rus
10.22184/1933-7296.FRos.2019.13.5.500.503
The scope of refractive optics has expanded significantly, significantly covering the area of application of traditional X‑ray optics – crystals and mirrors. But for astrophysical problems, X‑ray optics of squint gliding remains an indispensable tool. The complexity of the problem lies in the manufacture of multilayer interference mirrors, refractive lenses, and tunable refractive lenses – zoom lenses. To use their potential, X‑ray optics of diffraction quality are required. And in the field of X‑ray microtomography, the possibilities of increasing sensitivity are hidden in the use of X‑ray optical elements: capillary lenses, Fresnel zone plates, asymmetric reflecting crystals (Bragg magnifiers), multilayer X‑ray mirrors.
The scope of refractive optics has expanded significantly, significantly covering the area of application of traditional X‑ray optics – crystals and mirrors. But for astrophysical problems, X‑ray optics of squint gliding remains an indispensable tool. The complexity of the problem lies in the manufacture of multilayer interference mirrors, refractive lenses, and tunable refractive lenses – zoom lenses. To use their potential, X‑ray optics of diffraction quality are required. And in the field of X‑ray microtomography, the possibilities of increasing sensitivity are hidden in the use of X‑ray optical elements: capillary lenses, Fresnel zone plates, asymmetric reflecting crystals (Bragg magnifiers), multilayer X‑ray mirrors.
X-Ray Optics: How And What Will We See?
The scope of refractive optics has expanded significantly, significantly covering the area of application of traditional X‑ray optics – crystals and mirrors. But for astrophysical problems, X‑ray optics of squint gliding remains an indispensable tool. The complexity of the problem lies in the manufacture of multilayer interference mirrors, refractive lenses, and tunable refractive lenses – zoom lenses. To use their potential, X‑ray optics of diffraction quality are required. And in the field of X‑ray microtomography, the possibilities of increasing sensitivity are hidden in the use of X‑ray optical elements: capillary lenses, Fresnel zone plates, asymmetric reflecting crystals (Bragg magnifiers), multilayer X‑ray mirrors.
What are the prospects for using X‑ray optics? This is covered in the report «Refractive X‑ray optics: status, problems and prospects» by A. A. Snigirev (Immanuel Kant Baltic Federal University, Kaliningrad, Russia). Since the first successful experimental demonstration of focusing by refracting lenses of X‑rays [1], the field of application of refractive optics has expanded significantly, majorly covering the area of application of traditional X‑ray optics – crystals and mirrors. Today, such optics are actively used on all modern high-energy (> 2 GeV) 3rd generation synchrotron radiation sources and free electron lasers (XFEL). Such rapid development is due to successes both in the development of the optical elements themselves and in special tunable devices based on refractive lenses – zoom lenses [2], which allow working in a wide energy range from 2 to 200 keV. In addition to their application in traditional micro-focusing problems, they can also be used as capacitors with an adjustable beam size, collimators providing micro-radial beam divergence, monochromators – low-pass filter [2], devices for suppressing high harmonics [3], Fourier converters [4].
The improved characteristics of beams produced by new 4th generation synchrotron radiation sources with reduced horizontal emittance will open up a unique opportunity for creating efficient beam transport systems based on refractive optics. Due to a significant decrease in the horizontal size of the source and beam divergence, such systems can transmit a photon beam with almost no loss from the source to the sample under study or any intermediate nodes of the optical scheme (mirrors, crystals, lenses, etc.). Apparently, experimental stations will receive significant advantages when using easily tunable systems based on refractive lenses installed immediately after the source. In this regard, the development of radiation- and thermally stable diamond optics is crucial [5–8]. The implementation of a beam transportation system based on refractive lenses will greatly simplify the layout of most new stations [9], which opens up additional possibilities for studying materials under extreme conditions [10, 11]. This will also allow a smooth transition, in the course of modernization, from current beam parameters, at existing stations, to improved characteristics, avoiding major changes in the optical scheme [12].
Applications of refractive optics can be extended to the field of Fourier optics, coherent diffraction, and microscopy [12–16]. To study the 3D structure of photonic crystals and mesoscopic materials [17–19], coherent diffraction microscopy methods and high-resolution diffraction methods using a refractive lens as a Fourier transducer were proposed. The beam formers – axicons [20], which allow creating wavefronts of a given shape, are of a particular interest. In this regard, the use of new additive 3D printing technologies for modeling and creating X‑ray micro-optics is difficult to overestimate [21,22].
