was brought out of the source chamber. The source sizes and the intensity distribution structures are shown. They are compared and shown to agree with the results from pinhole camera measurements. It is demonstrated that under operating conditions characteristic of the VETA-I test, all the source sizes have an FWHM of less than 0.45 mm. For a source of this size at 528 m away, the angular size to VETA is less than 0.17 arcsec, which is small compared to the on-ground VETA angular resolution. These results were crucial for VETA data analysis and for obtaining the on-ground and predicted in-orbit VETA point response function.

The alignment and X-ray imaging performance of the Advanced X-ray Astrophysics Facility (AXAF) Verification Engineering Test Article-I(VETA-I) was measured by the VETA-I X-Ray Detection System (VXDS). The VXDS was based on the X-ray detection system utilized in the AXAF Technology Mirror Assembly (TMA) program, upgraded to meet the more stringent requirements of the VETA-I test program. The VXDS includes two types of X-ray detectors: (1) a High Resolution Imager (HRI) which provides X-ray imaging capabilities; and (2) sealed and flow proportional counters which, in conjunction with apertures of various types and precision translation stages, provide the most accurate measurement of VETA-I performance. Herein we give an overview of the VXDS hardware including X-ray detectors, translation stages, apertures, proportional counters and flow counter gas supply system and associated electronics. We also describe the installation of the VXDS into the Marshall Space Flight Central (MSFC) X-Ray Calibration Facility (XRCF). We discuss in detail the design and performance of those elements of the VXDS which have not been discussed elsewhere; translation systems, flow counter gas supply system, apertures and thermal monitoring system.

We describe the X-ray Data Acquisition and Control System (XDACS) used together with the X-ray Detection System (XDS) to characterize the X-ray image during testing of the AXAF P1/H1 mirror pair at the MSFC X-ray Calibration Facility. A variety of X-ray data were acquired, analyzed and archived during the testing including: mirror alignment, encircled energy, effective area, point spread function, system housekeeping and proportional counter window uniformity data. The system architecture is presented with emphasis placed on key features that include a layered UNIX tool approach, dedicated subsystem controllers, real-time X-window displays, flexibility in combining tools, network connectivity and system extensibility. The VETA test data archive is also described.

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters, correcting for the reflectivity of the mirror and convolving with the detector response.

The AXAF VETA-I mirror encircled energy was measured with a series of apertures and two flow gas proportional counters at five X-ray energies ranging from 0.28 to 2.3 keV. The proportional counter has a thin plastic window with an opaque wire mesh supporting grid. Depending on the counter position, this mesh can cause the X-ray transmission to vary as much as +/- 9 percent, which directly translates into an error in the encircled energy. In order to correct this wire mesh effect, window scan measurements were made, in which the counter was scanned in both horizontal (Y) and vertical (Z) directions with the aperture fixed. Post VETA measurement of the VXDS setup were made to determine the exact geometry and position of the mesh grid. Computer models of the window mesh were developed to simulate the X-ray transmission based on this measurement. The window scan data were fitted to such mesh models and corrections were made. After this study, the mesh effect was well understood and the final results of the encircled energy were obtained with an uncertainty of less than 0.8 percent.

Measurements of the VETA encircled energies have been performed at 5 energies within 16 radii ranging from 0.05 to 200 arcseconds. We report here on the analysis of the accuracy of those measurements. A common 'error tree' structure applies, and we present representative numbers for the larger terms. At 0.277, 1.5, and 2.07 keV, and for radii of 3 arcsec and larger, our measurements have estimated 1 sigma errors of 0.6 to 1.5 percent. Effects of measurement statistics and of the VETA test mount limit the accuracy at smaller angles, and modulation by the counter window support structure together with the imperfect position repeatability limit the accuracy for the 0.93 and 2.3 keV energies. We expect to mitigate these limitations when calibrating the complete AXAF flight mirror assembly.

Initial core scan data of the VETA-1 X-ray mirror proved disappointing, showing considerable unpredicted image structure and poor measured FWHM. 2-D core scans were performed, providing important insight into the nature of the distortion. Image deconvolutions using a raytraced model PSF was performed successfully to reinforce our conclusion regarding the origin of the astigmatism. A mechanical correction was made to the optical structure, and the minor was tested successfully (FWHM 0.22 arcsec) as a result.

We employ the X-ray measurements of the VETA-I taken at the X-Ray Calibration Facility (XRCF) of the Marshall Space Flight Center (MSFC) to extract information about the surface finish quality of the outermost pair of AXAF mirrors. The particular measurements we consider are 1D scans of the core of the point response function (PRF) (FWHM scans), the encircled energy as a function of radius, and 1D scans of the wings of the PRF. We discuss briefly our raytrace model which incorporates the numerous effects present in the VETA-I test, such as the finite source distance, the size and shape of the X-ray source, the residual gravitational distortions of the optic, the despace of the VETA-I, and particulate contamination. We show how the data constrain the amplitude of mirror surface deviations for spatial frequencies greater than about 0.1/mm. Constraints on the average amplitude of circumferential slope errors are derived as well.

Relative surface brightness data from the VETA-1 test displayed an energy dependence which was inconsistent with models which assume surface roughness is the only cause of scattering. A means of separating an in-plane component of scattering caused by surface roughness from an azimuthally symmetric component, which is expected from dust, was afforded by images taken while only single quarters of the mirror surface were exposed. In this case, in-plane scattered X-rays should populate only opposing 90 deg azimuthal quadrants of an image centered on the focal point. As such, this approach is a novel, high sensitivity test for detecting extremely small (about 10 exp -5) fractional dust coverage on X-ray optics. Comparison of in-plane and out-of-plane quadrants in these tests indicated that most of the scattered data were azimuthally symmetric, and that the symmetric component was enhanced at lower energies. Both results support a model which invokes the wing scan results with a combination of dust and surface roughness induced scattering. The extent to which parameters such as the mirror surface roughness, dust size distribution, spatial distribution, and density may be determined using this approach is also discussed.

