It is the task of x-ray optics to adapt the raw beam generated by modern sources such as synchrotron storage rings to a great variety of experimental requirements in terms of intensity, spot size, polarization and other parameters. The very high quality of synchrotron radiation (source size of a few microns and beam divergence of a few micro-radians) and the extreme x-ray flux (power of several hundred Watts in a few square mm) make this task quite difficult. In particular the heat load aspect is very important in the conditioning process of the brute x-ray power to make it suitable for being used on the experimental stations. Cryogenically cooled silicon crystals and water-cooled diamond crystals can presently fulfill this task, but limits will soon be reached and new schemes and materials must be envisioned. A major tendency of instrument improvement has always been to concentrate more photons into a smaller spot utilizing a whole variety of focusing devices such as Fresnel zone plates, refractive lenses and systems based on bent surfaces, for example, Kirkpatrick-Baez systems. Apart from the resistance of the sample, the ultimate limits are determined by the source size and strength on one side, by materials properties, cooling, mounting and bending schemes on the other side, and fundamentally by the diffraction process. There is also the important aspect of coherence that can be both a nuisance and a blessing for the experiments, in particular for imaging techniques. Its conservation puts additional constraints on the quality of the optical elements. The overview of the present challenges includes the properties of present and also mentions aspects of future x-ray sources such as the “ultimate” storage ring and free electron lasers. These challenges range from the thermal performances of monochromators to the surface quality of mirrors, from coherence preservation of modern multilayers to short pulse preservation by crystals, and from micro- and nano-focusing techniques to the accuracy and stability of mechanical supports.

The technological limit on the beam quality when modern synchrotron radiation sources are used is determined by the geometrical accuracy of the optical components. This in turn is limited by the accuracy of the measuring technique which is within the range of up to 0.05 arcsec rms for one meter mirror length, which corresponds (in the absence of waviness) to an uncertainty of the topography of 5 nm rms. If the topography can be measured with higher accuracy, modern methods of ion beam processing allow the surface to be postprocessed with a high resolution of depth. We will present first tests with a novel measuring device which allows deflectometric measurements by the ESAD principle (Extended Shear Angle Difference) to be carried out. The basic item of this device is a commercial electronic autocollimator (AC) whose exit aperture is tripartite. By suitable evaluation one is in consequence able to simultaneously determine the angle information belonging to three surface points situated next to one another. According to the ESAD method, the angular topography can be completely reconstructed from two sets of angular difference data. The uncertainty of measurements of angular difference is transferred with a factor close to 1 to that of the set of reconstructed angle. First measurements show a reproducibility of about 25 milli-arcsec rms at a time of integration of 0.4 seconds per point. With this set-up, in the first order, no guide errors, vibrations or air turbulences enter.

Stitching interferometry, using small-aperture, high-resolution, phase-measuring interferometery, has been proposed for quite some time now as a metrology technique to obtain 3-dimensional profiles of surfaces of oversized optical components and substrates. The aim of this work is to apply this method to the specific case of long grazing-incidence x-ray mirrors, such as those used in beamlines at synchrotron radiation facilities around the world. Both fabrication and characterization of these mirrors would greatly benefit from this technique because it offers the potential for providing measurements with accuracy and resolution better than those obtained using existing noncontact laser profilers, such as the long trace profiler (LTP). Measurement data can be used as feedback for computer-controlled fabrication processes to correct for possible topography errors. The data can also be used for simulating and predicting mirror performance under realistic conditions. A semiautomated stitching system was built and tested at the X-ray Optics Metrology Laboratory of the Advanced Photon Source at Argonne National Laboratory. The initial objective was to achieve a measurement sensitivity on the order of 1 μrad rms. Preliminary tests on a 1m-long x-ray mirror showed system repeatability of less than 0.6 μrad rms. This value is comparable to that of a conventional LTP. The measurement accuracy was mostly affected by environmental perturbations and system calibration effects. With a fully automated and improved system (to be built in the near future), we expect to achieve measurement sensitivity on the order of 0.01 μrad rms or better. In this paper, after a brief review of basic principles and general technical difficulties and challenges of the stitching technique, a detailed description of the measurement setup is given and preliminary results obtained with it are analyzed and discussed.

