Optical element, method for manufacturing optical element, and optical instrument

Abstract

To provide an accurate optical element.SOLUTION: An optical element comprises a base material, and an optical shape layer formed on the base material and having a plurality of optical shape surfaces. The thickness of the optical shape layer is 10 μm or more and 3000 μm or less. The optical element is provided with grooves. Side faces of the optical shape layer along the contours of the plurality of optical shape surfaces and side faces of the base material form side walls of the grooves.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present technology relates to an optical element, a method for manufacturing an optical element, and an optical device.

Background Art

[0002] Optical elements such as a mirror array are suitable, for example, for measuring light of a predetermined wavelength in a surface spectroscopy optical element and a surface spectroscopy apparatus in the field of astronomical observation. In a surface spectroscopy apparatus having a surface spectroscopy optical system, the optical element of the mirror array can be used in an image slicer type. Surface spectroscopy is known as an observation method in the field of astronomical observation, and it is possible to simultaneously perform spectral observation on two-dimensional spatial information acquired by a single exposure. One type of observation device is an image slicer type, and typical optical elements include, for example, a pupils mirror array and a slits mirror array.

[0003] In observations in the field of astronomical observation, for example, when an optical element is placed in a harsh natural environment such as outer space, a desert, or a mountainous area, or when the optical element is placed in an extremely low temperature environment in order to reduce the influence of the thermal radiation of the optical element on the observation, there are cases. If there is a large temperature difference between the manufacturing environment and the use environment of the optical element, due to the difference in the thermal expansion coefficients of the materials constituting the optical element, the optical element is thermally deformed so much that it is difficult to maintain the shape accuracy, and the optical performance deteriorates.

[0004] In order to solve such problems, Patent Document 1 proposes an optical element in which a plurality of optical functional surfaces are formed on a single base material by cutting, and an intermediate layer is provided between the base material and the reflective layer, and the intermediate layer has an intermediate thermal expansion coefficient between the base material and the reflective layer. This makes it possible to provide an optical element that can maintain the relative positional relationship of a plurality of optical functional surfaces with high precision, simultaneously achieve a high-quality surface roughness, and maintain the shape accuracy even under the thermal influence of an extreme environment.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When there is a large temperature difference between the manufacturing environment and the usage environment of an optical element, in order to prevent deterioration of the optical performance of the optical element for surface spectroscopy, it is necessary to maintain not only the relative position of the optical functional surfaces but also the shape accuracy of each optical functional surface. However, in the optical element described in Patent Document 1, since a plurality of optical functional surfaces are formed on the surface of the same optical shape layer, the shapes after thermal deformation are different depending on the locations where the optical functional surfaces are arranged.

[0007] When forming an optical element by cutting, correction processing taking into account the amount of thermal deformation in the usage environment is performed. At that time, if the shapes after thermal deformation are different for each optical functional surface, it is conceivable to calculate different correction values for each optical functional surface. However, since it takes a long time to form a plurality of optical functional surfaces, there is room for improvement. Also, even if there is a slit between the optical functional surfaces, since the optical functional surfaces are formed on the surface of the same optical shape layer, the shapes after thermal deformation are different depending on the locations where the optical functional surfaces are arranged. Therefore, it is desired to simultaneously achieve suppression of thermal deformation of the entire optical element with high precision and suppression of the shape differences between the plurality of optical functional surfaces when each of the plurality of optical functional surfaces is thermally deformed.

[0008] The present disclosure has been made in view of such points, and an object thereof is to provide an optical element with high precision.

Means for Solving the Problems

[0009] The present disclosure is An optical element comprising a base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein the thickness of the optical shape layer is 10 μm or more and 3000 μm or less, wherein the optical element is provided with a groove, and side surfaces of the optical shape layer and side surfaces of the base material along contours of the plurality of optical shape surfaces form side walls of the groove. Further, the present disclosure relates to an optical element comprising a base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein an absolute value of a ratio of a coefficient of thermal expansion of the optical shape layer to a coefficient of thermal expansion of the base material is 3.0 or more, wherein the optical element is provided with a groove, and side surfaces of the optical shape layer and side surfaces of the base material along contours of the plurality of optical shape surfaces form side walls of the groove. Further, the present disclosure relates to an optical element comprising an opaque base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein the coefficient of thermal expansion of the base material is smaller than the coefficient of thermal expansion of the optical shape layer, wherein the optical element is provided with a groove, and side surfaces of the optical shape layer and side surfaces of the base material along contours of the plurality of optical shape surfaces form side walls of the groove. Further, the present disclosure relates to a method for manufacturing an optical element, comprising: a film forming step of forming the film on the base material; a groove forming step of processing the base material and the film to form a groove; and an optical shape surface forming step of processing the film to form the optical shape surface. The method is characterized by including the above steps. Further, the present disclosure relates to an optical device having the above optical element. Further, the present disclosure relates to an optical device comprising the above optical element and a cooling device for cooling the above optical element below the freezing point.

