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Multilayers for x-ray optics
Troy W. Barbee Jr.
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Soon after the discovery of x-rays and their property of constructive interference scattering (diffraction) by solids resulting from the ordered array of atoms forming the solids, it was proposed that man-made (synthetic) layered structures might extend the range of utility of this phenomena into spectral domains not accessible using naturally occurring crystalline materials. The synthesis of such layered materials has been of research interest since the 1920's and in the past decade processes for the formation of multilayer structures of quality sufficient for x-ray optic applications have been developed. In this talk, a short review of the history of this work is given first. The development of effec-tive synthesis processes is then considered and current approaches summarized. The current status of the field of multilayer x-ray optics is then discussed with emphasis on figured structures. Current limitations and the potential for both technological and scientific advances are then considered.
Sputter deposition system for controlled fabrication of multilayers
R. P. Di Nardo,
P. Z. Takacs,
C. F. Majkrzak,
et al.
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A detailed description of a sputter deposition system constructed specifically for the fabrication of x-ray and neutron multilayer monochromators and supermirrors is given. One of the principal design criteria is to maintain precise control of film thickness and uniformity over large substrate areas. Regulation of critical system parameters is fully automated so that response to feedback control information is rapid and complicated layer thickness sequences can be deposited accurately and efficiently. The use of either DC or RF magnetron sources makes it possible to satisfy the diverse material requirements of both x-ray and neutron optics.
Automatic deposition of multilayer X-ray coatings with laterally graded d-spacing
M. P. Bruijn,
P. Chakraborty,
H. van Essen,
et al.
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A computer controlled e-beam evaporation system is described, which allows fully automated production of soft X-ray reflection coatings with laterally graded d-spacing. Thickness control is done by measurement of the soft X-ray reflection coefficient on a reference substrate during deposition. Graded thickness is obtained by computer controlled movement of shutters. A result is given for automatic deposition of a multilayer coating.
Space qualification of multilayered optics
Jean-Pierre Delaboudiniere,
Jean-Pierre Chauvineau,
Jean-Paul Marioge
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In order to demonstrate the possibility of using wavelength selective solar imaging telescopes, as part of the SOHO mission (under study by ESA), we evaluate experimentally the stability of multilayered mirrors illuminated by the sun.
Calculated reduction of radiation damage on thin layered interference mirrors
Paul L. Csonka,
Hiroshi Watanabe
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Thin Layered h Interfertence Mirrors consist of a collection of m = 0, 1, 2, ...,N thin material layers, the layer having thickness dm. The layers are separated from each other by other material such as dielectrics (possibly vacuum, although that is more difficult to realize). To simplify the calculation, here we treat the case where the separating layers are vacuum, the radiation is monochromatic with wavelength λ , and normally incident on the mirror. The dominant radiation damage is assumed to be caused by heating due to induced currents. We present design examples when dm << λfor all m. In each example the mirror reflectance is close to 100%, and resistance to radiation damage is calculated to increase by a factor fr. In the optical region fr > 102. Because of competing damage mechanisms, the order of magnitude of fr is probably more significant than its calculated numerical value.
Preliminary investigation of changes in x-ray multilayer optics subjected to high radiation flux
M. P. Hockaday,
R. L. Blake,
J. S. Grosso,
et al.
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A variety of metal multilayers was exposed to high x-ray flux using Sandia National Laboratories' PROTO II machine in the gas puff mode. Fluxes incident on the multilayers above 700 MW/cm2 in total radiation, in nominal 20 ns pulses, were realized. The neon hydrogen- and helium-like resonance lines were used to probe the x-ray reflectivity properties of the multilayers as they underwent change of state during the heating pulse. A fluorescer-fiber optic-streak camera system was used to monitor the changes in x-ray reflectivity as a function of time and irradiance. Preliminary results are presented for a W/C multilayer. Work in progress to model the experiment is discussed.
Thermal Stability of W/C Multilayer Films
Yasuo Takagi,
Steven A. Flessa,
Keith L. Hart,
et al.
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W(10A)/C(40A), W(15A)/C(15A) and W(40A)/C(10A) periodic multilayer films were prepared by magnetron sputtering and subsequently annealed at 730°C. The resulting change of the layered and crystal structures was studied by X-ray diffraction. The resulting structures largely depended on the thickness ratio of W to C. For example, in the W(15Å)/C(15Å) sample a-W as formed without any peaks of carbon crystals; in W(40Å) C(10Å)only W2C (orthorhombic) peaks appeared.
