For the High Energy Density Instrument (HED) at the European XFEL a hard x-ray split-and-delay unit (SDU) is built covering photon energies in the range between 5 keV and 24 keV. This SDU enables time-resolved x-ray pump / x-ray probe experiments as well as sequential diffractive imaging on a femtosecond to picosecond time scale. The set-up is based on wavefront splitting that has successfully been implemented at an autocorrelator at FLASH. The x-ray FEL pulses will be split by a sharp edge of a silicon mirror coated with Mo/B4C and W/B4C multilayers. Both partial beams then pass variable delay lines. For different photon energies the angle of incidence onto the multilayer mirrors is adjusted in order to match the Bragg condition. Hence, maximum delays between +/- 1 ps at 24 keV and up to +/- 23 ps at 5 keV will be possible. Time-dependent wave-optics simulations are performed with Synchrotron Radiation Workshop (SRW) software. The XFEL radiation is simulated using the output of the time-dependent SASE code FAST. For the simulations diffraction on the edge of the beam-splitter as well as height and slope errors of all eight mirror surfaces are taken into account. The impact of these effects on the ability to focus the beam by means of compound refractive lenses (CRL) is analyzed.
The application of thin film coating processes for the fabrication of diffractive X-ray optical elements like sputteredsliced zone plates or multilayer Laue lenses (MLL) is a very promising approach for X-ray focusing down to spot sizes of < 10 nm. However, for practical useful focal length in the order of several millimeters or a few centimeters, multilayer thicknesses of several 10 μm up to a few 100 μm are necessary in order to have large enough numerical apertures of the lenses. Currently one of the main challenges is to coat low-stress multilayers with large total thicknesses in the order of 100 μm. Usually sputter deposition results in thin films with significant compressive stress. With new material combinations such as Mo/MoSi2/Si/MoSi2 and W/WSi2/Si/WSi2 the overall stress can be reduced to almost zero if the individual thicknesses are properly adapted. In the case of these four-layer-systems only the period thickness dp follows the zone plate law. In case of Mo/MoSi2/Si/MoSi2, stress-free multilayers are obtained with dMo = 0.5*dp, dMoSi2 = 0.16*dp and dSi = 0.34*dp.
A higher achievable scan speed and the capability to integrate two scan axes in a very compact device are fundamental
advantages of MEMS scanning mirrors over conventional galvanometric scanners. There is a growing demand for
biaxial high speed scanning systems complementing the rapid progress of high power lasers for enabling the
development of new high throughput manufacturing processes. This paper presents concept, design, fabrication and test
of biaxial large aperture MEMS scanning mirrors (LAMM) with aperture sizes up to 20 mm for use in high-power laser
applications. To keep static and dynamic deformation of the mirror acceptably low all MEMS mirrors exhibit full
substrate thickness of 725 μm. The LAMM-scanners are being vacuum packaged on wafer-level based on a stack of 4
wafers. Scanners with aperture sizes up to 12 mm are designed as a 4-DOF-oscillator with amplitude magnification
applying electrostatic actuation for driving a motor-frame. As an example a 7-mm-scanner is presented that achieves an
optical scan angle of 32 degrees at 3.2 kHz. LAMM-scanners with apertures sizes of 20 mm are designed as passive
high-Q-resonators to be externally excited by low-cost electromagnetic or piezoelectric drives. Multi-layer dielectric
coatings with a reflectivity higher than 99.9 % have enabled to apply cw-laser power loads of more than 600 W without
damaging the MEMS mirror. Finally, a new excitation concept for resonant scanners is presented providing
advantageous shaping of intensity profiles of projected laser patterns without modulating the laser. This is of interest in
lighting applications such as automotive laser headlights.
For the High Energy Density (HED) experiment  at the European XFEL  an x-ray split- and delay-unit (SDU) is
built covering photon energies from 5 keV up to 20 keV . This SDU will enable time-resolved x-ray pump / x-ray
probe experiments [4,5] as well as sequential diffractive imaging  on a femtosecond to picosecond time scale.
