Optical element

Abstract

To provide an optical element equipped with a light-shielding film that achieves both thinness and light-shielding properties. [Solution] The optical element comprises a transparent substrate containing a first glass, and a light-shielding film provided on at least a portion of the surface of the transparent substrate, which is a sintered body containing a second glass and a pigment. The thickness of the light-shielding film of the above optical element is 100 μm or less, the optical density of the light-shielding film at a wavelength of 524 nm is 4 or more in OD value, and the reflectance of the interface between the transparent substrate and the light-shielding film is 0.5% or less.

Description

Technical Field

[0001] The present disclosure relates to an optical element.

Background Art

[0002] The optical element described in Patent Document 1 is an optical element having a glass body, and has a colored layer located inside the glass body and outside the effective diameter of the optical element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the colored layer of Patent Document 1 is applied to an optical element that requires high light-shielding properties, it is necessary to increase the thickness of the colored layer. As a result, it may not be possible to achieve both the thinness and the light-shielding property of the light-shielding film.

[0005] An embodiment of the present disclosure aims to provide an optical element including a light-shielding film that can achieve both thinness and light-shielding property.

Means for Solving the Problems

[0006] The optical element according to an embodiment of the present disclosure includes a transparent substrate including a first glass, and a light-shielding film provided on at least a part of the surface of the transparent substrate, the light-shielding film being a sintered body including a second glass and a pigment.

Effects of the Invention

[0007] According to an embodiment of the present disclosure, it is possible to provide an optical element including a light-shielding film that can achieve both thinness and light-shielding property.

Brief Description of the Drawings

[0008] [Figure 1] Figure 1(A) is a plan view of an optical element according to one embodiment, and Figure 1(B) is a cross-sectional view of the optical element according to one embodiment. [Modes for carrying out the invention]

[0009] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, identical or similar components are denoted by the same reference numerals, and their descriptions may be omitted. In this specification, the "~" indicating a numerical range means that the numbers written before and after it are included as the lower and upper limits. The numerical range includes the rounded range. In addition, in this embodiment, the lower and upper limits can be combined as appropriate. That is, for example, if a lower limit is listed for a parameter and an upper limit is listed for that parameter, the parameter may have any value selected from the listed lower limits as its lower limit and any value selected from the listed upper limits as its upper limit.

[0010] The optical element 10 according to this embodiment is, for example, an aperture used as an optical unit in a camera optical unit. The application of the optical element 10 is not particularly limited, and the optical element 10 may be, for example, an optical filter or a prism.

[0011] Figure 1(A) is a plan view of an optical element according to one embodiment, and Figure 1(B) is a cross-sectional view of the optical element according to one embodiment. An optical element 10 according to one embodiment will be described with reference to Figures 1(A) and 1(B). The optical element 10 comprises a transparent substrate 20 and a light-shielding film 30. The transparent substrate 20 has a first surface 21 and a recess 22 formed in a part of the first surface 21. The light-shielding film 30 is provided in the recess 22 and has a second surface 31. The first surface 21 and the second surface 31 are planar in this embodiment, but are not limited to this, and may be curved surfaces, for example.

[0012] Viewed from a first direction, the shape of the optical element 10 is rectangular, as shown in Figure 1(A), for example. The rectangle includes a square. In the example in Figure 1, the light-shielding region A2 is provided along the four sides of the rectangle, but this is merely an example and is not limited to this. Furthermore, the shape of the optical element 10 viewed from a first direction is not limited to a rectangle; the shape of the optical element 10 viewed from a first direction may be other shapes, such as a circle.

[0013] As shown in Figure 1(A), when viewed from a first direction (hereinafter simply referred to as the "first direction") perpendicular to the first surface 21 of the transparent substrate 20, the optical element 10 comprises a transmission region A1 that transmits a portion of the light LB of a desired wavelength and a light-shielding region A2 that blocks another portion of the light LB. The transmission region A1 is formed on the first surface 21 excluding the recess 22, and the light-shielding region A2 is formed on the second surface 31. The optical element 10 shapes the light LB with the light-shielding region A2. In Figure 1(A), A3 is the boundary line between the transmission region A1 and the light-shielding region A2, that is, the boundary line between the first surface 21 and the second surface 31. Note that the transmission region A1 is not an essential component, and the optical element 10 may consist only of the light-shielding region A2. That is, the entire surface of the first surface 21 of the transparent substrate 20 may be covered with the light-shielding film 30.

