JP2017138544A - Optical instrument and prism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical instrument including a prism having a small phase difference between an s-polarization and a p-polarization before and after an incident light flux is reflected.SOLUTION: The optical instrument comprises a prism including a pair of reflection surfaces intersecting with each other at a nominal surface angle 90°, and an observation optical system including at least one lens. The prism is arranged so that edge lines of the pair of reflection surfaces divide the pupil of the observation optical system, and the pair of reflection surfaces of the prism includes (a) a dielectric multilayer consisting of at least two dielectric films, and (b) a metal film laminated on the dielectric multilayer. In the dielectric multilayer, the adjacent dielectric films have refractive indices different from each other, and an optical film thickness of each dielectric film is 5 nm or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an observation optical apparatus having an observation optical system including at least one lens and a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and to convert the object image into an erect image by inverting the image. The present invention relates to a prism, particularly a Dach prism.

  The Dach prism used in observation optical equipment such as microscopes, telescopes, binoculars, single-lens reflex cameras, single-lens reflex cameras, surveying instruments, etc., splits the pupil of the observation optical system by the ridgeline of a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °. Therefore, high processing accuracy is required, but since the prism can be made smaller than other upright prisms such as Porro prisms, 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 component and the p-polarized component of the light wave that are orthogonal to each other before and after the surface. In an optical system in which the pupil is divided at the ridgeline as in the Dach prism, there is a difference in the polarization state of the light emitted from the Dach prism between one and the other of the divided pupils. Deteriorate. As the phase difference generated on the reflection surface increases, the difference in polarization state generated increases, and a double image is observed or the contrast decreases as in the case where the processing accuracy of the surface angle is low.

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

  Patent Document 1 (Japanese Patent Laid-Open No. 11-326781) discloses a dielectric film having a refractive index of M1, M2, and M3 on the roof surface of a roof prism (however, 2.0 <M1 <2.1, 1.35 <M2 <1.4 and 1.45 <M3 <1.5). ) Is laminated, and a multilayer film with reduced retardation is disclosed, and is described as being effective in reducing the phase difference of visible wavelength light for 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 the s-polarized light and the p-polarized light before and after the reflection of the light beam incident on the pair of reflecting surfaces of the roof prism, and suppresses the deterioration of the wavefront aberration. This has the effect of improving the performance of the observed image.

  However, the phase difference reducing multilayer film described in Patent Document 1 uses total reflection that occurs when the incident angle of the light reflected from the inner surface of the substrate exceeds the critical angle, so that dust, dirt, etc. are present on the outer surface of the substrate. When the toner adheres, there is a problem that the reflected light of the inner surface is scattered and absorbed to reduce the contrast of the observation image.

  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 single layer film on the reflecting surface and 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 the reflecting surface on which the metal single layer film is formed, the phase difference between s-polarized light and p-polarized light is 20 ° or more. It becomes. In this way, when the difference in the polarization state on the reflecting surface is large, there arises a problem that a double image is observed, the contrast is lowered, or a color difference is generated between the two roof surfaces in an image including a polarization component.

Japanese Patent Laid-Open No. 11-326781

  Accordingly, 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 beam, and an optical apparatus including the prism.

  As a result of diligent research in view of the above object, the present inventors adjusted the phase difference between s-polarized light and p-polarized light by forming two or more dielectric films having different refractive indexes between the metal film and the substrate. The inventors have found that this is possible and have come up with the present invention.

That is, the optical apparatus of the present invention is an optical apparatus having an observation optical system including a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and at least one lens,
The prism is arranged so that a ridge line of the pair of reflecting surfaces divides a pupil of the observation optical system,
The pair of reflecting surfaces of the prism is
(a) a dielectric multilayer film composed of at least two dielectric films, and
(b) having a metal film laminated on the dielectric multilayer film;
The dielectric multilayer films are 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 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, the high refractive index film, the low refractive index film, The refractive index difference is preferably 0.2 or more.

