Spectral confocal dispersion objective lens based on a radial GRIN lens

Abstract

The present invention discloses a spectral confocal dispersion objective lens based on a radial GRIN lens, which solves the technical problems that when the dispersion range of the existing dispersion objective lens meets the requirements, the linearity is poor, affecting the sensitivity and measurement accuracy of the spectral confocal displacement sensing system; when the linearity is good, the axial dispersion range is insufficient, affecting the measurement range of the spectral confocal displacement sensing system. Specifically, it includes a gradient refractive index lens, an optimization lens, a first concave lens, a first convex lens, a first cemented lens, and a second cemented lens arranged in sequence from left to right; the central axes of the gradient refractive index lens, the optimization lens, the first concave lens, the first convex lens, the first cemented lens, and the second cemented lens are all located on the same straight line. This spectral confocal dispersion objective lens can make the entire system small in volume, low in cost, and high in linearity, and can also achieve the light weight of the optical system, improving the sensitivity and measurement accuracy of the spectral confocal displacement sensing system.

Description

Technical Field

[0001] The present invention relates to a spectral confocal dispersion objective lens, and particularly to a spectral confocal dispersion objective lens based on a radial GRIN (gradient index) lens. Background Art

[0002] A spectral confocal displacement sensor is an ideal optical sensor for realizing high-precision non-contact measurement. The spectral confocal displacement sensor utilizes the spectral confocal principle to establish a linear correspondence between the spectral focusing position and the wavelength through an optical dispersion lens. According to the principle of optical path reversibility, light beams of different wavelengths return to the spectrometer through a beam splitter, and the corresponding position information is obtained through decoding and analysis to obtain the measurement value. Compared with other sensors, the spectral confocal displacement sensor has lower requirements for surface texture, object temperature, and surface roughness, and can achieve non-contact, high-precision, and rapid measurement. In a spectral confocal displacement sensing system, the dispersion lens is a key device for generating axial dispersion, and the measurement range of the sensor depends on the axial dispersion of the dispersion lens of the spectral confocal displacement sensor.

[0003] In research, a dispersion probe with a magnification of 0.3 times is usually used to achieve a dispersion range of 400 μm in the range of 450 nm to 623 nm; diffractive optical elements are used to provide focusing wavelength coding for depth measurement using dispersion, and a measurement range of 55 μm can be achieved; an objective lens designed with a double cemented lens and a single lens with a working wavelength range of 486 nm to 656 nm has a spectral width of 170 nm and a resolution of 3 μm; FK7l, LAF4, and ZF72A glasses are used to generate linear positive dispersion and negative dispersion respectively, and an axial dispersion of 1 mm can be generated in the range of 430 nm to 710 nm; an axial dispersion of 1.05 mm is designed using N-KZFS11, N-SF66, and N-PK52A combined with 3 single lenses and 2 double cemented lenses. In the above research results, the linearity of the dispersion objective lens with a satisfactory dispersion range is poor, which affects the sensitivity and measurement accuracy of the spectral confocal displacement sensing system; when the linearity of the dispersion objective lens is good, the axial dispersion range is insufficient, which affects the measurement range of the spectral confocal displacement sensing system. Summary of the Invention

[0004] The purpose of the present invention is to provide a spectral confocal dispersion objective lens based on a radial GRIN lens to solve the technical problems that when the existing dispersion objective lens meets the requirements of its dispersion range, its linearity is poor, which affects the sensitivity and measurement accuracy of the spectral confocal displacement sensing system; when the linearity is good, the axial dispersion range is insufficient, which affects the measurement range of the spectral confocal displacement sensing system.

[0005] The refractive index of the gradient refractive index element shows a gradient distribution, and its effect is equivalent to that of a homogeneous optical element with a complex multi-faceted shape, high processing requirements, and high cost. The refractive index of a radial GRIN lens continuously changes from the center to the edge in a direction perpendicular to the optical axis. Generally, it has the advantages of simple geometric shape, light weight, small volume, excellent optical performance, etc., and also has the characteristics of being convenient for integration.

