JP3312061B2 - Microscope objective lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used in an optical system such as a microscope, and more particularly to an objective lens used in an optical system such as a microscope using ultraviolet light.

[0002]

2. Description of the Related Art A conventional objective lens for an ultraviolet microscope is:
When the wavelength is shorter than 330 nm, glass materials usable as lenses are limited to fluorite and quartz. Therefore, color correction is performed by frequently using a cemented lens in which lenses using these glass materials are cemented. However, the two types of glass materials had poor color correction ability and could only perform color correction in a narrow range. Further, fluorite has poor workability, and there is no suitable bonding agent at a wavelength of 300 nm or less, and only quartz is a suitable glass material in the deep ultraviolet region. However, since color correction cannot be performed with an objective lens made of only quartz, only one kind of laser that oscillates in a narrow band can be used as a light source.

Recently, a diffractive optical element (DO) has been used as an optical element.
An optical system using E) has attracted attention. An objective lens using the diffractive optical element, which is similar to the objective lens of the present invention, is disclosed in Japanese Patent Application Laid-Open Nos.
Japanese Patent Application Laid-Open No. 361201 and JP-A-4-214516.

A diffractive optical element utilizing the above-mentioned diffraction phenomenon, that is, a diffractive optical element
[Diffractive Optical Elem
ents (DOE)] is a small optical element for optical designers Nos . 6 and 7 published by Optronics.
Chapter, "SPIE" Vol. 126, pp. 46-53 (197
7 years), and the principle is briefly described as follows.

[0005] Ordinary optical glass is refracted according to Snell's law represented by the following equation in FIG.

N sin θ = n ′ sin θ ′ (1) where n is the refractive index of the incident side medium, n ′ is the refractive index of the exit side medium, θ is the incident angle of the light beam, and θ ′ is the exit angle of the light beam. is there.

On the other hand, in the diffraction phenomenon, light is bent according to the law of diffraction represented by the following equation (2) as shown in FIG.

N sin θ−n ′ sin θ ′ = mλ / d (2) where m is the order of the diffracted light, λ is the wavelength, and d is the lattice spacing.

An optical element that bends a light beam according to the above equation (2) is a diffractive optical element. Although FIG. 14 shows that the shielding part and the transmitting part are arranged side by side at a distance d, as shown in FIG. 15, a transparent surface is provided with a diffraction surface having a sawtooth cross section, or is blazed. A high diffraction efficiency can be obtained by performing the binary approximation.

Next, advantages of using the above-described diffractive optical element will be described.

In the case of a dioptric thin lens, the following equation (3) is used.
Is established.

1 / f = (n−1) (1 / r ₁ −1 / r ₂ ) (3) where f is the focal length, r ₁ and r ₂ are the radii of curvature of the entrance surface and the exit surface, respectively, and n Is the refractive index of the lens.

When both sides of the above equation (3) are differentiated by the wavelength λ, the following equation (4) is obtained.

Df / dλ = −f (dn / dλ) / (n−1) ∴Δf = −f ｛Δn / (n−1)｝ (4) Excluding the coefficient doubling effect, Δn / ( Since n-1) represents the dispersion characteristic, the dispersion value ν can be defined as follows.

Ν≡ (n−1) / Δn (5) Accordingly, the dispersion characteristic (Abbe number ν _d ) in the visible region is as follows.

Ν _d = ( _nd −1) / (n _F −n _c ) (6) On the other hand, in the case of a diffractive optical element, the focal length of the diffractive optical element is f, and the ray height h of the incident parallel light is h. Assuming that the lattice spacing at the point is d _h , the following equation (7) is obtained.

[0017] f = h / (n'sin θ ' ) = (d h h) / (mλ) (7) If the diffractive optical element aplanatic, since d _h h is constant, f = C / λ (C is a constant). When both sides of f = C / λ are differentiated by λ, Expression (8) is obtained as follows.

Df / dλ = −C / λ ² = −f / λ∴Δf = −f (Δλ / λ) (8) Since Δn / (n−1) = ν, equations (4) and (8) ), Ν = λ / Δλ. Therefore, the Abbe number ν _d of the diffractive optical element in the visible region is as follows.

