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X-ray radiation channeling in micro-channel plates: Spectroscopy with a synchrotron radiation beam
Nuclear Instruments and Methods in Physics Research B 355 (2015) 293–296
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
X-ray radiation channeling in micro-channel plates: Spectroscopy with a synchrotron radiation beam M.I. Mazuritskiy a,⇑, S.B. Dabagov b,c,d, A. Marcelli b,e, K. Dziedzic-Kocurek f, A.M. Lerer a a
Physics Department, Southern Federal University, Rostov-on-Don, Russia INFN Laboratori Nazionali di Frascati, 00044 Frascati, Italy c RAS P.N. Lebedev Physical Institute, Leninsky pr. 53, 119991 Moscow, Russia d National Research Nuclear University MEPhI, Kashirskoe shosse 31, 115409 Moscow, Russia e RICMASS, Rome International Center for Materials Science Superstripes, via dei Sabelli 119A, 00185 Rome, Italy f M. Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland b
a r t i c l e
i n f o
Article history: Received 9 November 2014 Received in revised form 2 February 2015 Accepted 9 February 2015 Available online 5 March 2015 Keywords: X-ray capillary waveguides X-ray scattering X-ray fluorescence channeling X-ray spectroscopy X-ray angular distribution
a b s t r a c t We present here the angular distribution of the radiation propagated inside MultiChannel Plates with micro-channels of 3 lm diameter. The spectra collected at the exit of the channels present a complex distribution with contributions that can be assigned to the fluorescence radiation, originated from the excitation of the micro-channel walls. For radiation above the absorption edge, when the monochromatic energy in the region of the Si L-edge hits the micro-channel walls with a grazing angle h P 5°, or at the O K-edge when h P 2° a fluorescence radiation is detected. Additional information associated to the fine structures of the XANES spectra detected at the exit of MCPs are also presented and discussed. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction The propagation of X-rays through a capillary system is a complex phenomenon that depends on the optical layout, the capillary parameters, the radiation properties, etc., whose knowledge is still a matter of debate. Actually, because the technology based on the capillary optical elements may, in principle, deliver a high flux density within a sub-micrometer spot, its understanding is mandatory to develop novel optical systems. Such systems would be capable to increase the radiation density and eventually to shape X-ray beams without the use of the long optical focusing devices. Channeling based devices may indeed guide and shape an X-ray beam in order to control the intensity, the spot size, the divergence and the homogeneity [1]. At present, studies of X-ray transmission through the micro-capillary structures, aimed at the R&D of dedicated optics working in the ‘‘water window’’ spectral region are limited. Being large and effective low weight optics, the micro-channel plates (MCPs) have been already used in case of the low power instruments for different scientific applications and techniques development [2]. Their characteristics make them suitable for many other applications, for example, such as focusing of the excited radiation. Moreover, their broadband characteristics make ⇑ Corresponding author. http://dx.doi.org/10.1016/j.nimb.2015.02.033 0168-583X/Ó 2015 Elsevier B.V. All rights reserved.
them applicable for micro beam X-ray fluorescence, for scanning microscopy or as filters [3]. Our previous studies [4–7] were devoted to the characterization of the propagation of radiation hitting the walls inside a hollow channel, when the excited fluorescence radiation can be transported by MCP polycapillary structures. Underneath, we show and discuss X-ray fluorescence synchrotron radiation spectra and the angular distribution of the intensity collected at the exit of MCPs. In particular, we analyze the low energy inelastic scattering experiments in the region of the anomalous dispersion at the Si L-edge and at the O K-edge. 2. Experimental set-up The experimental layout shown in Fig. 1, describes the optical configuration available at the Polarimeter end-station of the UE52_SGM at the BESSY II synchrotron radiation facility. We used for the experiments 0.3 mm thick MCPs with a hexagonal shape in the transverse cross-section, made with a lead silicate (PbSiO3) composition, manufactured by the BASPIK [8]. Such compact optical devices contain regular holey channels with a diameter of 3.4 lm and with a pitch size of 4.2 lm. As shown in Fig. 1, the top surface of the MCP was illuminated by a monochromatic beam with a divergence <5 mrad. The radiation propagating inside the
