EP1942506A2 - Device for improving the resolution of an optical X-ray device - Google Patents

Abstract

The device has a reflector element with a reflector slope. The reflector slope is formed by a cylindrical shell section around a slope axis. The reflector element is arranged in rotating manner around an axis, extending in radial direction, opposite to the incident direction, such that the slope axis is inclined opposite to the incident direction.

Description

The invention relates to a device for improving the spatial resolution of a microporous optic for X-rays according to claim 1.

When constructing a telescope for X-rays, there is the problem that no suitable lenses exist for X-rays because of the low refraction and the strong absorption in matter. It is also not possible to use mirrors in the usual sense, since the reflectivity for X-rays is far too low, unlike for visible light. Only for very large angles of incidence near 90 degrees, sufficient reflectivity values result. This effect can be used to build an X-ray reflector telescope, provided suitably designed surfaces are found. The X-rays have to hit the reflective surface very flat (grazing incidence). X-rays are reflected by polished surfaces, namely only when the incidence of the rays is almost grazing. One possibility for the realization of an X-ray telescope is therefore the use of a parabolic mirror. However, this has under the conditions of a grazing incidence very large aberrations.

The prior art discloses a Wolter I type telescope (see, for example, the publication " Mirror systems of grazing incidence as imaging optics for X-rays ", H. Wolter, Analen der Physik, 10, 1952, pp. 94-114 ). Such a telescope exploits the reflection of X-rays in grazing incidence on metal surfaces. The basic idea is that behind the paraboloid as a correction mirror a hyperboloid is set, at which the X-rays are reflected a second time.

The Wolter-I mirror arrangement is composed of many metallic nested (often only coated) paraboloidal rotors, each followed by a hyperboloid of revolution. Together these mirrors have similar imaging properties to ordinary telescopes in the visible range of light. With him, the rays are first reflected on a small section of a parabolic mirror and then on a section of a Hyperbolspiegels. To achieve greater intensities, several such mirror systems were interlaced. Because each mirror pair has because of the grazing incidence only a very narrow area in which it can record X-rays and focus in the focal point. For example, in the mirror system of the X-ray satellite ROSAT, four Wolter double mirrors of the same focal length are nested in one another in order to achieve a large collecting surface.

Further, an approximation of the Wolter I optic is known in the prior art which uses multiple stacks of single inclined cylindrical surfaces which replace the paraboloids and hyperboloids. Such an approximation is tolerable when large focal lengths are chosen.

Further, an X-ray lens has heretofore been produced by pore optics whose reflective surfaces approximate an ideal Wolter I optic through two cylindrical surfaces. Such a pore appearance is shown in FIGS. 1A and 1B. An approximation is done for production-relevant reasons: On a cylindrical base 10, as shown in Figure 1A, the cylindrical mirror shells 12 are applied layer by layer (see Figure 1 B). A mirror bowl is polished on the front and on the back with many webs 14 provided. The webs 14 of the last applied mirror shell 12 with the mirror surface of the underlying mirror shell 12th connected, so that the last mirror surface is curved as well as the underlying mirror again. This manufacturing method requires that the gaps remaining between the lands 14 and the mirror shells 12, the pores, have a rectangular cross-section.

The advantage of a pore look is to be able to produce many mirror shells precisely and hold them one behind the other. The mirror shells are interconnected by webs, which leads to the geometry of many small pores. A disadvantage of the prior art, however, is that the spatial resolution of the X-ray optics known solutions no longer meets today's requirements.

It is therefore an object of the present invention to provide an apparatus for X-ray optics which achieves improved spatial resolution compared to the prior art.

This object is achieved by a device according to claim 1.
Preferred embodiments of the invention will become apparent from the dependent claims.

