A Wolter-I type X-ray focusing optical system with a conical structure and a design method thereof

Abstract

The present application relates to a kind of Wolter-I type X-ray focusing optical system of conical structure and its design method, belong to optical precision machinery technical field, solve the technical problems that X-ray grazing incidence angle of outer lens of X-ray focusing mirror exists, reflectivity is lower, the contribution of effective area to optical system is smaller, its X-ray focusing optical system includes lens, conical hub, light shield shaft, lens housing and flange, lens is conical structure, by several layers of single lens nesting, several layers of single lens is the same optical axis.The method for designing X-ray focusing optical system, including lens design, the lens design, total evaluation function is used to optimize lens parameter and response characteristic, the product of the total evaluation function is the product of the evaluation function considering point spread function, the evaluation function considering energy envelope function, the evaluation function considering minimum scattering, the evaluation function considering maximum effective area.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical precision machinery, and particularly relates to a conical structure Wolter-I type X-ray focusing optical system and a design method thereof. BACKGROUND

[0002] With the development of X-ray space observation, a series of space astronomical satellites have been launched one after another, and the demand for X-ray focusing telescopes is becoming more and more widespread. The Wolter-I type focusing mirror can obtain a larger effective area and higher spatial resolution by virtue of its multi-layer nested structure, and has become the mainstream focusing optical system in the field of X-ray space observation. X-rays are reflected twice by a parabolic surface and a hyperbolic surface to reach the focal point, and the multi-layer nesting can significantly improve the effective light collection area. However, the outer mirror of the focusing mirror has a large X-ray grazing incidence angle and low reflectivity, which contributes less to the effective area of the optical system, which greatly limits the further improvement of the performance indicators of the focusing mirror. In order to meet the demand of X-ray space observation tasks for wide field of view, high resolution and large effective area optical system, the design of lightweight X-ray focusing mirror under the constraint of manufacturability has become a problem to be solved. SUMMARY

[0003] In order to overcome the problems of the outer mirror of the X-ray focusing mirror, such as large X-ray grazing incidence angle, low reflectivity and small contribution to the effective area of the optical system, the application provides a conical structure Wolter-I type X-ray focusing optical system and a design method thereof.

[0004] The technical solution adopted by the application to solve the technical problem is:

[0005] A conical structure Wolter-I type X-ray focusing optical system, comprising a mirror, a conical hub, a light-shielding shaft, a lens housing and a flange, wherein:

[0006] The mirror is of a conical structure and is composed of a plurality of layers of single mirrors nested together, and the plurality of layers of single mirrors have the same optical axis;

[0007] The conical hub is used for supporting and fixing the mirror;

[0008] The light-shielding shaft is used for shielding incident photons in the ineffective aperture;

[0009] The lens housing is used for enveloping the mirror;

[0010] The flange is used for connecting the conical hub, the light-shielding shaft and the lens housing.

[0011] The X-ray focusing optical system described above has a total of 40 lens layers, with a thickness of 0.1 mm for each lens; the innermost single lens has a diameter of 80 mm and a shell length of 250 mm; the shell length of each single lens increases linearly with the diameter; and the outermost single lens has a diameter of 180 mm and a shell length of 300 mm.

[0012] The tapered hub has 9 spokes, each with a groove. A single lens is located in the groove, and the tapered hub is bonded to the lens.

[0013] The outer diameter of the light-shielding shaft is 75mm, and the height is 250mm.

[0014] The lens housing has an inner diameter of 185mm and a height of 320mm.

[0015] In the aforementioned X-ray focusing optical system, the lens is a nickel-cobalt alloy coated with a power-law hierarchical stacked Pt / C multilayer film.

[0016] In the aforementioned X-ray focusing optical system, the lens is coated with a Pt / C multilayer film, the maximum double layer thickness is 2nm to 11.5nm, and the ratio of the Pt layer thickness to the double layer thickness is 0.72.

[0017] The X-ray focusing optical system described above uses an Inconel 600 material for its conical hub.

[0018] In the aforementioned X-ray focusing optical system, the light-shielding axis is made of aluminum alloy.

[0019] In the aforementioned X-ray focusing optical system, the lens housing is made of aluminum alloy.

[0020] In the aforementioned X-ray focusing optical system, the flange is made of Inconel 600 material.

[0021] A method for designing a Wolter-I type X-ray focusing optical system with a conical structure, including lens design;

[0022] The lens design employs a total evaluation function to optimize lens parameters and response characteristics.

[0023] The overall evaluation function is the product of the evaluation function considering the point spread function, the evaluation function considering the energy enclosure function, the evaluation function considering the minimum scattering, and the evaluation function considering the maximum effective area.

[0024] The method for designing the above-described X-ray focusing optical system uses an evaluation function that considers the point spread function, which is C*exp{-(HPD-25″). 2 / [2*(20″) 2 ]}, where C is the normalization factor with a value of 1.3, and HPD is the half-power diameter.