X-ray testing of the AXAF outer mirror pairs, in the VETA-1 configuration, reveals a point spread function (PSF) with unexpectedly large wings at low energies. Although the angular dependence in the wings of the PSF is close to that expected for diffractive scattering from surface roughness, the energy dependence differs substantially. Analyses of the observed X-ray PSF, images near ring focus, and single-quadrant images at conjugate focus suggest that the excess scattering observed at low X-ray energies results from diffractive scattering by relatively small grains (as small as a few tenths micrometer in radius). We develop a simple model for the contribution of scattering by particulates to the PSF. Merging this model with that for scattering by surface roughness, we fit the combined model to the observed energy-dependent PSF, in order to estimate parameters and associated uncertainties characterizing the grain-size distribution and the surface-roughness power spectral density. In particular, we find that the fractional coverage of the mirrors by particulates is approximately 1 x 10 exp -4 (for grain radii between 0.1 and 10 microns), and that the rms surface-roughness is approximately 0.7 nm (for spatial frequencies between 1/mm and 1000/mm).

The study measures the X-ray reflectivity of the AXAF VETA-I optic and compares it with theoretical predictions. Measurements made at energies of 0.28, 0.9, 1.5, 2.1, and 2.3 keV are compared with predictions based on ray trace calculations. Results on the variation of the reflectivity with energy as well as the absolute value of the reflectivity are presented. A synchrotron reflectivity measurement with a high-energy resolution over the range 0.26 to 1.8 keV on a flat Zerodur sample is also reported. Evidence is found for contamination of the flat by a thin layer of carbon on the surface, and the possibility of alteration of the surface composition of the VETA-I mirror, perhaps by the polishing technique. The overall agreement between the measured and calculated effective area of VETA-I is between 2.6 and 10 percent. Measurements at individual energies deviate from the best-fitting calculation to 0.3 to 0.8 percent, averaging 0.6 percent at energies below the high energy cutoff of the mirror reflectivity, and are as high as 20.7 percent at the cutoff.

By the end of this decade, the two missions comprising the Advanced X-ray Astrophysics Facility (AXAF) will become the X-ray component of NASA's Great Observatories. In order to meet some of the ambitious scientific objectives, the AXAF team plans to calibrate the telescopes and instruments to an accuracy of a few percent. Particulate and molecular contamination potentially limit this precision, because they would likely change between ground calibration and orbital operation. To avoid this requires careful control over procedures affecting the coated optical surfaces, to ensure that neither particulate nor molecular contamination compromise the calibration. In particular, the fractional areal coverage by particulates or condensed droplets must be less than 0.005 projected onto the aperture plane; the thickness of any molecular film must be less than a few tens of angstrom.

We are developing a system to calibrate reflectances of witness coupons to the AXAF flight mirrors at the National Synchrotron Light Source over the 0.05-12 keV energy range. These witness coupons will be coated in the same process as the AXAF mirror elements. One of the key issues is the accurate determination of mirror efficiencies across the absorption edges of the mirror coating elements. We present a series of reflectance measurements with 2 eV resolution of a nickel-coated flat mirror in the region of the Ni L-II (870 eV) and L-III (853 eV) absorption edges. Scans of reflectance versus grazing angle at fixed energies in this region show distinct interference fringes at grazing angles larger than the critical angle which are extinguished as the photon energy is increased beyond the low point of the L-III edge, indicating total absorption of the evanescent wave within the Ni film. At 51 arc minutes grazing angle, measured reflectance decreases smoothly by 35 percent and then recovers in an 8 eV band at the L-III edge. We have also measured reflectances in the M absorption edge region for gold, platinum, and iridium coated mirrors. We derive optical parameters n and k specific to the film for comparison to the existing data tables.

Line radiation from Fe K-alpha(1), Cu K-alpha(1), and Ag K-alpha(1) is used to study the high energy X-ray reflectivity and scattering behavior of flight-quality X-ray mirrors having various Al substrates. When both the specular and the scattered radiation are integrated, near theoretical reflectivities are found for all mirrors. Results of scattering studies show that scattering is strongly correlated with the Al foil type. Mirrors based on new 0.4 mm Al foil are found to have a typical scattering FWHM of about 1.1 arcmin, whereas mirrors based on 0.3 mm Al foil have an FWHM of greater than 1.5 arcmin. For all mirrors and for all energies, the scattering is found to exhibit the characteristic asymmetries predicted by a first order vector scattering theory.

The study predicts, on the basis of surface topology measurements, the optical performance of thin-walled Wolter type 1 mirror shells over the specified energy range of the XMM telescope (0.3-8 keV). To analyze the effect of deformations which can be treated by geometrical optics, a Monte Carlo code was developed which uses a 3D model of the telescope to trace individual rays through the telescope. The computed point spread functions are found to be in excellent agreement with the ones measured in a full-aperture test at 1.5 keV X-ray energy. At 8 keV, a loss in optical performance was observed. A comparison of the surface data with mirrors that performed efficiently at 8 keV showed deformations with spatial wavelengths below 1 mm to be responsible for the degradation at 8 keV X-ray energy. It is concluded that in the transition region between Rayleigh limit and smooth surface limit, approximate optical predictions can be achieved by applying geometrical optics.

Attention is given to the ESA High Throughput X-ray Spectroscopy Mission (XMM), a telescope with three modules each consisting of 58 highly nested Wolter I mirrors with a focal length of 7.5 m. The envisaged resolution for an XMM module is 27 arcsec half energy width (HEW) at 8 keV X-ray energy. Results are presented of production and performance tests of the medium-size XMM CFRP/EPOXY mirror shell, including: the production of CFRP carriers as the mirror shell substrate with a global ovality PTV(R) of less than 50 microns and HEW contribution due to roundness of less than 10 arcsec; the replication of Wolter I shaped reflecting gold surface on the CFRP substrate; the measurement of optical performance (HEW is less than 17 arcsec at 1.5 keV X-ray energy); and an investigation of long-term stability for the 10-yr mission time. It is shown that the CFRP/EPOXY mirror shell replication technology can meet the XMM mission requirements.