X‑ray interferometry is another promising direction in the development of refractive optics. Recently proposed multi-lens interferometers can generate an interference field with a variable period in the range from tens of nanometers to tens of micrometers [23–25]. This simple way of creating an X‑ray standing wave in paraxial geometry opens up the possibility of developing new methods of X‑ray interferometry for studying natural and artificial nanomaterials, such as self-organizing biosystems, photonic and colloidal crystals, and nano-electronic objects. Such a device can be used as a classical interferometer for constructing phase-contrast images and radiography, and can also be useful for characterizing the coherent properties of high-energy X‑ray sources.
The fact that the progress of recent years in the technology of growth of multilayer interference mirrors (MIS) of normal incidence allows us to begin solving the ambitious task of transferring traditional methods of controlling light beams to extreme ultraviolet (EUV) and soft X‑ray (SX) wavelength ranges, the seminar participants learned from a speech by the employees of the Institute of Physics of Microstructures of the Russian Academy of Sciences, Nizhny Novgorod, (N. I. Chkhalo, A. E. Pestov, V. N. Polkovnikov, N. N. Salashchenko, M. N. Toropov) «Diffraction Quality X‑ray Optics: Technology, Metrology, Applications».
Due to the short wavelength, low scattering and resonant nature of the interaction with matter, radiation of this range provides unique opportunities for nanophysics, nanotechnology and nano-diagnostics of substances. The largest amount of information about the physical processes occurring on the Sun is obtained from studies of the corona of the Sun in the EUV and SX ranges. Broadband MIS allows you to transport, focus, conduct spectral analysis of atto- and sub-atto-second pulses of electromagnetic radiation without «blurring» the wave packet, or even shorten it in time.
To use the potential of MIS for the image and transport of beams without distortion of the wave fronts, diffraction-quality optics for the X‑ray range are required. Compared to traditional optics, its accuracy should be at least two orders of magnitude higher. Traditional methods of manufacturing and studying mirrors do not provide these requirements. The report reported on new methods of fabrication and characterization of diffraction-quality optics developed at the IMP of RAS for the EUV and SX ranges. Examples of the use of the discussed X‑ray optical elements of optics for extraterrestrial astronomy, X‑ray microscopy, and lithography were presented.
The report «Multilayer Beryllium-Based X‑ray Optics» (V. N. Polkovnikov, N. N. Salashchenko, N. I. Chkhalo, Institute of Microstructure Physics of RAS, Nizhny Novgorod) was devoted to the study of beryllium-containing multilayer mirrors (MM). Back in the 1990s, beryllium was used in the soft X‑ray (SX) and extreme ultraviolet (EUV) ranges as a weakly absorbing material (spacer). However, the Be-based spacer MMs provided high reflection coefficients only in a very narrow wavelength range of 11.2–12.4 nm. At other wavelengths, beryllium-containing MMs were inferior to traditional MMs based on Si, Al, and Mg spacers. In the course of our work, it was shown that in the wavelength range λ>17.1 nm, beryllium has a unique combination of the imaginary and real parts of the refractive index. This makes it possible to use Be as a scattering material and, as such, simultaneously obtain record high reflection coefficients and spectral selectivity. The smoothness of the dispersion dependence of the refractive index Be allows it to be used in the short-wavelength part of the SX spectrum as the basis of the MM intended for use in a wide range of wavelengths. In addition, the application of the barrier layer technique allowed us to achieve record reflection values of beryllium-containing MM in the range of 11.2–14 nm.
Methods for increasing resolution and sensitivity in microtomography using X‑ray optical elements were considered in a report by V. E. Asadchikova, A. V. Shubnikov Institute of Crystallography of the Federal Research Center «Crystallography and Photonics» of RAS. Currently, X‑ray tomography is a widespread method for studying the spatial structure of objects in various fields of science and technology. Computed (X‑ray) tomography has become one of the main diagnostic methods in modern medicine. However, the spatial resolution and sensitivity achieved in these devices are insufficient for using the devices in many other applications. A significant drawback of serial X‑ray tomographs is the fact that the instruments provide the ability to determine the absorption only in the relative Hounsfield scale.
