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Nuclear Instruments and Methods in Physics Research A 543 (2005) 322–325 www.elsevier.com/locate/nima
Planar parabolic X-ray refractive lens made of glassy carbon A.N. Artemieva,, A. Snigirevb, V. Kohna, I. Snigirevab, N. Artemieva,c, M. Grigorievd, S. Peredkove, L. Glikinf, M. Levtonovf, V. Kvardakova, A. Zabelina, A. Maevskiya a
Russian Research Center ‘‘Kurchatov Institute’’, Kurchatov Sq. 1, 123182 Moscow, Russian Federation b European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France c Laboratoire d’Optique Appliquee, ENSTA, Ecole Polytechnique, F-91761 Palaiseau, France d Institute of Microelectronics Technology RAS, 142432, Chernogolovka, Russian Federation e MAXLAB, Lund University, Box-118, 22100 Lund, Sweden f Company ‘‘Mechatron’’, Zelenograd, Russian Federation Available online 2 March 2005
Abstract Experimental results of synchrotron radiation focusing by parabolic planar compound refractive lenses, made of glassy carbon, are presented. The lenses with the curvature radius of 5 and 200 mm, and with the geometric aperture of 40 and 900 mm were developed. The number of bi-concave elements in the compound lenses was from 4 to 200. The experiments were performed at the ESRF at the bending magnet beamline BM-5. The minimum size of the focus was observed as 1.4 mm. r 2005 Elsevier B.V. All rights reserved. PACS: 07.85 Keywords: Planar parabolic X-ray compound refractive lens
1. Introduction The refractive X-ray lenses become an important tool for synchrotron radiation beams of third generation sources. For these beams the lens aperture of several fractions of a millimeter and Corresponding author. Tel.:+7 095 1967538;
fax: +7 095 1967538. E-mail address:
[email protected] (A.N. Artemiev).
the focal length of the order of a meter are admissible. It was shown [1–3] the intensity gain as the ratio of sizes of the effective aperture and the focus for the parabolic lens, is equal approximately to the parameter d=b: The absorption index b is related to the linear absorption coefficient as m ¼ 4pb=l; where l is the radiation wavelength. Therefore, the most efficient lenses are manufactured from materials with low atomic numbers Z or, more exactly, with low values of the ratio b=d:
0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.01.249
ARTICLE IN PRESS A.N. Artemiev et al. / Nuclear Instruments and Methods in Physics Research A 543 (2005) 322–325
The first high-quality parabolic lenses with the 2D round aperture were manufactured from aluminum [4] because of its high technological properties. These lenses allow one to focus the 2D synchrotron radiation beam, or more precisely, to obtain a high-quality two-dimensional image of the source. In addition, the lenses can operate in the mode of an X-ray microscope [5], and record enlarged images of the inner structure of microobjects. For the aluminum lens at E ¼ 12 keV; the value of the parameter g ¼ b=d is equal to 0.0084. Various plastics (see, for example, Ref. [6]) were also applied for lens fabrication. However, the polymers do not have high radiation stability. Recently, similar lenses were manufactured from beryllium [7] and lithium [8] possessing extremely low values of the parameter g. However, there exist some problems with technology conditioned by Be toxic properties. The Li is a dangerous material and one needs special handling.
Fig. 1. Mask projection scheme of the lens development. Here, 1 is a spherical mirror, 2 is a mask, 3 is a laser, 4 is a flat mirror, 5 is a projection lens, and 6 is a glassy carbon block.
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Carbon in various forms is very attractive material for the lens development as X-ray optical element. In this paper, we present a new material, glassy carbon, and a new technique of lens preparation using laser beam. The density of commercial glassy carbon is 1.5 g/ccm.
2. Lens development The planar compound X-ray lenses were developed by means of the laser evaporation. Two methods were applied. The first method consists of direct evaporation of the glassy carbon on the surface of a sample by means of laser beam heating. Diameter of the laser beam was about 30 mm. The translation step along two coordinates on the glassy carbon surface was about 5 mm. Such a method is admissible for a rather large curvature radius of about some fractions of a millimeter. It allows one to develop a rather deep relief of order of one millimeter. The setup of the second method is shown schematically in Fig. 1. The copper vapor laser developed by the company ‘‘Mechatron’’ was used. The mask was imaged with a demagnification factor up to 200 on the polished surface of the glassy carbon block, which was used as one of the resonator’s mirror. The mask was made of a thin sheet of metal. The time of production for one cavity (i.e. one elementary X-ray lens) depends on the focal length of projection lens used, and in all cases was not more than a few seconds. The parameters of all the lenses, developed in this work, are shown in Table 1. Fig. 2 presents the scanning electron microscopy (SEM) micrograph of the lens, named CRL-4.
