The manufacture of grazing incidence X-ray mirrors must be accompanied by metrology at all stages of production. Traditional interferometric methods of measurement are less suited to grazing incidence optics than automated probes linked to computers. Stylus probes can be used at all stages of production, whereas non-contact optical probes are mainly useful at the final stages of polishing and figure adjustment. To characterize an X-ray mirror fully, the metrology must not only have high sensitivity, but also the ability to detect perturbations over a wide range of spatial frequencies.
The Phase Measuring Interferometer (PMI) technique has been adapted to the measurement of small scale features of very high quality (low scatter) optical surfaces. The method described has good vertical and lateral resolution over a wide range of fields. It is non-contacting, applicable to various materials and coatings, and can be extended to spherical and aspherical surfaces. The compact PMI device can be modified to provide in-situ measurements on both small and very large optical surfaces. Data, including rms surface roughness and surface contour maps, are presented for several surfaces. The nature and effect of the principal error sources are also discussed.
Previous work has demonstrated the use of the LINNIK Point Diffraction Interferometer for the measurement of wavefront error in soft x-ray imaging systems. Operational wave-lengths from 632.8nm (He-Ne) down to 313.1nm (Hg) have been used. This paper describes our extension of the technique to 253.7nm together with a demonstration. of feasibility at 121.6 nm (Hydrogen. Lyman-α), we believe for the first time. Finally the possibility of working at soft X-Ray wavelengths is considered.
The use of focusing X-ray systems depends upon the specular reflection of grazing incidence. These systems require mirrors with both excellent surface figure and superior surface finish. In order to obtain an efficient predictable method of fabricating such optics, Perkin-Elmer's computer-controlled polishing techniques have been adapted for grinding and polishing cylindrical mirrors. This process accurately controls the time that the tool polishes at each surface location to achieve the prescribed surface material removal.
Displacement measurement and motion control are discussed for rotary and linear axes of motion, as necessary for the dimensional measurement and diamond-tool machining of grazing incidence x-ray optics. Examples of available performance levels are drawn from measurements made on current developmental hardware, and are coupled with speculation on possible future extensions.
In fabricating and testing of mirror surfaces for X-ray optics profile measurements with a height resolution of the order of one Å are required. This measurement accuracy is not provided by conventional interferometric test methods applied in the optical industry. Very powerfull instruments, however, are ac-interferometers which have been developed in recent years. AC-interferometers are capable of detecting height differences with a precision approaching one Å. The first part of this paper gives a survey of various ac-interferometers. Their main concepts and limitations will be discussed. In the second part a newly developed ac-technique will be presented. A step height measuring microscope built on this principle will be described. With a response time of 1 msec, this instrument is capable of detecting height differences smaller than 10 Å. This very practical measurement tool is primarily used to measure topographies of machined etched or sputtered surfaces. Application to slope mapping of spherical surfaces is feasible. Results of various measurements are presented.
Radiography, or the technique of recording an x-ray image of a specimen in contact with a photographic film, came into being almost simultaneously with the discovery of x-rays themselves. A few years later, in 1913, Goby added the use of the optical microscope to enlarge the radiographic image, creating the technique of microradiography. The imaging of very thin specimens was precluded by the hardness of the x-rays used, but in 1936 Lamarque and Turchini made the first microradiographs using soft x-rays, opening up the possibility of working with single biological cells or subcellular components. In the 1950s, the need for higher magnification for such studies led to a division of effort into three rather distinct approaches: the use of x-ray optical devices, the point projection method, and the line initiated by Ladd, Hess, and Ladd, who showed that essentially grainless x-ray sensitive materials can be used in place of silver-halide photographic film and the image viewed at high magnification in the electron microscope. The present conference is devoted to topics which are related to the first of these; nevertheless the organizers of the conference, working we think on the sound principle that knowledge about parallel approaches may be of value, have asked us to report briefly on the status of the last approach. We will do this under two headings: current usage and current technique.
The operational range of low angle X-ray scattering was extended to particles and structures of about 1-2 μm by using CKα-radiation with a wavelength of 44.7 Å. For particles of about 1 μm in diameter, the central scattering was not observed accurately with characteristic X-rays such as CuKα. The size, shape and hydration of chloroplast have been measured by using low angle soft X-ray scattering with CKα-radiation, emitted from a high power X-ray tube and from synchrotron radiation. Chloroplasts were found to have a radius of gyration of 2.15 ± 0.5 μm, corresponding to a particle diameter of 5.8 ± 0.2 μm. The volume was calculated from Porod's invariant and was found to be 41.0 ± 12.0 μm3. Absolute measurements were performed directly, without weakening the primary beam, permitting the calculation of the mass of a chloroplast. The mass of the chloroplast was found to be 40.0 ± 0.07 pg, containing 0.45 pg H20/pg chloroplast. The maximum enlargement of the chloroplast particle was determined from the pair distribution function and was found to be 5.8 ± 0.2 pm. The central scattering for the chloroplast with a diameter of 6.0 μm was observed with-in 20' of the scattering angle with CKα-radiation. The origin of the difference from the nominal value in the Guinier region can be ascribed to the effect of interparticle interference when changing the density of the solvent to 10% glycerol. It should be pointed out that the use of this radiation and a synchrotron source enables us to obtain scattering of particles of μm size, almost free from the influence of the direct beam and parasitic scattering. Furthermore, by recording the intensity autocorrelation function, from which the weight average and number averaged radii of gyration, size and size distribution can be obtained, we are enabled to study the relative dispersion from dilute particle dispersion within 0.01 arcsec and the physico-chemical changes of whole cells and organelles with respect to aging, surface, and electrostatic interactions.