The present invention provides an apparatus for improving the resolving power of an X-ray optical apparatus for an X-ray incident from an incident direction, comprising
a mirror element having a mirror edge, wherein the first mirror edge is formed by a first cylindrical shell portion around a flank axis and the mirror element is spaced apart in a radial direction with respect to a focal axis parallel to the incident direction by a focal point of the X-ray optical apparatus, and wherein the mirror element is further spaced radially extending axis relative to the direction of incidence is arranged rotated such that the flank axis is inclined relative to the direction of incidence.

The present invention is based on the finding that an approximation of the parabolic and hyperbolic shape can be achieved by a rotation of the mirror element about the radial axis, which is oriented closer to the optimum shape than a simple approximation of cylindrical shells allows.

The device according to the invention has the advantage that it can lead to an improvement in the spatial resolution of an X-ray image, which can find a wide range of applications in a wide application of X-ray optical devices. In other words, an advantage of the device according to the invention is that it results in less blurring of the image, which in turn leads to a better image quality. The desired reduction in image blurring may depend on the staple length and focal length. The improvement of the resolution may, for example, be in the range of a factor of 3.

According to an embodiment of the invention, a second mirror flank adjoining the mirror flank may be provided, which is formed by a second cylindrical shell section about a second flank axis, wherein the mirror element may be arranged such that a plane comprising the flank axis and second flank axis is inclined with respect to the direction of incidence , This has the advantage that now not only the transition between the first and second mirror edge can be better approximated, but also the second edge of the mirror can be produced cost-effectively by the cylinder approximation in addition to the mirror edge.

In order to produce a mirror element that best suits the Wolter I optic, according to an embodiment of the invention, the mirror edge may correspond to an approximation of a parabolic shape and the second mirror edge may correspond to an approximation of a hyperbolic shape.

In order for the mirror element to represent a particularly good approximation of the Wolter-1 optic, according to a further embodiment of the invention, the mirror element can have a width which is less than approximately one tenth of the radial distance of the mirror element with respect to the focus axis. This makes it possible to ensure that the approximation range does not become too large, so that the approximation does not become inadmissible.

According to one embodiment of the invention, the mirror element may have a width corresponding to an arc length of less than about two degrees in the radial direction. This range of the width of the mirror element provides an even better approximation to the shape of the Wolter I optic, since the region to be approximated is very small compared to the entire parabolic and hyperbolic shape of the Wolter I optic, so that the approximation does not cause much error ,

Also, according to an embodiment of the invention, an inclination between the flank axis and the incidence direction may be in a range of between about one-half degree and about five degrees, which is a particularly good tilt range for improving the resolving power of the X-ray optical apparatus.

In order to achieve a further improvement in the resolution behavior of the X-ray optical apparatus, according to one embodiment of the invention, a further mirror element may be provided with a third mirror edge and a fourth mirror edge adjacent to the third mirror edge, wherein the third mirror edge is formed by a third cylindrical shell portion around a third edge axis and the further mirror element is arranged spaced apart in a further radial direction with respect to the focus axis, and wherein the further mirror element is further arranged so rotated about a further axis extending in the further radial direction with respect to the direction of incidence, that the third flank axis with respect to the direction of incidence is inclined. By providing such a further mirror element, an improvement in the yield of the incident X-rays can thus be achieved.

According to one embodiment of the invention, the further mirror element may adjoin the mirror element and be arranged at a distance from the focus axis corresponding to the distance of the mirror element from the focus axis, and a lateral transition between the mirror element and the further mirror element may have a step offset. As a result of this tilted arrangement of the mirror elements, the area of the vertical extension of the boundary line between the first and second mirror flanks and the third and fourth mirror flanks can be kept within a very narrow range, so that incident X-rays at both mirror elements have a very small focus area can be distracted. If the arrangement of the mirror elements were selected such that the boundary lines between the first and second mirror flanks and the third and fourth mirror flanks would touch, such an arrangement would not cause optimal focusing on a common focus point.

