Optical system and optical apparatus

Abstract

To provide an optical system in which the shape accuracy of a reflection surface is high and the change of optical characteristics is small even when temperature changes.SOLUTION: A slice mirror having a first surface including a first reflection region that reflects a part of the light flux in a first direction, a second surface including a second reflection region that reflects another part of the light flux in a second direction different from the first direction, and a third surface that connects the first surface and the second surface, the slice mirror is disposed such that a region of the first surface closer to the second surface than the first reflection region is hidden behind a portion defined by the second surface and the third surface and is not irradiated with a light flux incident from a predetermined direction, and the first reflection region and the second reflection region are irradiated with the light flux incident from the predetermined direction.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present invention relates to an optical system, an optical device, and the like used in the field of astronomical observation and the like. [Background technology]

[0002] In the field of astronomy, a technique called full-field spectroscopy is known, which allows simultaneous observation of two-dimensional spatial information and spectral information. Microlens array, fiber bundle, and image slicer types are known as optical systems used to achieve full-field spectroscopy.

[0003] Although the image slicer type has a more complex optical system, it is known to have little loss of spatial information and high spatial resolution even with a narrow field of view. In the image slicer type, a surface spectroscopic system is constructed by combining a slice mirror, a pupil mirror, a slit mirror, etc. The slice mirror is a mirror that divides the focal plane image of the telescope into multiple elongated images. The pupil mirror is a mirror that rearranges the images divided by the slice mirror in one dimension. The slit mirror is a mirror that emits the light image rearranged by the pupil mirror in a slit shape toward the spectrograph.

[0004] Patent Document 1 discloses a slice mirror configured by fastening a plurality of plane mirrors having elongated mirror surfaces to a fixing member using bolts.

[0005] Patent Document 2 discloses an optical element that can be used for image slicer-type area spectroscopy, in which an intermediate layer having a thermal expansion coefficient intermediate between those of the substrate and the reflective layer is disposed between the substrate and the reflective layer. By providing the intermediate layer, damage, deformation, etc. of the optical element due to thermal influences are suppressed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 203975 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-21057 Summary of the Invention [Problem to be solved by the invention]

[0007] For example, in the field of astronomy, optical elements require high shape precision to achieve high-precision observations. On the other hand, when observations are conducted in outer space, mountainous regions, deserts, etc., optical elements may be placed in environmental temperatures that differ from the temperature at which they were manufactured (typically room temperature). Furthermore, when the observation wavelength includes the infrared region, infrared light emitted by the optical element itself as a blackbody can become observation noise, so optical elements are cooled to temperatures lower than room temperature.

[0008] Although the slice mirror described in Patent Document 1 has the advantage of being relatively easy to assemble, as mentioned above, if it is placed in a temperature environment different from that at the time of manufacture, it is difficult to maintain the position, posture, and shape of the fastened plane mirror with high precision.

[0009] The optical element described in Patent Document 2 includes an intermediate layer whose thermal expansion coefficient is intermediate between that of the substrate and the reflective layer, thereby suppressing damage, deformation, etc. of the optical element to a certain extent even when the temperature changes. In Patent Document 2, the intermediate layer is formed on the substrate by plating or the like, and then the surface of the intermediate layer is cut and shaped with a diamond tool, and the reflective layer is formed on the shaped intermediate layer. However, when shaping the intermediate layer, there are some areas that are difficult to shape sufficiently due to limitations in the range of motion of the cutting tool, etc. If irregular areas remain on the surface of the intermediate layer, the shape accuracy of the reflective layer formed in those areas will be reduced. Furthermore, in areas where the underlying intermediate layer is irregular, the surface shape of the reflective layer tends to change locally when the temperature changes.

[0010] Therefore, there was a demand for an optical system with high accuracy in the shape of the reflecting surface and small changes in optical characteristics even when the temperature changes. [Means for solving the problem]

[0011] A first aspect of the present invention is an optical system that divides an incident light beam, comprising a slice mirror having a first surface including a first reflective area that reflects a portion of the light beam in a first direction, a second surface including a second reflective area that reflects another portion of the light beam in a second direction different from the first direction, and a third surface that connects the first surface and the second surface, wherein the slice mirror is arranged such that an area on the first surface that is closer to the second surface than the first reflective area is hidden in the shadow of the portion defined by the second surface and the third surface and is not illuminated by the light beam incident from a predetermined direction, and the first reflective area and the second reflective area are illuminated by the light beam incident from the predetermined direction. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an optical system in which the shape accuracy of the reflecting surface is high and the change in optical characteristics is small even when the temperature changes. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating the overall configuration of an optical device according to a first embodiment. [Figure 2] 10(a) is a schematic perspective view showing the appearance of a slice mirror according to embodiment 2. (b) is a view of the normal line NL projected onto the ZX plane. (c) is a view of the normal line NL projected onto the ZY plane. [Figure 3] FIG. 2(b) is a partial cross-sectional view of the slice mirror taken along line A1-A1 in FIG. 2(a). [Figure 4] 10A and 10B are diagrams for explaining an area RR illuminated by incident light and an area NOP not illuminated by incident light. [Figure 5] FIG. 4 is a diagram for explaining reflected light reflected in a region RR. [Figure 6] Graph showing how much the surface shape of surface P changed when the slice mirror was cooled from room temperature to minus 196°C. [Figure 7]10(a) is a schematic perspective view showing the appearance of a slice mirror according to embodiment 3. (b) is a view of the normal line NL projected onto the ZX plane. (c) is a view of the normal line NL projected onto the ZY plane. [Figure 8] FIG. 7( a ) is a partial cross-sectional view of the slice mirror taken along line A3-A3 in FIG. 7( a ). [Figure 9] (a) A schematic perspective view showing the appearance of a slice mirror according to embodiment 4. (b) A plan view of the surface P2. (c) A plan view distinguishing between the region RR2 and the region NOP2 (non-optical region) that is shaded by the eaves and is not irradiated with incident light. [Figure 10] (a) A schematic perspective view showing the appearance of a slice mirror according to embodiment 5. (b) A plan view of the surface P2. (c) A plan view distinguishing between the region RR2 and the region NOP2 (non-optical region) that is shaded by the eaves and is not irradiated with incident light. [Figure 11] 2A to 2C are diagrams for explaining the internal structure and manufacturing method of a slice mirror. [Figure 12] 1A is a schematic perspective view showing the appearance of the slice mirror according to embodiment 1. FIG. 1B is a view of the normal line NL projected onto the ZX plane. FIG. 1C is a view of the normal line NL projected onto the ZY plane. [Figure 13] 12(a) is a partial cross-sectional view of the slice mirror taken along line B1-B1 in FIG. 12(a), illustrating a region RR illuminated by incident light and a region NOP not illuminated by incident light. [Figure 14] FIG. 4 is a diagram for explaining reflected light reflected in a region RR. DETAILED DESCRIPTION OF THE INVENTION

[0014] An optical system, an optical element, an optical apparatus, etc. according to an embodiment of the present invention will be described with reference to the drawings. The embodiments shown below are merely examples, and those skilled in the art can appropriately modify and implement the detailed configurations, for example, without departing from the spirit and scope of the present invention.

