JP6941919B2 - Optical instruments and prisms - Google Patents

Description

The present invention is an observation optical device having an observation optical system having a prism having a pair of reflecting surfaces intersecting at a nominal angle of 90 ° and at least one lens, and an object image is inverted vertically and horizontally and converted into an upright orthodox image. Regarding prisms, especially roof prisms.

The roof prism used in observation optical instruments such as microscopes, telescopes, binoculars, single-lens reflex cameras, single-lens reflex digital cameras, and surveying instruments has the pupils of the observation optical system divided by the ridges of a pair of reflective surfaces that intersect at a nominal angle of 90 °. Therefore, high processing accuracy is required, but since the prism can be made smaller than other upright prisms such as the Porro prism, there is an advantage that the optical device can be made smaller and lighter.

On the other hand, it is known that when a light beam is reflected by a reflecting surface, a phase difference occurs between the s-polarized light component and the p-polarized light component, which are orthogonal to each other, before and after the surface. In an optical system in which the pupil is divided by a ridge like a roof prism, the polarization state of the light emitted from the roof prism differs between one of the divided pupils and the other, which causes wavefront aberration and the imaging performance of the observed image. Deteriorate. The larger the phase difference generated on the reflecting surface, the larger the difference in the polarization state generated, and the dihedral image is observed and the contrast is lowered as in the case where the processing accuracy of the surface angle is low.

Conventionally, in order to reduce the phase difference generated on the reflective surface of the roof prism, a metal film of aluminum or silver has been formed on the reflective surface. However, as the processing accuracy of the roof prism is improved, it has been pointed out that the metal film is insufficient in the effect of reducing the phase difference in question.

Patent Document 1 (Japanese Patent Laid-Open No. 11-326781) describes a dielectric film having refractive indexes M1, M2 and M3 (however, 2.0 <M1 <2.1, 1.35 <M2 <1.4 and 1.45 <M3 <1.5) on the roof surface of the roof prism. ) Is disclosed, and it is described that it is effective in reducing the phase difference of visible wavelength light with respect to a roof prism made of a base material having a refractive index of 1.46 to 1.6. .. That is, the phase difference reducing multilayer film described in Patent Document 1 suppresses the change in the phase difference between s-polarized light and p-polarized light before and after the reflection of the light flux incident on the pair of reflecting surfaces of the roof prism, and suppresses the deterioration of wavefront aberration. It has the effect of improving the performance of the observed image.

However, since the phase difference reducing multilayer film described in Patent Document 1 utilizes total reflection that occurs when the incident angle of the light reflected on the inner surface of the base material exceeds the critical angle, dust, dirt, etc. on the outer surface of the base material are used. When the light is attached, the drawback is that the internally reflected light is scattered or absorbed, and the contrast of the observed image is lowered.

In order to prevent the influence of dust and dirt on the outer surface of the base material, it is effective to form a metal monolayer film on the reflective surface to block light from the outside of the roof prism. However, for example, in a base material having a refractive index of 1.516, when light from the inside of the base material is reflected at an incident angle of 49 ° on a reflective surface on which a metal monolayer film is formed, the phase difference between s-polarized light and p-polarized light is 20 ° or more. It becomes. When the difference in the polarization state on the reflecting surface is large as described above, there are problems that a double image is observed, the contrast is lowered, and a color difference is generated between the two roof surfaces in the image containing the polarization component.

Japanese Unexamined Patent Publication No. 11-326781

Therefore, an object of the present invention is to provide a prism having a small phase difference between s-polarized light and p-polarized light before and after reflection of an incident light flux, and an optical device provided with the prism.

As a result of diligent research in view of the above objectives, the present inventors adjusted the phase difference between s-polarized light and p-polarized light by forming two or more layers of dielectric films having different refractive indexes between the metal film and the base material. He found what he could do and came up with the present invention.

That is, the optical device of the present invention is an optical device having an observation optical system including a prism having a pair of reflecting surfaces intersecting at a nominal surface angle of 90 ° and at least one lens.
The prism is arranged so that the ridges of the pair of reflecting surfaces divide the pupil of the observation optical system.
The pair of reflective surfaces of the prism
(a) A dielectric multilayer film consisting of at least two layers of dielectric film, and
(b) It has a metal film laminated on the dielectric multilayer film.
The dielectric multilayer film is characterized in that the refractive indexes of adjacent dielectric films are different from each other, and the optical film thickness of each dielectric film is 5 nm or more.

