Andreas K. Freund

INCOHERENT X-RAY MIRROR SURFACE METROLOGY

In this paper we describe an x-ray long trace profiler that takes an x-ray synchrotron beam as a wavefront reference. According to results of experiments conducted on the Optics Beamline at the ESRF, this instrument allows us to measure surface slope errors with precision and accuracy better than 25 nrad (rms) and 50 nrad (rms), respectively, with a lateral resolution of 5 mm in the meridional and less than 1 mm in the sagittal direction. A very similar technique was developed to figure in situ mirrors mounted on mechanical benders into a stigmatic shape for microfocusing purposes. Micron spot sizes were achieved without difficulty and submicron precision should be possible. The technique is particularly useful if energy tunability is needed. The emphasis has been put on automation and speed of the measurement.

Diamond planar refractive lenses for third- and fourth-generation X-ray sources

The fabrication and testing of planar refractive hard X-ray lenses made from bulk CVD diamond substrates is reported. The lens structures were generated by electron-beam lithography and transferred by reactive-ion etching into the diamond. Various lens designs were fabricated and tested at 12.4 and 17.5 keV photon energy. Efficiencies of up to 71% and gains of up to 26 were achieved. A line focus of 3.2 micro m (FWHM) was measured. These lenses should be able to withstand the extreme flux densities expected at the planned fourth-generation X-ray sources.

Cryogenic cooling of monochromators

In this paper, we report on the design and x‐ray diffraction properties of cryocooled silicon single crystals exposed to the following wiggler beams: power density: 150 W/mm2, total power: 75 W and power density: 0.5 W/mm2, total power: 100 W. First, thermomechanical and engineering aspects of low‐temperature crystal cooling are discussed, leading to two basic cooling geometries: internal cooling and side cooling. Experimental tests of both these cooling schemes at NSLS on beam lines X25 and X17 are then described and discussed. Finally, engineering problems related to the integration of cryogenic cooling on ESRF beam lines are presented.

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.

Mosaic crystal monochromators for synchrotron radiation instrumentation

Abstract The diffraction properties of perfect single crystals match the properties of X-ray beams emitted by high energy storage rings in many cases. However, under certain circumstances imperfect crystals are better adapted to the experimental requirements and should therefore be considered as devices for beam definition. In particular progress has recently been made in the development of low mosaic spread beryllium and silicon single crystals. The results of calculations given in the present paper show that up to two orders of magnitude can be gained in flux on the sample when perfect crystals are replaced by mosaic crystals.

Diamond single crystals: the ultimate monochromator material for high-power x-ray beams

A review of the performance of diamond single crystals as a high heat load optical component for synchrotron x rays is given. It has been proven experimentally that the bandpass and the angular divergence of the monochromatic beam provided by a relatively thin diamond crystal used in an undulator beam are not degraded by thermal effects for a total power up to 280 W (8.7 W absorbed) at a heat flux up to 3.5 kW/mm 2 (109 W/mm 2 absorbed). These high heat load tests and model calculations have shown that edge-cooled diamond crystals at room temperature provide an easy and widely satisfactory solution to the heat load problems generated by undulator beams that are currently foreseen at the third-generation storage rings of the European Synchrotron Radiation Facility, the Advanced Photon Source, and the SPring-8 facilities. For this cooling geometry, diamond single crystals offer the additional advantage that beam multiplexing can be used. Currently available synthetic diamond crystals are sufficiently big for undulator beams and their crystalline perfection is adequate. Most of the crystals actually in use were prepared with their big surfaces (about 30 mm 2 in size) oriented parallel to the (100) netplanes, but more recently bigger samples whose surfaces are parallel to the (111) lattice planes were obtained. Thus, diamond single crystals are superior to all other monochromator materials for undulators and for cases where a loss of a factor of 2 in flux combined with a similar gain in resolution (as compared to silicon) are compatible with the experiments.

Multilayered supermirror structures for hard x-ray synchrotron and astrophysics instrumentation

By varying the thickness of the layers in a multilayer down through the structure, it is possible to produce wide-band reflectors. We report measurements and modeling of the reflectivity of Ni/C, Mo/Si and W/Si supermirrors, at energies ranging from 8 to 130 keV, and discuss the performance of two possible applications: a Kirkpatrick-Baez telescope, and a multiwavelength hard X-ray focusing reflector. The supermirrors perform as expected, and model-fits over the full range have been attempted with some success. We conclude that the supermirror coatings do indeed look very promising as hard x-ray optics for synchrotron applications, while some work on highly nested structures and supermirror coatings on very thin large substrates is necessary, before the feasibility of employing large-area supermirrors for hard X-ray astronomy is determined.

X-ray mirrors for the European Synchrotron Radiation Facility

The present paper outlines the requirements for the performance of x-ray mirrors at the European Synchrotron Radiation Facility (ESRF), to be built in Grenoble, France. It is shown that present-day surface preparation techniques are about adequate to achieve conservation of the source emittance, although some improvements are needed in special cases. It is much harder to conserve brilliance, where thermal deformation is the major obstacle. Here substantial research and development efforts are absolutely indispensable. Two possible ways are indicated to solve the heat problem: cryogenic cooling of silicon-based mirrors and adaptive optical systems. In the first case thermal deformations are drastically reduced, and in the second they can be compensated by mechanical forces. Our results are based on theoretical considerations of scattering by nonideal surfaces and on a thermomechanical analysis, which are also given. For layered synthetic microstructures the technological problems appear to be still more difficult. Because the critical photon energy of the ESRF 6 GeV storage ring and of most of its insertion devices is between 10 and 20 keV or even higher, the discussion is limited to hard x-ray optics.

Multiple station beamline at an undulator X-ray source

Abstract The undulator X-ray source is an ideal source for many applications: the beam is brilliant, highly collimated in all directions, quasi-monochromatic, pulsed and linearly polarized. Such a precious source can feed several independently operated instruments by utilizing a downstream series of X-ray transparent monochromator crystals. Diamond in particular is an attractive monochromator as it is rather X-ray transparent and can be fabricated to a high degree of crystal perfection. Moreover, it has a very high heat conductivity and a rather small thermal expansion so the beam X-ray heat load problem is easily overcome. We describe a possible setup with three successive monochromators. We present data and analysis for focusing the beam in both the horizontal and vertical direction and discuss the focusing properties in both the Laue and Bragg geometry.

The historical development of cryogenically cooled monochromators for third-generation synchrotron radiation sources

In the period of the late-1980s, before the construction of multi-GeV third-generation storage rings with their intense insertion-device sources, the perceived number one problem for X-ray instrumentation was proper cooling of the first optical element in the beamline. This article, first given as an acceptance speech for the Compton Award ceremony at the Advanced Photon Source, presents a somewhat historical and anecdotal overview of how cryogenically cooled monochromator optics have been developed to provide a monochromator cooling solution adequate for todays power levels. A series of workshops and international collaborations were the key components for the progress and final success of this development.