JP2005208519A - Optical element having antireflection film and medical application optical equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element having antireflection films which have excellent durability to steam of a high temperature and high pressure and therefore permit high temperature-high pressure steam sterilization treatment and have an excellent antireflection characteristic and medical application optical equipment having such optical element. <P>SOLUTION: The optical element has the antireflection films on a base surface, wherein the antireflection films alternately have high-refractive index layers composed of hafnium dioxide or ditantalum pentaoxide and low-refractive index layers composed of aluminum oxide or silicon oxide and the number of the layers is ≥7. The surface layer on an incident medium side is the high-refractive index layer and its physical layer thickness is 1 to 16 nm. The reflectivity to visible light incident thereon at an angle of any from 0 to 50° is ≤1.5%. The medical application optical equipment has such optical element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element having an antireflection film, and particularly to an optical element having excellent durability against high-pressure and high-temperature steam (autoclave) treatment and excellent transmittance for visible light, and suitable for medical optical equipment.

  In recent years, endoscopes have come to be used not only as diagnostic means but also as therapeutic means in the medical field, and the frequency of use of endoscopes has increased. Since an endoscope is inserted into a body cavity, it must be sufficiently sterilized before use in order to prevent infections and the like.

  Conventionally, endoscopes have been sterilized by a chemical method using a sterilizing agent such as ethylene oxide gas. However, these chemical sterilization methods are costly because gas safety measures and waste liquid treatment occur. Therefore, recently, high-temperature high-pressure steam (autoclave) sterilization without complicated work is becoming mainstream. High-temperature and high-pressure steam sterilization has an advantage that an endoscope can be used immediately after sterilization. According to US plan ANSI / AAMI ST37-1992, the conditions for high-temperature and high-pressure steam sterilization are 10 minutes at a saturated steam pressure at 132 ° C.

  The endoscope has optical elements such as an objective lens and a prism. Since it is desirable that the portion of the endoscope that is inserted into the body cavity is as small as possible, it is desirable that the objective lens provided in the endoscope insertion portion is as small as possible. For this reason, an antireflection film is formed on the surface of the objective lens or the like so that the amount of transmitted light can be secured even if it is small by efficiently transmitting light.

  However, when an optical element having a conventional antireflection film is treated with high-temperature and high-pressure steam under the above-described conditions, there is a problem that the antireflection film deteriorates and the optical performance cannot be maintained. For example, a single-layer antireflection film made of magnesium fluoride, which is widely used as an antireflection film, reacts with high-temperature and high-pressure water vapor to completely disappear. In the case of an antireflection film having a silicon oxide layer on the surface, high-temperature and high-pressure steam treatment leaves water-drop-like dirt that cannot be wiped off on the surface, resulting in a decrease in optical performance.

Japanese Patent Laid-Open No. 5-34505 (refer to Patent Document 1) states that “the first and third layers on the substrate side are ZrO ₂ , Ta ₂ O ₅ , a mixture of ZrO ₂ and Ta ₂ O ₅ , or ZrO ₂ and TiO _{2. The} chemical-resistant antireflective film is characterized in that a mixture with ₂ is laminated and SiO ₂ is laminated on the second layer. Since this anti-reflective coating is formed using ion beam assisted deposition (IAD), it has a relatively large filling rate (film density) and the surface is ZrO ₂ , Ta ₂ O _5. Alternatively, it is described as having durability against acids, alkali solutions, and the like because it is composed of a mixture of ZrO ₂ and Ta ₂ O ₅ .

The chemical-resistant antireflection film described in Patent Document 1 is resistant to disinfection or sterilization with a cleaning solution or a disinfecting solution. However, it does not have sufficient durability against high-temperature and high-pressure steam, and the anti-reflective performance decreases when repeated high-temperature and high-pressure steam treatment. As described above, the antireflection performance is deteriorated because the third layer (surface layer) made of ZrO ₂ and / or Ta ₂ O _{5 formed} by ion beam assisted deposition does not have a sufficiently large density. For this reason, it is considered that the high-temperature and high-pressure water vapor passes through the third layer and comes into contact with the SiO ₂ layer inside. Since the SiO ₂ layer does not have a very high moisture resistance, it deteriorates due to contact with high-temperature and high-pressure steam. As described above, it is considered that the antireflection film needs to have a large density in order to have durability against high-temperature and high-pressure steam. The chemical-resistant antireflection film exhibits a good antireflection effect on the long wavelength side of visible light, but does not have an excellent antireflection effect on the short wavelength side. For example, the reflectance for visible light having a wavelength of about 400 nm is 4% or more.