[0015] In the drawings referred to in the following description of the embodiments, elements denoted by the same reference numerals have the same functions unless otherwise specified. When a plurality of identical elements are arranged in a drawing, the reference numerals and their descriptions may be omitted.

[0016] Furthermore, the drawings may be represented schematically for the convenience of illustration and explanation, and the shape, size, arrangement, etc. of the elements depicted in the drawings may not necessarily be strictly identical to the actual objects.

[0017] In the following description, for example, when "X plus direction" is written, it refers to the same direction as the X axis arrow in the coordinate system shown, and when "X minus direction" is written, it refers to the direction 180 degrees opposite to the direction of the X axis arrow in the coordinate system shown. Also, when simply written as "X direction," it refers to the direction parallel to the X axis, regardless of whether it is different from the direction of the X axis arrow in the drawings. The same applies to directions other than X.

[0018] [Embodiment 1] [Overall configuration of optical equipment] The overall configuration of an optical system (optical device) according to embodiment 1 will be described with reference to Fig. 1. An image slicer-type area spectrometer 21 as an optical device includes an entrance slit 24, a slice mirror 1, a flat mirror array 26, a curved mirror array 27, an exit slit 28, and a light-receiving sensor 29. Area spectrometer 21 is preferably used for astronomical observations, but can also be used for various purposes including consumer and industrial use.

[0019] When used for astronomical observations, incident light 23 (image, light beam) enters field spectrometer 21 from a telescope (not shown) through entrance slit 24, and travels in the negative Z direction (a predetermined direction) to reach slice mirror 1. The telescope's focal plane image is divided into multiple partial images by slice mirror 1, and each partial image (divided image, divided light beam) is reflected in a different direction. Slice mirror 1 has multiple reflecting surfaces, and the telescope's focal plane image is divided into multiple partial images and reflected in different directions. However, for ease of illustration, FIG. 1 shows three reflected light rays: reflected light 25-1, reflected light 25-2, and reflected light 25-3.

[0020] The reflected light rays corresponding to each partial image are reflected by the plane mirrors that make up the plane mirror array 26, and the optical path is bent. By arranging the plane mirror array 26, it is possible to reduce the optical path space, thereby making it possible to make the size of the spectroscopic device compact.

[0021] The light reflected by the plane mirror array 26 is reflected by each optical surface of the curved mirror array 27 which has a light-condensing effect, passes through an exit slit 28 and is guided to a light-receiving sensor 29 .

[0022] It should be noted that a pupil mirror and a slit mirror may be arranged instead of the plane mirror array 26, the curved mirror array 27, and the exit slit 28. The pupil mirror is a mirror for rearranging the image split by the slice mirror one-dimensionally. The slit mirror is a mirror for emitting the optical image rearranged by the pupil mirror in a slit shape toward the light receiving sensor.

[0023] In order to reduce observation noise, the area spectrometer 21 of this embodiment is configured to be cooled by a cooling device 22. As the cooling device 22, a device using liquid nitrogen, a device using liquid helium, or another device can be used as appropriate depending on the desired cooling temperature.

[0024] For example, a semiconductor sensor is preferably used for the light receiving sensor 29, and in order to reduce dark current, which is a noise source, it is cooled by a cooling device 22. The optimum temperature for operation varies depending on the observation wavelength and the type of light receiving sensor, but it is desirable to cool it to 30[K] to 80[K] when observing near-infrared light, and to 6[K] to 10[K] when observing mid-infrared light, for example.

[0025] Furthermore, if the image to be observed contains light in the infrared region with a wavelength of, for example, 2 μm or more, infrared radiation emitted from various optical elements such as slice mirror 1 and structures such as the housing of surface spectrometer 21 can be a noise source, and therefore these are cooled by cooling device 22. For example, slice mirror 1 is cooled to 100 K or less when observing near-infrared light, and to 30 K or less when observing mid-infrared light. Furthermore, cooling to around 4 K may be desirable in some cases.

[0026] [Slice mirror configuration] In the optical system and optical device according to the first embodiment, a slice mirror 61, which will be described below, is implemented as the slice mirror 1 shown in Fig. 1. Fig. 12(a) is a schematic perspective view showing the appearance of the slice mirror 61. For convenience of illustration, a form having three reflective surfaces is shown, but the slice mirror 61 can have a greater number of reflective surfaces.

[0027] Slice mirror 61 has surfaces P1, P2, and P3 arranged at positions irradiated with incident light 23 entering through entrance slit 24 (FIG. 1). Surfaces P1 and P2 are connected by connecting surface CP12, and surfaces P2 and P3 are connected by connecting surface CP23. In the following description, when mounted in the optical device shown in FIG. 1, the portion defined by connecting surface CP12 and surface P2 and protruding in the minus X direction, and the portion defined by connecting surface CP23 and surface P3 and protruding in the minus X direction may be referred to as eaves portions.

[0028] As will be described later, each of surfaces P1, P2, and P3 has a reflective area (optical area) that reflects incident light 23 incident along the negative Z direction, and a non-optical area that is hidden in the shadow of the eaves and is not irradiated with incident light 23 and does not function as a reflective area. In Fig. 12(a), the normal line passing through the center of gravity of the reflective area (optical area) of surface P1 and perpendicular to surface P1 is shown as NL1, and the normal line passing through the center of gravity of the reflective area (optical area) of surface P2 and perpendicular to surface P2 is shown as NL2. Similarly, the normal line passing through the center of gravity of the reflective area (optical area) of surface P3 and perpendicular to surface P3 is shown as NL3.

[0029] Surfaces P1, P2, and P3 each divide the telescope's focal plane image into partial images and reflect them in different directions, so NL1, NL2, and NL3 face in different directions. That is, NL1, NL2, and NL3 are not parallel to one another. As shown in Figure 12(b), if the angle between the normal NL and the X axis when projected onto the ZX plane is θX, and as shown in Figure 12(c), the angle between the normal NL and the Y axis when projected onto the ZY plane is θY, then NL1 to NL3 have different θX values ​​and different θY values.