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micro-channels was collected by a single photodiode placed on the other side of the polycapillary structure. Data have been collected at the Polarimeter with a beam size of 60 lm (hor./vert.) while the diaphragm of the photodiode’s window has a diameter of 0.2 mm. The distance between the sample and the window of the photodiode is 145 mm. Looking at the layout of Fig. 1, the angle corresponding to the ‘‘zero’’ position of the polarimeter has been identified, without the MCP, as the direction, for which the primary beam hits the photodiode. In the transmission geometry, the grazing angle h between the incident primary beam and MCP microchannel walls was set while rotating the device around the ‘‘h’’ axis (see Fig. 1). It was assumed that microchannel walls were oriented parallel to the normal of the MCP surface. Inserting the MCP along the radiation path, the ‘‘normal’’ direction to the MCP surface corresponds to the relative ‘‘zero’’ position of the measured angular scans. After setting the grazing angle h of the polarimeter, scanning the detector position the angular distributions of the radiation behind the MCP were collected. The angular distribution of the radiation, i.e., the intensity vs. angle at the exit of a MCP, in the total external reflection condition for different grazing angles of the incident beam has been investigated. Performing the angular scan of the photodiode position sets at the exit of the MCP (angles ‘‘/’’ of the photodiode), we can identify the positions where the maximum intensity of emitted radiation occurs. For any fixed value of the h-angle between the incident monochromatic radiation and MCP microchannel walls, the intensity distribution between two maxima / = ±h in the angular range h 6 / 6 h has been measured. Finally, the spectra for different h angles and for different positions of the photodiode: /1, /2, /3, . . ., /n, have been collected.
3. Results and discussion The angular distributions of the radiation intensity at the exit of a MCP sample, at different h-angles and different photodiode positions (/-angles) have been collected in the transmission mode. The multiple reflection radiation distributions and corresponding maxima in the spectra shown by dash lines in Fig. 1, are the main characteristics of the measured angular distributions. At the Si L-edge energy the critical angle hc is 8°. In Fig. 2 we compare three angular scans performed at different energies just below and above the energy of the absorption edge. The recorded distributions have shown that the spectra taken at the grazing angle h = 3° are almost symmetric with two intense specular maxima
Fig. 1. Layout of the transmission experiments for a MCP installed at the Polarimeter station at BESSY II.
Fig. 2. Angular resolved spectra measured at the grazing angle of h = 3° (see layout in Fig. 1) for different values of the incident radiation below and above the Si Ledge.
due to the reflection contributions of the primary radiation: A (/ = 3°) and A0 (/ = 3°). At the Polarimeter station we had the possibility to set the position of the photodiode independently of the two maxima. In Fig. 3 we compare energy spectra in the region of the Si L-edge collected at the grazing angle of h = 3° at the MCP exit for / = 3° and / = 3°. The observed fine structures of both spectra resemble the fine structure of the reflection spectrum of this lead silicate and of MCPs previously measured and published [3]. It should be underlined, that the fine structures of the spectra measured at the output of a MCP sample are basically similar to the characteristics of a simple reflection spectrum. The spectra shown in Fig. 4 are slightly more complex and asymmetric. They reveal two maxima at the positions A (/ = 5°) and A0 (/ = 5°) corresponding to defined photodiode positions and due to multiple reflections of the incident radiation at the grazing angle of h = 5°. These maxima have the same nature, i.e., multiple reflected radiation, of the peak observed at the grazing angle of h = 3° in Fig. 2. At the same time, Fig. 4 shows other structures observed in both spectra, such as those marked by positions B, C and D. Although being similar, they give different contributions observed in the spectra of Fig. 2.
Fig. 3. Reflection spectra vs. energy measured for two symmetric angular positions of the photodiode.
M.I. Mazuritskiy et al. / Nuclear Instruments and Methods in Physics Research B 355 (2015) 293–296
Fig. 4. Angular resolved spectra measured at the grazing angle of h = 5° (see layout in Fig. 1) for different values of the incident radiation below and above the Si Ledge.