The dielectric multilayer film preferably has a refractive index difference of 0.2 or more between the dielectric film having the highest refractive index and the dielectric film having the lowest refractive index.

The dielectric multilayer film preferably has a refractive index difference of 0.2 or more between the dielectric film having the highest refractive index and the dielectric film on the side closest to the metal film.

The dielectric multilayer film includes at least one high refractive index film having a refractive index of 1.8 or more and at least one low refractive index film having a refractive index of less than 1.8, and the high refractive index film and the low refractive index film. The difference in refractive index of is preferably 0.2 or more.

The dielectric film on the side closest to the prism among the dielectric films is adjacent to the prism, and the metal film has a film thickness at least such that the transmittance with respect to visible light is substantially 0%. Is preferable.

The metal film is a simple substance film composed of one selected from the metal group consisting of silver, aluminum, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium, or at least one selected from the metal group. It is preferably a film of an alloy containing seeds.

The dielectric film is TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , ZrO ₂ , HfO ₂ , Y ₂ O ₃ , WO ₃ , CeO ₂ , SnO ₂ , MgO, SiO, Al ₂ O ₃ , CeF ₃ , YF ₃ , LaF ₃ , SiO ₂ , CaF ₂ , MgF ₂ and AlF ₃ from at least one selected from the dielectric group, or from a compound containing at least one selected from the dielectric group. It is preferable to be.

The prism of the present invention is a prism having a pair of reflecting surfaces intersecting at a nominal angle of 90 °.
The pair of reflective surfaces
(a) A dielectric multilayer film consisting of at least two layers of dielectric film, and
(b) It has a metal film laminated on the dielectric multilayer film.
The dielectric multilayer film is characterized in that the refractive indexes of adjacent dielectric films are different from each other, and the optical film thickness of each dielectric film is 5 nm or more.
The prism is preferably a pentadha prism, a Peshan prism or an amici prism.

Since the prism provided in the optical instrument of the present invention can reduce the phase difference between s-polarized light and p-polarized light, it can be used in various observation optical instruments.

It is a schematic diagram for demonstrating the change of the phase difference between s-polarized light and p-polarized light when the light flux from the inside of a base material is reflected by the surface (the interface with air). It is a graph which shows the incident angle dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside of a base material is reflected on the surface. It is a schematic diagram which shows the optical path of the light flux incident on a Peshan prism. It is a schematic diagram which shows the optical path of the light flux incident on a pentaprism. It is a schematic diagram which shows the optical path of the light flux incident on the amici prism. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided only with the metal monolayer film (Ag: silver, Al: aluminum, Au: gold). Wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected on a base material provided with only a metal monolayer film (Ag: silver, Al: aluminum, Au: gold). It is a graph which shows. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided only with the metal monolayer film (one of Cu: copper, Ni: nickel, Cr: chromium). Wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected on a base material provided with only a metal single-layer film (Cu: copper, Ni: nickel, Cr: chromium). It is a graph which shows. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 1. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 1. FIG. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Reference Example 2. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Reference Example 2. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Reference Example 3. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Reference Example 3. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 4. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 4. FIG. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 5. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 5. FIG. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 6. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 6. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 7. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 7. FIG. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 8. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the multilayer film of Example 8. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 1. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 1. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 2. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 2. It is a graph which shows the wavelength dependence of the reflectance when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 3. It is a graph which shows the wavelength dependence of the phase difference between s-polarized light and p-polarized light when the light flux from the inside is reflected by the base material provided with the reflective film of Comparative Example 3.

[1] Optical device The optical device of the present invention is an optical device having an observation optical system including a prism having a pair of reflecting surfaces intersecting at a nominal surface angle of 90 ° and at least one lens, and the prism. Is arranged so that the ridges of the pair of reflecting surfaces divide the pupil of the observation optical system, and the pair of reflecting surfaces of the prism are (a) a dielectric multilayer film composed of at least two layers of dielectric film. , And (b) have a metal film laminated on the dielectric multilayer film, and the dielectric multilayer film has different refractive coefficients of adjacent dielectric films, and the optical film of each dielectric film is different from each other. It is characterized by a thickness of 5 nm or more.

