Optical unit, spectroscopic analyzer, optical device, and method of manufacturing optical unit

Abstract

To provide an optical unit which ensures an optical path length by reflecting light, and which is equipped with anti-reflection means capable of suppressing stray light.SOLUTION: An optical unit is provided, comprising a reflective optical element and an anti-reflection structure, with an average height and average pitch greater than the maximum wavelength of light included in an effective luminous flux, located on the outside of an optical path of the effective luminous flux and provided with multiple protrusions extending in a given direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an optical unit or the like having an anti-reflection structure. [Background technology]

[0002] In the field of optical devices, attempts have been made to miniaturize devices while maintaining a long optical path by using optical units that bend or return the optical path. In particular, in the fields of astronomical telescopes, microscopes, various cameras, and other devices equipped with spectroscopic analysis devices, there is a demand for compact optical units that repeatedly reflect light rays while maintaining a long optical path, depending on conditions such as the aperture size, the required spectroscopic performance, and the diffraction distance.

[0003] On the other hand, in the field of image display devices, etc., antireflection means using a so-called moth-eye structure are known. The moth-eye structure is a structure in which a large number of minute pyramidal protrusions are arranged at a pitch equal to or shorter than the shortest wavelength in the wavelength band for which antireflection is desired, so that the effective refractive index for incident light changes continuously, eliminating discontinuous interfaces in the refractive index, thereby achieving an antireflection effect.

[0004] Patent Document 1 describes a moth-eye structure in which minute protrusions are arranged on a transparent substrate at a pitch finer than the shortest wavelength in the visible light region, and the minute protrusions are tilted from the normal direction to the surface of the transparent substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-6390 Summary of the Invention [Problem to be solved by the invention]

[0006] In optical units that ensure optical path length by repeatedly reflecting light rays, the internal structure must be laid out so that structures supporting reflective members and the like do not interfere with the optical path. Attempting to miniaturize optical units limits the available internal space, making it difficult to freely position an aperture to cut unwanted light. This can result in unwanted light traveling within the optical unit that deviates from the principal ray by a small angle outside the effective light beam. When this unwanted light collides with, for example, a structural member supporting a reflective member and is reflected, the reflected light can become stray light. Furthermore, when this reflected light collides with and is reflected by another member, further stray light traveling in a different direction can be generated. If a portion of this stray light is superimposed on the effective light beam, the stray light can degrade the quality of the information observed.

[0007] Therefore, it is conceivable to provide anti-reflection means in advance at the locations where unwanted light impinges. For example, it is conceivable to paint the locations with black paint. However, black paint generally generates gases and organic matter over a long period of time, which may contaminate the optical surfaces of optical elements and the light-receiving surfaces of sensors, so black paint is not a preferable anti-reflection means.

[0008] Furthermore, when using a moth-eye structure as an anti-reflection means, it is necessary to form a fine structure below the shortest wavelength in the wavelength band for which reflection is to be prevented, so that the effective refractive index for the target wavelength changes continuously. However, it is not easy to manufacture a fine structure below the shortest wavelength. Furthermore, in the case of a moth-eye structure, in order to achieve a continuous change in the effective refractive index, it is preferable that the direction in which the cone-shaped protrusions protrude from the substrate (the axial direction of the cone) is parallel to the direction in which light is incident, but this makes it easier for specular reflection to occur at the apex of the protrusion.

[0009] For example, in the moth-eye structure in which the axis of the cone is aligned with the direction of incidence of stray light using the method described in Patent Document 1, numerous protrusions are arranged at a fine pitch less than the wavelength of the target light, so the arrangement density of vertices where specular reflection occurs is high, making specular reflection more likely to occur. As a result, the anti-reflection effect of the moth-eye structure is likely to be insufficient. Furthermore, the reflectance of the moth-eye structure tends to increase significantly when the direction of incidence of light deviates from the axis of the cone.

[0010] Therefore, in an optical unit that ensures an optical path length by reflecting light rays, it has been desired to realize an anti-reflection means that can suppress the generation of stray light. [Means for solving the problem]

[0011] A first aspect of the present invention is an optical unit comprising: a reflective optical element; and an anti-reflection structure having a plurality of convex portions extending in a predetermined direction, the anti-reflection structure having an average height and an average pitch greater than the maximum wavelength of light contained in an effective light beam, the anti-reflection structure being positioned outside the optical path of the effective light beam. [Effects of the Invention]

[0012] According to the present invention, it was expected that an anti-reflection means capable of suppressing the generation of stray light would be realized in an optical unit that ensures an optical path length by reflecting light rays. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the configuration of an optical unit 10 according to a first embodiment. [Figure 2] FIG. 1 is a schematic perspective view illustrating an antireflection structure according to an embodiment. [Figure 3] 1A is a diagram for explaining that the generation of stray light is suppressed by the anti-reflection structure according to the embodiment, and FIG. 1B is a diagram showing an example in which an anti-reflection structure 20 is provided in a transmission section 18 provided in a structural member 13. [Figure 4] 1(a) is a diagram showing an example in which an anti-reflection structure 20 is provided on the surface of a support portion 12. FIG. 1(b) is a diagram showing an example in which an anti-reflection structure 20 is provided on a cover member. [Figure 5] FIG. 1 is a schematic diagram illustrating a reflectance measurement system. [Figure 6] 1 is a graph showing the relationship between the incident angle and the average reflectance. [Figure 7] FIG. 10 is a diagram illustrating an example of an electron microscope photograph of an anti-reflection structure. [Figure 8] FIG. 10 is a diagram showing the configuration of an optical unit 60 according to a second embodiment. [Figure 9] FIG. 10 is a diagram showing the configuration of an optical unit 70 according to a third embodiment. [Figure 10] FIG. 10 is a diagram showing the configuration of an optical unit 80 according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] With reference to the drawings, several embodiments of an optical unit having an anti-reflection structure according to the present invention will be described. The embodiments and examples shown below are merely examples, and those skilled in the art can appropriately modify and implement the detailed configurations within the scope of the present invention.