[0030] Fig. 13 is a partial cross-sectional view of slice mirror 61 taken along line B1-B1 in Fig. 12(a). Fig. 13 is a schematic diagram illustrating that slice mirror 61 is arranged so that when incident light 23 enters slice mirror 61 along the minus Z direction, a region RR is irradiated by incident light 23 and a region NOP is not irradiated.

[0031] 13, the incident light 23 is irradiated onto the region RR1 on the surface P1, the region RR2 on the surface P2, and the region RR3 on the surface P3. On the other hand, the region NOP1 on the surface P1 and the region NOP2 on the surface P2 are hidden by the eaves protruding in the minus X direction, and are therefore not irradiated with the incident light 23 incident along the minus Z direction. In other words, the regions RR1, RR2, and RR3 function as reflective regions (optical regions) that reflect the incident light 23, while the regions NOP1 and NOP2 are non-optical regions that do not function as reflective regions because they are not irradiated with the incident light 23.

[0032] 14 shows reflected light 25-1, which is incident light 23 that has been incident on region RR1 of surface P1 and reflected therefrom; reflected light 25-2, which is incident light 23 that has been incident on region RR2 of surface P2 and reflected therefrom; and reflected light 25-3, which is incident light 23 that has been incident on region RR3 of surface P3 and reflected therefrom. As described with reference to FIGS. 12(a) to 12(c), because surfaces P1 to P3 are not parallel to one another, incident light 23 is split and reflected, traveling in different directions. That is, reflected light 25-1, reflected light 25-2, and reflected light 25-3 are reflected toward individual flat mirrors that make up the flat mirror array 26 (FIG. 1). Note that the optical axes of reflected light 25-1 to reflected light 25-3 are not parallel to one another whether projected onto the XZ plane or the YZ plane.

[0033] [Manufacturing method of slice mirror] Next, the internal structure and manufacturing method of slice mirror 61, which is an optical element, will be described with reference to FIGS. 13 and 14. The substrate SUB, which is the base of slice mirror 61, can be made of an alloy material with a low thermal expansion coefficient, such as Invar, which has a thermal expansion coefficient of 0.03 ppm at -196°C. In addition to Invar, the substrate SUB can be made of any material selected from a group of low thermal expansion coefficient materials, such as pre-hardened steel obtained by heat-treating martensitic stainless steel SUS420J2, quartz, glass, and ceramics. Specific examples include martensitic stainless steel STAVAX (registered trademark), and optical glasses BK7, ULE (registered trademark), ZERODUR (registered trademark), and Clearceram (registered trademark).

[0034] For example, the substrate SUB of slice mirror 61 is fabricated from bulk Invar material using machining methods such as cutting or wire electric discharge machining. It is desirable to machine the flatness and orthogonality with high precision for the portions used as positioning references when installing in surface spectrometer 21, such as corners that serve as contact references.

[0035] Next, a metal coating 7 is formed on at least the portions that will become surfaces P1 to P3. The metal coating 7 is preferably made of a material that can be easily mirror-finished after deposition, and for example, an electrolytic plating coating containing copper as its main component can be used. Specifically, a dense layered coating can be formed by copper sulfate plating, which is a wet process. The metal coating 7 is formed on at least the portions that will become surfaces P1 to P3, but in order to ensure adhesion to the base material SUB and shape stability, it is desirable that a continuous coating also be formed on connecting surfaces CP12 and CP23.

[0036] The metal coating 7 is formed to a thickness sufficient for mirror finishing. It is also formed to a sufficient thickness so that cracks and film peeling do not occur even when the slice mirror 61 is cooled by the cooling device 22 (FIG. 1). Specifically, it is formed to a thickness of, for example, 10 μm or more and 3000 μm or less, and preferably 50 μm or more and 300 μm or less.

[0037] Next, precision cutting is performed on the metal coating 7 to improve the flatness of the regions irradiated by the incident light 23, i.e., regions RR1 to RR3 of surfaces P1 to P3. For example, a diamond tool with a cutting edge is used to form a smooth mirror surface with a surface roughness Ra of approximately 1 nm in the portions that will become regions RR1 to RR3. Note that the portions not irradiated by the incident light 23, i.e., regions NOP1 and NOP2 and connecting surfaces CP12 and CP23, do not necessarily need to be mirror-finished. However, in order to stably mirror-finish regions RR1 to RR3 or to improve the adhesion of the reflective layer, which will be described next, these portions not irradiated by the incident light 23 may also be mirror-finished.

[0038] Next, the areas irradiated by the incident light 23, i.e., the surfaces of areas RR1 to RR3 on surfaces P1 to P3, are coated with a reflective film (not shown) having high reflectivity in the wavelength range to be observed. The thickness of the reflective film is appropriately set, for example, to 40 nm, so that it faithfully follows the mirror-polished underlying topography, sufficiently reflects the light to be observed, and is formed with a uniform thickness. The reflective film can be formed from, for example, a metal film such as aluminum or gold, or a dielectric multilayer film.

[0039] 13, a reflective film can be formed only on the surfaces of regions RR1 to RR3. Alternatively, a non-directional film formation method such as sputtering, vapor deposition, or CVD can be used to form a film not only on regions RR1 to RR3 but also on regions NOP1 and NOP2, connecting surface CP12, and connecting surface CP23. Since the incident light 23 is not irradiated onto these portions, they do not function as optical films. However, by forming these portions integrally with the reflective film formed on regions RR1 to RR3, the ability to prevent peeling of the reflective film due to temperature changes, for example, can be improved.

[0040] [Advantages of the slice mirror according to the embodiment] The advantages of mounting the slice mirror 61 according to this embodiment on the surface spectrometer 21 will now be described. During the process of manufacturing the slice mirror 61, when processing the surface of the region NOP, which is located near the intersection line where the surface P and the connecting surface CP intersect, the processing accuracy tends to be lower than that of the region RR due to reasons such as limited freedom of movement of the cutting tool blade. According to this embodiment, the slice mirror 61 is arranged so that the region RR, which has a high surface shape accuracy, is a reflective surface (optical surface), and the region NOP, which has a low shape accuracy, is a non-optical region. The surface spectrometer 21, which is mounted with the slice mirror 61 having a high-precision reflective surface, can exhibit high spectroscopic accuracy.

[0041] As described above, surface spectrometer 21 is configured to be coolable by cooling device 22. For example, when slice mirror 61 is cooled from room temperature to a temperature condition suitable for observing infrared light, the shapes of each part change due to contraction. The substrate constituting slice mirror 61, the metal film formed on the substrate, and the reflective film formed on the metal film all have different linear expansion coefficients, so when slice mirror 61 is cooled, the surface shape of surface P changes. On the surface of region RR of face P, even when temperature changes occur, the amount of deformation in the Z direction is small, maintaining a high level of flatness, and allowing the incident light 23 to be reflected in a predetermined direction. In contrast, on the surface of region NOP, the amount of deformation in the Z direction is large, causing the surface to tilt. Although the reason for this large amount of deformation in region NOP has not been clearly elucidated, it is thought that this is because stress caused by thermal deformation tends to concentrate near the line (valley line VL) where face P and connection face CP intersect.