(1) Dielectric multilayer film In the optical device of the present invention, a dielectric multilayer film composed of two or more layers of dielectric films is provided between a base material (prism) and a metal film. In the dielectric multilayer film, the refractive indexes of adjacent dielectric films are different from each other, and the optical film thickness of each dielectric film is 5 nm or more. Among the dielectric films, the difference in refractive index between the dielectric film having the highest refractive index and the dielectric film having the lowest refractive index is preferably 0.2 or more. Further, it is preferable that the difference in refractive index between the dielectric film having the highest refractive index and the dielectric film on the side closest to the metal film is 0.2 or more. It is preferable that the dielectric film on the side closest to the prism among the dielectric films is adjacent to the prism.

It is preferable that at least one layer of the dielectric film is a high refractive index film having a refractive index of 1.8 or more, and at least one layer is a low refractive index film having a refractive index of less than 1.8. At this time, the difference in refractive index between the high refractive index film and the low refractive index film is preferably 0.2 or more. The film adjacent to the metal film is preferably a low refractive index film.

For example, in the case of two layers of dielectric film, the base material side is a high refractive index film with a refractive index of 1.8 or more, and the metal film side is a low refractive index film with a refractive index of less than 1.8, and the difference in refractive index between them is 0.2. The above is preferable. When composed of three or more layers of dielectric film, the film adjacent to the substrate may be a high refractive index film or a low refractive index film, but the film adjacent to the metal film is a low refractive index film. Is preferable.

For example, in the case of three layers, it is composed of a high refractive index film, a low refractive index film and a low refractive index film from the base material side, or a low refractive index film, a high refractive index film and a low refractive index film from the base material side. The configuration is preferred. In the case of four layers, the composition is composed of a high refractive index film, a low refractive index film, a high refractive index film and a low refractive index film from the base material side, or a low refractive index film, a high refractive index film and a low refractive index from the base material side. A structure composed of a rate film and a low refractive index film is preferable, and in the case of a five-layer structure, a structure composed of a high refractive index film, a low refractive index film, a high refractive index film, a low refractive index film and a low refractive index film from the base material side. , Or a configuration composed of a low refractive index film, a high refractive index film, a low refractive index film, a high refractive index film, and a low refractive index film from the substrate side is preferable. A dielectric multilayer film having a structure of 6 or more can be designed in the same manner as these.

When there are a plurality of high refractive index films, the refractive indexes of those dielectric films may be the same or different. Similarly, when there are a plurality of low refractive index films, the refractive indexes of those dielectric films may be the same or different.

Even when the film is composed of three or more layers of a dielectric film, the difference in refractive index between the high refractive index film and the low refractive index film is preferably 0.2 or more. At this time, it is preferable to design so that the difference in refractive index between the high refractive index film and the low refractive index film is 0.2 or more no matter how they are combined. That is, the refractive index difference between the dielectric film having the lowest refractive index among the high refractive index films and the dielectric film having the highest refractive index among the low refractive index films is designed to be 0.2 or more.

The number of layers of the dielectric multilayer film is preferably 2 to 5 layers. It is possible to obtain a multilayer film that has the effect of reducing the phase difference even with 6 or more layers, but even with 6 or more layers, there is almost no difference from the characteristics (design characteristics) obtained with 5 layers, and the number of layers increases. Since the number of manufacturing processes increases, there is a demerit that the characteristics as designed cannot be obtained due to the accumulation of manufacturing errors.

The optical film thickness of the dielectric film is preferably 5 nm or more for both the high-refractive index film and the low-refractive index film. If the optical film thickness of the dielectric film is less than 5 nm, the effect of reducing the phase difference between the s-polarized light component and the p-polarized light component of the reflected light may be reduced. By optimizing the optical film thickness of each layer as a film structure having such a film thickness, a dielectric multilayer film with an optimized interference effect can be obtained. By forming these dielectric multilayer films on a base material (prism) having a refractive index of 1.43 to 2.1, the phase difference between the s-polarized light and the p-polarized light of the reflected light can be made less than ± 20 °.