  The dielectric film closest to the prism among the dielectric films is adjacent to the prism, and the metal film has a film thickness at which the transmittance for at least visible light is substantially 0%. Is preferred.

  The metal film is a single film selected from a 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 An alloy film containing seeds is preferred.

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 selected from the dielectric group, or a compound containing at least one selected from the dielectric group Preferably it is.

The prism of the present invention is a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °,
The pair of reflective surfaces is
(a) a dielectric multilayer film composed of at least two dielectric films, and
(b) having a metal film laminated on the dielectric multilayer film;
The dielectric multilayer films are 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 penta roof prism, a Pechan prism or an amic prism.

  Since the prism provided in the optical apparatus 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 apparatuses.

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

[1] Optical apparatus The optical apparatus of the present invention is an optical apparatus having an observation optical system including a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and at least one lens. Are arranged such that the ridge lines 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 films. And (b) a metal film laminated on the dielectric multilayer film, wherein the dielectric multilayer films have different refractive indexes of adjacent dielectric films, and the optical films of the respective dielectric films The thickness is 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 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. Of 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. Furthermore, it is preferable that the refractive index difference between the dielectric film having the highest refractive index and the dielectric film closest to the metal film is 0.2 or more. It is preferable that the dielectric film closest to the prism among the dielectric films is adjacent to the prism.

  At least one layer of the dielectric film is preferably a high refractive index film having a refractive index of 1.8 or more, and at least one layer is preferably 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 a two-layer dielectric film, the substrate side is a high refractive index film having a refractive index of 1.8 or more, the metal film side is a low refractive index film having a refractive index of less than 1.8, and the difference in refractive index between them is 0.2. The above is preferable. When the dielectric film is composed of three or more layers, 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 preferred.

  For example, in the case of three layers, a structure consisting of a high refractive index film, a low refractive index film and a low refractive index film from the substrate side, or a low refractive index film, a high refractive index film and a low refractive index film from the substrate side. A configuration is preferred. In the case of four layers, a structure consisting of 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, or a low refractive index film, a high refractive index film and a low refractive index from the substrate side. A structure composed of a refractive index 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 substrate side. Or the structure which consists of a low refractive index film | membrane, a high refractive index film | membrane, a low refractive index film | membrane, a high refractive index film | membrane, and a low refractive index film | membrane from the base material side is preferable. A dielectric multilayer film having a six-layer structure or more can also be designed in the same manner.

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

  Even when the dielectric film is composed of three or more layers, 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 that the high refractive index film and the low refractive index film are designed so that the refractive index difference between them is 0.2 or more. 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. Although it is possible to obtain a multilayer film that exhibits the effect of reducing the phase difference even when there are 6 layers or more, the characteristics (design characteristics) obtained with 5 layers are almost the same even when there are 6 layers or more, and the number of layers increases. Since the number of manufacturing processes increases, there is a demerit that characteristics as designed cannot be obtained due to 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 component and the p-polarized 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 selected from the dielectric group, or a compound containing at least one selected from the dielectric group Preferably it is. Examples of the compound include LaTiO ₃ and LaAlO ₃ . Dielectric films composed of these dielectrics and compounds can be formed by physical vapor deposition such as vacuum vapor deposition, sputtering, ion plating, chemical vapor deposition such as thermal CVD, plasma CVD, and photo-CVD. .

(3) Metal film The metal film is selected from a single film selected from the metal group consisting of silver, aluminum, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium, or the metal group. An alloy containing at least one selected from the above is preferable. A metal film made of these materials can be formed by physical vapor deposition such as vacuum vapor deposition, sputtering, or ion plating. A plurality of different types of metal films may be formed. The metal film is preferably formed with a thickness that prevents visible light from the outside from entering, that is, a thickness that is opaque (transmittance to visible light is substantially 0%). The transmittance of the metal film for the visible light is preferably 0.01% or less, and more preferably 0.001 or less.