Figure Tolerancing Study of an Axisymmetric X-ray Microscope
T. F. Zehnpfennig
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The effects of various types of figure defects and misalignments on the imaging proper-ties of a grazing incidence x-ray microscope were investigated in detail using a special ray tracing program. The microscope, designed for use as a diagnostic instrument in laser fusion research, was of the Wolter Type-1 configuration, consisting of an ellipsoid and a confocal, coaxial hyperboloid. Figure tolerances which were investigated included those on roundness, the average slope, the mean diameter, and the variation in average slope with azimuthal position. The effects of surface ripples both in and out of the plane of the incidence were studied. The effects of angular and translational misalignments between the ellipsoid and the hyperboloid were investigated. The results of these tolerancing studies are summarized, and the tolerance budget which was then used to govern the fabrication process is described.
The Development of Single and Multilayered Wolter X-ray Microscopes
A. Franks,
B. Gale
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Scanning Wolter X-ray microscopes having resolutions of at least 0.1 pm at wavelengths down to 0.15 nm are being developed. The initial objective of the work is to produce a microscope mirror substrate which will be evaluated and used at 4 nm as a non-multilayered microscope. It will have virtually the same geometry as the mirror which will subsequently be used in multilayered form at much shorter wavelengths. The problems of substrate manufacture to the required tolerances together with the development of the associated specialised metrological instrumentation will be similar for both microscopes. A theoretical study has been undertaken in which the images produced by multilayered mirror systems are calculated by ray tracing, using geometrical diffraction optics and the Debye approximation. Each element of the wavefront is described by a ray carrying the field vectors. An optimisation procedure for calculating the layer structure has been derived. For maximum flux throughput, the variation of the layer structure and roughness must be controlled to about 0.1 nm.
X-Ray microscope using multilayer optics with a laser-produced plasma source
J. A. Trail,
R. L. Byer
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All present X-ray microscopes involving focusing optics use synchrotrons as their source of soft X-rays. We describe our design and development to date of a scanning microscope which uses normal incidence multilayer mirrors in a Schwarzschild configuration to focus soft X-rays from a laser produced plasma to a spot diameter of less than 1000A. We compare the expected flux for this microscope with the fluxes expected and achieved by other investigators. The alignment tolerances for the objective were determined by raytracing. These tolerances and proposed means of achieving them will be discussed.
Elliptical X-ray analyzer spectrograph application to a laser-produced plasma
Tina J. Tanaka,
Merrill A. Palmer,
Burton L. Henke
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A preliminary experimental study was conducted on the application of an elliptical analyzer spectrograph to X-ray diagnostics of pulsed plasmas. This spectrograph was designed to record a range of 100-2000 eV X-rays on calibrated Kodak RAR-21497 film. Using point calibrations and theoretical models, the spectrograph efficiency was predicted. Basic spectrograph geometry and photographic calibrations are presented in companion papers. A 20 J, 6 ns duration Nd:glass laser pulse was focussed upon planar targets of gold, aluminum, teflon and boron carbide. Sample spectra for line and X-ray yields analysis are presented.
Survey Of The Collective French Effort On X-Ray Multi Layered Optics
P. Dhez
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In this overview we emphasise the present effort on multilayers studies in France. Several French laboratories have coordinated a research program in view to develop the different technologies now used to prepare multilayered optics.This program takes into account the needs to overcome the constraints of the grazing incidence X-UV optics for the synchrotron source users, plasmas physicists and astrophysicists.
A Unified Geometrical Insight for the Design of Toroidal Reflectors with Multilayered Optical Coatings: Figured X-ray Optics
Gerald F. Marshall
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An isoangle is the locus of the points of incidence for rays with the same grazing angle of incidence from a point source. An isobragg is the locus of the points of intersection with a surface of reflected rays with the same wavelength. The geometrical and spectral radiant flux collection characteristics of toroidally shaped reflectors are explored by studying the evolving patterns of isoangles and isobraggs as the form of the reflecting surface changes. The analysis is applied to x-ray multilayered structures which reflect according to Bragg's Law. This investigation leads to the design considerations for optimizing the reflected flux with increased wavelength resolution.
