The resolving power and relative efficiency of two off-axis reflection zone plates (RZPs) in the soft X-ray range between 1 nm and 5 nm were investigated. RZPs focus only a very narrow bandwidth around the design wavelength. By misaligning the RZP, the focused wavelength can be tuned through a much wider spectral range. Using a laser-produced plasma source, we demonstrate that a single RZP can be efficiently used for spectroscopy at arbitrary wavelengths in the investigated soft X-ray range.DFG, 313838950,  Neuartiges Laborspektrometer für Pump-Probe NEXAFS-Untersuchungen an Biomolekülen in wässriger Lösun

Jonas, Adrian

Kanngießer, Birgit

Mantouvalou, Ioanna

Meurer, Thomas

Review of Scientific Instruments

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Adrian Jonas, Thomas Meurer, Birgit Kanngießer, IoannaMantouvalouNote: Reflection zone plates as highly resolvingbroadband optics for soft X-ray laboratoryspectrometersOpen Access via institutional repository of Technische Universität BerlinDocument typeJournal article | Published version(i. e. publisher-created published version, that has been (peer-) reviewed and copyedited; also known as:Version of Record (VOR), Final Published Version)This version is available athttps://doi.org/10.14279/depositonce-15601Citation detailsThis article may be downloaded for personal use only. Any other use requires prior permission of the authorand AIP Publishing. This article appeared inJonas, A., Meurer, T., Kanngießer, B., Mantouvalou, I. (2018). Note: Reflection zone plates as highly resolvingbroadband optics for soft X-ray laboratory spectrometers. In Review of Scientific Instruments (Vol. 89, Issue 2,p. 026108). AIP Publishing.and may be found at https://doi.org/10.1063/1.5018910.Terms of useThis work is protected by copyright and/or related rights. You are free to use this work in any way permitted bythe copyright and related rights legislation that applies to your usage. For other uses, you must obtainpermission from the rights-holder(s).Rev. Sci. Instrum. 89, 026108 (2018); https://doi.org/10.1063/1.5018910 89, 026108© 2018 Author(s).Note: Reflection zone plates as highlyresolving broadband optics for soft X-raylaboratory spectrometersCite as: Rev. Sci. Instrum. 89, 026108 (2018); https://doi.org/10.1063/1.5018910Submitted: 11 December 2017 • Accepted: 08 February 2018 • Published Online: 26 February 2018A. Jonas, T. Meurer, B. Kanngießer, et al.ARTICLES YOU MAY BE INTERESTED INSingle shot near edge x-ray absorption fine structure spectroscopy in the laboratoryApplied Physics Letters 108, 201106 (2016); https://doi.org/10.1063/1.4951000Off-axis reflection zone plate for quantitative soft x-ray source characterizationApplied Physics Letters 71, 190 (1997); https://doi.org/10.1063/1.119497High average power, highly brilliant laser-produced plasma source for soft X-rayspectroscopyReview of Scientific Instruments 86, 035116 (2015); https://doi.org/10.1063/1.4916193REVIEW OF SCIENTIFIC INSTRUMENTS 89, 026108 (2018)Note: Reflection zone plates as highly resolving broadband opticsfor soft X-ray laboratory spectrometersA. Jonas, T. Meurer, B. Kanngießer, and I. MantouvalouTU Berlin, Analytical X-Ray Physics, D-10587 Berlin, Germany(Received 11 December 2017; accepted 8 February 2018; published online 26 February 2018)The resolving power and relative efficiency of two off-axis reflection zone plates (RZPs) in the softX-ray range between 1 nm and 5 nm were investigated. RZPs focus only a very narrow bandwidtharound the design wavelength. By misaligning the RZP, the focused wavelength can be tuned througha much wider spectral range. Using a laser-produced plasma source, we demonstrate that a singleRZP can be efficiently used for spectroscopy at arbitrary wavelengths in the investigated soft X-rayrange. Published by AIP Publishing. https://doi.org/10.1063/1.5018910Soft X-ray spectroscopy in the range between 1 nm and5 nm (1200 eV–200 eV) is still most commonly performed atlarge scale facilities. This is due to the lack of efficient labora-tory sources for the soft X-ray region. To meet the increasingdemand for spectroscopic techniques such as