Mirrors and telescopes

Abstract

To provide a split mirror that is less deformed by temperature change and vibration.SOLUTION: A mirror of the present disclosure comprises: a plurality of main body members that each include a front face on which a reflecting member is arranged, a rear face, and a side face connecting the front face and the rear face with each other, and include, on the rear face, a concave part and a rib part surrounding the concave part and constituting the side face; and fixing members that are arranged on the rear face side of the main body members and fix the rib parts to each other. The side faces of the adjacent main body members are in proximity to each other with a gap therebetween.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a mirror and a telescope using the mirror. [Background technology]

[0002] Optical instruments such as astronomical telescopes used on the ground or in space are equipped with mirrors to collect and guide the light of the object to be observed. The mirrors used in astronomical telescopes have been required to have larger apertures in order to capture weaker celestial light and obtain higher resolution images of celestial bodies. The size of the mirror is, for example, more than 1m, but such a large integrated mirror is expensive and takes a long time to develop. Since mirrors are generally made of brittle materials, they are prone to breakage due to handling errors during the manufacturing process, and there is also the problem that recovery requires a lot of resources. To avoid these drawbacks, there is a method called segmented mirror, in which multiple small mirrors are arranged along an ideal optical surface to form a single mirror. This technology is used in the Keck Telescope, a large terrestrial telescope, and the James Webb Telescope, a next-generation space telescope.

[0003] However, segment mirrors also have their own problems. In commonly used segment mirrors, gaps are provided between adjacent mirrors to enable alignment of each mirror. However, such gaps complicate the diffraction image (point spread function) obtained by the telescope, leading to degradation of resolution, and also significantly reducing the sensitivity of the infrared image due to thermal radiation generated from the gaps. Therefore, for example, Patent Document 1 discloses a segment mirror in which multiple members made of low thermal expansion ceramics are fixed in contact with each other to eliminate gaps. Although this gap-free segment mirror has eliminated the drawbacks of segment mirrors, telescope mirrors used on the ground and in space are subject to temperature changes and vibrations, and therefore may experience surface shape deformation and positional deviation (alignment error) due to contact and interference between the mirrors caused by thermal stress and vibration displacement of the individual mirrors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-34757 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a segmented mirror that is less susceptible to deformation and positional deviation due to temperature changes and vibrations. [Means for solving the problem]

[0006] The mirror of the present disclosure is a mirror comprising a plurality of main body members each having a front surface on which a reflective member is arranged, a back surface, and a side surface connecting the front surface and the back surface, the main body members each having a recess on the back surface and a rib portion surrounding the recess to form the side surface, and a fixing member arranged on the back surface side of the main body members and fixing the rib portions to each other, wherein the side surfaces of adjacent main body members are adjacent to each other via a gap. Effect of the Invention

[0007] The mirror of the present disclosure is less susceptible to deformation due to temperature changes or vibrations. [Brief description of the drawings]

[0008] [Figure 1] 2 is a schematic diagram of a surface of a mirror in one embodiment. [Diagram 2] FIG. 2 is a schematic diagram of the rear surface of a mirror in one embodiment. [Diagram 3] FIG. 4 is a schematic diagram of a mirror according to another embodiment. [Figure 4] FIG. 4 is a schematic diagram of a mirror according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Mirrors and telescopes> DETAILED DESCRIPTION OF THE DRAWINGS The embodiments of the mirror of the present disclosure will be described in detail below with reference to the drawings.

[0010] 1 and 2, the mirror 10 of this embodiment includes multiple body members 1 each having a front surface 1a, a back surface 1b, and a side surface 1c connecting the front surface 1a and the back surface 1b. A reflective member (not shown) is disposed on the front surface 1a, and the multiple body members 1 form an integrated mirror 10.

