Reflectance standard unit

Abstract

A reflectance standard unit (1) is provided with: a reflectance standard (20); and a transmissive protection member (12) provided opposing the reflectance standard (20) on one side of the reflectance standard (20) in the thickness direction thereof. An anti-reflection structure (12b) is provided at least on an opposing surface (12a) of the transmissive protection member (12) opposing the reflectance standard (20).

Description

Standard Reflector Unit

[0001] The present invention relates to a standard reflector unit used for calibrating optical characteristic measuring devices and the like.

[0002] When measuring an object (sample) using an optical property measuring device, it is common to calibrate the sample's measurement data to calculate accurate optical property values ​​(see, for example, Patent Document 1). This calibration is performed using a standard reflector provided with reflectance data conforming to international standards. Specifically, the reflectance of the standard reflector is measured using the optical property measuring device used to measure the sample, and this measurement value is used to calibrate the sample's measurement data. For this reason, it is desirable for the standard reflector to be made of a long-term stable material whose reflectance does not fluctuate with environmental loads such as temperature, humidity, and ultraviolet rays. Lead-containing optical glass, for example, has traditionally been used as a standard reflector. However, there is a concern that lead-containing optical glass will be subject to environmental regulations in the future. For this reason, efforts are underway to replace standard reflectors made of other materials.

[0003] However, materials other than lead-containing optical glass have issues with respect to the long-term stability of reflectance, resistance to photochromism, ease of cleaning the material surface, and uniformity of reflectance in the ultraviolet to near-infrared wavelength range, depending on the material.

[0004] Among these materials, barium sulfate and PTFE are excellent in terms of long-term stability of reflectance, resistance to photochromism, and uniformity of reflectance in the ultraviolet to near-infrared wavelength range. However, when reflectors made of these materials are scratched or soiled on the surface, it is difficult to remove the scratches or dirt.

[0005] Japanese Patent Application Laid-Open No. 2002-243550

[0006] Therefore, in order to prevent scratches and dirt from occurring on the material surface, it is conceivable to cover the reflector made of a material such as barium sulfate or PTFE with a transparent protective member.

[0007] However, when this was actually manufactured and verified, it was discovered that the surface reflections occurring on both sides (front and back) of the transparent protective member made the reflection characteristics different from those of conventional optical glass, and that the same calibration results could not be obtained.

[0008] An object of the present invention is to provide a standard reflector unit that allows highly accurate calibration even when a material that is susceptible to scratches and dirt is used as the standard reflector.

[0009] The above object can be achieved by the following means: (1) A standard reflector unit comprising a standard reflector and a transmissive protective member provided opposite the standard reflector on one side of the standard reflector in the thickness direction, wherein an anti-reflection structure is provided on at least the surface of the transmissive protective member facing the standard reflector. (2) The standard reflector unit according to the preceding paragraph 1, in which a space is formed between the standard reflector and the transmissive protective member. (3) The standard reflector unit according to the preceding paragraph 1 or 2, in which the transmissive protective member constitutes a part of the unit body, and the standard reflector is held in an enclosed space within the unit body. (4) The standard reflector unit according to the preceding paragraph 1 or 2, in which the gap between the standard reflector and the transmissive protective member is 0.5 mm or less. (5) The standard reflector unit according to the preceding paragraph 1 or 2, in which the transmissive protective member is made of glass. (6) The standard reflector unit according to the preceding paragraph 1 or 2, in which the standard reflector is made of a white material. (7) The standard reflector unit according to the preceding paragraph 6, in which the standard reflector is made of PTFE. (8) The standard reflector unit according to the preceding paragraph 1 or 2, wherein the anti-reflection structure provided on the transparent protective member is an anti-reflection coating made of an optical thin film formed on the surface of the transparent protective member. (9) The standard reflector unit according to the preceding paragraph 1 or 2, wherein the reflectance of the surface of the transparent protective member on which the anti-reflection structure is provided is 3% or less for normal incidence in visible light wavelengths.

[0010] The standard reflector unit according to the present invention includes a transparent protective member provided opposite the standard reflector on one side of the standard reflector in the thickness direction. Therefore, the surface of the standard reflector is protected by the transparent protective member, which prevents the surface of the standard reflector from coming into contact with the fingertips of the measurer or external members. This prevents the standard reflector from being deformed or its surface from being scratched or soiled by external forces acting on it.

