The performance of x-ray beamlines at 3^rd generation synchrotron radiation sources and Free Electron Lasers (FELs) is limited by the quality of the state of the art optical elements. Proposed FEL beamlines require optical components which are of better quality than is available from the optical manufacturing technology of today. As a result of a joint research project (Nanometer Optik Komponenten - NOK) coordinated by BESSY, involving both metrologists and manufacturers it is possible now to manufacture optical components beyond the former limit of 0.1 arcsec rms slope error [1, 2]. To achieve the surface finishing of optical components with a slope error in the range of 0.04 arcsec rms (for flat or spherical surfaces up to 300 mm in length) by polishing and finally by ion beam figuring technology it is essential that the optical surface be mapped and the mapping data used as input for the multiple ion beam figuring stages. Metrology tools of at least five times superior accuracy to that required of the component have been developed in the course of the project. The Nanometer Optical Component measuring Machine (NOM) was developed at BESSY for line and area measurements of the figure of optical components used at grazing incidence in synchrotron radiation beamlines. Surfaces up to 730 cm² have been measured with the NOM a measuring uncertainty in the range of 0.01 arcsec rms and a correspondingly high reproducibility [3]. Three dimensional measurements were used to correct polishing errors some nanometers high and only millimeters in lateral size by ion beam treatment. The design of the NOM, measurement results and results of NOM supported surface finishing by ion beam figuring will be discussed in detail. The improvement of beamline performance by the use of such high quality optical elements is demonstrated.

SOLEIL Long Trace Profiler (LTP) is a custom made instrument developed in the former LURE. As many instruments of its kind, it is based on pencil beam interferometry and uses the principle of stabilisation of the probe beam by a pentaprism equivalent reflector. The interferometer however is a polarization interferometer located close to the surface under test. The optics head can be configured to measure the optics in its working position: face up, face down or sideways. Particular care is given to absolute calibration because the precise knowledge of radii of curvature is required to determine the grazing angle and align accurately the synchrotron beamlines. A reproducible calibration procedure has been defined and checked against various reference surfaces. The main limitation to accuracy is the beam instability due to aur turbulence and thermal drifts. Careful confinement, oversampled acquisitions, and data averaging can minimize this effect. Noise is not uniformly distributed over spatial frequencies. In order to better understand the influence of beam footprint on the surface under test, and the characteristics of the beam fluctuation, we have constructed a special head where two measurements, one with a narrow pencil beam and interferometric detection and another with a large unmodulated beam and centroid detection, can be done simultaneously. The first results obtained from this device are presented here.

The Long Trace Profiler (LTP) is a useful optical metrology instrument for measuring the figure and slope error of cylindrical aspheres commonly used as synchrotron radiation (SR) optics. It is used extensively at a number of synchrotron radiation laboratories around the world. In order to improve SR beam line quality and resolution, the National Synchrotron Radiation Laboratory (NSRL) of China is developing a versatile LTP that can be used to measure both SR optics and more conventional "normal" optical surfaces. The optical metrology laboratories at Brookhaven National Laboratory (BNL) and NSRL are collaborating in developing a multiple functions LTP (LTP-MF). Characteristics of the LTP-MF are: a very compact and lightweight optical head, a large angular test range (±16 mrad) and high accuracy. The LTP-MF can be used in various configurations: as a laboratory-based LTP, an in-situ LTP or penta-prism LTP, as an angle monitor, a portable LTP, and a small radius of curvature test instrument. The schematic design of the compact optical head and a new compact slide are introduced. Analysis of different measurements modes and systematic error correction methods are introduced.

The Long Trace Profiler (LTP) is well-suited for the measurement of the axial figure of cylindrical mirrors that usually have a long radius of curvature in the axial direction but have a short radius of curvature in the sagittal direction. The sagittal curvature causes the probe beam to diverge in the transverse direction without coming to a focus on the detector, resulting in a very weak signal. It is useful to place a cylinder lens into the optical system above the mirror under test to refocus the sagittal divergence and increase the signal level. A positive cylinder lens can be placed at two positions above the surface: the Cat's Eye reflection position and the Wavefront-Matching position. The Cat's Eye position is very tolerant to mirror misalignment, which is not good if absolute axial radius of curvature is to be measured. Lateral positioning and rotational misalignments of the lens and mirror combine to produce unusual profile results. This paper looks at various alignment issues with measurements and by raytrace simulations to determine the best strategy to minimize radius of curvature errors in the measurement of cylindrical aspheres.