Multilayer Mirrors as X-ray Filters for Slit Scan Radiography
Robert S. Nelson,
Zoran L. Barbaric,
Anthony R. Ricci,
et al.
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X-rays from a radiographic W-anode tube are reflected from a planar multilayer mirror into a slit-like beam of narrow energy bandwidth. The multilayer mirror functions as a tuneable energy filter which could be useful for radiological applications where a high contrast image (mammography, angiography) or tissue composition information (lesions, bone mineral loss) is desired. Low reflectivity at undesired energies permits; 1. operation of the W-anode tube at much higher voltage levels than is possible with conventional filtration, 2. the removal of most of all non-fixed beam filtration. These modifications significantly enhance the useable x-ray fluence. The slit scan imaging format also minimizes detected scattered x-rays and so improves image contrast. A simple model is used to optimize the energy dependent detected signal-to-noise ratio (SNR) with respect to the total energy absorbed by the patient. Theoretical reflectivity curves for ReW-C mirrors which include the effects of surface roughness and layer thickness errors are presented along with W-anode tube spectra reflected from a 2x4 inch ReW-C mirror (11-22Å).
Thin Films And Gratings: Theories Used To Optimize The High Reflectivity Of Mirrors And Gratings For X-Ray Optics
B. Vidal,
P. Vincent,
P. Dhez,
et al.
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Near normal incidence is necessary to design low aberrations X-Ray systems. High reflectivity may be obtained with suitable multilayers deposited on gratings. Classical thin film theories previously used for analysis and synthesis of dielectric multilayers for the visible spectral region are applied in this paper in the UV and soft X-ray range. The optimal multilayer determined by these methods can be deposited onto a grating in order to increase its efficiency. For incidence angles lower than 40; and low wavelength-to-groove-spacing ratios, the efficiency of the total system may be predicted with a scalar theory. Then, the reflectivity is the product of the efficiency red on a universal grating efficiency curve by the multilayer reflectivity. Results will be given for several gratings geometries and various multilayers.
Structural Study Of Multilayered Vanadium/Nickel Superlattices
Hitoshi Homma,
Yves Lepetre,
James M. Murduck,
et al.
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We have studied the microstructure of V/Ni metallic superlattice, using x-ray and neutron diffraction. We find a sharp and broad rocking curves around the first order Bragg peak, and attribute them to a columnar structure which gives rise to two modulation structures; one the ordinary layered structure within the columns and the other the averaged modulation structure which produces the sharp rocking peak.
Multi Layers X-Ray Polarizers
A. Khandar,
P. Dhez
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The importance to have polarizers in the X-ray range is first justified. By comparaison to the other parts of the electromagnetic wavelength range, the different ways to get such polarizers is then briefly described . Artificial Bragg reflectors obtained by multilayers used like linear X-UV polarizers are finally considered and evaluated. An experimental device using two 45° reflections on multilayers, and analogous to crossed polarizers, is presented. For a demonstrative purpose, in the case of the 304A wavelength corresponding to the Hell line, first results of polarization rate measured by using Hf/Si multilayers is given.
Computing X-Ray Reflectance of Focusing Multilayer Films
Dwight W. Berreman
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F. Abeles developed an exact 2X2 matrix method for computing reflectance and transmittance of flat stratified structures of arbitrary complex refractive index profile. By distorting the coordinate system for his method from rectagular to confocal ellipsoids of revolution, the same method can be applied to focusing systems. The well-known 1:1 toroidal focusing geometry occurs at the equators of the ellipsoids. Near the equator, if the Bragg angle is not too small, and also close to the axis of foci, curved layers of uniform thickness are often close enough to the ideal profile for satisfactory spatial and spectral resolution. In very thick multilayers with small absorption, uniform layer thickness in the toroidal geometry results in some dispersion with PendellOsung fringes. Away from the equator or axis, and particularly at low Bragg angles, profiling or gradation of thickness may be necessary for satisfactory resolution. Examples of computations with Abeles's method are shown.
Disorder And Diffusion In Thin-Film Multilayers
A. M. Saxena
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Practical multilayer devices usually have some in-built imperfections that adversely affect their properties. An analysis of the diffraction properties of a multilayer, and its comparison with the results obtained from a theoretical model of a multilayer with imperfections, can give information about the type and magnitude of imperfections in the multilayer. This information can then be used to make multilayers with better characteristics.