[0011] Furthermore, since an anti-reflection structure is provided on at least the surface of the transmissive protective member facing the standard reflector, the following effect is also achieved. That is, when no transmissive protective member is present, the standard reflector experiences one surface reflection. However, when the standard reflector is covered with a transmissive protective member, in addition to the surface reflection of the standard reflector, surface reflections on both sides of the transmissive protective member are added, resulting in a total of three surface reflections. As a result, the reflection characteristics are not the same as when only the standard reflector is used. To avoid this, by providing an anti-reflection structure on at least the surface of the transmissive protective member facing the standard reflector, it is possible to approach the reflection characteristics when only the standard reflector is used. Furthermore, since an anti-reflection structure is provided on the surface of the transmissive protective member facing the standard reflector, there is no concern that the anti-reflection structure will peel off due to friction during use, etc.

[0012] FIG. 1A is a partially cutaway perspective view of a standard reflector unit 1 according to one embodiment of the present invention, FIG. 1B is a plan view of the standard reflector unit 1, and FIG. 1C is a cross-sectional view taken along line IC-IC in FIG. 1B. It is a cross-sectional view of a standard reflector unit 1 according to another embodiment of the present invention taken along a line in the diameter direction. FIG. 3A is a plan view of a standard reflector unit 1 according to yet another embodiment of the present invention, and FIG. 3B is a cross-sectional view of the standard reflector unit of FIG. 3A taken along line IIIB-IIIB in the diameter direction. It is a schematic explanatory diagram of the reflection characteristics of a standard reflector unit. It is an explanatory diagram for explaining the state of reflection when a standard reflector and a transmissive protective member are facing each other.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] FIG. 1A is a perspective view showing a standard reflector unit 1 according to one embodiment of the present invention, with a portion cut away, FIG. 1B is a plan view of the standard reflector unit 1, and FIG. 1C is a cross-sectional view taken along line IC-IC in FIG. 1B.

[0015] As shown in these figures, the standard reflector unit 1 comprises a lower holder 11 made of, for example, resin and having an open top, and a transparent protective member 12 that closes the upper opening of the lower holder 11, and the unit main body 10 is formed by the lower holder 11 and the transparent protective member 12.

[0016] The lower holder 11 has a circular bottom wall 11a and a short cylindrical peripheral wall 11b integrally formed on the outer periphery thereof. The permeable protective member 12 is a circular plate-like member that is disposed at the upper end of the lower holder 11 and has its peripheral edge integrally joined to the lower holder 11.

[0017] The circular standard reflector 20 is held in the space within the unit body 10 via an annular first spacer 31 arranged on one side (upper side) in the thickness direction of the standard reflector 20 and an annular second spacer 32 arranged on the other side (lower side) in the thickness direction of the standard reflector 20. The outer diameters of the first and second spacers 31, 32 are both set to be approximately the same as or slightly smaller than the inner diameter of the peripheral wall portion 11b of the lower holder 11.

[0018] The lower surface of the lower second spacer 32 is supported by the upper surface of the bottom wall 11a of the lower holder 11, and the peripheral edge of the lower surface of the standard reflector 20 is supported by the upper surface of the second spacer 32. The lower surface of the upper first spacer 31 contacts the peripheral edge of the upper surface of the standard reflector 20, and the upper surface of the first spacer 31 contacts the lower surface of the transmissive protective member 12. Therefore, while being supported by the first and second spacers 31, 32, the standard reflector 20 is arranged parallel to the bottom wall 11a of the lower holder 11 and the standard reflector 20 at the intermediate position in the height direction of the internal space of the unit main body 10. The outer diameter of the standard reflector 20 is set smaller than the inner diameter of the peripheral wall 11b of the lower holder 11.

[0019] Due to the presence of the first spacer 31, a first space 41 having a thickness corresponding to the thickness of the first spacer 31 is formed between the standard reflector 20 and the transmissive protective member 12. On the other hand, due to the presence of the second spacer 32, a second space 42 having a thickness corresponding to the thickness of the second spacer 32 is formed between the standard reflector 20 and the upper surface of the bottom wall portion 11a of the lower holder 11 (corresponding to the opposing surface of the unit body).