Fig. 4 shows the peaks B, C and D measured at the energy of the incident radiation of 120 eV and 140 eV, actually greater than the Si L-edge (100 eV). They exhibit a much higher intensity than the same peaks present in the spectrum collected at the energy of 90 eV, slightly below the Si L-edge. As a consequence the B, C and D features probe the intensity of the excited fluorescence radiation propagating through the MCP microchannels. The fluorescence radiation observed in the spectra collected at the exit of MCPs at the grazing angle of h = 5° are shown by solid and dashed lines in Fig. 1. In fact, a comparison between the spectra (Figs 2 and 4) at h = 5° and h = 3° points out that in the latter spectrum only two structures corresponding to reflection radiation are present: the peaks A and A0 . In other words, the fluorescence radiation is not detectable at the exit of the MCP’s investigated for radiation incident at a grazing angle h less than hc/2. For better understanding the transmission process, fine structures of experimental spectra, as well as angular distributions of the radiation through the microchannels have been measured and analyzed in the energy range corresponding to the anomalous dispersion region of the O K-edge. Assuming that the total external reflection angle at the energy of the O K-edge (540 eV) is 3°, the grazing angle h between the primary incident radiation and the MCP microchannel walls has been set in the range between 2° and 3°. Figs. 5 and 6 present angular resolved spectra collected at the energies just below and above the O K-edge: 515 eV and 565 eV, respectively. The analysis of the angular scan structures at the O K-edge is shown in Figs. 5 and in 6. We applied the same procedure as for the Si L-edge. Actually, at small grazing angles (h = 2°), we mainly observe the radiation corresponding to multiple reflections of the primary radiation (similar maxima are observed in Fig. 5). At variance, the fluorescence radiation, i.e., the peaks B, C and D observed in Fig. 6 at the grazing angle h = 3°, for the angular positions of the photodiode in the h < / < h range has been collected. Especially, the fluorescence radiation is detected in a narrower angular range and the spectrum collected corresponds to the distribution of the radiation propagated through the micro-channels. As an example, at h = 3° and with the detector sets in the position corresponding to the B maximum in Fig. 6 (/ = 1.5°), we show in Fig. 7 the spectrum with its fine structures collected in the energy range of the O K-edge. It should be underlined here, that the spectrum in Fig. 7 is similar to the classical total fluorescence yield spectra published in
295
Fig. 5. Angular resolved spectra measured at the grazing angle of h = 2° (see layout in Fig. 1) for different incident radiation below and above the O K-edge.
Fig. 6. Angular resolved spectra measured at the grazing angle of h = 3° (see layout in Fig. 1) for different incident radiation below and above the O K-edge.
Fig. 7. Fluorescence energy spectrum around the O K-edge collected with the photodiode sets at the angle / = 1.5°.
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Refs. [9,10]. So, the spectroscopic nature of the B maximum confirms that the radiation observed at the exit of MCPs is fluorescence radiation excited by the primary beam. This observation is a clear experimental confirmation of the channeling phenomenon of the excited fluorescence radiation inside a media. Actually, these characteristic spectroscopic features could allow identifying optimal transport conditions for the excited fluorescence radiation inside microcapillary structures at the energy of the Si L-edge or at the O K-edge. This observation is an additional experimental evidence of the channeling phenomenon of the excited fluorescence radiation inside a media [11]. 4. Conclusion We have presented and discussed the angular distributions of the radiation in the energy range of the Si L- and O K-edges for the MCPs, with a microchannel diameter of 3 microns. The angular distributions of the radiation intensity at the exit of the MCPs show intensity maxima corresponding to fluorescence radiation propagated inside these structures. If we define h as the angle between the primary beam and the microchannel walls, for an energy of the primary radiation greater than the absorption edge, the fluorescence radiation can be detected at the exit of the MCPs only for grazing angles greater than half of the critical angle (h P hc/2) of the material composing MCP’s (at the Si L-edge h P 5° while h P 2° at the O K-edge). Moreover, fine structures in the XANES spectra of the radiation collected at the exit of MCPs carries out additional information on the nature of the radiation channeling inside the microchannels. Structured spectra clearly measured at the exit of the MCPs, correspond to both reflection and fluorescence radiation of the material. The results we presented, in particular the angular dependence, are extremely useful for the development of X-ray fluorescence spectrometry imaging [12]. This technique can be designed for fast collection of the chemical composition or to probe the elemental