[0006] Based on the above characteristics and in order to achieve the above object, the present invention provides a spectral confocal dispersion objective lens based on a radial GRIN lens, which is characterized in that it includes a gradient refractive index lens, an optimization lens, a first concave lens, a first convex lens, a first cemented lens, and a second cemented lens arranged in sequence from left to right;

[0007] The central axes of the gradient refractive index lens, the optimization lens, the first concave lens, the first convex lens, the first cemented lens, and the second cemented lens are all located on the same straight line.

[0008] Further, the first cemented lens is formed by cementing a second convex lens and a third convex lens, and the second convex lens is located on the side close to the first convex lens;

[0009] The second cemented lens is formed by cementing a fourth convex lens and a second concave lens, and the fourth convex lens is located on the side close to the third convex lens.

[0010] Further, the range of the front surface curvature radius of the gradient refractive index lens is 40.58 ± 0.02 mm, the rear surface is a plane, and the thickness range is 2.00 ± 0.01 mm;

[0011] The front surface and the rear surface of the optimization lens are both planes, and the thickness range is 2.00 ± 0.01 mm;

[0012] The range of the front surface curvature radius of the first concave lens is -33.68 ± 0.02 mm, the range of the rear surface curvature radius is 33.68 ± 0.02 mm, and the thickness range is 1.00 ± 0.01 mm;

[0013] The range of the front surface curvature radius of the first convex lens is 90.68 ± 0.02 mm, the range of the rear surface curvature radius is -77.68 ± 0.02 mm, and the thickness range is 2.00 ± 0.01 mm;

[0014] The range of the front surface curvature radius of the second convex lens is 27.74 ± 0.02 mm, the range of the rear surface curvature radius is -33.68 ± 0.02 mm, and the thickness range is 2.00 ± 0.01 mm;

[0015] The front surface radius of curvature of the third convex lens ranges from -33.68 ± 0.02 mm, the rear surface radius of curvature ranges from -33.66 ± 0.02 mm, and the thickness ranges from 1.50 ± 0.01 mm;

[0016] The front surface radius of curvature of the fourth convex lens ranges from 90.68 ± 0.02 mm, the rear surface radius of curvature ranges from -82.68 ± 0.02 mm, and the thickness ranges from 1.80 ± 0.01 mm;

[0017] The front surface radius of curvature of the second concave lens ranges from -82.68 ± 0.02 mm, the rear surface radius of curvature ranges from 33.68 ± 0.02 mm, and the thickness ranges from 1.50 ± 0.01 mm.

[0018] Further, the front surface radius of curvature of the gradient index lens is 40.58 mm, the rear surface is flat, and the thickness is 2.00 mm;

[0019] The front surface and the rear surface of the optimized lens are both flat, and the thickness is 2.00 ± 0.01 mm;

[0020] The front surface radius of curvature of the first concave lens is -33.68 mm, the rear surface radius of curvature is 33.68 mm, and the thickness is 1.00 mm;

[0021] The front surface radius of curvature of the first convex lens is 90.68 mm, the rear surface radius of curvature is -77.68 mm, and the thickness is 2.00 mm;

[0022] The front surface radius of curvature of the second convex lens is 27.74 mm, the rear surface radius of curvature is -33.68 mm, and the thickness is 2.00 mm;

[0023] The front surface radius of curvature of the third convex lens is -33.68 mm, the rear surface radius of curvature is -33.66 mm, and the thickness is 1.50 mm;

[0024] The front surface radius of curvature of the fourth convex lens is 90.68 mm, the rear surface radius of curvature is -82.68 mm, and the thickness is 1.80 mm;

[0025] The front surface radius of curvature of the second concave lens is -82.68 mm, the rear surface radius of curvature is 33.68 mm, and the thickness is 1.50 mm.