Japanese Patent Application Laid-Open No. 7-234302 (see Patent Document 2) states that “an antireflective film made of a plurality of layers formed on an optical glass substrate, and a high refractive index material layer made of HfO ₂ or Ta ₂ O ₅ ; And a low-refractive-index material layer made of SiO ₂ , and the atmospheric outermost layer is the high-refractive-index material layer ”. It is described that this moisture-resistant antireflection film can be produced by a vacuum deposition method, a sputtering method, an ion plating method, and an ion beam assist method. The air-side surface of this antireflection film is made of HfO ₂ or Ta ₂ O ₅ having moisture resistance. Therefore, even if the antireflection film is exposed to a high humidity atmosphere and water droplets are generated on the surface, it remains after evaporation of the water droplets. The flow mark can be easily wiped off. However, this moisture-resistant antireflection film also does not have sufficient durability against high-temperature and high-pressure steam, and when high-temperature and high-pressure steam treatment is repeatedly performed, the antireflection performance is lowered. Further, the reflectance for visible light having a wavelength of about 450 nm is 4% or more, and it does not have an excellent antireflection effect.

Japanese Patent Laid-Open No. 7-287101 (see Patent Document 3) states that “a first layer made of SiO ₂ having an optical film thickness of 234 to 316 nm and an optical film thickness of 43 to 58 nm on an optical glass substrate at a design wavelength of 550 nm. A second layer made of HfO ₂ or Ta ₂ O ₅ , a third layer made of SiO _{2 with} an optical thickness of 34 to 46 nm, a fourth layer made of HfO ₂ or Ta ₂ O _{5 with} an optical thickness of 113 to 153 nm, A moisture-resistant antireflection film comprising a fifth layer made of SiO ₂ having an optical film thickness of 115 to 155 nm and a sixth layer made of perfluoroalkylsilazane having an optical film thickness of 5 to 15 nm. Is disclosed. Since this moisture-resistant antireflection film has a layer made of perfluoroalkylsilazane, which is a water-repellent polymer, as the outermost layer, it has excellent moisture resistance. However, it cannot be said that it has sufficient durability against high-temperature and high-pressure steam, and the antireflection performance decreases when autoclaving is performed. Moreover, the reflectance with respect to visible light having a wavelength of about 400 nm is 2% or more and does not have an excellent antireflection effect.

Japanese Patent Laid-Open No. 5-34505 Japanese Unexamined Patent Publication No. 7-234302 JP-A-7-287101

  Accordingly, an object of the present invention is to provide an optical element having an antireflective film that can be sterilized at high temperature and high pressure steam and has excellent antireflection properties because it has excellent durability against high temperature and high pressure steam. That is.

  As a result of earnest research in view of the above object, the present inventor determined that (a) the surface layer on the incident medium side of the antireflection film is a high-density layer made of hafnium dioxide or tantalum pentoxide, And (b) an antireflection film having a high refractive index layer and a low refractive index layer alternately, and having a high refractive index layer on the surface, the thickness of the surface layer is small, It was discovered that when the total number of layers of the high refractive index layer and the low refractive index layer was 7 or more, an excellent antireflection effect was exhibited in a wide wavelength range, and the present invention was conceived.

  That is, the optical element of the present invention has an antireflection film on the substrate surface, and the antireflection film has a high refractive index layer made of hafnium dioxide or tantalum pentoxide and a low refractive index made of aluminum oxide or silicon oxide. The surface layer on the incident medium side is the high refractive index layer, has a physical layer thickness of 1 to 16 nm, and is incident at an angle of 0 to 50 °. The reflectance for visible light is 1.5% or less.

  Among the layers of the antireflection film, at least the surface layer is preferably formed by the reactive ion beam sputtering method, and all the layers are more preferably formed by the reactive ion beam sputtering method. The substrate is preferably made of lanthanum glass or synthetic quartz glass.