[0011] The back surface 1b has a recess 2 and a rib portion 3 surrounding the recess 2, and the rib portion 3 constitutes the side surface 1c. By having such recess 2 and rib portion 3, the mirror 10 can be made lighter while maintaining the necessary mechanical strength, making it suitable for use as a mirror for a space telescope mounted on an artificial satellite or the like.

[0012] The side surfaces 1c of adjacent main body members 1 of the mirror 10 are not in contact with each other, but are adjacent to each other via a gap 14. A plate-shaped fixing member (plate-shaped member) 11 is disposed on the back surface 1b side of the main body member 1, and connects and fixes the rib portions 3 to each other.

[0013] The mirror 10 may be used in a relatively harsh environment, such as with temperature changes and vibrations. For example, a mirror 10 for a telescope used in space is subject to temperature changes and vibrations during launch. If the main body members 1 are in contact with each other and fixed, excessive stress is applied to the main body members 1 due to expansion and vibration caused by temperature changes, which makes them prone to misalignment and deformation. However, readjustment after launch into space is very difficult. Therefore, by making the main body members 1 non-contact with each other and providing a gap 14, it is possible to avoid contact between the main body members 1 even in an environment subject to temperature changes and vibrations, and to reduce deformation and misalignment due to contact.

[0014] The telescope (not shown) of the present disclosure includes a mirror 10 .

[0015] The diameter of the mirror 10 is, for example, 300 mm or more, and may be 1 m or more. The mirror 10 can be made larger because it is composed of multiple body members 1. Furthermore, when a body member 1 is damaged, only the body member 1 where the damage occurred can be removed and replaced.

[0016] In this embodiment, the outer shape of the mirror 10 is circular, but the present invention is not limited to this and may be polygonal. The mirror 10 may be a flat mirror, a curved mirror having a curvature, or a free-form surface.

[0017] The spacing of the gap 14 is preferably 1 / 800 or less of the external dimensions of the mirror 10 (the diameter if circular, or the maximum width if polygonal, etc.). The light reflected by the mirror 10 reaches a light receiving element such as an image sensor via an optical system such as a lens. If the number of pixels of the image sensor is 800 x 800, the resolution of the captured image is 1 / 800 of the image dimensions. In general, the resolution of the light receiving element attached to a telescope is 1 / 800 or less, so if the spacing of the gap 14 is 1 / 800 or less of the external dimensions of the mirror 10, it will be recognized as a single mirror without gap 14. When used in combination with a light receiving element with even higher resolution, the spacing of the gap 14 should be made even smaller. For example, for a light receiving element with a resolution of 1 / 1000 (number of pixels is 1M), the spacing of the gap 14 should be 1 / 1000 of the external dimensions of the mirror 10 and 1 / 20 of the external dimensions of the mirror 10. For a light receiving element having a pixel count of 1.00 (4M pixels), the spacing of gap 14 should be 1 / 2000 of the external dimension of mirror 10. Manufacturing is easier if the spacing of gap 14 is uniform within the reflecting surface. The spacing of gap 14 may be larger than the wavelength of the light to be observed, as long as it is smaller than the image resolution (diameter of mirror 10 / resolution of element).

[0018] As described later, the width of the gap 14 is preferably 1 / 10000 or more of the diameter of the mirror 10, and more preferably 1 / 5000 or more.

[0019] The rib portion 3 forming the side surface 1c has a first portion (diameter portion) 3a adjacent to another adjacent main body member 1, and a second portion (outer portion) 3b forming the outer shape of the mirror 10. Furthermore, as shown in FIG. 1, it may have a third portion (inner portion) 3c forming the optical path of the incident and outgoing light.

[0020] 1 and 2 show an example in which the rib portion 3 is composed of the concentric arc-shaped second portion 3b and the third portion 3c, and two linear first portions 3a having a length corresponding to the difference between the radii of the respective arcs, but this is not limited thereto, and the second portion 3b and the third portion 3c may be linear (for example, a chord of a circle). The mirror 10 may be composed of a plurality of polygonal body members 1 arranged in a honeycomb shape. If the first portion 3a is linear in the radial direction of the mirror 10, a circle can be composed of an assembly of the first portions 3a of the same shape, for example, a sector shape divided equally, so that the mirror 10 having a circular outer shape can be easily manufactured. In addition, stress generated by assembly, temperature change, etc. can be isotropically dispersed.