Advantages of the Invention

[0010] According to the present disclosure, a high-precision optical element can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, embodiments of the optical element according to the present disclosure will be described by taking the application to an optical device as an example. However, the application of the optical element according to the present embodiment is not limited to optical devices. The embodiments and examples shown below are illustrative. For example, regarding the detailed configuration, those skilled in the art can appropriately modify and implement it without departing from the gist of the present disclosure. In the drawings referred to in the following description, unless otherwise specified, elements denoted by the same reference numerals have the same functions.

[0013] <First Embodiment> The first embodiment of the present disclosure relates to an optical element. The optical element of the present disclosure is an optical element including a substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein the thickness of the optical shape layer is 10 μm or more and 3000 μm or less, a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along contours of the plurality of optical shape surfaces form side walls of the groove. Further, the optical element of the present disclosure is an optical element including a substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein an absolute value of a ratio of a coefficient of thermal expansion of the optical shape layer to a coefficient of thermal expansion of the substrate is 3.0 or more, a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along contours of the plurality of optical shape surfaces form side walls of the groove. Further, the optical element of the present disclosure is an optical element including an opaque substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein the coefficient of thermal expansion of the substrate is smaller than that of the optical shape layer, a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along contours of the plurality of optical shape surfaces form side walls of the groove. Hereinafter, the overall outline and each item will be described.

[0014] An optical element having a plurality of optical shape surfaces will be described as an embodiment of the present disclosure. FIG. 1 is a diagram showing an example of the shape of the optical element. FIG. 2 is a diagram showing a cross section taken along line A-A of FIG. 1. In FIGS. 1 and 2, the optical element has a substrate 1, an optical shape layer 2, an optical shape surface 3, a groove 4, and a reflective layer 5.

[0015] As shown in Fig. 2(a), the optical element according to the present disclosure includes a substrate 1 and an optical shape layer 2 formed on the substrate 1 and having a plurality of optical shape surfaces 3. On the surface of at least one layer of the optical shape layer 2 laminated on the substrate 1 serving as the base of the element, the optical shape surfaces 3 are arranged. The optical shape surfaces 3 are flat or curved surfaces and have smooth mirror surfaces. Further, a plurality of the optical shape surfaces 3 are arranged in a plurality on the substrate 1, and the positional relationship and surface shape between the plurality of optical shape surfaces are formed with high precision in order to exhibit desired optical characteristics.

[0016] [Substrate] The material of the above-mentioned substrate is not limited, but in order to alleviate the deformation phenomenon due to the difference in the thermal expansion coefficients of the substrate 1 and the optical shape layer 2 in the case where the temperature difference between the manufacturing environment and the use environment of the above-mentioned problems is large, a material with a thermal expansion coefficient smaller than that of the optical shape layer 2 is selected for the substrate 1. Also, considering use in an extremely low temperature environment, a material generally called a low thermal expansion material may be selected.

[0017] In the optical element of the present disclosure, the thermal expansion coefficient of the substrate 1 is smaller than that of the optical shape layer 2. In the optical element of the present disclosure, the absolute value of the ratio of the thermal expansion coefficient of the optical shape layer 2 to the thermal expansion coefficient of the substrate 1 is 3.0 or more, preferably 50 or more, and more preferably 500 or more. Alternatively, from the viewpoint of suppressing the thermal shrinkage of the entire optical element as much as possible, the thermal expansion coefficient of the substrate 1 is preferably 0.21 ppm / K or less, and more preferably 0.05 ppm / K or less. In the optical element of the present disclosure, the thermal expansion coefficient of the optical shape layer 2 is preferably 10 ppm / K or more. In the present disclosure, the thermal expansion coefficient refers to the linear expansion coefficient (thermal expansion coefficient) at the temperature during use of the optical element. The temperature during the manufacture of the optical element is preferably room temperature, and the temperature during the use of the optical element is preferably liquid nitrogen temperature (77K).

[0018] By doing so, the optical element of the present disclosure can suppress thermal deformation of the optical element due to the difference in the thermal expansion coefficients between the base material 1 and the optical shape layer 2 when the temperature difference between the manufacturing environment and the use environment is large. In the present disclosure, the thermal expansion coefficient can be obtained, for example, by thermomechanical analysis.

[0019] The base material of the optical element of the present disclosure is opaque so that the light of the observation target does not reflect inside the base material. In the present disclosure, "opaque" means that the transmittance of the wavelength to be observed is less than 70%. That is, in the optical element of the present disclosure, it is preferable that the light transmittance of the base material 1 is less than 70% in the band of visible light and infrared light. In the present disclosure, the light transmittance can be measured, for example, with a spectrophotometer or the like.

