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The third flight of the High-Resolution Coronal Imager (Hi-C 2.1) occurred on May 29, 2018, the Sounding Rocket was launched from White Sands Missile Range in New Mexico. The instrument has been modified from its original configuration (Hi-C 1) to observe the solar corona in a passband that peaks near 172 Angstrom and uses a new, custom-built low-noise camera. The instrument targeted Active Region 12712, and captured 78 images at a cadence of 4.4 sec (18:56:22 - 19:01:57 UT; 5 min and 35 sec observing time). The image spatial resolution varies due to quasi-periodic motion blur from the rocket; sharp images contain resolved features of at least 0.47 arcsec. There are coordinated observations from multiple ground- and space-based telescopes providing an unprecedented opportunity to observe the mass and energy coupling between the chromosphere and the corona. Details of the instrument and the data set are presented in this paper., Comment: 26 pages, 15 figures, submitted to Solar Physics

The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet imager and spectrograph instrument concept for tracking coronal mass ejections through the region where they experience the majority of their acceleration: the difficult-to-observe middle corona. It contains a wide field of view (0–4 R⊙) imager and a 1 Å spectral-resolution-irradiance spectrograph spanning 170–340 Å. It leverages new detector technology to read out different areas of the detector with different integration times, resulting in what we call “simultaneous high dynamic range”, as opposed to the traditional high dynamic range camera technique of subsequent full-frame images that are then combined in post-processing. This allows us to image the bright solar disk with short integration time, the middle corona with a long integration time, and the spectra with their own, independent integration time. Thus, SunCET does not require the use of an opaque or filtered occulter. SunCET is also compact – ~15 × 15 × 10 cm in volume – making it an ideal instrument for a CubeSat or a small, complementary addition to a larger mission. Indeed, SunCET is presently in a NASA-funded, competitive Phase A as a CubeSat and has also been proposed to NASA as an instrument onboard a 184 kg Mission of Opportunity.

The High-Energy X-ray Probe (HEX-P) is a probe-class next-generation high-energy X-ray mission concept that will vastly extend the reach of broadband X-ray observations. Studying the 2-200 keV energy range, HEXP has 40 times the sensitivity of any previous mission in the 10-80 keV band, and will be the first focusing instrument in the 80-200 keV band. A successor to the Nuclear Spectroscopic Telescope Array (NuSTAR), a NASA Small Explorer launched in 2012, HEX-P addresses key NASA science objectives, and will serve as an important complement to ESA's L-class Athena mission. HEX-P will utilize multilayer coated X-ray optics, and in this paper we present the details of the optical design, and discuss the multilayer prescriptions necessary for the reflection of hard X-ray photons. We consider multiple module designs with the aim of investigating the tradeoff between high- and low-energy effective area, and review the technology development necessary to reach that goal within the next decade.

We present continued development of components for measuring linear X-ray polarization over the 0.2-0.8 keV (15-62 Angstrom) band. We present results from measurements of new laterally graded multilayer mirrors and critical angle transmission gratings essential to the approach. While the lab is designed to verify components to be used in a soft X-ray polarimeter, it is reconfigurable and has been used to verify grating efficiencies with our new CCD detector. Our development work is the basis for a sounding rocket mission (Rocket Experiment Demonstration of a Soft X-ray Polarimeter) and future orbital missions.

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈ 0.3 – 0.4′′), high-cadence (≈ 5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′ pixel−1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.

The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe xviii (94 A), Fe viii, xxi (131 A), Fe ix (171 A), Fe xii, xxiv (193 A), Fe xiv (211 A), He ii (304 A), and Fe xvi (335 A). One telescope observes C iv (near 1600 A) and the nearby continuum (1700 A) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA’s Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun’s energy is stored and released into the heliosphere and geospace.

