Amparo Rommeveaux

Submicron focusing of hard x rays with reflecting surfaces at the ESRF

We describe Kirkpatrick-Baez (KB) reflecting mirror systems that have been developed at the European Synchrotron Radiation Facility (ESRF). They are intended to be used mainly in the hard x-ray domain from 10 KeV to 30 KeV for microfluorescence, microdiffraction and projection microscopy applications. At 19 KeV a full width at half maximum (FWHM) spot size of 200x600 nanometers has been measured and with an estimated irradiance gain of 3.5x105. The alignment and bending processes of the system are automated based on the wavefront information obtained by sequentially scanning slits and reading a position-sensitive device located in the focal plane. The sub-microradian sensitivity of this method allows us to predict the spot size and ot provide a metrology map of the surfaces for future improvements of the performances. A novel device based on specular reflection by a micromachined platinum mirror has been used to determine the spot size with an equivalent slit size of less than 100 nanometers. Projection phase images of submicron structures are presented which clearly show both the high potential and also the present limitations of the system. First microfluorescence images obtained at 20.6 KeV are shown. Finally, a roadmap towards diffraction-limited performance with metal and multilayer surfaces is presented.

Nanofocusing at ESRF Using Graded Multilayer Mirrors

Dynamically bent graded multilayer mirrors have been developed at ESRF for their large energy bandwidth acceptance, energy tunability and large numerical aperture for limited mirror size. Kirkpatrick Baez systems with spot sizes below 100 nanometers have been installed on two beamlines. A diffraction limited line width of 41 nanometers FWHM was obtained at 24 keV on ID19. This experiment directly confirms that the penetration depth of the X‐rays in the multilayer coating does not limit the obtainable focal spot size. The resolution limits of such a nanofocusing device are discussed as well as figure accuracy and vibration level issues.

The present state of Kirkpatrick-Baez mirror systems at the ESRF

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.

Graded multilayers for focusing hard x-rays below 50 nm

Laterally graded W/B4C multilayers were conceived for the focusing of hard X rays at 3rd generation synchrotron sources. They were deposited using a differential sputter coating technique. The multilayer mirror was bent to the correct shape on a dynamical bending device applying automated alignment routines. During experiments on the ESRF beamline ID19 the undulator source was focused vertically to a 41 nm (FWHM) wide line using a photon energy of 24 keV. The measured line width can be attributed to the finite source size, to diffraction effects, and to slope errors of the mirror. The potential impact of beam penetration into the multilayer will be discussed.

Mirror metrology and bender characterization at ESRF

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.

Global High‐Accuracy Intercomparison of Slope Measuring Instruments

The upcoming generation of high accuracy synchrotron radiation (SR) optics will be characterized by a slope deviation from ideal shape in the range of some 0.05μrad rms at a sampling interval of about 1mm. To certify and improve the measurement capabilities of metrology tools to inspect these stringent specifications, an essential step is a worldwide intercomparison of these measurements based on a set of transfer standards. It is the aim of these cross measurements to verify the “absolute” correctness and comparability of the measurement results obtained by the cooperating partners when measuring the topography of specific reference optics (ROs) using their latest metrology tools and methods. Organized by members of the SR‐optics community, new national and international cross measurement comparisons of typical synchrotron radiation mirrors have been realized during the last few years: A round robin test by the European COST‐program (BESSY, Elettra, ESRF, Soleil) during the years 2004–2005 and a similar ...

The toroidal mirror for single-pulse experiments on ID09B

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.

X-ray Optics at the ESRF

For nearly 20 years, the X-ray Optics Group of the ESRF has been playing a major role in the development of new X-ray optical systems, many of which are widely used at synchrotrons around the globe.

ESRF metrology laboratory: overview of instrumentation, measurement techniques and data analysis

The ESRF has initiated an ambitious ten-year upgrade program involving the construction of eight new beamlines and significant refurbishment of existing instruments. The availability of high-precision X-ray optical elements will be a key factor in ensuring the successful implementation of these beamline projects. Particular challenges are to ensure the necessary optical quality for X-ray beam coherence preservation and high numerical-aperture high focusing systems. Surface optical metrology is a key tool, not only for the quality control, but also in improving the manufacturing processes of such components. Amongst the most demanding tasks is the characterisation of the surface topography of highly aspheric surfaces for reflective nanofocusing technologies which typically require measurement of shape errors in the nm range. In order to satisfy these new demands, the ESRF metrology laboratory has recently been equipped with two new instruments: a Fizeau interferometer and a micro-interferometer. In parallel the long trace profiler has been continuously developed to increase both stability and accuracy. In this paper we will present the new instrumentation and associated techniques like micro-stitching interferometry used to measure typical high quality X-ray mirrors. We will also focus on the parameters that can affect repeatability and accuracy of the radius of curvature assessment of flat optical surfaces, in particular when measuring with the long trace profiler. Finally an example of the power spectral density function based on our instrument measurements of a typical high quality x-ray mirror will be shown.

Design and performance of the flexural-hinge-based mirror bender at the SLS protein crystallography beamline X06SA

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.