[0014] In Figures 1(A) and 1(B), the transparent substrate 20 is plate-shaped, but the shape of the transparent substrate 20 is not particularly limited and may be a rectangular prism, a triangular prism, or the like. The first surface 21 of the transparent substrate 20 is, for example, the surface on which light LB is emitted from the inside of the transparent substrate 20 to the outside. However, the first surface 21 of the transparent substrate 20 may also be the surface on which light LB is incident from the outside of the transparent substrate 20 to the inside. Furthermore, the first surface 21 of the transparent substrate 20 may also be the surface on which light LB is reflected from the inside of the transparent substrate 20 to the inside.

[0015] In the example shown in Figure 1(B), the transparent substrate 20 has a first surface 21 and a recess 22 formed in a part of the first surface 21. A light-shielding film 30 is embedded in the recess 22. The light-shielding film 30 is provided in the recess 22 and has a second surface 31 that is formed continuously with the first surface 21 without any step difference. Note that the recess 22 is not an essential component; for example, the first surface 21 may be flush with the surface, and the light-shielding film 30 may be laminated on a part or all of the first surface 21.

[0016] The transparent substrate 20 is a substrate that transmits visible light. The content of the first glass in the transparent substrate 20 is preferably 85% to 100% by volume, more preferably 90% to 100% by volume, even more preferably 95% to 100% by volume, and most preferably 100% by volume. This suppresses the influence of temperature changes on optical properties (e.g., refractive index and extinction coefficient).

[0017] The first glass is not particularly limited, but may include, for example, soda-lime glass, borosilicate glass, aluminosilicate glass, lead glass, optical glass, synthetic quartz glass, or crystallized glass. The composition of the glass can be measured by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy). Optical glass is broadly classified into crown glass and flint glass, and further classified by composition, properties, etc. Here are some examples of optical glass. Borosilicate crown glass is a type of crown glass, for example, a glass containing 60-85% by mass of SiO2, 7-20% by mass of B2O3, 0-10% by mass of Na2O, 0-10% by mass of K2O, 0-10% by mass of Al2O3, 0-10% by mass of CaO, and 0-10% by mass of BaO. Lanthanum crown glass is a type of crown glass that contains, for example, 2-30 mass% SiO2, 10-40 mass% La2O, 5-35 mass% B2O3, 0-25 mass% ZnO, and 0-15 mass% Nb2O5. Titanium glass is a type of flint glass, for example, a glass containing 30 to 70% by mass of SiO2, 3 to 30% by mass of TiO2, 0 to 25% by mass of BaO, 0 to 15% by mass of ZnO, 0 to 15% by mass of Na2O, 0 to 10% by mass of K2O, and 0 to 15% by mass of B2O3. Niobium flint glass is a type of flint glass, for example, a glass containing 0 to 30% by mass of SiO2, 15 to 55% by mass of Nb2O5, 0 to 30% by mass of P2O5, 0 to 10% by mass of Na2O, and 0 to 10% by mass of K2O.

[0018] The light-shielding film 30 contains, for example, a second glass. The content of the second glass in the light-shielding film 30 is 70% to 99% by volume, more preferably 80% to 98% by volume, and even more preferably 85% to 97% by volume. Thereby, the change in optical properties (such as refractive index and attenuation coefficient) due to temperature change of the light-shielding film 30 can be reduced. The light-shielding film 30 may be partially crystallized. The content of the second glass in the light-shielding film 30 can be measured by SEM-EDX.

[0019] The light-shielding film 30 is a sintered body of a second glass and a pigment. The light-shielding film 30 contains the pigment dispersed in the second glass. Thereby, the light-shielding property of the light-shielding film can be improved. Here, if the pigment can be observed as particles without being dissolved in the second glass in the SEM (Scanning Electron Microscope) image of the light-shielding film 30, it can be determined that the light-shielding film 30 is a sintered body of a second glass and a pigment.

[0020] The porosity of the light-shielding film 30 is preferably 0% to 10% by volume, more preferably 0% to 5% by volume, and even more preferably 0% to 2% by volume. Thereby, the light-shielding property of the light-shielding film 30 becomes good.

[0021] In the light-shielding film 30, the average particle diameter of the pigment particles is preferably 1 nm or more and 1000 nm or less, more preferably 1 nm or more and 500 nm or less, and even more preferably 1 nm or more and 300 nm or less. Thereby, the light-shielding property of the light-shielding film 30 can be improved. The particle diameter of the pigment particles can be measured by obtaining a cross-sectional SEM (Scanning Electron Microscope) image of the light-shielding film 30, measuring the particle diameter of the pigment particles 50 from the SEM image by binarization, and taking the arithmetic mean of the particle diameters as the average particle diameter of the pigment particles.