  In a preferred embodiment of the present invention, the high refractive index layer is made of tantalum pentoxide, the low refractive index layer is made of silicon oxide, and the antireflection film has a physical layer thickness of 3 to 33 nm in order from the substrate side. Tantalum pentoxide layer, physical layer thickness 15-61 nm silicon oxide layer, physical layer thickness 34-50 nm tantalum pentoxide layer, physical layer thickness 27-49 nm silicon oxide layer, physical layer thickness 24- 46 nm tantalum pentoxide layer, physical layer thickness 37-63 nm silicon oxide layer, physical layer thickness 31-57 nm tantalum pentoxide layer, physical layer thickness 8-30 nm silicon oxide layer, physical layer thickness It has a tantalum pentoxide layer having a thickness of 44 to 74 nm, a silicon oxide layer having a physical layer thickness of 63 to 87 nm, and a tantalum pentoxide layer having a physical layer thickness of 1 to 16 nm.

  In another preferred embodiment of the present invention, the high refractive index layer is made of hafnium dioxide, the low refractive index layer is made of aluminum oxide or silicon oxide, and the antireflection film has a physical layer thickness of 30 in order from the substrate side. -85 nm aluminum oxide layer, physical layer thickness 1-99 nm hafnium dioxide layer, physical layer thickness 1-95 nm aluminum oxide layer, physical layer thickness 15-36 nm hafnium dioxide layer, physical layer thickness 32-70 nm aluminum oxide layer, physical layer thickness 1 to 57 nm hafnium dioxide layer, physical layer thickness 21 to 53 nm aluminum oxide layer, physical layer thickness 13 to 57 nm hafnium dioxide layer, physical layer thickness 5 to 44 nm It has an aluminum oxide layer, a hafnium dioxide layer having a physical layer thickness of 36 to 75 nm, a silicon oxide layer having a physical layer thickness of 58 to 93 nm, and a high refractive index layer having a physical layer thickness of 1 to 16 nm.

  The medical optical instrument of the present invention has the optical element of the present invention.

  In the optical element of the present invention, the incident medium side surface layer is a layer made of hafnium dioxide or tantalum pentoxide, and the thickness of the surface layer is as small as 1 to 16 nm. The total number of high refractive index layers and low refractive index layers is 7 or more. For this reason, it has excellent durability against high-temperature and high-pressure water vapor, and also exhibits excellent antireflection characteristics in a wide wavelength range. An optical element having an antireflection film that is resistant to high-temperature and high-pressure steam can be sterilized at high-temperature and high-pressure steam (autoclave), and thus is suitable for an optical element such as an objective lens for an endoscope.

[1] Optical Element The optical element of the present invention comprises a base material and an antireflection film formed on at least one surface of the base material.
(1) Base material Examples of the base material include flat plates, lenses, prisms, gratings, and composites thereof. The substrate is preferably made of lanthanum glass or synthetic quartz glass. A substrate made of lanthanum-based glass or synthetic quartz glass has durability against high-temperature and high-pressure steam, and thus can be sterilized with high-temperature and high-pressure steam.

(2) Antireflection film A high refractive index layer made of hafnium dioxide or tantalum pentoxide and a low refractive index layer made of aluminum oxide or silicon oxide are alternately laminated on the surface of the substrate. When layers having different refractive indexes are stacked, incident light is refracted at the interface between the layers. Therefore, an antireflection film having excellent antireflection characteristics can be formed by alternately laminating layers having different refractive indexes.

  The total number of layers of the high refractive index layer and the low refractive index layer is 7 or more. When the number of layers is less than 7, the wavelength region showing an excellent antireflection effect is too narrow. An antireflection film having seven or more layers exhibits an excellent antireflection effect in a wide wavelength region. Specifically, the reflectance with respect to light having a wavelength of 400 to 700 nm and incident on the optical element at any angle of 0 to 50 ° is 1.5% or less. A preferred optical element has a reflectance of 1.5% or less for visible light having an incident angle of 5 ° or more. Thus, when it has a low reflectance in a wide range of the visible light region, visible light can be transmitted efficiently.

  The surface layer on the incident medium side is a high refractive index layer. When a high refractive index layer made of hafnium dioxide or tantalum pentoxide is formed on the surface with high density, the antireflection film exhibits excellent durability against high-pressure and high-temperature water vapor. The physical layer thickness of the surface layer is 1 to 16 nm. When the physical layer thickness is less than 1 nm, an antireflection film having sufficient durability cannot be obtained. When the physical layer thickness exceeds 16 nm, the antireflection effect is too small.