[0015] The present invention is applicable to various optical devices, but is particularly suitable for implementation in various optical devices equipped with spectroscopic analysis devices, such as astronomical telescopes, microscopes, and various cameras. For example, the present invention is suitable for implementation in an optical unit equipped with reflective optical elements, such as mirrors, reflective diffraction gratings, and transmissive internal reflection diffraction gratings, that reflect an effective light beam to ensure an optical path length. Here, the effective light beam refers to the light beam that should be utilized according to the application or intended use of the optical device, and does not refer to light that is unnecessary for the application or intended use. For example, in the case of a spectroscopic analysis device, the effective light beam refers to the light beam that should be guided to a light receiving element. This embodiment can suppress the generation of stray light due to reflection of unnecessary light that deviates from the principal ray by a small angle on a component, thereby preventing a decrease in the performance of the spectroscopic analysis device. In the drawings referred to in the following description of the embodiments and examples, elements designated with the same reference numerals have similar functions unless otherwise noted.

[0016] [Embodiment 1] An optical unit equipped with an anti-reflection structure according to embodiment 1 will be described with reference to the drawings. Note that the drawings referred to below include some parts that are represented schematically for the convenience of illustration and explanation, and may not strictly match the actual shape, size, arrangement, etc.

[0017] (Optical unit configuration) FIG. 1 is a diagram showing the configuration of an optical unit 10 according to a first embodiment. The optical unit 10 includes an incident portion 11, a support portion 12, a structural member 13, an exit portion 14, a reflecting portion 15, and a light-receiving element 16. The optical unit receives a light beam from the incident portion 11, reflects the light beam at two reflecting portions 15 to change the optical path, and then emits the light beam from the exit portion 14 to guide the light beam to the light-receiving element 16. In the figure, the light beam is indicated by a dotted arrow and the optical axis is indicated by a dashed-dotted line. In this example, a long optical path is ensured by folding the light path at two reflecting portions 15, but a configuration in which more reflecting portions are provided to increase the number of folding times may also be used.

[0018] The incident section 11 is a section that allows a light beam containing optical information or image information from the object surface to enter the optical unit, and is configured, for example, as an opening provided in the housing 17 or a transparent window made of a material that transmits the target light.

[0019] A reflecting unit 15 is disposed on the optical path to reflect the light beam in a predetermined direction. Each reflecting unit 15 may be a mirror with a single optical surface, or a mirror array with multiple optical surfaces. By forming the reflecting surface of the reflecting unit 15 into a predetermined curved shape, the light beam can be shaped into a desired diameter or cross-sectional shape. The reflecting unit 15 is positioned and fixed to the structural member 13 via the support unit 12.

[0020] The mirror may be a mirror having a reflective film formed by optical plating containing copper or nickel, or by aluminum vapor deposition, or may have a reflection-enhancing film applied to its surface. The reflection-enhancing film may be a film containing any of gold, silver, and aluminum, and may further have an oxide film such as silicon oxide, titanium oxide, or alumina applied to it.

[0021] The structural member 13 is a member that constitutes the body of the optical unit together with the housing 17. Since the internal space of the optical unit is limited, the structural member 13 is provided with a transmitting section 18 for passing light beams as needed. The transmitting section 18 is formed, for example, as an opening or recess in the structural member 13, but in some cases it may also be configured by attaching a transmitting window made of a material that transmits light beams to the structural member 13.

[0022] The exit portion 14 is an extraction portion for extracting the light beam from the optical unit, and is formed, for example, as an opening provided in the housing 17, but it may also be configured by attaching a transparent window made of a material that allows the light beam to pass through to the housing 17.

[0023] The light receiving element 16 is an element that receives a light beam and converts it into an electrical signal, and an appropriate element is used depending on the application of the optical device. Typically, an imaging element such as a CMOS sensor or a CCD element that can measure the light intensity distribution in the cross section of the light beam is used, but other elements may also be used.

[0024] (Arrangement of anti-reflection structure) 1, an anti-reflection structure is provided on the outer surface of the portion surrounded by the dotted line in the drawing to prevent unwanted light that deviates from the principal ray by a small angle from generating stray light. Details of the anti-reflection structure according to this embodiment will be described later, but first, a position where the anti-reflection structure is preferably provided will be described.

[0025] First, incident section 11, onto which the light beam emitted from the object surface is incident, may also serve as a pupil for extracting an effective light beam (for example, a necessary image portion). Therefore, if incident section 11 is an opening formed in housing 17, an anti-reflection structure is provided on the edge surface around the opening, onto which unwanted light may be irradiated, and on the inner surface of a hole penetrating housing 17. If incident section 11 is a transmission window made of a material that transmits light beams, an anti-reflection structure is provided on the surface of housing 17 around the transmission window, onto which unwanted light may be irradiated.