Table 1 Parameters of the lenses developed Name of lens
Number of biconcave elements, N
Curvature radius, R (mm)
Thin part of the bi-concave element, d (mm)
Relief deep, h (mm)
Geometric Development aperture, A (mm) method
CRL-4 CRL-200
4 200
200 5
p100 p20
E1000 E50
900 40
Direct Mask
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A.N. Artemiev et al. / Nuclear Instruments and Methods in Physics Research A 543 (2005) 322–325
3. Experiment with lenses The experiment was done at the bending magnet beamline BM-5 at the ESRF, Grenoble, France. The scheme of the experimental setup is shown in Fig. 3. The transverse sizes of the source were 350 mm horizontally and 80 mm vertically. The source-to-lens distance was rs ¼ 40 m: The monochromator consists of two silicon single crystals (1 1 1). First, we applied the high-resolution position-sensitive detector FReLoN camera designed at the ESRF [9]. One pixel of this camera has a linear size 0.75 mm. FReLon camera was placed at the distance of rpc ¼ 1 m for experiments with CRL-4 lenses to record the phase contrast images [10] of the lens itself. In some experiments, the first lens CRL-4 was followed by the similar second lens installed in the position of the horizontal focusing of the beam. The total effect of both lenses give rise to the formation of a point like focus.
Second, one more position sensitive detector, a CCD-matrix, was installed at the distance ris downstream the lenses to record the intensity distribution in their focus plane. The distance was equal to the source imaging distance ris ¼ 19 m: Fig. 4 shows the intensity distribution at the energy of the best focusing obtained by means of CCD detector. In both fragments the exposure time was 2 s. The calculated integral intensity of
Fig. 4. (A) Linear focus made by one lens CRL-4, (B) point focus made by two lenses CRL-4 in crossed geometry.
Fig. 2. Micrograph of a fragment of the parabolic planar compound lens CRL-4.
Fig. 3. The scheme of the experimental setup.
Fig. 5. Knife scan of the focus made by the lens CRL-200. The curvature radius is 5 mm, the number of bi-concave elements is 200, the energy E ¼ 25 keV: The dots present measured intensity values for various knife position. The solid line is the corresponding derivative. The FWHM of the derivative curve is 1.4 mm. The inset is the image of the linear focus made by FReLon camera.
ARTICLE IN PRESS A.N. Artemiev et al. / Nuclear Instruments and Methods in Physics Research A 543 (2005) 322–325
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Table 2 Results of the lenses test Lenses tested
E (keV)
Focus distance (cm), calculated
Focus size (mm), calculated
Focus size (mm), measured
Gain, measured
CRL-4 Two CRL-4 in crossed geometry CRL-200
12.2 12.2
1194 1194
34 34163
73 73292
4.8 6.4
25
2.8
0.05
1.4
3.3
fragment B was smaller by 25% compared to the integral intensity of fragment A, which is explained mainly by absorption in the second lens. The most interesting result, obtained with the compound planar parabolic lens CRL-200, is shown in Fig. 5. Here, the inset shows the image of linear focus measured by FReLon camera placed at the distance of the best focusing (2.8 cm at E ¼ 25 keV). The width of the focus is close to the resolution limit for the FReLon camera. To have accurate value for the focus width we have made the knife scan. The procedure consists of a registration of the integral intensity at the various positions of some opaque screen (knife) across the focus. The derivative of this dependence gives us the focus profile. The gauss-fit of the solid line allows one to estimate the size of the focus as 1.4 mm.
form. Nevertheless the lenses can be used in applications. The first possible application of developed lenses can be in micro-fluorescence and micro-EXAFS measurements. Secondly, the application of the glassy carbon lenses follows from the good thermal and radiation stability of glassy carbon. Such lenses can be used as a first element of an optical setup for a preliminary beam collimation in front of a monochromator.
Acknowledgements The authors would like to thank V.M. Frolov and V.Yu. Kireev from RRC KI, as well as L.G. Saprikin from firm ‘‘Laser equipment’’ for provision of CRL-4 lens. The work was supported by RFBR Grant no. 03-02-16971.
4. Discussion References Table 2 presents the results for all tested CRL prototypes. The minimum linear focus size of 1.4 mm was achieved with CRL-200 prototype. However, this value is larger than that predicted by the theory as the source size projection of 0.05 mm in the case of the perfect detector. We assume that causes for the focus broadening may be the small-angle scattering from heterogeneities of the glassy carbon density as well as the deviation of surface shape from the parabolic
[1] [2] [3] [4] [5] [6] [7] [8] [9]
A. Snigirev, et al., Nature 384 (1996) 49. V.G. Kohn, JETP Lett. 76 (2002) 701. V.G. Kohn, JETP 97 (2003) 204. B. Lengeler, et al., Appl. Phys. Lett. 74 (1999) 3924. C.G. Schroer, et al., Rev. Sci. Instr. 73 (2002) 1640. J.T. Cremer, et al., Rev. Sci. Instr. 70 (1999) 3545. C.G. Schroer, et al., Proc. SPIE 4783 (2002) 10. J. Cremer, et al., Rev. Sci. Instr. 74 (2003) 2262. Internet resource, http://www.esrf.fr/computing/bliss/ guides/detection/ccd/frelon [10] A. Snigirev, et al., Rev. Sci. Instr. 66 (1995) 5486.