The Long Trace Profiler (LTP) has proved to be one of the major metrological aids for the characterization of synchrotron radiation optics. Currently the optical components installed at the beamlines face higher and higher demands, requiring a precise calibration and control of the measuring conditions. One important parameter to be considered while scanning is the temperature drifts afflicting the measuring sessions. We will review our experiences about the influence of this parameter on the LTP ability in measuring very accurate optical surfaces. It is possible to discriminate at least four major sources of perturbations due to temperature changes: air turbulence, deformation in the optical train inside the LTP optics head, deformation of the optical surface under test (SUT) and deformation of the holders of the SUT itself. Some addresses on the curing of these perturbations can be obtained.

The task of reconstructing a function f(x) from a set of measurements of the first or second derivative is considered. Methods for numerical integration are briefly outlined and discussed with regard to their potential application to the current task. Furthermore, cubic spline interpolation of the data followed by integration of the interpolation spline is proposed, and the influence of noise on the accuracy of the reconstructed function f(x) is examined. Results of numerical simulations for several test problems are presented for both noiseless and noisy data, and the efficiency of different methods is compared. Best results were obtained by cubic spline interpolation and subsequent integration of the spline function. The examples presented demonstrate that the reconstruction of a function f(x) from a set of measurements of the first or second derivative can be performed with high accuracy.

A new technique to improve the image quality of Ni replicated X-ray mirror is presented. During the manufacturing of XMM Mirror Module between 1994 to 1999, the classical manufacturing process showed its limits. In 1995, the XMM Mirror Module Qualification Model HEW was around 20 arcsec. In 1998, the fifth Flight Model Mirror Module reached 11 arcsec HEW, with a single mirror shell achieving 8 arcsec HEW. The performance of this technology is namely limited by the integration process of the shells. The new technique is based on the following philosophy : Firstly, an accurate measurement of each mirror shell after integration. A dedicated metrology system has been built and allows a precise metrology of the actual surface. Secondly, a modification of the mirror shell and of the support to transfer the stress to a non optical active area. Finally, an ion figuring run to correct the residual shape error of the mirror. The control and evaluation of the process is assured by EUV PSF assessment achieved in the FOCAL X facility developed for XMM. The advantages of this new process are to shape the mirrors in their final hardware configuration and the versality of the process enabling improvement of other kinds of high accuracy mirrors.

Elliptical mirrors for X-ray microfocusing were manufactured using the new fabrication methods of elastic emission machining (EEM) and plasma chemical vaporization machining (CVM). Surface profiles measured with stitching interferometry showed a maximum deviation around the ideal figure of about 5nm in peak-to-valley. The mirror showed nearly diffraction-limited focusing performance, with a 200 nm line width at the focus. Wave-optical calculation, taking the measured surface profile into consideration, well reproduced the measured focusing properties both at the beam waist and around the beam waist. In addition, two-dimensional focusing unit using K-B mirror arrangement was also developed and evaluated to have about 200 × 200 nm² focusing performance.

Nanofocused x-ray beams provide a powerful tool for studying materials at the submicron level. One approach to achieve such a small-sized focused beam is to use a pair of mirrors, in the Kirkpatrick Baez (KB) arrangement. Each mirror focuses the beam in one direction and has an elliptical profile. To focus hard x-rays generated from high-brilliance third-generation synchrotron sources to nanometer spots, it is necessary that the mirror figure errors, defined as the deviation of the surface from the ideal ellipse, be in the submicroradian range, or about an order of magnitude smaller than those presently in use. In this paper, the advances in deterministic figuring of extreme ultraviolet (EUV) lithography optics is discussed and is proposed as a technique for developing elliptical mirrors. Such elliptical mirrors with slope errors under 0.2 μrad rms are expected to provide nanometer-focused beams at third-generation synchrotron radiation facilities. The minimum focal size will then be governed by diffraction limit rather than optics quality. An alternative approach to developing an elliptically surface is to use flat or spherical mirrors of the same surface quality, and bend or differentially coat them to attain elliptical profiles. These additional steps would be unnecessary if an elliptical profile is directly polished into the substrate. In any case, the substrate is finally coated with a thin layer (< 400 Å) of a high-atomic-number metal to increase the total external reflection critical angle and thereby increase the aperture.