[0020] For example, it is preferable that the base material 1 of the optical element of the present disclosure includes one or more selected from the group consisting of prehardened steel, low thermal expansion material, quartz, and glass, and it is more preferable that the base material 1 is any one of prehardened steel corresponding to SUS420J2, low thermal expansion material, quartz, and glass. Specifically, STAVAX (registered trademark), BK7, Invar, ULE (registered trademark), Zero-Dura, ClearCeram (registered trademark) are listed as candidate materials. In addition, examples of the base material 1 include alloys such as iron alloys, copper alloys, aluminum alloys, nickel alloys, and magnesium alloys. In the optical element of the present disclosure, it is preferable that the base material 1 includes an alloy. The alloy constituting the base material 1 can be selected according to required conditions such as low thermal expansion property, heat resistance, workability, corrosion resistance, light weight, rigidity, and economy. According to the present embodiment, by providing the groove 4, deformation of the optical element can be suppressed. From the viewpoint of low thermal expansion property, it is more preferable that the base material 1 includes Invar. By doing so, even in a temperature environment different from that during manufacturing, the base material 1 can suppress deformation due to thermal expansion and thermal contraction.

[0021] In the optical element of the present disclosure, it is preferable that the thickness of the portion of the base material overlapping the groove (the thickness from the bottom surface of the base material to the bottom surface of the groove measured from the bottom surface of the base material) is 30 mm or more and 60 mm or less. In the present disclosure, the thickness, film thickness, and size can be measured, for example, by photographing with a camera for dimensional measurement and image analysis, optical microscope observation of a cross-section or the like, or scanning electron microscope (SEM) observation.

[0022] [Optical shape layer] For the material used for the optical shape layer 2, it is preferable to select a material that is easy to process into an optical functional shape. In particular, due to the function of the surface spectroscopic optical element, it is important to form the relative positional relationship of the plurality of optical shape surfaces 3 with high precision and to form a smooth mirror surface so that the light of the observation object is not scattered more than necessary. Therefore, it is desirable to select a material with excellent mirror surface properties in cutting using a diamond tool.

[0023] In the optical element of the present disclosure, it is preferable that the optical shape layer 2 is a film mainly composed of Cu or Ni. For example, it is more preferable that the optical shape layer 2 is a plating film mainly composed of Cu or Ni with excellent mirror surface properties. Further, in order to alleviate the deformation phenomenon due to the difference in the thermal expansion coefficients of the base material 1 and the optical shape layer 2, it is preferable to select a material with a small difference in the thermal expansion coefficients between the base material 1 and the optical shape layer 2. Further, the optical shape layer 2 may be formed by laminating a plurality of materials. In that case, among the plurality of materials, it is preferable that the material of the layer directly contacting the base material 1 has the smallest difference from the thermal expansion coefficient of the base material 1.

[0024] The thickness of the optical shape layer 2 is particularly preferably, for example, 300 μm in order to suppress peeling and cracking of the optical shape surface due to thermal effects even in an extreme environment and to perform precise cutting. In the optical element of the present disclosure, the thickness of the optical shape layer 2 is 10 μm or more and 3000 μm or less.

[0025] The lower limit of the film thickness of the optical shape layer 2 may be a value that can secure machining errors in cutting and a certain amount of removal, and is preferably about 10 μm. Further, the upper limit of the film thickness of the optical shape layer 2 may be such that a fine plating film for creating a smooth mirror surface can be formed, and is preferably about 3000 μm from the viewpoint of suppressing an increase in internal stress of the plating.

[0026] [Optical shape surface] In the optical element of the present disclosure, it is preferable that the optical shape layer 2 has a plurality of optical shape surfaces 3 and the surface of at least one optical shape layer 2 laminated on the substrate 1 has an optical shape surface 3. The optical shape surface 3 has a flat or curved shape and has a smooth mirror surface. Further, a plurality of optical shape surfaces 3 are arranged in a plurality on the substrate 1, and the positional relationship and surface shape between the plurality of optical shape surfaces 3 are formed with high precision in order to exhibit desired optical characteristics (for example, to guide light reflected by the optical element in a desired direction).

[0027] When the optical element does not have the reflection layer 5 described later on the optical shape surface 3, the optical shape surface 3 plays a role of reflecting light. In the optical element of the present disclosure, the area of one optical shape surface among the plurality of optical shape surfaces 3 is 1 mm 2 or more and 625 mm 2 or less, which is preferable.