XMM is a Cornerstone Mission of the European Space Agency for X-ray Astronomy. It consists of three X-ray telescopes with identical mirror systems. Each mirror system is composed of 58 nested coaxial and cofocal mirror shell (MS). The telescopes operate in the energy range 0.2-10 KeV with a total collecting area greater than 4800 sq cm at 2 KeV. The angular resolution is specified to HEW less than 30 arcsec at 8 KeV. The high packing density requires the production of very thin MS to minimize the loss of collecting area due to the thickness of the shells. The replica technique by electroforming nickel MS from mandrels allow the production of MS with a thickness of a few tenths of a mm. This technique has been successfully applied for the SAX and JET-X X-ray telescopes. In order to demonstrate the capabilities of this technology for the XMM project, a mirror support structure has been manufactured which allows the integration of one MS with different diameters and thickness between 0.4 to 1.0 mm. Mirror shells of different thickness and diameters have been manufactured and X-ray tested. The preliminary results of these measurements are presented.

Relevant for the JET-X Mission a post-processor of the Finite Element Code SAPV has been developed for the numerical assessment of the behavior of Mirror Module submitted to random vibration. Standard deviation and mean extreme values depending on the duration of time-excitation and on damping factor have been assessed for the most significant components of displacement and stress. The standard deviation values have been computed by combining by the square root of the sum of the square (SRSS) rule the results obtained exciting the system along three normal directions. This is consistent with the assumption that the three components of excitation are uncorrelated. We report in this paper the theoretical background and the most significant results.

The encircled energy of grazing incidence Wolter telescopes has been studied by application of Saha's transverse ray aberration theory. A formula has been derived for the encircled energy of the Wolter telescopes. It has been used to the calculate the encircled energy of several Wolter I and II grazing incidence telescopes. The results derived from the formula have been compared with those obtained by exact ray tracing. The effects of third, fifth, and seventh-order aberration theory have been studied.

The Joint European X-Ray Telescope, JET-X, is one of the core instruments of the scientific payload of the Russian SPECTRUM-X astrophysics mission due for launch in 1995. JET-X is designed to study the emission from X-ray sources in the band from 0.3 to 10 keV, particularly to meet primary scientific goals in cosmology and extragalactic astronomy. JET-X consists of two identical, coaligned X-ray imaging telescopes, each with a spatial resolution of 30 arcsecond (Half Energy Width, HEW) or better. Each telescope is composed of a nested array of 12 mirrors with an aperture of 0.3 m and a focal length of 3.5 m. The mirror shells have Wolter I geometry and are replicated by an electroforming process for which Carl Zeiss manufactured the 12 monolithic Nickel coated aluminum mandrels. In order to determine the mandrel limited HEW, several measurement and analysis steps including raytracing calculations are performed. The major contributions to the error budget, axial slopes and roundness errors, as well as the position of the focus are investigated. The results are reported and discussed.

Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmitting the 28.4 nm FeXV line are needed for observations of the solar corona. Light traps, based on multilayered structures, using moderately absorbing diffractor layers of SiO2 and aluminum as spacer material, have been successfully fabricated providing dramatically high rejection ratios. However, accurate tuning at the desired wavelength has proven to be extremely difficult to achieve in combination with high nominal reflectivity. Very slight deviations of thicknesses or optical constants can easily destroy the desired antiresonance effect. Classical Mo/Si structures, although somewhat less selective, can also be specially designed for this application and they prove more amenable to proper adjustment.

Our goal for FY 91 was to develop the capability to deposit multilayer thin film coatings of prescribed period gradient onto planar and figured substrates. To accomplish this goal we have extended our use of deposition flux masking to create laterally graded multilayer coatings. In addition, we have constructed a planetary substrate rotation fixture for deposition of axisymmetric graded thickness multilayer structures on planar and figured optics. Materials combinations for the layered synthetic microstructures (LSM's) we have fabricated by these techniques include: tungsten/carbon, molybdenum/silicon, molybdenum disilicide/silicon and chromium carbide/carbon. Soft X-ray diffraction characterization of the LSM's has verified that we have deposited controlled thickness graded period structures.

W/C multilayers were deposited on plastic films, which had thin thickness and light weight. TEM images showed the surface roughness of the plastic films and the boundary roughness of the multilayers. X-ray reflectivities were measured at wavelengths of 0.154 nm, 0.834 nm, and 0.3 to 0.7 nm. The boundary roughness values of the multilayers deposited on a polyimide film and a Si wafer were estimated to be 1.2 nm and 0.7 nm, respectively.

A test facility for measurements of reflectivity of multilayer coated mirrors, in the 30-300 A domain is described. The facility uses as a source of continuum radiation a plasma produced by focusing a laser beam on a target of high Z material. The laser used is a Q-switched Nd-YLF producing pulses of up to 20 J of energy and of 15 ns duration. The radiation reflected by the mirror under test is dispersed by a grazing incidence spectrograph and recorded with an intensified CCD detector. The facility is quite simple to operate and versatile. Examples of measurements from different mirrors in the range 50-130 A taken with the facility are presented.

We have measured the diffraction peak of a W:Si synthetic multilayer reflector at 104 keV using the High Energy Bonse-Hart Camera at the X-17B hard X-ray wiggler beam line of the National Synchrotron Light Source at Brookhaven National Laboratory. The characteristics of the diffraction peak are described and compared to theory.