Two bendable elliptical cylinder mirrors arranged in a Kirkpatrick-Baez (KB) geometry are installed at the Nanospectroscopy beamline at ELETTRA for refocusing soft x-rays provided by an APPLE II type undulator. This achromatic focusing device delivers the beam to a micrometer-scale, high photon density spot, which is the source for a Spectroscopic Photoemission and Low Energy Electron Microscope (SPELEEM). A similar second pair of KB mirrors will refocus the monochromated light in a second experimental station for a different imaging microscope. These four mirrors, developed by S.E.S.O., are manufactured from Glidcop™ in a U shaped design with 380mm length. They are electroless nickel plated for polishing and are bent into an elliptical shape applying two unequal end moments. They have been tested in the optical metrology laboratory of ELETTRA using an in-house modified version of the Long Trace Profiler (LTP): the surface slope variation as a function of the bender actuators has been measured to characterize the behavior of the bender mechanism and the accuracy of the elliptical profiles that can be achieved. Both metrological optical data and x-rays performances show the achievement of a microradian accuracy for the different profiles in which each mirror can be bent and the possibility to vary the focal distance by about 30-40% around the nominal value.

This paper describes the mechanical design of Kirkpatrick-Baez (KB) mirror systems that have been developed at the ESRF over several years. These very compact and stable though flexible focusing devices for synchrotron x-ray beams are based on bending an initially flat, superpolished plate, which permits to vary the focusing conditions. Nowadays a whole family of mechanical benders exists at the ESRF that allows us to choose the most adapted system according to the properties defined by the experiment such as the energy and energy range, the focusing parameters such as magnification and focusing distance and the substrate coatings, i.e. single-layer mirrors or multilayers. The geometrical characteristics of these KB systems can be chosen in terms of focal distances ranging from 0.1 to 3 m and circular or elliptical bending radii from 20 to 1000m. Mirror substrates such as silicon or pyrex, single-layer or multilayer coatings require different motorisations and deformation systems. The very challenging requirements for mechanical resolution and sensitivity have led to the development of several generations of micro-motors. The ESRF has built a special multi-purpose micropusher that provides the required resolution and linearity, a thrust up to 80 N and finally a good position latching. Issues such as mounting interfaces, stress in the bent mirror and the dynamic bender, local mirror deformation and curvature stability had to be addressed and were solved. The ESRF has developed mirror clamping technologies controlled by mechanical and optical metrologies. The dynamic stability and reproducibility requirements to achieve a spot size variable from sub-micron to tens of microns required by various beamlines necessitate a very high degree of stiffness.

The mirror bender installed at the SLS protein crystallography beamline is designed to be capable of adjusting the vertical phase space of the undulator to the acceptance of protein crystals, i.e. to produce micro-beams as well as essentially parallel beams. The two-moment bender is based on the flexural hinge design pioneered at the ESRF but adapted to high-vacuum by making use of in-vacuum motors and high resolution worm-gears. Special care was taken in the design and fabrication of the clamps and the application of the clamping torque. The Rh-coated fused silica substrate (Zeiss) has a free length of 400 mm and a thickness of 30 mm. Metrology tests at ESRF indicate the high quality of the mirror and the bender. Over the useful length of 350 mm the meridional slope error was found to be 0.17-0.3 μrad (rms) prior to, and less than 0.5 μrad after clamping to the bender. In practice this allows the full central cone of an in-vacuum undulator to be focussed to 7 μm at an image distance of 7.1 m and to 2.1 μm at 1.75 m, corresponding to effective slope errors of less than 0.25 μrad. The bending is very reproducible and is well described by an interaction matrix. Finally, the long range tails were measured in the context of the generation of fs-pulses by means of bunch slicing. Their level cannot be attributed to the surface roughness of 2.9 Å (rms) but rather to scattering from other beamline components such as Be-windows.

We report the experience of the Advanced Light Source group in designing and building a series of nine electroless nickel-plated invar mirrors. The first four mirrors constructed appeared initially to be good but later it became evident that the nickel plating on all nine had been done improperly. The problem first appeared as blister-like defects about half a micron high and one to three centimeters wide. The cause turned out to be local separation of the plating from the substrate. In this paper we discuss the technical issues involved in building mirrors from invar and in preparing for and applying the needed electroless nickel coatings. We describe the studies that we carried out to evaluate the questions of adhesion, stress and polishability and report broad success in remanufacturing four of the mirrors. At time of writing one of the four has met specification showing good figure (0.8 μr rms) and finish (6 Å rms).