  A preferred example of the structure of the antireflection film is shown in Table 1. This antireflection film has a high refractive index layer made of tantalum pentoxide and a low refractive index layer made of silicon oxide, and has an 11-layer structure. For convenience, the first layer, the second layer,.

  Table 2 shows another preferable example of the configuration of the antireflection film. The antireflection film shown in this example has a high refractive index layer made of hafnium dioxide and a low refractive index layer made of aluminum oxide or silicon oxide, and has a 12-layer structure. For convenience, the first layer, the second layer,.

[2] Film formation method of antireflection film The antireflection film is preferably formed by a reactive ion beam sputtering method. According to the reactive ion beam sputtering method, each layer can be formed with high purity. Further, an antireflection film having a high packing density and excellent durability against high-temperature and high-pressure water vapor can be obtained. In this specification, the reactive ion beam sputtering method is a method in which an ion beam collides with a metal target, and the ejected metal target atoms and / or molecules react with oxygen to form a metal oxide layer on a substrate. Say.

  In general, when forming a multilayer antireflection film, it is inexpensive to form each layer by the same film formation method, but different methods may be used. When using a different method, it is preferable to form at least the high refractive index layer on the surface by reactive ion beam sputtering. When the high refractive index layer on the surface is formed by the reactive ion beam sputtering method, high-temperature and high-pressure water vapor is difficult to contact the low refractive index layer formed on the inside thereof. For this reason, even if the optical element is repeatedly subjected to high-temperature and high-pressure steam sterilization treatment, the antireflection film tends to deteriorate.

In FIG. 1, the outline | summary of the apparatus for forming the antireflection film in the base material S is shown. As shown in FIG. 1, the sputtering apparatus 100 includes a sputtering chamber 1 and an ion source 2 attached to an opening of the sputtering chamber 1. In the sputtering chamber 1, a target member 12 having a base holder 11 and a target holder 123 provided so as to be inclined with respect to the support 110 of the base holder 11 is provided. Further, the sputtering chamber 1 includes an exhaust port 13 and an oxygen introduction port 14. The target member 12 includes a support 121 and target holders 123, 124, and 125 attached to the upper end of the support 121 via a connection part 122. Targets T ₁ , T ₂ , and T ₃ are placed on the target holders 123, 124, and 125, respectively. The support 121 is configured to rotate. When the support 121 is rotated by 120 °, the second target holder 124 faces the substrate S. The third target holder 125 faces the substrate S when the support 121 is further rotated 120 ° from the position. The connecting portion 122 can adjust the inclination angle of the target holders 123, 124, and 125 with respect to the base material holder 11.

The ion source 2 has an inert gas inlet 21. An extraction electrode 22 is provided on the connection surface between the ion source 2 and the sputtering chamber 1. The inert gas introduced from the inlet 21 is ionized in the ion source 2 and then irradiated to the target T ₁ , target T _2, or target T ₃ as an ion beam by the extraction electrode 22.

In order to form an antireflection film using the apparatus shown in FIG. 1, first, the targets T ₁ and T ₂ (or targets T ₁ , T ₂ , T ₃ ) are placed on the target holders 123 and 124 (or target holders 123, 124, and 125). ) Is placed. For example, when the antireflection film having the structure shown in Table 1 is formed, a tantalum (V) metal target and a metal silicon target are placed on the target holders 123 and 124, respectively. Since the first layer is a tantalum pentoxide layer, the target member 12 is set so that the tantalum (V) metal target faces the substrate S. A substrate S is placed on the substrate holder 11. When the antireflection film having the structure shown in Table 2 is formed, a hafnium (IV) metal target, an aluminum metal target, and a metal silicon target are placed on the target holders 123, 124, and 125, respectively. It is sufficient to face material S.

After the inside of the sputtering chamber 1 is decompressed to 1.0 × 10 ^{−8 to} 1.0 × 10 ⁻⁵ Torr by a vacuum pump (not shown) connected to the exhaust port 13, oxygen gas is introduced from the oxygen introduction port 14, and the sputtering chamber The oxygen pressure in 1 is set to 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻³ Torr.

  It is preferable to keep the substrate S at 10 to 300 ° C. before sputtering. By keeping the temperature of the substrate S within this range, a dense film having an amorphous structure can be efficiently formed. It is preferable to provide a shutter between the base material and the target, and open the shutter after the base material S is brought to 10 to 300 ° C. with the shutter closed.

An inert gas such as argon gas is introduced from the introduction port 21, and the inert gas pressure in the ion source 2 is set to 5.0 × 10 ^{−5 to} 1.5 × 10 ⁻⁴ Torr. Next, the ion source 2 is operated so that ion irradiation to the target T ₁ becomes 1 to 10 mA / cm ³ . Ions generated in the ion source 2 are irradiated to the target. The particles of the target T ₁ ejected by the collision of the ion beam react with oxygen in the sputtering chamber 1 to become oxides and deposit on the substrate S. As a result, a layer made of the oxide of the target T ₁ is formed on the substrate S. The physical layer thickness of each layer formed on the substrate can be controlled by sputtering time, inert gas supply rate, ion current density, and the like. For example, in order to form a tantalum pentoxide layer having a thickness of 100 to 200 nm, the ion current density to the target T ₁ may be set to 1 to 10 mA / cm ³ and the sputtering time may be set to 10 to 20 minutes.

After the oxide layer of the target T ₁ is formed to have a desired thickness, the supply of the ion beam is stopped, and the support 121 is rotated so that the target T ₂ faces the substrate S. When the ion source 2 is operated again, the target T ₂ is irradiated with an ion beam, and a layer made of the target T ₂ oxide is formed on the target T ₁ oxide layer. Thus, by repeating sputtering of the target T ₁ and sputtering of the target T ₂ , the target T ₁ and the target T ₂ can be alternately stacked.

[3] Medical optical device The optical element of the present invention has both durability against high-temperature and high-pressure steam and excellent antireflection properties. For this reason, it is suitable for medical optical instruments that require sterilization. Examples of the medical optical device include a flexible endoscope, a rigid endoscope, a capsule endoscope, and a laser treatment apparatus.

  2 and 3 schematically show an example of an endoscope having the optical element of the present invention. As shown in FIG. 2, the endoscope insertion unit 300 includes an outer cylinder 31, and an illumination optical system A and an observation optical system B that extend in the axial direction of the outer cylinder 31. The illumination optical system A is connected to the illumination device 50 by a light guide fiber bundle (hereinafter abbreviated as “light guide”) 33. The observation optical system B is connected to the eyepiece optical system C by an image guide fiber bundle (hereinafter abbreviated as image guide) 36.

  FIG. 3 shows an enlarged cross section of the tip portion P. As shown in FIG. A boundary portion 32 is provided in the axial direction in the outer cylinder 31, and both sides of the boundary portion 32 form two independent storage spaces a and b having a circular cross section. An observation optical system B is accommodated in one space (upper space in the figure) b, and an illumination optical system A is accommodated in the other space (lower space in the figure) a.

  In order to illuminate the inside of the body cavity, the illumination light is guided from the illumination device 50 to the endoscope distal end portion P by the light guide 33. A cylindrical base 34 is fitted at the tip of the light guide 33, and the base 34 is fixed in the accommodation space a of the outer cylinder 31. For positioning, the base 34 is bonded to the inner surface of the outer cylinder 31 with an adhesive or wax as required. The end face of the base 34 on the distal end side of the outer cylinder 31 is covered with a cover glass 35. The cover glass 35 has a function of satisfactorily transmitting illumination light from the light guide 33 in addition to a function of sealing the internal space a in which the illumination optical system A in the outer cylinder 31 is disposed. The space between the cover glass 35 and the outer cylinder 31 is sealed so that water vapor or the like does not enter the outer cylinder 31. The cover glass 35 is preferably made of glass (for example, synthetic quartz glass) having durability against high-temperature and high-pressure steam.

  A cylindrical base 37 is fitted to the tip of the image guide 36 of the observation optical system B, and the base 37 is fixed in the lens frame 38. The lens frame 38 is fixed in the accommodation space b, and the objective lenses 40, 41, and 42 are held inside the lens frame 38 at a predetermined interval. In the example shown in FIGS. 2 and 3, the observation optical system B includes three objective lenses, but the number of optical elements included in the medical optical device of the present invention is not limited to this. Further, in the case of a device having a plurality of optical elements, it is only necessary to have at least one optical element of the present invention.