Carbon alternated with metallic elements such as Ni, Co, Cr, Rh, Fe, W, or Ti offers the best potentialities in terms of soft X-ray reflection in the range 44 - 100 A. Deposition of this type of device requires a very accurate control of nanometric film deposition with a high regularity and sharp interfaces. We have made a precise investigation of the influence of the deposition conditions on the nanostructure of these systems using ultrahigh vacuum rf-sputtering technique. Conventional plasma conditions such as pressure and power levels have been investigated and also more unusual conditions such as target resistivity or sample temperature. It appears that the optimization process always results in a reduction of the amount of energy applied to the surface during growth. Medium argon pressure, low power levels, low target autobias and deposition at low temperature give the best structural quality and the best performance at the carbon K-alpha line. Metallic layer crystallization and the parasitic etching process are limited especially for the most sensitive Ni/C and Rh/C systems. The second part of the study is devoted to the comparison of Ni, Rh, Co, Fe, Cr, Ti, and W alternated with carbon. Thermal stability of the different systems is evaluated and related to the nanostructural behavior. When carbide formation is thermodynamically favorable, parasitics effects due to the crystallization are limited and the thermal stability is improved.

In response to the metrology needs of the soft X-ray community, the National Institute of Standards and Technology (NIST) has initiated a program devoted to the characterization of multilayer coated optics in the 4-40 nm wavelength region. In this paper, we describe the synchrotron based XUV reflectometers in use and under construction at NIST. We review the characteristics of the Synchrotron Ultraviolet Radiation Facility storage ring (SURF II) discuss the capabilities of the existing reflectometry facility, and present the final design parameters, expected performance, and construction status of a new reflectometry beam line.

A series of six WC(x)/B4C multilayers was produced by dc magnetron sputtering in an atmosphere of argon with methane additions (from 0 to 15 percent). The microstructure and chemistry of these multilayers was studied using transmission/HREM, XRD, XPS, electron probe microanalysis, and ion beam analysis with MeV helium beams. The multilayers were shown to be completely amorphous. In addition to carbon incorporation, a significant amount of hydrogen was incorporated. The amounts of hydrogen and carbon present increased with the percentage of methane (up to the 12 percent sample), but the atom percent of argon in the multilayers was constant, regardless of the methane concentration. It was found that reflectivity values for Mg K-alpha radiation improved as the methane concentration increased, with the sample produced in a 12 percent methane atmosphere showing the highest reflectivity. Annealing of a representative sample caused a significant loss of hydrogen, and a decrease of the bilayer spacing.

Molybdenum/silicon multilayers were deposited by ion beam sputtering and radio-frequency magnetron sputtering. X-ray reflection, transmission electron microscopy and Auger electron spectroscopy studies were performed to characterize these multilayers. There was a difference in soft x-ray reflectivity. The reason for the difference was found to be the difference in the thickness of silicide layers which were formed at each interface of the multilayers.

The design, development, and optimization of the thin film filters used on the Extreme Ultraviolet Explorer (EUVE) Satellite to define the EUV wavelength bandpasses of the individual instruments was a complicated task. The bandpasses had to be optimized for the astrophysical goals of the EUVE mission and constrained by the strong geocoronal EUV background emission. Materials with optical constants that met these requirements had to be found and tested. In many cases these materials were not compatible or were not strong enough to survive the intense vibrations of a rocket launch. Other effects, such as photoelectron 'halo' produced in the filters, were not discovered until flight qualification. The final set of flight filters included: lexan/boron, aluminum/carbon, titanium/antimony/aluminum, and tin/silicon monoxide. This paper discusses the lessons learned in the development of these filters, including the optimization process, material interactions and problems, calibration techniques, vibration susceptibility, thermal tests, and photoelectron emission. We feel the experiences gained over the last 10 years creating the filter sets for EUVE will be invaluable for future missions that use thin film filters.

At short wavelengths, such as FUV, transparent, optically active materials are scarce. Reflection phase retardation by a multilayer thin film can be a good alternative in this wavelength region. We design a multilayer quarterwave retarder by calculating the electric fields at each boundary in the multilayer thin film. Using this method, we achieve designs of FUV multilayers which provide high, matched reflectances for both s- and p-polarization states, and at the same time a phase difference between these two states of nearly 90 deg. For example, a quarterwave retarder designed at the Lyman-alpha line (121.6 nm) has 81.05 percent reflectance for the s-polarization and 81.04 percent for the p-polarization state. The phase difference between these two polarization states is 90.07 deg. For convenience the retarders are designed for 45 deg angle of incidence, but our design approach can be used for any other angle of incidence. Aluminum and MgF2 are used as film materials and an opaque thick film of aluminum as the substrate.

We use a concept of induced transmission and absorption to design multilayer thin film reflection polarizers in the FUV region. We achieve high s-polarization reflectance and a high degree of polarization by means of a MgF2/Al/MgF2 three layer structure on an opaque thick film of aluminum as the substrate. For convenience they are designed at a 45 deg angle of incidence. For example, our polarizer designed for the Lyman-alpha line (121.6 nm) has 88.67 percent reflectance for the s-polarization case, and 1.21 percent for the p-polarization case, with a degree of polarization of 97.31 percent. If we make a double surface polarizer with this design, it will have a degree of polarization of 99.96 percent and s-polarization throughput of 78.62 percent.

We discuss and analyze the possible sources of observational and instrumental uncertainty that can be encountered in measuring magnetic fields of the solar corona through polarimetric observations of the Hanle effect of the coronal Ly-alpha line. The Hanle effect is the modification of the linear polarization of a resonantly scattered line, due to the presence of a magnetic field. Simulated observations are used to examine how polarimetric measurements of this effect are affected by the line-of-sight integration, the electron collisions, and the Ly-alpha geocorona. We plan to implement the coronal magnetic field diagnostics via the Ly-alpha Hanle effect using an all-reflecting Ly-alpha coronagraph/polarimeter (Ly-alphaCoPo) which employs reflecting multilayer mirrors, polarizers, and filters. We discuss here the requirements for such an instrument, and analyze the sources of instrumental uncertainty for polarimetric observations of the coronal Ly-alpha Hanle effect. We conclude that the anticipated polarization signal from the corona and the expected performance of the Ly-alphaCoPo instrument are such that the Ly-alpha Hanle effect method for coronal field diagnostics is feasible.

