Reflection zone plates
The company commercially offers custom-designed reflection zone plates (RZP) and 2-dimensional variable line space (VLS) gratings based on total external reflection on lamellar diffraction structures.
The standard substrate size is 100 mm (L) x 30 mm (W) x 10 mm, (H) super-polished down to 0.2 nm, with slope errors below 0.1 arc sec rms.
Other sizes are possible upon request.
Energy range 10 eV – 2000 eV
Absolute efficiency up to 20% (10 eV – 600 eV) and up to 10% (600 eV – 2000 eV)
Experimentally confirmed energy resolving power up to 2000.
Minimal focal distance 70 mm
Laminar profile line density up to 5000 l/mm, profile depth (5 nm – 200 nm) ± 0.5 nm
2D VLS gratings with 1000% or more period variation
Planar and curved substrates possible upon request.
Aberration corrected gratings for Hattrick -Underwood spectrometers
Single RZP multi-channel spectrometer optics
Special optics for fs spectroscopy
Time-delay compensating monochromators
Synchrotron radiation Femto-second monochromator
The FemtoSpeX beamline at BESSY II was constructed and commissioned, fulfilling the directions of present and future scientific demands in the field of ultra-fast time-resolved X-ray spectroscopy . As its main constituents, the beamline contains a monochromator, based on a multi-channel reflection zone plates array (RZPA), as well as an end station to calibrate the beamline and to perform time-resolved experiments as shown in figure 1. The optical element (RZPA, yellow) can be translated perpendicular to the optical axis, to select a specific RZP and in this way another photon energy range. A laser – coupled into the X-ray beam line (orange) – as a principle component of the setup, enables pump-probe experiments with a variable pump wavelength from the UV to the far IR at a high numerical aperture (NA).
Figure 1. Layout of the “slicing“ reflection zone plate monochromator (RZPM) at the FemtoSpeX beamline with RZP (yellow) and laser in the visible spectral range (orange).
The Si wafer with the RZPA depicted in figure 2(a), is shown along the direction from the source to the detector. The high energy RZPs (Co, Ni, Gd, Dy) are located on the left side (Figure 2a) and are separated from the low energy ones (Fe, Mn, O, N) by a 5 mm wide gap. The RZP “FeHR” was designed for a wavelength resolving power of lambda/delta lambda = 2000. The spectra recorded with this RZP are shown in figure 2 (b). Time resolution is of 150 fs.
Figure 2. (a) RZP array, designed for the FemtoSpeX beamline. (b) Transmission spectra recorded following the transmission through a diverse range of thin films on Si3N4 membranes.
This unique setup relies on a scheme with one optical element, an “off-axis” RZP. The
constructed slicing beamline thus offers a greater than 20-fold transmission efficiency enhancement with respect to alternative monochromatisation schemes based on lower-order diffractive elements.
High harmonic generator (HHG) monochromators
For the first time, a novel approach for the monochromatization and focusing of HHG sources in the vacuum ultraviolet and soft X-ray regime – as generated by femtosecond lasers operating in the near-infrared spectral region – was developed and realized with a single optical element, that is the RZP .
Figure 3. (a) Schematic representation of the experimental setup, labels: (I) iris diaphragm, (W) quarter wave plate, (L) RZP, (DP) differential pump, (A) aperture, (F) Al foil, (ZP) zone plate, (S) slit, (P) movable photo diode, (TM) toroidal mirror, (M) movable plane mirror, (D) position sensitive detector, (TOF) electron time-of-flight spectrometer. (b) Photo of the reflection zone plate array for the 17th, 19th and 21st harmonics of 800 nm.
The “off-axis” RZPs, used as focusing monochromators, allow optimizing the trade-off between energy resolution and temporal dispersion of the femtosecond pulses efficiently. In the design according to figure 3(a), a single harmonic with an effective pulse length of 45 fs is selected. Hence, high transmission efficiency (about 28% at 32.55 eV) and a simplified handling of the XUV beam result from these capabilities.
The RZPs of the monochromator according to figure 3(b) have been designed for the selection of a specific harmonic with an optimal trade-off between energy and time resolution. This relation corresponds to the criterion of the Fourier transform of the generated pulses: In particular, the initial XUV pulse duration in the present setup was 25 fs, while the choice of a spectral resolving power was lambda/delta lambda = 167 just entailed a temporal stretching that was comparable to the length of the
transmitted pulses. The balance between energy and time resolution can be adjusted within a single RZP by the usage of cutouts with different line densities. This ensures a flexible application of an RZP based monochromator.
X-ray laser spectroscopy of highly diluted materials
The spectroscopy at the L-edge of 3d transition metals provides important information related to the electronic structure of molecules/materials and has been used in numerous fields. Nevertheless, thus far, it has rarely been applied to study dilute aqueous systems such as metalloenzymes, due to high susceptibilities to radiation damage and the lack of suitable high collection efficiency detection systems. In the developed spectrometer, the fluorescence signal (Mn L2/3) is focused into the (-1) order of the RZP diffraction grating and the background from the O K-edge is spatially separated as a blurred line .