According to one embodiment of the invention, it may be advantageous if the device according to the invention comprises a plurality of additional mirror elements which form a ring of mirror elements about the focus axis. This causes X-rays from a plurality of mirror elements to be deflected to a single focus area, which in turn increases the intensity of the light spot in the focal point. As a result, a better detection or evaluation capability of the incoming X-rays is possible.

Also, the device according to an embodiment of the invention may comprise an additional mirror element, which in the radial direction of the focal axis is arranged at a distance, wherein a distance of the additional mirror element from the focus axis is greater than the distance of the mirror element to the focus axis. In particular, such a device is advantageous when the additional mirror element has two mirror edges which have an inclination to each other, so that an incident in the incident direction of the X-ray beam is reflected to a substantially identical focal point, such as an X-ray beam, which is deflected at the mirror element. Thus, by a nested arrangement also an improvement of the dissolution behavior can be achieved.

Further advantages and possible applications of the present invention will become apparent from the following description in conjunction with the embodiments illustrated in the drawings.

In the description, in the claims, in the abstract and in the drawings, the terms and associated reference numerals used in the list of reference numerals recited below are used.

Fig. 1A und 1 B

Darstellungen des Aufbaus einer Porenoptik;

Fig. 2

eine schematische Darstellung von zwei aufeinanderfolgenden Spiegelschalen gemäß der Wolter-l-Anordnung;

Fig. 3

eine Darstellung von Zylindersegmenten einer Spiegelschale;

Fig. 4

eine Darstellung eines Ausführungsbeispiels der Drehung von Zylindersegmenten um die radiale Achse der Teleskopanordnung;

Fig. 5A und 5B

Darstellungen eines Ausführungsbeispiels der vorliegenden Erfindung in zwei unterschiedlichen Schnittansichten;

Fig. 6

eine Darstellung der Ablenkung von Lichtstrahlen an dem Teleskop;

Fig. 7

ein Spotdiagramm in der Fokalebene, wobei konische Spiegelschalen zur Erzeugung des Spotdiagramms verwendet werden;

Fig. 8

ein Diagramm der Abweichung bei Verwendung eines Spiegelelementes aus zwei Zylinderflächen;

Fig. 9A und 9B

Diagramme der Abweichung der Zylindernäherung einer konischen Fläche für einen Paraboloiden (Fig. 9A) bzw. eine Hyperboliden (Fig. 9B);

Fig. 10

eine Darstellung der Beleuchtung des Spiegelelementes aus zwei Zylinderschalen;

Fig. 11

ein Spotdiagramm in der Fokalebene, das durch ein Spiegelelement mit Zylinderflächen erzeugt wird;

Fig. 12A und 12B

Diagramme der Abweichung eines Ausführungsbeispiels der vorliegenden Erfindung von einer unmodifizierten Zylinderapproximation für die erste Spiegelflanke (Fig. 12A) und die zweite Spiegelflanke (Fig. 12B); und

Fig. 13

ein Spotdiagram in der Fokalebene, das durch ein Spiegelelement gemäß einem Ausführungsbeispiel der vorliegenden Erfindung erhalten wird.

The drawings show in:

FIGS. 1A and 1B

Representations of the structure of a pore appearance;

Fig. 2

a schematic representation of two successive mirror shells according to the Wolter-l arrangement;

Fig. 3

a representation of cylinder segments of a mirror shell;

Fig. 4

a representation of an embodiment of the rotation of cylinder segments about the radial axis of the telescope assembly;

Figs. 5A and 5B

Illustrations of an embodiment of the present invention in two different sectional views;

Fig. 6

a representation of the deflection of light rays on the telescope;

Fig. 7

a spot diagram in the focal plane, wherein conical mirror shells are used to generate the spot diagram;

Fig. 8

a diagram of the deviation when using a mirror element of two cylindrical surfaces;

Figs. 9A and 9B

Diagram of the deviation of the cylinder approximation of a conical surface for a paraboloid (FIG. 9A) or a hyperboloid (FIG. 9B);

Fig. 10

a representation of the illumination of the mirror element of two cylindrical shells;

Fig. 11

a spot diagram in the focal plane, which is generated by a mirror element with cylindrical surfaces;

Figs. 12A and 12B

Diagrams of the deviation of an embodiment of the present invention from an unmodified cylinder approximation for the first mirror edge (FIG. 12A) and the second mirror edge (FIG. 12B); and

Fig. 13

a spot diagram in the focal plane obtained by a mirror element according to an embodiment of the present invention.