[0042] If incident light were to be irradiated onto the region NOP having an inclined surface, it would be reflected in an unintended direction. However, the slice mirror 61 according to the embodiment is arranged (configured) so that the region NOP (regions NOP1 to NOP2) having an inclined surface is shaded by the eaves and is not irradiated with the incident light 23. This prevents the incident light 23 from being reflected in an unintended direction (i.e., a direction different from that of a predetermined plane mirror in the plane mirror array 26). That is, the slice mirror 61 according to the embodiment has the advantage that the reflective region maintains high shape accuracy even when the temperature changes, and changes in optical characteristics are small. An area spectroscopic device 21 including a slice mirror 61 that changes the optical path of reflected light little even when cooled can achieve high spectroscopic accuracy.

[0043] [Embodiment 2] In the optical system and optical device according to the second embodiment, the slice mirror 1 described below is implemented as the slice mirror 1 shown in Fig. 1. The slice mirror 1 according to this embodiment is characterized by the angle formed between the connection plane CP and the plane P, as will be described later.

[0044] [Slice mirror configuration] Next, we will explain the slice mirror 1, which is an optical element according to embodiment 2. Fig. 2(a) is a schematic perspective view showing the appearance of the slice mirror 1. For convenience of illustration, a form with three reflective surfaces is shown, but the slice mirror 1 can be provided with a greater number of reflective surfaces.

[0045] Slice mirror 1 has surfaces P1, P2, and P3 arranged at positions irradiated with incident light 23 entering through entrance slit 24 (FIG. 1). Surfaces P1 and P2 are connected by connecting surface CP12, and surfaces P2 and P3 are connected by connecting surface CP23. In the following description, the portion that includes connecting surface CP12 and protrudes in the minus X direction, and the portion that includes connecting surface CP23 and protrudes in the minus X direction may be referred to as eaves portions.

[0046] As will be described later, each of surfaces P1, P2, and P3 has a reflective area (optical area) that reflects incident light 23 incident along the negative Z direction, and a non-optical area that is not irradiated with incident light 23 and does not function as a reflective area. In Fig. 2(a), the normal line passing through the center of gravity of the reflective area (optical area) of surface P1 and perpendicular to surface P1 is indicated as NL1, and the normal line passing through the center of gravity of the reflective area (optical area) of surface P2 and perpendicular to surface P2 is indicated as NL2. Similarly, the normal line passing through the center of gravity of the reflective area (optical area) of surface P3 and perpendicular to surface P3 is indicated as NL3.

[0047] Surfaces P1, P2, and P3 each divide the telescope's focal plane image into partial images and reflect them in different directions, so NL1, NL2, and NL3 face in different directions. In other words, NL1, NL2, and NL3 are not parallel to each other. As shown in Figure 2(b), if the angle between the normal NL and the X axis when projected onto the ZX plane is θX, and as shown in Figure 2(c), the angle between the normal NL and the Y axis when projected onto the ZY plane is θY, then NL1 to NL3 have different θX values ​​and different θY values.

[0048] 3 shows a partial cross-sectional view of the slice mirror 1 taken along line A1-A1 in FIG. 2(a). The angle between plane P1 and connecting plane CP12 is θ1 on the outside of the slice mirror 1, and the angle between connecting plane CP12 and plane P2 is θ2 on the inside of the slice mirror 1. The angle between plane P2 and connecting plane CP23 is θ3 on the outside of the slice mirror 1, and the angle between connecting plane CP23 and plane P3 is θ4 on the inside of the slice mirror 1.

[0049] In the slice mirror 1 according to this embodiment, θ1, θ2, θ3, and θ4 are all acute angles less than 90 degrees (θ1<90°, θ2<90°, θ3<90°, θ4<90°). While FIG. 3 shows a cross section taken along line A1-A1 in FIG. 2(a), even in a cross section taken at another position, such as line A2-A2, θ1, θ2, θ3, and θ4 are all acute angles less than 90 degrees. Even if the slice mirror 1 has more than three surfaces at the position where the incident light 23 (FIG. 1) is irradiated, the angles between each surface and the connecting surface are similarly acute angles.

[0050] 4 is a schematic diagram for explaining that when incident light 23 is incident on the slice mirror 1 along the minus Z direction, a region RR illuminated by the incident light 23 and a region NOP not illuminated by the incident light 23 are generated. In FIG. 4, a partial cross section taken along line A1-A1 in FIG. 1 is shown at the top, and a partial cross section taken along line A2-A2 is shown at the bottom.

[0051] As explained with reference to Figure 3, θ1 to θ4 are configured as acute angles smaller than 90 degrees, so that the incident light 23 is irradiated onto region RR1 on surface P1, region RR2 on surface P2, and region RR3 on surface P3. On the other hand, region NOP1 on surface P1 and region NOP2 on surface P2 are in the shadow of the eaves protruding in the minus X direction, and are therefore not irradiated with the incident light 23 incident along the minus Z direction. In other words, region RR1, region RR2, and region RR3 function as reflective regions (optical regions) that reflect the incident light 23, while region NOP1 and region NOP2 are non-optical regions that do not function as reflective regions because they are not irradiated with the incident light 23.

[0052] As described with reference to Figures 2(a) to 2(c), the surfaces P1 to P3 are not parallel to one another, and therefore the widths of the regions NOP1 and NOP2 in the X direction vary depending on the cut surface, as shown in Figure 4. That is, the shapes of the regions NOP1 and NOP2 as non-optical regions each have a width that varies in the short direction along the long direction.

[0053] 5 shows reflected light 25-1, which is incident light 23 that has been incident on region RR1 of surface P1 and reflected therefrom; reflected light 25-2, which is incident light 23 that has been incident on region RR2 of surface P2 and reflected therefrom; and reflected light 25-3, which is incident light 23 that has been incident on region RR3 of surface P3 and reflected therefrom. As described with reference to FIGS. 2(a) to 2(c), because surfaces P1 to P3 are not parallel to one another, incident light 23 is split and reflected, traveling in different directions. That is, reflected light 25-1, reflected light 25-2, and reflected light 25-3 are reflected toward individual flat mirrors that make up the flat mirror array 26 (FIG. 1). Note that the optical axes of reflected light 25-1 to reflected light 25-3 are not parallel to one another when projected onto either the XZ plane or the YZ plane.