[0020] The first spacer 31 is made of a hard material (e.g., metal or hard resin) with little change in thickness, and the second spacer 32 is made of an elastic material such as rubber or resin. This minimizes change in thickness of the upper spacer 31, thereby maintaining a constant distance with high precision between the standard reflector 20 and the transmissive protective member 12. The reason why the lower spacer 32 is made of an elastic material is to absorb dimensional variations in the bottom wall portion 11a of the lower holder 11 with the elastic material. In this embodiment, the thicknesses and widths of the first spacer 31 and the second spacer 32 are set so that the volumes of the first space 41 and the second space 42 are equal.

[0021] As described above, the first space 41 and the second space 42 are respectively formed by the first spacer 31 and the second spacer 32, so that the first space 41 and the second space 42 can be formed without joining the respective components.

[0022] The gap between the standard reflector 20 and the transmissive protective member 12, in other words, the thickness of the first space 41, is preferably set to 0.5 mm or less. By keeping the gap between the standard reflector 20 and the transmissive protective member 12 small, at 0.5 mm or less, the reflecting surface of the standard reflector 20 comes closer to the optical characteristic measuring device, and the reflection characteristics come closer to those of a conventional standard reflector.

[0023] The standard reflector 20 is used to calibrate an optical property measuring device. For this purpose, the standard reflector 20 is required to have a reflection angle characteristic close to that of a perfect diffuse reflecting surface, and a high stability in its spectral reflectance. However, the reflection characteristics of the standard reflector 20 are limited to the measurement wavelength range of the optical property measuring device, and characteristics outside the measurement wavelength range are not considered.

[0024] When the standard reflector 20 is used for white calibration, for example, materials for the standard reflector 20 that provide a stable white color include barium sulfate, titanium oxide, PTFE (polytetrafluoroethylene), ceramic, and silicone rubber. PTFE is particularly desirable because it has excellent environmental stability and can achieve high reflectance over the entire wavelength range of visible light. The color of the standard reflector 20 is not limited to white, and the color of the standard reflector 20 can be set according to the color to be calibrated.

[0025] The transparent protective member 12 is made of, but not limited to, transparent glass, transparent resin, etc. Glass is particularly desirable because it is inexpensive, readily available, and hard, so it is resistant to scratches even when used repeatedly.

[0026] The transparent protective member 12 is disposed in front of the standard reflector 20 to protect the standard reflector 20. Specifically, if the standard reflector 20 made of a material such as PTFE is used alone as a calibration reflector, there is a problem that the surface is prone to scratches and dirt, which are difficult to remove. Furthermore, if the standard reflector 20 is directly exposed to the atmosphere, it is susceptible to the effects of temperature and humidity. Therefore, covering the front of the standard reflector 20 with the transparent protective member 12 prevents the occurrence of scratches and dirt on the surface. Furthermore, since the transparent protective member 12 is integrally joined to the lower holder 11, the interior of the unit body 10, which is composed of the lower holder 11 and the transparent protective member 12, is sealed. This prevents the standard reflector 20 from being directly exposed to the atmosphere, further reducing the effects of temperature and humidity.

[0027] The transmission characteristics of the transparent protective member 12 are limited to the measurement wavelength range of the optical characteristic measuring device, and it is sufficient that the transmission characteristics are maintained within the measurement wavelength range, and the characteristics outside the measurement wavelength range are not important.

[0028] In this embodiment, an anti-reflection structure 12b is applied to at least the surface 12a of the transmissive protective member 12 facing the standard reflector 20 (the back surface of the transmissive protective member 12). One example of the anti-reflection structure 12b is an anti-reflection coating (AR coating) made of an optical thin film. AR coatings made of optical thin films are currently the most common and inexpensive method for preventing reflection in chemical components. The AR coating may be a single layer or a multi-layer. Furthermore, the anti-reflection structure may be a microstructure on the surface of the standard reflector 20 (moth-eye structure).

