Polycapillary optical unit

Abstract

The invention relates to a polycapillary optical unit, in particular for X-ray radiation, consisting of a bundle of capillaries (32), with the capillaries (32) each having a length which is a multiple of a diameter of the capillary (32), having an entry side (34) for a radiation to be coupled in from a radiation source, having an exit side (36) which is opposite the entry side (34), from where the input-coupled radiation arrives at the exit side (36) by way of total-internal reflection off the respective inner wall, and which is where said input-coupled radiation exits, wherein the capillaries (32) are curved toward the exit side (36) such that the exiting radiation is focused on a focus (37) at a focal length (f2), wherein the at least one capillary (32) has a capillary portion (38) oriented toward the exit side (36), the inner wall (31) of the at least one capillary (32) having a surface (33) that prevents total-internal reflection at least in sections along said capillary portion.

Description

[0001] Polycapillary optics

[0002] The invention relates to a polycapillary optic, in particular for X-ray radiation.

[0003] A polycapillary optic is known from DE 101 12 928 CI. This polycapillary optic consists of a bundle of capillaries used to shape and focus X-rays. Such a polycapillary optic is also referred to as a polycapillary lens. It comprises an entrance side, which is oriented for coupling radiation to an X-ray source. Opposite this, the polycapillary optic includes an exit side, from which the coupled radiation emerges. The radiation is guided through each capillary by total internal reflection at the inner wall. The capillaries are curved towards the exit side of the polycapillary optic, so that the radiation emerging from each capillary is focused at a focal point with a predetermined focal length.

[0004] From DE 199 54 520 A1, a device for guiding X-rays from a radiation source to a measuring object is known. This device comprises two mutually aligned reflective surfaces, between which a slit is formed.

[0005] From EP 0 723 272 Bl, a method for guiding neutral and / or charged particles is known. This device consists of an optical system of successive media of different densities, which form beam transfer channels, wherein the device has a medium-to-medium interface for multiple reflections of the particles. Additionally, a rough layer is arranged on the medium-to-medium interface.

[0006] From DE 10 2022 105 838 B3, an X-ray fluorescence analysis device is known in which a polycapillary optic is used. This polycapillary optic is held by an adjustment device, which allows the polycapillary optic to be aligned with the X-ray source. This ensures

[0007] MM 60106P0.docx Creation date: 10.07.2024

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[0009] Page 2 of 12 allows the polycapillary optics to be adjusted in case of any drift of the X-ray radiation towards the beam axis, in order to focus a high intensity of the X-ray radiation onto a measuring point on the surface of a measuring object.

[0010] Due to the targeted deformation of the capillaries, which are bundled together, polycapillary optics exhibit defined properties that determine the focal length and focal point size. With existing polycapillary optics, a focal point size of 10 pm or 20 pm can be achieved with a sufficiently large working distance between the exit end of the polycapillary optic and the object being measured, using an X-ray energy spectrum of 1 to 50 keV. This allows for collision-free positioning of the polycapillary optic relative to the object being measured, even when using autofocus in the X-ray fluorescence analyzer.

[0011] Increasingly, a higher resolution is required for the measurement spot on the object being measured, meaning that the size of the focal spot of the polycapillary optics must be reduced to, for example, 5 pm. However, this would result in the working distance between the exit side of the polycapillary optics and the object being equal to or less than 1.5 mm. This increases the risk of the polycapillary optics colliding with the object under investigation.

[0012] The invention is based on the objective of proposing a polycapillary optic in which a relatively large working distance between the exit side of the polycapillary optic and the object being measured is enabled with a small focal spot.

[0013] This problem is solved by a polycapillary optic consisting of a bundle of capillaries, wherein at least one capillary comprises a capillary section oriented towards the exit side, along which a surface of the inner wall of the respective capillary has a surface that prevents total internal reflection, at least partially.

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[0015] Page 3 of 12. Within this capillary section, the surface of the inner wall differs, at least partially, from the reflective area of ​​the capillary extending from the entrance of the polycapillary optics to the capillary section, where the inner wall of the capillary has a smooth surface for total internal reflection of the radiation. The capillary section within the capillaries reduces or prevents total internal reflection, allowing this section to act as a quasi-passive collimator. This reduces the divergence of the radiation exiting each capillary. Consequently, the radiation exiting the polycapillary optics is focused into a smaller focal spot at the same focal length. This allows the working distance between the exit of the polycapillary optics and the surface of the object being measured to be increased.