For microfocusing x-ray mirrors, an ellipse shape is desirable for aberration-free optics. However, it is difficult to polish elliptical mirrors to x-ray quality smoothness. A differential coating method to convert a cylindrical mirror to an elliptical one has been previously reported The differential coating was obtained by varying the sputter source power while the mirror was passed through. Here we report a new method of profile coating to achieve the same goal more effectively. In the profile coating, the sputter source power is kept constant, while the substrate is passed over a contoured mask at a constant speed. The mask is placed very close to the substrate level (within 1.0 mm) on a shield-can over the sputter gun. Four-inch-diameter Si wafers were coated through a 100-mm-long by 152-mm-wide aperture on the top of the shield-can. The thickness distribution was then obtained using a spectroscopic ellipsometer with computer-controlled X-Y translation stages. A model has been developed to fit the measured thickness distribution of stationary growth. The relative thickness weightings are then digitized at every point 1 mm apart for the entire open area of the aperture. When the substrate is moving across the shield-can during a deposition, the film thickness is directly proportional to the length of the opening on the can along the moving direction. By equating the summation of relative weighting to the required relative thickness at the same position, the length of the opening at that position can be determined. By repeating the same process for the whole length of the required profile, a contour can be obtained for a desired thickness profile. The contoured mask is then placed on the opening of the shield-can. The number of passes and the moving speed of the substrate are determined according to the required thickness and the growth-rate calibration. The mirror coating profile is determined from the ideal surface figure of a focus ellipse and that obtained from a long trace profiler on the substrate. Preliminary test results using Au as a coating material are presented.

As part of the TESLA (TeV-Energy Superconducting Linear Accelerator) project a free electron laser (FEL) in the XUV (Extreme Ultra-Violet, (6-200 eV)) and X-ray (0.5-15 keV) range is being developed at DESY (Deutsches Elektronen Synchrotron, Hamburg). At the TESLA Test Facility (TTF) a prototype FEL has recently demonstrated maximum light amplification in the range of 80 nm to 120 nm. It is expected that the FEL will provide intense, sub-picosecond radiation pulses with photon energies up to 200 eV in the next development stage. In a joint project between DESY and GKSS, thin film optical elements with very high radiation stability, as required for FEL applications, are currently being developed. Sputter-deposited amorphous carbon coatings have been prepared for use as total reflection X-ray mirrors. The optical characterization of the mirrors has been carried out using the soft X-ray reflectometer at HASYLAB (Hamburger Synchrotronstrahlungslabor) beamline G1. The reflectivity of the carbon films at 2 deg incidence angle is close to the theoretical reflectivity of 95.6 %, demonstrating the high quality of the coatings. For comparison, layers produced by different methods (e.g. Chemical vapor deposition, Pulsed laser deposition) have been characterized as well. Annealing experiments have been performed to evaluate the thermal stability of the amorphous carbon films. Further investigations concerning the radiation stability of the X-ray mirrors have also been conducted. The mirrors were irradiated in the FELIS (Free Electron Laser-Interaction with Solids) experiment at the TTF-FEL. Microscopic investigations demonstrate that the carbon mirrors are fairly stable.

Intensity interferometry was applied for characterizing hard synchrotron radiation. Propagation of transverse coherence was evaluated by a couple of coincidence measurements, which have different source-to-image distances. Influences of phase object under several conditions were measured and discussed. X-ray pulse width was determined with high accuracy by scanning bandwidth of monochromator. Application to the next generation synchrotron sources was discussed.

The performance of the SPring-8 cryogenic cooling system was examined extensively, especially, on the features closely related to the actual experimental situations. The cryogenic cooling system has sufficient cooling capability to handle the permitted highest heat load of 478 W at BL29XUL which equips the SPring-8 standard in-vacuum undulator. The effect of the heat load on the beam profile and the rocking curve width was reasonably small. The rocking curve width with Si 333 diffraction at 18.7 keV was close to the theoretical width 0.86”. Thus the monochromator conserves the good spatial coherence originating from the small source size of the undulator. Mechanical vibrations at frequencies of 30-100 Hz degraded the parallelism between the two monochromator crystals. The angular width of the mechanical vibration was measured to be 0.2” independent of the heat load and the flow rate of the circulating liquid nitrogen. The output intensity was stable and had no drift under any heat load. On the other hand, it took a few hours before the output energy stabilized, when the heat load was increased from 0.135 to 112 W.