distribution of a relatively large sample, avoiding the use of a time consuming scanning procedure. Acknowledgements We like to thanks A. Sokolov and F. Schäfers for their assistance and suggestions during experimental runs at BESSY. This work was partially supported by the Helmholtz Zentrum Berlin, BESSY II (Project no. 14100626), by the EU within the CALIPSO program and by Southern Federal University (Project no. 213.01-07-2014/ 08). One of us (SD) acknowledges the support by the Ministry of Education and Science of Russian Federation in the frames of Competitiveness Growth Program of NRNU MEPhI, Agreement 02.A03.21.0005. References [1] S.B. Dabagov, Physics Uspekhi 46 (10) (2003) 1053–1075. [2] Qi Zhang, Qi Zhang, Kun Zhao, Jie Li, Michael Chini, Yan Cheng, Wu Yi, Eric Cunningham, Zenghu Chang, Opt. Lett. 39 (2014) 3670–3673. [3] K. Tsuji, J. Injuk, R. Van Grieken (Eds.), X-Ray Spectrometry: Recent Technological Advances, Wiley, 2004. [4] M.I. Mazuritskiy, J. Synchrotron Rad. 19 (2012) 129–131, http://dx.doi.org/ 10.1107/S0909049511043263. [5] M.I. Mazuritskiy, S.B. Dabagov, K. Dziedzic-Kocurek, A. Marcelli, NIMB 309 (2013) 240–243, http://dx.doi.org/10.1016/j.nimb.2013.02.017. [6] M.I. Mazuritskiy, A.M. Lerer, A.A. Novakovich, R.V. Vedritskii, JETP Lett. 98 (2013) 150–154, http://dx.doi.org/10.1134/S0021364013160108. [7] M.I. Mazuritskiy, S.B. Dabagov, A. Marcelli, A. Lerer, A. Novakovich, K. DziedzicKocurek, J. Opt. Soc. Am. B 31 (2014) 1–6, http://dx.doi.org/10.1364/ JOSAB.31.002182. [8] Vladikavkaz Technological Center ‘‘BASPIK’’, Microchannel Plates http://www. baspik.com/eng/products/nauka/. [9] Z.Y. Wu, F. Jollet, F. Seifert, J. Phys.: Condens. Matter 10 (1998) 8083–8092. [10] B. Gilbert, B.H. Frazer, F. Naab, J. Fournelle, J.W. Valley, G. de Stasio, Am. Mineral. 88 (2003) 763–769. [11] S.B. Dabagov, A. Marcelli, Appl. Opt. 38 (1999) 7494–7497. [12] T. Yonehara, M. Yamaguchi, K. Tsuji, Spectrochim. Acta, Part B 65 (2010) 441– 444.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
X-ray radiation channeling in micro-channel plates: Spectroscopy with a synchrotron radiation beam M.I. Mazuritskiy a,⇑, S.B. Dabagov b,c,d, A. Marcelli b,e, K. Dziedzic-Kocurek f, A.M. Lerer a a
Physics Department, Southern Federal University, Rostov-on-Don, Russia INFN Laboratori Nazionali di Frascati, 00044 Frascati, Italy c RAS P.N. Lebedev Physical Institute, Leninsky pr. 53, 119991 Moscow, Russia d National Research Nuclear University MEPhI, Kashirskoe shosse 31, 115409 Moscow, Russia e RICMASS, Rome International Center for Materials Science Superstripes, via dei Sabelli 119A, 00185 Rome, Italy f M. Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland b
a r t i c l e
i n f o
Article history: Received 9 November 2014 Received in revised form 2 February 2015 Accepted 9 February 2015 Available online 5 March 2015 Keywords: X-ray capillary waveguides X-ray scattering X-ray fluorescence channeling X-ray spectroscopy X-ray angular distribution
a b s t r a c t We present here the angular distribution of the radiation propagated inside MultiChannel Plates with micro-channels of 3 lm diameter. The spectra collected at the exit of the channels present a complex distribution with contributions that can be assigned to the fluorescence radiation, originated from the excitation of the micro-channel walls. For radiation above the absorption edge, when the monochromatic energy in the region of the Si L-edge hits the micro-channel walls with a grazing angle h P 5°, or at the O K-edge when h P 2° a fluorescence radiation is detected. Additional information associated to the fine structures of the XANES spectra detected at the exit of MCPs are also presented and discussed. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction The propagation of X-rays through a capillary system is a complex phenomenon that depends on the optical layout, the capillary parameters, the radiation properties, etc., whose knowledge is still a matter of debate. Actually, because the technology based on the capillary optical elements may, in principle, deliver a high flux density within a sub-micrometer spot, its understanding is mandatory to develop novel optical systems. Such systems would be capable to increase the radiation density and eventually to shape X-ray beams without the use of the long optical focusing devices. Channeling based devices may indeed guide and shape an X-ray beam in order to control the intensity, the spot size, the divergence and the homogeneity [1]. At present, studies of X-ray transmission through the micro-capillary structures, aimed at the R&D of dedicated optics working in the ‘‘water window’’ spectral region are limited. Being large and effective low weight optics, the micro-channel plates (MCPs) have been already used in case of the low power instruments for different scientific applications and techniques development [2]. Their characteristics make them suitable for many other applications, for example, such as focusing of the excited radiation. Moreover, their broadband characteristics make ⇑ Corresponding author. http://dx.doi.org/10.1016/j.nimb.2015.02.033 0168-583X/Ó 2015 Elsevier B.V. All rights reserved.