  The front end of the lens frame 38 is set to be flush with the front end of the outer cylinder 31. An antireflection film is formed on the surface of the objective lens. Sealing is provided between the objective lens 42 and the lens frame 38 and between the lens frame 38 and the outer cylinder 31 so that water vapor or the like does not enter the outer cylinder 31. The objective lens 42 that comes in contact with high-temperature and high-pressure water vapor during sterilization has excellent durability and prevents water vapor from entering the outer cylinder 31. High-temperature and high-pressure steam sterilization is possible.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
A flat plate S made of S-LAH58 (Ohara Optical Co., Ltd., nd = 1.883, νd = 40.8), which is a lanthanum glass, was placed on the substrate holder 11 of the apparatus shown in FIG. A tantalum (V) metal (purity 99.99%) target was placed on the target holder 123, and a silicon (purity 99.99%) target was placed on the target holder 124. A tantalum (V) metal target is made to face the flat plate S, argon is introduced from the inlet 21, and an ion current density of 2.0 mA / cm ³ is supplied into the sputter material 1 to form a layer made of Ta ₂ O _5. did. The supply of argon was performed until the physical layer thickness of the Ta ₂ O ₅ layer reached 22.1 nm. Next, the silicon target was made to face the flat plate S, and argon ions were supplied at a current density of about 2.0 mA / cm ³ to form a SiO ₂ layer having a physical layer thickness of 25 nm.

In this way, a multilayer antireflection film having the structure shown in Table 3 was formed on the surface of the flat plate S by reactive ion beam sputtering using tantalum (V) metal targets and silicon targets alternately. Each Ta ₂ O ₅ layer had a refractive index of 2.25, and each SiO ₂ layer had a refractive index of 1.49.

Example 2
Using a hafnium (IV) metal (purity 99.99%) target, a silicon (purity 99.99%) target and an aluminum metal (purity 99.99%) target, Suprasil-P30 (made by Shin-Etsu Quartz Co., Ltd., nd = 1.458) A multilayer antireflection film was formed in the same manner as in Example 1 except that the layers shown in Table 4 were formed on the surface of the flat plate S made of νd = 67.7). Each HfO ₂ layer had a refractive index of 2.15, and each Al ₂ O ₃ layer had a refractive index of 1.68.

Comparative Example 1
On the surface of a flat plate made of S-LAH58 (Ohara Optical Co., Ltd., nd = 1.883, νd = 40.8), which is a lanthanum glass, a three-layer film having the structure shown in Table 5 was formed by the ion beam assist method.

Comparative Example 2
On the surface of a flat plate made of Suprasil-P30 (Shin-Etsu quartz Co., Ltd., nd = 1.458, νd = 67.7), which is a synthetic quartz glass, a five-layer film having the structure shown in Table 6 was formed by vacuum deposition.

Comparative Example 3
A six-layer film having the structure shown in Table 7 was formed on the surface of a flat plate made of synthetic silica glass Suprasil-P30 (manufactured by Shin-Etsu Quartz Co., Ltd., nd = 1.458, νd = 67.7). The SiO ₂ layer, HfO ₂ layer, and perfluoromethylsilazane (manufactured by Shin-Etsu Chemical Co., Ltd., refractive index: about 1.4) layer were all formed by vacuum deposition.

  The optical elements of Examples 1 and 2 and Comparative Examples 1 to 3 were irradiated with parallel light having a wavelength of 350 to 750 nm so that the incident angle was 5 °, and the spectral reflectance was measured. The results are shown in FIGS. 4 and 5, it was found that the optical element of the example had a reflectance of less than 1.5% with respect to light having a wavelength of 400 to 700 nm.

  A treatment for 10 minutes in a saturated water vapor pressure at 132 ° C. was performed 200 times on each optical element of the example and the comparative example. Thereafter, water droplets adhering to the surface of each optical element were wiped off with a cleaning paper soaked with a mixed solvent composed of diethyl ether and methyl alcohol (volume ratio 7: 3). Table 8 shows the results of observation of the surface after wiping. In Table 8, ◯ indicates that no waterdrop-shaped flow mark remained on the surface and that the surface was wiped cleanly, and x indicates that a waterdrop-shaped flow mark remained on the surface. The appearance of the optical element surface of the example was almost the same as that before the high-temperature and high-pressure steam sterilization treatment. From this, it was found that the optical elements of the examples had excellent durability against high-temperature and high-pressure steam.