Ν _d = λ _d / (λ _F −λ _C ) = − 3.453 (9) As described above, the diffractive optical element has a very large negative dispersion characteristic. Since the dispersion characteristic of ordinary glass is about 20 to 95, it can be seen that the diffractive optical element has a very large inverse dispersion characteristic. Further, it can be seen from the same calculation that the diffractive optical element has anomalous dispersion.

Each of the above-mentioned conventional examples basically relates to a lens for a stepper, and is an optical system composed only of quartz, which corrects chromatic aberration and the like. Of these, the optical system disclosed in Japanese Patent Application Laid-Open No. 2-1109 is characterized in that a diffractive optical element is arranged at a pupil position. The optical system disclosed in Japanese Patent Application Laid-Open No. 4-361201 is characterized in that diffracted light having a higher order is used in the periphery of the diffractive optical element than in the center. Further, JP-A-4-21451
The optical system of No. 6 is characterized in that a diffractive optical element is arranged at a place where the light beam height is high. These conventional examples can be applied to a low-magnification microscope objective lens, but cannot be applied to a much higher magnification and high-NA microscope objective lens.

[0021]

SUMMARY OF THE INVENTION In view of the above, the present invention is a lens system capable of coping with a high magnification and a high NA. Even if only one kind of quartz is used, it is effective by using a diffractive optical element. An object of the present invention is to provide a microscope objective lens in which various aberrations, particularly chromatic aberration, are corrected.

[0022]

A microscope objective lens according to the present invention comprises, in order from the object side, a plano-convex lens having a flat object side or a meniscus lens having a concave surface facing the object side. And a second group including at least one diffractive optical element, wherein the following condition (1) is satisfied, and at least one diffractive optical element satisfies condition (2).
And (3) are satisfied. (1) 0.5 <| R | / t <5 (2) D 1 /D>0.8 (3) (h × f) / (L × I)> 0.07 wherein, R is the meniscus lens marginal beam diameter, D is the maximum marginal light flux diameter in the microscope <br/> objective lens image side surface radius of curvature of, t is the thickness of the meniscus lens, D ₁ is in terms of the diffractive optical element , h is the principal ray height at the surface of the diffractive optical element, f is the microscope objective
Focal length of the, L is parfocal distance of the microscope objective lens, I is the maximum image height on the sample surface. And the above conditions
In a configuration satisfying (1) and (2), the object side is a flat surface.
Plano-convex lens or meniscus lens with concave surface facing the object side
Is located closest to the object . In addition, the first group
And each of the refractive lenses constituting the second group is a single lens.
It is. In addition, the first group and the second group are configured.
Refractive lenses are all made of the same glass material.

In a high NA, high magnification objective lens, it is necessary to provide a high power surface on the front lens in order to convert the high NA divergent light emitted from the object side into convergent light. If this high power surface is used for a lens having a convex surface facing the object side, various aberrations generated on the surface will be very large. Therefore, the front lens necessarily becomes a meniscus lens having a flat or concave surface facing the object side. The power of the image side surface of the meniscus lens must be increased, and the radius of curvature of this surface becomes very small.
The front ball is almost hemispherical to secure the rim . The condition (1) defines the meniscus lens of the first lens. If the lower limit of 0.5 of the condition (1) is exceeded, the rim of the meniscus lens cannot be secured. Conversely, if the upper limit of 5 is exceeded, the power of the surface becomes too weak and light from the object is effectively converged. I can't turn it into light.

In the objective lens according to the present invention, the light beam converged by the meniscus lens is further converged by several positive lenses in the first group and guided to the second group including the diffractive optical element. The second group corrects chromatic aberration and the like.

Chromatic aberration is roughly classified into two types, axial chromatic aberration and magnification chromatic aberration. The former is a shift of the focal position by wavelength, and the latter is a shift of the focal length (magnification) by wavelength.