them applicable for micro beam X-ray fluorescence, for scanning microscopy or as filters [3]. Our previous studies [4–7] were devoted to the characterization of the propagation of radiation hitting the walls inside a hollow channel, when the excited fluorescence radiation can be transported by MCP polycapillary structures. Underneath, we show and discuss X-ray fluorescence synchrotron radiation spectra and the angular distribution of the intensity collected at the exit of MCPs. In particular, we analyze the low energy inelastic scattering experiments in the region of the anomalous dispersion at the Si L-edge and at the O K-edge. 2. Experimental set-up The experimental layout shown in Fig. 1, describes the optical configuration available at the Polarimeter end-station of the UE52_SGM at the BESSY II synchrotron radiation facility. We used for the experiments 0.3 mm thick MCPs with a hexagonal shape in the transverse cross-section, made with a lead silicate (PbSiO3) composition, manufactured by the BASPIK [8]. Such compact optical devices contain regular holey channels with a diameter of 3.4 lm and with a pitch size of 4.2 lm. As shown in Fig. 1, the top surface of the MCP was illuminated by a monochromatic beam with a divergence <5 mrad. The radiation propagating inside the
294
M.I. Mazuritskiy et al. / Nuclear Instruments and Methods in Physics Research B 355 (2015) 293–296
micro-channels was collected by a single photodiode placed on the other side of the polycapillary structure. Data have been collected at the Polarimeter with a beam size of 60 lm (hor./vert.) while the diaphragm of the photodiode’s window has a diameter of 0.2 mm. The distance between the sample and the window of the photodiode is 145 mm. Looking at the layout of Fig. 1, the angle corresponding to the ‘‘zero’’ position of the polarimeter has been identified, without the MCP, as the direction, for which the primary beam hits the photodiode. In the transmission geometry, the grazing angle h between the incident primary beam and MCP microchannel walls was set while rotating the device around the ‘‘h’’ axis (see Fig. 1). It was assumed that microchannel walls were oriented parallel to the normal of the MCP surface. Inserting the MCP along the radiation path, the ‘‘normal’’ direction to the MCP surface corresponds to the relative ‘‘zero’’ position of the measured angular scans. After setting the grazing angle h of the polarimeter, scanning the detector position the angular distributions of the radiation behind the MCP were collected. The angular distribution of the radiation, i.e., the intensity vs. angle at the exit of a MCP, in the total external reflection condition for different grazing angles of the incident beam has been investigated. Performing the angular scan of the photodiode position sets at the exit of the MCP (angles ‘‘/’’ of the photodiode), we can identify the positions where the maximum intensity of emitted radiation occurs. For any fixed value of the h-angle between the incident monochromatic radiation and MCP microchannel walls, the intensity distribution between two maxima / = ±h in the angular range h 6 / 6 h has been measured. Finally, the spectra for different h angles and for different positions of the photodiode: /1, /2, /3, . . ., /n, have been collected.
3. Results and discussion The angular distributions of the radiation intensity at the exit of a MCP sample, at different h-angles and different photodiode positions (/-angles) have been collected in the transmission mode. The multiple reflection radiation distributions and corresponding maxima in the spectra shown by dash lines in Fig. 1, are the main characteristics of the measured angular distributions. At the Si L-edge energy the critical angle hc is 8°. In Fig. 2 we compare three angular scans performed at different energies just below and above the energy of the absorption edge. The recorded distributions have shown that the spectra taken at the grazing angle h = 3° are almost symmetric with two intense specular maxima
Fig. 1. Layout of the transmission experiments for a MCP installed at the Polarimeter station at BESSY II.