An increase in resolution and sensitivity at present (due to a number of limitations) can be achieved only with a decrease in the field of view. For this reason, research is actively ongoing in the field of X‑ray microtomography. The main possibilities for increasing resolution are projection magnification using microfocus sources and / or the use of X‑ray optical elements. These include capillary lenses, Fresnel zone plates, asymmetric reflective crystals (Bragg magnifiers), and multilayer X‑ray mirrors, which, however, can only be effectively applied to soft X‑rays. Note that the use of monochromatic radiation allows us to determine the values of linear absorption coefficients, which significantly improves the quality of the information received.
The report showed the possibilities of using these elements in X‑ray microtomography both in our country and abroad. The speaker paid special attention to the issue of increasing the sensitivity of X‑ray tomographs by applying phase-sensitive effective methods. This is also achieved using various X‑ray optical elements. In addition to the above, the latter also include diffraction gratings (Talbot interferometry). Examples were given of studying the three-dimensional structure of samples of different nature with varying spatial resolution.
X‑ray optics of oblique incidence and its application in the Spectrum-RG orbital astrophysical observatory project were considered in a report of the same name by a group of authors from Space Research Institute of RAS and Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physics, Sarov (M. N. Pavlinsky, A. A. Lutovinov, A. Yu. Tkachenko (Space Research Institute of RAS, Moscow); S. V. Grigorovich (Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physics, Sarov). From 2007 to 2016, the work was carried out at the Space Research Institute of RAS and Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physic to develop the ART-XC squint incidence X‑ray mirror telescope for Spectrum-RG orbital astrophysical observatory (the launch of the observatory is scheduled for June 21, 2019.) Within the framework of these works, the development of technologies for the manufacture of X‑ray mirrors by the method of electroforming based on nickel and nickel-cobalt with iridium coating was carried out. The task was complicated in the manufacture of mirrors allowing operation up to energies of ~30 keV
with an angular resolution of ≤1“ in the field view more than ≥30“. The participants of the discussion were presented with technological developments, the solution of the problem of metrological support and the results of ground tests at a specialized calibration stand of oblique X‑ray optics drops coupled with the developed position-sensitive and CdTe-based spectrometric semiconductor detector. Together, the seven mirror systems of the ART-XC telescope provide an effective area of ~460 cm2 along the axis of view at an energy of 8 keV.
REFERENCE
A. Snigirev, V. Kohn, I. Snigireva, B. Lengeler. Nature. 1996; 384: 49.
G. B. M. Vaughan, J. P. Wright, A. Bytchkov et al. J. Synchrotron Rad. 2011; 18: 125.
M. Polikarpov, I. Snigireva, A. Snigirev. J. Synchrotron Rad. 2014; 21: 484.
M. Lyubomirskiy, I. Snigireva, A. Snigirev. Optics express. 2016; 24: 13679.
M. Polikarpov, I. Snigireva, J. Morse et al. J. Synchrotron Rad. 2015; 22: 23.
S. Terentyev, V. Blank, S. Polyakov et al. Appl. Phys. Let. 2015; 107: 111108.
M. Polikarpov, I. Snigireva, A. Snigirev. AIP Conference Proceedings. 2016; 1741: 040024.
Q. Zhang et al. J. Synchrotron Rad. 2019; 26:109.
M. W. Bowler, D. Nurizzo, R. Barrett et al. J. Synchrotron Rad. 2015; 22: 1540.
N. Dubrovinskaia, L. Dubrovinsky, N. A. Solopova et al. Sci. Adv. 2016; 2: e1600341.
F. Wilhelm, G. Garbarino, J. Jacobs et al. High Pressure Research. 2016; 36: 445.
Orange Book «ESRF Upgrade programme Phase II 92015–2022). Technical Design Study», G. Admans et al eds. 2014.
