A long object distance linear dispersion objective lens

Abstract

The present invention discloses a long object distance linear dispersion objective lens, the dispersion objective lens comprises a single lens and a plurality of double cemented lenses placed coaxially, after a point light source of a continuous spectrum passes through the dispersion objective lens, lights of different wavelengths converge to different positions on the optical axis, the axial dispersion range, imaging quality and the linear relationship between dispersion and wavelength are optimized and balanced, by sacrificing part of the dispersion linearity, using a quadratic function to fit the dispersion curve, thereby obtaining better imaging quality and a large dispersion range. Considering the tolerance and the difficulty of processing and assembly, the number of special meniscus lenses is reduced. The dispersion objective lens has a long object distance, which is convenient for adjusting the optical path of the front end of the lens, and is applied to different measurement systems.

Description

Technical Field

[0001] The invention belongs to the field of optical objective lenses, and in particular relates to an axial linear dispersion objective lens with a long object distance. Background Art

[0002] Color spectrum confocal technology is a non-contact optical measurement method that uses axial dispersion to encode the position on the axis, replacing the axial scanning of the confocal microscope, greatly improving the measurement speed, and the resolution can reach micro- and nanometer levels. In addition, compared with traditional measurement methods such as laser triangulation reflection measurement systems, white light interferometers, and inductive sensors, color spectrum confocal sensors are light in weight, small in size, have lower requirements on surface conditions, and allow larger tilt angles. Therefore, they are widely used in different fields such as surface morphology detection, precision measurement, biomedical imaging, and ultra-precision manufacturing.

[0003] The axial dispersion of spectral confocal is achieved by a dispersive objective lens. Therefore, the performance of the dispersive objective lens determines the accuracy, resolution, measurement range and other parameter indicators of the measurement system to a certain extent. Domestic and foreign scholars have carried out a series of research work on the design of dispersive objective lenses, which can be roughly divided into refractive and diffractive types according to the principle of dispersion. Since the refractive index of glass materials is nonlinear with wavelength in the visible light range, linear dispersion cannot be produced using a single glass material. It is necessary to select a suitable glass material combination to reduce nonlinearity, but it cannot achieve complete linearity. The dispersion of diffractive optical elements is linearly related to wavelength, but there are large aberrations, and lens groups are needed to reduce aberrations. However, the introduction of lens groups will destroy the linear relationship between dispersion and wavelength, and diffractive optical elements are difficult to process and it is difficult to achieve a large numerical aperture. Therefore, considering all factors, refractive lens groups are still the main research direction of linear dispersive elements.

[0004] The dispersion range of the dispersive objective lens affects the range of the measurement system, the linearity between dispersion and wavelength determines the measurement accuracy, and the image-side numerical aperture of the dispersive objective lens determines the resolution of the measurement system, and these indicators often restrict each other. In the current patents related to dispersive objective lenses, in order to obtain better imaging quality and linearity between dispersion and wavelength, meniscus lenses are usually involved in the optical structure, and some special meniscus lenses will also increase the difficulty and cost of processing. Therefore, how to achieve a balance between various indicators is a problem that needs to be solved. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a long object distance linear dispersion objective lens, which sacrifices part of the dispersion linearity and uses a quadratic function to fit the relationship between dispersion and wavelength, so that the objective lens has a large dispersion range, and each wavelength has a good imaging quality at its respective focal plane, while minimizing the number of special meniscus lenses and relaxing the tolerance. Increasing the object distance of the dispersion objective lens facilitates the adjustment of the front optical path of the lens and is applied to different measurement systems.

[0006] In order to achieve the purpose of the invention, the technical solution provided by the present invention is

[0007] A long object distance linear dispersion objective lens, characterized in that it comprises a dispersion lens group consisting of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are coaxially arranged in sequence from the object side to the image side;

[0008] in,

[0009] The dispersion lens group meets the following constraints:

[0010]

[0011] in is the focal length of the single lens, υ di is the Abbe number of the i-th glass material, and N is the number of glass material types;

[0012] is the dispersion linearity of the glass material;

[0013] Among them, P i is the relative partial dispersion of the i-th glass material, λ F , d , C are the wavelengths of the characteristic lights of F, d, and C, respectively, n Fi 、n di 、n Ci are the refractive indices of the i-th glass material under characteristic light of F, d, and C respectively.

