Dispersion objective lens with numerical aperture of 0.75

Abstract

The invention discloses a dispersion objective lens with a numerical aperture of 0.75. The dispersion objective lens comprises a triplet lens, three doublet lenses and three single lenses which are coaxially arranged, and after a continuous spectrum point light source passes through the dispersion objective lens, light with different wavelengths realizes differential convergence on an optical axis; a dispersion curve is fitted through a quadratic function, a small amount of dispersion linearity is sacrificed, better balance of an axial dispersion range and imaging quality is realized, and double targets of large dispersion range and high-quality imaging are achieved. The device has the advantage of long object distance, is convenient for front-end light path adjustment, and can be flexibly applied to various measurement systems.

Description

Technical Field

[0001] This invention belongs to the field of optical objectives, and specifically relates to a dispersive objective with a numerical aperture of 0.75. Background Technology

[0002] With the rapid development of precision manufacturing, semiconductors, biomedicine, and other fields, industrial production and scientific research are placing increasingly stringent demands on the accuracy, speed, and adaptability of measurement technologies. Color spectroscopy confocal technology, as an excellent non-contact optical measurement method, utilizes the core mechanism of axial dispersion encoding of on-axis position to eliminate the axial scanning process of traditional confocal microscopes. It achieves high-resolution measurements at the micro- and nano-scale while significantly improving measurement efficiency. Furthermore, its sensors offer advantages such as lightweight and small size, low requirements on the condition of the measured surface, and tolerance for larger tilt angles, making it a core technology choice for surface morphology inspection and ultra-precision measurement.

[0003] Dispersive objectives are the core components for achieving axial dispersion in color spectral confocal measurement systems. Their performance directly determines key indicators such as the accuracy, resolution, and measurement range of the measurement system. Therefore, the design and optimization of dispersive objectives has always been a research focus in this field. Current research on dispersive objectives mainly falls into two categories: refractive and diffractive. While diffractive optical elements can achieve a linear correlation between dispersion and wavelength, they suffer from drawbacks such as large aberrations, the need for lens group correction (which easily disrupts the linear dispersion characteristics), high fabrication difficulty, and difficulty in achieving large numerical apertures. Refractive schemes, due to their superior technical feasibility and performance stability, have become the mainstream research direction for linear dispersive elements. However, limited by the properties of glass materials, the refractive index of glass exhibits a non-linear relationship with wavelength in the visible light range. A single glass material cannot achieve linear dispersion; a combination of multiple glass materials is required to reduce the non-linearity, but achieving a completely linear dispersion effect remains challenging.

[0004] Crucially, existing dispersive objectives generally suffer from low numerical apertures, severely limiting further improvements in measurement system resolution. Furthermore, the core performance indicators of dispersive objectives, such as dispersion range (affecting measurement range), dispersion-wavelength linearity (determining measurement accuracy), and image-space numerical aperture (dominantly determining resolution), are mutually restrictive. To balance image quality and dispersion linearity, current technologies often employ meniscus lens designs, which not only increase manufacturing difficulty and production costs but also make it difficult to balance various performance indicators while simultaneously increasing the numerical aperture.

[0005] With the ever-increasing demand for high-precision measurement, existing dispersive objectives, due to their insufficient numerical aperture, suffer from resolution limitations and can no longer meet the application requirements of high-end scenarios such as semiconductor defect detection and ultra-precision component topography measurement. Therefore, developing a high numerical aperture dispersive objective with a numerical aperture of 0.75, which can improve measurement resolution while achieving an optimal balance between dispersion range, linearity, and manufacturing cost, has become a pressing technical challenge in this field and has significant industrial application value. Summary of the Invention