[0026] Furthermore, when a transmitting section 18 for transmitting a light beam is provided in the structural member 13 within the optical unit, the transmitting section 18 may also serve as a pupil for extracting an effective light beam (for example, a necessary image portion). Therefore, when the transmitting section 18 is an opening formed in the structural member 13, an anti-reflection structure is provided on the edge surface around the opening, onto which unwanted light may be irradiated, or on the inner surface of a hole penetrating the structural member 13. When the transmitting section 18 is a transmitting window made of a material that transmits light beams, an anti-reflection structure is provided on the surface of the structural member 13 around the transmitting window, onto which unwanted light may be irradiated.

[0027] Furthermore, the reflecting portion 15 may also serve as a pupil for extracting an effective light beam (for example, a necessary image portion). Therefore, an anti-reflection structure is provided on the surface of the supporting portion 12, which may be irradiated with unnecessary light, and on the surface of the structural member 13 to which the supporting portion 12 is fixed.

[0028] Furthermore, exit unit 14, which emits the light beam, may also serve as a pupil for extracting an effective light beam (for example, a necessary image portion). Therefore, if exit unit 14 is an opening formed in housing 17, an anti-reflection structure is provided on the edge surface around the opening, onto which unwanted light may be irradiated, and on the inner surface of a hole penetrating housing 17. If exit unit 14 is a transmission window made of a material that transmits light beams, an anti-reflection structure is provided on the surface of housing 17 around the transmission window, onto which unwanted light may be irradiated.

[0029] In areas where these anti-reflection structures are provided, unwanted light outside the effective light beam may strike the surface of the component. When this unwanted light is reflected by the surface of the component, the reflected light itself becomes stray light, and the reflected light may then be reflected by the surfaces of other components, generating secondary stray light.

[0030] Unwanted light incident from outside the effective light beam is often a ray that deviates from the optical axis direction by a small angle. For example, when irradiating the edge surface around the opening of the housing 17 or structural member 13, or the area around the transmission window, the light is irradiated at a relatively small angle of incidence. Even if a moth-eye structure is provided in this area, as already mentioned, the moth-eye structure is prone to regular reflection at the apexes of the tiny cones arranged at high density, so the moth-eye structure cannot be expected to sufficiently suppress the generation of stray light.

[0031] Furthermore, when unwanted light irradiates the inner surface of a hole penetrating the housing 17 or the structural member 13, it is incident at a large angle of incidence. If an anti-reflection structure were not provided, the large angle of incidence would likely result in reflection, resulting in the generation of stray light. Even if a moth-eye structure were provided in this area, if the axial direction of the cone-shaped protrusions were perpendicular to the inner surface of the hole, the structure would not have a continuously changing refractive index in the direction of propagation of the unwanted light. Therefore, sufficient anti-reflection effects would not be expected due to the dependence on the angle of incidence. On the other hand, it is not easy to form extremely small cones arranged at a fine pitch less than the shortest wavelength with the axial direction of the cones tilted toward the optical axis, as in Patent Document 1, on the inner surface of such a hole. Even if tilting were possible, as mentioned above, regular reflection is likely to occur at the apexes of the densely arranged cones, and therefore the moth-eye structure would not be able to sufficiently suppress the generation of stray light.

[0032] Furthermore, there is a high possibility that stray light will be generated when unwanted light irradiates the surface of the support portion 12 that supports the reflector 15 or the surface of the structural member 13 to which the support portion 12 is fixed. As mentioned above, the anti-reflection function of the moth-eye structure is angle-dependent, so it is necessary to bring the axis of the cone close to the optical axis direction, but even if this is possible, regular reflection is likely to occur at the apex of the cones that are arranged at a high density, so it cannot be expected that the generation of stray light will be sufficiently suppressed.

[0033] Therefore, in this embodiment, an anti-reflection structure different from the moth-eye structure is provided in these locations. The anti-reflection structure according to this embodiment will be described below.

[0034] (Anti-reflection structure) 2 is a schematic perspective view illustrating an antireflection structure 20 according to this embodiment. The antireflection structure 20 includes a large number of protrusions 21 formed on a base surface. In the example of FIG. 2, the large number of protrusions 21 are formed on a flat base surface, but the base surface (i.e., the base underlying the protrusions 21) does not necessarily have to be a flat surface and may be, for example, a curved surface.

[0035] The material of the protrusions 21 can be, for example, a metal such as iron, stainless steel, aluminum, copper, or titanium, or a material containing an alloy of these as a main component. A film capable of absorbing light of a target wavelength, such as a metal oxide film or an alloy oxide film, may be formed on the surface of the protrusions 21. The surface of the protrusions 21 may be smooth, or may be a rough surface with minute irregularities 22 formed thereon. For example, if the protrusions 21 are formed by laser processing in the atmosphere, an oxide film capable of absorbing unwanted light can be simultaneously formed on the surface of the protrusions 21, allowing for the manufacture of an excellent anti-reflection structure with high mass productivity.