[0021] 1 and 2 show an example in which the number of main body members 1 is six, but the number of main body members 1 is not limited thereto and may be two or more. FIG. 3 shows an example of a mirror 10 consisting of 12 main body members 1, six on the inner periphery side and six on the outer periphery side, assuming a larger mirror 10. In this case, a gap 14 is also provided between the main body member 1A on the inner periphery side and the main body member 1B on the outer periphery side. That is, the rib portion 3 of the main body member 1A on the inner periphery side is composed of a first portion 3a and a third portion 3c, and the rib portion 3 of the main body member 1B on the outer periphery side is composed of a first portion 3a and a second portion 3b. As described later, the gap 14 can be formed by assembling the main body members 1 by disposing a metal plate or the like between the main body members 1. The mirror 10 shown in FIG. 3 is easy to assemble because the gap 14 between the main body members 1A on the inner periphery side and the gap 14 between the main body members 1B on the outer periphery side are arranged in the same straight line, and the spatial precision of the gap 14 can be easily achieved. Furthermore, the first portion 3a can be polished in a state in which the inner circumferential side body member 1A and the outer circumferential side body member 1B are assembled, which makes it easy to improve the precision of the gap 14. If the gap 14 between the inner circumferential side body member 1A and the outer circumferential side body member 1B is linear, assembly is easy and the precision is easily improved.

[0022] When each surface of a block-shaped member such as the main body member 1 is polished, roll-off occurs at the connection between the surfaces. The roll-off is particularly large at corners. If there are a large number of main body members 1 adjacent to the intersections of multiple gaps 14, corners with large roll-offs will gather at the intersections, and the width of the gaps 14 will likely be larger than the design value. For this reason, it is preferable that the number of main body members 1 adjacent to the intersections of the gaps 14 is small, and in particular, three or less. Figure 4 shows an example of a mirror 10 having an inner body member 1A and an outer body member 1B, in which the number of main body members 1 adjacent to the intersections is three or less.

[0023] The main body member 1 has a non-through hole 8 on the back surface side of the first rib portion 3a. The non-through hole 8 is formed in a direction that opens to the back surface 1b toward the front surface 1a, and a screw groove is formed inside. The plate-like member 11 has a through hole 12 corresponding to the non-through hole 8 of the main body member 1, and is in contact with the main body member 1 so that the non-through hole 8 and the through hole 12 are in communication. Adjacent main body members 1 are fastened and fixed to each other by fastening members 13 inserted into the through holes 12 and the non-through holes 8. The fastening members 13 are, for example, bolts or the like. The plate-like member 11 is fastened to the back surface 1b of the main body member 1 (first portion 3a). Fastening and fixing the fixing member 11 to the plate-like member 11 in the thickness direction of the mirror 10 (direction from the front surface 1a to the back surface 1b) makes it difficult for mechanical interference between the main body members 1 due to thermal expansion or vibration to occur. The material of the fastening member 13 is preferably one that has a small difference in thermal expansion coefficient from that of the main body member 1, and for example, when low expansion glass, low expansion glass ceramics, or low expansion ceramics is used for the mirror member, a metal with a relatively small thermal expansion coefficient such as an Fe-Ni alloy is suitable. The number of fastening members 13 may be any number as long as the plate-like member 11 and the main body member 1 are stably fixed.

[0024] When the main body member 1 and the plate-like member 11 are made of ceramics, the mirror 10 has high mechanical strength and high heat resistance. Examples of ceramics include cordierite ceramics, aluminum oxide ceramics, zirconium oxide ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, and mullite ceramics.