[0006] The present invention aims to address the shortcomings of the prior art by providing a dispersive objective lens with a numerical aperture of 0.75, which aims to achieve an optimal balance between dispersion range, linearity, and processing cost while improving measurement resolution, so as to be applied to scenarios such as surface morphology inspection and ultra-precision measurement.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The present invention provides a dispersive objective lens with a numerical aperture of 0.75, characterized in that it comprises: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens arranged coaxially from the object side to the image side. Wherein, the first lens and the second lens constitute a first cemented doublet lens, and the combined optical power of the cemented doublet lens is negative; The third lens is a convex lens with positive optical power; The fourth, fifth, and sixth lenses constitute a cemented triplet lens, and the combined optical power of the cemented triplet lens is negative. The seventh and eighth lenses constitute a second cemented doublet lens, and the combined optical power of the cemented doublet lens is positive. The ninth and tenth lenses constitute a third cemented doublet lens, and the combined optical power of the cemented doublet lens is positive. Both the eleventh and twelfth lenses are meniscus lenses, with the side closest to the object being convex, and the optical power is positive. The dispersive objective lens group shall satisfy the constraint condition shown in equation (1): (1) In equation (1), For the first The optical power of each lens For the first The Abbe number of each lens, Indicates the first Dispersion linearity of each lens; And: (2) In equation (2), For the first The relative partial dispersion of each lens, , , These are the wavelengths of the F-characteristic light, d-characteristic light, and C-characteristic light, respectively. , , The first The refractive index of a lens under F characteristic light, d characteristic light, and C characteristic light.

[0008] The dispersive objective lens with a numerical aperture of 0.75 described in this invention is also characterized by using equation (3) to obtain the dispersive range of the dispersive objective lens. : (3) In equation (3), The longest wavelength The distance between the point where the light rays converge on the axis and the last refractive surface of the dispersive objective lens. Shortest wavelength The distance between the point where the light rays are focused on the axis and the last refractive surface of the dispersive objective.

[0009] Furthermore, the sensitivity of the dispersive objective lens is obtained using equation (4). : (4) In equation (4), This refers to the operating wavelength range of the dispersive objective lens. This represents the dispersive range of the dispersive objective lens.

[0010] Furthermore, the wavelength of the dispersive objective lens is obtained using equation (5). Image distance The linear regression equation between them: (5) In equation (5), and Let be the slope and intercept of the linear regression equation, and we have: (6) In equation (6), The first of the working wavelengths of the dispersive objective lens The wavelength value of each wavelength. This is the average value of all wavelengths within the operating band. For the first Wavelength The actual value of the image distance. This is the average of all image distances generated in the working band. This indicates the number of wavelengths divided into the working bands of the dispersive objective lens; The correlation coefficient of the linear correlation of the dispersive objective lens is obtained using equation (7). : (7) In equation (7), For the first Wavelength The image distance fitting value.

[0011] Furthermore, each lens in the dispersive objective satisfies the constraint shown in equation (8): (8) In equation (8), This represents the total optical power of the dispersive objective lens.

[0012] Furthermore, the lateral resolution of the dispersive objective lens under the Rayleigh criterion is obtained using equation (9). : (9) In equation (9), For image-side numerical aperture, The wavelength incident on the dispersive objective lens, The aperture number of the dispersive objective lens is given.

[0013] Furthermore, the working distance between the last refractive surface of the twelfth lens in the dispersive objective and the object being measured is greater than 9 mm.

[0014] Furthermore, the dispersive objective lens operates in the wavelength range of 450-700 nm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention features a large numerical aperture, overcoming the resolution limitations of existing dispersive objectives caused by insufficient numerical aperture. It offers high lateral resolution and a large image-square numerical aperture. It is greater than 0.75, and an optimal balance between dispersion range, linearity and processing cost is achieved through a reasonable combination of glass materials.