A prototype system for breast imaging using monochromatic X-rays has been developed using a scanning multilayer X-ray mirror in combination with a conventional mammography tube and an imaging detector. The X-ray mirror produces a monochromatic fan beam tuned near 19 keV, with an energy bandpass of approximately 1.5 keV. Rotating the mirror about the tube’s focal spot in synchronization with the X-ray generator and detector enables the acquisition of monochromatic X-ray images over large areas. The X-ray mirror also can be rotated completely out of the beam so that conventional polychromatic images can be acquired using a K-edge filter, facilitating direct comparison between the two modes of operation. The system was used to image synthetic, tissue-equivalent breast phantoms in order to experimentally quantify the improvements in image quality and dose that can be realized using monochromatic radiation. Nine custom phantoms spanning a range of thicknesses and glandular/adipose ratios, each containing both glandular- and calcification-equivalent features, were used to measure contrast and signal-difference-to-noise ratio (SDNR). Mean glandular dose (MGD) was computed from measured entrance exposure, and a figure-of-merit (FOM) was computed as FOM = SDNR(2)/MGD in each case. Monochromatic MGD ranges from 0.606 to 0.134 of polychromatic MGD for images having comparable glandular SDNR, depending on breast thickness and glandularity; relative monochromatic dose decreases with increasing glandularity for all thicknesses. Monochromatic FOM values are higher than the corresponding polychromatic FOM values in all but one case. Additionally, the monochromatic contrast for glandular features is higher than the polychromatic contrast in all but one case as well. These results represent important steps toward the realization of clinically practical monochromatic X-ray breast imaging systems having lower dose and better image quality, including those for digital mammography, digital breast tomosynthesis, contrast-enhanced spectral mammography and other modalities, for safer, more accurate breast cancer detection, diagnosis and staging.

We describe an optical design and possible implementation of a broadband soft x-ray polarimeter. Our arrangement of gratings is designed optimally for the purpose of polarimetry with broadband focusing optics by matching the dispersion of the spectrometer channels to laterally graded multilayers (LGMLs). The system can achieve polarization modulation factors over 90%. We implement this design using a single optical system by dividing the entrance aperture into six sectors; high efficiency, blazed gratings from opposite sectors are oriented to disperse to a common LGML forming three channels covering the wavelength range from 35 to 75 Å (165 to 350 eV). The grating dispersions and LGML position angles for each channel are 120 deg to each other. CCD detectors then measure the intensities of the dispersed spectra after reflection and polarizing by the LGMLs, giving the three Stokes parameters needed to determine a source's linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe examples of the potential scientific return from instruments based on this design.

In order to advance significantly scientific objectives, future x-ray astronomy missions will likely call for x-ray telescopes with large aperture areas (≍ 3 m2) and fine angular resolution (≍ 12). Achieving such performance is programmatically and technologically challenging due to the mass and envelope constraints of space-borne telescopes and to the need for densely nested grazing-incidence optics. Such an x-ray telescope will require precision fabrication, alignment, mounting, and assembly of large areas (≍ 600 m2) of lightweight (≍ 2 kg/m2 areal density) high-quality mirrors, at an acceptable cost (≍ 1 M$/m2 of mirror surface area). This paper reviews relevant programmatic and technological issues, as well as possible approaches for addressing these issues-including direct fabrication of monocrystalline silicon mirrors, active (in-space adjustable) figure correction of replicated mirrors, static post-fabrication correction using ion implantation, differential erosion or deposition, and coating-stress manipulation of thin substrates....

The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona and upper transition region emission lines in the wavelength ranges 170 – 210 A and 250 – 290 A. The line centroid positions and profile widths will allow plasma velocities and turbulent or non-thermal line broadenings to be measured. We will derive local plasma temperatures and densities from the line intensities. The spectra will allow accurate determination of differential emission measure and element abundances within a variety of corona and transition region structures. These powerful spectroscopic diagnostics will allow identification and characterization of magnetic reconnection and wave propagation processes in the upper solar atmosphere. We will also directly study the detailed evolution and heating of coronal loops. The EIS instrument incorporates a unique two element, normal incidence design. The optics are coated with optimized multilayer coatings. We have selected highly efficient, backside-illuminated, thinned CCDs. These design features result in an instrument that has significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 – 5 s exposure times in the brightest lines. EIS can scan a field of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and 25 km s−1 per pixel. The instrument design, its absolute calibration, and performance are described in detail in this paper. EIS will be used along with the Solar Optical Telescope (SOT) and the X-ray Telescope (XRT) for a wide range of studies of the solar atmosphere.