[0036] The average height H of the convex portions 21 and the average pitch P between the convex portions are configured on a larger scale than the cones used in a moth-eye structure. The moth-eye structure achieves an anti-reflection effect by arranging tiny cones at a pitch finer than the shortest wavelength of the target light, thereby continuously changing the effective refractive index and eliminating discontinuous interfaces in the refractive index. In contrast, the present embodiment is a structure with convex portions 21 on a larger scale than the moth-eye structure, which absorbs target light while causing multiple reflections and suppresses reflection in directions that result in stray light. The pitch (e.g., average pitch) between the convex portions in this embodiment is set to be larger than the maximum wavelength of light guided to the light-receiving element 16. Specifically, the average height of the apexes of the convex portions and the average pitch between the apexes of the convex portions are preferably 1 μm or more and 100 μm or less. If the pitch is less than 1 μm, the wavelength at which reflection is desired to be prevented, i.e., the maximum wavelength of light handled by a spectrometer, for example, would be close to the wavelength at which reflection is desired to be prevented, resulting in light diffraction and changing the behavior of light from the intended anti-reflection effect using multiple reflections. Furthermore, if the thickness exceeds 100 μm, the space occupied by the convex portion becomes too large to be suitable for miniaturization of the device, and it becomes difficult to form the convex portion by laser processing, which is suitable for mass production.

[0037] In the example of FIG. 2, multiple protrusions 21 are regularly arranged along lattice points, but the arrangement of the protrusions is not necessarily limited to this example. A highly geometrically regular arrangement such as a honeycomb or staggered pattern is also acceptable. As shown in the photograph of FIG. 7, which will be described later, the statistical values ​​(e.g., average value and variance) of the height and pitch may be within a predetermined range, but the geometrically observed shape may have little regularity. The example shown in FIG. 7 is preferable in terms of anti-reflection function and ease of manufacture. That is, the protrusions 21 are not limited to a cone-like shape with a rounded curvature near the apex, as exemplified in FIG. 2. However, regardless of the shape, the average height H of the protrusions 21 and the average pitch P between the protrusions are set to be greater than the maximum wavelength of the light guided to the light-receiving element 16.

[0038] FIG. 3(a) is a diagram illustrating how the anti-reflection structure according to this embodiment suppresses the generation of stray light. If the direction in which the convex portions 21 extend is designated CD, in this example, CD is perpendicular to the base plane BP. Here, the base plane BP is an imaginary plane formed by connecting the boundaries 23 between the convex portions 21. In the example shown in FIG. 3(a), CD is perpendicular to the base plane BP, but as illustrated in FIGS. 3(b) and 4(a) to be referred to later, the CD direction can also be at an angle other than perpendicular to the base plane BP. As will be described later, when forming the convex portions by laser processing, for example, the extension direction of the convex portions 21 relative to the base plane BP can be controlled by the direction of laser irradiation.

[0039] The incident direction of the target light 34 whose reflection is to be suppressed is defined as an angle α with respect to the CD. The incident direction of the target light whose reflection is to be suppressed in the area where the anti-reflection structure is provided (e.g., the area surrounded by the dotted line in FIG. 1 ) may be approximately parallel to the optical axis direction (optical path) of the effective light beam. In the anti-reflection structure of this embodiment, the incident angle α of the target light is preferably 45 degrees or more and 60 degrees or less with respect to the CD. In this embodiment, to prevent the target light from reflecting and escaping as stray light, the target light is first made to strike the slopes of the convex portions 21, as shown in the figure. The reflected light is then repeatedly reflected between adjacent convex portions, gradually absorbed and attenuated by the convex portions. In this embodiment, the pitch between the convex portions is larger than that of the moth-eye structure, so the density of the peaks that generate the reflected light 33 that escapes to the outside is low. On the other hand, to increase the proportion of light that is attenuated by repeated reflection between the convex portions, it is preferable to set α to 45 degrees or more and 60 degrees or less.

[0040] In the case of a moth-eye structure, structures smaller than the wavelength range to be suppressed are created, and the change in refractive index is gradual to suppress reflected light, so the anti-reflection ability is affected by the wavelength dependency of the refractive index of the substrate. In this embodiment, the scale of the convex portions is larger than the wavelength of the target light, so the anti-reflection ability is less affected by the wavelength dependency of the refractive index of the substrate. In analytical devices such as microscopes, telescopes, and FT-IR, the direction of incidence of the target light to be prevented from being reflected is limited and can be considered to be approximately parallel to the optical axis. Therefore, a structure in which α is at least 45 degrees and not more than 60 degrees with respect to the optical axis is easy to design and can be said to be very effective.

[0041] FIG. 3(b) is a diagram showing an example in which an anti-reflection structure 20 is provided on the transmissive portion 18 (see FIG. 1) provided on the structural member 13. As shown in the figure, convex portions are provided on the inner surface of the opening of the transmissive portion 18 at an average pitch of 1 μm or more and 100 μm or less, oriented so that α is 45 degrees or more and 60 degrees or less with respect to the optical axis. Even if unwanted light that is approximately parallel to the optical axis exists outside the effective light beam and irradiates the inner surface of the through-hole of the structural member 13, the generation of reflected light that becomes stray light can be suppressed. When an anti-reflection structure is provided on the incident portion 11 or the exit portion 14 provided on the housing 17, an anti-reflection structure 20 having convex portions formed on the inner surface or edge of the opening at a similar orientation and pitch is provided.