Form measurements with scanning systems are well established. Many scanning systems are limited to almost flat surface forms. In parallel, there is a need for systems capable of measuring stronger curved specimens with a radius of curvature down to one meter or even below. The size of specimen is sometimes up to one meter and the form has to be known with nanometer uncertainty. Moreover, the desired lateral resolution is sometimes smaller than one millimeter. The realization of a form measuring system combining high lateral resolution, a large measurement range and low measurement uncertainty requires sophisticated measurement principles. A measurement principle suitable for this task is presented which uses a combination of multiple distance sensors and an angular sensor, and exemplary measurements for stronger curved surfaces are shown. As multiple distance sensor an interferometer is used. Exemplary measurements are shown and the limitations of the interferometer as multiple distance sensor are discussed.

A new ultra-precision profiler was developed to measure X-ray and EUV optics such as asymmetric and aspheric profiles. In the present study, the normal vectors at each point on the surface are determined by a reflected light beam that follows exactly the same path as the incident beam. The surface gradients at each point are calculated from the normal vector and the surface profile is obtained by integrating the gradient. The measuring instrument was designed according to the above principles. In the design, four goniometers and three-axis movers were applied to adjust the light axis to search for the normal vector at each point on the surface. The angle-positioning resolution and accuracy of each goniometer are respectively 1.8 x 10^-8 radian and 2 x 10^-7 radian. A SiC flat mirror 25.4 mm in diameter and an elliptical profile mirror for nanometer hard X-ray focusing were measured using the present instrument and compared to the measured profile using a Zygo Mark IVxp phase-measuring interferometer.

We are developing grazing-incidence x-ray optics for a balloon-borne hard-x-ray telescope (HERO). The instrument will have 200 cm² effective collecting area at 40 keV and an angular resolution goal of 15 arcsec. The HERO mirror shells are fabricated using electroformed-nickel replication off super-polished cylindrical mandrels. The angular resolution goal puts stringent requirements on the quality of the x-ray mirrors and, hence, on mandrel quality. We used metrology in an iterative approach to monitor and refine the x-ray mirror fabrication process. Comparison of axial slope measurements of the mandrel and the shells will be presented together with results from x-ray tests.

In 2002, first experiments at the Advanced Light Source (ALS) at Berkeley, allowed us to test a first prototype of EUV Hartmann wave-front sensor. Wave-front measurements were performed over a wide wavelength range from 7 to 25 nm. Accuracy of the sensor was proved to be better than λ_EUV/120 rms (λ_EUV = 13.4 nm, about 0.1 nm accuracy) with sensitivity exceeding λ_EUV/600 rms, demonstrating the high metrological performances of this system. At the Swiss Light Source (SLS), we succeeded recently in the automatic alignment of a synchrotron beamline by Hartmann technique. Experiments were performed, in the hard X-ray range (E = 3 keV, λ = 0.414 nm), using a 4-actuators Kirkpatrick-Baez (KB) active optic. An imaging system of the KB focal spot and a hard X-ray Hartmann wave-front sensor were used alternatively to control the KB. The imaging system used a genetic algorithm to achieve the highest energy in the smallest spot size, while the wave-front sensor used the KB influence functions to achieve the smallest phase distortions in the incoming beam. The corrected beam achieved with help of the imaging system was used to calibrate the wave-front sensor. With both closed loops, we focused the beam into a 6.8x9 μm² FWHM focal spot. These results are limited by the optical quality of the imaging system.

Two specially-designed visible-wavelength interferometers meet demanding performance requirements in the mid-spatial frequency regime for current and next generation free-form x-ray and EUV optics. A Fizeau phase shifting interferometer measures waviness in the spatial frequency range from 0.5 to 10 mm^-1 and an interferometric microscope measures finer-scale deviations from 1 to 1000 mm^-1. Uncertainty analysis and experimental work demonstrate <1-nm system error after calibration and 0.05-nm repeatability for both instruments working in a clean-room environment.

Comparisons between several at-wavelength metrological methods are reported. The comparisons are performed by measuring one test optic with several kinds of measurement methods from the viewpoints of accuracy, precision and practicality. According to our investigation, we found that the PDI, the LDI, and the CGLSI are the most suitable methods for evaluating optics for EUV lithography.