This paper describes recent progress in the development of new EUV multilayer coatings for solar physics. In particular, we present results obtained with Pd/B4C/Y, Al/Zr, and Al-Mg/SiC multilayers, designed for normal incidence operation in the 9 – 50 nm wavelength range. We describe the development of both periodic multilayer films designed for narrowband imaging, and non-periodic multilayers designed to have a broad-spectral response for spectroscopy. The higher EUV reflectance provided by these new coatings, relative to older-generation coatings such as Si/Mo, Mo/Y, and others, will facilitate the development of future solar physics instruments for both imaging and spectroscopy having higher spatial and spectral resolution, while supporting the exposure times and cadences necessary to capture the evolution of flares, jets, CMEs and other dynamic processes in the solar atmosphere.

This paper is focused on recent progress in the development of broad-band multilayer coatings designed for hard X-ray energies, for use in future astronomical telescopes. We describe a new laboratory-based hard X-ray reflectometer for atwavelength characterization of multilayer films, we present the results of an experimental comparison of the hard X-ray performance of several W-based periodic multilayer coatings, and we describe the optimization and experimental performance of new non-periodic Co-based multilayer coatings (both depth-graded and aperiodic), designed for continuous response through the W and Pt K-edges near 70 and 80 keV, respectively. We discuss future research directions in light of these new results.

This paper describes a new variation of the differential deposition/differential erosion technique for mid-frequency surface-height error correction. In our approach, the technique is extended to two dimensions in order to correct surfaceheight errors in thin-shell cylindrical mirror segments with high throughput. We describe the new infrastructure currently being developed to realize this technique, including an LTP system for surface metrology of mid-frequency surfaceheight errors, a new UHV linear stage for precise substrate motion during deposition or erosion, and most crucially, the development of electronically-actuated aperture arrays that are mounted in front of a rectangular magnetron cathode, or a rectangular ion source, in order to modulate the deposition/erosion rate of material in two dimensions, in real-time.

A laboratory-based X-ray reflectometer has been developed to measure the performance of hard X-ray multilayer coatings at their operational X-ray energies and incidence angles. The instrument uses a sealed-tube X-ray source with a tungsten anode that can operate up to 160 kV to provide usable radiation in the 15–150 keV energy band. Two sets of adjustable tungsten carbide slit assemblies, spaced 4.1 m apart, are used to produce a low-divergence white beam, typically set to 40 μm × 800 μm in size at the sample. Multilayer coatings under test are held flat using a vacuum chuck and are mounted at the center of a high-resolution goniometer used for precise angular positioning of the sample and detector; additionally, motorized linear stages provide both vertical and horizontal adjustments of the sample position relative to the incident beam. A CdTe energy-sensitive detector, located behind a third adjustable slit, is used in conjunction with pulse-shaping electronics and a multi-channel analyzer to capture both the incident and reflected spectra; the absolute reflectance of the coating under test is computed as the ratio of the two spectra. The instrument’s design, construction, and operation are described in detail, and example results are presented obtained with both periodic, narrow-band and depth-graded, wide-band hard X-ray multilayer coatings.