[0042] Furthermore, when the anti-reflection structure 20 is provided on the surface of the support 12 that supports the reflector 15 or on the surface of the structural member 13 to which the support 12 is fixed, the convex portions are provided at a pitch of 1 μm or more and 100 μm or less, oriented so that the angle α with respect to the optical axis is 45 degrees or more and 60 degrees or less. Note that the support 12 and the structural member 13 can be preferably made of low-thermal expansion Invar material, stainless steel, or aluminum.

[0043] 4(a) shows an example in which convex portions are provided as anti-reflection structure 20 at an average pitch of 1 μm or more and 100 μm or less on the surface of support portion 12 that supports reflector 15, with an angle α of 45 degrees or more and 60 degrees or less with respect to the optical axis. Even if unwanted light that is almost parallel to the optical axis exists outside the effective light beam and irradiates the surface of support portion 12, it is possible to suppress the generation of reflected light that becomes stray light.

[0044] Furthermore, the anti-reflection structure 20 does not necessarily have to be formed directly on the support portion 12, but may be formed on a separate member that covers the support portion 12. Figure 4(b) shows an example in which the anti-reflection structure 20 is formed on a cover member 12C that can cover the support portion 12. By fitting the recess 12A of the cover member 12C to the support portion 12, the same anti-reflection effect as when the anti-reflection structure 20 is formed directly on the support portion 12 can be obtained. This method of forming the anti-reflection structure on a separate member and covering the area where stray light is undesired with this separate member is advantageous in that the anti-reflection structure and its underlying material can be freely selected. Furthermore, retrofitting a separate member with an anti-reflection structure has the advantage of simplifying the handling of the area where stray light is undesired. For example, a material with a main component appropriate for the application of the optical unit, such as iron, aluminum, copper, or an alloy, is used to form a sheet metal with a thickness of, for example, 1 mm, and the surface is laser-processed to form the anti-reflection structure, thereby creating a cover member.

[0045] Alternatively, a previously formed anti-reflection structure can be transferred to a film- or sheet-shaped resin material member, for example, and used as a cover member. To transfer the anti-reflection structure, for example, a method can be used in which the anti-reflection structure is formed in a roll mold, and then a photo-curable resin material is applied in film or sheet form, cured, and transferred. A film- or sheet-shaped resin member with an anti-reflection structure can be attached by pasting or bonding to the location of the optical unit where reflection is desired to be prevented.

[0046] This embodiment can be suitably implemented in optical units built into various optical devices equipped with a spectroscopic analyzer, such as astronomical telescopes, microscopes, various cameras, etc. According to this embodiment, it is possible to suppress the generation of stray light caused by the reflection of unnecessary light that deviates from the principal ray by a small angle on a component, thereby effectively preventing a decrease in the performance of the spectroscopic analyzer.

[0047] [Example] An example of the anti-reflection structure according to the first embodiment will be specifically described. The anti-reflection structure 20 shown in FIG. -12 It can be manufactured by a processing method in which a short pulse laser of less than 10 seconds is irradiated onto a substrate (base material) to roughen the surface. -12 By irradiating the laser for 10 seconds or less with a peak power of 1 MW or more, a local temperature gradient is generated in the base material (parent material) whose main component is a metal or alloy, which generates a difference in surface tension, thereby efficiently creating protrusions. By irradiating the laser in an oxygen-containing atmosphere (e.g., air), it is also possible to form an oxide film on the surface of the protrusions 21, in which the material on the base material surface combines with oxygen in the air. The formation of an oxide film allows for effective light absorption during the repeated reflection process shown in Figure 3(a). The minute irregularities 22 on the surface of the protrusions 21 can be formed by the scattering and re-adhesion of high-temperature steam and fine particles from the workpiece during laser processing.

[0048] To create an anti-reflection structure by laser processing using a short-pulse laser, a base material can be selected from materials with a main component appropriate for the application of the optical system, such as iron, aluminum, copper, or alloy materials. In the examples, a SUS-based alloy was used. The short-pulse laser used here refers to a laser that repeatedly irradiates short pulses, as opposed to a laser that continuously irradiates. Among short-pulse lasers, those that irradiate pulses of several picoseconds to several hundred picoseconds are sometimes called picosecond lasers. Furthermore, those that irradiate pulses of several femtoseconds to several hundred femtoseconds, which are less than 1 picosecond, are sometimes called femtosecond lasers. In the examples, picosecond lasers and femtosecond lasers are preferably used.

[0049] The laser processing equipment used can arbitrarily select conditions such as laser irradiation intensity, pulse length, and pulse interval. For example, an ultrashort pulse laser oscillator manufactured by AMPLITUDE SYSTEMS can be used. The wavelength of the processing laser generated by such an ultrashort pulse laser oscillator is set to 1030 nm, and its pulse width is selected to be 350 fs (femtoseconds). The energy per pulse of the processing laser is set to 40 μJ, and a lens with a focal length of approximately 170 mm is used. The spot diameter of the irradiation area is adjusted to 40 μm by adjusting the distance between the lens and the substrate surface. The area of ​​the irradiation area of ​​one pulse is approximately 1.3 × 10 -3 [mm 2 ], and the energy density per pulse of the laser in the irradiation area is approximately 30 [kJ / m 2 ]. A galvanometer scanner is used to scan the laser and selectively process the area where the anti-reflection structure is to be formed. The scanning speed of the galvanometer scanner is, for example, 1000 [mm / sec], and the laser repetition frequency is 1000 [kHz]. The pulse time interval is 1 [μsec], and the interval between irradiation positions is 2 [μm].