We have investigated the possibility of adding grazing incidence relay optics (GIRO) to an advanced nested solar X-ray telescope in order to enhance or extend the overall performance of the system. The instruments studied include magnifiers and collimators. We envision that a particular GIRO instrument will be moved upon command into or out of the focal plane of the main telescope. Ray tracing studies reveal the optimum design among the several GIRO options.
Techniques have recently been developed for the fabrication, by sputtering, of multi-layer structures in which the individual layers may have thicknesses as little as a few atomic diameters. Diffraction experiments with x-rays of wavelength ranging from less than 1 Å to 113 Å have shown these layered synthetic microstructures to have a high degree of perfection. They act as efficient reflectors for x-rays and EUV radiation at angles of incidence from 0o to almost 90o (extreme glancing incidence). Experimental results using normal incidence imaging optics at soft x-ray wavelengths are shown. Such optics can be used in a variety of configurations for both solar and non-solar x-ray astronomy. The advantages of two particular systems - the single mirror and the hybrid Wolter-LSM system - are discussed and performance calculations presented.
Recently developed multilayer coatings permit use of normal incidence optics for soft x-rays promising a resolution that should be substantially better than that obtained with grazing incidence optics. We describe the design and assembly of a Schwarzschild objective for a scanning x-ray microscope. The Schwarzschild objective, consisting of two nearly concentric spherical mirrors promises diffraction-limited resolution for soft x-rays.
An X-ray microscope with a zone plate linear monochromator is described. A new micro zone plate for this microscope with one hundred zones was made. X-ray microscopy with synchrotron radiation has shown that a resolution in the 50 nm range has been achieved.
The present capabilities of microlithography are discussed, with emphasis placed on resolution and pattern distortion. The current limits of optical reduction lithography, electron beam lithography, and optical and x-ray proximity printing are presented. It is shown that currently the major factor limiting resolution in electron beam lithography is electron scattering in the resist and substrate. Recent progress in the theoretical understanding of this scattering limit is discussed, and new techniques for reducing the resolution degradation caused by this scattering are described.
One method for fabricating high resolution (≈.1μm) Fresnel zone plates suitable for focusing ultrasoft ≈3nm) x-rays is electron beam lithography. Present technology limits the device size to about 100μm. For a scanning microscope we need to produce a small focal spot free of background. This requires a central stop on the zone plate as well as a collimator to eliminate the zeroth order radiation. The apodized region is now a significant fraction of the zone plate area and the intensity in the focal plane is no longer the Airy pattern of an ideal amplitude zone plate. We have calculated the intensity distribu-tions of some feasible zone plates with 50 or fewer open zones. The results indicate that an acceptably small fraction of the first order radiation is shifted to the higher order lobes. In addition, we have calculated the wavelength bandpass and allowable off-axis tilt for zone plates and conclude that they should produce an intense nearly diffraction limited spot when used with suitably monochromatized synchrotron radiation.
The process to manufacturing free-standing diffracting transmission gratings with high ruling density and high efficiency is described. This process has been developed at the Dr. Johannes-Heidenhain GmbH in cooperation with the Max-Planck-Institut. Two steps are involved, the mechanical ruling of the original master and the photomechanical replication of the in dividual grating facets. At present gratings of up to 2000 l/mm are available. Measured X-ray efficiencies are close to the theoretically expected values.
Gold transmission gratings with 0.3 um spatial period, 0.6 μm thick have been fabricated, and are being used for the spectroscopy of high temperature, laser produced plasmas. A transmission grating has been coupled with a soft x-ray streak camera, producing the first time resolved (20 psec resolution) continuous x-ray spectrum over the range 0.1-1.5 keV from a laser produced plasma. In audition, a transmission grating has been coupled with a high resolution, Winter-design x-ray microscope to produce an imaging spectrometer of unprecedented spatial and spectral resolution. In laboratory experiments the imaging spectrometer demonstrated a spectral resolving power, λ of 200 and a spacial resolution of 1 μm.
We consider the advantages and disadvantages for astrophysical observations of a normal incidence X-ray telescope. Our baseline configuration is for a 2.4 meter diameter mirror operating at 0.23-0.28 keV with a CCD detector having a pixel size equivalent to 0.1 arcsec. This resolution enables X-ray images to be made comparable to those of Space Telescope (ST) in the optical and to those of the Very Large Array (VLA) in the radio for a large number of sources. Specific examples cover essentially the entire range of astrophysics.