[0016] In particular, each capillary has the capillary section along which the surface of the inner wall of the respective capillary has a surface that prevents total reflection, at least in sections.

[0017] In capillary optics, it is preferably provided that the surface preventing total internal reflection extends continuously along the capillary section. This has the advantage that the divergence of the emerging radiation can be reduced uniformly. This results in a smaller focal spot. The reduction of the focal spot size can be achieved across the entire energy range of X-rays used in X-ray analysis.

[0018] Preferably, the surface of the inner wall of the capillary is roughened at least partially along the capillary section. This prevents total reflection. In particular, it is preferred that the surface of the inner wall of the capillary is roughened along the entire length of the capillary section.

[0019] Advantageously, the surface of the inner wall within the capillary section is provided to have a roughness of Ra greater than 5 nm (nanometers), preferably greater than 50 nm. Below the value Ra

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[0021] On page 4 of 12, the mean roughness is understood as the average roughness of recorded absolute values ​​of the surface roughness depth within a predetermined measuring distance.

[0022] The capillary section preferably extends from the exit side towards the inlet side of the polycapillary optic. Thus, the capillary section preferably borders directly on the exit side. This is particularly advantageous for achieving a greater working distance.

[0023] The length of the capillary segment is preferably less than 20% of the total length of the capillary between its inlet and outlet. This allows the X-rays to be guided through the polycapillary optics with minimal losses within the reflective area, while still enabling a relatively large working distance to be achieved through the capillary segment.

[0024] Furthermore, it is preferably provided that the working distance can be increased with increasing length of the capillary section. In a remaining reflective area of ​​the capillary optics, i.e., the total length minus the capillary section, the inner wall of the capillary has a surface suitable for total internal reflection of the radiation.

[0025] Preferably, the length of the capillary segment is determined by the diameter of the capillary. The larger the diameter of the capillary, the longer the capillary segment should be. This compensates for, and in particular reduces, the increasing divergence that occurs with a larger capillary diameter.

[0026] The capillary bundle for polycapillary optics is typically made of glass.

[0027] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The features that can be derived from the description and the drawings can

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[0029] Page 5 of 12. The invention can be applied individually or in any combination. It shows:

[0030] Figure 1 shows a schematic sectional view of an X-ray fluorescence analyzer.

[0031] Figure 2 shows a schematic sectional view of a polycapillary optic.

[0032] Figure 3 shows a schematically enlarged view of a capillary according to the prior art.

[0033] Figure 4 shows a schematic view of a polycapillary optic with capillaries according to Figure 3.

[0034] Figure 5 shows a schematically enlarged sectional view of a capillary according to the invention, and

[0035] Figure 6 shows a schematic view of a polycapillary optic with capillaries according to Figure 5.

[0036] Figure 1 shows a simplified schematic representation of an X-ray fluorescence analyzer 11. This X-ray fluorescence analyzer 11 comprises an X-ray source 12, which is, for example, configured as an X-ray tube 14. This X-ray tube 14 includes a heated cathode 16, from which electrons are emitted and accelerated against an anode 17 by an applied accelerating voltage UB. There, the electrodes are decelerated, generating X-ray radiation 18. The wavelength range of the X-ray radiation 18 depends on the accelerating voltage UB, which is typically in the range of 10 kV, but can also be, for example, 50 kV. Tungsten or molybdenum, for example, can be used as the anode material.

[0037] The X-ray radiation 18 is focused by a polycapillary optic 19 onto a measurement object 21. The measurement object 21 can, for example, have a coating 22 or a layered system. In a measurement-

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[0039] Page 6 of 12. At spot 24 on or near the object 21, where the X-ray radiation 18 strikes the object 21, X-ray fluorescence radiation 26 is generated, which is detected by a detector 27, for example, a semiconductor detector. By evaluating a detected energy spectrum, for example, the material composition of the coating 22 or the object 21 and / or the layer thickness of at least one coating 22 can be determined.