near edge X-ray absorption fine structure (NEXAFS) spectroscopy, effortsare conducted to design efficient experimental setups in thelaboratory.One possibility is to use highly brilliant laser-producedplasma (lpp) sources which deliver isotropic broadband radi-ation.1,2 For the diagnostics of such sources but also for theenvisioned spectroscopic techniques, adapted spectrometersare needed with both high resolving power (RP) and broadbandefficiency. In most published work, the dispersive element usedfor spectroscopy is either a transmission grating3,4 or a con-cave [variable line-spaced (VLS)] grating.5,6 In recent years,reflection zone plates (RZPs) have been shown to enable effi-cient soft X-ray spectroscopy with laboratory sources such assingle shot NEXAFS7 due to their high reflectivity and largenumerical aperture. These two-dimensional grating structurescan be used for focusing,8 imaging,9 and dispersing10 ofX-radiation. Up until now, though, specially designed RZPsfor specific energy regions are utilized7 due to a fast degen-eration of RP caused by chromatic aberration, necessitatingmany high-priced optics if several absorption edges are ofinterest.We report that by misaligning the setup geometry, theusable wavelength range can be varied between 1 nm and5 nm without notable loss in efficiency or RP. The full wave-length range can be covered by one single RZP structure insequential measurements. To illustrate this behavior, emissionspectra of tungsten and copper obtained with a lpp sourceusing two different RZP structures are shown with differentsetup geometries. The setup utilizes a laboratory lpp sourcedescribed in Ref. 11, where a 1 ns, 100 Hz Yb:YAG thin disklaser (1030 nm) is used to produce soft X-rays in the rangeof 1 nm–5 nm with a variable emission spectrum.12 The highvacuum spectrometer consists of the RZP structures, a CCDcamera (GE 2048 512 X-ray, Greateyes GmbH), and a 200 nmAl filter which eliminates visible and IR light. The two RZPstructures which were designed for the investigation of theC and N K edge at 4.4 nm and 3 nm, respectively, with anobject distance F1 of 1500 mm and an image distance F2 of2500 mm are written on the same substrate and are thusexchangeable by a translation of the optic. They can be addi-tionally rotated in two directions and the CCD camera can bealigned in 3D.The RZP structure focusses only on radiations with thedesign wavelength in the CCD plane. The image of otherwavelengths is broadened in the vertical as well as the hor-izontal direction, resulting in a cross shaped pattern on theCCD; see Fig. 1. This allows long image distances F2 with-out losing detectable solid angle. Because only the outer part(off-axis) of the actual RZP structure is used, the gratingperiod d varies only slightly. Therefore, the conventional grat-ing formula can be used in good approximation. The gratingperiod in the middle of the RZP structure is 3.054 µm for Cand 2.115 µm for N resulting in a linear dispersion dx/dλ of13 mm/nm and 19 mm/nm, respectively. With a 25.4 mm longCCD chip, a wavelength range of approximately 1.5 nm canbe detected. For the measurement of the full lpp spectrumbetween 1 nm and 5 nm, the CCD must be shifted several cen-timeters along the dispersion axis. Using the grating formulaand geometric considerations, the RP can be expressed byλ∆λ=F2λSd sin(β).Here, S stands for the effective source size and β is the diffrac-tion angle. With F2 = 2500 mm and S = 50 µm (FWHM),λ/∆λ of about 1100 at the design wavelength λ for both RZPstructures is expected. The RP peaks at the design wavelengthand degenerates linearly in x and y to both sides, which isequivalent to 1/λ for small dλ. By changing either F2 or β,the focused wavelength in the detector plane can be changed.This ultimately tunes the wavelength of maximum RP, so otherwavelengths can be measured by misaligning the experimentalsetup. Changing F2 is not advisable because the misalign-ment for a notable change of focused wavelength is in theorder of a couple of meters. The diffraction angle β, on theother hand, only has to be changed a few mrad for a focuswavelength change of 0.1 nm. By introducing an aperture,the depth of the field can be increased, resulting in a slowerdegeneration of the RP. This can be accomplished with aknife edge which is placed in the middle of the RZP structure0034-6748/2018/89(2)/026108/3/$30.00 89, 026108-1 Published by AIP Publishing.026108-2 Jonas et al. Rev. Sci. Instrum. 