Image Formation in Multilayers Optics: the Schwartzschild Objective
B. Lai,
F. Cerrina,
J. H. Underwood
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The construction of efficient X-ray optics has been hampered in the past by the strong aberrations implicit in the use of grazing optics. This is in turn due to the necessity of working below the critical angle for total external reflection. For most materials this (grazing) angle fallsU.,2) in the range of a few degrees. The advent of Layered Synthetic Microstructures (LSM) has opened up new possibilities, as mirrors with high reflectivities at large incidence angles in the soft X-ray region, particularly below the Carbon edge, have been demonsated. 1:1 imaging with LSM deposited on a curved Silicon substrate has been obtained (')
F-beam Evaporated Multilayer Soft X-ray Coatings, Analyzed With Cu-K Radiation
M. P. Bruijn,
P. Chakraborty,
H. van Essen,
et al.
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Results are presented for deposition of multilayer soft X-ray coatings, monitored during deposition with soft X-ray reflection and analyzed afterwards with Cu-Ka reflection. Some calculations on and simulation of non ideal behaviour of multilayer coatings are presented, mainly focussed on roughness problems. Experimental results for e-beam evaporated and sputter-deposited multilayers are compared and a discussion of possible causes for the differences is given.
Sputter Deposited Multilayer V-UV Mirrors
Felix E. Fernandez,
Charles M. Falco
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The design and fgbrication of aluminum/niobium multilayers to be used as normal-incidence reflectors for 300 A radiation are presented. Preliminary characterization results are discussed showing the effects of interfacial roughness and diffusion.
The Characterization Of Multilayers Analyzers - Models And Measurements
B. L . Henke,
J. Y. Uejio,
R. E. Tackaberry,
et al.
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A procedure is described for the detailed characterization of multilayer analyzers which can be effectively applied to their design, optimization and application for absolute x-ray spectrometry. An accurate analytical model has been developed that is based upon a simple modification of the dynamical Darwin-Prins theory to extend its application to finite multilayer systems. Its equivalence to the optical E&M solution of the Fresnel equations at each interface is demonstrated by detailed calculation comparisons for the reflectivity of a multilayer throughout the angular range of incidence of 0 to 90° . A special spectrograph and experimental method is described for the measurement of the absolute reflectivity characteristics of the multilayer. The experimental measurements at three photon energies in the 100-2000 eV region are fit by the analytical modified Darwin-Prins equation (MDP) for I( 0), generating a detailed characterization of two "state of the art" multilayers, a sputtered tungsten-carbon of 2d 21 70 A and a molecular lead stearate of 2d 100 A. The fitting parameters that are determined in this procedure are applied to help establish the structural characteristics of the particular multilayer.
Synchrotron Based Measurements Of The Soft X-Rayperformance Of Thin Film Multilayer Structures
D. R . Kania,
R. J. Bartlett,
W. J. Trela
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There is a great interest in the application of thin film multilayer structures for x�ray optical elements. We have developed aparatus and techniques to measure the reflectivity of multilayer structures on flat substrates a function of energy at angles from grazing to near normal incidence using a synchrotron. We will present descriptions of our measurement techniques and aparatus along with a comparison between theoretical calculations and experimental data.
Determination Of Thickness Errors And Boundary Roughness From The Measured Performance Of A Multilayer Coating
Eberhard Spiller,
Alan E. Rosenbluth
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The influence of thickness errors and boundary imperfections on the performance of a multilayer x-ray mirror is discussed and it is shown that both can be obtained separately from a measured reflectivity curve at a short x-ray wavelength. Multilayers have greatly reduced scattering compared to single films, and for this reason rough boundaries and gradual transition layers between the film materials give practically identical performance. A simple Debye-Waller factor is not sufficient to describe the performance of a multilayer with many layers at short wavelengths.
Measured X-ray Performance of Synthetic Multilayers Compared To Calculated Effects of Layer Imperfection
James L. Wood,
Nicola J. Grupido,
Keith L. Hart,
et al.
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In connection with the manufacture of OVONYXTM multilayer x-ray optical elements, investigations have been carried out into the effects of various types of layer imperfections on the x-ray optical properties of multilayers. These have included extensive numerical modeling of real multilayers (using a computational scheme based on the complete dynamical theory) including simulations of interface diffusion, deviations from constant d-spacing, and interface roughness. Results are presented for several examples of Hf-Si and W-Si multilayers, including comparison of measurements at Cu-Kato the theoretical model.