V. Kohn, I. Snigireva, A. Snigirev. Opt. Comm. 2003; 216: 247.
M. Drakopoulos, A. Snigirev, I. Snigirev, J. Schilling. Appl. Phys. Lett. 2005; 86: 014102.
P. Ershov, S. Kuznetsov, I. Snigireva et al. Appl. Cryst. 2013; 46: 1475.
H. Simons, A. King, W. Ludwig et al. Nature Communications. 2015; 6: 6098.
A. Bosak, I. Snigireva, K. Napolskii, A. Snigirev. Adv. Mater. 2010; 22: 3256.
D. V. Byelov, J.-M. Meijer, I. Snigireva et al. RSC Advances. 2013; 3: 15670.V.
V. Kohn, I. Snigireva, A. Snigirev. J. Synchrotron Rad. 2014; 21: 729.
D. Zverev, A. Barannikov, I. Snigireva, A. Snigirev. Opt. Express. 2017; 25: 28469–28477.
A. K. Petrov, V. O. Bessonov, K. A. Abrashitova et al. Opt. Express. 2017; 25: 14173.
A. Barannikov, M. Polikarpov, P. Ershov et al. J. Synchrotron Rad. 2019.
A. Snigirev, I. Snigireva, V. Kohn et al. Phys. Rev. Lett. 2009; 103: 064801.
A. Snigirev, I. Snigireva, M. Lyubomirskiy et al. Optics express. 2014; 22(21): 25842.
M. Lyubomirskiy, I. Snigireva, V. Kohn et al. J. Synchrotron Rad. 2016; 23: 1104. gpad.ac.ru
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The scope of refractive optics has expanded significantly, significantly covering the area of application of traditional X‑ray optics – crystals and mirrors. But for astrophysical problems, X‑ray optics of squint gliding remains an indispensable tool. The complexity of the problem lies in the manufacture of multilayer interference mirrors, refractive lenses, and tunable refractive lenses – zoom lenses. To use their potential, X‑ray optics of diffraction quality are required. And in the field of X‑ray microtomography, the possibilities of increasing sensitivity are hidden in the use of X‑ray optical elements: capillary lenses, Fresnel zone plates, asymmetric reflecting crystals (Bragg magnifiers), multilayer X‑ray mirrors.
What are the prospects for using X‑ray optics? This is covered in the report «Refractive X‑ray optics: status, problems and prospects» by A. A. Snigirev (Immanuel Kant Baltic Federal University, Kaliningrad, Russia). Since the first successful experimental demonstration of focusing by refracting lenses of X‑rays [1], the field of application of refractive optics has expanded significantly, majorly covering the area of application of traditional X‑ray optics – crystals and mirrors. Today, such optics are actively used on all modern high-energy (> 2 GeV) 3rd generation synchrotron radiation sources and free electron lasers (XFEL). Such rapid development is due to successes both in the development of the optical elements themselves and in special tunable devices based on refractive lenses – zoom lenses [2], which allow working in a wide energy range from 2 to 200 keV. In addition to their application in traditional micro-focusing problems, they can also be used as capacitors with an adjustable beam size, collimators providing micro-radial beam divergence, monochromators – low-pass filter [2], devices for suppressing high harmonics [3], Fourier converters [4].
The improved characteristics of beams produced by new 4th generation synchrotron radiation sources with reduced horizontal emittance will open up a unique opportunity for creating efficient beam transport systems based on refractive optics. Due to a significant decrease in the horizontal size of the source and beam divergence, such systems can transmit a photon beam with almost no loss from the source to the sample under study or any intermediate nodes of the optical scheme (mirrors, crystals, lenses, etc.). Apparently, experimental stations will receive significant advantages when using easily tunable systems based on refractive lenses installed immediately after the source. In this regard, the development of radiation- and thermally stable diamond optics is crucial [5–8]. The implementation of a beam transportation system based on refractive lenses will greatly simplify the layout of most new stations [9], which opens up additional possibilities for studying materials under extreme conditions [10, 11]. This will also allow a smooth transition, in the course of modernization, from current beam parameters, at existing stations, to improved characteristics, avoiding major changes in the optical scheme [12].
Applications of refractive optics can be extended to the field of Fourier optics, coherent diffraction, and microscopy [12–16]. To study the 3D structure of photonic crystals and mesoscopic materials [17–19], coherent diffraction microscopy methods and high-resolution diffraction methods using a refractive lens as a Fourier transducer were proposed. The beam formers – axicons [20], which allow creating wavefronts of a given shape, are of a particular interest. In this regard, the use of new additive 3D printing technologies for modeling and creating X‑ray micro-optics is difficult to overestimate [21,22].
X‑ray interferometry is another promising direction in the development of refractive optics. Recently proposed multi-lens interferometers can generate an interference field with a variable period in the range from tens of nanometers to tens of micrometers [23–25]. This simple way of creating an X‑ray standing wave in paraxial geometry opens up the possibility of developing new methods of X‑ray interferometry for studying natural and artificial nanomaterials, such as self-organizing biosystems, photonic and colloidal crystals, and nano-electronic objects. Such a device can be used as a classical interferometer for constructing phase-contrast images and radiography, and can also be useful for characterizing the coherent properties of high-energy X‑ray sources.