[0016] 2. This invention sacrifices some dispersion linearity by using a quadratic function to fit the dispersion curve, achieving better image quality and a wider dispersion range. It also appropriately relaxes tolerances, reducing manufacturing costs. In its optical system design, this invention employs a differentiated performance trade-off strategy. By moderately sacrificing some dispersion linearity and instead using a quadratic function to accurately fit the dispersion curve, it achieves an optimized balance between image quality and dispersion range. Compared to the rigid constraints on dispersion characteristics imposed by traditional linear fitting schemes, quadratic function fitting can more flexibly adapt to the needs of complex optical scenarios. Its nonlinear fitting characteristics can accurately compensate for dispersion deviations of optical components over a wide spectral range, effectively correcting key issues affecting image sharpness such as chromatic aberration and spherical aberration, ultimately achieving higher imaging resolution, more uniform brightness distribution, and purer color reproduction. Simultaneously, the fitting characteristics of the quadratic function provide the system with a wider dispersion adjustment space, breaking through the inherent limitations of linear fitting in dispersion range, and meeting the stringent requirements for dispersion coverage in high-end applications such as multi-band detection and broadband imaging. 3. This invention further lowers the technical implementation threshold through scientific tolerance design: Considering the characteristics of the quadratic function fitting scheme, the processing and assembly tolerances of core optical parameters are reasonably relaxed. This avoids the surge in processing difficulty caused by excessive pursuit of extreme precision, and ensures, through precise error budget control, that the relaxed tolerance range will not have a substantial impact on the final image quality and dispersion performance. This design not only significantly reduces the processing difficulty of optical components and shortens the production cycle, but also effectively controls core costs such as raw material loss and investment in precision processing equipment. This allows the product to maintain high-end performance while possessing stronger market competitiveness and large-scale production potential, achieving three-dimensional optimization of technical performance, application scenarios, and production costs.

[0017] 4. The linearity of the quadratic function fitted between the observation wavelength and the image distance on the optical axis of the dispersive objective lens of the present invention is optimized to achieve a linearity better than 2%, thereby enabling the dispersive objective lens to have high measurement accuracy. 5. The working distance between the last refractive surface of the twelfth lens of the dispersive objective lens of the present invention and the object being measured is greater than 9mm, and the incident light is parallel light, which facilitates the adjustment of the optical path at the front end of the lens and can be applied to different measurement systems, such as spectral confocal interferometry measurement systems. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the optical system structure according to an embodiment of the present invention; Figure 2 This is a diagram showing the imaging points of light of different wavelengths passing through a dispersive objective lens in an embodiment of the present invention. Figure 3 This is a linear fitting curve of image distance versus wavelength in an embodiment of the present invention; The lenses in the diagram are labeled as follows: 1 First lens, 2 Second lens, 3 Third lens, 4 Fourth lens, 5 Fifth lens, 6 Sixth lens, 7 Seventh lens, 8 Eighth lens, 9 Ninth lens, 10 Tenth lens, 11 Eleventh lens, 12 Twelfth lens. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0020] In this embodiment, a dispersive objective lens with a numerical aperture of 0.75, such as... Figure 1 As shown, it includes: a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7, an eighth lens 8, a ninth lens 9, a tenth lens 10, an eleventh lens 11, and a twelfth lens 12, arranged coaxially from the object side to the image side. The first lens 1 and the second lens 2 constitute the first cemented doublet lens, and the combined optical power of the cemented doublet lens is negative. The third lens 3 is a convex lens with positive optical power; The fourth lens 4, the fifth lens 5, and the sixth lens 6 constitute a cemented triplet lens, and the combined optical power of the cemented triplet lens is negative; The seventh lens 7 and the eighth lens 8 constitute the second cemented doublet, and the combined optical power of the cemented doublet is positive. The ninth lens 9 and the tenth lens 10 constitute the third cemented doublet, and the combined optical power of the cemented doublet is positive. Both the eleventh lens 11 and the twelfth lens 12 are meniscus lenses, with the side closest to the object being convex, and the optical power is positive. The dispersive objective lens group should satisfy the following constraints in equation (1): (1) In equation (1), For the first The optical power of each lens For the first The Abbe number of each lens, Indicates the first Dispersion linearity of each lens; And: (2) In equation (2), For the first The relative partial dispersion of each lens, , , These are the wavelengths of the F-characteristic light, d-characteristic light, and C-characteristic light, respectively. , , The first The refractive index of each lens under F characteristic light, d characteristic light, and C characteristic light. In this embodiment, the dispersion range of the dispersive objective is obtained using equation (3). : (3) In equation (3), The longest wavelength The distance between the point where the light rays converge on the axis and the last refractive surface of the dispersive objective lens. Shortest wavelength The distance between the point where the light rays are focused on the axis and the last refractive surface of the dispersive objective.