[0050] As shown in FIGS. 3(b) and 4(a), the extension direction of the convex portions from the substrate (base surface BP) is controlled so that the angle α between the CD (direction in which the convex portions extend) and the optical axis of the target light falls within a predetermined range at the position where the anti-reflection structure 20 is provided. The CD (direction in which the convex portions extend) can be controlled by the angle of incidence when the processing laser is irradiated onto the substrate surface. By appropriately controlling the angle of incidence, pulse width, repetition frequency, scanning speed, and energy density of the irradiation spot of the processing laser, the extension direction of the convex portions, the average height and average pitch of the convex portions can be controlled. This laser processing method makes it possible to mass-produce anti-reflection structures with special shapes that are difficult to achieve using techniques such as cutting.

[0051] Figure 7 shows electron microscope images of an anti-reflection structure with controlled projection extension. The laser processing equipment was operated under the aforementioned conditions, and the projections formed when the laser incident angle to the SUS substrate was 30° and 60° were compared. In the image observed from the direction of laser incidence during laser processing, the entire area from the peak to the base can be seen, indicating that the projections extend in the observation direction. In contrast, when comparing images observed from the normal direction to the substrate surface, the extension direction of the projections is clearly different. The average height and average pitch of the projections were measured for these samples. Measurements using a Keyence VX-3000 laser microscope revealed that the average pitch was in the range of 20 μm to 50 μm, and the average height was in the range of 50 μm to 70 μm. This indicates that a structure larger in scale than the wavelength of the target light (e.g., visible light) to be prevented from reflecting was formed.

[0052] Next, an example is shown in which the anti-reflection characteristics of the anti-reflection structure according to this embodiment and a moth-eye structure are compared. FIG. 5 is a schematic diagram illustrating a reflectance measurement system 40 used to compare the anti-reflection characteristics. Light from a halogen lamp 41 is split by a prism 42, and wavelength-selected reference light is irradiated onto a measurement object 44 through a slit. The measurement object 44 is mounted on a rotating stage 43, and the angle of incidence of the reference light relative to the measurement object 44 can be changed by rotating the rotating stage 43. The reference light reflected by the measurement object 44 is directed to an integrating sphere 46 via a mirror 45. The mirror 45 and integrating sphere 46 are mounted on a stage 47, and moving the stage 47 allows the angle of the light to be detected from the light emitted from the measurement object 44 to be adjusted. The standard for reflectance measurement is 100% reflectance when all of the reference light is incident on the integrating sphere 46 without a measurement object placed on the rotating stage 43. Furthermore, a light blocking plate is placed on the rotating stage 43, the angle of incidence is set to 0 degrees, and the measurement value when the light entering the integrating sphere 46 is completely blocked is taken as a reflectance of 0%. Using this standard, the absolute reflectance of the object 44 to be measured is measured.

[0053] Figure 6 is a graph showing the relationship between the incident angle and average reflectance measured using the method described above. The horizontal axis represents the incident angle of light relative to the extension direction of the convex portions, and the vertical axis represents the average reflectance. The average reflectance was calculated by measuring the reflectance while changing the wavelength of the irradiated light in 10-nm increments in the range of 350 nm to 800 nm. The incident angle of the irradiated light was set to seven angles: 0 degrees, 45 degrees, 60 degrees, 70 degrees, 75 degrees, 80 degrees, and 85 degrees. The exit angle was set to the same angle of incidence as the incident angle in order to measure the specular reflection component. An absolute reflectance measuring instrument manufactured by JASCO Corporation was used for the measurements.

[0054] As described above, the antireflection structure according to the embodiment has an average protrusion pitch in the range of 20 μm to 50 μm, and an average protrusion height in the range of 50 μm to 70 μm. The moth-eye structure conforms to that described in Patent Document 1 (JP 2014-6390 A), and is a microstructure with a microprotrusion pitch of 100 nm to 300 nm.

[0055] As is clear from Figure 6, when comparing the average reflectance in the wavelength range of 350 nm to 800 nm, it is found that the antireflection structure of this embodiment has a lower reflectance than the moth-eye structure across the entire range of incident angles. Furthermore, it is found that the antireflection structure of this embodiment exhibits particularly low reflectance for light rays incident from a direction of 45 degrees or more and 60 degrees or less, and the incident angle at which the reflectance is minimum is within this range. Therefore, in the optical unit shown in Figure 1, the antireflection structure configured so that the extension direction of the convex portions is 45 degrees or more and 60 degrees or less with respect to the optical axis can exhibit extremely excellent antireflection function.

[0056] [Embodiment 2] An optical unit equipped with an anti-reflection structure according to embodiment 2 will be described with reference to the drawings. Note that the drawings referred to below include some parts that are represented schematically for the convenience of illustration and explanation, and may not strictly match the actual shape, size, arrangement, etc.

[0057] (Optical unit configuration) 8 is a diagram showing the configuration of an optical unit 60 according to embodiment 2. Components common to embodiment 1 are denoted by the same reference numerals in the drawing, and descriptions thereof will be simplified or omitted.