[0026] Further, the gradient index lens is made of Gradient 6;

[0027] The optimized lens is made of H-FK61 material;

[0028] The first concave lens is made of H-F51 material;

[0029] The first convex lens is made of N-SF66 material;

[0030] The second convex lens is made of H-ZF62 material;

[0031] The third convex lens is made of H-F51 material;

[0032] The fourth convex lens is made of H-F51 material;

[0033] The second concave lens is made of H-FK61 material.

[0034] Advantages of the present invention:

[0035] The spectral confocal dispersion objective lens based on a radial GRIN lens provided by the present invention is composed of a gradient refractive index lens, an optimization lens, a first concave lens, a first convex lens, a first cemented lens, and a second cemented lens; the optical power and axial dispersion structure of the spectral confocal dispersion objective lens based on a radial GRIN lens are established to achieve axial dispersion; the specific refractive index distribution of the radial GRIN lens can improve the image quality of the system, and make the entire system have the characteristics of small volume, low cost, and high linearity, enabling the lightweight of the optical system, and improving the sensitivity and measurement accuracy of the spectral confocal displacement sensing system, capable of meeting the measurement application requirements at the nanometer level, and having good axial dispersion linearity, meeting the high-precision measurement requirements of the spectral confocal displacement sensing system, and not affecting the measurement range of the spectral confocal displacement sensing system. Description of the drawings

[0036] Figure 1 is a schematic diagram of the refractive index distribution of a radial GRIN lens;

[0037] Figure 2 is a schematic diagram of the principle of a spectral confocal displacement sensing system;

[0038] Figure 3 is an axial dispersion diagram of a radial GRIN lens;

[0039] Figure 4 is a schematic structural diagram of an embodiment of the spectral confocal dispersion objective lens based on a radial GRIN lens of the present invention;

[0040] Figure 5 in (a)-(k) are spot diagrams at the focusing positions of each wavelength at intervals of 20 nm in the range of 420 nm to 620 nm in the embodiment of the present invention;

[0041] Figure 6 is an original curve graph between the axial dispersion and the wavelength generated by the embodiment of the present invention;

[0042] Figure 7 Wavelength-focal shift fitting curve graph of the embodiment of the present invention.

[0043] Reference numerals in the drawings:

[0044] 1 - gradient refractive index lens, 2 - optimized lens, 3 - first concave lens, 4 - first convex lens, 5 - first cemented lens, 51 - second convex lens, 52 - third convex lens, 6 - second cemented lens, 61 - fourth convex lens, 62 - second concave lens. Detailed implementation manners

[0045] I. Introduction to radial GRIN lens;

[0046] GRIN lenses can be classified according to different forms of refractive index gradient into: axial gradient refractive index, radial gradient refractive index, layered gradient refractive index, spherical gradient refractive index; their constant refractive index surfaces are respectively: planes perpendicular to the z-axis, cylindrical surfaces, planes parallel to the x-axis, spherical surfaces. A radial GRIN lens refers to a lens with a cylindrically symmetric refractive index distribution, where the refractive index n is a function of the radial radius r, and the constant refractive index surfaces are a series of cylindrical surfaces with the optical axis as the axis of rotational symmetry. Assuming that the constant l represents the direction cosine of the light ray, the differential equation of the light ray can be expressed as:

[0047]

[0048] Expressed in the Cartesian coordinate system as

[0049]

[0050] Schematic diagram of the refractive index distribution of a radial GRIN lens is as Figure 1 shown, and the general expression of the refractive index distribution function of a radial GRIN lens is:

[0051] n(r) = n 0 + n 1 r 2 + n 2 r 4 + … (3)

[0052] Assuming that the medium distribution is symmetric about the z-axis and r is the radial radius of the coordinate system, where r 2 = x 2 + y 2 , omitting the higher-order terms of r 4 (including) and above, then formula (4) can be rewritten as:

[0053]

[0054] Among them, n(r) is the refractive index at a distance r perpendicular to the optical axis, n 0$n_0$ is the refractive index at the optical axis center, $\beta$ is the refractive index distribution constant (focusing constant), and $r$ is the radial radius of the coordinate system.

