[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

This result confirms our assumption that in our

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2 keV). This result confirms our assumption that in our pinhole scan the edge effect influences mainly the measured value of the focal spot size.
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X-Ray Optics 107 0.02 0.00 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 20 40 60 80 100 X (mm) Y (mm) Intensity Fig. 3.11. Two-dimensional intensity distribution in the focal plane of the “minilens” Therefore, the actual size of the focal spot in the energy region above 29 keV is not larger than 19 µ m and the spatial resolution is not deteriorated. Figure 3.11 shows the intensity distribution in the focal spot of the “minilens” under consideration in the energy interval 15–20 keV. The mea- surement was performed by a two-dimensional scan with a 5- µ m pinhole. The focal spot is relative symmetric without any distortions and artefacts. Manufacturing Capillary Optics There are many different methods of manufacturing glass capillary optics. The standard technology uses large pulling machines with a furnace for heating glass and two drives (upper and lower) for pulling (see Fig. 3.12). If the velocity of the lower drive is much larger than the velocity of the upper drive, capillaries with small channel diameters can be obtained from glass tubes with large diameters. This is also a standard method of manufac- turing polycapillaries from a bundle of monocapillaries. Applying the method once more to a bundle of polycapillaries, it is possible to reduce further the channel diameters and to produce in this way polycapillaries with very small channels. Figure 3.13 presents a typical polycapillary structure with channel diameters of ca. 2 µ m. The image was obtained with a scanning electronic microscope. At present channel diameters of ca. 600 nm are achieved. The pulling method also allows producing tapered monocapillaries and polycapillaries (including X-ray lenses), if the velocities of the drives do not
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108 V. Arkadiev and A. Bjeoumikhov Polycapillary V 1 V 2 Upper drive lower drive Furnace Pulling ( V 2 > V 1 ) Fig. 3.12. Scheme of manufacturing capillary optics by pulling Fig. 3.13. Cross-section of a polycapillary structure remain constant but vary according to a given law. Usually the law of velocity variation has to be found empirically for obtaining the required shape of the glass array. Two main problems here are the shape accuracy and the repro- ducibility of the shape in a series of subsequent pullings. These problems can be avoided by another method [81], which is presented schematically in Fig. 3.14. A cylindrical monocapillary or polycapillary with closed (fused) ends is placed in a specially prepared form. While heating in an oven, the glass becomes soft and the air pressure inside the channels increases. As a result,
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X-Ray Optics 109 Form Polycapillary Heating and expanding Fig. 3.14. Scheme of manufacturing capillary optics by expanding Air-bubble Cutting Heating and pulling Fig. 3.15. Scheme of manufacturing elliptical capillaries the glass array expands and accepts the fixed external form. The method is suitable for manufacturing tapered capillary arrays (X-ray lenses) or tapered monocapillaries with high accuracy and reproducibility of the shape.
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