For a more detailed explanation of the present invention, the basic considerations that lead to the devices according to the invention will first be explained in more detail. Absolute size specifications in the following description and the drawings are only exemplary statements which do not limit the invention.

1. Conical approximation to the Wolter-I optic for X-ray astronomy

An X-ray telescope may consist of mirror shells 20, 22, which represent a so-called Wolter-I optics. Then, the mirror shell 20 facing the object is a section of a paraboloid and the mirror shell 22 facing the image plane is a section of a hyperboloid. Accordingly, the first mirror shell 20 would be the paraboloid cutout and the second mirror shell 22 would be the hyperboloid cutout, as shown in FIG.

In order to always work within the range of the grazing incidence of x-rays 24, the sections of the paraboloid and the hyperboloid are narrow mirror shells. They are usually arranged staggered to image a larger amount of light on the focal plane 23 at a distance 24a from the mirror shells 20, 22. It is common to approximate the narrow bowl-shaped sections of the paraboloid and the hyperboloid by conical elements. In this case, the mirrors 20 and 22 are annular cutouts of cone shells having a radius 26. The two underlying cones have a cone axis that is identical to the telescope symmetry axis (or focus axis 25). The cone angles are chosen so that the conical surfaces at the location of the mirror shells 20 and 22 tangentially cling to each other. in the Application example is described in the introduction a conical approximation of a Wolter-I optics.

A criterion for assessing the quality of the optical image is the diameter of the light spot 27 in the focal plane 23. A small spot 27 means that the resolution of the telescope is large, while for a large light spot 27 two objects lying close together can not be distinguished. Therefore, it is the goal of each optical telescope to generate the smallest possible light spot 27 in the focal plane 23.

2nd cylinder approximation

A production of entire mirror shells 20, 22 is expensive. It is expedient to perform an azimuthal segmentation 30, as shown in FIG. Such a mirror segment 32 or a mirror flank can be described approximately by a cutout surface of a cylinder jacket. This greatly facilitates the manufacture of the mirror shell segments. However, this approximation also causes the diameter of the light spot in the focal plane to increase.

The cylinder approximation is to fit a cylindrical surface to the conical surface that represents the paraboloid cutout. This works well, provided that the azimuthal segment size 30 is small compared to the radius of the shells 34, ie b _segment «R _shell applies. The consequence of this approximation is that the light spot in the focal plane becomes larger.

3. Cylinder approximation with rotated cylindrical surfaces

One embodiment of the invention is a modification of the cylinder approximation, which makes it possible to significantly reduce the light spot diameter compared with the cylinder approximation. This makes it possible, with cylindrical shell cutouts a spot of the size of the conical approximation to Wolter-1 optics. In this way, one has obtained the advantages of simpler manufacturing of cylindrical shell segments without significant loss of resolution of the telescope.

The modification according to one embodiment is that the cylinder segments 40 are rotated about the radial axis 42 of the mirror shell assembly of the telescope, which passes through the center of the mirror shell segment. Such an arrangement of the rotation of the cylinder segments about the radial axis of the telescopic arrangement is shown in Fig. 4. The application example shows that the diameter of the light spot in the focal plane can be reduced by a factor of three. The improvement depends on the distance of the mirror segment to the axis of symmetry: it increases with a smaller distance. Since the application example refers to a mirror tandem on the periphery of the telescope, significantly smaller light spot diameters are achieved for the inner mirror tandems.