Characterization Of Multilayered Structures For Soft X-Ray Mirrors
J. P. Chauvineau,
J. Corno,
D. Decanini,
et al.
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Three different experimental techniques are applied to the measurement of physical parameters involved in the determination of the optical performances of multilayers designed for soft X-ray mirrors. Geometrical parameterssuch as single layer thicknesses, multilayer period and interface roughness are evaluated by using soft X-ray reflectometry during the deposition process and grazing incidence X-ray reflectometry with the Cu K, radiation after the multilayer fabrication. The growth mechanism and surface composition of ultra-thin films constituting the multilayers are obtained by Auger electron spectroscopy performed during the layer deposition. The whole of these measurements is applied to elaborate a modelisa-tion of the real multilayers in view of their optical applications.
Measurement Of Multilayer Mirror Reflectivity And Stimulated Emission In The XUV Spectral Region
C. J. Keane,
C. H. Nam,
L. Meixler,
et al.
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In recent years there has been a great deal of work aimed at generating soft x-ray lasing action in the laboratiory, and a number of promising schemes to demonstrate this have been discussed at length'. Recently, there have been several encouraging experimental demonstrations of significant amplification of soft x-rays. The achieved gain length products have been as high as 6.0-6.5 in these experiments.2,3
Novel Characterization Of Thin Film Multilayered Structures: Microcleavage Transmission Electron Microscopy
Yves Lepetre,
Ivan K. Schuller,
George Rasigni,
et al.
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Microcleavage Transmission Electron Microscopy has been applied to the study of many properties of multilayered samples. We illustrate the unique capabilities of this technique to study long range perpendicular thickness drifts, lateral variations, roughness, substrate quality and island structures.
Construction Of A Multilayered X-Ray Telescope For Solar Coronal Studies From Space
Leon Golub,
George Nystrom,
Eberhard Spiller,
et al.
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We discuss the construction and flight of an ultrahigh resolution soft x-ray telescope which is to be flown on a NASA sounding rocket in 1986. The possibility of using normal incidence figured optics allows the construction of x-ray mirrors which, on a cost-for-cost basis, have an order of magnitude higher spatial resolution than do grazing-incidence mirrors. For the past two years our groups at the Smithsonian Astrophysical Observatory and the IBM Watson Research Center have been collaborating on x-ray multilayer testing (along with R. Bartlett of Los Alamos National Laboratory) and on the design and construction of a Ritchey-Chretien telescope. The initial use of this instrument will be to study the solar x-ray corona at very high spatial resolution; future uses will include simultane-ous high resolution imaging and spectroscopy and soft x-ray/XUV astronomy. The engineering requirements for flying this instrument on a sounding rocket are substan-tial and we will discuss the specialized design problems which have had to be overcome. The optical design parameters call for performance which exceeds the visible-light diffraction limit, while the multilayer coatings for soft x-ray wavelengths require substrate surface finish of the highest quality. We will also discuss some of the future astrophysical applications of the technique and some of the possible instruments which may be flown in the next few years.
Aspherization And Multilayer Coating Of A RITCHEY-CHRETIEN Telescope For A = 30.4 nm
J. P. Chauvineau,
D. Decanini,
M . Mullot,
et al.
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A high vacuum system designed for the deposition of multilayers for soft X-ray mirrors is described. It is applied to the aspherization and multilayer coating of the mirrors of a solar Ritchey-Chretien telescope. In a first step, laterally graded boron layers are deposited on flat polished silica substrate in order to determine their thickness profile by visible light interferometry. The next step consists in the characterization ofmultilayers deposited on top of the boron layer. Grazing incidence X-ray interferometry is applied to the measurement of interface roughness ; the results are used to predict the performances of W/Si multilayers ; it is found that reflectivity values of about 25 % could be obtained for normal reflection at 30.4 nm.