The fact that the progress of recent years in the technology of growth of multilayer interference mirrors (MIS) of normal incidence allows us to begin solving the ambitious task of transferring traditional methods of controlling light beams to extreme ultraviolet (EUV) and soft X‑ray (SX) wavelength ranges, the seminar participants learned from a speech by the employees of the Institute of Physics of Microstructures of the Russian Academy of Sciences, Nizhny Novgorod, (N. I. Chkhalo, A. E. Pestov, V. N. Polkovnikov, N. N. Salashchenko, M. N. Toropov) «Diffraction Quality X‑ray Optics: Technology, Metrology, Applications».
Due to the short wavelength, low scattering and resonant nature of the interaction with matter, radiation of this range provides unique opportunities for nanophysics, nanotechnology and nano-diagnostics of substances. The largest amount of information about the physical processes occurring on the Sun is obtained from studies of the corona of the Sun in the EUV and SX ranges. Broadband MIS allows you to transport, focus, conduct spectral analysis of atto- and sub-atto-second pulses of electromagnetic radiation without «blurring» the wave packet, or even shorten it in time.
To use the potential of MIS for the image and transport of beams without distortion of the wave fronts, diffraction-quality optics for the X‑ray range are required. Compared to traditional optics, its accuracy should be at least two orders of magnitude higher. Traditional methods of manufacturing and studying mirrors do not provide these requirements. The report reported on new methods of fabrication and characterization of diffraction-quality optics developed at the IMP of RAS for the EUV and SX ranges. Examples of the use of the discussed X‑ray optical elements of optics for extraterrestrial astronomy, X‑ray microscopy, and lithography were presented.
The report «Multilayer Beryllium-Based X‑ray Optics» (V. N. Polkovnikov, N. N. Salashchenko, N. I. Chkhalo, Institute of Microstructure Physics of RAS, Nizhny Novgorod) was devoted to the study of beryllium-containing multilayer mirrors (MM). Back in the 1990s, beryllium was used in the soft X‑ray (SX) and extreme ultraviolet (EUV) ranges as a weakly absorbing material (spacer). However, the Be-based spacer MMs provided high reflection coefficients only in a very narrow wavelength range of 11.2–12.4 nm. At other wavelengths, beryllium-containing MMs were inferior to traditional MMs based on Si, Al, and Mg spacers. In the course of our work, it was shown that in the wavelength range λ>17.1 nm, beryllium has a unique combination of the imaginary and real parts of the refractive index. This makes it possible to use Be as a scattering material and, as such, simultaneously obtain record high reflection coefficients and spectral selectivity. The smoothness of the dispersion dependence of the refractive index Be allows it to be used in the short-wavelength part of the SX spectrum as the basis of the MM intended for use in a wide range of wavelengths. In addition, the application of the barrier layer technique allowed us to achieve record reflection values of beryllium-containing MM in the range of 11.2–14 nm.
Methods for increasing resolution and sensitivity in microtomography using X‑ray optical elements were considered in a report by V. E. Asadchikova, A. V. Shubnikov Institute of Crystallography of the Federal Research Center «Crystallography and Photonics» of RAS. Currently, X‑ray tomography is a widespread method for studying the spatial structure of objects in various fields of science and technology. Computed (X‑ray) tomography has become one of the main diagnostic methods in modern medicine. However, the spatial resolution and sensitivity achieved in these devices are insufficient for using the devices in many other applications. A significant drawback of serial X‑ray tomographs is the fact that the instruments provide the ability to determine the absorption only in the relative Hounsfield scale.
An increase in resolution and sensitivity at present (due to a number of limitations) can be achieved only with a decrease in the field of view. For this reason, research is actively ongoing in the field of X‑ray microtomography. The main possibilities for increasing resolution are projection magnification using microfocus sources and / or the use of X‑ray optical elements. These include capillary lenses, Fresnel zone plates, asymmetric reflective crystals (Bragg magnifiers), and multilayer X‑ray mirrors, which, however, can only be effectively applied to soft X‑rays. Note that the use of monochromatic radiation allows us to determine the values of linear absorption coefficients, which significantly improves the quality of the information received.
The report showed the possibilities of using these elements in X‑ray microtomography both in our country and abroad. The speaker paid special attention to the issue of increasing the sensitivity of X‑ray tomographs by applying phase-sensitive effective methods. This is also achieved using various X‑ray optical elements. In addition to the above, the latter also include diffraction gratings (Talbot interferometry). Examples were given of studying the three-dimensional structure of samples of different nature with varying spatial resolution.