[0055] II. Basic principle of the spectral confocal displacement sensor;

[0056] As Figure 2 shown, the spectral confocal displacement sensing technology is based on the principle of optical dispersion. It makes a broadband light source generate axial dispersion through a dispersive objective lens, establishes the corresponding relationship between the spectral focusing position and the wavelength, uses a spectrometer to detect the dispersed spectrum that is focused on the object surface and reflected back, and decodes the peak wavelength of the spectral response, then the precise axial position or micro-displacement data can be calculated and obtained. Therefore, the spectral confocal displacement sensing technology is widely used in aspects such as displacement, thickness, and surface measurement.

[0057] As Figure 2 shown, the dispersive objective lens is the core component of the spectral confocal displacement sensing system. The dispersion range and linearity of the dispersive objective lens determine the measurement range and measurement accuracy of the entire system. The corresponding relationship between displacement and wavelength is achieved through the encoding and decoding of the axial dispersion of the dispersive objective lens.

[0058] III. Dioptric power and dispersion model of the radial GRIN lens in the spectral confocal displacement sensor;

[0059] To achieve axial dispersion and make light rays of different wavelengths focus at different positions on the optical axis, first, to determine the focusing characteristics of the lens, the ray tracing calculation of the phase wavefront in the geometric optical medium is performed using Fermat's theorem. Assume that the light rays are incident parallel in this lens element, so the wavefront is calculated along the optical axis Z perpendicular to the propagation direction as:

[0060]

[0061] where, $k$ 0 is the vacuum wave vector of light, $\Delta z(y)$ is the distance from the vertex plane to the lens surface at height $y$, $d$ is the central thickness of the lens, $r(y,z)$ is the gradient refractive index curvature radius at $(y,z)$ of the lens, and $n[r(y,z)]$ is the refractive index at $r(y,z)$.

[0062]

[0063]

[0064] $n[r(y,z)] = n$ 0 $+ a[r(y,z) - R$ G (8)

[0065] where, $n$ 0 is the refractive index at the vertex of the lens, $R$ GR is the radius of curvature of the gradient refractive index profile at the lens vertex, a is the rate of change of the refractive index with distance, and v is the Abbe number.

[0066] Integrating formula (8) with respect to z gives:

[0067]

[0068] where R L represents the radius of curvature of the lens:

[0069]

[0070] By simplifying the calculation, we get The expression of

[0071]

[0072] The wavefront that is completely focused at the focal length f can be written as:

[0073]

[0074] where Therefore, the approximate expression for the focal length f(λ) of the plano-convex gradient refractive index lens is:

[0075]

[0076] Therefore, for blue light and red light respectively from formula (13), the optical power can be expressed as:

[0077]

[0078]

[0079] The difference in optical power is:

[0080]

[0081] According to formula (16), the difference in optical power between blue light and red light can be evaluated, and then the magnitude of the axial chromatic aberration can be calculated; similarly, the refractive index and Abbe number data of other spectra can also be substituted to evaluate the linearity of the axial chromatic aberration of the system within the visible light range.

[0082] IV. Chromatic Aberration Objective Lens Structure Based on Radial GRIN Lens

[0083] According to the working principle of the dispersion objective lens of the spectral confocal displacement sensing system and the conditions for generating axial dispersion of the dispersion objective lens, the dispersion objective lens based on the radial GRIN lens is designed. First, the glass material of the dispersion objective lens based on the radial GRIN lens is selected. Combining with the aberration theory of the optical system, while ensuring axial dispersion, the linear relationship between the axial dispersion generated by the dispersion objective lens and the wavelength is improved. The imaging of the optical system of the dispersion objective lens is focused on the optical axis, and the off-axis aberration is negligible. Only the spherical aberration of the system needs to be considered. In order to strictly control the spherical aberration of the system, the radial GRIN dispersion objective lens and the doublet lens are combined for design. By dispersing the optical power of the system, the spherical aberration of the optical system can be effectively reduced; in addition, different types of lens materials can improve the linearity of the optical system. To meet the above conditions, the radial GRIN lens is used as a single lens, Gradient 6 is used, and the doublet lens uses H-FK61, H-F51, and H-ZF62.