Of these chromatic aberrations, the most effective position for correcting the axial chromatic aberration is the pupil position in the objective lens, but it is not necessary to accurately set the pupil position.
A large light beam diameter (axial marginal light beam diameter) near the pupil is effective in correcting axial chromatic aberration. The condition (2) is determined in consideration of this. Under the condition (2), if the lower limit is 0.8 or less, the axial chromatic aberration generated in another refractive optical element (lens) cannot be corrected by the diffractive optical element, and many cemented lenses are used in the refractive optical element. Must be used, and extraordinary dispersion glass is required, and the effect of using the diffractive optical element is not sufficient.

On the other hand, the most effective position for correcting the chromatic aberration of magnification is not the pupil position but the position where the principal ray slightly away from the pupil has a certain ray height. The condition (3) determines the arrangement position of the diffractive optical element for effectively correcting the chromatic aberration of this magnification. If the lower limit of 0.07 in the condition (3) is exceeded, chromatic aberration of magnification cannot be sufficiently corrected, and a large number of cemented lenses may be used for the refractive optical element,
It is necessary to use anomalous dispersion glass, and the effect of using the diffractive optical element cannot be sufficiently obtained.

As can be seen from the above description, in order to effectively correct chromatic aberration, it is necessary to arrange a diffractive optical element at an appropriate position according to its use.

In the condition (3), f, L, and I are for normalizing this condition, f / I is a parameter for the principal ray angle, and L is a parameter for scaling the size of the entire optical system. It is.

Further, the diffractive optical element has a manufacturing feature that the grating interval can be set arbitrarily. Therefore, the diffractive optical element can obtain an effect equivalent to an arbitrary aspherical lens by changing the lattice spacing variously, and is designed more than a normal aspherical lens such that there may be many inflection points. The degree of freedom is high and the manufacturing accuracy is good. Moreover, it is possible to correct chromatic aberration that cannot be corrected by an aspheric lens. Further, the gradient index lens can correct chromatic aberration, but the refractive index gradient lens that can be actually manufactured is limited, and it cannot sufficiently cope with ultraviolet rays or infrared rays. As described above, the diffractive optical element has more excellent aberration correcting ability than the aspherical lens and the gradient index lens, and is advantageous in manufacturing. Therefore, by using this as an objective lens as in the present invention, it is possible to improve the performance of the objective lens and reduce the cost, and it is also possible to design a new objective lens which has been impossible in the past.

[0031]

Next, an embodiment of the present invention will be described. First, the diffractive optical element used in the embodiment of the present invention will be described in more detail. The diffractive optical element (DOE) used in the embodiments described later is as described above, but as a design method of an optical system including such a diffractive optical element,
Ultra-high index method
What is known as Index methods) is known. This is a method in which a diffractive optical element is designed by replacing it with a virtual lens (ultra-high index lens) having an extremely large refractive index. Regarding this, "SPIE" Vol. 126, pp. 46-53 (197
7), but will be briefly described with reference to FIG. In FIG. 17, 1 is an ultra-high index lens, and 2 is a normal line. In this ultra-high index lens, the relationship represented by the following equation (11) is established.

(N _U −1) dz / dh = nsin θ−n′sin θ ′ (10) where n _U is the refractive index of the ultra-high index lens, and z is the optical axis direction of the ultra-high index lens. Coordinates, h is the distance from the optical axis, n and n 'are the refractive indices of the incident side medium and the exit side medium, and θ and θ', respectively.
Is the incident angle and the exit angle of the light beam.

From equations (2) and (10), the following equation (1)
1) is obtained.

(N _U −1) dz / dh = mλ / d (11) That is, between the surface shape of the ultra-high index lens (a refractive lens having an extremely large refractive index) and the pitch of the diffractive optical element. Satisfies the equivalent relation given by equation (11), and through this equation, the pitch of the diffractive optical element can be determined from the data designed by the ultra-high index method.