[0025] In particular, the main body member 1 and the plate-like member 11 have a thermal expansion coefficient of ±10×10 -6 / K or less, preferably ±1×10 -6 / K or less, deformation due to temperature changes is small and the main body members 1 are less likely to come into contact with each other, so reliability is high in environments with large temperature changes. Cordierite ceramics are suitable as low thermal expansion ceramics. Cordierite ceramics have a low specific gravity and a small thermal expansion coefficient, which allows the mirror 10 to be made lighter. The thermal expansion coefficient of cordierite ceramics is, for example, 0.02×10 -6 / K(@22℃).

[0026] Cordierite ceramics are ceramics that contain 80% by mass or more of cordierite (2MgO·2Al2O3·5SiO2) out of 100% by mass of all components that make up the ceramics. The material of the main body member 1 can be confirmed by the following method. X-ray diffraction measurement is performed in the range of 2θ=8 to 100° (2θ is the diffraction angle) using an X-ray diffractometer (XRD) using Cu Kα rays, and if the cordierite content determined using the Rietveld analysis program RIETAN is 80% by mass or more, the material is cordierite ceramics.

[0027] If the distance of gap 14 is 1 / 10,000 or more of the diameter of mirror 10, and more preferably 1 / 5,000 or more, contact between main body members 1 can be reduced even when subjected to temperature changes or vibration, and deformation of mirror 10 can be reduced.

[0028] In the mirror 10, the arithmetic mean roughness Ra and root mean square roughness Rq of the surface 1a of the main body member 1 must be sufficiently small relative to the wavelength of the light to be observed in order to maintain reflectance and resolution. When the light to be observed is visible light or infrared light, the arithmetic mean roughness Ra of the surface 1a is preferably smaller than 0.2 μm. This also reduces the generation of particles from the surface 1a. For example, the arithmetic mean roughness Ra of the surface 1a is 20 nm or less, and the root mean square roughness Rq is 10 nm or less.

[0029] Among the side surfaces 1c formed by the rib portion 3, the side surface of the first portion 3a is connected to the effective area of ​​the surface 1a used as a reflecting surface, and faces other main body members 1 via a gap 14. The arithmetic mean roughness Ra of the side surface of the first portion 3a is preferably smaller than 0.2 μm. This reduces the inclusion of particles in the effective area of ​​the surface 1a. Furthermore, it is preferable that the arithmetic mean roughness Ra of the side surface of the first portion 3a is smaller than the arithmetic mean roughness Ra of the surface 1a. For example, the arithmetic mean roughness Ra of the side surface of the first portion 3a is set to 10 nm or less. This allows the gap 14 to be formed with high precision.

[0030] Among the side surfaces 1c formed by the rib portion 3, the side surfaces of the second portion 3b and the third portion 3c are the surface 1 The second portion 3b and the third portion 3c are surfaces that connect to the outer periphery and inner periphery of the surface 1a. Since the outer periphery and inner periphery of the surface 1a can be areas that are not used as mirrors, the side surfaces of the second portion 3b and the third portion 3c may be non-mirror surfaces (surfaces with an arithmetic mean roughness Ra of 0.2 μm or more). By making the side surfaces of the second portion 3b and the third portion 3c have an arithmetic mean roughness Ra of 0.2 μm or more, for example 0.8 μm, processing becomes easier and manufacturing costs can be reduced.

[0031] Of the rear surface 1b of the rib portion 3, the rear surface of the first portion 3a is the surface that is in contact with and fixed to the plate-like member 11. When the arithmetic mean roughness Ra of the rear surface of the first portion 3a is 0.04 μm or less, the contact between the rear surface 1b of the main body member 1 and the plate-like fixing member 11 is good, and the surface precision of the reflective surface formed by an assembly of the surfaces 1a of the main body members 1 is improved.