[0029] The reason why the anti-reflection structure 12b is applied to at least the surface 12a of the transmissive protective member 12 facing the standard reflector 20 is as follows: When light is incident on the standard reflector unit 1, part of the light is surface-reflected by both surfaces (front and back) of the transmissive protective member 12 and the surface of the standard reflector 20, and the remaining light enters the interior of the standard reflector 20 and is transmitted and absorbed, or diffusely reflected. As shown in Figure 4, the reflection characteristics of the standard reflector unit 1 are a combination of these surface reflections and diffuse reflections. In Figure 4, L1 indicates incident light, L2 indicates diffusely reflected light, and L3 indicates reflected light.

[0030] In a conventional standard reflector made of optical glass, for example, the diffuse reflection characteristics are similar to those of the standard reflector unit 1 of the present invention. However, while optical glass has one surface reflection, in a configuration in which the standard reflector 20 and the transmissive protective member 12 face each other, as in the standard reflector unit 1 according to this embodiment, the reflection occurs as shown in Fig. 5. In other words, incident light L1 is reflected three times on the surface: reflection L4 on the surface of the transmissive protective member 12, reflection L5 on the back surface, and reflection L6 on the surface of the standard reflector 20. In this way, the amount of reflection increases as the number of surface reflections increases, resulting in a deviation from the reflection characteristics of a conventional standard reflector.

[0031] Therefore, in order to suppress this increase in surface reflection, an anti-reflection structure 12b is provided on the back surface 12a (opposing surface to the standard reflector 20) of the transmissive protective member 12. This makes it possible to suppress at least the reflection L5 on the back surface of the transmissive protective member 12.

[0032] In order to achieve reflection characteristics closer to those of a conventional standard reflector, it is desirable that the reflectance of the back surface of the transparent protective member 12 provided with the anti-reflection structure 12b for normal incidence at visible light wavelengths (380 to 780 nm) be 3% or less.

[0033] In this way, the reflection characteristics of the transparent protective member 12 are controlled to match the reflection characteristics of a conventional standard reflector. For example, even if the surface reflection of the transparent protective member 12 is high, by applying a multi-layer AR coating to both sides of the transparent protective member 12, the surface reflection of the transparent protective member 12 can be minimized, and the reflection characteristics can be made closer to those of optical glass, which is a conventional standard reflector.

[0034] Furthermore, when the anti-reflection structure 12b is provided on both the front and back surfaces of the transmissive protective member 12, the front surface may be coated with a single layer of AR and the back surface with a multi-layer AR coating, or vice versa. Alternatively, one of the front and back surfaces of the transmissive protective member 12 may be coated with AR and the other may be coated with a moth-eye structure.

[0035] If the standard reflector 20 and the transmissive protective member 12 are both flat and smooth, placing them one on top of the other will cause interference fringes due to the slight gap between them, resulting in a change in spectral reflectance. On the other hand, if the standard reflector 20 and the transmissive protective member 12 are placed apart, changing the distance between them will change the amount of reflected light, resulting in a change in spectral reflectance. Therefore, it is desirable to keep the distance between the standard reflector 20 and the transmissive protective member 12 constant.

[0036] Therefore, in this embodiment, the first spacer 31 is interposed between the standard reflector 20 and the transmissive protective member 12, thereby maintaining the distance between them constant and stable, preferably at 0.5 mm or less. In particular, as described above, by making the first spacer 31 from a hard material with little change in thickness, it is possible to further stabilize the distance between the standard reflector 20 and the transmissive protective member 12. It is desirable that the distance between the standard reflector 20 and the transmissive protective member 12 be a distance that does not cause interference within the measurement wavelength range.

[0037] However, when a relatively soft material such as resin or rubber is used as the standard reflector 20, the standard reflector 20 and the transmissive protective member 12 may be in contact without providing the first spacer 31. This is because the surface of a relatively soft material such as resin or rubber is rough, and the occurrence of interference fringes is suppressed even when the material is in contact with the transmissive protective member 12. In this case, too, the anti-reflection structure 12b is provided on at least the back surface 12a of the transmissive protective member 12. The anti-reflection structure 12b provided on the transmissive protective member 12 is also effective in suppressing the above-mentioned interference fringes.