A general axisymmetric aspherical surface is expressed as follows. ^{z = ch 2 / [1+ {} 1-c 2 (k + 1) h 2} 1/2] + Ah 4 + Bh 6 + Ch 8 + Dh 10 + ···· (12) However, z is a positive direction of the optical axis (image ), H is the coordinate axis in the meridional direction among the coordinate axes orthogonal to the z-axis with the intersection point of the plane and the z-axis as the origin, c is the curvature of the reference plane, and k is the conic constant A, B, C, D,. Are 4th, 6th, 8th, 1
.. Are aspheric coefficients of order 0,.

From formulas (11) and (12), the pitch d of the diffractive optical element equivalent to the aspheric surface at a certain ray height is:
It is represented by the following equation (13). d = mλ / [(n−1) ｛ch / ｛1+ (1-c ² (1 + k) h ² ) ^1/2 } +4 Ah ³ + 6Bh ⁵ + 8Ch ⁷ + 10Dh ⁹ +... In the following embodiments, the order of the aspherical terms is up to 10th, but the 12th, 14th,... Aspherical terms may be used.

Next, data of each embodiment will be shown. Example 1 Focal length = 3.6 mm, NA = 0.70, magnification = 50, parfocal distance =
45 mm sample surface maximum image height = 0.20 mm r ₀ = ∞ d ₀ = 0.8660 r ₁ = -1.9996 d ₁ = 3.8538 quartz r ₂ = -3.0051 d ₂ = 0.2 r ₃ = -18.9946 d ₃ = 2.8804 quartz r ₄ =- _{7.3945 d 4 = 0.2 r 5 =} 65.8028 d 5 = 2.7977 quartz _{r 6 = -16.8378 d 6 = 0.2} r 7 = ∞ d 7 = 1.0 quartz _{r 8 = ∞ d 8 = 0} r 9 = -3.2859 × 10 5 (DOE1 ) d ₉ = 0.2 r ₁₀ = 16.2471 d ₁₀ = 2.6929 Quartz r ₁₁ = 3946.0273 d ₁₁ = 2.0025 r ₁₂ = ∞ d ₁₂ = 1.0 Quartz r ₁₃ = ∞ d ₁₃ = 0 r ₁₄ = 0.4222 × 10 ⁶ (DOE2) d ₁₄ = 2.3926 r ₁₅ = 9.3997 d ₁₅ = 5.0 quartz r ₁₆ = 4.6739 DOE1 K = -1, A = −0.355512 × 10 ⁻⁸ , B = 0.255580 × 10 ⁻¹⁰ C = −0.276940 × 10 ⁻¹² , D = − 0.492542 × 10 ⁻¹⁵ DOE2 K = -1, A = 0.944679 × 10 ⁻⁸ , B = −0.372543 × 10 ⁻¹⁰ C = −0.135587 × 10 ⁻¹² , D = 0.627142 × 10 ⁻¹³ | R | /t=0.78 DOE1 D ₁ /D=1.00,(h×f)/(L×I)=0.106 DOE2 D ₁ / D = 0.80, (h × f) / (L × I) = 0.027