[0040] Additionally, the X-ray fluorescence analyzer 11 can include an optical device 29. This optical device 29 can be used to monitor and position the object 21 relative to the measurement position. This can also involve video monitoring. An adjustment device 30 is provided for arranging and mounting the polycapillary optics 19 in the X-ray fluorescence analyzer 11. This adjustment device 30 can be detachably attached to another component 28 of the X-ray fluorescence analyzer 11. In the exemplary embodiment, the component 28 can be a so-called shutter. The polycapillary optics 19 are aligned with the beam axis of the X-ray radiation 18. Preferably, the beam axis of the X-ray radiation 18 lies along a Z-axis. The adjustment device 30 allows the polycapillary optics 19 to be moved in a plane perpendicular to the beam axis of the X-ray radiation 18, i.e., the Z-axis.In particular, the adjustment device 30 enables an adjustment in an XY plane, so that the beam axis of the polycapillary optics 19 can be aligned to the beam axis of the X-ray radiation 18, in particular that they lie within each other.

[0041] Figure 2 shows a schematic sectional view of the polycapillary optics 19. These polycapillary optics 19 can be used in the previously described X-ray fluorescence analyzer 11. These polycapillary optics 19 can also be used for other applications in X-ray analysis.

[0042] This polycapillary optic 19 comprises a bundle of capillaries 32. The capillaries 32 are made of glass, specifically borosilicate glass. The polycapillary optic 19 includes an entrance face 34, which is oriented towards the X-ray source 12. The entrance face 34 has a defined diameter. Due to the curved orientation of the capillary 32 towards the X-ray source 12, the X-ray source 32 is oriented towards the X-ray source 12.

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[0045] A focal length fl is formed at the entrance side 34. The X-ray source 12 is positioned at the focal point of the focal length fl, so that optimal coupling of the X-ray radiation 18 into the polycapillary optics 19 is enabled according to the divergence of the X-ray radiation.

[0046] Opposite the entrance side 34, the polycapillary optics 19 has an exit side 36. This exit side 36 has a diameter that is, for example, larger than that of the entrance side 34. In the region of the exit side 36, the capillaries 32 are also curved. This creates a focal spot 37 at a distance from the exit side 36 determined by the focal length f2. The size of the focal spot 37 is determined by the divergence of the radiation exiting the individual capillaries 32 and the focal length f2, as well as the energy of the X-ray radiation 18. The focal length f2 defines the working distance between the exit side 36 of the polycapillary optics 19 and the surface of the object being measured 21.

[0047] Figure 3 shows a schematically enlarged representation of a capillary 32 of a polycapillary optic 19 known from the prior art, as shown in Figure 4. The capillary 32 comprises an inner wall 31 with a smooth surface, so that the coupled X-ray radiation 18 is guided through the capillary 32 by total internal reflection and exits at the end face. This results in a focal spot 37, for example, with a size of xl. By focusing the capillary 32 according to Figure 3 into the polycapillary optic 19 according to Figure 4, a focal spot 37 with a size of x2 is achieved at a focal length f2. The size x2 is smaller than the size xl. The size x2 corresponds, for example, to 10 pm or 20 pm. This size also depends on the energy of the X-ray radiation.

[0048] Figure 5 shows a schematic sectional view of a capillary 32 according to the invention, which is provided in a polycapillary optic 19 according to Figure 6. This capillary 32 has a capillary section 38 oriented towards the exit side 36. Along this capillary section 38, a surface 33 of the inner wall 31 of the capillary 32 is modified such that total reflection of the X-ray radiation 18 is prevented. The capillary 32 thus comprises from the

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[0051] From the entrance side 34 to the capillary section 38, there is a reflective region 39 in which the capillary 32 has a smooth surface, as described and illustrated, for example, in Figure 3. In the region of the capillary section 38, total internal reflection of the X-rays 18 in the capillary 32 is prevented. This causes this region of the capillary section 38 to act like a collimator. This makes it possible for the coupled X-rays 18, which are coupled into the capillary 32 according to Figure 5, for example, with the same energy as in the capillary 32 according to Figure 3, to produce a smaller focal spot 37 with a size of x3 compared to a size of xl, at the same focal length.When the individual X-ray beams 18 are superimposed within the respective capillary 32 in the polycapillary optics 19 according to Figure 6, a greater distance, i.e., a greater focal length, is then possible with a smaller focal spot 37 of size x4 compared to the prior art embodiment according to Figure 4. For size x4, the diameter of the focal spot 37 can, for example, be 5 pm.