During the twenty years in which X-ray imaging has been used for Solar studies, every major advance in image quality has resulted in significant scientific achievements. The rapid development of grazing-incidence (GI) techniques culminated in the enormous progress resulting from the Skylab missions. Additional improvements in mirror fabrication technology since that time show that arcsecond imaging is now achievable using traditional GI systems. An alternative scheme, using normal-incidence optics offers the promise of sub-stantially improved spatial resolution and considerable cost savings. We consider what scientific objectives could be pursued if 0.1 arcsecond imaging becomes a reality in Solar coronal studies.
Deposition of multilayered diffraction coatings on the reflecting surfaces of a Wolter type I X-ray telescope offers the potential of using Bragg reflection to achieve enhanced effective area in selected high energy bandpasses. The structure of a gold-carbon multilayer has been optimized for study of 1.8Å iron-line emission with an X-ray telescope designed for observations from Spacelab. The response of this mirror assembly has been calculated as a function of X-ray energy and the resulting effective area is enhanced by a factor of 10 and peaks at 160 cm2 with a bandpass of 0.4 keV FWHM. This enhanced response is sufficient to allow study of the angular distribution of iron-line emission from the 20 brightest cluster X-ray sources during a 7 day Spacelab mission. The possibility of achieving X-ray imaging in narrow bandpasses at even higher energies has been investigated. We conclude that it should be possible to achieve effective areas of approximately 5 cm in bandpasses ≈ 1 keV wide for energies in the 15-25 keV range, a spectral region of much importance during the impulsive phase of solar flares.
Normal incidence offers several advantages over the traditional grazing incidence designs of X-ray optics, but an actual normal incidence device had never previously been made. We describe the results of our measurements of the imaging performance of a normal incidence soft X-ray telescope at BKa (0.183 keV, 67.6 Å). The performance is quite good, and indicates that it is practical to consider normal incidence optics in the design of soft X-ray imaging systems. We describe our planned future tests and a possible astronomical application.
Proc. SPIE 0316, Reflectivity And Resolution Measurements Of Metallic Multilayers, Beryl, And Potassium Acid Phthalate (KAP) With Synchrotron Radiation In The 1 keV Region, 0000 (24 March 1982); doi: 10.1117/12.933151
A recently constructed reflectometer at LURE used with monochromatized intense synchrotron radiation offers new possibilities for absolute measurements of reflectivity and resolution for metallic multilayers, and natural and synthetic crystals in a wide range of wavelengths. Contrary to the procedure generally used for the reflectivity measurements, in the present arrangement the crystal or multilayer is set at a fixed angle θo corresponding to a desired energy Eo and the energy of the highly polarized incident photon beam is varied around this value by means of a double crystal monochromator. The reflectivity versus energy for a given polarization are obtained directly for the sample crystal. In this communication we give the first examples for the absolute reflectivity and resolution measurements around 1 keV of metallic multilayers, beryl and KAP thus illustrating the potential application of this method.
The results of high angular resolution grazing incidence scattering measurements of highly polished, coated optical flats in the X-ray spectral range of 1.5 to 6.4 κeV are reported. The interpretation of these results in terms of surface microtopography is presented and the implications for grazing incidence X-ray imaging are discussed.
X-ray scattering measurements of flat mirror samples taken with moderate (0.5 arcmin) and high (2.5 arc sec) angular resolution are reported. The measurements cover scatter angles ranging from a few arc seconds to ≈ 1 degree. By using standard scattering theories micro-roughness values are derived and spatial wavelength distributions inherent to the mirror surface are discussed.
A pulsed soft x-ray source for use in contact microscopy would provide high-resolution, high-contrast images with minimal radiation damage to the biological specimen involved. An x-ray plasma source offers some advantages over synchrotron radiation in terms of smaller physical size, lower cost, larger beam size, and higher flux per pulse. The operation of a pulsed plasma focus device is described and this system is compared to other plasma sources. Results of a radiation model calculation predict that the use of neon gas would produce 1.2- to 1.4-nm radiation in 50- to 100-J pulses (emitted into 47 sterradians) with an efficiency of 1%. The actual source is about 2 mm in diameter and the x-ray pulse lasts about 15 to 20 ns. By choosing the proper gas or electrode material, one can generate a combination of emission lines that cover the region between the carbon edge (300 eV) to 2 keV. The system operates in the pressure range of a few torr. With the x-ray resists being developed for submicron x-ray lithography, microradiographs can be produced that have resolutions of 0.1 pm. The intense pulsed output can provide enough flux to make possible the micrography of wet or alive specimens.
At present, a large imaging X-ray telescope with 80 cm aperture is being built in Germany. In order to support this program a 130m long X-ray test facility has been set up, which is successful in operation for about one year. One of its essential components are the focussing X-ray sours which have been developed by us with the following characteristics: flux density of 1013 counts sec-1 ster-1 at 1.5 keV, spatial uniformity of about 5%, temporal stability of 3% over 5 hours.
The main topics discussed at the Conference were multilayer mirror optics and their applications, the manufacture and metrology of X-ray optical components, and microfabrication, particularly of zone plates for X-ray microscopy. The attainment of high resolution and the full potential of multilayer mirrors will require advances to be made in manufacturing technology, metrology and in the selection of suitable substrate materials.