[0084] As Figure 3 shown, the radial GRIN lens can achieve a certain dispersion. On this basis, the system is optimized by adding lenses according to the above paragraph, so that the linear coefficient R2 between the wavelength and the axial dispersion is ≥ 0.995 to meet the linearity of the dispersion objective lens and increase the dispersion range; the wavelength λ is set to 420 nm to 620 nm, and the entrance pupil diameter is 2 mm.

[0085] Based on the above, the embodiment of the present invention optimizes and improves Figure 3 the initial lens that realizes dispersion with the radial GRIN lens, as Figure 4As shown in the figure, an embodiment of the present invention provides a spectral confocal dispersion objective lens based on a radial GRIN lens. The spectral confocal dispersion objective lens includes a gradient index lens 1, an optimization lens 2, a first concave lens 3, a first convex lens 4, a first cemented lens 5, and a second cemented lens 6 arranged in sequence from left to right. Among them, the first cemented lens 5 is formed by cementing a second convex lens 51 and a third convex lens 52, and the second convex lens 51 is located on the side close to the first convex lens 4. The second cemented lens 6 is formed by cementing a fourth convex lens 61 and a second concave lens 62, and the fourth convex lens 61 is located on the side close to the third convex lens 52. Specifically, the gradient index lens 1 is made of Gradient 6, its front surface curvature radius is 40.58 mm, the rear surface is a plane, and the thickness is 2.00 mm. The optimization lens 2 is made of H-FK61, its front surface and rear surface are both planes, and the thickness is 2.00 mm. The first concave lens 3 is made of H-F51, its front surface curvature radius is -33.68 mm, the rear surface curvature radius is 33.68 mm, and the thickness is 1.00 mm. The first convex lens 4 is made of N-SF66, its front surface curvature radius is 90.68 mm, the rear surface curvature radius is -77.68 mm, and the thickness is 2.00 mm. The second convex lens 51 is made of H-ZF62, its front surface curvature radius is 27.74 mm, the rear surface curvature radius is -33.68 mm, and the thickness is 2.00 mm. The third convex lens 52 is made of H-F51 material, its front surface curvature radius is -33.68 mm, the rear surface curvature radius is -33.66 mm, and the thickness is 1.50 mm. The fourth convex lens 61 is made of H-F51 material, its front surface curvature radius is 90.68 mm, the rear surface curvature radius is -82.68 mm, and the thickness is 1.80 mm. The second concave lens 62 is made of H-FK61 material, its front surface curvature radius is -82.68 mm, the rear surface curvature radius is 33.68 mm, and the thickness is 1.50 mm. It should be noted that in practical applications, each curvature radius and thickness can have an error of 0.01 - 0.02 mm.

[0086] The above spectral confocal dispersion objective lens based on a radial GRIN lens improves the focusing characteristics of the lens and reduces spherical aberration while ensuring the linearity between wavelength and focal shift. During the optimization process, the change of operation parameters is controlled, and AXCL is used to control the axial chromatic aberration and linearity generated by the optical system; CONF is used to optimize the entire structure of the system, and the two columns of target value and weight are used during the optimization process; the radial plano-convex GRIN dispersion objective lens adopts the COVA conic coefficient to obtain a plano-convex structure during the design process; LONA is used to control the spherical aberration of the system, and EFFL is used to control the focal length; IMAG is used to optimize the resolution of the lens.