We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at 215.7 A - the neutral hydrogen Ly-alpha line. It is shorter and faster than the telescope which produced solar Ly-alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-alpha line is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman-alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings to optimize the reflectivity and polarization properties at 1215.7 A. We describe some of the solar imaging results obtained with the MSSTA Lyman-alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter.

The measurement of the shape and optical performance of toroidal mirrors has always presented a challenge to the manufacturer and user of these types of optical elements. This report presents a technique for evaluating the complex shape and optical performance of long radius toroidal mirrors that are to be used in the EUV. The measurement techniques will be discussed and examples given. Interferometric analysis will be presented. Performance spot diagrams and MTF analysis will be discussed. Manufacturing techniques will be evaluated with respect to the application of more definitive measurement technology.

Two types of linear multilayer gratings have been investigated with special attention on the influence of the fabrication method on performance. Rh/C and Mo/Si systems have been realized for use above the carbon K-edge at 43.6 A and the silicon L3 edge at 125 A, respectively. We analyzed in detail the performance of the multilayer coatings in relation with their structural behavior. Mo/Si amplitude gratings were manufactured by suppressing the soft X-ray reflectivity of the multilayer mirror in selective areas with gold coating and lift off process. This method provides a well-defined 3 micron period Au grating. The soft X-ray reflectivity of the multilayer alone reached a maximum of 45 percent at normal incidence, whereas it was measured around 12.5 percent after Au grating deposition. Up to 13 grating orders were detected in the grating scan and detector scan showing the very good quality of these structures. A more unusual method was applied to manufacture Rh/C multilayer gratings. A carbon grating was first patterned on a silicon substrate and the multilayer was deposited at the end of the process. Measured reflectivity around 60 A in conventional 0 - 20 scan shows a reduction of the performances by a factor three. This is probably due to the surface roughness of the carbon grating prior to the multilayer deposition.

X-ray phase diffraction gratings can be designed to behave in a fashion similar to blazed gratings, directing the majority of the energy into certain desired orders. They should be easy to fabricate using conventional semiconductor production technology, and offer advantages in design flexibility and efficiency over conventional amplitude grating or blazed grating structures. As a multilayered structure, a phase grating has structure in depth as well as across the surface. Most theoretical analyses in the literature treat the embedded structure through simplifying approximations or assumptions. We will discuss a model which treats the embedded structure explicitly using the Fresnel-Kirchhoff integral in the Fraunhofer diffraction limit. This approach produces a set of equations which are identical to the result for an amplitude diffraction grating except for an additional factor which depends on the phase relationships of the various surfaces in the multilayer stack.

We present the results of the thin film filter lifetesting program conducted as part of the NASA Extreme Ultraviolet Explorer (EUVE) satellite mission. This lifetesting program is designed to monitor changes in the transmission and mechanical properties of the EUVE filters over the lifetime of the mission (fabrication, assembly, launch and operation). Witness test filters were fabricated from thin film foils identical to those used in the flight filters. The witness filters have been examined and calibrated periodically over the past seven years. The filters have been examined for evidence of pinholing, mechanical degradation, and oxidation. Absolute transmissions of the flight and witness filters have been measured in the extreme ultraviolet (EUV) over six orders of magnitude at numerous wavelengths using the Berkeley EUV Calibration Facility.

We review the scientific objectives, configuration, and initial flight results of the Multi- Spectral Solar Telescope Array (MSSTA). The MSSTA is a comprehensive solar rocket-borne observatory which utilizes multilayer coated optics to achieve high resolution thermally resolved images of the sun at FUV, EUV, and soft X-ray wavelengths. The MSSTA was successfully flown on May 13, 1991, obtaining high resolution images of chromospheric and coronal structures, including loops, filaments, polar plumes, and coronal holes. We also discuss plans to expand the capabilities of the MSSTA for future flights.

The Array of Low Energy X-ray Imaging Sensors (ALEXIS) experiment, a mini-satellite containing six wide angle EUV/ultrasoft X-ray telescopes, is scheduled to be launched by a Pegasus rocket into a 425 nautical mile orbit in 1992 to observe cosmic X-rays. The telescopes utilize near normal incidence optics featuring a 12.8 cm diameter, 13.52 cm radius of curvature spherical mirror with a Mo/Si multilayer coating. The multilayer coatings are tuned to wavelengths of 133, 171, and 186 A. In addition, the top layers are comprised of a unique 'wavetrap' designed to suppress the dominate background radiation at 304 A from the geocorona. We present measured performance data for these mirrors including the two dimensional uniformity of the multilayer as a function of both radius and angular rotation, the measured reflectivity at the primary wavelength and the effectiveness of the 'wavetrap'. We also discuss problems encountered due to contamination and design changes that have been made to mitigate the effect of contamination.

Attention is given to the Coronal Diagnostic Spectrometer (CDS), one of the key instruments on the ESA-cornerstone mission SOHO, scheduled for launch in 1995. It is designed to study the solar corona in the EUV. The on-axis resolution of the system is specified to 2 arcsec half-energy-width, which sets very stringent limits on the figuring and alignment tolerances. From the mechanical measurements and the optical tests a system HEW of 3.3 arcsec at EUV wavelengths is predicted. The HEW at 633 nm, including diffraction, is 2.2 arcsec. A performance comparable to ROSAT was achieved on the CDS mirrors which, due to the much higher asphericity, are at least 20 times more difficult to manufacture. Assembly techniques have been developed which allowed the high accurate alignment of the type II telescope, which is much more sensitive to misalignments than type I telescopes of comparable focal length and required correcting mirror displacements of as little as 20 nm while ensuring sufficient stiffness during glueing.