Fig. 2. Angular resolved spectra measured at the grazing angle of h = 3° (see layout in Fig. 1) for different values of the incident radiation below and above the Si Ledge.
due to the reflection contributions of the primary radiation: A (/ = 3°) and A0 (/ = 3°). At the Polarimeter station we had the possibility to set the position of the photodiode independently of the two maxima. In Fig. 3 we compare energy spectra in the region of the Si L-edge collected at the grazing angle of h = 3° at the MCP exit for / = 3° and / = 3°. The observed fine structures of both spectra resemble the fine structure of the reflection spectrum of this lead silicate and of MCPs previously measured and published [3]. It should be underlined, that the fine structures of the spectra measured at the output of a MCP sample are basically similar to the characteristics of a simple reflection spectrum. The spectra shown in Fig. 4 are slightly more complex and asymmetric. They reveal two maxima at the positions A (/ = 5°) and A0 (/ = 5°) corresponding to defined photodiode positions and due to multiple reflections of the incident radiation at the grazing angle of h = 5°. These maxima have the same nature, i.e., multiple reflected radiation, of the peak observed at the grazing angle of h = 3° in Fig. 2. At the same time, Fig. 4 shows other structures observed in both spectra, such as those marked by positions B, C and D. Although being similar, they give different contributions observed in the spectra of Fig. 2.
Fig. 3. Reflection spectra vs. energy measured for two symmetric angular positions of the photodiode.
M.I. Mazuritskiy et al. / Nuclear Instruments and Methods in Physics Research B 355 (2015) 293–296
Fig. 4. Angular resolved spectra measured at the grazing angle of h = 5° (see layout in Fig. 1) for different values of the incident radiation below and above the Si Ledge.
Fig. 4 shows the peaks B, C and D measured at the energy of the incident radiation of 120 eV and 140 eV, actually greater than the Si L-edge (100 eV). They exhibit a much higher intensity than the same peaks present in the spectrum collected at the energy of 90 eV, slightly below the Si L-edge. As a consequence the B, C and D features probe the intensity of the excited fluorescence radiation propagating through the MCP microchannels. The fluorescence radiation observed in the spectra collected at the exit of MCPs at the grazing angle of h = 5° are shown by solid and dashed lines in Fig. 1. In fact, a comparison between the spectra (Figs 2 and 4) at h = 5° and h = 3° points out that in the latter spectrum only two structures corresponding to reflection radiation are present: the peaks A and A0 . In other words, the fluorescence radiation is not detectable at the exit of the MCP’s investigated for radiation incident at a grazing angle h less than hc/2. For better understanding the transmission process, fine structures of experimental spectra, as well as angular distributions of the radiation through the microchannels have been measured and analyzed in the energy range corresponding to the anomalous dispersion region of the O K-edge. Assuming that the total external reflection angle at the energy of the O K-edge (540 eV) is 3°, the grazing angle h between the primary incident radiation and the MCP microchannel walls has been set in the range between 2° and 3°. Figs. 5 and 6 present angular resolved spectra collected at the energies just below and above the O K-edge: 515 eV and 565 eV, respectively. The analysis of the angular scan structures at the O K-edge is shown in Figs. 5 and in 6. We applied the same procedure as for the Si L-edge. Actually, at small grazing angles (h = 2°), we mainly observe the radiation corresponding to multiple reflections of the primary radiation (similar maxima are observed in Fig. 5). At variance, the fluorescence radiation, i.e., the peaks B, C and D observed in Fig. 6 at the grazing angle h = 3°, for the angular positions of the photodiode in the h < / < h range has been collected. Especially, the fluorescence radiation is detected in a narrower angular range and the spectrum collected corresponds to the distribution of the radiation propagated through the micro-channels. As an example, at h = 3° and with the detector sets in the position corresponding to the B maximum in Fig. 6 (/ = 1.5°), we show in Fig. 7 the spectrum with its fine structures collected in the energy range of the O K-edge. It should be underlined here, that the spectrum in Fig. 7 is similar to the classical total fluorescence yield spectra published in
295
Fig. 5. Angular resolved spectra measured at the grazing angle of h = 2° (see layout in Fig. 1) for different incident radiation below and above the O K-edge.
Fig. 6. Angular resolved spectra measured at the grazing angle of h = 3° (see layout in Fig. 1) for different incident radiation below and above the O K-edge.
Fig. 7. Fluorescence energy spectrum around the O K-edge collected with the photodiode sets at the angle / = 1.5°.