[0025] The evaluation function considering the energy envelope function is the ratio of the energy envelope function at the target point to the energy envelope function near the edge of the field of view.

[0026] The evaluation function considering the minimum scattering is the proportion of the light rays reaching the focal plane within a circle with a diameter of 1'.

[0027] The evaluation function considering the maximum effective area is the ratio of the effective area to the maximum effective area that can be achieved by the entire optical system.

[0028] The beneficial effects of the present application are:

[0029] The present application discloses a conical structure Wolter-I type X-ray focusing optical system, which adopts a conical structure multi-layer nested mirror, and the length of the lens shell is increased to compensate for the low reflectivity of the outer mirror due to the large X-ray grazing incidence angle, thereby significantly improving the contribution of the outer mirror to the effective area of the entire optical system.

[0030] The present application discloses a conical structure Wolter-I type X-ray focusing optical system, which adopts a conical structure multi-layer nested mirror, and the focal plane offset decreases with the increase of the diameter of the mirror shell, thereby effectively improving the off-axis angle resolution, and the conical structure Wolter-I type X-ray focusing optical system has a wider field of view compared with the traditional focusing optical system adopting the same length multi-layer nested mirror.

[0031] The present application discloses a conical structure Wolter-I type X-ray focusing optical system, which adopts a power-law hierarchical stack Pt / C multi-layer film, different energy photons are reflected at different depths of the stack, and higher integrated photon flux is obtained through the interference superposition of reflection at different interfaces, thereby effectively improving the reflectivity and energy response range of the mirror. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 FIG. 1 is a structural schematic diagram of a conical structure Wolter-I type X-ray focusing optical system according to an embodiment of the present application;

[0033] Figure 2 FIG. 2 is a sectional view of a conical structure Wolter-I type X-ray focusing optical system according to an embodiment of the present application;

[0034] Figure 3 FIG. 3 is a sectional view of a mirror according to an embodiment of the present application;

[0035] Figure 4 FIG. 4 is a schematic diagram of an optical path of a conical structure Wolter-I type X-ray focusing optical system according to an embodiment of the present application;

[0036] Figure 5 FIG. 5 is a schematic diagram of the change of the lens shell length of a conical structure multi-layer nested mirror with the diameter according to an embodiment of the present application.

[0037] Reference numerals: 1. lens, 2. conical hub, 3. light-shielding shaft, 4. lens housing, 5. flange. DETAILED DESCRIPTION

[0038] The present embodiment is implemented on the basis of the technical scheme of the present application, and gives a detailed implementation mode and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0039] Example 1

[0040] A conical structure Wolter-I type X-ray focusing optical system, as shown in Figure 1 , Figure 2 , comprises a plurality of layers of nested nickel-cobalt alloy lenses 1, a conical hub 2, a light-shielding shaft 3, a lens housing 4, and a connecting flange 5; a single lens of the plurality of layers of nested nickel-cobalt alloy lenses 1 is composed of a rotating parabolic surface and a hyperboloid, and lenses of different diameters are nested in multiple layers along the same optical axis; the conical hub 2 is used to support and fix the lenses; the light-shielding shaft 3 is used to shield incident photons in the ineffective aperture; the lens housing 4 is used to envelope the entire set of lenses; and the connecting flange 5 is used to connect the conical hub 2, the light-shielding shaft 3, and the lens housing 4.

[0041] The total number of layers of the plurality of layers of nested nickel-cobalt alloy lenses 1 is 40 layers, the thickness of a single layer of lenses is 0.1 mm, and the spacing of each layer of lenses and the included angle with the optical axis are designed to ensure that the multiple layers of lenses have a common focal point.

[0042] The plurality of layers of nested nickel-cobalt alloy lenses 1 adopts a conical structure, as shown in Figure 3 , the innermost layer of lenses has a diameter of 80 mm, the lens shell length is 250 mm, and the lens shell length increases linearly with the diameter, and the outermost layer of lenses has a diameter of 180 mm, and the lens shell length is 300 mm.

[0043] The plurality of layers of nested nickel-cobalt alloy lenses 1 is coated with a power-law hierarchical stack Pt / C multilayer film, the maximum Pt / C double-layer thickness is 11.5 nm, the minimum double-layer thickness is 2 nm, the ratio of Pt to double-layer thickness is 0.72, the power-law index is 0.4, the film logarithm is 100, and more than 90% high reflectivity can be achieved below 37 keV energy, and a wideband response of about 60% can be achieved in the energy range of 40-77 keV. The optical path of the conical structure Wolter-I type X-ray focusing optical system is shown in Figure 4 .

[0044] The conical hub 2 is made of Inconel 600 material, and has 9 spokes, each of which is engraved with a groove, and the multiple layers of lenses are inserted into the grooves in sequence and fixed by glue.