The interest of the scientific community in the use of synchrotron radiation has become higher and higher with the improvement of instrumentation and with publication of better and better results. For this reason, the concept of standard beamline could not be used anymore, and a lot of solutions must be considered to satisfy the requests of the different users. A very important part of these "solutions" involves mirrors, gratings and crystals adopted to carry out the light from the source to the experimental chamber. In the last years, for instance, we have seen an increased interest for the mechanically deformable mirrors, as well as normal incidence mirrors (for IR or UV photons). From the point of view of the optical metrology, this implies the use of different methods and different instruments to guarantee the quality of the optics and consequently of the delivered photons. In this work, we compare the performance of two "state of the art" instruments, aimed at the non-contact measuring of optical surface profiles. The first one is an in house modified version of the Long Trace Profiler (LTP) developed for grazing incidence optics by P.Z. Takacs and Al. The second is a Fizeau like interferometer (a WYKO RTI 4100), primarily used for 2D mapping of surfaces. The aim of this paper is to outline when, according to our experience, an instrument is preferable with respect to the other, what are the limits of both and what kind of improvement could be made. Some examples will be reported. Spatial frequency, calibration and systematic errors will be compared and outlined.

In third generation synchrotron radiation beamlines, a focussed X-ray beam is often employed. However, in some cases users need to modify their spot size in order to match the broad range of samples sizes. This is the case for XPEEM microscopy beamline which need a homogeneous beam with a spot size varying from 2 to 50 μm. These specifications requires that the beamline works out of focus, and in this case the spot becomes non homogenous (as already observed experimentally on several synchrotron beamlines). In this paper, we will explain, using a geometrical approach, that this effect on the spot is produced by mirrors slope errors. We propose a new optical solution that overcomes these difficulties. Our optical solution has been validated experimentally on the second branch of the Nanospectroscopy beamline at Elettra, where we have obtained homogenous spot sizes of 10, 20 and 30 μm with the same optical design.

The consistency of different instruments and methods for measuring two-dimensional (2D) power spectral density (PSD) distributions are investigated. The instruments are an interferometric microscope, an atomic force microscope (AFM) and the X-ray Reflectivity and Scattering experimental facility, all available at Lawrence Berkeley National Laboratory. The measurements were performed with a gold-coated mirror with a highly polished stainless steel substrate. It was shown that these three techniques provide essentially consistent results. For the stainless steel mirror, an envelope over all measured PSD distributions can be described with an inverse power-law PSD function. It is also shown that the measurements can be corrected for the specific spatial frequency dependent systematic errors of the instruments. The AFM and the X-ray scattering measurements were used to determine the modulation transfer function of the interferometric microscope. The corresponding correction procedure is discussed in detail. Lower frequency investigation of the 2D PSD distribution was also performed with a long trace profiler and a ZYGO GPI interferometer. These measurements are in some contradiction, suggesting that the reliability of the measurements has to be confirmed with additional investigation. Based on the crosscheck of the performance of all used methods, we discuss the ways for improving the 2D PSD characterization of X-ray optics.

In the framework of the European COoperation in the field of Scientific and Technical research action on "X-ray and Neutron Optic" (COST P7) and following the decision announced in the last International Workshop on Metrology for X-ray and neutron optic (Grenoble, April 2004), the metrology facilities of four European synchrotrons, Bessy, Elettra, ESRF and Soleil, have decided and started a program of instrument inter-comparison. Other synchrotrons are joining us and further interested Institutions are invited to participate in this open measurement comparison. The metrology instruments involved are different kinds of direct slope measurement devices, like the well known Long Trace Profiler (in house made or modified) and the Bessy N.O.M.. The Round Robin was started with 2 flat and 2 spherical mirrors (three made of Zerodur and one of fused silica) made available by Bessy and Elettra. A short radius of curvature spherical mirror of Silicon from SOLEIL was later added. First results show a very close match between the measurements of all facilities provided that the same procedures are followed. In particular, a special attention has to be given to the way of supporting the reference objects, as it will be illustrated by some examples. Another important issue is the characterization of the systematic errors of the different instruments and how they can be reduced or eliminated. The paper expects to open a discussion on the performances of different commercial and custom made or modified profilometers, and over standard procedures for calibration testing, including the definition of standard reference surfaces.