Figures 5A and 5B show an embodiment of the mirror element according to the invention in different sectional views. FIG. 5A shows a cross-sectional view of the exemplary embodiment of the mirror element according to the invention. The mirror element in this case comprises a first mirror edge 52 and a second mirror edge 54, which both adjoin one another. In this case, the first mirror flank 52 is arranged at a radial distance 56 about a first flank axis 58. The first mirror flank 52 formed from a cylinder segment or a cylinder surface section. Here, the first edge axis 58 is inclined relative to the focus axis 25. Furthermore, the second mirror flank 54 also consists of a cylinder surface section, which is arranged in a second radial distance 60 around a second flank axis 62. The second edge axis 62 is inclined relative to the first edge axis 58, so that from the first in mirror edge 52 and the second mirror edge 54 existing game element has a bent shape. This makes it possible to ensure that X-rays which impinge on the mirror element in an incident direction parallel to the focus axis 25 are focused onto a focal point (not shown in FIG. 5A).

FIG. 5B shows a plan view of the mirror element shown in FIG. 5A, wherein at the same time adjacently arranged mirror elements are also shown. FIG. 5B again shows the focus axis 25 as well as the first flank axis 58 and the second flank axis 62. The first and second mirror flanks 52 and 54 of the individual mirror elements are again cylinder surface sections, as has already been described in connection with FIG. 5A. Furthermore, it is shown in FIG. 5B that, according to the invention, rotation is rotated about a radial axis arranged at right angles to the focus axis 25 (not shown here), so that an offset angle 64 is created between the focus axis 25 under the first and second flank axes 58 and 62. By this offset angle 64, the improvement in the optical resolution can now be achieved, which is to be sought in accordance with the invention.

Furthermore, adjacent mirror elements, as represented by the reference numerals 66 and 68 in FIG. 5B, can also be arranged in a step offset 70, so that the structure shown in FIG. 5B results. This makes it possible to ensure that a boundary between the first mirror flank 52 and the second mirror flank 54 lies, as far as possible, in a narrow lateral area so that focusing of light beams or X-rays from different mirror elements is as far as possible focused on a small focal point. Also, by the structure shown in FIG. 5B, a ring shape may be formed around in the focus axis 25, as shown in FIG. 2, for example. Approaching such a form is already indicated in Fig. 4.

According to the invention, the improvement in the focusing of an X-ray beam is achieved in that a better approximation of the Wolter I optics can be achieved by the offset angle 64, than when the boundary line between one of the first mirror edge 52 and the second mirror edge 54 horizontally, that is is perpendicular to the focus axis 25.

In the following, a concrete embodiment of the present invention will be described in more detail in comparison with a conical as well as a simple cylinder approximation.

A model of the Wolter I optic conical approximation and the unmodified and modified cylinder approximation (i.e., one embodiment of the present invention) of the Wolter I optic conical approximation was made using the optics program "ASAP". Using geometrical-optical beam computations, the light spot in the focal plane of the arrangement (spot diagram) was calculated.

- Geometry parameters

Distance between mirror shells and focal plane: f = 50000mm
Radius of the mirror shells Limitation: R = 3500mm

- Conical approximation of the Wolter-I optics Light source:

Light rays 24 (especially X-rays) fall parallel to the axis of symmetry 25 of the telescope on the annular arrangement of a mirrored ende 40 consisting of the mirror shell representing the conical approximation of the paraboloid and the second mirror shell representing the conical approximation of the hyperboloid. The grid of the light beams is indicated in FIG. 6, the left partial image representing a plan view and the right partial image representing an elevational view of such a telescope.

Light spot in the focal plane:

This results in a rotationally symmetric light spot in the center of the focal plane, whose diameter is about 0.6 mm. This is evident from the dimensions of the diagram shown in Figure 7, which represents the points of incidence of the rays in the focal plane. As can be expected, the symmetry is preserved and the pixels of the individual beams lie on circles. A shift of the focal plane along the telescopic axis has the consequence that the light spot is larger, regardless of the direction of displacement. This shows that in fact the focal plane is present. FIG. 7 shows a spot diagram in the focal plane. The two conical mirror shells are illuminated with axial light rays. The spot diameter is 0.42mm.