[0032] The arithmetic mean roughness Ra can be determined by measurements in accordance with JIS B 0601 (1982). For example, a surface roughness and contour shape measuring instrument SEF680 manufactured by Kosaka Laboratory Co., Ltd. may be used, and the measurement conditions may be set to, for example, a measurement length of 2.5 mm or more, a cutoff value of 0.8 mm, and a stylus scanning speed of 0.5 mm / sec. Then, measurements may be taken at at least five points on the surface to be measured, and the average value may be determined.

[0033] In the mirror 10, at least one of the multiple body members 1 may have a thickness (the distance from the front surface 1a toward the back surface 1b) at the recess 2 that gradually decreases in thickness in a direction away from the center of the reflecting surface 4, as shown in Fig. 2. If such a configuration is satisfied, the mechanical strength of the mirror 10 is high and the weight of the mirror 10 can be reduced, compared to a case in which the thickness gradually decreases in a direction approaching the center of the reflecting surface 4. It goes without saying that if all of the body members 1 constituting the mirror 10 have the above configuration, the weight increase of the mirror 10 can be further suppressed even if the mirror 10 is made larger.

[0034] The mirror 10 can be used not only in optical devices that use ultraviolet light, visible light, and infrared light, but also in radio telescopes that use radio waves (electromagnetic waves with a frequency of 3 THz or less). The mirror 10 is suitable for use in environments where it is subject to temperature changes or vibrations, such as in space or outdoors.

[0035] <Mirror manufacturing method> Hereinafter, a method for manufacturing mirror 10 according to the present disclosure will be described taking as an example a case in which main body member 1 and plate-shaped member 11 are made of cordierite ceramics.

[0036] First, a synthetic cordierite powder is prepared by calcining a mixed powder of magnesium carbonate powder, aluminum oxide powder, and silicon oxide powder in a predetermined ratio. Next, the synthetic cordierite powder and a sintering aid powder are weighed in a predetermined ratio to prepare a primary raw material. Next, the primary raw material powder is wet-mixed, and a predetermined amount of binder is added to obtain a slurry.

[0037] Next, the slurry is sprayed using a spray granulation device (spray dryer) and granulated to obtain granules. The obtained granules are then molded by isostatic pressing (rubber press) or powder pressing to obtain a molded body that is cut to have an arbitrary shape. Next, the molded body is fired in a firing furnace at a maximum temperature of 1300°C to 1450°C in an air atmosphere to obtain a sintered body. Thereafter, the sintered body is subjected to grinding or polishing as necessary to obtain a body member 1 of an arbitrary shape having a surface 1a, a back surface 1b, and a side surface 1c. The surface 1a, the back surface 1b, and the side surface 1c of the body member 1 are processed by grinding or polishing so as to have a desired arithmetic mean roughness Ra, and non-through holes 8 are formed in the body member 1. The plate-like member 11 having the through holes 12 may be manufactured by the same manufacturing method as the body member 1 described above.

[0038] Next, the obtained main body member 1 and plate-like member 11 are fastened and fixed, respectively, using fastening members 13. At this time, a metal plate with a thickness corresponding to the distance of gap 14 is inserted between adjacent main body members 1, fastened, and then the metal plate is removed to obtain mirror 10. Next, surface 1a of main body member 1 is covered with a reflective member made of aluminum, silver, gold, a dielectric multilayer film, or the like. The reflective member may be formed before fastening main body member 1, but if it is formed after fastening, the reflective member will not come into contact with and peel off when the metal plate for gap control is inserted or removed.