The dielectric film is TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , ZrO ₂ , HfO ₂ , Y ₂ O ₃ , WO ₃ , CeO ₂ , SnO ₂ , MgO, SiO, Al ₂ O ₃ , CeF ₃ , YF ₃ , LaF ₃ , SiO ₂ , CaF ₂ , MgF ₂ and AlF ₃ from at least one selected from the dielectric group, or from a compound containing at least one selected from the dielectric group. It is preferable to be. Examples of the compound include LaTiO ₃ , LaAlO _{3, and the} like. The dielectric film composed of these dielectrics and compounds can be formed by a physical vapor deposition method such as a vacuum vapor deposition method, a sputtering method or an ion plating method, or a chemical vapor deposition method such as thermal CVD, plasma CVD or optical CVD. ..

(3) Metal film The metal film is selected from a single film composed of one selected from the metal group consisting of silver, aluminum, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium, or from the metal group. It is preferable that the alloy contains at least one of the above. The metal film made of these materials can be formed by a physical vapor deposition method such as a vacuum vapor deposition method, a sputtering method, or an ion plating method. Further, a plurality of different types of different metal films may be formed. The metal film is preferably formed with a thickness that does not allow visible light from the outside to enter, that is, a thickness that makes it opaque (transmittance with respect to visible light is substantially 0%). The transmittance of the metal film with respect to visible light is preferably 0.01% or less, more preferably 0.001 or less.

In order to improve durability and weather resistance, a dielectric film, a coating film, a water-repellent film, an oil-repellent film, a rust-preventive film, or the like may be applied on the metal film.

[2] Prism The prism of the present invention is a prism having a pair of reflective surfaces intersecting at a nominal surface angle of 90 °, and the pair of reflective surfaces are (a) a dielectric multilayer composed of at least two layers of dielectric films. It has a film and (b) a metal film laminated on the dielectric multilayer film, and the dielectric multilayer films have different refractive indexes of adjacent dielectric films, and the optics of each dielectric film are different from each other. It is characterized by having a film thickness of 5 nm or more.

The prism of the present invention is preferably used as a roof prism, and examples of such a roof prism include a Pechan prism shown in FIG. 3, a penta-dach prism (penta-prism) shown in FIG. 4, and an amici prism shown in FIG. In these figures, the angle at which the light beam indicated by the broken line arrow enters the roof surface 4 is 48 ° (Fig. 3) for the Pechan prism, 49 ° (Fig. 4) for the penta-Dach prism, and 60 ° (Fig. 5) for the Amici prism. Become. Optical instruments in which the pentadha prism is used as the observation optical system include single-lens reflex cameras and single-lens reflex digital cameras, and optical instruments in which the amici prism is used as the observation optical system include microscopes and surveying instruments. Examples of optical instruments in which the pechan prism is used as an observation optical system include binoculars and a telescope.

The present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

(1) Incident angle dependence of phase difference between s-polarized light and p-polarized light
The coordinates of the phase difference between s-polarized light and p-polarized light are defined as shown in Fig. 1. The incident light beam 1 and the outgoing light ray 2 are parallel to the paper surface, the ray direction is the z-axis, the direction parallel to the paper surface and perpendicular to the z-axis is the x-axis, and the direction perpendicular to the paper surface and exiting the paper surface is the y-axis. In this case, the y-axis corresponds to s-polarized light and the x-axis corresponds to p-polarized light. The ray incident angle θi and the emitted angle θo are equal from the definition of reflection. In the definition of phase difference, the phase difference between s-polarized light and p-polarized light at the interface 3 between the undeposited substrate and air is 0 ° until the incident light ray reaches the brewer angle, and from the brewer angle to the critical angle. At 180 ° and above the critical angle, the value depends on the angle. FIG. 2 shows the incident angle dependence of the phase difference between s-polarized light and p-polarized light at a wavelength of 550 nm when S-BSL7 (manufactured by OHARA Corporation) having a refractive index of nd = 1.516 is used as a base material. In FIG. 2, the brewster angle is 33.4 ° and the critical angle is 41.3 °.