A discussion is presented of the scientific objectives that can be pursued by simultaneous coronal/chromospheric observation with the Multi-Spectral Solar Telescope Array (MSSTA), and a new balloon-borne observatory called the Ultra-High Resolution Vacuum Ultraviolet Spectroheliograph (UHRVS). Attention is given to the proposed UHRVS observatory, which will incorporate two instruments, a 65-cm aperture telescope with narrowband filters for high resolution photographic and photoelectric spectroheliograms, and a very high resolution spectrograph which uses a 40-cm aperture telescope. The capabilities of the MSSTA, and the joint UHRVS/MSSTA observing program that is envisioned are reviewed.

The quest for ultrahigh resolution full-disk images of the sun at soft X-ray/EUV/FUV wavelengths has increased the demand for photographic films with broad spectral sensitivity, high spatial resolution, and wide dynamic range. These requirements were made more stringent by the recent development of multilayer telescopes and coronagraphs capable of operating at normal incidence at soft X-ray/EUV wavelengths. Photographic films are the only detectors now available with the information storage capacity and dynamic range such as is required for recording images of the solar disk and corona simultaneously with sub arc second spatial resolution. During the Stanford/MSFC/LLNL Rocket X-Ray Spectroheliograph and Multi-Spectral Solar Telescope Array (MSSTA) programs, we utilized photographic films to obtain high resolution full-disk images of the sun at selected soft X-ray/EUV/FUV wavelengths. In order to calibrate our instrumentation for quantitative analysis of our solar data and to select the best emulsions and processing conditions for the MSSTA reflight, we recently tested several photographic films. These studies were carried out at the NIST SURF II synchrotron and the Stanford Synchrotron Radiation Laboratory. In this paper, we provide the results of those investigations.

The Multi-Spectral Solar Telescope Array (MSSTA), a rocket-borne solar observatory, was successfully flown in May, 1991, obtaining solar images in eight XUV and FUV bands with 12 compact multilayer telescopes. Extensive measurements have recently been carried out on the multilayer telescopes and thin film filters at the Stanford Synchrotron Radiation Laboratory. These measurements are the first high spectral resolution calibrations of the MSSTA instruments. Previous measurements and/or calculations of telescope throughputs have been confirmed with greater accuracy. Results are presented on Mo/Si multilayer bandpass changes with time and experimental potassium bromide and tellurium filters.

A soft-X-ray projection lithography system using multilayer mirrors has been developed. To determine the feasibility of a high throughput and a large exposure area, a reduction system consisting of two-mirror optics and a reflection mask were designed, fabricated, and assembled; and some trial replications of fine patterns were carried out. A full 4-inch wafer reflection mask was fabricated using a new process, and a high contrast and uniform quality throughout was obtained. Using the reflection mask, fine patterns of less than 0.25 micrometers and covering an area of 2 mm X 0.6 mm were faithfully replicated at a demagnification of 1/5.

SXPL (soft X-ray projection lithography) is one of the most promising applications of X-ray reflecting optics using multilayer mirrors. Within our collaboration, such multilayer mirrors were fabricated, characterized, laterally structured and then used as reflection masks in a projecting lithography procedure. Mo/Si-multilayer mirrors were produced by electron beam evaporation in UHV under thermal treatment with an in-situ X-ray controlled thickness in the region of 2d equals 14 nm. The reflectivities measured at normal incidence reached up to 54%. Various surface analysis techniques have been applied in order to characterize and optimize the X-ray mirrors. The multilayers were patterned by reactive ion etching (RIE) with CF₄, using a photoresist as the etch mask, thus producing X-ray reflection masks. The masks were tested in the synchrotron radiation laboratory of the electron accelerator ELSA at the Physikalisches Institut of Bonn University. A double crystal X-ray monochromator was modified so as to allow about 0.5 cm² of the reflection mask to be illuminated by white synchrotron radiation. The reflected patterns were projected (with an energy of 100 eV) onto the resist (Hoechst AZ PF 514), which was mounted at an average distance of about 7 mm. In the first test-experiments, structure sizes down to 8 micrometers were nicely reproduced over the whole of the exposed area. Smaller structures were distorted by Fresnel-diffraction. The theoretically calculated diffraction images agree very well with the observed images.

For the wavelength region above the Si-L edge normal incidence soft X-ray mirrors are produced with peak reflectivities around 55 percent. The Mo/Si multilayer systems are fabricated by electron beam evaporation in ultrahigh vacuum. Analysis of the quality of the stack is made by using an in situ monitoring system measuring the reflection of the C-K line and ex situ grazing X-ray reflection of the Cu-K-alpha line. A smoothing of the boundaries and thereby a drastic enhancement of the reflectivity can be obtained by thermal treatment of the multilayer system during growth. The microstructure of the multilayer systems is investigated by means of Rutherford Backscattering spectroscopy and Sputter/AES technique. Baking the final stack after deposition up to 900 C is applied to study the thermal stability of the soft X-ray mirror. Near normal incidence mirrors even for short wavelengths, e.g., the water window (2.4 - 4.4 nm), are produced with a Mo/Si bilayer thickness of 2.6 nm. An improvement in the quality of the interfaces for such ultrathin multilayer systems can be obtained by bombardment of the deposited layers with Ar(+) ions as well as by thermal treatment of the multilayer system and mixing of Mo and Si in the absorber layer during the deposition run. We report on reflectivity measurements of the mirrors and their behavior as polarizers and analyzers and on the diffraction efficiencies of laterally structured multilayer systems as gratings.