[0054] [Manufacturing method of slice mirror] Next, with reference to FIG. 11 , the internal structure and manufacturing method of the slice mirror 1, which is an optical element, will be described. The substrate SUB, which is the base of the slice mirror 1, can be made of an alloy material with a low thermal expansion coefficient, such as Invar, which has a thermal expansion coefficient of −0.03 ppm at −196°C. In addition to Invar, the substrate SUB can be made of any material selected from a group of low thermal expansion coefficient materials, such as pre-hardened steel obtained by heat-treating martensitic stainless steel SUS420J2, quartz, glass, and ceramics. Specific examples include martensitic stainless steel STAVAX (registered trademark), and optical glasses such as BK7, ULE (registered trademark), ZERODUR (registered trademark), and Clearceram (registered trademark).

[0055] For example, the substrate SUB of the slice mirror 1 is fabricated from a bulk Invar material using a machining method such as cutting or wire electric discharge machining. It is desirable to machine the flatness and orthogonality with high precision for the portions used as positioning references when installing the surface spectrometer 21, such as the corners that serve as contact references.

[0056] Next, a metal coating 7 is formed on at least the portions that will become surfaces P1 to P3. The metal coating 7 is preferably made of a material that can be easily mirror-finished after deposition, and for example, an electrolytic plating coating containing copper as its main component can be used. Specifically, a dense layered coating can be formed by copper sulfate plating, which is a wet process. The metal coating 7 is formed on at least the portions that will become surfaces P1 to P3, but in order to ensure adhesion to the base material SUB and shape stability, it is desirable that a continuous coating also be formed on connecting surfaces CP12 and CP23.

[0057] The metal coating 7 is formed to a thickness sufficient for mirror finishing. It is also formed to a sufficient thickness so that cracks and film peeling do not occur even when the slice mirror 1 is cooled by the cooling device 22 (FIG. 1). Specifically, it is formed to a thickness of, for example, 10 μm or more and 3000 μm or less, and preferably 50 μm or more and 300 μm or less.

[0058] Next, precision cutting is performed on the metal coating 7 to improve the flatness of the regions irradiated by the incident light 23, i.e., regions RR1 to RR3 of surfaces P1 to P3. For example, a diamond tool with a cutting edge is used to form a smooth mirror surface with a surface roughness Ra of approximately 1 nm in the portions that will become regions RR1 to RR3. Note that the portions not irradiated by the incident light 23, i.e., regions NOP1 and NOP2 and connecting surfaces CP12 and CP23, do not necessarily need to be mirror-finished. However, in order to stably mirror-finish regions RR1 to RR3 or to improve the adhesion of the reflective layer, which will be described next, these portions not irradiated by the incident light 23 may also be mirror-finished.

[0059] Next, the areas irradiated by the incident light 23, i.e., the surfaces of areas RR1 to RR3 on surfaces P1 to P3, are coated with a reflective film (not shown) having high reflectivity in the wavelength range to be observed. The thickness of the reflective film is appropriately set, for example, to 40 nm, so that it faithfully follows the mirror-polished underlying topography, sufficiently reflects the light to be observed, and is formed with a uniform thickness. The reflective film can be formed from, for example, a metal film such as aluminum, gold, or silver, or a dielectric multilayer film.

[0060] By using a film formation method such as directional vapor deposition or directional sputtering, in which a material beam is emitted from the same direction as the incident light 23 shown in Figure 4, a reflective film can be formed only on the surfaces of regions RR1 to RR3. Alternatively, a film formation method such as non-directional sputtering, vapor deposition, or CVD may be used to form a film not only on regions RR1 to RR3 but also on regions NOP1 and NOP2, connecting surface CP12, and connecting surface CP23. Since the incident light 23 is not irradiated onto these portions, they do not function as optical films. However, by forming these portions integrally with the reflective film formed on regions RR1 to RR3, it is possible to improve the ability to prevent peeling of the reflective film due to temperature changes, for example.

[0061] [Advantages of the slice mirror according to the embodiment] The advantages of mounting the slice mirror 1 according to this embodiment on the surface spectrometer 21 will now be described. During the process of manufacturing the slice mirror 1, when processing the surface of the region NOP, which is located near the intersection line where the surface P and the connecting surface CP intersect, the processing accuracy tends to be lower than that of the region RR due to reasons such as limited freedom of movement of the cutting tool's cutting edge. According to this embodiment, the region RR, which has a high surface shape accuracy, is configured as a reflective surface (optical surface), and the region NOP, which has a low shape accuracy, is configured as a non-optical region. The surface spectrometer 21 mounted with the slice mirror 1 having a high-precision reflective surface can exhibit high spectroscopic accuracy.

[0062] As mentioned above, surface spectrometer 21 is configured to be coolable by cooling device 22. For example, when slice mirror 1 is cooled from room temperature to a temperature condition suitable for observing infrared light, the shapes of each part change due to contraction. The substrate constituting slice mirror 1, the metal film formed on the substrate, and the reflective film formed on the metal film all have different linear expansion coefficients, so when slice mirror 1 is cooled, the surface shape of surface P changes.

[0063] Fig. 6 is a graph showing how much the surface shape changed at each position on surface P when slice mirror 1 was cooled from room temperature to minus 196°C by cooling device 22 using liquid nitrogen. The horizontal axis of Fig. 6 indicates the position in the left-right direction (X direction) when surface P of slice mirror 1 is viewed from the same direction as Fig. 4, and the vertical axis of Fig. 6 indicates the amount of deformation of surface P in the traveling direction of incident light 23 (Z direction).

[0064] The specifications of the slice mirror on which the measurement results shown in Figure 6 were observed are as follows: The slice mirror's planar external dimensions are 29 mm × 35.5 mm, and its maximum height in the Z direction is 40 mm. It has 29 surfaces P, and the width of the region RR of each surface P in the X direction is 1 mm. Adjacent surfaces P are offset by 0.2 mm in the Z direction. The substrate SUB is an Invar material with a thermal expansion coefficient of -0.03 ppm / K. Surfaces P and connecting surfaces CP are coated with a 0.05 mm-thick copper sulfate plating film with a thermal expansion coefficient of 17.7 ppm / K. The angles θ1, θ2, θ3, and θ4 described with reference to Figure 3 are all set to 45° (the 29 surfaces P have the same angle setting).