We have combined experiments and atomistic modeling in order to better understand the growth and structure of metal films deposited onto sidewalls of trenches and vias. Using x-ray reflectance, atomic force microscopy, and high-resolution transmission electron microscopy to characterize the microstructure and morphology of Ta films grown by magnetron sputtering onto inclined substrates, we find that films deposited at larger incidence angles tend towards columnar microstructure with high roughness and low density. We have used a three-dimensional Monte Carlo model (ADEPT) to simulate the growth process, under conditions close to those investigated experimentally. A binary collision model is included in the Monte Carlo deposition procedure to describe the interaction of energetic particles with the surface. Examination of the film microstructure and morphology resulting from the simulations indicates that the energetic impinging particles are necessary to produce film densities comparable to those found ex...

We present a new instrument for space-based observational solar physics, recently flown successfully on a sounding rocket, designed to provide high spatial resolution, time-resolved images of the solar corona at specific wavelengths in the extreme ultraviolet (XUV). The primary instrument employs multilayer x-ray mirrors in a novel geometry that affords quasi-monochromatic imaging at wavelengths tunable continuously over the spectral range from 17.1 to 21.1 nm. The secondary instrument also uses multilayer x-ray mirrors to provide high-resolution imaging at three fixed XUV wavelength bands. Both instruments use charge coupled device detectors and thin A1 filters for rejection of unwanted wavelengths. We describe the design, construction, and performance of the instrument and discuss prospects for the future.

Future astronomical X-ray telescopes, including the balloon-borne High-Energy Focusing Telescope (HEFT) and the Constellation-X Hard X-ray Telescope (Con-X HXT) plan to incorporate depth-graded multilayer coatings in order to extend sensitivity into the hard X-ray ( 10≲E≲80 keV ) band. In this paper, we present measurements of the reflectance in the 18–170 keV energy range of a cylindrical prototype nested optic taken at the European Synchrotron Radiation Facility (ESRF). The mirror segments, mounted in a single bounce stack, are coated with depth-graded W/Si multilayers optimized for broadband performance up to 69.5 keV (WK-edge). These designs are ideal for both the HEFT and Con-X HXT applications. We compare the measurements to model calculations to demonstrate that the reflectivity can be well described by the intended power law distribution of the bilayer thicknesses, and that the coatings are uniform at the 5% level over the mirror surface. Finally, we apply the measurements to predict effective areas achievable for HEFT and Con-X HXT using these W/Si designs.

The stresses in periodic Mo/Si, W/Si, and Mo/C multilayer films were determined from wafer-curvature measurements. The layer thickness of each material was varied systematically, and parametric stress contours were generated, showing contours of constant stress in the two-dimensional layer thickness parameter space. These results illustrate that the net stress in a periodic multilayer is not an intrinsic property of the film (for specific deposition conditions) but, rather, depends strongly on the individual layer thicknesses. X-ray diffraction measurements show (a) how the lattice spacing in the W and Mo crystallites varies with layer thickness, and (b) in the case of the W/Si films, how the phase composition of the polycrystalline W layers vary with W layer thickness. In the case of the W/Si and Mo/Si multilayers, irreversible stress changes were observed after the samples were stored in air at room temperature for a period of several months. Stress–temperature measurements made on the as-deposited W/Si...

We present continued development of laterally graded multilayer mirrors (LGMLs) for a telescope design capable of measuring linear X-ray polarization over a broad spectral band. The multilayer-coated mirrors are used as Bragg reflectors at the Brewster angle. By matching to the dispersion of a spectrometer, one may take advantage of high multilayer reflectivities and achieve modulation factors over 50% over the entire 0.2-0.8 keV band. In Phase II of the polarimetry beam-line development, we demonstrated that the system provides 100% polarized X-rays at 0.525 keV (Marshall et al. 2013). Here, we present results from phase III of our development, where a LGML is used at the source and laterally manipulated in order to select and polarize X-rays from emission lines for a variety of source anodes. The beamline will then provide the capability to test polarimeter components across the 0.15-0.70 keV band. We also present plans for a suborbital rocket experiment designed to detect a polarization level of better than 10% for an active galactic nucleus., Comment: 9 pages, 8 figures, to be published in the proceedings of the SPIE, volume 9144