A system for X-ray lithography has been developed at the Institute for X-Ray Optical Systems (Moscow) which utilizes a powerful plasma pulse source of VUV and soft rays together with an X-ray optical system (XOS) of the Kumakhov lens type. The XOS provides the opportunity to control the distribution and divergence of the X-ray emission. The source of X-rays is a micropinch narrowing of a plasma pulse electric discharge of the low-inductive 'vacuum spark' type in the vapors of the electrode material. Typical parameters of the source are: energy stored in the capacitors, 500 Joules; emitted energy of X-rays in a band near 1 Kev, 8 - 10 J (efficiency to 2%); energy of VUV emission (20 - 1000 A), about 50 J; emission pulse time, 10 ns, frequency of discharges up to 15 Hz. The dimensions of the micropinch spot is 50 - 100 micrometers but the position of the pulse varies up to 3 mm. The capillary optic system contains about 3000 glass capillaries with variable cross-section and is 600 mm in length. The diameter of the output cross-section of the 'semilens' is 60 mm which provides uniform illumination of a 40 X 40 mm² mask. The distance between the source and the XOS input is 100 mm. The density of X-rays at the XOS input is 200 mW/cm². With a 50% transmission efficiency and a relative input-to-output cross-section of 0.2, the density of X-ray emission on the wafer is expected to be about 10 mW/cm². Using a negative resist with a sensitivity of 20 mJ/cm², this leads to an exposure time of about 2 seconds per field. With the use of a capillary lens, the angular divergence is not controlled by the c position jitter but by the lens and is about 3 milliradians. The current status of this system will be described.

The concept, implementation, and performance of the motion detection system (MDS) designed as a diagnostic for X-ray ground testing for AXAF are described. The purpose of the MDS is to measure the magnitude of a relative rigid body motion among the AXAF test optic, the X-ray source, and X-ray focal plane detector. The MDS consists of a point source, lens, centroid detector, transimpedance amplifier, and computer system. Measurement of the centroid position of the image of the optical point source provides a direct measure of the motions of the X-ray optical system. The outputs from the detector and filter/amplifier are digitized and processed using the calibration with a 50 Hz bandwidth to give the centroid's location on the detector. Resolution of 0.008 arcsec has been achieved by this system. Data illustrating the performance of the motion detection system are also presented.

The first high resolution X-ray images of an astronomical object (the solar corona) formed with normal incidence multilayer optics, were obtained in late 1987. We review the developments which have occurred in multilayer optics technology since 1987, and discuss the advantages that these developments present for solar observations. The most significant advantages of multilayer optics are: (1) telescopes with modest apertures (about 0.1-0.5 meters) can achieve images with very high (about 0.1-0.3 arcsec) resolution; and (2) the spectral selectivity of multilayers permits the investigation of thermal structures with resolution T/(Delta)T is about 5-10. We describe the analysis of polar plumes observed in 1987 and of small X-ray emitting regions called 'bright points' observed in 1991 to illustrate the power of multilayer optics for astronomical studies.

We have designed, analyzed, fabricated, and tested Schwarzschild multilayer X-ray microscopes. These instruments use flow-polished Zerodur mirror substrates which have been coated with multilayers optimized for maximum reflectivity at normal incidence at 135 A. They are being developed as prototypes for the Water Window Imaging X-Ray Microscope. Ultrasmooth mirror sets of hemlite grade sapphire have been fabricated and they are now being coated with multilayers to reflect soft X-rays at 38 A, within the biologically important 'water window'. In this paper, we discuss the fabrication of the microscope optics and structural components as well as the mounting of the optics and assembly of the microscopes. We also describe the optical alignment, interferometric and visible light testing of the microscopes, present interferometrically measured performance data, and provide the first results of optical imaging tests.

At present natural crystal TLAP used usually is replaced by artificial coated with multilayer for X-ray fluorescence (XRF) spectral analysis. X-ray multilayer monochromator can be used for analyzing light elements such as F, Na, Mg etc. Diffraction intensity of the multilayer component is 5 times higher than that of TLAP. This paper describes operating principle, Fabrication method and technique of the X-ray multilayer monochromator and the components are used Model 3080 E sequential X-ray fluorescence spectroscope. The multilayer diffraction components are fabricated by means of coating alternatively multilayer with high and low electron density elements on single crystal silicon substrate by vapor deposition or sputtering. Gap between multilayers is d to be equivalent to lattice constant of crystal. Sample is excited to emit fluorescence with multi-wavelength when X-ray beam illuminates surface of the sample. Fluorescence emitted passes through collimator and incidences on multilayer diffraction component to be diffracted into various wavelengths which are corresponding some angles. Contents of elements in samples can be detected according to Bragg diffraction principle. Key technologies fabricating multilayer diffraction components are how to polish supersmooth surface substrate and to control d value of thickness of multilayer. Roughness of Si(111) substrate polished by us is up to 0.1 nm RMS. Gap d 2.5 nm between multilayers. It is very difficult to realize specification as mentioned above. Thicknesses of layers are controlled by quartz piezoelectric crystal and their monitor controlling errors is about 0.34 nm RMS. Ion sputtering device is adopted to improve surface finish and construct specialty of the layers. Finally we have developed multilayer diffraction components which have been used to analyze F, Na and Mg etc. by X-ray fluorescence spectroscope.

The possibility of using the multilayer structures in X-ray technics for generation and transfer of the hard X-radiation is shown.

The following procedure is used to evaluate modifications of the optical performances of the JET-X telescope mirror shells (MS) due to manufacturing, integration tolerancing, gravity, and thermal gradients: analysis of the deformed shape of the MS by means of the ADINA finite element (FE) code, and optical performance analysis by means of a ray tracing code (RTC) for the Wolter 1 telescope directly interfaced with the FE code output. For the different conditions analyzed, half power radius, encircled energy, and spot diagrams are computed. Numerical analyses are performed for the single mirror shells and for the whole mirror module. The numerical models used are described, and the main features of the RTC and the relevant results are discussed.