(2) As the metal single-layer film prism, the effect of the metal single-layer film will be described by taking as an example the case of the pentadach prism used in the finder optical system of a single-lens reflex camera. In this case, the light flux diffused by the focal plate of the single-lens reflex camera is incident on the roof surface of the penta-dach prism as a light flux centered at an incident angle of 49 °. S-BSL7 (nd = 1.516, critical angle θ = 41.3 °) is used as the base material of the pentadach prism, and the metal single-layer film of Ag, Al, Au, Cu, Ni and Cr is opaque on its reflection surface (dach surface). It was formed with a film thickness that would be (impermeable). At this time, the phase difference between the s-polarized light and the p-polarized light was 134 °.

The wavelength dependence of the reflectance of light incident on the reflecting surface from the inside of the S-BSL7 base material at an incident angle of 49 ° when these metal films of Ag, Al, Au, Cu, Ni and Cr are formed is shown in Fig. 6 -1 and Fig. 6-3 show the phase difference between s-polarized light and p-polarized light in Fig. 6-2 and Fig. 6-4. From Fig. 6-2 and Fig. 6-4, the phase difference between s-polarized light and p-polarized light at wavelengths of 400 to 700 nm in the visible wavelength range is 20 ° or more for all metal monolayers, and only for metal monolayers. It can be seen that there is a large difference in the polarization state on the reflecting surface.

Example 1
S-BSL7 (nd = 1.516) base material with _{a dielectric film of TiO 2} (nd = 2.304) with an optical thickness of 55 nm and a dielectric film of Al ₂ O ₃ (nd = 1.635) with an optical thickness of 103 nm. The films were sequentially formed, and a metal film made of silver (nd = 0.059, kd = 3.634, kd is the absorption coefficient at the d line) was formed with a film thickness that became opaque. Fig. 7-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 base material on the surface on which the dielectric and metal multilayer film is formed, and Fig. 7-2 shows the phase difference between s-polarized light and p-polarized light. Shown in.

Reference example 2
S-LAH66 (nd = 1.773) manufactured by O'Hara Co., Ltd. A dielectric film with an optical film thickness of 33 nm _{made of Ta 2} O _{5 (nd = 2.038) and an optical film thickness of 67 made of SiO 2} (nd = 1.468) on a substrate. A dielectric film of nm was sequentially formed, and a metal film made of aluminum (nd = 0.932, kd = 6.241) was further formed with a film thickness that became opaque. The reflectance of light incident at 49 ° from the inside of the S-LAH66 substrate on the surface on which the dielectric and metal multilayer film is formed is shown in Fig. 8-1, and the phase difference between s-polarized light and p-polarized light is shown in Fig. 8-2. Shown in.

Reference example 3
S-LAL14 (nd = 1.697) manufactured by O'Hara Co., Ltd. Dielectric film with an optical film thickness of 101 nm _{made of TiO 2} (nd = 2.304) and dielectric film with an optical film thickness of 29 nm made of _{MgF 2 (nd = 1.388) on a substrate.} A body film and _{a dielectric film with an optical thickness of 30 nm made of Al 2} O ₃ (nd = 1.635) are sequentially formed, and a metal film made of gold (nd = 0.276, kd = 2.916) becomes opaque. Formed with. The reflectance of light incident at 49 ° from the inside of the S-LAL14 substrate on the surface on which the dielectric and metal multilayer film is formed is shown in Fig. 9-1, and the phase difference between s-polarized light and p-polarized light is shown in Fig. 9-2. Shown in.

Example 4
S-FSL5 (nd = 1.488) made by OHARA Co., Ltd. Dielectric film with an optical film thickness of 120 nm _{made of ZrO 2} (nd = 1.936) and dielectric film with an optical film thickness of 31 nm made of _{SiO 2 (nd = 1.468) on a substrate.} A body film and _{a dielectric film with an optical thickness of 30 nm made of Al 2} O ₃ (nd = 1.635) are sequentially formed, and a metal film made of copper (nd = 0.538, kd = 2.861) becomes opaque. Formed with. Fig. 10-1 shows the reflectance of light incident at 49 ° from the inside of the S-FSL5 base material on the surface on which the dielectric and metal multilayer film was formed, and Fig. 10-2 shows the phase difference between s-polarized light and p-polarized light. Shown in.