ID09 is a dual-purpose beamline dedicated to time-resolved and high-pressure experiments. The time-resolved experiments use a high-speed chopper to isolate single pulses of x-rays. The chopper is installed near the sample (focal spot) and the shortest opening time depends on the height of the tunnel in the chopper, i.e. the sharpness of the vertical focus. In the 16-bunch mode, the opening window of the chopper has to be smaller than 0.352 μs in order to isolate single pulses of x-rays. This requires reducing the height of the tunnel to 0.143 mm. To ensure a reasonable transmission though the tunnel, we have designed a very precise toroidal mirror that focuses the beam 22.4 m downstream with a magnification M = 0.677. The 1.0 m long silicon mirror is curved by gravity into a nearly perfect toroid with a meridional radius of 9.9 km. The curvature is fine-tuned by a stepper motor that pushes via a spring from below the mirror. The overall figure error from the gravity sag and the corrective force is less than 0.3 μrad. The polishing error is 0.7 μrad (rms) averaged over the central 450 mm of the 1000 mm long mirror. The measured size of the polychromatic focus is 0.100 mm × 0.070 mm (h x v) in agreement with the prediction from the ESRF long trace profiler data. The small focal spot, which integrates the full central cone of the U17 undulator, is the result of very high optical quality, curvature fine-tuning, strain-free mount, vibration free cooling and careful alignment.

The deposition and X-ray performance of multilayer structures with d-spacings ranging from 1.2nm to 3.5nm has been presented. Different pairs of materials such as W (Mo, Ni, Cr, and La)/B₄C, Ni (Cr, Co, V)/C have been considered. X-ray reflectivity of the multilayers has been measured in the photon energy range from ~0.18keV to ~100keV. W/B₄C structures with d~1.5nm showed reflectivity greater than 30% at Cu-K_α (E~8keV). Performance of a W/B₄C structure with d~1.5nm has been compared with TIAP crystal performance in analysis of Si-K_α (1.74keV), Al-K_α (1.5keV), Mg-K_α (1.25keV) and Na-K_α (1.04keV) radiation. Results showed that small d-spacing multilayers can be considered for TIAP crystal replacement in Wavelength Dispersive X-Ray Fluorescence (WDXRF) spectrometers. The absolute reflectivity of near normal incidence structures at O-K_α (~293eV), C-K_α (~277eV) and B-K_α (~183eV) radiation lines has been measured to be ~1.5%, 14% and 43% respectively with spectral resolution of up to ~0.6%.

To synthesize X-ray optical multilayers showing both high resolution and high reflectivity, spacer and absorber materials with low absorption coefficients for the desired spectral range are required. Beside the well-known candidates the material system Carbon / Carbon is interesting because of its low absorption coefficient over a wide spectral range and the opportunity, to deposit C-layers with different modifications, i.e. different optical properties. Simulations of C/C multilayers with different period thicknesses d and single layer densities ρ show, that reflectivities R (Cu Kα ) > 80% and a resolution ΔΘ≈0.002° can be achieved for C/C layer stacks with d= 3 nm and N= 1000 periods. An advanced large area Pulsed Laser Deposition (LA-PLD) technology was used to deposit C/C multilayers on Si-substrates up to 4" diameter. The carbon film growth conditions for the spacer and absorber layers were optimised by the variation of selected laser parameters like pulse energy and ablation wavelength, to achieve a sufficient density contrast and smooth interfaces. C/C multilayers with period thickness d= 1.1...7.0 nm and more than 500 periods were deposited. The X-ray optical performance of the C/C multilayers was characterized by means of X-ray reflectometry. A reflectivity R > 50 % (CuKα) was measured for C/C multilayers with d= 17.2 nm and N= 106 periods. A peak resolution (Δλ/λ) ≈ 1.1 % was obtained for a C/C multilayer structure with N= 80 periods and a period thickness d= 1.1nm. Results of TEM investigations indicate a regular morphology as well as smooth interfaces in the C-C layer stacks. Low compressive stresses were determined in C/C multilayers with different period thicknesses using X-ray diffraction techniques.

Recent progress in the design and the manufacturing of wide bandpass x-ray multilayers has opened up new possibilities in hard x-ray optics, particularly in astrophysics and synchrotron x-ray applications. In contrast to previous design based on semi-empirical laws or extensive computer calculation, the recent development of an analytical expression has greatly improved the design of aperiodic multilayer mirrors, allowing to generate any given spectral dependence of the reflectivity. In practice, an approximate differential equation is used to derive an in-depth multilayer composition profile whose reflectivity response approaches the desired one. Based on this asymptotic solution, usually sufficiently close to the final solution, the optimum multilayer composition profile is calculated numerically using a classical downhill algorithm. We have studied the intrinsic characteristics of depth-graded multilayers using the procedure described above, with an emphasis put on the important case of a flat reflectivity response over a large but limited spectral range. The performance of depth-graded multilayer mirrors manufactured at ESRF and characterized at the BM5 beamline are presented. The necessity to account at the design level for deposition process parameters, such as chemical composition and thickness errors, and for the effective optical constants is highlighted.