[0087] The spectral confocal dispersion objective lens based on a radial GRIN lens provided by the embodiments of the present invention is evaluated as follows:

[0088] On the one hand, it is evaluated according to the spot diagrams at different wavelengths. For example, Figure 5 as shown, sampling is performed every 20 nm to form spot diagrams at the focusing positions of each wavelength with an interval of 20 nm in the wavelength range of 420 nm to 620 nm, and the image quality of the optical system of this spectral confocal dispersion objective lens is evaluated. It can be seen from Figure 5 that the radius of the spot diagram corresponding to each wavelength with an interval of 20 nm in the wavelength range of 420 nm to 620 nm is smaller than the radius of the Airy disk. The focusing effect of the lens is good, and almost all the light rays at the focusing positions of each wavelength are within the Airy ring, and the system reaches the diffraction limit.

[0089] On the other hand, it is evaluated according to the wavelength-focal shift curve. The original curve between the axial dispersion and the wavelength generated by the spectral confocal dispersion objective lens based on a radial GRIN lens in the embodiments of the present invention is as shown in Figure 6 . The chromatic focal shift is about 1215 μm, and the dispersion range exceeds 1 mm. For the wavelength-focal shift curve of the optical system composed of the spectral confocal dispersion objective lens based on a radial GRIN lens provided by the embodiments of the present invention, the text data uses the least squares method to linearly fit the wavelength-focal shift curve. The fitting result is as shown in Figure 7 . The linear correlation coefficient R 2 between the wavelength and the axial dispersion is 99.69%, and the linearity is good. The fitting correlation function between the wavelength and the axial dispersion is:

[0090] y = 5.9759x - 3.0446 (17)

[0091] The wavelength of the system is 420 nm to 620 nm, and the existing resolution of the spectrometer is 10 -3 nm. Then the system sensitivity of the spectral confocal dispersion objective lens based on a radial GRIN lens provided by the embodiments of the present invention is:

[0092]

[0093] where Δd is the measurement range of the sensor; σ λ is the resolution of the spectrometer; σ s is the system resolution; and Δλ is the spectral working range. Therefore, the resolution of the spectral confocal displacement sensing system dispersion objective lens based on a radial GRIN lens provided by the embodiments of the present invention is 6.075 nm, which ensures good linearity while satisfying a large measurement range and has a high resolution.

[0094] The spectral confocal dispersion objective lens based on a radial GRIN lens provided by an embodiment of the present invention can improve the image quality of the system compared with a traditional dispersion objective lens. The GRIN lens has the characteristics of small volume, low cost, and high performance, making the system structure compact and the image quality excellent, and realizing the lightweight of the optical system. In the specification, the refractive index distribution characteristics and optical characteristics of the radial GRIN lens are deduced and analyzed, an optical power and axial dispersion model of the radial GRIN lens is established, and the refractive index distribution of the GRIN lens and the analysis and design of the dispersion objective lens are carried out respectively. Finally, the optimized design of the spectral confocal dispersion objective lens based on the radial GRIN lens is completed. The results show that the spectral confocal dispersion objective lens based on the radial GRIN lens provided by the embodiment of the present invention can achieve an axial dispersion of 1215 μm in the wavelength range of 420 nm to 620 nm, and the linear correlation coefficient R 2 is 99.69%. The resolution of the dispersion objective lens is 6.075 nm, and the dispersion spots of the spot diagram are all within the Airy disk range. The lens is well focused and can meet the requirements of the spectral confocal dispersion objective lens.

[0095] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A spectral confocal dispersion objective lens based on a radial GRIN lens, characterized in that: it includes a gradient refractive index lens (1), an optimization lens (2), a first concave lens (3), a first convex lens (4), a first cemented lens (5), and a second cemented lens (6) arranged in sequence from left to right; the central axes of the gradient refractive index lens (1), the optimization lens (2), the first concave lens (3), the first convex lens (4), the first cemented lens (5), and the second cemented lens (6) are all located on the same straight line.