[0058] The optical unit 60 according to this embodiment uses a reflective diffraction grating in at least a part of the reflecting portion. In the optical unit 60 illustrated in Fig. 8, the reflecting portion 15 is a mirror, but a reflective diffraction grating is used in the reflecting portion 67. The optical unit 60 according to this embodiment also has an anti-reflection structure similar to that described in the first embodiment with reference to Fig. 2 etc., but the position where the anti-reflection structure is provided is different.

[0059] In this embodiment, anti-reflection structures are also provided near the incident portion 11 where the light beam emitted from the object surface is incident, near the transmitting portion provided on the structural member, near the support portion 12 supporting the reflector 15 and the support portion 62 supporting the reflector 67, and near the exit portion 14. However, from the reflective diffraction grating of the reflector 67, diffracted light diffracted within a range of ±1st or ±2nd orders relative to the desired diffraction order may be emitted in a direction different from the useful light beam. For this reason, in an optical unit using a reflective diffraction grating, unwanted diffracted light may strike the inner surface of the housing 17, which may reflect the diffracted light and generate stray light. Therefore, in this embodiment, an anti-reflection structure is provided on the inner surface of the housing 17, particularly on the portion visible from the diffraction grating, as indicated by the dotted line in the figure. Note that it is also effective to provide an anti-reflection structure not only on the inner surface of the housing 17 but also on structural members visible from the diffraction grating.

[0060] This embodiment can be suitably implemented in optical units built into various optical devices equipped with a spectroscopic analysis device, such as astronomical telescopes, microscopes, and various cameras. According to this embodiment, it is possible to prevent unwanted light that deviates from the principal ray by a small angle from reflecting off components and generating stray light, thereby effectively preventing a decrease in performance of the spectroscopic analysis device. Furthermore, it is possible to prevent unwanted orders of diffracted light emitted from a reflective diffraction grating from reflecting off a housing or the like and generating stray light.

[0061] [Embodiment 3] An optical unit equipped with an anti-reflection structure according to embodiment 3 will be described with reference to the drawings. Note that the drawings referred to below include some parts that are represented schematically for the convenience of illustration and explanation, and may not strictly match the actual shape, size, arrangement, etc.

[0062] (Optical unit configuration) 9 is a diagram showing the configuration of an optical unit 70 according to embodiment 3. Components common to embodiment 1 are denoted by the same reference numerals in the drawing, and descriptions thereof will be simplified or omitted.

[0063] The optical unit 70 according to this embodiment uses a transmission-internal reflection type diffraction grating (also called an immersion diffraction grating) in at least a part of the reflecting portion. In the optical unit 70 illustrated in FIG. 9, the reflecting portion 15 is a mirror, but a transmission-internal reflection type diffraction grating is used in the reflecting portion 77. The optical unit 70 according to this embodiment also has an anti-reflection structure similar to that described in the first embodiment with reference to FIG. 2 etc., but the position where the anti-reflection structure is provided is different.

[0064] In this embodiment, anti-reflection structures are also provided near the incident portion 11 where the light beam emitted from the object surface is incident, near the transmitting portion provided on the structural member, near the support portion 12 supporting the reflector 15 and the support portion 62 supporting the reflector 67, and near the exit portion 14. However, from the reflector 77, which is a transmission-internal reflection type diffraction grating, diffracted light diffracted within a range of ±1 order or ±2 orders relative to the desired diffraction order may be emitted in a direction different from the useful light beam. Furthermore, diffracted light that deviates from the useful light beam may be further reflected by the inner surface of the transmission element and emitted in a different direction, resulting in stray light. For this reason, in an optical unit using a transmission-internal reflection type diffraction grating, unwanted diffracted light may reach the inner surface of the housing 17, which may reflect the diffracted light and generate stray light. Therefore, in this embodiment, an anti-reflection structure is provided on the inner surface of the housing 17, particularly in the area visible from the diffraction grating, as indicated by the dotted line in the figure. It is also effective to provide an anti-reflection structure not only on the inner surface of the housing 17 but also on structural materials visible from the diffraction grating and on the support portion 72 of the diffraction grating.

[0065] This embodiment can be suitably implemented in optical units built into various optical devices equipped with a spectroscopic analysis device, such as astronomical telescopes, microscopes, and various cameras. According to this embodiment, it is possible to prevent unwanted light that deviates from the principal ray by a small angle from reflecting off components and generating stray light, thereby effectively preventing a decrease in performance of the spectroscopic analysis device. Furthermore, it is possible to prevent unwanted orders of diffracted light emitted from a transmission-internal reflection type diffraction grating from reflecting off a housing or the like and generating stray light.

[0066] [Embodiment 4] An optical unit equipped with an anti-reflection structure according to embodiment 4 will be described with reference to the drawings. Note that the drawings referred to below include some parts that are represented schematically for the convenience of illustration and explanation, and may not strictly match the actual shape, size, arrangement, etc.

[0067] (Optical unit configuration) 10 is a diagram showing the configuration of an optical unit 80 according to embodiment 4. Components common to embodiment 1 are denoted by the same reference numerals in the drawing, and descriptions thereof will be simplified or omitted.

[0068] In addition to the reflecting portion 15, the optical unit 80 according to this embodiment includes a transmission type diffraction grating 87 (sometimes referred to as a grism diffraction grating) and its support portion 82. The optical unit 80 according to this embodiment also includes an anti-reflection structure similar to the anti-reflection structure described in the first embodiment with reference to FIG. 2 etc., but the position where the anti-reflection structure is provided is different.