[0038] Example 2 a focal length = 1.8 mm, NA = 0.90, magnification = 100, parfocal distance = 45 mm specimen surface maximum image height _{= 0.10mm r 0 = ∞ d 0} = 0.5202 r 1 = -3.5097 d 1 = 3.9565 Quartz r ₂ = -3.1721 d ₂ = 0.2 r ₃ = -25.5673 d ₃ = 3.6571 Quartz r ₄ = -7.7297 d ₄ = 0.2 r ₅ = ∞ d ₅ = 1.0 Quartz r ₆ = ∞ d ₆ = 0 r ₇ = 1.6281 × 10 ⁶ (DOE1) d ₇ = 0.2 r ₈ = 15.4510 d ₈ = 5.0 quartz r ₉ = -16.2334 d ₉ = 0.2 r ₁₀ = ∞ d ₁₀ = 1.0 quartz r ₁₁ = ∞ d ₁₁ = 0 r ₁₂ = -3.8924 × 10 ⁵ (DOE2) d ₁₂ = 0.2 r ₁₃ = 28.6396 d ₁₃ = 2.8321 Quartz r ₁₄ = -91.0899 d ₁₄ = 3.6190 r ₁₅ = -6.8166 d ₁₅ = 2.0 Quartz r ₁₆ = -10.6927 d ₁₆ = 0.2003 r ₁₇ = 8.4376 d ₁₇ = 2.5850 quartz _{r 18 = 4.9177 d 18 = 3.5485} r 19 = ∞ d 19 = 1.0 quartz _{r 20 = ∞ d 20 = 0} r 21 = 0.5853 × 10 6 (DOE3) d 21 = 0.2 r 22 = 5.2022 d ₂₂ = 3.5626 quartz _{r 23 = 48.6437 d 23 = 3.9752} r 24 = -3.5803 d ₂₄ = 5.0 quartz r ₂₅ = 23.3843 DOE1 K = -1, A = -0.586575 × 10 ^-8 , B = 0.105584 × 10 ^-10 C = -0.114914 × 10 ^-11 , D = 0.438189 × 10 ^-13 DOE2 K = -1, A = 0.315284 × 10 -8, B = -0.139031 × 10 -10 C = 0.111483 × 10 -11, D = -0.324566 × 10 -13 DOE3 K = -1, A = -0.157706 × 10 - ⁸ , B = −0.411489 × 10 ⁻⁹ C = 0.647800 × 10 ⁻¹¹ , D = −0.118926 × 10 ⁻¹¹ | R | /t=0.80 DOE1 D ₁ /D=0.90, ( h × f) / (L × _{I) = 0.045 DOE2 D 1 /D=0.95,(h×f)/(L×I)=0.019} DOE3 D 1 /D=0.52,(h×f)/(L×I)=0.086

[0039] Example 3 a focal length = 3.6 mm, NA = 0.90, magnification = 100, parfocal distance = 100 mm sample surface the maximum image height _{= 0.10mm r 0 = ∞ d 0} = 0.8232 r 1 = -4.5891 d 1 = 4.2051 quartz _{r 2 = -3.5905 d 2 = 0.15} r 3 = -18.1769 d 3 = 3.4758 quartz _{r 4 = -8.6006 d 4 = 0.15} r 5 = -42.4203 d 5 = 2.8290 quartz _{r 6 = -18.3477 d 6 = 0.15} r 7 = ∞ d ₇ = 1.0 quartz _{r 8 = ∞ d 8 = 0} r 9 = -4.6500 × 10 5 (DOE1) d 9 = 2.3380 r 10 = 18.6150 d 10 = 6.8566 quartz _{r 11 = -70.6680 d 11 = 0.4264} r 12 = -684.8949 d ₁₂ = 2.0 quartz _{r 13 = 31.2416 d 13 = 4.6278} r 14 = -9.5514 d 14 = 2.0 quartz _{r 15 = -14.7720 d 15 = 0.15} r 16 = ∞ d 16 = 1.0 quartz r ₁₇ = ∞ d _{17 = 0 r 18 = 2.3143 × 10} 7 (DOE2) d 18 = 0.15 r 19 = 118.9395 d 19 = 3.0545 quartz _{r 20 = -24.0674 d 20 = 6.0351} r 21 = 18.8858 d 21 = 5.9248 quartz r ₂₂ = ∞ d ₂₂ = ^{_{0 r 23 = -3.6009 × 10 6}} (DOE3) _{23 = 0.15 r 24 = 16.4878 d} 24 = 3.3455 quartz _{r 25 = 151.2259 d 25 = 2.0635} r 26 = -9.6929 d 26 = 3.2223 quartz _{r 27 = 8.6410 d 27 = 6.0496} r 28 = -9.5754 d 28 = 6.2379 quartz r ₂₉ = -136.3117 d ₂₉ = 25.9711 r ₃₀ = -22.5706 d ₃₀ = 7.00 Quartz r ₃₁ = -18.2056 DOE1 K = -1, A = -0.978136 × 10 ^-9 , B = -0.552784 × 10 ^-11 C = -0.151562 × 10 ^-12 , D = 0.142616 × 10 ^-14 DOE2 K = -1, A = 0.405846 × 10 ^-9 , B = 0.125266 × 10 ^-10 C = 0.161396 × 10 ^-12 , D = -0.142574 × 10 ^-15 DOE3 K = -1, A = 0.232811 × 10 ⁻⁸ , B = 0.742643 × 10 ⁻¹¹ C = −0.309069 × 10 ⁻¹³ , D = 0.731189 × 10 ⁻¹⁴ | R | /t=0.85 DOE1 D ₁ /D=0.98, (h × f) / (L × I) = 0.033 DOE2 D 1 /D=0.81,(h×f)/(L×I)=0.042 DOE3 D 1 /D=0.64,(h×f)/(L × I) = 0.106