[0028] [Groove] In the optical element of the present disclosure, a groove 4 is provided, and the side surface of the optical shape layer 2 along the contour of each of the plurality of optical shape surfaces 3 and the side surface of the substrate form the side wall of the groove 4. The dimensions of the groove 4 are not limited, but the width of the groove 4 needs to be small enough not to impair the effective area of the optical shape surface 3. The depth of the groove 4 preferably has a depth sufficient to suppress a decrease in optical performance due to a deformation phenomenon caused by the difference in thermal expansion coefficients between the substrate 1 and the optical shape layer 2. The shape of the groove 4 may be a tapered shape that widens from the optical shape surface 3 toward the substrate 1 or a V-groove that narrows from the optical shape surface 3 toward the substrate 1.

[0029] The optical element of the present disclosure preferably includes a groove 4 along the contour of the optical shaping surface 3 on the base material 1 and the optical shaping layer 2 such that the side surfaces of the base material 1 and the optical shaping layer 2 form one surface (continuous surface). The continuous surface may be such that the base material surface and the optical shaping layer surface are directly continuous, or the side surface of an intermediate layer between the base material 1 and the optical shaping layer 2 may be interposed.

[0030] Figures 3(a) and 3(b) show top views schematically showing an example of the shape of the optical element of the present disclosure. Here, Figures 3(a) and 3(b) are examples of the top views of Figure 1 or Figure 2(a). As shown in Figure 3(a), the grooves 4 may be arranged so as to separate each optical shaping layer 2, and as shown in Figure 3(b), the grooves 4 may be arranged so as to separate a part of the optical shaping layer 2 and the other part is continuous. The arrangement pattern of the optical shaping layer 2 is not limited to the arrangement patterns such as those in Figures 3(a) and 3(b), and may be staggered as in Figure 1, or anything.

[0031] The numerical range of the width of the groove 4 may be any numerical value for machining. In the optical element of the present disclosure, the width of the groove 4 is preferably 0.02 mm or more and 3 mm or less. In order to suppress a decrease in optical performance due to a deformation phenomenon caused by a difference in the coefficient of thermal expansion between the base material 1 and the optical shaping layer 2, the depth of the groove 4 is preferably 5 mm or more and 20 mm or less. In order to alleviate a deformation phenomenon caused by a difference in the coefficient of thermal expansion between the base material 1 and a reflection layer 5 described later, it is preferable that at least a part of the side surface of the groove 4 exposes the base material 1.

[0032] [Reflection layer] As shown in Fig. 2(b), the optical element of the present disclosure preferably includes a reflective layer provided on the optical shaping surface, and preferably includes a reflective layer 5 on the optical shaping surface 3 and the bottom surface of the groove 4 according to the wavelength of the light to be observed. The side wall of the groove 4 may be covered with the reflective layer 5 or the like. As the material used for the reflective layer, a material that can reflect the wavelength of the light to be observed and can obtain a certain reflection efficiency is selected. In particular, in order to have a reflection function without deforming the shape of the optical shaping surface 3, a metal material suitable for vapor deposition that is easy to form may be selected as a thin film. In the optical element of the present disclosure, it is preferable that the thickness of the reflective layer 5 is smaller than the thickness of the optical shaping layer 2.

[0033] In the optical element of the present disclosure, it is preferable that the material of the reflective layer 5 adheres to the substrate 1 in the groove 4. In the optical element of the present disclosure, it is preferable that the reflective layer 5 is a layer mainly composed of one selected from the group consisting of Au, Ag, and Al, and it is preferable that the reflective layer 5 is a metal film mainly composed of any of Au, Ag, and Al having excellent reflection characteristics in the visible light region. Further, the reflective layer 5 may be a layer in which dielectric multilayer films are laminated.

[0034] [Others] The optical element of the present disclosure is not limited to having the above-described size, but is also effective when having the following ratios. The ratio of the total area of the groove 4 when the optical element is viewed from above to the total area of the optical shaping surface 3 is preferably 0.04 or more and 5 or less. The ratio of the depth of the groove 4 to the thickness of the optical shaping layer 2 is preferably 1.6 or more and 1000 or less. The ratio of the thickness of the portion of the substrate 1 excluding the depth of the groove 4 to the thickness of the optical shaping layer 2 is preferably 10 or more and 3000 or less. The ratio of the width of the groove 4 to the depth of the groove 4 is preferably 0.001 or more and 0.6 or less. By doing so, it is possible to simultaneously achieve suppression of thermal deformation of the entire optical element and suppression of the shape difference between the plurality of optical shaping surfaces 3 when each of the plurality of optical shaping surfaces 3 is thermally deformed.