[0052] In the capillary section 38 of the polycapillary optic 19 according to Figures 5 and 6, the surface 33 of the inner wall 31 of the capillary 32 is roughened. In other words, the inner wall of the capillary 32 in the capillary section 38 is treated or damaged so that total reflection of the coupled X-ray radiation 18 is not possible in or along the capillary section 38. The roughened surface 33 of the inner wall 31 in the capillary 32 advantageously extends completely over the entire length of the capillary section 38. Likewise, the roughened surface of the inner wall preferably extends completely within the capillary 32.

[0053] The capillary section 38 terminates at the exit side 36 of the polycapillary optic 19. The length of the capillary section 38 extends from the exit side 36 towards the inlet side 34 of the polycapillary optic 19. The capillary section 38 has, for example, a length of at least 1 mm. For example, with a focal length f2 of 3 mm for the polycapillary 19, the capillary section 38 can have a length of 1 mm or more, for example, up to 20 mm. Preferably, the roughened surface 33 of the inner wall 31 of the capillary

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[0055] Page 9 of 12

[0056] 32 comprises a mean roughness of Ra greater than 5 nm (nanometers). In particular, a roughness Ra in the range of 50 nm to 100 nm can be provided. Through this capillary section 38, with the same focal length of the polycapillary 19, the size of the focal spot can be reduced by a factor of 1.5 to 3.5, in particular by a factor of 2 to 2.5.

[0057] This capillary section 38, with its surface roughness on the inner wall of the capillary 32, allows for an increased focal length and a smaller focal spot 37. For example, the focal spot 37 can be reduced to a size of 5 pm.

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Claims

MM 60106 Page 10 of 12 Claims 1. Polycapillary optics, in particular for X-rays, comprising a bundle of capillaries (32), wherein the capillaries (32) have a length that is a multiple of the diameter of the capillary (32), with an inlet side (34) for coupled radiation from a radiation source, with an outlet side (36) opposite the inlet side (34) from which the coupled radiation passes to the outlet side (36) and exits by total internal reflection at the respective inner wall, wherein the capillaries (32) are curved towards the outlet side (36) so that the exiting radiation is focused with a focal length (f2) on a focal spot (37), characterized in that the at least one capillary (32) has a capillary section (38) oriented towards the outlet side (36),along which the inner wall (31) of the at least one capillary (32) has a surface (33) that prevents total reflection at least in sections.

2. Polycapillary optics according to claim 1, characterized in that in all capillaries (32) the capillary section (38) is formed along which the inner wall (31) of the respective capillary (32) has the surface (33) which prevents total reflection at least partially.

3. Polycapillary optics according to claim 1 or 2, characterized in that the surface (33) preventing total reflection extends continuously along the capillary section (38). MM 60106P0.docx MM 60106 Page 11 of 12 4. Polycapillary optics according to one of the preceding claims, characterized in that the surface (33) of the inner wall (31) of the capillary (32) is at least partially roughened along the capillary section (38).

5. Polycapillary optics according to claim 4, characterized in that the surface (33) of the inner wall (31) of the capillary (32) is roughened completely along the length of the capillary section (38) and completely.

6. Polycapillary optics according to claim 4 or 5, characterized in that the inner wall (31) of the capillary (32) in the capillary section (38) has a roughness Ra of greater than 5 nm, preferably greater than 50 nm.

7. Polycapillary optics according to one of the preceding claims, characterized in that the capillary section (38) extends from the exit side (36) towards the entry side (34).

8. Polycapillary optics according to one of the preceding claims, characterized in that the size of the focal spot (37) decreases with increasing length of the capillary section (38).

9. Polycapillary optics according to one of the preceding claims, characterized in that the length of the capillary section (38) is less than 20% of the total length (L) of the capillary (32).

10. Polycapillary optics according to one of the preceding claims, characterized in that the length of the capillary section (38) depends on the diameter of the capillary (32), in particular the larger the diameter of the capillary (32), the longer the capillary section (32).

11. Polycapillary optics according to one of the preceding claims, characterized in that the capillaries (32) are made of glass. MM 60106P0.docx

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