[0040] Example 4 a focal length = 3.6 mm, NA = 0.90, magnification = 100, parfocal distance = 100 mm sample surface the maximum image height _{= 0.10mm r 0 = ∞ d 0} = 0.8755 r 1 = -4.8102 d 1 = 5.3204 Quartz r ₂ = -4.3657 d ₂ = 0.1573 r ₃ = -11.9270 d ₃ = 3.8504 Quartz r ₄ = -8.2848 d ₄ = 0.15 r ₅ = -24.8350 d ₅ = 3.6041 Quartz r ₆ = -24.6366 d ₆ = 0.15 r ₇ = ∞ d ₇ = 1.0 quartz _{r 8 = ∞ d 8 = 0} r 9 = -4.8658 × 10 5 (DOE) d 9 = 1.4144 r 10 = 24.4149 d 10 = 6.9009 quartz _{r 11 = -27.4833 d 11 = 1.2232} r 12 = -106.5697 d ₁₂ = 2.0 quartz _{r 13 = 27.2764 d 13 = 6.6174} r 14 = -10.4558 d 14 = 2.8083 quartz _{r 15 = -16.1963 d 15 = 0.8542} r 16 = 168.5767 d 16 = 4.1096 quartz r ₁₇ = -22.5842 d _{17 = 0.15 r 18 = 17.4537 d} 18 = 4.0673 quartz _{r 19 = 344.2078 d 19 = 0.15} r 20 = 16.7564 d 20 = 3.7221 quartz _{r 21 = 71.3470 d 21 = 2.7494} r 22 = -17.0797 d 22 = 2.4919 quartz r _{2 3 = 8.7006 d 23 = 8.1241 r} 24 = 253.5226 d 24 = 4.9548 quartz _{r 25 = 7.7408 d 25 = 29.8340} r 26 = -13.6864 d 26 = 4.102532 quartz _{r 27 = -13.1893 DOE K = -1} , A = -0.136158 × ^{10 -9, B = -0.377494 × 10} -14 C = -0.369325 × 10 -14, D = 0.323198 × 10 -16 | R | /t=0.82 DOE D 1 /D=0.96,(h×f) / ( L × I) = 0.042 where r ₀ , r ₁ , r ₂ ,... Are the radii of curvature of the respective surfaces, d
_{0, d 1, d 2,} ··· in the face distances, r ₀ is the object surface, d ₀
Is the working distance.

Embodiments 1 and 2 are objective lenses for a scanning laser microscope (LSM) using a He-Cd laser with the structure shown in FIGS. 1 and 4, respectively.
Chromatic aberration is corrected at two wavelengths of 441 nm and 325 nm. In the first embodiment, two diffractive optical elements (DOEs) are used. The DOE 1 mainly corrects longitudinal and chromatic aberration of magnification, and the DOE 2 further corrects residual axial chromatic aberration. In the first embodiment, 19.71 is located on the image side of r _16.
43 mm is the body attachment position. In Example 2, three diffractive optical elements are used, DOE1 and DOE2 mainly correct axial chromatic aberration, and DOE3 corrects lateral chromatic aberration. Cylinder with the position of this second embodiment is 0.3434mm on the image side of the surface r _25.