We are developing instrumentation for a telescope design capable of measuring linear X-ray polarization over a broad-band using conventional spectroscopic optics. Multilayer-coated mirrors are key to this approach, being used as Bragg reflectors at the Brewster angle. By laterally grading the multilayer mirrors and matching to the dispersion of a spectrometer, one may take advantage of high multilayer reflectivities and achieve modulation factors over 50% over the entire 0.2-0.8 keV band. We present progress on laboratory work to demonstrate the capabilities of an existing laterally graded multilayer coated mirror pair. We also present plans for a suborbital rocket experiment designed to detect a polarization level of 12-17% for an active galactic nucleus in the 0.1-1.0 keV band., Comment: 11 pages, 12 figures, to appear in the proceedings of the SPIE, volume 8861, on Optics for EUV, X-Ray, and Gamma-Ray Astronomy

We have measured the stress in Mo/Si multilayer films deposited by magnetron sputtering, using the wafer‐curvature technique, and find a strong dependence on background pressure. We find that for multilayers containing 40 bilayers of ∼4.3 nm Si layers and ∼2.6 nm Mo layers, the stress increases from approximately −280 MPa (compressive) to −450 MPa as the background pressure in the deposition chamber (i.e., measured just prior to deposition) decreases from 1.0×10−5 to 6.0×10−8 Torr. For multilayers of the same period but with thicker Mo layers, the dependence on background pressure is even stronger. X‐ray (λ=0.154 nm) diffraction measurements reveal only a slight increase in interfacial roughness for films deposited at high background pressure, but no evidence was found for any differences in the microstructure of the polycrystalline Mo layers that comprise these structures. The peak soft x‐ray (λ=13 nm) reflectance, which is sensitive to interfacial roughness at longer spatial wavelengths, also shows no correlation with background pressure or stress. Atomic concentrations of incorporated oxygen and carbon, measured with Auger electron spectroscopy, were found to be less than ∼0.5 at. % for all samples. However, the average hydrogen concentration, as determined from forward‐recoil‐scattering measurements made using a 2.6 MeV He beam, was found to increase linearly with background pressure. We discuss possible mechanisms for the observed dependence of film stress on background pressure, including gas incorporation and the affect of residual gas atoms on adatom mobility.

The Solar Ultraviolet Imager (SUVI) is one of several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites (GOES) -R and -S platforms, as part of NOAA's space weather monitoring fleet. SUVI is a Generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 A. Once operational, over the mission lifetime expected to last up to 10 years, SUVI will record full disk, EUV spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented herein will touch upon general aspects of the SUVI optical design, as well as the fabrication, super polishing and metrology of the fabricated mirrors, including measured EUV spectral performance.

X-ray reflective coating for next generation's lightweight, high resolution, optics for astronomy requires thin-film deposition that is precisely fine-tuned so that it will not distort the thin sub-mm substrates. Film of very low stress is required. Alternatively, mirror distortion can be cancelled by precisely balancing the deformation from multiple films. We will present results on metallic film deposition for the lightweight optics under development. These efforts include: low-stress deposition by magnetron sputtering and atomic layer deposition of the metals, balancing of gross deformation with two-layer depositions of opposite stresses and with depositions on both sides of the thin mirrors.

Experimental multilayer reflectance data on flight mirrors and witnesses for three extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA) instrument aboard NASA’s Solar Dynamics Observatory are presented and compared to theoretical models. The relevance of these results to the performance of the AIA instrument is discussed.

In this work we present the design of a Pd/B₄C multilayer structure optimized for high reflectance at 6.67 nm. The structure has been deposited and also characterized along one year in order to investigate its temporal stability. This coating has been developed for the beam transport system of FERMI@Elettra Free Electron Laser: the use of an additional aperiodic capping layer on top of the structure combines the high reflectance with filter properties useful in rejecting the fundamental harmonic when the goal is to select the third FEL harmonic.