- Cylinder approximation

An azimuthal segment, for example, corresponds to a 360th of a circular arc, ie one degree. For a circle radius of 3500mm this means an arc length of b = (2π / 360) 1 deg 3500mm = 61 mm. In each case, a cylindrical surface has been adapted to the conical surfaces 1 and 2, which correspond to the mirror surfaces 52 and 54. This is very possible because the arc length is much smaller than the circle radius. Fig. 8 shows an illustration of such a tandem of two cylindrical surfaces.

The deviation of the cylindrical surfaces from the conical surfaces is always smaller than one micrometer. FIGS. 9A and 9B show that the difference in the case of mirror surface 1 (corresponding to mirror edge 52, therefore denoted by reference numeral 52 ') is less than 10 nm (FIG. 9A), in the case of mirror surface 2 (corresponding to mirror edge 54) , therefore designated by the reference numeral 54 ') are less than 200 nm (Figure 9B). Thus, in Fig. 9A, the deviation from the conical approximation is shown as the difference between the cylinder approximation of the conical surface and the paraboloid of Wolter-I optic while in Fig. 9B the deviation from the conical approximation is shown as the difference between the cylinder approximation of the conical surface describing the hyperboloid of the Wolter-1 optic. The y-axis indicates the deviation in micrometers.

Light source:

The tandem of cylindrical mirrors 52 ', 54' is illuminated with light rays 24. The light beams 24 are parallel to the telescopic axis 25, their spatial arrangement is shown in Figure 10, in which the lighting of the tandem of two cylindrical shells 52 'and 54' is shown. The circular arc detail is exaggerated; in fact, the azimuth angle is about 1 degree.

Light spot in the focal plane:

A cylindrical mirror tandem produces a light spot in the center of the focal plane which is unbalanced. Its maximum extension is in the direction perpendicular to the mirror tandem and is about 0.82 mm, as can be seen in the spot diagram of FIG. 11. An arrangement of several Zylinderspiegeltandems such that a complete ring of mirror shells is formed, then has a round light spot in the center of the focal plane result, the diameter of about 0.82mm. 11 shows a spot diagram in the focal plane which generates a tandem of two described cylindrical surfaces from the axially incident light beams. The spot diameter is 0.82mm.

Cylinder approximation with rotated cylindrical surfaces (arrangement according to an embodiment of the present invention)

The surfaces of the modified (ie, rotated according to the invention) and unmodified cylinder approximation of mirror surface 52 and 52 'differ by less than 40 microns; the surfaces of the modified and unmodified cylinder approximation of mirror surface 54 and 54 'differ by less than 60 microns. Although that are small numbers compared to the lateral dimensions of the mirror surfaces, they represent significant deviations, considering that the difference between cylinder and conical approximation is smaller by three orders of magnitude. FIG. 12A shows the deviation of the modified (rotated) and unmodified cylinder approximation for the mirror surface 52 and 52 ', whereas FIG. 12B shows the deviation of the modified (rotated) and unmodified cylinder approximation for the mirror surface 2 of the mirror element.

Light source:

To have a direct comparison, the same light source as in the previous section has been used.