Aperiodic multilayer structures (MSs) show promise as broadband soft X-ray mirrors for stigmatic diffraction spectroscopic instruments. We have derived aperiodic MSs optimized for maximum uniform normal-incidence reflectivity throughout a prescribed wavelength range, e.g., 130 - 190 Å (R=24 %), 125 - 250 Å (16 %), etc. Each of these aperiodic MSs exhibits an unparalleled integral reflectivity which substantially exceeds that of any periodic multilayer mirror pertaining to the corresponding wavelength range. Several Mo/Si aperiodic MSs were synthesized by magnetron sputtering on concave substrates to exhibit a relatively uniform reflectivity of (15 - 11)% in the 125 - 250 Å range, close to the theoretical predictions. These multilayers served as the focusing elements of high-transmission stigmatic transmission grating spectrograph with a plate scale of 20 or 4 Å/mm. The spectrograph was employed to investigate the laser plasma - gas jet interaction and characterize the Xe gas-jet laser-plasma XUV radiation source simultaneously with spatial and spectral resolution in the wavelength range above 124 Å. We have theoretically explored into the reflection of extremely short X-ray pulses by MSs. Special-design aperiodic MSs were shown to possess the unrivaled capacity to reflect few-cycle X-ray pulses ranging into the attoseconds. Aperiodic MSs have been calculated that are capable of reflecting pulses which comprise only three wave periods of an X-ray electromagnetic wave.

Mo/Si multilayers with and without diffusion barrier layers have been prepared by dc magnetron sputter deposition. The introduction of C and B₄C barrier layers reduces the formation of the well-known MoSi_x intermixing zones on the interfaces and improves the optical contrast between absorber and spacer layers. Using these barriers the EUV reflectivity was increased from 68.7% (λ=13.46nm, α=1.5°) for pure Mo/Si multilayers to 69.9% (λ=13.5nm, α=1.5°) for Mo/B₄C/Si/C multilayers. The microstructure of the layers has been investigated by HRTEM, X-ray diffractometry, Cu-Kα-and EUV-reflectometry. The introduction of thin C and B₄C barrier layers (d=0.2-0.5nm) on the Mo-on-Si interface shifts the amorphous-to-crystalline transition to Mo layer thicknesses >2nm and reduces the size of the Mo crystallites. In multilayers with period thicknesses between 6.5nm and 7.0nm the optimum Mo layer thickness is close to the transition thickness. Therefore small changes of the ratio =d_Mo/d_period result in amorphous or crystalline Mo layers. In both cases EUV reflectivities >69% are observed.

EUV multilayer mirrors with as well an increased as a reduced bandwidth in their spectral and angular reflectance have been designed and deposited with a commercial magnetron sputtering system. Concerning the broadband mirrors, a non-periodic multilayer design based on the thickness optimization of each layer by a stochastic method is compared to a design that consists of 3 different stacks. In addition, narrowband multilayer mirrors with a significantly reduced bandwidth based on high order reflection have been designed and fabricated. The EUV reflection of the samples was investigated with synchrotron radiation at the reflectometer of the PTB (Physikalisch-Technische Bundesanstalt) at BESSY II in Berlin. A reflectivity of more than 15% was reached in the whole wavelength range from 13 nm to 15 nm and a reflectivity of more than 30% was obtained for incidence angles from 0° to 20° with both designs. Both the increase and the reduction of the reflection bandwidth are unavoidably connected with a decrease of peak reflectivity. Therefore, the application of such mirrors involves areas where a maximum peak reflectivity is not required, e.g. in EUV spectroscopy and for the metrology for EUV sources. Furthermore, the use of such mirrors in combination with a broadband plasma source will result in a higher integral reflectivity.

An extreme ultra-violet phase-shifting point diffraction interferometer (PS/PDI) was studied by using the NewSUBARU[1] undulator radiation. The beam line was equipped with a monochromator for PDI measurement. To improve the converging performance of the undulator radiation, a new beam line suitable for PDI was designed. From the examination of monochromaticity required for PDI, the 0^th-order light of the monochromator was used in the experiment. The higher-order radiation of the undulator was eliminated by the reflection band of the Mo/Si multilayer mirrors. By means of improvements of the pre-alignment method and of the mask structure, a higher contrast than ever was achieved in the interference fringes.