SiC/Mg multilayers have been used as coatings of the Sounding-rocket CORonagraphic Experiment (SCORE) telescope mirrors launched during the NASA HERSCHEL program. This materials couple has been largely studied by researchers since it provides higher performances than a standard Mo/Si multilayer; the SCORE mirrors show in fact a peak reflectance of around 40% at HeII 30.4 nm. Nevertheless, long term stability of this coating is an open problem. A study on the aging and stability of this multilayer has been carried on. SiC/Mg multilayer samples characterized by different structural parameters have been deposited. They have been measured just after deposition and four years later to verify degradation based on natural aging. Experimental results and analysis are presented.

The NuSTAR mission will be the first mission to carry a hard X-ray(5-80 keV) focusing telescope to orbit. The optics are based on the use of multilayer coated thin slumped glass. Two different material combinations were used for the flight optics, namely W/Si and Pt/C. In this paper we describe the entire coating effort including the final coating design that was used for the two flight optics. We also present data on the performance verification of the coatings both on Si witness samples as well as on individual flight mirrors.

We have examined the correlations between direct surface-finish metrology techniques and normal-incidence, soft x-ray reflectance measurements of highly polished x-ray multilayer mirrors. We find that, to maintain high reflectance, the rms surface roughness of these mirrors must be less than ~1 A over the range of spatial frequencies extending approximately from 1 to 100 μm−1 (i.e., spatial wavelengths from 1 μm to 10 nm). This range of spatial frequencies is accessible directly only through scanning-probe metrology. Because the surface-finish Fourier spectrum of such highly polished mirrors is described approximately by an inverse power law (unlike a conventional surface), bandwidth-limited rms roughness values measured with instruments that are sensitive to only lower spatial frequencies (i.e., optical or stylus profileres) are generally uncorrelated with the soft x-ray reflectance and can lead to erroneous conclusions regarding the expected performance of substrates for x-ray mirrors.

A molybdenum/silicon multilayer-coated 1:1 ring-field optic with a numerical aperture of 0.0835 is used to carry out soft-x-ray projection imaging with undulator radiation at 12.9 nm. An ideal optic of this type should be able to image 0.1-μm features with a contrast exceeding 90% at this wavelength. The useful resolution of our ring-field optic is experimentally found to be approximately 0.2 μm, probably because of the presence of substrate figuring errors.

Soft-x-ray projection imaging is demonstrated by the use of 14-nm radiation from a laser plasma source and a single-surface multilayer-coated ellipsoidal condenser. Aberrations in the condenser and the Schwarzschild imaging objective are characterized and correlated with imaging performance. A new Schwarzschild housing, designed for improved alignment stability, is described.

We describe a variety of technologies for patterning transmissive and reflective soft x-ray projection lithography masks containing features as small as 0.1 μm. The transmission masks fabricated for use at 13 nm are of one type, a Ge-absorbing layer patterned on a boron-doped Si membrane. Reflective masks were patterned by various methods that included absorbing layers formed on top of multilayer reflectors, multilayer-reflector-coating removal by reactive ion etching, and ion damage of multilayer regions by ion implantation. For the first time, we believe, a process for absorber repair that does not significantly damage the reflectance of the multilayer coating on the reflection mask is demonstrated.

The results of an attempt to coat optical flats and replace echelle gratings with ion-deposited SiC are reported. Deposition was performed by bombarding a SiC target with an ion beam angled 45 deg relative to the target. Half the target was covered with stainless steel to furnish a comparison opportunity. After precleaning SiC coatings of 300-2200 A thickness were deposited. The specimens had previously been coated with either Au or Al or were left blank. Reflectance and diffraction data were taken of the finished flats and gratings. The SiC-coated flats performed as well as uncoated flats while the echelles exhibited deteriorating performance with increasing coating thickness. Further studies are indicated on the effect of coating thickness on surface roughness.