Example 5
S-BSL7 (nd = 1.516) base material with _{a dielectric film of Mg F 2} (nd = 1.388) with an optical thickness of 34 nm and a dielectric film of Ta ₂ O ₅ (nd = 2.038) with an optical thickness of 57 nm. , And MgF ₂ (nd = 1.388) with an optical thickness of 127 nm were sequentially formed, and a metal film made of nickel (nd = 1.850, kd = 3.465) was formed with an opaque thickness. Fig. 11-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 substrate on the surface on which the dielectric and metal multilayer film was formed, and Fig. 11-2 shows the phase difference between s-polarized light and p-polarized light. Shown in.

Example 6
S-BSL7 (nd = 1.516) base material with _{a dielectric film of Ta 2} O ₅ (nd = 2.038) with an optical thickness of 15 nm and SiO ₂ (nd = 1.468) with an optical thickness of 101 nm. , Ta ₂ O ₅ (nd = 2.038) with an optical thickness of 52 nm, and SiO ₂ (nd = 1.468) with an optical thickness of 146 nm are formed in sequence, and then chromium (nd = A metal film consisting of 2.902, kd = 2.045) was formed with a thickness that made it opaque. Fig. 12-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 substrate on the surface on which the dielectric and metal multilayer film was formed, and Fig. 12-2 shows the phase difference between s-polarized light and p-polarized light. Shown in.

Example 7
S-BSL7 (nd = 1.516) substrate made of TiO ₂ (nd = 2.304) with an optical thickness of 17 nm, a dielectric film made of SiO ₂ (nd = 1.468) with an optical thickness of 90 nm, TiO A dielectric film with an optical thickness of 59 nm consisting of _{2 (nd = 2.304), a dielectric film with an optical thickness of 78 nm consisting of SiO 2} (nd = 1.468), and an optical composition consisting of Al ₂ O ₃ (nd = 1.635). A dielectric film having a thickness of 30 nm was sequentially formed, and a metal film made of silver (nd = 0.059, kd = 3.634) was further formed with an opaque thickness. The reflectance of light incident at 41 ° from the inside of the S-BSL7 substrate on the surface on which the dielectric and metal multilayer film is formed is shown in Fig. 13-1, and the phase difference between s-polarized light and p-polarized light is shown in Fig. 13-2. Shown in.

Example 8
S-LAH66 (nd = 1.773) substrate made of TiO ₂ (nd = 2.304) with an optical thickness of 36 nm, and Al ₂ O ₃ (nd = 1.635) with an optical thickness of 102 nm. , A dielectric film having an optical thickness of 95 nm made of _{TiO 2 (nd = 2.304) and a dielectric film having an optical thickness of 146 nm made of Al 2} O ₃ (nd = 1.635) were sequentially formed, and further silver (nd) was formed. A metal film consisting of = 0.059 and kd = 3.634) was formed with a thickness that made it opaque. The reflectance of light incident at 60 ° from the inside of the S-LAH66 substrate on the surface on which the dielectric and metal multilayer film is formed is shown in Fig. 14-1, and the phase difference between s-polarized light and p-polarized light is shown in Fig. 14-2. Shown in.

Comparative Example 1
A metal film made of silver (nd = 0.059, kd = 3.643) was formed on the S-BSL7 (nd = 1.516) substrate with a film thickness that became opaque. Fig. 15-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 base material on the surface on which the reflective film made of this metal film was formed, and Fig. 15-2 shows the phase difference between s-polarized light and p-polarized light. show.

Comparative example 2
_{A dielectric film with an optical thickness of 213 nm made of Al 2} O ₃ (nd = 1.635) is formed on the S-BSL7 (nd = 1.516) base material, and a metal film made of silver (nd = 0.059, kd = 3.643). Was formed with a film thickness that became opaque. Fig. 16-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 base material on the surface on which the reflective film made of the dielectric film and metal film is formed, and the phase difference between s-polarized light and p-polarized light is shown. Shown in 16-2.

Comparative example 3
_{A dielectric film with an optical film thickness of 52 nm made of SiO 2} (nd = 1.468) is formed on the S-BSL7 (nd = 1.516) substrate, and a metal film made of silver (nd = 0.059, kd = 3.643) is made opaque. It was formed with a film thickness of Fig. 17-1 shows the reflectance of light incident on the surface of the reflective film made of a dielectric film and a metal film at 49 ° from the inside of S-BSL7, and Fig. 17- shows the phase difference between s-polarized light and p-polarized light. Shown in 2.