[0022] The content rate of the pigment in the light-shielding film 30 is preferably 1% by volume or more and 30% by volume or less, more preferably 2% by volume or more and 20% by volume or less, and even more preferably 3% by volume or more and 15% by volume or less. Thereby, while suppressing the difference in linear expansion coefficient and refractive index difference between the transparent base material 20 and the light-shielding film 30, the light-shielding property of the light-shielding film 30 can be improved. The volume percentage of the second glass and the pigment in the light-shielding film 30 is obtained by acquiring a cross-sectional SEM (Scanning Electron Microscope) image of the light-shielding film 30, separating the glass region and the pigment region from the SEM image by binarization, and calculating the volume percentage from the respective area ratios.

[0023] The pigment is, for example, a black pigment. The pigment is preferably an inorganic pigment. The inorganic pigment is, for example, a metal oxide, a metal, or a carbon-based material. The metal oxide or metal used as the pigment is preferably a metal oxide or metal containing at least one of copper, chromium, manganese, iron, cobalt, and titanium. A mixture of copper, chromium, and manganese is more preferable as the metal oxide or metal used as the pigment. The carbon-based material used as the pigment is preferably graphite or carbon black. Graphite is crystalline and carbon black is amorphous. Here, the carbon-based material used as the pigment is more preferable from the viewpoints of controlling the particle diameter of the pigment and the color tone of the light-shielding film 30. The light-shielding film 30 may contain a plurality of types of pigments in order to adjust the wavelength dependence of the transmittance of the light LB.

[0024] The second glass is, for example, a glass mainly composed of SiO2, a bismuth-based glass, or a vanadium-based glass. Bismuth-based glass contains Bi2O3. Vanadium-based glass contains V2O5. Glass mainly composed of SiO2 tends to have a lower refractive index than bismuth-based glass and vanadium-based glass. Alternatively, lanthanum borate-based glass may be used as the second glass. In this disclosure, "main component" refers to the component that is present in the largest amount among the components, preferably 50% by mass or more. When measuring the composition of the second glass, the pigment should be avoided when measuring the composition of the glass.

[0025] The light-shielding film 30 is obtained by firing a glass paste containing, for example, glass powder of a second glass and pigment powder. The glass powder is also called glass frit. The glass paste may also contain additives other than glass powder and pigment, such as a resin binder such as methylcellulose, ethylcellulose, carboxymethylcellulose, oxyethylcellulose, benzylcellulose, propylcellulose, or nitrocellulose. The resin binder is removed before firing the glass paste.

[0026] A preferred combination of the first glass and the second glass is, for example, a combination in which the first glass is borosilicate crown glass and the second glass is zinc borosilicate glass. This reduces the refractive index difference between the first glass and the second glass, thereby reducing the reflectance of light incident from the transparent substrate 20 to the light-shielding film 30. As a result, when the optical element has a transmission region A1, the reflectance of light incident from the transparent substrate 20 to the light-shielding film 30 can be reduced, and stray light can be suppressed.

[0027] A preferred combination of the second glass and pigment is, for example, a combination in which the second glass is borosilicate crown glass and the pigment is carbon black pigment. This allows for the formation of a good sintered body with the second glass and pigment, thereby improving the light-shielding properties of the light-shielding film 30.

[0028] It is more preferable that the first glass and the second glass have the same composition. When the first glass and the second glass have the same composition, the second glass is transparent. This reduces the difference in the coefficient of thermal expansion between the transparent substrate 20 and the light-shielding film 30, thereby reducing stress. Furthermore, the difference in refractive index between the transparent substrate 20 and the light-shielding film 30 can be made smaller, reducing the reflectance of light incident from the transparent substrate 20 to the light-shielding film 30. As a result, when the optical element has a transmission region A1, the reflectance of light incident from the transparent substrate 20 to the light-shielding film 30 can be reduced, and stray light can be further suppressed.