The reported optical constants of uranium differ from that of vacuum significantly more than other elements do over the range of about 150 to 350 eV. This suggests that uranium could be used to produce high reflectance imaging mirrors for many soft x-ray applications. Elemental uranium is too chemically active to be used as a front surface mirror without protection. We computed the expected reflectance of carbon-coated uranium films and of uranium-nickel alloys for low-angle reflectors. Carbon is mostly transparent below its K absorption edge at about 283 eV. The reflectance at 10 degrees from grazing is computed to be greater than 50% at 277 eV (C K_α). For comparison, about 5 degrees is the maximum grazing incidence angle for which conventional materials are computed to have comparable reflectance. We sputter deposited and measured the reflectance of carbon-coated uranium layers at 44.7 Å (C K_α). Sample reflectance was a factor of two greater than that of nickel, the material used for low-angle mirrors. The initial oxidation behavior of sputtered uranium-nickel alloys is similar to pure U so their reflectance was not determined. Coatings based on uranium should be considered for all applications where high-reflectance, broadband, low-angle soft x-ray mirrors are required

The experimental fabrication of a Fabry-Perot interferometer for the x-ray region is reported. Based on state of the art thin film deposition technology at Osmic Inc., challenging requirements for making the interferometer for x-rays have been met.

It is now possible to reliably implement multilayer-coated diffraction gratings in spaceflight and laboratory spectrometers that operate at normal incidence and with high efficiency in the 9 nm to 40 nm wavelength range. The design and fabrication of the grating groove profile and the matching multilayer coating are based on computational modeling using the computer program PCGRATE. The multilayer gratings are characterized using atomic force microscopy and by measuring the diffraction efficiency using synchrotron radiation. Recent research has focused on multilayer coatings other than Mo/Si such as Sc/Si for 40 nm, MoRu/Be for 11 nm, and Mo/Y for 9 nm.

Synchrotron bending magnet radiation at the Advanced Photon Source was used to measure x-ray diffuse scattering of tungsten/carbon multilayers having period of 28 Å. Scattering not only near the first Bragg sheet in reciprocal space, but also near sheets corresponding to Kiessig fringes was simulated in the Born approximation. Full roughness propagation starting with the substrate was used in the simulation. We conclude that the differential equation that describes the kinetic roughening during sputtering is second order, i.e., the Langevin equation. For thermal-diffusion-related kinetic roughening either a third-or fourth-order equation should apply, and we conclude that thermal mechanisms for kinetic roughening need not be invoked

We established an efficient ultra-precision figuring process in which a numerically controlled plasma chemical vaporization machining (NC-PCVM) and a numerically controlled elastic emission machining (NC-EEM) are utilized serially. Intensity images of the X-rays reflected by total reflection mirrors greatly fluctuates with respect to the figure error having spatial wavelength ranging from the submillimeter to 10mm. In the present study, elliptical mirrors for the Kirkpatrick-Baez (K-B) focusing unit was manufactured by NC-PCVM and NC-EEM, and figure accuracy higher than 3nm (p-v) was achieved over the spatial wavelength range longer than 0.5mm. The focusing property was evaluated at the BL29XUL of SPring-8, and spot size of 0.2×0.2 μm² (FWHM) was realized at 15keV.

Focusing methods using mirror optics are intensively studied in the field of X-ray microscopy because mirror optics has useful features such as high photon efficiency and no chromatic aberrations. Employing a wave-optical method, we investigated the relationship between the natures of figure errors on the mirror surface and optics performances such as sizes, intensities and satellite peak structures of the focused X-ray beam. We also evaluated uniformity of intensity in the spherically diverging beam from the focal point as a point source. Obtained results showed unprecedented degrees of surface figure accuracy such as higher than 1nm in all over the spatial wavelength range longer than 0.5mm was required to realize nearly diffraction-limited focusing including satellite structures and intensity flatness at the spherically diverging wavefront.

The Mo/Si multilayers inserted with the SiO₂ layers with 2.0 nm in thickness have been proven to be thermally more stable than the conventional Mo/Si multilayer. The Mo/Si/SiO₂ multilayer inserted with the SiO₂ layers at the Mo-on-Si interfaces had a relatively high soft X-ray reflectivity even after annealing at 400°C. The Mo/SiO₂/Si/SiO₂ multilayer was structurally the most stable against annealing but the soft X-ray reflectivity of this multilayer was quite small because of the absorption of X-rays by oxygen. To minimize the deterioration of the soft X-ray reflectivity of the Mo/SiO₂/Si/SiO₂ multilayer with keeping the high heat stability, the optimum thicknesses of the inserted SiO₂ layers have been investigated. We have found that the Mo/SiO₂/Si/SiO₂ multilayer having asymmetric SiO₂ layer thicknesses at the Si-on-Mo interface (0.5 nm) and at the Mo-on-Si interface (1.5 nm) has thermally the most stable structure and maintains a high soft X-ray reflectivity after annealing.