Further, direct measurements of the temporal coherence properties will be possible by making use of a linear
autocorrelation [7,8]. The set-up is based on geometric wavefront beam splitting, which has successfully been
implemented at an autocorrelator at FLASH . The x-ray FEL pulses are split by a sharp edge of a silicon mirror
coated with multilayers. Both partial beams will then pass variable delay lines. For different photon energies the angle
of incidence onto the multilayer mirrors will be adjusted in order to match the Bragg condition. For a photon energy of
hν = 20 keV a grazing angle of θ = 0.57° has to be set, which results in a footprint of the beam (6σ) on the mirror of
l = 98 mm. At this photon energy the reflectance of a Mo/B4C multi layer coating with a multilayer period of d = 3.2 nm
and N = 200 layers amounts to R = 0.92. In order to enhance the maximum transmission for photon energies of hν = 8
keV and below, a Ni/B4C multilayer coating can be applied beside the Mo/B4C coating for this spectral region. Because
of the different incidence angles, the path lengths of the beams will differ as a function of wavelength. Hence, maximum
delays between +/- 2.5 ps at hν = 20 keV and up to +/- 23 ps at hν = 5 keV will be possible.
Most of the currently used reflective coatings for EUV and X-ray mirrors are periodic nanometer multilayers. Depending
on the number of periods and the absorption in the multilayer stack a certain band width of the incoming radiation can be
reflected. In order to increase the integral reflectance or to accept larger ranges of incidence angles, non-periodic
multilayers are needed. With the transition from periodic to non-periodic multilayers new challenges arise for the
deposition process. Since the reflectance spectra are sensitive to every single layer thickness a precise coating control
and an exact knowledge of the interface reactions are required. Furthermore substrate roughness influences the
reflectance spectra. With an advanced coating process using additional ion bombardment during thin film growth the
integrated reflectance of broadband mirrors can be conserved even for an initial substrate roughness of about 0.7 nm rms.
For the European XFEL  an x-ray split- and delay-unit (SDU) is built covering photon energies from 5 keV up to 20 keV . This SDU will enable time-resolved x-ray pump / x-ray probe experiments as well as sequential diffractive imaging  on a femtosecond to picosecond time scale. Further, direct measurements of the temporal coherence properties will be possible by making use of a linear autocorrelation. The set-up is based on geometric wavefront beam splitting, which has successfully been implemented at an autocorrelator at FLASH . The x-ray FEL pulses will be split by a sharp edge of a silicon mirror coated with Mo/B4C multi layers. Both partial beams will then pass variable delay lines. For different wavelengths the angle of incidence onto the multilayer mirrors will be adjusted in order to match the Bragg condition. For a photon energy of hν = 20 keV a grazing angle of θ = 0.57° has to be set, which results in a footprint of the beam (6σ) on the mirror of l = 120 mm. At this photon energy the reflectance of a Mo/B4C multi layer coating with a multi layer period of d = 3.2 nm and N = 200 layers amounts to R = 0.92. In order to enhance the maximum transmission for photon energies of hν = 8 keV and below, a Ni/B4C multilayer coating can be applied beside the Mo/B4C coating for this spectral region. Because of the different incidence angles, the path lengths of the beams will differ as a function of wavelength. Hence, maximum delays between +/- 2.5 ps at hν 20 keV and up to +/- 23 ps at hν = 5 keV will be possible.
We have investigated the use of atomic-hydrogen-based cleaning to remove Sn contamination from extreme ultraviolet (EUV) multilayer mirrors. Mo and Si surfaces were cleaned at a relatively slow rate due to catalyzed dissociation of tin hydride on these surfaces. Mo/Si mirrors with B4C and Si3N4 cap layers and DLC-terminated DLC/Si mirrors showed complete removal of 10 nm Sn in 20 sec with full restoration of EUV reflectance. In addition, a prolonged cleaning treatment of 300 sec of a DLC/Si mirror resulted in only a minor EUV peak reflection loss of 1.2% absolute and no significant changes in infrared reflectance.
In this paper, a new type of spectral filter mirrors for extreme ultraviolet radiation based on DLC/Si multilayer coatings
is presented (DLC - diamond-like carbon). The coating is nearly transparent for infrared radiation (IR) of λ = 10.6 nm
but highly reflective at λ = 13.5 nm (EUV). We deposited DLC/Si multilayers by ion beam sputter deposition with 40
and 60 periods exhibiting maximum EUV reflectances of about Rmax = 43 % and Rmax = 50 %, respectively. Combining
IR antireflective and EUV reflective coatings, first prototype mirrors have been fabricated with an EUV reflectance of
about 42.5 % and an IR reflectance of about 4.4 % at the same time.