Design And Analysis Of Spectral Slicing X-Ray Telescope Systems
Richard B. Hoover,
Shao-Hua Chao,
David L. Shealy
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Layered Synthetic Microstructure (LSM) x-ray optics can he used to couple a conventional Wolter Type I or Wolter-Schwarzschild x-ray mirror to a high sensitivity/broad wavelength response detector. Since the LSM mirror can effectively reflect only a narrow spectral slice of the incident radiation, this new instrument is referred to as a "Spectral Slicing X-Ray Telescope." By the use of figured multilayer (LSM) optics, it is possible to alter the plate scale of the primary mirrors to allow improved spatial resolution to he realized with solid state detectors. We will present the results of theoretical design and analysis studies of several spectral slicing x-ray telescope systems utilizing LSMs figured as hyperboloids, spheres, ellipsoids, and constant optical path aspheric elements. The RMS spot size and point spread function calculations will be presented for systems in which the LSM optics are figured to yield magnifications of 2X, 6X, and 8X, and it will be demonstrated that these systems yield superior off-axis performance over the primary optic alone.
Formula For The Meridional Section Of The Point Spread Function Of Wolter I X-Ray Telescope And Thin-Film Multilayered Optics
Shao-Hua Chao,
David L. Shealy
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The flux flow equation of Burkhard and Shealy1 is a simplified equation which can be used to evaluate the energy flux density at the image plane for a general optical system. Since the flux flow equation is based on the differential geometry of the wave front passing through the system, the energy flux density at the image plane can be computed by tracing a single ray through the system and using the flux flow equation. This technique has been used to calculate the meridional section of the point spread function of Wolter I x-ray telescopes and thin-film multilayered optics. Results, which have been obtained by the flux flow ray tracing method for the point spread function of several Wolter I x-ray telescopes and hybrid x-ray telescopes using convexed thin-film multilayered optics located near the primary focus, are compared with the RMS blur circle results and the point spread function results obtained by conventional ray tracing techniques.
Layered Synthetic Microstructures for Solar EUV Telescopes
Ritva A. M. Keski-Kuha,
Roger J. Thomas,
Gabriel L. Epstein,
et al.
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Due to the recent development of the design and production of layered synthetic microstructures (LSMs) we can entertain concepts for EUV instrument design that use normal incidence components. Thus, LSMs offer the possibility of producing an efficient extreme ultraviolet (EUV) telescope for solar studies that takes advantage of contemporary normal incidence mirror technology. This paper discusses the applica-tion of LSMs to figured mirrors suitable for solar EUV instruments. Initial studies were performed for a single mirror telescope consisting of an f/18, 200cm focal length, off-axis paraboloid. The design trades in terms of peak reflectance and broad bandpass in the 300Å region and deposition considerations will be discussed.
Design And Fabrication Of Carbon-Tungsten Multilayers Using Ellipsometry
Eric Ziegler,
Philippe Houdy,
Louis Nevot
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Recently, there has been increased interest in near normal incidence optical sytems for use in the soft x-ray domain (10Å < A < 100A). This region of the x-ray spectrum is important because many organic constituents have their K-absorption edges in this range. One important application of near normal incidence soft X-rays optical systems is lithography, for which 44.7Å radiation is particularly well suited. Hence we have concentrated our studies at this wavelength. Stacks of alternating layers with low and high electron densities can be used to obtain mirrors with substantial reflection coefficients. We have developed a model to obtain the optical properties of such a stack in a fashion similar to that used for visible light. This model can be shown to be quite accurate for near normal incidence and for wavelengths long compared to the interatomic spacing. We have also shown from this model that a smooth, 200 layer, carbon-tungsten stack would provide a reflectivity of approximately 25% at 44.7Å when used in normal incidence. Sputtering techniques (diode, triode) were used to produce carbon-tungsten multilayers with each tungsten film approximately 10A thick. Grazing X-ray reflection and X-ray photoelectron spectroscopy have shown that layers with minimal roughness and adequate densities have been achieved. The dielectric functions for the materials have been determined by ellipsometry. We have been able to calculate and to show experimentally that an ellipsometry monitoring system allows very precise in-situ control of layer growth. Calculations and preliminary measurements show the use of ellipsometry to achieve an ideal multilayer growth.
Multilayer, Convex Surfaces For Soft X-Ray Diffraction
P. G. Burkhalter,
D. B. Brown,
P. D. Rockett,
et al.
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X-ray spectral analysis plays a major role as a diagnostic for hot, dense plasmas. One means for collecting spectra is the use of convex-curved diffraction crystals. Synthetic multilayer structures offer high reflectivity for soft x-rays. Convex diffraction surfaces can be formed by sputtering onto smooth surfaces and by dipping into solutions such as lead myristate. Convex-curved multilayer structures have been evaluated by analytical diffraction models and experimentally by collecting aluminum spectra from plasmas generated by exploded wires sources and by focused laser beams.