[0065] In region RR, which is irradiated by incident light 23 coming from the Z direction, the maximum deformation in the Z direction is about 70 nm, as shown in Figure 6, maintaining a high level of flatness and allowing the incident light 23 to be reflected in a predetermined direction. In contrast, in region NOP, the maximum deformation in the Z direction is about 210 nm, as shown in Figure 6, causing the surface to tilt. The reason for this large deformation in region NOP has not been clearly elucidated, but it is thought that this may be because stress caused by thermal deformation tends to concentrate near the line (valley line) where surface P and connection surface CP intersect.

[0066] If incident light were to be irradiated onto the inclined surface region NOP, it would be reflected in an unintended direction. However, in the slice mirror 1 according to the embodiment, the inclined surface region NOP (regions NOP1 to NOP2) is shaded by the eaves and is not irradiated with the incident light 23. This prevents the incident light 23 from being reflected in an unintended direction (i.e., a direction different from that of a predetermined plane mirror in the plane mirror array 26). That is, the slice mirror 1 according to the embodiment has the advantage that the reflective region maintains high shape accuracy even when the temperature changes, and changes in optical characteristics are small. An area spectroscopic device 21 equipped with a slice mirror 1 that changes the optical path of reflected light little even when cooled can achieve high spectroscopic accuracy.

[0067] [Embodiment 3] In the slice mirrors 1 according to the first and second embodiments, the region RR functioning as a reflective surface is configured as a flat surface, but the embodiments of the present invention are not limited to this example. As the third embodiment, an example of a slice mirror in which the region RR functioning as a reflective surface is configured as a curved surface is shown. In the optical system and optical device according to the third embodiment, a slice mirror 31, which will be described below, is implemented as the slice mirror 1 shown in FIG. 1. The description of matters similar to those in the first and second embodiments will be simplified or omitted.

[0068] [Slice mirror configuration] A slice mirror 31, which is an optical element according to embodiment 3, will now be described. Fig. 7(a) is a schematic perspective view showing the appearance of slice mirror 31. For convenience of illustration, a form having three reflective surfaces is shown, but slice mirror 31 can have a greater number of reflective surfaces.

[0069] Slice mirror 31 has surfaces P1, P2, and P3 arranged at positions irradiated with incident light 23 entering through entrance slit 24 (FIG. 1). Surfaces P1 and P2 are connected by connecting surface CP12, and surfaces P2 and P3 are connected by connecting surface CP23. In the following description, the portion that includes connecting surface CP12 and protrudes in the minus X direction, and the portion that includes connecting surface CP23 and protrudes in the minus X direction may be referred to as eaves portions.

[0070] As in the first embodiment, each of surfaces P1, P2, and P3 includes a reflective area (optical area) that reflects incident light 23 incident along the negative Z direction, and a non-optical area that does not function as a reflective area because it is not irradiated with incident light 23. In Fig. 7(a), the normal line passing through the center of gravity of the reflective area (optical area) of surface P1 and perpendicular to surface P1 is indicated as NL1, and the normal line passing through the center of gravity of the reflective area (optical area) of surface P2 and perpendicular to surface P2 is indicated as NL2. Similarly, the normal line passing through the center of gravity of the reflective area (optical area) of surface P3 and perpendicular to surface P3 is indicated as NL3.

[0071] Surfaces P1, P2, and P3 divide the focal plane image of the telescope into partial images and reflect them in different directions, so NL1, NL2, and NL3 face in different directions. As shown in Figure 7(b), if the angle between the normal NL and the X axis when projected onto the ZX plane is θX, and as shown in Figure 7(c), the angle between the normal NL and the Y axis when projected onto the ZY plane is θY, then NL1 to NL3 have different θX values ​​and different θY values.

[0072] Furthermore, each of the surfaces P1, P2, and P3 has a curved (concave) shape in order to focus the focal plane image of the telescope, which has been divided into partial images, at predetermined positions different from each other. That is, the region RR (optical region) of each of the surfaces P1, P2, and P3 is configured with a curved shape so as to function as a concave mirror.

[0073] 8 shows a partial cross-sectional view of slice mirror 31 taken along line A3-A3 in FIG. 7(a). The angle between plane P1 and connecting plane CP12 is assumed to be θ1 on the outside of slice mirror 31, and the angle between connecting plane CP12 and plane P2 is assumed to be θ2 on the inside of slice mirror 31. The angle between plane P2 and connecting plane CP23 is assumed to be θ3 on the outside of slice mirror 31, and the angle between connecting plane CP23 and plane P3 is assumed to be θ4 on the inside of slice mirror 31.

[0074] In slice mirror 31 according to this embodiment, θ1, θ2, θ3, and θ4 are all acute angles less than 90 degrees (θ1<90°, θ2<90°, θ3<90°, θ4<90°). While Fig. 8 shows a cross section taken along line A3-A3 in Fig. 7(a), even in a cross section cut at another position, θ1, θ2, θ3, and θ4 are all acute angles less than 90 degrees. Even if slice mirror 31 has more than three surfaces at the position where incident light 23 (Fig. 1) is irradiated, the angles between each surface and the connecting surface are similarly acute angles.

[0075] In this embodiment, similarly to Embodiments 1 and 2, the region RR with high surface shape accuracy is configured as a reflective surface (optical surface), and the region NOP with low accuracy is configured as a non-optical region. Therefore, the surface spectroscopic device 21 equipped with the slice mirror 31 can exhibit high spectroscopic accuracy.

[0076] Furthermore, as in the first and second embodiments, the slice mirror 31 according to this embodiment has the advantage that the reflection area maintains high shape accuracy even when the temperature changes, and the change in optical properties is small. The surface spectroscopic device 21 equipped with the slice mirror 31, which changes the optical path of reflected light little even when cooled, can exhibit high spectroscopic accuracy.

[0077] [Embodiment 4] In the slice mirrors 1 according to the first and second embodiments, the shape of the surface P including the region RR functioning as a reflective surface is rectangular when viewed in a plan view from the direction of the incident light 23 (Z direction), but the embodiments of the present invention are not limited to this example. As the fourth embodiment, an example of a slice mirror will be shown in which the shape of the surface P including the region RR functioning as a reflective surface is trapezoidal when viewed in a plan view from the direction of the incident light (Z direction). In the optical system and optical device according to the fourth embodiment, a slice mirror 41, which will be described below, is implemented as the slice mirror 1 shown in FIG. 1. The description of matters similar to those in the first and second embodiments will be simplified or omitted.

[0078] [Slice mirror configuration] A slice mirror 41, which is an optical element according to embodiment 4, will now be described. Fig. 9(a) is a schematic perspective view showing the appearance of slice mirror 41. For convenience of illustration, a form having three reflective surfaces is shown, but slice mirror 41 may have a greater number of reflective surfaces.