[0035] <Second Embodiment> The second embodiment of the present disclosure relates to a method for manufacturing an optical element. The manufacturing method of the optical element of the present disclosure includes a film forming step of forming the film on a substrate, a groove forming step of processing the substrate and the film to form a groove, and an optical shape surface forming step of processing the film to form the optical shape surface, and is characterized by including these steps. Hereinafter, each step of the manufacturing method of the optical element will be described. The manufacturing method of the optical element is preferably performed in the order of a preparation step, a lamination step, a groove forming step, and an optical shape surface forming step. Since each item of the optical element is the same as described above, the description may be omitted.

[0036] [Preparation Step] The manufacturing method of the optical element of the present disclosure preferably includes a preparation step of preparing a substrate 1. FIGS. 4(a) to 4(d) are schematic views showing the manufacturing process of the optical element. First, as shown in FIG. 4(a), as the substrate 1, for example, an Invar material having a thermal expansion coefficient of 0.03 ppm even in an environment of -196°C is selected, and a rectangular parallelepiped of, for example, approximately 15 mm × 270 mm × 58 mm is cut out from the bulk material. It is desirable to process with high precision the flatness and perpendicularity of at least the portion (for example, the corner portion) serving as the installation reference when processing the optical element.

[0037] As a base for forming the optical shape surface 3 in the surface spectroscopic optical system designed and arranged to obtain desired optical characteristics, additional processing may be performed so that the upper part of the rectangular parallelepiped has a shape along the optical shape surface 3 in consideration of the positional relationship from the above installation reference.

[0038] [Film Forming Step] The manufacturing method of the optical element of the present disclosure includes a film forming step of forming a film on the substrate 1. In the film forming step, films for forming a plurality of optical shape surfaces are laminated. In particular, for example, copper sulfate plating is selected as a material excellent in mirror finishability. Copper sulfate plating is an electrolytic plating film mainly composed of copper, and forms a fine layered film by a wet process.

[0039] The thickness of the film is, for example, 300 μm in order to suppress peeling and cracking of the optical surface due to thermal effects even in extreme environments and to perform precise cutting. However, it is not limited to this, and it may be 10 μm or more and 3000 μm or less.

[0040] The lower limit value of the film thickness of the film may be a value that can secure processing errors and a certain removal amount in cutting, and about 10 μm is preferable. Further, the upper limit value of the film thickness of the film may be such that a fine plating film for creating a smooth mirror surface can be formed, and about 3000 μm is preferable from the viewpoint of suppressing an increase in internal stress of the plating.

[0041] [Groove forming step] The method for manufacturing an optical element according to the present disclosure includes a groove forming step of processing a substrate 1 and a film to form a groove 4. In the groove forming step, as shown in FIG. 4(b), a groove 4 is formed by machining in order to simultaneously suppress thermal deformation of the entire optical element and suppress the shape difference after thermal deformation of each of the plurality of optical surfaces 3.

[0042] The width of the groove 4 may be within a numerically range that allows machining, and is preferably 0.02 mm or more and 3 mm or less. The depth of the groove is preferably 5 mm or more and 20 mm or less in order to suppress a decrease in optical performance due to a deformation phenomenon caused by a difference in thermal expansion coefficient between the substrate 1 and the optical shape layer 2.

[0043] In the groove forming step of the method for manufacturing an optical element according to the present disclosure, it is preferable to include machining as a method for forming a groove, and for example, it is preferable to include end mill machining, wire cut machining, or fine cut machining. For example, a groove having a width of 1 mm and a depth of 7.5 mm is machined by end mill machining on an optical surface of 13 mm × 7 mm. The method for forming a groove is not limited to machining, and for example, wet etching, dry etching, or the like may be used.

[0044] [Optical surface forming step] The manufacturing method of the optical element of the present disclosure includes an optical shape surface forming step of processing a film to form the optical shape surface 3. In the manufacturing method of the optical element of the present disclosure, it is preferable to perform the optical shape surface forming step after the groove forming step. In the optical shape surface forming step, as shown in FIG. 4(c), while considering the positional relationship with respect to the installation reference described above, for example, by precision cutting using a diamond tool having a curved portion on the cutting edge to remove the film, an optical shape surface 3 having a curved surface is formed.

[0045] In precision cutting, it is necessary to form a smooth mirror surface with a roughness of about 1 nm RMS so that the light of the observation target is not scattered more than necessary. At this time, it is preferable to make the removal thickness as thin as possible as a processing condition. For example, the curved portion of the tool is set to R20 mm, and the target cusp height is set to be PV2 nm or less.

[0046] [Reflection layer forming step] The manufacturing method of the optical element of the present disclosure preferably includes a reflection layer forming step of forming a reflection layer 5 on the optical shape surface 3. In the reflection layer forming step, as shown in FIG. 4(d), for example, a reflection layer 5 containing gold having excellent reflection characteristics in the visible light region is formed.