Multilayers On Flexible Mica
D. J. Nagel,
J. V. Gilfrich,
D. B. Brown,
et al.
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X-Ray optics can be broadly classified as being either reflective or transmissive, with either broad or narrow band pass, configured to be either non-focusing or focusing. Multilayers which reflect (diffract) soft x-rays with intermediate resolution, which can be elastically bent into either convex, non-focusing or concave, focusing geometries, are of interest in this work. Preparation and characteristics of the multilayers are described with the experimental details of the concave and convex geometries following in the succeeding two sections.
Image Quality Of Figured Multilayered Optics
Bryan G. Peterson,
Larry V. Knight,
Hans K. Pew
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The reflectivity and resolution of a multilayer structure is strongly affected by the roughness at the interfaces between two successive layers and by the amount that the constituent materials will diffuse into one another at the interfaces. Performance is also affected by the variations in individual layer thicknesses and by inhomogeneities in the materials. These deviations from the ideal multilayer will also affect the quality of the image from a figured multilayer optical element. The theory used to model the effects of non-ideal multilayers on the image quality of figured optics will be discussed. The relationship between image quality and multilayer structure quality will be illustrated with several examples.
Physical And Chemical Characterization Of Multilayered Structures
J. M. Thorne,
L. V. Knight,
B. G . Peterson
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It is important to know the physical and chemical properties of a multilayer if its performance is to be compared to theoretical predictions, or if guidance is needed for the production of superior multilayers. Accurate, nondestructive analytical methods, such as neutron activation analysis, are restricted to certain elements. Certain destructive methods, such as total carbon analysis by combustion, can be sensitive enough for use with very small samples. The method of choice depends upon sensitivity and specificity, both of which are discussed in this paper.
Simplified X-Ray Multilayer Reflectivity Calculations Using Lossy Transmission Line Theory
Paul D. Rockett,
James H. Lupton
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Lossy transmission line theory is shown to be a physically meaningful technique for calculating the reflectivity of thin-film multilayer structures with complex indices of refraction. The problem is approached by treating each layer as a transmission line characterized by a given impedance. Reflections are naturally due to impedance mismatches; the impedance is shown to be simply the ratio of the electric and magnetic fields of the plane waves. Both normal and oblique incidence results match conventional calculations, but the transmission line approach requires minimal coding.
LSM-based X-Ray Diagnostics For Magnetic Fusion Energy Applications
E. D. Franco,
M. J. Boyle
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The use of layered synthetic microstructures (LSMs) as components of a radiation-hardened x-ray diagnostic designed to observe plasma instabilities in magnetic fusion energy (MFE) devices is discussed. Off-axis paraboloidal LSM optics are analytically evaluated as a means of mitigating the neutron- and gamma-induced detector noise and damage associated with deuterium-tritium operation that afflict direct line-of-sight instruments. Neutron-induced LSM damage is experimentally observed at a 14 MeV neutron fluence of 3.3 x 1014 n/cm2.
Multilayer Structures For X-Ray Laser Cavities
N. M. Ceglio,
D. G. Stearns,
A. M. Hawryluk
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Recent demonstrations of the generation of amplified spontaneous emission (ASE) at soft x-ray wavelengths have spurred interest in normal incidence multilayer structures for use as x-ray laser (XRL) cavity mirrors. Calculations indicate that cavity mirrors can provide significant enhancement of XRL output, and drive the oscillations to the saturation limit. Novel ideas for cavity output coupling may expand the versatility of XRL devices, while encouraging the marriage of lithographic and multilayer technologies to the general benefit of x-ray optics. Preliminary tests of a double pass cavity have already been conducted. These tests point out the importance of detailed cavity design issues, such as precision mirror alignment, mirror damage dynamics, and detailed mirror calibration to the future success of this field.
Experience With The In Situ Monitor System For The Fabrication Of X-Ray Mirrors
Eberhard Spiller
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Practical consideration for the fabrication of multilayer x-ray mirrors using in situ monitoring of the reflectivity for soft x-rays during deposition are discussed.
Layered Synthetic Microstructures for Long Wavelength X-Ray Spectrometry
J. A. Nicolosi,
R. Jenkins,
J. P. Groven,
et al.