X‑ray optics of oblique incidence and its application in the Spectrum-RG orbital astrophysical observatory project were considered in a report of the same name by a group of authors from Space Research Institute of RAS and Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physics, Sarov (M. N. Pavlinsky, A. A. Lutovinov, A. Yu. Tkachenko (Space Research Institute of RAS, Moscow); S. V. Grigorovich (Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physics, Sarov). From 2007 to 2016, the work was carried out at the Space Research Institute of RAS and Russian Federal Nuclear Center – All-Russian Research Institute of Experimental Physic to develop the ART-XC squint incidence X‑ray mirror telescope for Spectrum-RG orbital astrophysical observatory (the launch of the observatory is scheduled for June 21, 2019.) Within the framework of these works, the development of technologies for the manufacture of X‑ray mirrors by the method of electroforming based on nickel and nickel-cobalt with iridium coating was carried out. The task was complicated in the manufacture of mirrors allowing operation up to energies of ~30 keV
with an angular resolution of ≤1“ in the field view more than ≥30“. The participants of the discussion were presented with technological developments, the solution of the problem of metrological support and the results of ground tests at a specialized calibration stand of oblique X‑ray optics drops coupled with the developed position-sensitive and CdTe-based spectrometric semiconductor detector. Together, the seven mirror systems of the ART-XC telescope provide an effective area of ~460 cm2 along the axis of view at an energy of 8 keV.
REFERENCE
A. Snigirev, V. Kohn, I. Snigireva, B. Lengeler. Nature. 1996; 384: 49.
G. B. M. Vaughan, J. P. Wright, A. Bytchkov et al. J. Synchrotron Rad. 2011; 18: 125.
M. Polikarpov, I. Snigireva, A. Snigirev. J. Synchrotron Rad. 2014; 21: 484.
M. Lyubomirskiy, I. Snigireva, A. Snigirev. Optics express. 2016; 24: 13679.
M. Polikarpov, I. Snigireva, J. Morse et al. J. Synchrotron Rad. 2015; 22: 23.
S. Terentyev, V. Blank, S. Polyakov et al. Appl. Phys. Let. 2015; 107: 111108.
M. Polikarpov, I. Snigireva, A. Snigirev. AIP Conference Proceedings. 2016; 1741: 040024.
Q. Zhang et al. J. Synchrotron Rad. 2019; 26:109.
M. W. Bowler, D. Nurizzo, R. Barrett et al. J. Synchrotron Rad. 2015; 22: 1540.
N. Dubrovinskaia, L. Dubrovinsky, N. A. Solopova et al. Sci. Adv. 2016; 2: e1600341.
F. Wilhelm, G. Garbarino, J. Jacobs et al. High Pressure Research. 2016; 36: 445.
Orange Book «ESRF Upgrade programme Phase II 92015–2022). Technical Design Study», G. Admans et al eds. 2014.
V. Kohn, I. Snigireva, A. Snigirev. Opt. Comm. 2003; 216: 247.
M. Drakopoulos, A. Snigirev, I. Snigirev, J. Schilling. Appl. Phys. Lett. 2005; 86: 014102.
P. Ershov, S. Kuznetsov, I. Snigireva et al. Appl. Cryst. 2013; 46: 1475.
H. Simons, A. King, W. Ludwig et al. Nature Communications. 2015; 6: 6098.
A. Bosak, I. Snigireva, K. Napolskii, A. Snigirev. Adv. Mater. 2010; 22: 3256.
D. V. Byelov, J.-M. Meijer, I. Snigireva et al. RSC Advances. 2013; 3: 15670.V.
V. Kohn, I. Snigireva, A. Snigirev. J. Synchrotron Rad. 2014; 21: 729.
D. Zverev, A. Barannikov, I. Snigireva, A. Snigirev. Opt. Express. 2017; 25: 28469–28477.
A. K. Petrov, V. O. Bessonov, K. A. Abrashitova et al. Opt. Express. 2017; 25: 14173.
A. Barannikov, M. Polikarpov, P. Ershov et al. J. Synchrotron Rad. 2019.
A. Snigirev, I. Snigireva, V. Kohn et al. Phys. Rev. Lett. 2009; 103: 064801.
A. Snigirev, I. Snigireva, M. Lyubomirskiy et al. Optics express. 2014; 22(21): 25842.
M. Lyubomirskiy, I. Snigireva, V. Kohn et al. J. Synchrotron Rad. 2016; 23: 1104. gpad.ac.ru
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