[0047] Since the reflection layer 5 needs to be a thin film with a certain thickness so as not to break the shape of the optical shape surface 3 formed on the optical shape layer 2 as much as possible, it is preferable to form the film by sputtering, but it is not limited thereto. Any other physical vapor deposition method or various manufacturing methods generally called dry processes such as chemical vapor deposition method may be used as long as a process capable of forming a thin film of a predetermined material with a certain film thickness is used. The reflection layer 5 forms a film with a thickness of, for example, 40 nm in consideration of the film thickness stability of the coating film and the reflectivity of the light of the observation target.

[0048] [Application example] The application example of the present disclosure is about an optical device. The optical device of the present disclosure preferably has the above-described optical element. Further, the optical device of the present disclosure preferably includes the above-described optical element and a cooling device that cools the above-described optical element below the freezing point.

[0049] An optical device having the optical element of the present embodiment and having a cooling function will be described. FIG. 5 is a schematic diagram showing an optical device having a cooling function and having an optical element according to an embodiment of the present disclosure. In FIG. 5, the optical device includes a surface spectroscopic device 41, a cooling device 42, a light beam 43, an incident slit 44, a slicer mirror 45, a plane mirror array 46, a curved mirror array 47, and an exit slit 48. The optical element of the present disclosure is applicable to the plane mirror array 46 and the curved mirror array 47.

[0050] The configuration of the optical device in the present embodiment is an example. For example, as long as it is a configuration including an optical element having a plurality of optical shaped surfaces described in claim 1, there is no limitation to other configurations, and various components may be combined.

[0051] In FIG. 5, the cooling device 42 is connected to the surface spectroscopic device 41, and the inside of the surface spectroscopic device 41 can be cooled by the cooling device 42. The light beam 43 passes through the incident slit 44 facing the surface spectroscopic device 41 cooled by the cooling device 42, and is split into a plurality of light beams by a slicer mirror 45 capable of splitting the light beam. Each of the split light beams is reflected by each optical shaped surface of the plane mirror array 46 for reducing the size of the optical device, and the light beam is bent. The reflected light beam is condensed and reflected by each optical shaped surface of the curved mirror array 47 having a condensing action, passes through the exit slit 48, and is guided to a light receiver (not shown).

[0052] As elements that determine the performance of the optical device according to the present embodiment, while maintaining the relative positional relationship of the plurality of optical shaped surfaces of the diffractive optical element with high precision, simultaneously achieving a high-quality surface roughness, and maintaining the shape accuracy even under the thermal influence of an extreme environment, it is necessary to split the light beam to a desired position. An optical device excellent in environmental resistance can be provided by an optical device having a cooling function and having an optical element according to an embodiment of the present disclosure. As high-precision optical elements, they are not limited to astronomical applications, but are diverse in consumer applications, industrial applications, etc. Further, the application of optical elements is not limited to optical devices, and may be a condensing device, a reflecting device, etc., or may be used in a reduction optical system, an enlargement optical system, or a correction optical system.

Example

[0053] This comparative example will describe an optical element including an optical shape layer having a plurality of optical shape surfaces formed on a conventional substrate to which the present disclosure is not applied.

[0054] FIG. 6 is a schematic diagram showing a cross section of the optical element of the comparative example (conventional example). In FIG. 6, the optical element has a substrate 1, an optical shape layer 2, and an optical shape surface 3. From FIG. 6, in the conventional optical element, a plurality of optical shape surfaces 3 are formed on the surface of the same optical shape layer 2 on the substrate 1.

[0055] FIGS. 7(a) and 7(b) are graphs comparing the shapes after thermal deformation of the optical element according to the embodiment of the present disclosure (optical element of the example) and the optical element of the comparative example. FIG. 7(a) represents the shape after thermal deformation of the optical element of the example, and FIG. 7(b) represents the shape after thermal deformation of the optical element of the comparative example.

[0056] The optical element of the example and the optical element of the comparative example had a substrate height of 57.5 mm, an optical shape surface size of 13 mm × 7 mm, an interval between optical shape surfaces of 1 mm, the number of optical shape surfaces of 3 surfaces × 2 rows, a thickness of the optical shape layer of 0.05 mm, and the optical shape surface was assumed to be a flat surface. The temperature change amount between the manufacturing time and the use time of the optical element (the value obtained by subtracting the temperature at the manufacturing time of the optical element from the temperature at the use time of the optical element) was -219 K (the temperature at the manufacturing time of the optical element was room temperature (296 K (+23 °C)), and the temperature at the use time of the optical element was liquid nitrogen temperature (77 K)).