[0014] Preferably, the first lens is a single lens, the second lens and the third lens constitute a doublet lens I, the fourth lens and the fifth lens constitute a doublet lens II, and the sixth lens and the seventh lens constitute a doublet lens II.

[0015] Preferably, the first lens is a plano-concave lens, the side close to the object side is a plane, the refractive index n satisfies 1.90≤n≤2.00, the center thickness is 5 mm, and the air gap between the center of the first lens and the center of the second lens is 7 mm.

[0016] Preferably, the refractive index n of the second lens satisfies 1.49≤n≤1.51, and the center thickness is 4.5 mm; the refractive index n of the third lens satisfies 1.73≤n≤1.78, and the center thickness is 5 mm; the air gap between the center of the double glued lens I and the center of the fourth lens is 7.25 mm.

[0017] Preferably, the refractive index n of the fourth lens satisfies 1.90≤n≤2.00, and the center thickness is 3 mm; the refractive index n of the fifth lens satisfies 1.73≤n≤1.78, and the center thickness is 5.5 mm; the air gap between the center of the doublet lens II and the center of the sixth lens is 7.5 mm.

[0018] Preferably, the refractive index n of the sixth lens satisfies 1.73≤n≤1.78, and the center thickness is 5.5 mm; the refractive index n of the seventh lens satisfies 1.49≤n≤1.51, and the center thickness is 4 mm.

[0019] Preferably, the operating wavelength band of the dispersion objective lens group is 430-710 nm.

[0020] Preferably, the object distance of the dispersion lens group is greater than 80 mm, the distance from the last lens surface of the dispersion lens group to the image plane is greater than 29 mm, and the image-side numerical aperture is greater than 0.28.

[0021] The beneficial effects of the present invention include:

[0022] (1) Large numerical aperture, high lateral resolution, image-side numerical aperture NA greater than 0.28;

[0023] (2) Sacrificing some dispersion linearity, using a quadratic function to fit the dispersion curve to obtain better imaging quality and a larger dispersion range, while reducing the number of special meniscus lenses in the optical structure, appropriately relaxing the tolerance, and reducing the processing cost;

[0024] (3) It has a large object distance, which makes it easy to adjust the optical path at the front end of the lens and is applied to different measurement systems, such as spectral confocal interferometry measurement system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the optical system structure of an embodiment of the present invention;

[0027] Figure 2 is a spot diagram of different spectral components in their respective focal planes according to an embodiment of the present invention;

[0028] Figure 3 This is an experimental diagram of the relationship between dispersion and wavelength in an embodiment of the present invention; DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings.

[0030] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application, rather than to limit the scope of protection of the present invention in any way. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which the present application belongs.

[0031] like Figure 1 As shown, the present invention discloses a dispersive objective lens, which includes a dispersive lens group consisting of a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6 and a seventh lens 7 which are coaxially arranged from the object side to the image side.

[0032] The dispersion lens group meets the following constraints:

[0033]

[0034] in is the focal length of the single lens, υ di is the Abbe number of the i-th glass material, N is the number of glass material types, is the dispersion linearity of the glass material. Since the refractive index of the glass material is nonlinear with the wavelength in the visible light range, a single glass material cannot produce linear dispersion, and at least two optical glass materials are required. Selecting too many types of optical materials will increase the cost. Preferably, three glass materials are selected in this embodiment.

[0035] In this embodiment, the first lens 1 is a single lens, the second lens 2 and the third lens 3 constitute a doublet lens I, the fourth lens 4 and the fifth lens 5 constitute a doublet lens II, and the sixth lens 6 and the seventh lens 7 constitute a doublet lens III.

[0036] In this embodiment, the first lens 1 is a plano-concave lens, the surface close to the object side is a plane, the glass material used is double crown glass, the refractive index n satisfies 1.90≤n≤2.00, the center thickness is 5, and the air gap between the center of the first lens 1 and the center of the second lens 2 is 1 mm.

[0037] In this embodiment, the glass material used for the second lens 2 is fluor crown glass, the refractive index n satisfies 1.49≤n≤1.51, and the center thickness is 4.5mm. The glass material used for the third lens 3 is lanthanum flint glass, the refractive index n satisfies 1.73≤n≤1.78, and the center thickness is 5mm. The air gap between the center of the doublet lens I formed by the second lens 2 and the third lens 3 and the center of the fourth lens is 7.25mm.