[0021] In this embodiment, the sensitivity of the dispersive objective lens is obtained using equation (4). : (4) In equation (4), This refers to the operating wavelength range of the dispersive objective lens. This represents the dispersive range of the dispersive objective lens.

[0022] In this embodiment, the wavelength of the dispersive objective is obtained using equation (5). Image distance The linear regression equation between them: (5) In equation (5), and Let be the slope and intercept of the linear regression equation, and we have: (6) In equation (6), The first in the working wavelength range of the dispersive objective lens The wavelength value of each wavelength. This is the average value of all wavelengths within the operating band. For the first Wavelength The actual value of the image distance. This is the average of all image distances generated in the working band. This indicates the number of wavelengths divided into the working bands of the dispersive objective lens.

[0023] The correlation coefficient of the linear correlation of dispersive objectives is obtained using equation (7). : (7) In equation (7), For the first Wavelength The image distance fitting value.

[0024] In this embodiment, linear dispersion cannot be achieved using a single lens for the dispersive objective; multiple lenses must be combined, and the constraint shown in equation (8) must be satisfied: (8) In equation (8), This represents the total optical power of the dispersive objective lens.

[0025] In this embodiment, the lateral resolution of the dispersive objective lens under the Rayleigh criterion is obtained using equation (9). : (9) In equation (9), For image-side numerical aperture, The wavelength incident on the dispersive objective lens, The aperture number of the dispersive objective lens is given.

[0026] In this embodiment, the refractive index n1 of the first lens 1 satisfies 1.7≤n1≤2.0, and the center thickness is 6.9mm. The first lens and the second lens constitute the first cemented doublet lens.

[0027] In this embodiment, the refractive index n2 of the second lens 2 satisfies 1.71≤n2≤1.74, the center thickness is 11.5mm, and the air gap between the second lens and the third lens is 2.39mm.

[0028] In this embodiment, the refractive index n3 of the third lens 3 satisfies 1.98≤n3≤2.08, the center thickness is 12mm, and the air gap between the third lens and the fourth lens is 19.83mm.

[0029] In this embodiment, the refractive index n4 of the fourth lens 4 satisfies 1.40≤n4≤1.45, and the center thickness is 6.4mm.

[0030] In this embodiment, the refractive index n5 of the fifth lens 5 satisfies 1.7≤n5≤2.0, and the center thickness is 3.5mm. The fourth lens, the fifth lens, and the sixth lens constitute a cemented triplet lens.

[0031] In this embodiment, the refractive index n6 of the sixth lens 6 satisfies 1.40≤n6≤1.45, the center thickness is 8.6mm, and the air gap between the sixth lens and the seventh lens is 1.04mm.

[0032] In this embodiment, the refractive index n7 of the seventh lens 7 satisfies 1.63≤n7≤1.66, and the center thickness is 6.7mm. The seventh lens and the eighth lens constitute the second cemented doublet lens.

[0033] In this embodiment, the refractive index n8 of the eighth lens 8 satisfies 1.65≤n8≤1.70, the center thickness is 11.5mm, and the air gap between the eighth lens and the ninth lens is 1.62mm.

[0034] In this embodiment, the refractive index n9 of the ninth lens 9 satisfies 1.60≤n9≤1.65, and the center thickness is 8.1mm. The ninth lens and the tenth lens constitute the third cemented doublet lens.

[0035] In this embodiment, the refractive index n of the tenth lens 10 10 Satisfying 1.63≤n 10 ≤1.67, center thickness is 12mm, and the air gap between the tenth and eleventh lenses is 0.10mm.

[0036] In this embodiment, the refractive index n of the eleventh lens 11 11 Satisfying 1.57≤n 11 ≤1.62, center thickness is 5mm, and the air gap between the center of the eleventh lens and the center of the twelfth lens is 0.10mm.

[0037] In this embodiment, the refractive index n of the twelfth lens 12 12 Satisfying 1.98≤n 12 ≤2.02, center thickness is 4.1mm.