89, 026108 (2018)FIG. 1 . Schematic view of the spectrometer principle. Different wavelengthsare focused at different positions on the optical axis.perpendicular to the grooves. Assuming a 0.25 mm distancebetween the knife edge and the RZP structure, the apertureis reduced by a factor of 10 with an accompanying tenfoldreduction of intensity. Due to the intrinsic RZP structure, thenumber of illuminated grooves is not reduced, therefore pre-serving the RP. The calculated average efficiency for the usedoptics is 17.4% for the C structure and 17.1% for the N struc-ture. It is dependent of the line density, angle of incidence,the silicon wafer surface properties, and the grating profiledepth.5To acquire the spectrum from the CCD image, the back-ground is subtracted and the counts in each pixel row aresummed up. This simple summarization is well justified due tothe negligible curvature of the equi-energy lines near die hor-izontal focus. For the determination of the relative efficiency,the whole plasma emission range from 1 nm to 5 nm was mea-sured by moving the detector along the direction of dispersion.The angle of the RZP was optimized to focus 2.5 nm verticallyin the middle of the CCD. Because of the limited size of theCCD chip size, the CCD had to be shifted three times. The aper-ture was decreased by a factor of ten to increase the RP outof focus. Despite the closed aperture, the measuring time with120 mJ of laser energy was between 0.5 s and 10 s, dependingon the distance to the horizontal focus. The wavelength axiswas calibrated using the NIST database for the atomic copperlines. Measurements were performed with both RZP structures(C, N) successively and copper as well as tungsten as the tar-get material; see Fig. 2. As the setup is not fully calibrated,only the relative efficiency can be discussed. For comparison,a spectrum that has been collected with a VLS spectrometer(description see Ref. 7) is shown.The y-axis is normalized to the acquisition time and theNA of the RZP structure. No correction was performed con-cerning the filter and the CCD as they were used for all mea-surements. The shape of the spectra is similar for the referencespectrum and the spectrum collected with the C structure. Theefficiency of the N structure decreases to smaller wavelengths,which is contrary to a possible efficiency decrease with dis-tance to the design wavelength. This behavior is presumed tooriginate from diffraction effects caused by the profile depthor the quality of the structure.To determine the RP, isolated lines in the Cu spectrumcan be used by calculating the FWHM of the respective lines.The hereby obtained values are the lower limit for the RPbecause the natural linewidth is neglected. The achieved RPFIG. 2. Tungsten (top) and copper (bottom) plasma emission spectrumobtained with the N (blue) and C (black) RZP structures and a VLS spec-trometer (grey). The VLS grating has a C containing contamination layervisible in a C K-edge feature in the spectrum. The RZP structures show Ocontamination.while peaking at the design wavelength and degrading to bothhigher and lower wavelengths is for all wavelengths betterthan λ/∆λ = 140, comparable to the lower performance ofcommercially available VLS gratings.For the determination of the optimally achievable RP,several measurements with different RZP angles and openaperture were conducted. Figure 3 presents an example on howthe spectrum changes with different RZP angles and empha-sizes the small depth of the field with open aperture. The copperspectrum measured with the N-RZP is shown. The spectrumconsists of Cu relaxation lines from up to 20-times ionized Cu.The focus wavelength clearly moves between the two measure-ments. The change is most notably for the Cu XX line doubletat 1.257 nm and 1.2827 nm belonging to 2p-3s transitions.The determination of the RP for selected isolated atomiclines over the whole spectral range is shown with the help of tensingle overlapping measurements (depicted with different lineFIG. 