Diffraction Gratings Based on Multilayer Structures
Development of High Efficiency Diffraction Gratings on the Basis of Multilayer Structures for Monochromators and Polychromators of X-Ray Synchrotron Radiation and for Ultra-High Spectral Resolution X-Ray Diagnostics in the 0.1 – 10 Kev Energy Range
Tech Area / Field
- PHY-SSP/Solid State Physics/Physics
- PHY-OPL/Optics and Lasers/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
VNIIEF, Russia, N. Novgorod reg., Sarov
- Budker Institute of Nuclear Physics, Russia, Novosibirsk reg., Akademgorodok\nFIAN Lebedev / Quantum Radiophysics Department of the Lebedev Physical Institute of Russian Academy of Sciences, Russia, Moscow
- URA 0073/Universite Paris-Sud / Laboratoire pour l'Utilisation du Rayonnement Electromagnetique (LURE), France, Orsay
Project summaryThe recent decade is characterized by extensive development of synchrotron sources (SS) of X-radiation (XR). Today, already the third generation of synchrotrons that are remarkable for their very high of high level of brightness has been put into operation. To use completely the unique characteristics of these synchrotrons the high-efficiency dispersion elements worked in hn ~ 0.1 – 10 keV range are need to form mono- and polychromatic X-ray beams for fundamental and applied research (a material technology, X-ray lithography, a certification of spectral elements and the X-ray diagnostic means, etc.). In this case the parameters of the dispersion elements must remain stable not only on long storage but under the action of synchrotron radiation beams as well. The same dispersion elements are required in fact, for rapidly developing in recent years spectral XR diagnostics of laboratory and astrophysical plasma, monochromatization of laser-plasma X-ray source radiation, microanalysis and biological applications as well.
Unfortunately, conventional gratings of grazing incidence gratings, transmission gratings and multilayer X-ray mirrors (MXRM) as well as crystals do not completely meet the above requirements for dispersion elements. The grazing incidence gratings have a low (of an order of several percents) diffraction efficiency and a high diffusing background at a potentially high spectral resolution. We understand the effectiveness as the ratio of diffracted radiation energy flux to an energy flux for a certain wavelength. Moreover, the significant aberrations are takes place at grazing incidence. Therefore the focusing gratings of this type could be hardly practically applied. Transmission gratings have low spectral resolution (≤ 50) and a small illumination. To add, gratings of both types work satisfactory only in the area of soft X-ray (SXR) hn Ј 1 keV. Multilayer X-ray mirrors’ besides high efficiency, have low spectral resolution (~ 80-100). The crystals, though having a high resolution in the range above 3 keV, have small diffraction efficiency.
A considerable progress in developing high-efficiency spectral elements has been achieved during a recent decade. The remarkable paper  on this subject was published and the first samples of gratings on the basis of multilayer structures were created in the USA [2,3], and also by the authors of the present project in Russia [4,5]. The English term for such dispersion elements is “multilayer gratings” (MGs). Combining a periodic structure of a grating and a multilayer coating, MGs posses their advantages that are a good spectral resolution at a high efficiency of reflection. Notice that the first, but imperfect, technological realization of such combination (a blazed grating with multilayer coating) was proposed by Spiller in 1981 . The most rational way of high-quality MG creation is using ready multilayer coating with the help of existing microlithography methods (electronic, holographic, ion-beam etching) [7,8].
The recent theoretical and experimental research works [4,7-9] show that MGs are an advanced spectroscopic elements having a high dispersion and efficiency (for example, for the range of hn ~ 0.8-1.5 keV a resolution l ⁄Δl up to 103 at Rmax~ 10ё15% and angular aperture 2-8 mrad are achieved). The MG was demonstrated to have property to focus practically all the output radiation into one of the diffraction orders with almost complete surpression of others, including a zero order. A perspective of using MG not only within a soft interval but also within a hard (up to 10 keV with Rmax ~ 10%) interval of spectrum has been shown.
In fact, being a polychromatic element, unlike crystals, MG allows implement in this area a simultaneous recording of a wide X-ray spectrum with a relatively high resolution. In particular, the authors of the project proposed a fine structure Flash-XAFS-spectroscopy method of the substance absorption edge with a nanosecond time resolution . The calculations of MG characteristics with considerations for absorption and scattering radiation inside the grating are possible with application of numerical method [4,11,12].
A new type of a multilayer grating that allows to increase the angular dispersion and the width of a spectrum interval where a high reflectance is observed has been recently suggested by the project authors . Such grating (named by sliced multilayer grating or SMG) is a cross-slice of a multilayer structure usually used as a multilayer X-ray mirror, which is made at a certain angle.
Such approach makes it possible to create gratings with very small spacing and high diffraction efficiency. For example, it has been shown that using such grating based on the MoSi2-SI structure with a spacing ~ 20nm and the number of layers being 500 one may obtain a spectral resolution in the first order ~103 .
Therewith the exposure is by a factor of ~20 less than required for a grazing incidence spectrograph on the ordinary grating and on the depth of definition being larger than an order of magnitude. Further increase of resolution can be achieved by increasing the number of layers. Transition to a shorter wavelength can be made using suitable selecting of the layer materials.
It should be emphasized that despite the first promising results, the multilayer gratings are so far the novel elements of the X-ray optics, and their properties as well as a potential of application have not been studied enough. The first objective of a project is improvement of manufacturing technology and optimization of the characteristics of gratings based on multilayer structures. In particular, authors hope to create the gratings of MG type with sufficiently high X-ray damage threshold. The second objective is creating on their base of mono- and polychromators of power synchrotron radiation and high-illumination X-ray spectrometers (XRS) with high (order of 104-105) spectral resolution within the 0.1-10 keV range. Such devices are needed for solving of the fundamental physics problems, carry out applied research, develop of new technologies, as well as, to investigate a laboratory plasma and X-radiation of the astrophysical objects.
The proposed project meet completely the ISTC goals, since it provides a good opportunity for the the scientists and other specialists formerly engaged in the nuclear weapons development and production to apply their knowledge and experience to the long-term activities in civilian areas of science and technology.
Project participants of RFNC-VNIIEF and INP SB RSA have sufficiently large experience on developing technologies, studying the mulilayer structure parameters, measuring the spectral characteristics of laboratory plasma XR and applying a synchrotron radiation to solve the applied problems. A number of papers were written by project authors on these issues have been published. The participating institutions have all the necessary equipment and instrumentation which ensure a successful implementation of the tasks stated in the project.
In the context of a project it is expected to:
– to improve a manufacturing technology of high-efficiency multilayer gratings for the quantum energy range being hn ~ 0.1-10 keV;
– to fulfil optimization of the grating parameters to work within hn ~ 0.1-1 keV and 1-10 keV of the given range;
– to receipt the data on grating resistance against high-power fluxes of synchrotron radiation;
– to develop and manufacture, based on the producing gratings, a monochromator model of a synchrotron radiation with high (~103-104) spectral resolution within range hn ~ 0.1-10 keV and to test it on the synchrotron;
– to develop, fabricate and test in experiments the high-illumination multilayer grating spectrographs to analyze the laboratory plasma X-ray within ranges hn~0.1-1 keV and 1-10 keV with high ~ 103-104 spectral resolution;
– to work out a computational-theoretical justification of a technology to manufacture gratings, which allows to predict and optimize their parameters.
The experience gained during the realization of project will be used for performance of fundamental and applied investigations on the synchrotron of the third and the fourth generations, for designing of high-illumination spectral instruments for fundamental and applied research of laboratory and astrophysical plasma X-ray with a high spectral resolution. It is anticipated that the project will be accomplished within 2.5 years.
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