A variety of low-angle X-ray diffraction (LAXRD) techniques are applied to the characterization of Si/Mo multilayers with the aim of developing nonspecular X-ray scattering as a characterization tool. Multilayers were sputter-deposited at different pressures in order to produce a wide variation in the intrinsic interface roughness. For each sample, four types of LAXRD measurements were performed: 0-20 (specular), offset 0-20, rocking curves (RCs), and scatter curves (SCs). In an offset 0-20 scan, the sample is misaligned just off the specular peak in order to measure the diffuse component of the 0-20 spectrum. These scans show that the diffuse scattering is modulated in a way similar to the specular. RCs taken on low-angle Bragg peak positions are characterized by a sharp specular spike on top of a broad diffuse hump. For an SC, the incident angle is held fixed and the detector swept. Structural parameters, such as spatial frequencies of the correlated roughness and a coherence length for the correlations, are determined.

High performance in normal incidence soft X-ray optical systems requires accurate control of the d-spacing across the surface of each mirror in the system. As a first step towards being able to fabricate any desired d-spacing variation, we demonstrate the ability to produce large (25 x 150 mm) flat Mo/Si multilayer coated mirrors with a d-spacing uniformity of +/- 0.4 percent. Instead of applying the approach most often taken to minimize the d-spacing variation physical shielding of the deposition source, we use a mask with a corrected profile positioned just in front of the rotating substrate to compensate for the nonuniform deposition flux. Results obtained from hard (lambda = 0.154 nm) and soft (wavelength of interest) X-ray mapping of the surface are presented along with a discussion of the technique used to control the d-spacing distribution.

Improved mirror reflectivity measurement techniques have been introduced to permit more accurate determinations of optical constants delta and beta in the complex index of refraction n = 1 - delta - i(beta) over the energy range 50 to 5000 eV. When the density has been determined by X-ray or other means, one can calculate the real and imaginary parts, f-prime and f-double prime, of the complex atomic scattering factor f = f(o) + f-prime + if-double prime from delta and beta. Preliminary results are given for the Ni LIII edge around 852 eV, and the Au M edge region from 2150 to 3500 eV. Since these are the first experimental evaluations of delta for these element edges, they are compared with appropriate reservations to semiempirical tabulations. There is much potential for this technique applied to synchrotron sources.

The X-ray test of the largest pair of nearly cylindrical mirrors for the Advanced X-ray Astrophysics Facility (AXAF) was completed in October 1991 at Marshall Space Flight Center. The test assembly was named the Verification Engineering Test Article I (VETA-I). The ring-focus portion of the test measured the imaging quality of azimuthal sections of VETA-I. This gives information about the core of the on-orbit image. The finite source distance, VETA-I mirror spacing, and VETA-I structural deformation caused the core of the image to be spread over a diameter of nearly 4 arc seconds at the VETA-I overall focus. The results of a preliminary analysis of the ring-focus data and the implications for the on-orbit image of the telescope are discussed. An upper limit for the on-orbit encircled-energy fraction at 1 arc second diameter was determined to be 0.82 at 0.277 keV X-ray energy. This assumes that the bottoms of the mirrors in the VETA-I arrangement are representative of the mirror surfaces and that the on-orbit system would be aligned using a combination of preliminary measurements and predictions for the mirror surface shapes.

Advances in optical coating and materials technology have made possible the development of instruments with substantially improved efficiency and made possible to consider more complex optical designs in the EUV. The importance of recent developments in chemical vapor deposited silicon carbide (CVD-SiC), SiC films and multilayer coatings is discussed in the context of EUV instrumentation design. The EUV performance of these coatings as well as some strengths and problem areas for their use in space will be addressed.

The TEREK imaging telescope installed on the Phobos-I spacecraft, and the TEREK-C telescope and spectroheliometer, designed for use in the Coronas project, are examined. In comparison with the TEREK instrument, the TEREK-C has an improved spatial resolution in the MX channel of up to 2 arcsec. The main parameters of the TEREK-C and the spectroheliometer are presented in tabular form, and an optical scheme of the TEREK instrument is given.

Tungsten/carbon (W/C) multilayer thin films prepared by sputtering on unheated Si(100) substrates were encapsulated with various types of layer having low x-ray absorption. Isochronal annealings for 1 hr in the temperature range from 300 to 600 degree(s)C and isothermal annealings at 300 and 400 degree(s)C were carried out under ambient conditions (in air) on coated and uncoated multilayers. The encapsulated layers are: SiN_x and SiO₂ prepared by plasma enhanced chemical vapor deposition (PECVD) and SiC, Al₂O₃, C and B₄C prepared by sputtering techniques. Previous studies have shown that unprotected W/C multilayers annealed in air exhibit oxidation at relatively low temperatures (approximately 300 degree(s)C). In the present study, we have used Raman scattering (RS), Auger depth profiling and scanning electron microscopy (SEM) to investigate the effects of thermal treatments on the encapsulated W/C multilayers. The results indicate that oxidation of both W and C layers takes place during annealing at temperatures which depend on the type of protective layer. For example, in the isochronal annealing experiments, multilayers coated with C, Al₂O₃ and B₄C suffer oxidation during annealing at 400 degree(s)C, whereas multilayers coated with the other three types of protective films prevent multilayers from oxidation at annealing temperatures as high as 600 degree(s)C. SEM micrographs show that the formation of pinholes through the protective layer occurred during annealing at the temperatures for which oxidation was first detected. Auger profiling shows the loss of compositional modulation in the region reached by oxygen. A WO₃ phase is identified by RS in the oxidized region, and the loss of the C layers is most likely due to the formation of carbon oxide vapors.