[0038] In this embodiment, the glass material used for the fourth lens 4 is the same as that used for the first lens 1, and the center thickness is 3 mm. The glass material used for the fifth lens 5 is the same as that used for the third lens 3, and the center thickness is 5.5 mm. The air gap between the center of the doublet lens II formed by the fourth lens 4 and the fifth lens 5 and the center of the sixth lens 6 is 7.5 mm.

[0039] In this embodiment, the glass material used for the sixth lens 6 is the same as that used for the third lens 3, and the center thickness is 5.5 mm. The glass material used for the seventh lens 7 is the same as that used for the second lens 2, and the center thickness is 4 mm.

[0040] The specific parameters of each lens in the optical system of this embodiment are shown in the following table:

[0041]

[0042] The working band of the dispersion objective lens is 430-710nm, and the imaging quality of each spectral component is good. Figure 2 As shown, eight wavelengths are set at equal intervals in the range of 430-710 nm, and the diffuse spots of each spectral component on its own designed focal plane are smaller than the Airy disk.

[0043] In this embodiment, the object distance of the dispersion lens group is greater than 80mm, which is convenient for adding other optical elements at the front end and applied to different measurement systems, such as spectral confocal interferometry system. The distance from the last surface of the lens to the image plane is greater than 29mm, and the image side numerical aperture NA is greater than 0.28. According to the Rayleigh criterion The lateral resolution is about 1.5 μm.

[0044] The dispersion range of the dispersion objective lens in the working band is 983.8252 μm. The relationship between the focusing distance and wavelength of each wavelength is as follows: Figure 3 As shown, a quadratic function is used to fit it, using the formula The fitting degree was evaluated and it was found that the quadratic function had a high fitting degree of 99.9975% for the relationship between the focusing distance and the wavelength of each wavelength.

[0045] Unless otherwise stated, any technical solution disclosed in the present invention disclosed above, if it discloses a numerical range, then the disclosed numerical range is a preferred numerical range, and any technician in the field should understand that the preferred numerical range is only a numerical value with a more obvious technical effect or representative value among many implementable numerical values. Since there are too many numerical values ​​to be exhaustive, the present invention discloses only some numerical values ​​to illustrate the technical solution of the present invention, and the numerical values ​​listed above should not constitute a limitation on the scope of protection of the present invention.

Claims

1. A long object distance linear dispersion objective lens, characterized in that: A dispersion lens group comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are coaxially arranged in sequence from the object side to the image side; in, The dispersion lens group meets the following constraints: in is the focal length of the single lens, v di is the Abbe number of the i-th glass material, and N is the number of glass material types; is the dispersion linearity of the glass material; Among them, P i is the relative partial dispersion of the i-th glass material, λ F , d , C are the wavelengths of the characteristic lights of F, d, and C, respectively, n Fi 、n di 、n Ci are the refractive indices of the i-th glass material under characteristic light of F, d, and C respectively; The first lens is a single lens, the second lens and the third lens constitute a doublet lens I, the fourth lens and the fifth lens constitute a doublet lens II, and the sixth lens and the seventh lens constitute a doublet lens II; The first lens is a plano-concave lens, the side close to the object side is a plane, the refractive index n satisfies 1.90≤n≤2.00, the center thickness is 5mm, and the air gap between the center of the first lens and the center of the second lens is 7mm; The refractive index n of the second lens satisfies 1.49≤n≤1.51, and the center thickness is 4.5 mm; the refractive index n of the third lens satisfies 1.73≤n≤1.78, and the center thickness is 5 mm; the air gap between the center of the doublet lens I and the center of the fourth lens is 7.25 mm; The refractive index n of the fourth lens satisfies 1.90≤n≤2.00, and the center thickness is 3 mm; the refractive index n of the fifth lens satisfies 1.73≤n≤1.78, and the center thickness is 5.5 mm; the air gap between the center of the doublet lens II and the center of the sixth lens is 7.5 mm; The refractive index n of the sixth lens satisfies 1.73≤n≤1.78, and the center thickness is 5.5 mm; the refractive index n of the seventh lens satisfies 1.49≤n≤1.51, and the center thickness is 4 mm; The working band of the dispersion objective lens group is 430-710nm; The object distance of the dispersion lens group is greater than 80 mm, the distance from the last lens surface of the dispersion lens group to the image plane is greater than 29 mm, and the image side numerical aperture is greater than 0.28.

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