The structural and optical properties of Mo/Si and Ru/Si x‐ray multilayers prepared by sputter deposition in argon have been examined using high‐resolution transmission electron microscopy, optical profilometry, and x‐ray and soft x‐ray reflectance. We find that for Ru/Si, similar to previous results for Mo/Si, lower argon pressure during deposition results in smoother layers and higher reflectance. For low‐pressure deposited multilayers, interfacial roughness is negligible compared to interfacial diffuseness; the presence of amorphous interlayer regions in both of these systems is the major cause of reduced reflectance.

It has been shown that it is possible to produce near diffraction limited images with soft x rays of wavelength 13.8 nm using normal incidence Si/Mo‐multilayered coated optics. Initial experiments with a 20X reduction Schwarzschild optic produced features as small as 50 nm. It is considered that soft x‐ray projection lithography may be a likely candidate for the future generation of lithographic tools needed to produce 0.1‐μm features for integrated circuits around the turn of the century.

Future solar experiments designed to perform solar plasma diagnostics will also be based on extreme-ultravilet observations. Multilayer (ML) optics are essential in this spectral region since these coatings have high reflectivity at normal incidence. Typically, the reflectivity curve of a ML coating has a small but finite bandwidth, and this can be a serious drawback when several spectral lines fall within the bandwidth. In fact, spectral lines emitted by different ion species can correspond to different plasma conditions. We present the design, realization, and characterization of an innovative ML structure with high reflectivity coupled with a strong rejection ratio for two adjacent spectral features. The key element is an optimized capping layer structure deposited on top of the ML that preserves the performance reflectance at the target wavelength and at the same time suppresses the reflectance at specific adjacent wavelengths. Application to the Fe xv3x10(6) K coronal emission line at 28.4 nm with rejection of the He ii Lyman-alpha line at 30.4 nm is presented.

We compare the performance, stability and microstructure of Si/Gd multilayers containing thin barrier layers of W, B(4)C, or SiN(x), and determine that multilayers containing 0.6 nm thick W barrier layers at each interface provide the best compromise between high peak reflectance in the extreme ultraviolet near lambda=60 nm and good stability upon heating. The Si/W/Gd films have sharper interfaces and also show vastly superior thermal stability relative to Si/Gd multilayers without barrier layers. We find that these structures have relatively small compressive film stresses, and show good temporal stability thus far. We measured a peak reflectance of 29.7% at lambda=62.5 nm, and a spectral bandpass of Deltalambda=9 nm (FWHM), for an optimized Si/W/Gd multilayer having a period d=32.0 nm.

Projection imaging of 0.1-microm lines and spaces is demonstrated with a Mo/Si multilayer coated Schwarzschild objective and 14-nm illumination from a laser plasma source. This structure has been etched into a silicon wafer by using a trilevel resist and reactive ion etching. Low-contrast modulation at 0.05-microm lines and spaces is observed in polymethylmethacrylate.

We report on the performance, structure and stability of periodic multilayer films containing silicon carbide (SiC) and aluminum (Al) layers designed for use as reflective coatings in the extreme ultraviolet (EUV). We find that SiC/Al multilayers prepared by magnetron sputtering have low stress, good temporal and thermal stability, and provide good performance in the EUV, particularly for applications requiring a narrow spectral bandpass, such as monochromatic solar imaging. Transmission electron microscopy reveals amorphous SiC layers and polycrystalline Al layers having a strong texture, and relatively large roughness associated with the Al crystallites. Fits to EUV reflectance measurements also indicate large interface widths, consistent with the electron microscopy results. SiC/Al multilayers deposited by reactive sputtering with nitrogen comprise Al layers that are nearly amorphous and considerably smoother than films deposited nonreactively, but no improvements in EUV reflectance were obtained.