2. The spectral confocal dispersion objective lens based on a radial GRIN lens according to claim 1, characterized in that: the first cemented lens (5) is formed by cementing a second convex lens (51) and a third convex lens (52), and the second convex lens (51) is located on the side close to the first convex lens (4); the second cemented lens (6) is formed by cementing a fourth convex lens (61) and a second concave lens (62), and the fourth convex lens (61) is located on the side close to the third convex lens (52).

3. The spectral confocal dispersion objective lens based on a radial GRIN lens according to claim 2, characterized in that: the front surface curvature radius of the gradient refractive index lens (1) ranges from 40.58 ± 0.02 mm, the rear surface is a plane, and the thickness ranges from 2.00 ± 0.01 mm; the front surface and the rear surface of the optimization lens (2) are both planes, and the thickness ranges from 2.00 ± 0.01 mm; the front surface curvature radius of the first concave lens (3) ranges from -33.68 ± 0.02 mm, the rear surface curvature radius ranges from 33.68 ± 0.02 mm, and the thickness ranges from 1.00 ± 0.01 mm; the front surface curvature radius of the first convex lens (4) ranges from 90.68 ± 0.02 mm, the rear surface curvature radius ranges from -77.68 ± 0.02 mm, and the thickness ranges from 2.00 ± 0.01 mm; the front surface curvature radius of the second convex lens (51) ranges from 27.74 ± 0.02 mm, the rear surface curvature radius ranges from -33.68 ± 0.02 mm, and the thickness ranges from 2.00 ± 0.01 mm; the front surface curvature radius of the third convex lens (52) ranges from -33.68 ± 0.02 mm, the rear surface curvature radius ranges from -33.66 ± 0.02 mm, and the thickness ranges from 1.50 ± 0.01 mm; the front surface curvature radius of the fourth convex lens (61) ranges from 90.68 ± 0.02 mm, the rear surface curvature radius ranges from -82.68 ± 0.02 mm, and the thickness ranges from 1.80 ± 0.01 mm; the front surface curvature radius of the second concave lens (62) ranges from -82.68 ± 0.02 mm, the rear surface curvature radius ranges from 33.68 ± 0.02 mm, and the thickness ranges from 1.50 ± 0.01 mm.

4. The spectral confocal dispersion objective lens based on a radial GRIN lens according to claim 3, characterized in that: The front surface curvature radius of the gradient index lens (1) is 40.58 mm, the rear surface is a plane, and the thickness is 2.00 mm; The front surface and rear surface of the optimized lens (2) are both planes, and the thickness is 2.00 ± 0.01 mm; The front surface curvature radius of the first concave lens (3) is -33.68 mm, the rear surface curvature radius is 33.68 mm, and the thickness is 1.00 mm; The front surface curvature radius of the first convex lens (4) is 90.68 mm, the rear surface curvature radius is -77.68 mm, and the thickness is 2.00 mm; The front surface curvature radius of the second convex lens (51) is 27.74 mm, the rear surface curvature radius is -33.68 mm, and the thickness is 2.00 mm; The front surface curvature radius of the third convex lens (52) is -33.68 mm, the rear surface curvature radius is -33.66 mm, and the thickness is 1.50 mm; The front surface curvature radius of the fourth convex lens (61) is 90.68 mm, the rear surface curvature radius is -82.68 mm, and the thickness is 1.80 mm; The front surface curvature radius of the second concave lens (62) is -82.68 mm, the rear surface curvature radius is 33.68 mm, and the thickness is 1.50 mm.

5. The spectral confocal dispersion objective lens based on a radial GRIN lens according to claim 2 or 3 or 4, characterized in that: The gradient index lens (1) is made of Gradient 6; The optimized lens (2) is made of H-FK61 material; The first concave lens (3) is made of H-F51 material; The first convex lens (4) is made of N-SF66 material; The second convex lens (51) is made of H-ZF62 material; The third convex lens (52) is made of H-F51 material; The fourth convex lens (61) is made of H-F51 material; The second concave lens (62) is made of H-FK61 material.

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