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M.I. Mazuritskiy et al. / Nuclear Instruments and Methods in Physics Research B 355 (2015) 293–296
Refs. [9,10]. So, the spectroscopic nature of the B maximum confirms that the radiation observed at the exit of MCPs is fluorescence radiation excited by the primary beam. This observation is a clear experimental confirmation of the channeling phenomenon of the excited fluorescence radiation inside a media. Actually, these characteristic spectroscopic features could allow identifying optimal transport conditions for the excited fluorescence radiation inside microcapillary structures at the energy of the Si L-edge or at the O K-edge. This observation is an additional experimental evidence of the channeling phenomenon of the excited fluorescence radiation inside a media [11]. 4. Conclusion We have presented and discussed the angular distributions of the radiation in the energy range of the Si L- and O K-edges for the MCPs, with a microchannel diameter of 3 microns. The angular distributions of the radiation intensity at the exit of the MCPs show intensity maxima corresponding to fluorescence radiation propagated inside these structures. If we define h as the angle between the primary beam and the microchannel walls, for an energy of the primary radiation greater than the absorption edge, the fluorescence radiation can be detected at the exit of the MCPs only for grazing angles greater than half of the critical angle (h P hc/2) of the material composing MCP’s (at the Si L-edge h P 5° while h P 2° at the O K-edge). Moreover, fine structures in the XANES spectra of the radiation collected at the exit of MCPs carries out additional information on the nature of the radiation channeling inside the microchannels. Structured spectra clearly measured at the exit of the MCPs, correspond to both reflection and fluorescence radiation of the material. The results we presented, in particular the angular dependence, are extremely useful for the development of X-ray fluorescence spectrometry imaging [12]. This technique can be designed for fast collection of the chemical composition or to probe the elemental
distribution of a relatively large sample, avoiding the use of a time consuming scanning procedure. Acknowledgements We like to thanks A. Sokolov and F. Schäfers for their assistance and suggestions during experimental runs at BESSY. This work was partially supported by the Helmholtz Zentrum Berlin, BESSY II (Project no. 14100626), by the EU within the CALIPSO program and by Southern Federal University (Project no. 213.01-07-2014/ 08). One of us (SD) acknowledges the support by the Ministry of Education and Science of Russian Federation in the frames of Competitiveness Growth Program of NRNU MEPhI, Agreement 02.A03.21.0005. References [1] S.B. Dabagov, Physics Uspekhi 46 (10) (2003) 1053–1075. [2] Qi Zhang, Qi Zhang, Kun Zhao, Jie Li, Michael Chini, Yan Cheng, Wu Yi, Eric Cunningham, Zenghu Chang, Opt. Lett. 39 (2014) 3670–3673. [3] K. Tsuji, J. Injuk, R. Van Grieken (Eds.), X-Ray Spectrometry: Recent Technological Advances, Wiley, 2004. [4] M.I. Mazuritskiy, J. Synchrotron Rad. 19 (2012) 129–131, http://dx.doi.org/ 10.1107/S0909049511043263. [5] M.I. Mazuritskiy, S.B. Dabagov, K. Dziedzic-Kocurek, A. Marcelli, NIMB 309 (2013) 240–243, http://dx.doi.org/10.1016/j.nimb.2013.02.017. [6] M.I. Mazuritskiy, A.M. Lerer, A.A. Novakovich, R.V. Vedritskii, JETP Lett. 98 (2013) 150–154, http://dx.doi.org/10.1134/S0021364013160108. [7] M.I. Mazuritskiy, S.B. Dabagov, A. Marcelli, A. Lerer, A. Novakovich, K. DziedzicKocurek, J. Opt. Soc. Am. B 31 (2014) 1–6, http://dx.doi.org/10.1364/ JOSAB.31.002182. [8] Vladikavkaz Technological Center ‘‘BASPIK’’, Microchannel Plates http://www. baspik.com/eng/products/nauka/. [9] Z.Y. Wu, F. Jollet, F. Seifert, J. Phys.: Condens. Matter 10 (1998) 8083–8092. [10] B. Gilbert, B.H. Frazer, F. Naab, J. Fournelle, J.W. Valley, G. de Stasio, Am. Mineral. 88 (2003) 763–769. [11] S.B. Dabagov, A. Marcelli, Appl. Opt. 38 (1999) 7494–7497. [12] T. Yonehara, M. Yamaguchi, K. Tsuji, Spectrochim. Acta, Part B 65 (2010) 441– 444.