The polarization axis of the FEL pulses is highlighted by the dotted blue arrow in figure 4. On the right, a Mn2+ L2/3-edge fluorescence spectrum (“partial fluorescence yield”, PFY) of a fixed MnO sample is shown. The insets in the presentation of the spectrum depict CCD detector recordings for FEL excitation energy below (upper image, no fluorescence) and above the Mn Ledge (lower image, with signal). Here, a highly efficientRZP-based spectrometer was produced, optimized for the discrimination of the signal near the Mn L-edge from the predominant background at the O K-edge, which originates from the water and from proteins.
Figure 4. (a) Experimental setup of the highly efficient RZP spectrometer with a perspective view of the CCD and (b) measured spectrum of Mn L2/3.
For the first time, spectra from dilute Mn-containing samples in aqueous environments were acquired using a new spectrometer with 3D structured optics at an FEL – specifically at the “Linac Coherent Light Source” (LCLS) in Stanford. This facility provides bright, ultrashort Xray pulses, which allow spectral signatures ofsamples that are susceptible to radiation damage to be recorded without interference from photoproductsusing a “measure before destroy” data collection principle.
Low-energy X-ray fluorescence spectroscopy in scanning electron microscope (SEM)
A new concept for a wavelength dispersive X-ray spectrometer (WDS) at an SEM was also developed.
The WDS instrument shown in figure 5a, and described below, was designed to cover an energy band from 45 eV to 1150 eV by means of an RZPA equipped with a laminar profile. Additional optics were not required. The proposed WDS may be used simultaneously with other detectors, along with additional ones e.g. together with a secondary electron detector.
Figure 5a. WDS instrument (a), flanged to (b) a scanning electron microscope of the type “Zeiss EVO® 40”
This spectrometer allowed us to detect the Li K-edge emission from sample surfaces of metallic Lithium via scanning electron microscopy (see figure5b). In this way, it was successfully demonstrated that this WDS instrument provides new possibilities for the chemical analysis of a wide variety of novel functional materials and fundamental research on compounds, especially those containing Li .
Figure 5b. Normalized spectrum of metallic Li with a distribution at the Fermi edge (dashed).
XANES transmission spectroscopy with a laser produced plasma (LPP) source
By means of adapted, “off-axis” operated reflection zone plates, fine structure X-ray absorption spectra were recorded within a measurement time of 1.2 ns near the K-edge of C and N, respectively (figure 6).
Figure 6 Experimental setup with the LPP source (left). Its broadband radiation is focused and dispersive imaged onto a CCD camera. On the right, NEXAFS spectra from N in a Si3N4 membrane are depicted: The characteristic NEXAFS signatures are already distinguishable in the single pulse spectrum .
The transmission experiments were performed with a laboratory-based laser-driven plasma source thatfacilitated time-resolved measurements. A resolving power of E/delta E ~ 950 was demonstrated at the corresponding absorption edges. Considering figure 6, the comparison of single shot spectra with longer-term acquisitions proved that all characteristics of the used reference samples (Si3N4 and polyimide) could be resolved in 1.2 ns.
High resolution X-ray spectroscopy
A newly designed compact and flexible soft X-ray spectrometer for resonant inelastic X-ray scattering (RIXS) is presented in studies within an energy range from 380 eV to 410 eV, which includes the K alpha emission lines of vital elements like nitrogen . An off-axis reflection zone plate (RZP) has been used as the wavelength selective element with a maximum line density of 10000 l/mm. A higher energy resolution over a broader range of ± 15 eV around the designed energy was achieved by displacing the RZP. Additionally, for the first time, an actual optical side effect, the so-called chromatic aberration was exploited to increase the energy resolution. First results show a resolving power in the order of 1300 for photon energy of 395 eV, which is comparable to a commercial varied line spacing grating (VLS).
X-ray fluorescence lines of life relevant elements of carbon, nitrogen and oxygen are located in the soft X-ray regime and call for suitable spectrometer devices. In this work, we present a high resolution spectrum ofliquid water, recorded with a soft X-ray spectrometer based on a reflection zone plate design (RZP) . The RZP based spectrometer for 526 eV designed energy is shown in figure 7a offersextremely high detection efficiency and at the same time as high energy resolution. It was possible reproduce the well-known splitting of liquid water in the lone pair regime with 10 s acquisition time.The RZP based spectrometer for 277 eV is shown in figure 7b.
Figure 7a. The RZP based spectrometer for 526 eV with meridional variation of line space density from 2953 l/mm to 3757 l/mm.
Figure 7b. The RZP based spectrometer for 277 eV with meridional variation of line space density from 1555 eV l/mm to 1978 l/mm.
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