[0039] The present disclosure is not limited to the above-described embodiment, and various modifications and improvements are possible without departing from the gist of the present disclosure. EXAMPLES

[0040] Using the above method, the thermal expansion coefficient is 0.02 × 10 -6A mirror 10 having a diameter of 300 mm and a gap 14 of 0.15 mm was manufactured using six main body members 1 as shown in Fig. 1 and Fig. 2 from cordierite ceramics having a temperature of 100 ° C (@ 22 ° C). A temperature cycle test and a vibration test were performed in succession, and the shape of the reflecting surface of the mirror 10 before and after the test was measured by using a laser interferometer to focus the reflected light from the mirror 10 on a light receiving part, and it was recognized as a one-piece mirror 10 without a gap 14. The measurement wavelength was 633 nm, and the resolution was 0.36 mm. The temperature cycle test was performed for 10 cycles from 70 ° to -40 ° C, and the vibration test was performed using a random wave vibration tester with a vibration frequency of 10 to 2000 Hz and an acceleration of 10 G (effective value). These tests were performed assuming the environment at the time of launching an artificial satellite. In the comparative example in which there was no gap 14 (the main body members 1 were in contact with each other), the warping of the reflective surface (the sum of the distances from the least squares plane to the highest and lowest points) changed from 0.22 μm to 7.12 μm before and after the test, whereas in the example, the warping of the reflective surface only changed from 0.15 μm to 1.27 μm before and after the test. [Explanation of symbols]

[0041] 1: Main body material 1a: surface 1b: Back side 1c: Side 2: Recess 3: Rib section 3a: 1st part 3b:Second part 3c: 3rd part 8: Non-through hole 10: Mirror 11: Fixed member (plate-shaped member) 12:Through hole 13: Fastening member 14: Gap

Claims

1. A plurality of main body members each having a surface on which a reflective member is arranged, a back surface, and a side surface connecting the surface and the back surface, the back surface having a recess and a rib portion surrounding the recess to form the side surface; a fixing member disposed on the back surface side of the main body member and fixing the rib portions to each other; A mirror comprising: The rib portion has a first portion adjacent to another of the body members adjacent thereto, and back surfaces of the first portions are fixed to each other by the fixing member, Each opposing surface of the adjacent first portions does not have a fixing surface of the fixing member, The first portions are adjacent to each other in a non-contact manner via a gap. mirror.

2. A mirror as described in claim 1, wherein the arithmetic mean roughness Ra of the rear surface of the first portion is 0.04 μm or less.

3. The outer diameter is circular or polygonal, The body member and the fixing member have a thermal expansion coefficient of ±10×10 －６ 3. The mirror according to claim 1, wherein the mirror is made of a low thermal expansion ceramic having a thermal expansion coefficient of 1 / 1000 or less and the gap width is 1 / 800 or less of an outer dimension of the mirror (a diameter in the case of a circle, or a maximum width in the case of a polygon).

4. 4. The mirror according to claim 3, wherein the gap is equal to or smaller than 1 / 1000 of an outer dimension of the mirror.

5. 5. The mirror according to claim 4, wherein the gap is equal to or greater than 1 / 10,000 of an outer dimension of the mirror.

6. 6. The mirror according to claim 3, wherein the body member and the fixing member are made of cordierite ceramics.

7. The mirror according to claim 1 , wherein the fixing member is a plate-like member having a thickness thinner than the first portion in a thickness direction of the mirror.

8. The mirror according to claim 1 , wherein the rear surface of the first portion and the fixing member are fastened in a thickness direction of the mirror by a fastening member.

9. 9. The mirror according to claim 1, wherein the rib portion forming the side surface has at least one of a second portion forming an outer shape of the mirror and a third portion forming an inner shape of the mirror.

10. 10. The mirror according to claim 1, wherein the surface and the side surface of the first portion have an arithmetic mean roughness Ra of less than 0.2 μm.

11. The mirror according to claim 10 , wherein the arithmetic mean roughness Ra of the side surface of the first portion is smaller than the arithmetic mean roughness Ra of the surface.

12. The mirror according to claim 9 , wherein the side surfaces of the second portion and the third portion have an arithmetic mean roughness Ra of 0.2 μm or more.

13. A telescope comprising the mirror according to any one of claims 1 to 12.

14. Further comprising an image sensor, 14. The telescope of claim 13, wherein the gap spacing is less than or equal to the resolution of the imaging element associated with the telescope.

Images