[0079] Slice mirror 41 has surfaces P1, P2, and P3 arranged at positions irradiated with incident light 23 entering through entrance slit 24 (FIG. 1). Surfaces P1 and P2 are connected by connecting surface CP12, and surfaces P2 and P3 are connected by connecting surface CP23. In the following description, the portion including connecting surface CP12 and protruding in the minus X direction, and the portion including connecting surface CP23 and protruding in the minus X direction may be referred to as eaves portions.

[0080] As in embodiments 1 and 2, each of surfaces P1, P2, and P3 has a reflective area (optical area) that reflects incident light 23 incident along the negative Z direction, and a non-optical area that is not irradiated with incident light 23 and therefore does not function as a reflective area.

[0081] FIG. 9(b) shows a plan view of surface P2 viewed from the direction of incident light (Z direction). As shown, surface P2 has a trapezoidal shape. FIG. 9(c) shows a plan view of surface P2, distinguishing between region RR2, which functions as a reflective surface, and region NOP2 (non-optical region), which is shaded by the eaves and is not irradiated by incident light 23. Region RR2, which functions as a reflective surface, is rectangular, but it can be seen that the width of region NOP2 (non-optical region) in the short direction (X direction) changes along the long direction (Y direction) of surface P2. While FIGS. 9(b) and 9(c) illustrate surface P2, surfaces P1 and P3 are also configured in the same way.

[0082] In this embodiment, similarly to Embodiments 1 and 2, the region RR with high surface shape accuracy is configured as a reflective surface (optical surface), and the region NOP with low accuracy is configured as a non-optical region. Therefore, the surface spectroscopic device 21 equipped with the slice mirror 41 can exhibit high spectroscopic accuracy.

[0083] Furthermore, as in the first and second embodiments, the slice mirror 41 according to this embodiment has the advantage that the reflection area maintains high shape accuracy even when the temperature changes, and the change in optical characteristics is small. The surface spectroscopic device 21 equipped with the slice mirror 41, which changes the optical path of reflected light little even when cooled, can achieve high spectroscopic accuracy.

[0084] [Embodiment 5] As the fifth embodiment, an example of a slice mirror will be shown in which the shape of the surface P including the region RR that functions as a reflecting surface is hexagonal when viewed in plan from the direction of the incident light (Z direction). In the optical system and optical device according to the fifth embodiment, a slice mirror 51 described below is implemented as the slice mirror 1 shown in FIG. 1. Explanations of matters similar to those in the first and second embodiments will be simplified or omitted.

[0085] [Slice mirror configuration] A slice mirror 51, which is an optical element according to embodiment 5, will be described. Fig. 10(a) is a schematic perspective view showing the appearance of the slice mirror 51. For convenience of illustration, a form having three reflective surfaces is shown, but the slice mirror 51 may have a greater number of reflective surfaces.

[0086] Slice mirror 51 has surfaces P1, P2, and P3 arranged at positions irradiated with incident light 23 entering through entrance slit 24 (FIG. 1). Surfaces P1 and P2 are connected by connecting surface CP12, and surfaces P2 and P3 are connected by connecting surface CP23. In the following description, the portion that includes connecting surface CP12 and protrudes in the minus X direction, and the portion that includes connecting surface CP23 and protrudes in the minus X direction may be referred to as eaves portions.

[0087] As in embodiment 1, each of surfaces P1, P2, and P3 has a reflective area (optical area) that reflects incident light 23 incident along the negative Z direction, and a non-optical area that is not irradiated by incident light 23 and therefore does not function as a reflective area.

[0088] FIG. 10(b) shows a plan view of surface P2 viewed from the direction of incident light (Z direction). As shown, surface P2 has a hexagonal shape. FIG. 10(c) shows a plan view of surface P2, distinguishing between region RR2, which functions as a reflective surface, and region NOP2 (non-optical region), which is shaded by the eaves and not irradiated by incident light 23. Region RR2, which functions as a reflective surface, is rectangular, but it can be seen that the width of regions NOP2 (non-optical regions), located in two locations, varies in the short-side direction (X direction) along the long-side direction (Y direction) of surface P2. While FIGS. 10(b) and 10(c) illustrate surface P2, surfaces P1 and P3 are similarly configured.

[0089] In this embodiment, similarly to Embodiments 1 and 2, the region RR with high surface shape accuracy is configured as a reflective surface (optical surface), and the region NOP with low accuracy is configured as a non-optical region. Therefore, the surface spectroscopic device 21 equipped with the slice mirror 51 can exhibit high spectroscopic accuracy.

[0090] Furthermore, as in the first and second embodiments, the slice mirror 51 according to this embodiment has the advantage that the reflection area maintains high shape accuracy even when the temperature changes, and the change in optical properties is small. The surface spectroscopic device 21 equipped with the slice mirror 51, which changes the optical path of reflected light little even when cooled, can achieve high spectroscopic accuracy.

[0091] [Other embodiments] The present invention is not limited to the above-described embodiments, and many modifications are possible within the technical spirit of the present invention. For example, the above-described different embodiments and examples may be combined in whole or in part.

[0092] For example, the curved surface shape described in the third embodiment may be used for the reflecting surface of the slice mirror in the fourth or fifth embodiment.

[0093] In the example described with reference to Fig. 11, the base material SUB is coated with a metal coating 7 and then a reflective film (not shown) is formed thereon, but the configuration and manufacturing method are not limited to this example as long as the region RR provided on each surface P has high shape accuracy and reflective function. For example, the region RR may be formed by mirror-finishing the base material SUB itself without providing the metal coating 7 or reflective film. Alternatively, a reflective film may be formed directly on the base material SUB, or the region RR may be formed by mirror-finishing the metal coating 7 formed on the base material SUB without providing a reflective film.

[0094] The present invention is not limited to optical systems that use a cooling device to cool optical elements, but can be suitably applied to optical systems that are used in temperature environments lower than room temperature (for example, 293° C.).