[0029] The thickness of the light-shielding film is 100 μm or less, and the light-shielding rate of the light-shielding film for light with a wavelength of 524 nm is preferably such that the optical density of the light-shielding film 30 at a wavelength of 524 nm is 4 or more in terms of OD value. Furthermore, when the thickness of the light-shielding film is 100 μm, the optical density (OD) of the light-shielding film 30 at a wavelength of 524 nm is preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more. When the thickness of the light-shielding film is 100 μm, the optical density (OD) of the light-shielding film 30 at a wavelength of 524 nm is preferably 10 or less. Furthermore, the minimum thickness at which the optical density of the light-shielding film 30 at a wavelength of 524 nm becomes OD4 is preferably 5 μm to 100 μm, more preferably 7 μm to 50 μm, and even more preferably 10 μm to 40 μm. This makes it possible to provide an optical element that achieves both thinness and light-shielding performance of the light-shielding film 30. The optical density of the light-shielding film 30 according to this disclosure can be calculated based on the optical density of the transmitted light from the optical element for light at a wavelength of 524 nm and the optical density of the transmitted light from the transparent substrate 20 for light at a wavelength of 524 nm.

[0030] The reflectance at the interface between the transparent substrate 20 and the light-shielding film 30 is preferably 0% to 0.5%, more preferably 0% to 0.2%, and even more preferably 0% to 0.1%. This makes it possible to provide an optical element with high light-shielding properties of the light-shielding film 30. Here, the reflectance at the interface between the transparent substrate 20 and the light-shielding film 30 according to this disclosure is measured using a microspectrometer. For example, the USPM-RU-W manufactured by Evident Co., Ltd. is used as the microspectrometer. When measuring the reflectance, a 10x objective lens is used, and the amount of reflected light on the BK7 glass (borosilicate crown glass) mirror surface is used as a reference to measure the reflectance of the object under measurement. More specifically, the measurement can be performed by directing light from the side of the transparent substrate 20 where the light-shielding film 30 is not provided toward the light-shielding film 30 through the transparent substrate 20, and focusing on the interface between the transparent substrate 20 and the light-shielding film 30. In this case, if a light-shielding film 30 is provided on both sides of the transparent substrate 20, the sample obtained by removing the light-shielding film 30 on one side by polishing or the like can be used for reflectance measurement.

[0031] The refractive index difference Δnd = nd2 - nd1 between the refractive index nd1 of the transparent substrate 20 in the sodium d line (light with a wavelength of 589 nm) and the refractive index nd2 of the light-shielding film 30 in the sodium d line is preferably 0 or more and 0.2 or less, more preferably 0 or more and 0.1 or less, and even more preferably 0 or more and 0.05 or less. As a result, when there is a transmission region A1 in the optical element, the reflectance of light incident from the transparent substrate 20 to the light-shielding film 30 can be reduced, and stray light can be suppressed.

[0032] The absolute value of the difference between the linear expansion coefficient of the transparent substrate 20 and the linear expansion coefficient of the light-shielding film 30 is preferably 0 / °C or higher, or 3 × 10⁻⁶. -6 It is below / ℃, more preferably 0 / ℃ or higher, and 2 × 10 × 10 -6 / ℃ or less, more preferably 0 / ℃ or more, 1 × 10 -6 The temperature is below / °C. This reduces the internal stress of the optical element. The coefficient of linear expansion is measured using a thermomechanical analyzer (TMA).

[0033] (Other embodiments) The following describes optical elements according to other embodiments. An optical element according to other embodiments is, for example, a component of an imaging device used in outer space, in which the transparent substrate 20 has a transparent region on the first surface where no light-shielding film is provided.

[0034] When a transmission region is irradiated with gamma rays from a cobalt-60 source such that the absorbed dose is 0.2 kGy, the transmittance of light at a wavelength of 524 nm in the transmission region before gamma ray irradiation is defined as T1 (%), and the transmittance of light at a wavelength of 524 nm in the transmission region after gamma ray irradiation is defined as T2 (%). In this case, the ratio of the difference in transmittance ΔT (ΔT=|T1-T2|) to the transmittance T1 is preferably 0% to 20%, more preferably 0% to 15%, and even more preferably 0% to 10%. This suppresses the influence of radiation such as cosmic rays on the optical properties. Here, the transmittance can be measured, for example, by measuring the transmitted light at a wavelength of 524 nm using an ultraviolet-visible spectrophotometer (Hitachi High-Tech Corporation (UH4150 model)).