It is the schematic which shows an example of the apparatus which forms the antireflection film of the optical element of this invention. It is a schematic sectional drawing which shows an example of the medical optical instrument of this invention. It is an expanded sectional view which shows the front-end | tip part of a medical optical instrument. It is a graph which shows the spectral reflectance of the optical element of Example 1 and 2. It is a graph which shows the spectral reflectance of the optical element of Comparative Examples 1-3.

Explanation of symbols

100 ... Sputtering equipment 1 ... Sputtering chamber
11 ... Base material holder
110 ... Support surface
12 ... Target material
120 ... prop
122 ・ ・ ・ Connection
123, 124 ... Target holder 2 ... Ion source
21 ... Inert gas inlet
22 ... Extraction electrode
S ... Base material
T ₁ , T ₂ ... Target
300 ・ ・ ・ Endoscope insertion part
31 ... Outer cylinder
32 ... Boundary part
33 Light guide
34, 37 ... base
35 ... Cover glass
36 ・ ・ ・ Image guide
38 ... Lens frame
40, 41, 42 ... objective lens
50 ... Lighting device
a 、 b ・ ・ ・ Containment space
A: Illumination optics
B ... Observation optical system
C ... Eyepiece optical system
P ・ ・ ・ Tip

Claims (7)

  An optical element having an antireflection film on a surface of a substrate, wherein the antireflection film comprises alternately a high refractive index layer made of hafnium dioxide or tantalum pentoxide and a low refractive index layer made of aluminum oxide or silicon oxide. The surface layer on the incident medium side is a high refractive index layer having a physical layer thickness of 1 to 16 nm, and has a reflectivity for visible light incident at any angle of 0 to 50 °. An optical element characterized by being 1.5% or less.   2. The optical element according to claim 1, wherein the surface layer is formed by a reactive ion beam sputtering method.   3. The optical element according to claim 1, wherein each layer of the antireflection film is formed by a reactive ion beam sputtering method.   The optical element according to claim 1, wherein the base material is made of lanthanum-based glass or synthetic quartz glass.   5. The optical element according to claim 1, wherein the high refractive index layer is made of tantalum pentoxide, the low refractive index layer is made of silicon oxide, and a physical layer thickness of 3 to 3 in order from the substrate side. 33 nm tantalum pentoxide layer, physical layer thickness 15-61 nm silicon oxide layer, physical layer thickness 34-50 nm tantalum pentoxide layer, physical layer thickness 27-49 nm silicon oxide layer, physical layer thickness 24 to 46 nm tantalum pentoxide layer, physical layer thickness 37 to 63 nm silicon oxide layer, physical layer thickness 31 to 57 nm tantalum pentoxide layer, physical layer thickness 8 to 30 nm silicon oxide layer, physical An optical element comprising a tantalum pentoxide layer having a layer thickness of 44 to 74 nm, a silicon oxide layer having a physical layer thickness of 63 to 87 nm, and a tantalum pentoxide layer having a physical layer thickness of 1 to 16 nm.   5. The optical element according to claim 1, wherein the high refractive index layer is made of hafnium dioxide, the low refractive index layer is made of aluminum oxide or silicon oxide, and a physical layer thickness of 30 in order from the base material side. -85 nm aluminum oxide layer, physical layer thickness 1-99 nm hafnium dioxide layer, physical layer thickness 1-95 nm aluminum oxide layer, physical layer thickness 15-36 nm hafnium dioxide layer, physical layer thickness 32-70 nm aluminum oxide layer, physical layer thickness 1 to 57 nm hafnium dioxide layer, physical layer thickness 21 to 53 nm aluminum oxide layer, physical layer thickness 13 to 57 nm hafnium dioxide layer, physical layer thickness 5 to 44 nm An optical element comprising an aluminum oxide layer, a hafnium dioxide layer having a physical layer thickness of 36 to 75 nm, a silicon oxide layer having a physical layer thickness of 58 to 93 nm, and a hafnium dioxide layer having a physical layer thickness of 1 to 16 nm. A medical optical apparatus comprising the optical element according to claim 1.

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