Embodiments 3 and 4 have the configurations shown in FIGS. 7 and 10, respectively, and have a DUV (DEEP ULTRA VIOLET).
T) Scanning laser microscope using laser (LSM)
Similarly, the glass material is only quartz. The third embodiment performs chromatic aberration correction at λ = 266 ± 2 nm. This embodiment uses three diffractive optical elements and a DOE
1 indicates axial chromatic aberration, DOE3 indicates lateral chromatic aberration, and D
OE2 corrects both residual aberrations. Example 4
Uses a single-plate diffractive optical element, which mainly corrects axial chromatic aberration. The body-attached positions in these examples are indicated by reference symbols B in the cross-sectional views, and
₃₁ from 1.386133mm the object side, the fourth embodiment is r ₂₇
1.3819 mm closer to the object side.

In all the embodiments, spherical aberration, coma and the like are corrected by the aspherical effect of the diffractive optical element. It is designed with n _u = 10001. The sectional view of each embodiment, the right side (r ₀ side) the object side, each aberration diagram is shown those when an image is formed on the object surface by tracing back.

[0044]

The objective lens of the present invention has a high NA and a high magnification with only a single glass material, and various aberrations, especially chromatic aberration, are corrected well.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a diagram showing a spherical aberration, astigmatism, and distortion curve of Example 1 of the present invention.

FIG. 3 is a diagram showing a coma aberration curve according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a second embodiment of the present invention.

FIG. 5 is a diagram showing spherical aberration, astigmatism, and distortion curves of Example 2 of the present invention.

FIG. 6 is a diagram illustrating a coma aberration curve according to the second embodiment of the present invention.

FIG. 7 is a sectional view of a third embodiment of the present invention.

FIG. 8 is a spherical aberration, astigmatism, and distortion curve diagram of Example 3 of the present invention.

FIG. 9 is a diagram showing a coma aberration curve according to Example 3 of the present invention.

FIG. 10 is a sectional view of a fourth embodiment of the present invention.

FIG. 11 is a spherical aberration, astigmatism, and distortion curve diagram of Example 4 of the present invention.

FIG. 12 is a diagram showing a coma aberration curve according to the third embodiment of the present invention.

FIG. 13 is a diagram showing a state of refraction in normal glass.

FIG. 14 is a diagram showing a state of refraction of light due to a diffraction phenomenon.

FIG. 15 is a cross-sectional view of the diffractive optical element in a blazed state.

FIG. 16 is a sectional view of a diffraction-type optical element obtained by performing binary approximation.

FIG. 17 is a diagram showing a state of refraction of light in an ultra-high index lens.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 21/02 G02B 13/00 G02B 9/00

Claims (4)

(57) [Claims] 1. A plano-convex lens having a flat object side or a meniscus lens having a concave surface facing the object side is the most suitable object in order from the object side .
A first group which has a positive refractive power as a whole and is included on the body side, and a second group which includes at least one diffractive optical element, satisfies the following condition (1), and has at least one diffractive optical element A microscope objective lens whose optical element satisfies the condition (2) . (1) 0.5 <| R | / t <5 (2) D 1 /D>0.8 Here, R is the radius of curvature of the image side surface of the meniscus lens, t is the thickness of the meniscus lens, D ₁ is marginal beam diameter in terms of the diffractive optical element, D is the maximum marginal light flux diameter in the microscope <br/> objective lens. 2. A plano-convex lens having a flat object side in order from the object side.
Lens or a meniscus lens with a concave surface facing the object side.
A first group of positive refractive power as a body and at least one diffraction
A second group including a mold optical element, and the following condition (1):
Is satisfied, and at least one diffractive optical element is a condition.
A microscope objective lens that satisfies (3). (1) 0.5 <| R | / t <5 (3) (h × f) / (L × I)> 0.07 where R is the half curvature of the image-side surface of the meniscus lens.
Diameter, t is the thickness of the meniscus lens, h is diffractive optical
Principal ray height at element surface, f is focal length of whole system, L is confocal
The distance, I, is the maximum image height on the specimen surface. 3. A refraction type lens forming the first group and the second group.
3. The microscope according to claim 1, wherein each of the lenses is a single lens.
Microscope objective lens. 4. A refraction type lens forming the first group and the second group.
3. The lens according to claim 1, wherein the lenses are made of the same glass material.
Microscope objective.