Cr/Sc multilayer mirrors were designed for grazing (30 and 60 degrees) and normal incidence reflection at about 3.16 nm (NKα line) wavelength. The multilayer coatings have been grown on Si-substrates using ion-assisted sputtering deposition. X-ray scattering of CuKα radiation and transmission electron microscopy were used for the characterization of the multilayer interface quality. The reflective properties of the Cr/Sc multilayers were measured with synchrotron radiation at different angles of incidence. Reflectivity values between R = 15% for near normal incidence (θ=5) and R = 29.6% or θ=60 were measured. Multilayer mirrors with periods less than 1.9 nm have amorphous Cr and Sc layers. The transition from amorphous to crystalline Cr and Sc layers takes place for multilayer periods of more than 3.1 nm and results in interface roughness development. The annealing effect in short-period Cr/Sc multilayers was studied in the temperature range from 50°C to 500°C by X-ray scattering and transmission electron microscopy. Structural and phase transformations and the corresponding changes of the optical properties are presented and discussed.

Extensive investigations on the lifetime of EUVL optics using synchrotron radiation [1, 2, 3] have been performed at the radiometry laboratory [4] of the Physikalisch-Technische Bundesanstalt (PTB) at the BESSY II electron storage ring in the past. Nevertheless, synchrotron radiation shows a very different time structure as compared to the radiation of EUVL sources to be used in lithography tools. To assess the question, whether the different time structure of the radiation has an impact on the contamination behavior of EUVL optics, an irradiation experiment was performed using synchrotron radiation of different time structure available at the BESSY II electron storage ring: Keeping all other parameters constant, radiation from the normal operation mode of BESSY II, which resembles quasi-cw- illumination, and the special single bunch operation mode, which gives pulsed synchrotron radiation with 1.25 MHz repetition rate were used to irradiate samples in a defined residual gas environment. The reflectance of the samples were measured before and after the illumination to determine the loss in reflectance due to irradiation. Although the time structure of the single bunch mode still differs considerably from those of potential EUVL sources, trends in the contamination behavior could possibly be observed.

A new type of monochromators that incorporates two kinds of Monk-Gillieson monochromators has been designed and constructed for the purpose of realizing an evaluation beamline for characterizing soft X-ray optical elements in a wide wavelength range of 0.7-25 nm. One of the monochromators is a conventional type equipped with three varied-line-spacing plane gratings, allowing a choice of two inclusion angles. The other is a new type that employs a scanning mechanism based on Surface Normal Rotation (SNR). The SNR scheme provides high throughput at short wavelengths and simple scanning mechanism by means of a grating rotation about its normal. The monochromators is operated in the SNR and conventional modes over the ranges of 0.7-2.0 nm and 2.0-25 nm, respectively. The system was installed on a beamline of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. In this paper we describe the optical and mechanical designs of the monochromators, and a practical method of wavelength calibration. Also experimental data are shown which demonstrate the performance and versatility of the new type of Monk-Gillieson monochromators.

In this paper we review various improvements that we made in the development of multilayer mirror optics for home-lab x-ray analytical equipment in recent years. For the detection of light elements using x-ray fluorescence spectrometry, we developed a number of new multilayers with improved detection limits. In detail, we found that La/B4C multilayers improve the detection limit of boron by 29 % compared to the previous Mo/B₄C multilayers. For the detection of carbon, TiO₂/C multilayers improve the detection limit also by 29 % compared to the V/C multilayers previously used. For the detection of aluminum, WSi₂/Si or Ta/Si multilayers can lead to detection limit improvements over the current W/Si multilayers of up to 60 % for samples on silicon wafers. For the use as beam-conditioning elements in x-ray diffractometry, curved optics coated with laterally d-spacing graded multilayers give rise to major improvements concerning usable x-ray intensity and beam quality. Recent developments lead to a high quality of these multilayer optics concerning beam intensity, divergence, beam uniformity and spectral purity. For example, x-ray reflectometry instruments equipped with such multilayer optics have dynamic ranges previously only available at synchrotron sources. Two-dimensional focusing multilayer optics are shown to become essential optical elements in protein crystallography and structural proteomics.