[0038] By forming the second spacer 32 from an elastic material, as described above, dimensional variations in the bottom wall portion 11a of the lower holder 11 can be absorbed, and the following effect is also achieved. That is, when a relatively soft material such as resin or rubber is used for the standard reflector 20, these materials deform (bend) due to temperature, external force, etc. Therefore, it becomes difficult to maintain a constant distance between the standard reflector 20 and the transmissive protective member 12 over the entire surface of the standard reflector 20. Therefore, in this embodiment, as described above, the second spacer 32 made of an elastic material presses the standard reflector 20 toward the transmissive protective member 12 to float it, so that the distance between the standard reflector 20 and the transmissive protective member 12 does not fluctuate due to impact from a drop, etc.

[0039] Furthermore, the air layers in the first space 41 and the second space 42, which sandwich the standard reflector 20 and are necessary for floating the standard reflector 20, expand due to changes in the environmental temperature. If there is a difference in volume between the first space and the second space, a pressure difference will occur in the air layers in both spaces, which may cause deformation (bending) of the standard reflector 20. For this reason, as described above, in this embodiment, the volumes of the first space 41 and the second space 42 are set to be equal, preventing a pressure difference from occurring in the air layers in both spaces.

[0040] 1A to 1C, a first space 41 is formed between the standard reflector 20 and the transmissive protective member 15 on one side in the thickness direction of the standard reflector 20. Furthermore, a second space 42 is formed between the standard reflector 20 and the opposing surface of the unit body 1 on the other side in the thickness direction of the standard reflector 20. This prevents deformation of the standard reflector 20, such as bending or curvature due to changes in environmental temperature, as occurs when a different member is in contact with the standard reflector 20. Furthermore, because the first space is provided on the transmissive protective member 12 side, the occurrence of interference fringes is suppressed and the spectral reflectance is stabilized.

[0041] Furthermore, since the surface of the standard reflector 20 is protected by the transparent protective member 12, the surface of the standard reflector 20 is prevented from coming into contact with the fingertips of the measurer or external members by the transparent protective member 12. This makes it possible to prevent the standard reflector from being deformed or its surface from being scratched or soiled due to the application of external force to the standard reflector.

[0042] Furthermore, since the anti-reflection structure 12b is provided on at least the back surface 12a of the transmissive protective member 12 facing the standard reflector 20, it is possible to achieve reflection characteristics close to those of only the standard reflector 20. Furthermore, since the anti-reflection structure 12b is provided on the back surface 12a of the transmissive protective member, there is no concern that the anti-reflection structure will peel off due to friction during use.

[0043] As a result, it is possible to provide a standard reflector unit 1 that has a reflectance equivalent to that of a conventional standard reflector and that is stable over the long term.

[0044] Next, a standard reflector unit 1 according to another embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view of the standard reflector unit 1 taken along a line in the diameter direction.

[0045] In this embodiment, instead of the second spacer 32, an annular step 13 is formed integrally with the lower holder 11 along the circular inner circumferential corner of the lower holder 11. This step 13 has an annular horizontal surface 13a and an annular vertical surface 13b, and the lower peripheral edge of the standard reflector 20 abuts and is supported on the annular horizontal surface 13a. The presence of this step 13 separates the standard reflector 20 from the bottom wall 11a of the lower holder 11, and a second space 42 is formed between the bottom wall 11a and the standard reflector 20.

[0046] 1A to 1C. The standard reflector 20, the first spacer 31, and the transmissive protective member 12 have the same configuration as the standard reflector unit 1 shown in FIGS. 1A to 1C. An anti-reflection structure 12b may also be provided on the surface of the transmissive protective member 12.

[0047] In addition, instead of the first spacer 31, a ring-shaped downward convex portion may be formed integrally with the transparent protective member 12 on the peripheral portion of the lower surface of the transparent protective member 12, and the first space 41 may be formed between the transparent protective member 12 and the standard reflector 20 by bringing this convex portion into contact with the standard reflector 20.

[0048] Next, a standard reflector unit 1 according to still another embodiment of the present invention will be described with reference to Figures 3A and 3B. Figure 3A is a plan view of the standard reflector unit 1, and Figure 3B is a cross-sectional view of the standard reflector unit 1 of Figure 3A taken along line IIIB-IIIB in the diameter direction.