3. Copper spectrum around 1.2 nm measured with the N-RZP at twodifferent RZP angles. The full aperture was used and the RP for four selectedlines is depicted.026108-3 Jonas et al. Rev. Sci. Instrum. 89, 026108 (2018)FIG. 4. RP for selected isolated plasma lines at different setup geometriesmeasured with the C structure.FIG. 5. RP for selected isolated plasma lines at different setup geometriesmeasured with the N structure.style) in Fig. 4 (C structure) and Fig. 5 (N structure). For eachmeasurement, the fast degeneration of the RP is evident. Thehighest determined RP for each measurement is marked with apentagram. Please note that there are no atomic lines between1.3 nm and 2.4 nm available in the spectrum. The maximummeasured RP for both RZP structures degenerates from around1100 at 4.7 nm to 600 at 1.05 nm. These values must be takenas the lower limit, as for some of the measurements, suitableisolated lines are missing; see Fig. 1. The N-RZP shows ahigher overall performance. There seems to be no correlationbetween RP and RZP structure design energy.The usability of a single RZP structure as a broadbanddispersive element for soft X-ray spectroscopy was demon-strated. By misaligning the structure and collecting the spectrasequentially, the range between 1 nm and 5 nm can be coveredwith a high efficiency (>10%) and RP (>600). Compared towidely used VLS gratings, an improvement of a factor of 2–4was achieved. As RZP structure sizes are limited to lines/mmdepending on the manufacturing technique, and this is differentfor different design wavelengths, the use of one RZP struc-ture designed for center wavelength of the source emissionmight be advantageous for efficient spectroscopy at arbitrarywavelengths in the investigated soft X-ray range.The authors thank H. Stiel, H. Löchel, and A. Erko forfruitful discussions. The work was conducted in the frameworkof DFG Project No. 313838950.1G. M. Zeng, H. Daido, K. Murai, Y. Kato, M. Nakatsuka, and S. Nakai,J. Appl. Phys. 72, 3355 (1992).2I. Mantouvalou, R. Jung, J. Tuemmler, H. Legall, T. Bidu, H. Stiel,W. Malzer, B. Kanngiesser, and W. Sandner, Rev. Sci. Instrum. 82, 66103(2011).3D. Adjei, M. G. Ayele, P. Wachulak, A. Bartnik, Ł. Wegrzynski,H. Fiedorowicz, L. Vyšı́n, A. Wiechec, J. Lekki, W. M. Kwiatek, L. Pina,M. Davı́dková, and L. Juha, Nucl. Instrum. Methods Phys. Res., Sect. B364, 27 (2015).4A. S. Moore, T. M. Guymer, J. L. Kline, J. Morton, M. Taccetti, N. E. Lanier,C. Bentley, J. Workman, B. Peterson, K. Mussack, J. Cowan, R. Prasad,M. Richardson, S. Burns, D. H. Kalantar, L. R. Benedetti, P. Bell, D. Bradley,W. Hsing, and M. Stevenson, Rev. Sci. Instrum. 83, 10E132 (2012).5C. Fujikawa, N. Yamaguchi, T. Hara, T. Kawachi, H. Oyama, K. Ando, andY. Aoyagi, Rev. Sci. Instrum. 69, 2849 (1998).6M. Müller, F.-C. Kühl, P. Großmann, P. Vrba, and K. Mann, Opt. Express21, 12831 (2013).7I. Mantouvalou, K. Witte, W. Martyanov, A. Jonas, D. Grötzsch, C. Streeck,H. Löchel, I. Rudolph, A. Erko, H. Stiel, and B. Kanngießer, Appl. Phys.Lett. 108, 201106 (2016).8M. Ibek, T. Leitner, A. Erko, A. Firsov, and P. Wernet, Rev. Sci. Instrum.84, 103102 (2013).9C. Braig, H. Lochel, A. Firsov, M. Brzhezinskaya, A. Hafner, J. Rehanek,M. Wojcik, A. Macrander, L. Assoufid, and A. Erko, Opt. Lett. 41, 29(2016).10T. Wilhein, D. Hambach, B. Niemann, M. Berglund, L. Rymell, and H. M.Hertz, Appl. Phys. Lett. 71, 190 (1997).11I. Mantouvalou, K. Witte, D. Grötzsch, M. Neitzel, S. Günther, J. Baumann,R. Jung, H. Stiel, B. Kanngiesser, and W. Sandner, Rev. Sci. Instrum. 86,35116 (2015).12I. Mantouvalou, A. Jonas, K. Witte, R. Jung, H. Stiel, and B. Kanngießer,Proc. SPIE 10243, 1024308 (2017).

Note: Reflection zone plates as highly resolving broadband optics for soft X-ray laboratory spectrometers

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Note: Reflection zone plates as highly resolving broadband optics for soft X-ray laboratory spectrometers

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