We have investigated the performance, structure and stability of periodic multilayer films containing silicon carbide (SiC) and aluminum (Al) layers designed for use as reflective coatings in the extreme ultraviolet (EUV). We find that SiC/Al multilayers prepared by magnetron sputtering have low stress, good temporal and thermal stability, and provide good performance in the EUV, particularly for applications requiring a narrow spectral bandpass such as monochromatic solar imaging. Transmission electron microscopy reveals amorphous SiC layers and polycrystalline Al layers having a strong texture, and relatively large roughness associated with the Al crystallites. Fits to EUV reflectance measurements also indicate large interface widths, consistent with the electron microscopy results. SiC/Al multilayers deposited by reactive sputtering with nitrogen comprise Al layers that are nearly amorphous and considerably smoother than films deposited non-reactively, but no improvements in EUV reflectance were obtained.

We have used reactive sputtering with nitrogen to deposit both periodic and depth-graded Co/C X-ray multilayers intended for use at grazing incidence for astronomical applications. In comparison to Co/C films deposited nonreactively, reactively-sputtered films show lower stress and lower roughness. Consequently we have been able to fabricate Co/C multilayers that have much smaller periods relative to what can be achieved using non-reactive sputtering. We have thus far produced several prototype Co/C multilayers, including a depth-graded film containing 500 bilayers for use below 10 keV, and a depth-graded film containing 1100 bilayers for use up to 100 keV. Both of these films show excellent X-ray performance, low film stress, and excellent temporal stability.

The experimental characterization of an aperiodic reflecting multilayer (ML) structure designed to reflect and compress attosecond pulses in the extreme ultraviolet spectral region is presented. The MLs are designed for the 75-105 eV spectral interval with suitable reflectance and phase behavior, in particular high total spectral reflectivity coupled with very wide bandwidth and spectral phase compensation. The experimental phase behavior of the multilayer has been obtained through electron photoemission signal using an innovative method that is presented and discussed in this paper. With this ML we have demonstrated pulse compression by reflection from 450 as to 130 as.

We have demonstrated soft x-ray projection lithography using radiation at wavelengths of 14 nm and 37 nm with a commercially available 20X reduction Schwarzschild camera. Line widths as small as 0.05 microns have been printed. The resolution obtained was essentially diffraction limited. Iridium coated mirrors were used with 37 nm radiation and Mo/Si multilayer coated mirrors with 14 nm radiation. A 1:1 magnification Offner Ring-field system with iridium coated mirrors has been used with 42 nm radiation. This optic has imaged line widths as small as 0.2 microns, which is close to the diffraction limit for this system. Transmission masks were used for all these experiments and the radiation was obtained from an undulator in the Vacuum Ultraviolet Synchrotron Storage Ring at Brookhaven National Laboratory.

We have designed and tested a-periodic multilayer structures containing protective capping layers in order to obtain improved stability with respect to any possible changes of the capping layer optical properties (due to oxidation and contamination, for example)-while simultaneously maximizing the EUV reflection efficiency for specific applications, and in particular for EUV lithography. Such coatings may be particularly useful in EUV lithographic apparatus, because they provide both high integrated photon flux and higher stability to the harsh operating environment, which can affect seriously the performance of the multilayer-coated projector system optics. In this work, an evolutive algorithm has been developed in order to design these a-periodic structures, which have been proven to have also the property of stable performance with respect to random layer thickness errors that might occur during coating deposition. Prototypes have been fabricated, and tested with EUV and X-ray reflectometry, and secondary electron spectroscopy. The experimental results clearly show improved performance of our new a-periodic coatings design compared with standard periodic multilayer structures. (C) 2008 Optical Society of America.

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

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

Si/Gd multilayers designed as narrowband reflective coatings near 63 nm were developed. The highest peak reflectance of 26.2% at a 5 degrees incident angle was obtained at 62 nm, and the spectral bandwidth was 7.3 nm FWHM. The fits for x-ray and extreme ultraviolet reflectance data of Si/Gd multilayers indicate the possibility of silicide formation at the Si-Gd interfaces. B(4)C, W, and SiN were deposited as interface barrier layers to improve the reflectance of Si/Gd multilayers. More than an 8% increase in reflectance was observed from the interface-engineered Si/W/Gd and Si/B(4)C/Gd multilayers.