This paper presents the first series of round-robin metrology measurements of x-ray mirrors organized at the Advanced Photon Source (APS) in the USA, the European Synchrotron Radiation Facility in France, and the Super Photon Ring (SPring-8) (in a collaboration with Osaka University,) in Japan. This work is part of the three institutions' three-way agreement to promote a direct exchange of research information and experience amongst their specialists. The purpose of the metrology round robin is to compare the performance and limitations of the instrumentation used at the optical metrology laboratories of these facilities and to set the basis for establishing guidelines and procedures to accurately perform the measurements. The optics used in the measurements were selected to reflect typical, as well as state of the art, in mirror fabrication. The first series of the round robin measurements focuses on flat and cylindrical mirrors with varying sizes and quality. Three mirrors (two flats and one cylinder) were successively measured using long trace profilers. Although the three facilities' LTPs are of different design, the measurements were found to be in excellent agreement. The maximum discrepancy of the rms slope error values is 0.1 μrad, that of the rms shape error was 3 nm, and they all relate to the measurement of the cylindrical mirror. The next round-robin measurements will deal with elliptical and spherical optics.

The Long Trace Profiler (LTP) is a precise angle measurement instrument, with a sensitivity and accuracy that can be in the sub-micron radian range. LTP characteristics depend on the particular LTP system schematic design, and the quality of components and assembly. The conditions of temperature, alignment, and mirror support during the measurement proccess vary between different laboratories, which influences significantly the test repeatability and accuracy. In this paper we introduce a direct comparison method to test the same object at the same point in the same environment at the same time by using two LTPs, which significantly increases the reliability of the comparison. A compact, portable LTP (PTLTP), which can be carried to different laboratories around the world, is used for comparison testing. Stability comparison experiments between the LTP II at the National Synchrotron Radiation Research Center (NSRRC), and the PTLTP of Brookhaven National Laboratory (BNL) reveal significant differences in performance between the instruments. The experiment is set up so that each optical head simultaneously records both its own sample probe beam and also the probe beam from the other optical head. The two probe beams are reflected from same point on the mirror. Tests show that the stability of the PTLTP with a monolithic beam splitter is 10 times better than the stability of the LTP II which has a separated beam splitter unit. A scheme for comparing scanning measurements of a mirror is introduced. Experimental results show a significant difference between the two LTPs due mainly to distortions in the optical components inside the optical head. A new scheme is proposed for further mirror comparison scanning tests.

The optical metrology laboratory of Elettra is equipped with some state of the art instruments for the characterization of high precision optical components for the UV and x-ray energy range. Among them, the most important is the Long Trace Profiler, which is capable of very accurate measurement of the shape of long aspheric mirrors. It is a direct slope measurement device, able to measure slope errors below the mrad level, once properly operated and calibrated. Our device is an LTP II model dating back to 1992. Nevertheless, it has been deeply in house modified during these years. Recently we have assembled a second optic head (OH) that could be used in spite of (or together with) the original one. This second OH works without folding mirrors and uses a set of short focal distance Fourier Transform lenses. The absence of folding mirrors reduces the source of systematic errors and the use of short focal distance lenses increases the angular acceptance of the instrument. This fact is particularly useful when short radius of curvature mirrors as well as high groove density variation gratings have to be measured. Some other modifications have been made to help the stitching procedure or to change the measurement set-up. These will be described in details.

We developed the computer-controlled figuring system having controllability of removal depths with nanometer accuracy and spatial resolutions close to 0.1mm. In this system, Elastic Emission Machining (EEM) using nozzle-type EEM head and Microstitching Interferometry (MSI) are employed as a machining method and a figure measurement method. In EEM, very small stationary spot profiles ware obtained, selecting small circle nozzle aperture of a 0.15 mm diameter. Surface figuring is performed with controlling scanning speeds of sample stages, so that a measured profile turned into designed one. MSI, which was developed on the basis of interferometric stitching technologies, has reproducibility at subnanometer level and with spatial resolution of 0.03 mm. In this study, we demonstrated computer controlled figuring, focusing on removal of high frequency figurer errors. Figure accuracy of 0.2 nm (RMS) was achieved in a cross-section profile with a length of 90mm.

The ESRF optics metrology laboratory was created 15 years ago. Various measurement devices have been progressively installed and the present status of available equipment will be briefly presented. Since the beginning of the first beamline construction, all X-ray mirrors have been tested before their installation. Most of the mirrors are mounted on mechanical bending systems, and it is mandatory to characterize optical elements under working conditions and to calibrate the systems before their installation on a beamline. These calibrations are now part of the acceptance tests whenever a system is delivered. Optics tests carried out on the Long Trace Profiler (LTP) will be described, with particular emphasis on the special configuration developed for mirrors facing down. Measurement reproducibility and accuracy achieved with the LTP will be discussed. The emerging micro focusing needs at ESRF have promoted the development of Kirkpatrick-Baez systems. Precise metrology plays an important role to control the mirror clamping using interferometry techniques and to predict the performance of the system using the LTP. The automatic shaping procedure will be described.