Light spot in the focal plane:

By rotating the tandem from the two cylindrical mirrors 52 and 54 about the radial axis of the telescope assembly by 1.00713 degrees, the diameter of the light spot can be significantly reduced. As shown in Fig. 13, the maximum extent of the light spot is about 0.25 mm. An arrangement of several Zylinderspiegeltandems such that a complete rings of mirror shells is formed, then results in a round light spot in the center of the focal plane, whose diameter is about 0.25 mm. This is smaller by a factor of 3.3 than in the case of the unmodified cylinder approximation and by a factor of 2.4 smaller than in the case of the conical approximation of the Wolter-I optics.
13 shows a spot diagram in the focal plane, which generates a tandem of two rotated cylindrical surfaces from the axially incident light beams. The spot diameter is 0.25mm.

reference numeral

10

document

12

cylindrical mirror shells

14

Stege

20.22

mirror shells

23

focal plane

24

Light rays, X-rays

24a

Distance between the focal plane and the mirror shells

25

Focus axis, telescope axis

26

Radius of the mirror shells

27

light spot

30

azimuthal segmentation

32

mirror segment

34

Radius of the shells of the cylinder approximation

40

cylinder segment

42

radial axis, radial axis

52

first mirror flank

54

second mirror flank

56

radial distance from the first mirror edge to the first edge axis 58th

58

first flank axis

60

radial distance from the second mirror edge to the second edge axis 62nd

62

second flank axis

64

offset angle

66.68

further mirror elements

70

step mismatch

Claims (10)

An apparatus for improving the resolving power of an X-ray optical apparatus for an incident X-ray beam (24) comprising
a mirror element (52, 54) having a mirror flank (52), wherein the mirror flank (52) is formed by a cylindrical shell section around a flank axis (58) and the mirror element (52, 54) is directed through a focal point with respect to a focal axis (25) parallel to the incidence direction of the X-ray optical apparatus is arranged in a radial direction (42), and wherein the mirror element (52, 54) is further arranged rotated about an axis extending in the radial direction (42) relative to the direction of incidence such that the flank axis (58) with respect to the direction of incidence is inclined. Device according to claim 1,
characterized in that
a second mirror flank (54) adjoining the mirror flank (52), which is formed by a second cylindrical shell section about a second flank axis (62), wherein the mirror element (52, 54) is arranged such that one flank axis (58) and second flank axis (62) is inclined with respect to the direction of incidence. Device according to claim 2,
characterized in that
the mirror edge (52) corresponds to an approximation of a hyperbolic shape and the second mirror edge (54) corresponds to an approximation of a parabolic shape. Device according to one of claims 1 to 3,
characterized in that
the mirror element (52, 54) has a width that is less than about one tenth of the radial distance of the mirror element with respect to the focus axis (25). Device according to claim 4,
characterized in that
the mirror element (52, 54) has a width corresponding to an arc length of less than about two degrees in the radial direction (42). Device according to one of claims 1 to 5,
characterized in that
an inclination between the flank axis (58) and the direction of incidence ranges between about one-half degree and about 5 degrees. Device according to one of claims 1 to 6,
characterized in that
the device comprises a further mirror element (66, 68) having a third mirror edge (52) and a fourth mirror edge (54) adjoining the third mirror edge (52), wherein the third mirror edge (52) is formed by a third cylindrical shell section around a third edge axis and the further mirror element (66, 68) is arranged spaced apart in a further radial direction with respect to the focus axis, and wherein the further mirror element (66, 68) is further arranged such that it rotates about a further axis extending in the further radial direction with respect to the direction of incidence the third flank axis is inclined with respect to the direction of incidence. Device according to claim 7,
characterized in that
the further mirror element (66, 68) adjoins the mirror element (52, 54) and is arranged at a distance from the focus axis (25) which corresponds to the distance of the mirror element (52, 54) from the focus axis (25) and wherein Transition between the mirror element (52, 54) and the further mirror element (66, 68) has a step offset (70). Device according to claim 7 or 8,
characterized in that
the device comprises a plurality of additional mirror elements (66, 68) forming a ring of mirror elements about the focus axis. Device according to one of claims 1 to 9,
characterized in that
the device has an additional mirror element which is arranged in the radial direction spaced from the focus axis, wherein a distance of the additional mirror element from the focus axis (25) is greater than the distance of the mirror element (52, 54) to the focus axis (25).

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