[0035] In this embodiment, the first glass of the transparent substrate 20 preferably contains cerium oxide (CeO2). This allows the transparent substrate 20 to suppress discoloration caused by radiation such as cosmic rays. The cerium oxide content of the first glass of the transparent substrate 20 is preferably 0.1% by mass or more and 3.0% by mass or less, more preferably 0.15% by mass or more and 2.0% by mass or less, and even more preferably 0.2% by mass or more and 1.7% by mass or less, based on oxide. The cerium oxide content of the first glass of the transparent substrate 20 and the cerium oxide content of the second glass of the light-shielding film 30 can be measured by SEM-EDX.

[0036] In the outgassing test, the optical element 10 preferably has a total mass loss (TML) of 0% to 1%, more preferably 0% to 0.5%, and even more preferably 0% to 0.3%. Furthermore, in the outgassing test, the optical element 10 preferably has a collected volatile condensable material (CVCM) of 0% to 0.1%, more preferably 0% to 0.05%, and even more preferably 0% to 0.01%. In this disclosure, the outgassing test refers to the "standard test method for total mass loss and collected volatile condensable material from outgassing in a vacuum environment" as defined in ASTM E595. By meeting this standard, an optical element suitable as a component for optical equipment used in outer space or vacuum environments can be provided.

[0037] (effect) As described above, the optical element according to the first aspect of this disclosure comprises a transparent substrate including a first glass, and a light-shielding film provided on at least a portion of the surface of the transparent substrate, which is a sintered body containing a second glass and a pigment. This makes it possible to provide an optical element with a light-shielding film that can achieve both thinness and light-shielding properties.

[0038] The optical element according to the second aspect of this disclosure is the optical element according to the first aspect, wherein the optical density of the light-shielding film at a wavelength of 524 nm is 4 or higher in terms of OD value. This makes it possible to provide an optical element equipped with a light-shielding film that can achieve both thinness and light-shielding properties.

[0039] An optical element according to a third aspect of this disclosure is an optical element according to the first or second aspect, wherein the reflectance at the interface between the transparent substrate and the light-shielding film is 0.5% or less. This makes it possible to provide an optical element equipped with a light-shielding film that has higher light-shielding properties.

[0040] The optical element according to the fourth aspect of this disclosure is an optical element according to any one of the first to third aspects, wherein the first glass and the second glass have the same composition. This makes it possible to provide an optical element equipped with a light-shielding film that has higher light-shielding properties.

[0041] The optical element according to the fifth aspect of this disclosure is an optical element according to any one of the first to fourth aspects, wherein the pigment contains carbon. This makes it possible to provide an optical element having a light-shielding film with higher light-shielding properties.

[0042] The optical element according to the sixth aspect of this disclosure is an optical element according to any one of the first to fourth aspects, wherein the pigment contains at least one oxide from copper, chromium, manganese, iron, and cobalt. This makes it possible to provide an optical element having a light-shielding film with higher light-shielding properties.

[0043] The optical element according to the seventh aspect of this disclosure is an optical element according to any one of the first to fifth aspects, wherein the transparent substrate has a transparent region on its surface where no light-shielding film is provided, and when gamma rays from a cobalt-60 source are irradiated to the absorbed dose of 0.2 kGy, the ratio of the difference in transmittance ΔT (ΔT=|T1-T2|) between the transmittance T1 (%) of light at a wavelength of 524 nm in the transparent region before gamma ray irradiation and the transmittance T2 (%) of light at a wavelength of 524 nm in the transparent region after gamma ray irradiation is 20% or less. This makes it possible to provide an optical element that can suppress the influence of radiation such as cosmic rays on optical properties.

[0044] The optical element according to the eighth aspect of this disclosure is an optical element according to any one of the first to seventh aspects, wherein in an outgassing test, the total mass loss is 1% by mass or less and the recondensed mass ratio is 0.1% by mass or less. This makes it possible to provide an optical element suitable as a component of imaging equipment used in outer space or vacuum environments.

[0045] The optical element according to the eighth aspect of this disclosure is an optical element according to any one of the first to eighth aspects, wherein the transparent substrate contains 0.1% by mass or more and 1.7% by mass or less of cerium oxide. As a result, the transparent substrate can transmit visible light well while suppressing the effect of radiation on its optical properties.

[0046] (Examples) The following describes some examples. Note that the embodiments may be modified as long as the effects of the invention are achieved.

[0047] Table 1 shows the coating layers for the optical elements in Examples 1 to 3.