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

[2] Prism The prism of the present invention is a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and the pair of reflecting surfaces are (a) a dielectric multilayer composed of at least two dielectric films. And (b) a metal film laminated on the dielectric multilayer film, wherein the dielectric multilayer film has different refractive indexes of adjacent dielectric films, and the optical characteristics of each dielectric film are different from each other. The film thickness is 5 nm or more.

  The prism of the present invention is preferably used as a roof prism. Examples of such roof prisms include a Pechan prism shown in FIG. 3, a penta roof prism (penta prism) shown in FIG. 4, and an amic prism shown in FIG. In these figures, the angle at which the light beam indicated by the broken-line arrow is incident on the roof surface 4 is 48 ° (FIG. 3) for the Pechan prism, 49 ° (FIG. 4) for the penta roof prism, and 60 ° (FIG. 5) for the Amichi prism. Become. Examples of the optical equipment in which the penta roof prism is used as an observation optical system include a single-lens reflex camera and a single-lens reflex digital camera. Examples of the optical equipment in which the amichi prism is used as an observation optical system include a microscope and a surveying instrument. Examples of optical instruments in which the Pechan prism is used as an observation optical system include binoculars and telescopes.

  The present invention will be described in more detail with reference to 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. The incident light beam 1 and the outgoing light beam 2 are parallel to the paper surface, the light beam 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 from 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 light incident angle θi and the outgoing 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 non-deposited substrate and air is 0 ° until the incident light beam reaches the Brewster angle, and from the Brewster angle to the critical angle. Above 180 °, 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 (made by OHARA INC.) Having a refractive index of nd = 1.516 is used as a substrate. In FIG. 2, the Brewster angle is 33.4 ° and the critical angle is 41.3 °.

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

  Figure 6 shows the wavelength dependence of the reflectance of light incident on the reflecting surface at an incident angle of 49 ° from the inside of the S-BSL7 substrate when these Ag, Al, Au, Cu, Ni, and Cr metal films are formed. -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 in the visible wavelength range of 400 to 700 nm is 20 ° or more in any metal single layer film, and only in the metal single layer film It turns out that a big difference arises in the polarization state in a reflective surface.

Example 1
S-BSL7 (nd = 1.516) base material, TiO ₂ (nd = 2.304) optical film thickness 55 nm dielectric film, and Al ₂ O ₃ (nd = 1.635) optical film thickness 103 nm dielectric material A film was sequentially formed, and a metal film made of silver (nd = 0.059, kd = 3.643, kd is an absorption coefficient at the d-line) was formed to an opaque film thickness. Fig. 7-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 substrate on the surface on which this 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

Example 2
OHARA Co., Ltd. S-LAH66 (nd = 1.773) base material Ta ₂ O ₅ (nd = 2.038) optical film thickness 33 nm dielectric film, and SiO ₂ (nd = 1.468) optical film thickness 67 A dielectric film having a thickness of nm was sequentially formed, and a metal film made of aluminum (nd = 0.932, kd = 6.241) was formed to have an opaque film thickness. Fig. 8-1 shows the reflectance of light incident at 49 ° from the inside of the S-LAH66 substrate on the surface on which this dielectric and metal multilayer film is formed, and Fig. 8-2 shows the phase difference between s-polarized light and p-polarized light. Shown in

Example 3
OHARA S-LAL14 (nd = 1.697) substrate with TiO ₂ (nd = 2.304) optical film thickness 101 nm dielectric film, MgF ₂ (nd = 1.388) optical film thickness 29 nm dielectric film A body film and a dielectric film having an optical film 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) is made opaque. Formed with. Fig. 9-1 shows the reflectance of light incident at 49 ° from the inside of the S-LAL14 substrate on this dielectric and metal multilayer film, and Fig. 9-2 shows the phase difference between s-polarized light and p-polarized light. Shown in