[0045] The light-shielding shaft 3 is made of aluminum alloy material, and has an outer diameter of 75 mm and a height of 250 mm.

[0046] Lens housing 4 is aluminum alloy material, its inner diameter is 185mm, height is 320mm, the length of lens housing 4 changes with the diameter as shown in the figure. Figure 5

[0047] Connecting flange 5 is Inconel 600 material, its size corresponds to conical hub 2, light shielding shaft 3 and lens housing 4.

[0048] A design method of a conical structure Wolter-I type X-ray focusing optical system, multi-layer nested nickel-cobalt alloy lens 1 comprehensively considers lens size, weight and total effective area in design, and introduces evaluation functions considering point spread function, energy containment function, minimum scattering and maximum effective area to evaluate and optimize lens parameters and response characteristics.

[0049] The evaluation function considering point spread function is a flat weighted function, which is used to describe the sharpness of point spread function, and its expression form is C*exp{-(HPD-25″) 2 / [2*(20″) 2 ]}, wherein C is a normalization factor, and takes a value of 1.3, and HPD is a half-power diameter.

[0050] The evaluation function considering energy containment function is the ratio of energy containment function at the target point to energy containment function near the edge of the field of view.

[0051] The evaluation function considering minimum scattering is the proportion of light reaching the focal plane within a circle with a diameter of 1'.

[0052] The evaluation function considering maximum effective area is the ratio of effective area to the maximum effective area that can be achieved by the entire optical system.

[0053] The product of the evaluation functions considering point spread function, energy containment function, minimum scattering and maximum effective area is the total evaluation function, which changes with lens shell diameter, lens shell length, focal plane offset, off-axis angle and photon energy, and the larger the value is, the better the lens response characteristics are, and thus the optimized design of the optical system can be realized.

[0054] The above describes the preferred embodiments of the present application in detail. It should be understood that those skilled in the art can make modifications and changes to the technical solutions of the present application without creative efforts. Therefore, any technical solutions obtained by logical analysis, reasoning or limited experiments based on the technical essence of the present application on the basis of the prior art should be within the protection scope determined by the claims.​

Claims

1. A method for designing a Wolter-I type X-ray focusing optical system with a conical structure, characterized in that, Including lens design; The lens design employs a total evaluation function to optimize lens parameters and response characteristics. The overall evaluation function is the product of the evaluation function considering the point spread function, the evaluation function considering the energy enclosure function, the evaluation function considering the minimum scattering, and the evaluation function considering the maximum effective area. The conical Wolter-I type X-ray focusing optical system includes a lens (1), a conical hub (2), a light-blocking axis (3), a lens housing (4), and a flange (5); in: The lens (1) has a conical structure and is composed of several nested single lenses. The several single lenses are on the same optical axis, and the length of the lens shell of each single lens increases linearly with the increase of the diameter. The conical hub (2) is used to support and fix the lens (1); The light-blocking axis (3) is used to block incident photons in the ineffective aperture; The lens housing (4) is used to enclose the lens (1). The flange (5) is used to connect the tapered hub (2), the light-shielding shaft (3), and the lens housing (4).

2. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The lens (1) has a total of 40 layers, and the thickness of a single lens is 0.1 mm; the innermost single lens has a diameter of 80 mm and a lens shell length of 250 mm; the outermost single lens has a diameter of 180 mm and a lens shell length of 300 mm. The conical hub (2) has 9 spokes, each with a groove. A single lens is located in the groove, and the conical hub (2) is bonded to the lens (1). The outer diameter of the light-shielding axis (3) is 75 mm and the height is 250 mm; The inner diameter of the lens housing (4) is 185 mm and the height is 320 mm.

3. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The lens (1) is a nickel-cobalt alloy coated with a power-law hierarchical stacked Pt / C multilayer film.

4. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 3, characterized in that, The lens (1) is coated with a Pt / C multilayer film, the thickness of the double layer is 2 nm to 11.5 nm, and the ratio of the thickness of the Pt layer to the thickness of the double layer is 0.

72.

5. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The tapered hub (2) is made of Inconel 600 material.

6. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The light-shielding shaft (3) is made of aluminum alloy.

7. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The lens housing (4) is made of aluminum alloy.

8. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The flange (5) is made of Inconel 600 material.

9. The method for designing a conical Wolter-I type X-ray focusing optical system according to claim 1, characterized in that, The evaluation function considering the point spread function is C*exp{-(HPD-25′′)} 2 / [2*(20′′) 2 ]}, where C is the normalization factor with a value of 1.3, and HPD is the half-power diameter; The evaluation function considering the energy enclosure function is the ratio of the energy enclosure function at the target point to the energy enclosure function near the edge of the field of view; The evaluation function considering minimum scattering is the proportion of light rays reaching the focal plane contained within a circle of diameter 1′. The evaluation function considering the maximum effective area is the ratio of the effective area to the maximum effective area achievable by the entire optical system.

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