[0048] [Table 1]

[0049] (Example 1) In Example 1, the transparent substrate 20 was a 5 mm thick plate-shaped substrate using Ohara S-BSL7 as the first glass. In Example 1, an optical element was fabricated by forming a light-shielding film on one side of the transparent substrate 20. In Example 1, the light-shielding film used colored glass (Shoct NG1) as the second glass, and was formed as a layer of the thickness shown in Table 1. In Example 1, the optical density (OD value) of the transmitted light through the light-shielding film was measured with light of a wavelength of 524 nm, and the minimum thickness of the light-shielding film required to achieve an OD of 4 was calculated based on the obtained OD value.

[0050] (Example 2) In Example 2, the optical element was fabricated and measured in the same manner as in Example 1, except that the light-shielding film was a layer of the thickness shown in Table 1, containing 95% by volume of glass with the same composition as the first glass in Example 1 and 5% by volume of carbon pigment as a colorant. The carbon pigment used was gas black manufactured by Orion Engineered Carbons Co., Ltd.

[0051] (Example 3) In Example 3, the optical element was fabricated and measured in the same manner as in Example 1, except that the light-shielding film was a layer of the thickness shown in Table 1, containing 90% by volume of glass with the same composition as the first glass in Example 1 and 10% by volume of metal oxide pigment as a colorant. As the metal oxide pigment, 42-302A from Tokan Material Technology Co., Ltd. was used.

[0052] (evaluation) As shown in Table 1, in Examples 2 and 3, where pigments were used as colorants, high light-shielding performance was achieved with a thinner thickness compared to Example 1, where coloring components were used as colorants. Specifically, in Examples 3 and 4, the thickness of the light-shielding film at an optical density of OD4 is 100 μm or less, indicating that it is possible to achieve both a light-shielding film thickness of 100 μm or less and a light-shielding rate of OD4 or higher.

[0053] Table 2 shows the optical elements related to Examples 4 to 6.

[0054] [Table 2]

[0055] (Examples 4-9) In Examples 4 to 9, the optical elements were fabricated in the same manner as in Example 2, except that the combination of the first glass of the transparent substrate 20 and the second glass of the light-shielding film 30 was as shown in Table 2. Here, the reflectance shown in Table 2 was measured using the method described above.

[0056] (evaluation) As shown in Table 2, Examples 6-9, in which the first and second glasses had the same composition, showed lower reflectivity compared to Examples 4 and 5, in which the first and second glasses were different types of glass. This indicates that the reflectivity can be further reduced by using the same composition for the first and second glasses.

[0057] The optical elements relating to this disclosure have been described above, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope described in the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of symbols]

[0058] 10 Optical elements 20 Transparent base material 21 1st surface 22 recess 30 Light-shielding film 31 Second surface

Claims

1. A transparent substrate containing the first glass, A light-shielding film is provided on at least a portion of the surface of the transparent substrate, and is a sintered body containing a second glass and a pigment. An optical element equipped with the following features.

2. The thickness of the light-shielding film is 100 μm or less. The optical element according to claim 1, wherein the optical density of the light-shielding film at a wavelength of 524 nm is 4 or more in terms of OD value.

3. The optical element according to claim 1, wherein the reflectance of the interface between the transparent substrate and the light-shielding film is 0.5% or less.

4. The optical element according to claim 1, wherein the first glass and the second glass have the same composition.

5. The optical element according to claim 1, wherein the pigment contains carbon.

6. The optical element according to claim 1, wherein the pigment comprises an oxide of at least one of copper, chromium, manganese, iron, and cobalt.

7. The transparent substrate has a transparent region on its surface where the light-shielding film is not provided. The optical element according to claim 1, wherein when gamma rays from a cobalt-60 source are irradiated such that the absorbed dose is 0.2 kGy, the ratio of the difference in transmittance ΔT (ΔT = |T1 - T2|) between the transmittance T1 (%) of light with a wavelength of 524 nm in the transmission region before irradiation with the gamma rays and the transmittance T2 (%) of light with a wavelength of 524 nm in the transmission region after irradiation with the gamma rays is 20% or less.

8. The optical element according to claim 7, wherein the transparent substrate contains 0.1% by mass or more and 3.0% by mass or less of cerium oxide.

9. An optical element according to any one of claims 1 to 8, wherein in an outgassing test, the total mass loss is 1% by mass or less and the recondensed material ratio is 0.1% by mass or less.

10. The optical element according to claim 1, wherein the first glass includes at least one of the following types of glass: soda-lime glass, borosilicate glass, aluminosilicate glass, lead glass, synthetic quartz glass, crown glass, and flint glass.

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