Example 4
OHARA Co., Ltd. S-FSL5 (nd = 1.488) base material with ZrO ₂ (nd = 1.936) optical film thickness 120 nm dielectric film, SiO ₂ (nd = 1.468) optical film thickness 31 nm dielectric The body film and the dielectric film with an optical film thickness of 30 nm made of Al ₂ O ₃ (nd = 1.635) are sequentially formed, and the metal film made of copper (nd = 0.538, kd = 2.861) is made opaque. Formed with. Figure 10-1 shows the reflectance of light incident at 49 ° from the inside of the S-FSL5 substrate on the surface on which this dielectric and metal multilayer film is formed, and Figure 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, MgF ₂ (nd = 1.388) optical film thickness 34 nm dielectric film, Ta ₂ O ₅ (nd = 2.038) optical film thickness 57 nm dielectric film , And MgF ₂ (nd = 1.388) were sequentially formed as a dielectric film having a thickness of 127 nm, and a nickel film (nd = 1.850, kd = 3.465) was formed as an opaque film. Figure 11-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 substrate on the surface on which this dielectric and metal multilayer film is formed, and Figure 11-2 shows the phase difference between s-polarized light and p-polarized light. Shown in

Example 6
An S-BSL7 (nd = 1.516) substrate with an optical film thickness of 15 nm made of Ta ₂ O ₅ (nd = 2.038) and an optical film thickness of 101 nm made of SiO ₂ (nd = 1.468) Then, a dielectric film having an optical film thickness of 52 nm made of Ta ₂ O ₅ (nd = 2.038) and a dielectric film having an optical film thickness of 146 nm made of SiO ₂ (nd = 1.468) were sequentially formed, and further chromium (nd = A metal film made of 2.902, kd = 2.045) was formed with an opaque film thickness. Figure 12-1 shows the reflectance of light incident at 49 ° from the inside of the S-BSL7 substrate on the surface on which this dielectric and metal multilayer film is formed, and Figure 12-2 shows the phase difference between s-polarized light and p-polarized light. Shown in

Example 7
S-BSL7 (nd = 1.516) base material, 17 nm optical film thickness dielectric film made of TiO ₂ (nd = 2.304), 90 nm optical film thickness dielectric film made of SiO ₂ (nd = 1.468), TiO ₂ (nd = 2.304) optical film thickness 59 nm dielectric film, SiO ₂ (nd = 1.468) optical film thickness 78 nm dielectric film, and Al ₂ O ₃ (nd = 1.635) optical film A dielectric film having a film thickness of 30 nm was sequentially formed, and a metal film made of silver (nd = 0.059, kd = 3.643) was formed with an opaque film thickness. Figure 13-1 shows the reflectivity of light incident at 41 ° from the inside of the S-BSL7 substrate on the surface on which this dielectric and metal multilayer film is formed. Figure 13-2 shows the phase difference between s-polarized light and p-polarized light. Shown in

Example 8
S-LAH66 (nd = 1.773) substrate with TiO ₂ (nd = 2.304) optical film thickness 36 nm dielectric film, Al ₂ O ₃ (nd = 1.635) optical film thickness 102 nm dielectric film Then, a dielectric film with an optical film thickness of 95 nm made of TiO ₂ (nd = 2.304) and a dielectric film with an optical film thickness of 146 nm made of Al ₂ O ₃ (nd = 1.635) are formed in order, and silver (nd = 0.059, kd = 3.643) was formed with an opaque film thickness. Figure 14-1 shows the reflectance of light incident at 60 ° from the inside of the S-LAH66 substrate on the surface on which this dielectric and metal multilayer film is formed, and Figure 14-2 shows the phase difference between s-polarized light and p-polarized light. 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 so as to become opaque. Figure 15-1 shows the reflectivity of light incident at 49 ° from the inside of the S-BSL7 substrate, and Figure 15-2 shows the phase difference between s-polarized light and p-polarized light. Show.