Graphs of phase differences of Examples 1, Reference Examples 2 , 3 and Examples 4 to 8 (Fig. 7-2, Fig. 8-2, Fig. 9-2, Fig. 10-2, Fig. 11-2, Fig. 12-2). , Fig. 13-2 and Fig. 14-2) and the graphs of the phase difference of Comparative Examples 1 to 3 (Fig. 15-2, Fig. 16-2 and Fig. 17-2). By forming two or more dielectric films with a refractive index difference of 0.2 or more between the metal films, it has the effect of making the phase difference between s-polarized light and p-polarized light less than ± 20 ° in the visible wavelength range of 400 to 700 nm. A multilayer film with reduced retardation could be obtained.

1 ... Incident ray 2 ... Emission ray 3 ... Interface 4 ... Dach surface

Claims (10)

An optical instrument having an observation optical system including a prism having a pair of reflecting surfaces intersecting at a nominal angle of 90 ° and at least one lens.
The prism is arranged so that the ridges of the pair of reflecting surfaces divide the pupil of the observation optical system.
The pair of reflective surfaces of the prism
(a) A dielectric multilayer film consisting of at least two layers of dielectric film, and
(b) It has a metal film laminated on the dielectric multilayer film.
The dielectric multilayer films have different refractive indexes of adjacent dielectric films, each dielectric film has an optical film thickness of 5 nm or more, and has the highest refractive index and the lowest refractive index. The difference in refractive index from the dielectric film is 0.2 or more and 0.836 or less.
The metal film is a single film composed of one selected from the metal group consisting of silver, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium, or at least one selected from the metal group. It is a film of alloy containing
An optical instrument characterized in that the phase difference between s-polarized light and p-polarized light when a luminous flux from the inside of the prism is reflected by the reflecting surface at a wavelength of 400 to 700 nm in the visible wavelength range is less than ± 20 °. In the optical instrument according to claim 1, the dielectric multilayer film has a refractive index difference of 0.2 or more between the dielectric film having the highest refractive index and the dielectric film on the side closest to the metal film. Characteristic optical equipment. In the optical device according to claim 1 or 2, the dielectric multilayer film includes at least one high refractive index film having a refractive index of 1.8 or more and at least one low refractive index film having a refractive index of less than 1.8. An optical device characterized in that the difference in refractive index between the high refractive index film and the low refractive index film is 0.2 or more. In the optical instrument according to any one of claims 1 to 3, the dielectric film on the side closest to the prism among the dielectric films is adjacent to the prism, and the metal film has a transmittance for visible light. An optical device characterized by having a film thickness of substantially 0%. In the optical device according to any one of claims 1 to 4 _{, the dielectric film is TiO 2} , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , ZrO ₂ , HfO ₂ , Y ₂ O ₃ , WO _{3. , CeO 2, SnO 2, MgO} , SiO, Al 2 O 3, CeF 3, YF 3, LaF 3, SiO 2, CaF 2, at least one selected from the dielectric group consisting of MgF ₂ and AlF _3, or An optical device comprising a compound containing at least one selected from the dielectric group. The optical device according to any one of claims 1 to 5 , wherein the number of layers of the dielectric multilayer film is 2 to 5. A prism having a pair of reflecting surfaces that intersect at a nominal angle of 90 °.
The pair of reflective surfaces
(a) A dielectric multilayer film consisting of at least two layers of dielectric film, and
(b) It has a metal film laminated on the dielectric multilayer film.
The dielectric multilayer films have different refractive indexes of adjacent dielectric films, each dielectric film has an optical film thickness of 5 nm or more, and has the highest refractive index and the lowest refractive index. The difference in refractive index from the dielectric film is 0.2 or more and 0.836 or less.
The metal film is a single film composed of one selected from the metal group consisting of silver, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium, or at least one selected from the metal group. It is a film of alloy containing
A prism characterized in that the phase difference between s-polarized light and p-polarized light when a luminous flux from the inside of the prism is reflected by the reflecting surface at a wavelength of 400 to 700 nm in the visible wavelength range is less than ± 20 °. The prism according to claim 7 , wherein the prism is a pentadach prism. The prism according to claim 7 , wherein the prism is a Peshan prism. The prism according to claim 7 is an amici prism.

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