[0057] Furthermore, for the optical element of the example and the optical element of the comparative example, the base material was an invar material (IC-DX) with a coefficient of thermal expansion of -0.03 ppm / K, and the optical shape layer was a copper layer with a coefficient of thermal expansion of 17.7 ppm / K, which was produced by copper sulfate plating. For the optical element of the example, the depth of the groove was 7.5 mm and the width of the groove was 1 mm. No groove was made in the optical element of the comparative example. Under the above conditions, the shapes after thermal deformation of the outer edges of the optical shape surfaces in a 3-sided × 1-row arrangement were compared.

[0058] As a result of the comparison, the shapes after thermal deformation of the optical element of the example shown in Fig. 7(a) have small differences among the respective optical shape surfaces. On the other hand, the shapes after thermal deformation of the optical element of the comparative example shown in Fig. 7(b) are different for each optical shape surface, and the differences are large.

[0059] From this result, the present disclosure provides a groove such that the side surfaces of the base material and the side surfaces of the optical shape layer form one surface along the contour of each optical shape surface, so that the island-shaped convex portions composed of the base material and the optical shape layer are independently deformed, thereby simultaneously achieving suppression of thermal deformation of the entire optical element and suppression of thermal deformation of each of the plurality of optical shape surfaces.

[0060] The disclosure of the present embodiment includes the following configurations and methods. (Configuration 1) An optical element including a base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein the thickness of the optical shape layer is 10 μm or more and 3000 μm or less, and the optical element is provided with a groove, and the side surfaces of the optical shape layer and the side surfaces of the base material along the contour of each of the plurality of optical shape surfaces form the side walls of the groove. (Configuration 2) An optical element including a base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein the absolute value of the ratio of the coefficient of thermal expansion of the optical shape layer to the coefficient of thermal expansion of the base material is 3.0 or more, The optical element is provided with a groove, and side surfaces of the optical shape layer and the base material along contours of respective ones of the plurality of optical shape surfaces form side walls of the groove. (Configuration 3) An optical element including an opaque base material and an optical shape layer formed on the base material and having a plurality of optical shape surfaces, wherein a coefficient of thermal expansion of the base material is smaller than a coefficient of thermal expansion of the optical shape layer, The optical element is provided with a groove, and side surfaces of the optical shape layer and the base material along contours of respective ones of the plurality of optical shape surfaces form side walls of the groove. (Configuration 4) The optical element according to any one of Configurations 1 to 3, further including a reflective layer provided on the optical shape surface. (Configuration 5) The optical element according to Configuration 4, wherein a material of the reflective layer adheres to the base material in the groove. (Configuration 6) The optical element according to Configuration 4 or 5, wherein the reflective layer is a layer having, as a main component, one selected from the group consisting of Au, Ag, and Al. (Configuration 7) The optical element according to any one of Configurations 1 to 6, wherein the coefficient of thermal expansion of the base material is 0.21 ppm / K or less. (Configuration 8) The optical element according to any one of Configurations 1 to 7, wherein the coefficient of thermal expansion of the optical shape layer is 10 ppm / K or more. (Configuration 9) The optical element according to any one of Configurations 1 to 8, wherein a width of the groove is 0.02 mm or more and 3 mm or less. (Configuration 10) The optical element according to any one of claims 1 to 9, wherein a depth of the groove is 5 mm or more and 20 mm or less. (Configuration 11) The optical element according to any one of Configurations 1 to 10, wherein a thickness of a portion of the base material overlapping the groove is 30 mm or more and 60 mm or less. (Configuration 12) An area of one of the plurality of optical shape surfaces is 1 mm2 625 mm or less 2 The optical element according to any one of claims 1 to 11, which is 625 mm or less. (Configuration 13) The optical element according to any one of claims 1 to 12, wherein the total area of the grooves when the optical element is viewed from above is 0.04 or more and 5 or less with respect to the total area of the optical shape surface. (Configuration 14) The optical element according to any one of claims 1 to 13, wherein the ratio of the depth of the groove to the thickness of the optical shape layer is 1.6 or more and 1000 or less. (Configuration 15) The optical element according to any one of claims 1 to 14, wherein the ratio of the thickness of the portion of the substrate overlapping the groove to the thickness of the optical shape layer is 10 or more and 3000 or less. (Configuration 16) The optical element according to any one of claims 1 to 15, wherein the ratio of the width of the groove to the depth of the groove is 0.001 or more and 0.6 or less. (Configuration 17) The optical element according to any one of claims 1 to 16, wherein the substrate has a light transmittance of less than 70% in the visible light and infrared light bands. (Configuration 18) The optical element according to any one of claims 1 to 17, wherein the substrate contains an alloy. (Configuration 19) The optical element according to any one of claims 1 to 18, wherein the optical shape layer is a layer mainly composed of Cu or Ni. (Configuration 20) An optical device having the optical element according to any one of Configurations 1 to 19. (Configuration 21) An optical device including the optical element according to any one of Configurations 1 to 19 and a cooling device for cooling the optical element below the freezing point. (Method 1) A film forming step of forming the film on the substrate, A groove forming step of processing the substrate and the film to form a groove, An optical shape surface forming step of processing the film to form the optical shape surface A method for manufacturing an optical element, characterized by including (Method 2) The method for manufacturing an optical element according to Method 1, including a reflective layer forming step of forming a reflective layer on the optical shaping surface. (Method 3) The method for manufacturing an optical element according to Method 1 or 2, in which the optical shaping surface forming step is performed after the groove forming step. Explanation of compliance