Comparative Example 2
A dielectric film with an optical film thickness of 213 nm made of Al ₂ O ₃ (nd = 1.635) is formed on a S-BSL7 (nd = 1.516) substrate, and further a metal film made of silver (nd = 0.059, kd = 3.643) Was formed with an opaque film thickness. Figure 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 this dielectric film and metal film is formed, and the phase difference between s-polarized light and p-polarized light. Shown in 16-2.

Comparative Example 3
An S-BSL7 (nd = 1.516) base material is formed with a dielectric film with an optical film thickness of 52 nm made of SiO ₂ (nd = 1.468), and a metal film made of silver (nd = 0.059, kd = 3.643) is made opaque. The film thickness was formed as follows. Fig. 17-1 shows the reflectivity of light incident at 49 ° from the inside of S-BSL7 on the surface on which this dielectric film and metal film is formed, and Fig. 17- shows the phase difference between s-polarized light and p-polarized light. Shown in 2.

  Graphs of phase differences in Examples 1 to 8 (FIGS. 7-2, 8-2, 9-2, 10-2, 11-2, 12-2, 13-2, and 14-2) ) And the phase difference graphs of Comparative Examples 1 to 3 (FIGS. 15-2, 16-2, and 17-2), the refractive index difference between the substrate and the metal film is 0.2 or more. By forming two or more dielectric films, a phase difference reducing multilayer film that has the effect of reducing the phase difference between s-polarized light and p-polarized light to less than ± 20 ° in the visible wavelength range of 400 to 700 nm can be obtained. It was.

DESCRIPTION OF SYMBOLS 1 ... Incident ray 2 ... Outgoing ray 3 ... Interface 4 ... Dach surface

Claims (11)

An optical instrument having an observation optical system comprising a prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °, and at least one lens,
The prism is arranged so that a ridge line of the pair of reflecting surfaces divides a pupil of the observation optical system,
The pair of reflecting surfaces of the prism is
(a) a dielectric multilayer film composed of at least two dielectric films, and
(b) having a metal film laminated on the dielectric multilayer film;
In the optical multilayered film, the refractive index of adjacent dielectric films is different from each other, and the optical film thickness of each dielectric film is 5 nm or more.   2. The optical device according to claim 1, wherein the dielectric multilayer film has a refractive index difference of 0.2 or more between a dielectric film having the highest refractive index and a dielectric film having the lowest refractive index. Optical equipment.   3. The optical device according to claim 1, wherein the dielectric multilayer film has a refractive index difference of 0.2 or more between a dielectric film having the highest refractive index and a dielectric film closest to the metal film. An optical apparatus characterized by that.   The optical device according to any one of claims 1 to 3, wherein 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 apparatus comprising: a refractive index difference between the high refractive index film and the low refractive index film being 0.2 or more.   5. The optical device according to claim 1, wherein the dielectric film 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 instrument characterized by having a film thickness of substantially 0%.   6. The optical apparatus according to claim 1, wherein the metal film is selected from a metal group consisting of silver, aluminum, gold, copper, nickel, chromium, platinum, rhodium, tin, zinc and magnesium. An optical device, characterized in that the optical device is a single film made of or an alloy film containing at least one selected from the metal group. The optical apparatus according to claim 1, ₂ dielectric film _{TiO, 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 , or at least one selected from the group of dielectrics, or An optical apparatus comprising a compound containing at least one selected from the dielectric group. A prism having a pair of reflecting surfaces that intersect at a nominal surface angle of 90 °,
The pair of reflective surfaces is
(a) a dielectric multilayer film composed of at least two dielectric films, and
(b) having a metal film laminated on the dielectric multilayer film;
The dielectric multilayer film is a prism characterized in that adjacent dielectric films have different refractive indexes, and each dielectric film has an optical film thickness of 5 nm or more.   The prism according to claim 8 is a penta roof prism.   The prism according to claim 8, wherein the prism is a Pechan prism.   The prism according to claim 8, wherein the prism is an amic prism.

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