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We have recently, briefly described the properties of several types of Layered Synthetic Microstructures, (LSM) and their use in the measurement of elements traditionally covered by the acid Phthalate and Langmuir - Blodgett diffracting structures.1 In this application, the wavelength range is extended to cover oxygen, nitrogen, carbon and boron. One of the major problems in working in the longer wavelength region is that the large incremental difference in wavelength per atomic number step makes it difficult to achieve a good comprise between the wavelength range coverable with a given d-spacing and the angular dispersion achievable. It is possible to optimize these structures to provide excellent diffraction and dispersion properties over most of the long wavelength characteristic x-ray emission region. By developing structures which suppress higher order spectra and by clever selection of substrate composition, both performance and range of application are extended beyond initial expectations. This paper describes some of the work that has been done to provide such optimization and then discusses results obtained with typical LSM's.
Performance of a LSM Spectrogoniometer For Characteristic X-ray lines
M. Arbaoui,
R. Barchewitz,
J. M. Andre,
et al.
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A spectrogoniometer designed to measure the quality of X-ray and X-UV dispersive devices is described. The reflgctivityoof Laye;ed Synthetic Microstructures (LSM's) is presented at three wavelengths (13 Å, 44.8 Å, 67.7 Å) corresponding to the emission lines of Cu, C and B respectively, emitted from a windowless X-ray tube. In particular, performance of Fabry-Perot etalons in the soft X-ray range is discussed. The observation of Cu 2p emission spectrum obtained with an optimized LSM dispersor provides a specific example of LSM's possibilities for X-ray spectroscopy.
Performance Of Layered Synthetic Microstructures In Monochromator Applications In The Soft X-Ray Region
P. Pianetta,
R. Redaelli,
T. W. Barbee Jr.
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Wide bandwidth, high throughput monochromators for synchrotron radiation applications have been developed using Layered Synthetic Microstructures (LSM's). A double crystal LSM monochromator has been demonstrated with an energy resolution of 3% at 1.5 keV and a tuning range of 0.8 to 3.5 keV. In addition, techniques for extending the tuning range to lower energies as well as studies of substrate perfection using soft X-ray topography will be described.
Measurements of Surface Scattering of X-rays Using a Triple Axis X-ray Spectrometer
F. E. Christensen,
N. J. Westergaard,
H. W. Schnopper
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In the process of developing a concentrating telescope for the next generation of X-ray satellites various techniques have been employed to deposit thin films of Au, Pt or Ni on a smooth substrate, Among these the following three methods are of particular interest in terms of making a high throughput X-ray telescope. The first method involves vacuum sputtering of the relevant thin film material onto a polished glass mandrel followed by replication onto a carbon fiber shell. In the second a thin film is deposited directly on lacquered Alfoils by vacuum sputtering. In the third a thin Ni shell is generated by electroforming. In all cases the thin film is deposited on thin shells and it is possible to achieve a large effective collection area by nesting them. X-ray scattering measurements made with a triple axis X-ray spectrometer have been used to test the smoothness of testsurfaces. In this spectrometer a perfect, channelcut Sicrystal extracts Fe Karadiation from a conventional X-ray tube. The radiation is incident on the thin film surface and the specularly reflected and scattered radiation from the thin film is analyzed by another perfect, channelcut Sicrystal. An essentially "tailless" probe of the scattered X-rays is obtained when the X-rays are reflected several times in the channelcut crystals. Measurements on surfaces obtained from various substrate materials and deposition techniques are presented and compared with measurements on a high quality Au testflat and a similar Pt testflat, produced by coating highly polished glassubstrates. It is demonstrated that the measurement technique provides an excellent and detailed test of the quality of the mirror surface.
Calibration Of Surface Roughness Transducers At Angstrom Levels Using X-Ray Interferometry
D. K. Bowen,
D. G. Chetwynd,
S. T. Davies
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An x-ray interferometer for calibration of microdisplacement transducers at sub nm levels is under development. Using the lattice spacing of high perfection semiconductor industry grade silicon as a reference, the objective is to produce a portable, absolute length standard with a precision of 1 part in 108 traceable to primary standards. The interferometer is of the Hart design and fabricated from a monolith of single crystal silicon. The triple-blade construction utilises Lauecase diffraction in beam splitter, mirror and analyser and is capable of an ultimate resolution of about 10 pm. The system is now operational, and the first trials, reported in this paper, have been entirely successful.