[0049] In this embodiment, the unit body 10 is composed of a covered, short, cylindrical upper holder 14 with an open bottom, and a bottom plate 15 that is joined to the peripheral edge of the bottom of the upper holder 14 and closes the bottom opening of the upper holder 14. The top plate portion of the upper holder 14 is the transmissive protective member 12, and the upper holder 14 is integrally formed from the same material as the transmissive protective member 12. Therefore, in this embodiment as well, the transmissive protective member 12 is provided above the standard reflector 20, facing it with the first spacer 31 interposed therebetween. An anti-reflection structure 12b is provided on the back surface 12a of the transmissive protective member 12. An anti-reflection structure 12b may also be provided on the front surface of the transmissive protective member 12.

[0050] The configurations of the standard reflector 20 and the first and second spacers 31 and 32 other than the unit body 10 are the same as those of the embodiment shown in FIGS. 1A to 1C.

[0051] The standard reflector unit 1 according to the embodiment of the present invention is used for calibrating an optical characteristic measuring device. The optical characteristic measuring device has a measurement aperture, an illumination unit that illuminates the measurement aperture surface, and a light receiving unit that receives reflected light from the measurement aperture surface.

[0052] When calibrating the optical property measuring device, the standard reflector unit 1 is illuminated by the illumination unit of the optical property measuring device with the measurement aperture surface in contact with the surface of the transparent protective member 12 of the standard reflector unit 1. After passing through the transparent protective member 12, the illumination light is reflected by the standard reflector 20. A portion of the reflected light passes through the measurement aperture again and is received by a sensor installed in the light receiving unit of the optical property measuring device, and a measurement value corresponding to the amount of received light is output from the optical property measuring device. A calibration coefficient is calculated from this measurement value and the reflectance data of the standard reflector unit 1 that is attached in advance, and the calibration is completed.

[0053] In this embodiment, the anti-reflection structure 12b is provided on at least the surface 12a of the transmissive protective member 12 of the standard reflector unit 1 facing the standard reflector 20, so the reflectance data of the standard reflector unit 1 is equivalent to that of a conventional standard reflector. Therefore, high-precision calibration can be performed in the same way as with a conventional standard reflector.

[0054] This application claims priority from Japanese Patent Application No. 2024-083545, filed on May 22, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0055] The present invention can be used as a standard reflector unit used for calibrating optical property measuring devices and the like.

[0056] REFERENCE SIGNS LIST 1 Standard reflector unit 10 Unit body 11 Lower holder 11a Bottom wall 12 Transmissive protective member 12a Back surface (surface facing standard reflector) 13 Step 13a Horizontal surface 13b Vertical surface 14 Upper holder 15 Bottom plate 20 Standard reflector 31 First spacer 32 Second spacer 41 First space 42 Second space

Claims

1. A standard reflector unit comprising: a standard reflector; and a transparent protective member arranged opposite the standard reflector on one side of the standard reflector in the thickness direction, wherein an anti-reflection structure is provided on at least the surface of the transparent protective member facing the standard reflector.

2. The standard reflector unit according to claim 1, wherein a space is formed between the standard reflector and the transparent protective member.

3. A standard reflector unit according to claim 1 or 2, wherein the transparent protective member constitutes a part of the unit body, and the standard reflector is held in an enclosed space within the unit body.

4. A standard reflector unit according to claim 1 or 2, wherein the distance between the standard reflector and the transparent protective member is 0.5 mm or less.

5. A standard reflector unit according to claim 1 or 2, wherein the transparent protective member is made of glass.

6. A standard reflector unit according to claim 1 or 2, wherein the standard reflector is made of a white material.

7. The standard reflector unit according to claim 6, wherein the standard reflector is made of PTFE.

8. A standard reflector unit according to claim 1 or 2, wherein the anti-reflection structure provided on the transparent protective member is an anti-reflection coating made of an optical thin film formed on the surface of the transparent protective member.

9. A standard reflector unit according to claim 1 or 2, wherein the reflectance of the surface of said transparent protective member on which said anti-reflection structure is provided is 3% or less for normal incidence in visible light wavelengths.

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