[0069] In this embodiment, anti-reflection structures are also provided near the entrance portion 11 where the light beam emitted from the object surface is incident, near the transmission portion provided on the structural member 13, near the support portion 12 that supports the reflection portion 15, and near the exit portion 14. However, from the transmission diffraction grating 87, diffracted light diffracted within a range of ±1st or ±2nd orders relative to the desired diffraction order may be emitted in a direction different from the useful light beam. For this reason, in an optical unit using the transmission diffraction grating 87, unwanted diffracted light may reach the inner surface of the housing 17, the support portion 82, the structural member 13, etc., and be reflected as stray light. Therefore, in this embodiment, anti-reflection structures are provided on the inner surface of the housing 17, the support portion 82, and the structural member 13, particularly in the portions visible from the transmission diffraction grating 87, as shown by the dotted lines in the figure.

[0070] This embodiment can be suitably implemented in optical units built into various optical devices equipped with a spectroscopic analysis device, such as astronomical telescopes, microscopes, and various cameras. According to this embodiment, it is possible to prevent unwanted light that deviates from the principal ray by a small angle from reflecting off components and generating stray light, thereby effectively preventing a decrease in performance of the spectroscopic analysis device. Furthermore, it is possible to prevent unwanted orders of diffracted light emitted from a transmission diffraction grating from reflecting off a housing or the like and generating stray light.

[0071] [Other embodiments] The present invention is not limited to the above-described embodiments and examples, and many modifications are possible within the technical concept of the present invention. For example, the above-described different embodiments and examples may be combined and implemented. [Explanation of symbols]

[0072] 10 Optical unit / 11 Incident part / 12 Support part / 12A Recess / 12C Cover member / 13 Structural member / 14 Output part / 15 Reflection part / 16 Light receiving element / 17 Housing / 18 Transmitting part / 20 Anti-reflection structure / 21 Convex part / 22 Concave / convex / 23 Boundary / 33 Reflected light / 34 Target light / 40 Reflectance measurement System / 41···Halogen lamp / 42···Prism / 43··Rotation stage / 44···Object to be measured / 45···Mirror / 46···Integrating sphere / 47···Stage / 60···Optical unit / 62···Support part / 67···Reflector / 70···Optical unit / 72···Support part / 77···Reflector / 80···Optical unit / 82···Support part / 87···Transmission diffraction grating

Claims

1. A reflective optical element; an anti-reflection structure having an average height and an average pitch larger than the maximum wavelength of light contained in an effective light beam, the anti-reflection structure being disposed outside an optical path of the effective light beam and having a plurality of convex portions; an angle between a direction in which the plurality of convex portions extend and the optical path of the effective light beam is 45 degrees or more and 60 degrees or less; An optical unit characterized by:

2. The average pitch is 1 μm or more and 100 μm or less.

2. The optical unit according to claim 1.

3. The plurality of protrusions have an oxide film.

3. The optical unit according to claim 1, wherein the first and second optical components are arranged in a first plane.

4. The main component of the plurality of protrusions is a metal or an alloy.

4. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first plane.

5. The apexes of the plurality of protrusions have a curvature.

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

6. A convex portion having a pitch smaller than that of the plurality of convex portions is formed on the surface of the plurality of convex portions.

6. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first direction.

7. an incident angle of light at which the reflectance of the anti-reflection structure is minimized is within a range of 45 degrees or more and 60 degrees or less with respect to the direction in which the plurality of protrusions extend; 7. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first plane.

8. the anti-reflection structure is provided on an incident portion through which the effective light beam enters the optical unit and / or an exit portion through which the effective light beam exits from the optical unit; 8. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first plane.

9. The anti-reflection structure is provided on a support portion that supports the reflecting optical element.

9. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first direction.

10. The material of the support part is any one of a low thermal expansion Invar material, a stainless steel material, and aluminum.

10. The optical unit according to claim 9.

11. The anti-reflection structure is provided on an inner surface of a housing of the optical unit and / or a surface of a structural member of the optical unit.

11. The optical unit according to claim 1 .

12. The anti-reflection structure is provided at a position visible from the reflecting optical element.

12. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first direction.

13. the plurality of convex portions are formed on a base having the same main component as the plurality of convex portions; 13. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first direction.

14. The plurality of protrusions are formed on a member whose main component is a resin material.

13. The optical unit according to claim 1, wherein the first and second lenses are arranged in a first direction.

15. The reflective optical element is any one of a mirror, a reflective diffraction grating, and a transmission internal reflection type diffraction grating.

15. The optical unit according to claim 1,

16. Further, the optical fiber 100 includes a transmission type diffraction grating.

16. The optical unit according to claim 1,

17. Further, a light receiving element is provided.

17. The optical unit according to claim 1,

18. A spectroscopic analyzer comprising the optical unit according to claim 1 .

19. An optical device comprising the spectroscopic analysis device according to claim 18.

20. A method for producing the optical unit according to any one of claims 1 to 17, comprising the steps of: A base material whose main component is a metal or an alloy is irradiated with a picosecond laser or a femtosecond laser to form the plurality of convex portions. A method for manufacturing an optical unit comprising the steps of:

21. irradiating the picosecond laser or the femtosecond laser in an atmosphere containing oxygen to form an oxide film on the plurality of protrusions; 21. The method for manufacturing an optical unit according to claim 20.

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