Investigations on the thermal behavior of the multilayer stack and the cleaning properties for tin contaminated mirror
surfaces have been carried out. Excellent stabilities of EUV peak position and reflectance values have been found using
annealing temperatures of up to 700 °C. Furthermore, several cycles of Sn etching under H2 reactive conditions have
been applied to the mirrors without significant changes of the filter performance.
Ion beam sputtering has been applied for polishing, figuring and multilayer coating on silicon and quartz glass substrates for the fabrication of x-ray mirrors. For high-performance x-ray optics extremely low microroughnesses of the substrates have to be achieved. Particularly for low d-spacing multilayers (d = 1...2 nm) even small improvements of the surface quality result in significant performance gains of the mirrors. By ion beam polishing silicon substrate surfaces could be smoothed from 0.18 nm rms to 0.11 nm rms (AFM scan length = 5 μm). Furthermore figuring of spherical substrates into elliptical or parabolic surface contours has been developed and applied. Spherical quartz glass substrates with initial rms roughnesses of 0.73 nm and 0.52 nm show reduced roughnesses after figuring and multilayer coating of 0.26 nm and 0.10 nm using AFM scan lengths of 20 μm and 5 μm, respectively. The testing of the ion beam figured mirrors for the application as parallel beam and focussing optics shows very promising results: The comparison of collimating mirrors, produced either by ion beam figuring or bending, shows very similar x-ray intensities. However, the ion beam figured
mirrors open the perspective for further reduced figure errors, improved long-term stability and 2-dimensional focusing.
Most important requirements for the deposition of x-ray optical multilayers are a) using a stable and reproducible
deposition technique and b) to find growth conditions where the interfaces between adjacent layers are abrupt (no
interdiffusion σd) and smooth (no roughness σr). The interface width σ (σ2 = σd2 + σr2) becomes increasingly important
for smaller period thicknesses. Furthermore, the kinetic energies of the condensing particles on the substrate surface are
of special importance for the interface formation. The ion beam sputter deposition technique (IBSD) provides stable and
well adjustable particle energies combined with medium to high deposition rates allowing the fabrication of precise
multilayer stacks for x-ray optical applications.
We will present our newly installed large area IBSD facility with 400 x 100 mm2 linear ion sources and substrate sizes of
up to 200 mm diameter (circular) or 500 x 100 mm2 (rectangular) and its characteristics concerning thickness
homogeneity and process stability. First experimental results of metal/non-metal multilayer depositions with thickness
uniformities of 99,9% over the entire substrate area are discussed. Different material combinations (Ni/B4C, Ni/C,
Mo/Si) with period thicknesses between 2 nm and 10 nm have been fabricated and characterized by x-ray and EUV
reflectometry. Interface widths are typically in the order of 0.3 nm. For the Ni-based multilayers Cu-Kα reflectances of
R > 80 % can be obtained with period thicknesses dP greater than or equal to 2.5 nm (Ni/B4C) and dP greater than or equal to 3.0 nm (Ni/C). EUV reflectances of the
Mo/Si multilayers are as high as R = 68,0 % at λ = 13,5 nm (incidence angle α = 5 deg).
In the paper we describe the development of a reflective optical system for EUV-microscopy containing an ellipsoidal formed collector optics and a Schwarzschild objective (magnification M=21, numerical aperture NA=0.2) for EUV radiation of a wavelength λ=13.5nm. In order to collect the maximum intensity of an EUV gas discharge plasma source, the grazing incidence collector has been inside-coated with molybdenum by Pulsed Laser Deposition (PLD). This method enables the deposition of uniform and highly reflective molybdenum layers, which have been protected against oxydation by using thin carbon top layers. The two mirrors of the Schwarzschild objective consist of highly reflective Mo/Si- multilayers produced by Magnetron Sputter Deposition (MSD). In order to obtain the best optical performance, laterally graded multilayers with rotational symmetry have been deposited by using a new mask-deposition technique. Thus the multilayer thickness corresponds at each point of the curved mirrors to wavelength and incidence angle of the EUV beam. Ray tracing simulations were performed for the two optical elements, collector optics and Schwarzschild objective. The results of these calculations are shown and compared with the results obtained by the EUV-microscope.