[0095] This specification discloses at least the following: [Item 1] An optical system that splits an incident light beam, a slice mirror having a first surface including a first reflective area that reflects a part of the light beam in a first direction, a second surface including a second reflective area that reflects another part of the light beam in a second direction different from the first direction, and a third surface that connects the first surface and the second surface; The slice mirror is an area of ​​the first surface closer to the second surface than the first reflective area is hidden in the shadow of a portion defined by the second surface and the third surface and is not irradiated with the light beam incident from a predetermined direction; The first reflective area and the second reflective area are arranged so as to be irradiated by the light beam incident from the predetermined direction. An optical system characterized by: [Matter 2] a first non-optical area on the first surface of the slice mirror that is not irradiated with the light beam incident from the predetermined direction; the first non-optical region and the third surface form an acute angle on the outside of the optical element; the second reflective area and the third surface form an acute angle on the inside of the optical element; 2. The optical system described in item 1. [Matter 3] a normal to the first surface passing through the center of gravity of the first reflective area and a normal to the second surface passing through the center of gravity of the second reflective area are not parallel to each other; 3. The optical system according to item 1 or 2. [Matter 4] a first non-optical area on the first surface of the slice mirror that is not irradiated with the light beam incident from the predetermined direction; The width of the first non-optical area in the short side direction varies along the longitudinal direction of the first reflective area. 4. The optical system according to any one of items 1 to 3, characterized in that [Matter 5] Each of the first reflective area and the second reflective area is a flat surface. 5. The optical system according to any one of items 1 to 4. [Matter 6] Each of the first reflective area and the second reflective area is a concave surface. 5. The optical system according to any one of items 1 to 4. [Matter 7] Each of the first reflective area and the second reflective area is rectangular. 7. The optical system according to any one of items 1 to 6, [Matter 8] The first surface is trapezoidal. 8. The optical system according to any one of items 1 to 7, [Matter 9] The first surface is hexagonal. 8. The optical system according to any one of items 1 to 7, [Matter 10] a metal coating that covers a base is disposed on at least the first reflective area of ​​the first surface and at least the second reflective area of ​​the second surface; 10. The optical system according to any one of items 1 to 9. [Matter 11] A metal coating that covers the base is disposed on the first surface, the second surface, and the third surface. 11. The optical system according to any one of items 1 to 10. [Matter 12] a reflective film is disposed on at least the surface of the first reflective region of the first surface and on at least the surface of the second reflective region of the second surface; 12. The optical system according to any one of items 1 to 11. [Matter 13] the metal coating is disposed on at least the surface of the first reflection region of the first surface and on at least the surface of the second reflection region of the second surface, and 12. The optical system according to item 10 or 11. [Matter 14] a mirror-finished substrate is disposed on at least the surface of the first reflection region of the first surface and on at least the surface of the second reflection region of the second surface; 10. The optical system according to any one of items 1 to 9. [Matter 15] An optical system according to any one of items 1 to 14, a cooling device for cooling the slice mirror, An optical device characterized by: [Matter 16] An optical system according to any one of items 1 to 14, a plane mirror array that reflects the plurality of split light beams reflected by the slice mirror; a curved mirror array that reflects the light beam reflected by the flat mirror array toward an exit slit, An optical device characterized by: [Matter 17] An optical system according to any one of items 1 to 14, a pupil mirror that arranges the plurality of split light beams reflected by the slice mirror in one dimension; a slit mirror that outputs the light beam arranged by the pupil mirror in a slit shape toward a spectroscope, An optical device characterized by: [Matter 18] An optical system according to any one of items 1 to 14, a light-receiving sensor that receives the plurality of split light beams reflected by the slice mirror, An optical device characterized by: [Explanation of symbols]

[0096] 1···Slice mirror / 7···Metal coating / 21···Surface spectrometer / 22···Cooling device / 23···Incident light / 24···Inlet slit / 25-1, 25-2, 25-3···Reflected light / 26···Flat mirror array / 27···Curved mirror array / 28···Outlet slit / 29···Light receiving sensor / 31···Slice mirror / 41···Slice mirror / 51···Slice mirror / 61···Slice mirror / CP12, CP13···Connection surface / NL1, NL2, NL3···Normal line / NOP1, NOP2···Area not irradiated by incident light / P1, P2, P3···Surface / RR1, RR2, RR3···Area irradiated by incident light / SUB···Base material

Claims

1. An optical system that splits an incident light beam, a slice mirror having a first surface including a first reflective area that reflects a part of the light beam in a first direction, a second surface including a second reflective area that reflects another part of the light beam in a second direction different from the first direction, and a third surface that connects the first surface and the second surface, The slice mirror is an area of ​​the first surface closer to the second surface than the first reflective area is hidden in the shadow of a portion defined by the second surface and the third surface and is not irradiated with the light beam incident from a predetermined direction; The first reflective area and the second reflective area are arranged so as to be irradiated by the light beam incident from the predetermined direction. An optical system characterized by:

2. a first non-optical area on the first surface of the slice mirror that is not irradiated with the light beam incident from the predetermined direction; the first non-optical area and the third surface form an acute angle on the outside of the optical element; the second reflective area and the third surface form an acute angle on the inside of the optical element; 2. The optical system according to claim 1.

3. a normal to the first surface passing through the center of gravity of the first reflective area and a normal to the second surface passing through the center of gravity of the second reflective area are not parallel to each other; 2. The optical system according to claim 1.

4. a first non-optical area on the first surface of the slice mirror that is not irradiated with the light beam incident from the predetermined direction; The width of the first non-optical area in the short side direction varies along the longitudinal direction of the first reflective area.

2. The optical system according to claim 1.

5. Each of the first reflective area and the second reflective area is a flat surface.

5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

6. Each of the first reflective area and the second reflective area is a concave surface.

5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

7. Each of the first reflective area and the second reflective area is rectangular.

5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

8. The first surface is trapezoidal.

5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

9. The first surface is hexagonal.

5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

10. a metal coating that covers a base is disposed on at least the first reflection area of ​​the first surface and at least the second reflection area of ​​the second surface; 5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

11. a metal coating that covers the base is disposed on the first surface, the second surface, and the third surface; 5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

12. a reflective film is disposed on at least the surface of the first reflective region of the first surface and on at least the surface of the second reflective region of the second surface; 5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

13. the metal coating is disposed on at least the surface of the first reflection region of the first surface and on at least the surface of the second reflection region of the second surface, and The optical system according to claim 10 .

14. a mirror-finished substrate is disposed on at least the surface of the first reflection region of the first surface and on at least the surface of the second reflection region of the second surface; 5. The optical system according to claim 1, wherein the first and second lenses are arranged in a plane parallel to each other.

15. An optical system according to any one of claims 1 to 4; a cooling device for cooling the slice mirror, An optical device characterized by:

16. An optical system according to any one of claims 1 to 4; a plane mirror array that reflects the plurality of split light beams reflected by the slice mirror; a curved mirror array that reflects the light beam reflected by the flat mirror array toward an exit slit, An optical device characterized by:

17. An optical system according to any one of claims 1 to 4; a pupil mirror that arranges the plurality of split light beams reflected by the slice mirror in one dimension; a slit mirror that outputs the light beam arranged by the pupil mirror in a slit shape toward a spectroscope, An optical device characterized by:

18. An optical system according to any one of claims 1 to 4; a light-receiving sensor that receives the plurality of split light beams reflected by the slice mirror, An optical device characterized by:

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