[0061] 1 Substrate 2 Optical shaping layer 3 Optical shaping surface 4 Groove 5 Reflective layer 41 Surface spectroscopic device 42 Cooling device 43 Light ray 44 Incident slit 45 Slicer mirror 46 Plane mirror array 47 Curved mirror array 48 Exit slit

Claims

1. An optical element comprising a substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein the thickness of the optical shape layer is 10 μm or more and 3000 μm or less, and a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along respective contours of the plurality of optical shape surfaces form side walls of the groove. An optical element characterized by this.

2. An optical element comprising a substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein an absolute value of a ratio of a coefficient of thermal expansion of the optical shape layer to a coefficient of thermal expansion of the substrate is 3.0 or more, and a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along respective contours of the plurality of optical shape surfaces form side walls of the groove. An optical element characterized by this.

3. An optical element comprising an opaque substrate and an optical shape layer formed on the substrate and having a plurality of optical shape surfaces, wherein the coefficient of thermal expansion of the substrate is smaller than the coefficient of thermal expansion of the optical shape layer, and a groove is provided in the optical element, and side surfaces of the optical shape layer and the substrate along respective contours of the plurality of optical shape surfaces form side walls of the groove. An optical element characterized by this.

4. The optical element according to any one of claims 1 to 3, further comprising a reflective layer provided on the optical shape surface.

5. The optical element according to claim 4, wherein a material of the reflective layer adheres to the substrate in the groove.

6. The optical element according to claim 4, wherein the reflective layer is a layer having, as a main component, one selected from the group consisting of Au, Ag, and Al.

7. The optical element according to any one of claims 1 to 3, wherein the coefficient of thermal expansion of the substrate is 0.21 ppm / K or less.

8. The optical element according to any one of claims 1 to 3, wherein the coefficient of thermal expansion of the optical shape layer is 10 ppm / K or more.

9. The optical element according to any one of claims 1 to 3, wherein a width of the groove is 0.02 mm or more and 3 mm or less.

10. The optical element according to any one of claims 1 to 3, wherein a depth of the groove is 5 mm or more and 20 mm or less.

11. The optical element according to any one of claims 1 to 3, wherein a thickness of a portion of the substrate overlapping the groove is 30 mm or more and 60 mm or less.

12. The area of one of the plurality of optical shaped surfaces is 1 mm ２ or more and 625 mm ２ or less. The optical element according to any one of claims 1 to 3.

13. The optical element according to any one of claims 1 to 3, wherein the total area of the grooves when the optical element is viewed from above is 0.04 or more and 5 or less with respect to the total area of the optical shaped surface.

14. The optical element according to any one of claims 1 to 3, wherein the ratio of the depth of the groove to the thickness of the optical shaped layer is 1.6 or more and 1000 or less.

15. The optical element according to any one of claims 1 to 3, wherein the ratio of the thickness of the portion of the substrate overlapping the groove to the thickness of the optical shaped layer is 10 or more and 3000 or less.

16. The optical element according to any one of claims 1 to 3, wherein the ratio of the width of the groove to the depth of the groove is 0.001 or more and 0.6 or less.

17. The optical element according to any one of claims 1 to 3, wherein the substrate has a light transmittance of less than 70% in the visible light and infrared light bands.

18. The optical element according to any one of claims 1 to 3, wherein the substrate contains an alloy.

19. The optical element according to any one of claims 1 to 3, wherein the optical shaped layer is a layer mainly composed of Cu or Ni.

20. An optical device having the optical element according to any one of claims 1 to 3.

21. An optical device comprising the optical element according to any one of claims 1 to 3 and a cooling device for cooling the optical element below the freezing point.

22. A film forming step of forming the film on the substrate, A groove forming step of processing the substrate and the film to form a groove, An optical shaped surface forming step of processing the film to form the optical shaped surface A method for manufacturing an optical element, characterized by including the above steps.

23. The method for manufacturing an optical element according to claim 22, including a reflective layer forming step of forming a reflective layer on the optical shaped surface.

24. The method for manufacturing an optical element according to claim 22 or 23, wherein the optical shaped surface forming step is performed after the groove forming step.

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