[0038] The specific parameters of each lens in the optical system of this embodiment are shown in Table 1: Table 1 like Figure 2 The dispersive objective shown operates in the 450-700nm band and has good imaging quality. It utilizes multiple structures to set six wavelengths of 450, 500, 550, 600, 650 and 700nm at equal intervals in the 450-700nm range. The dispersion spots of the six structures are all smaller than the Airy disk.

[0039] In this embodiment, the dispersive lens receives parallel incident light, facilitating the addition of other optical elements at the front end for application in different measurement systems, such as a spectral confocal interferometry measurement system. The distance from the last surface of the lens to the image plane is greater than 9 mm, and the image-side numerical aperture NA is greater than 0.75, according to the Rayleigh criterion. The lateral resolution is approximately 0.366 μm.

[0040] The dispersive objective lens has a dispersive range of 49.2 μm within the working wavelength range. The relationship between the focusing distance and the wavelength for each wavelength is as follows: Figure 3 As shown, a quadratic function is used to fit it, using the formula... The goodness of fit was evaluated and found that the quadratic function had a high goodness of fit to the relationship between the focusing distance and the wavelength for each wavelength, reaching 99.93%.

[0041] Unless otherwise stated, if any of the technical solutions disclosed in this invention specify a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely one among many feasible numerical values ​​where the technical effect is more obvious or representative. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

Claims

1. A dispersive objective lens with a numerical aperture of 0.75, characterized in that, include: The first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens, tenth lens, eleventh lens, and twelfth lens are arranged coaxially from the object side to the image side. Wherein, the first lens and the second lens constitute a first cemented doublet lens, and the combined optical power of the cemented doublet lens is negative; The third lens is a convex lens with positive optical power; The fourth, fifth, and sixth lenses constitute a cemented triplet lens, and the combined optical power of the cemented triplet lens is negative. The seventh and eighth lenses constitute a second cemented doublet lens, and the combined optical power of the cemented doublet lens is positive. The ninth and tenth lenses constitute a third cemented doublet lens, and the combined optical power of the cemented doublet lens is positive. Both the eleventh and twelfth lenses are meniscus lenses, with the side closest to the object being convex, and the optical power is positive. The dispersive objective lens group shall satisfy the constraint condition shown in equation (1): (1) In equation (1), For the first The optical power of each lens For the first The Abbe number of each lens, Indicates the first Dispersion linearity of each lens; And: (2) In equation (2), For the first The relative partial dispersion of each lens, , , These are the wavelengths of the F-characteristic light, d-characteristic light, and C-characteristic light, respectively. , , The first The refractive index of a lens under F characteristic light, d characteristic light, and C characteristic light.

2. The dispersive objective lens with a numerical aperture of 0.75 according to claim 1, characterized in that, The dispersive range of the dispersive objective lens is obtained using equation (3). : (3) In equation (3), Longest wavelength The distance between the point where the light rays converge on the axis and the last refractive surface of the dispersive objective lens. Shortest wavelength The distance between the point where the light rays are focused on the axis and the last refractive surface of the dispersive objective.

3. A dispersive objective lens with a numerical aperture of 0.75 according to claim 1, characterized in that, The sensitivity of the dispersive objective lens is obtained using equation (4). : (4) In equation (4), This refers to the operating wavelength range of the dispersive objective lens. This represents the dispersive range of the dispersive objective lens.

4. A dispersive objective lens with a numerical aperture of 0.75 according to claim 1, characterized in that, The wavelength of the dispersive objective lens is obtained using equation (5). Image distance The linear regression equation between them: (5) In equation (5), and Let be the slope and intercept of the linear regression equation, and we have: (6) In equation (6), The first of the working wavelengths of the dispersive objective lens The wavelength value of each wavelength. This is the average value of all wavelengths within the operating band. For the first wavelength The actual value of the image distance. This is the average of all image distances generated in the working band. This indicates the number of wavelengths divided into the working bands of the dispersive objective lens; The correlation coefficient of the linear correlation of the dispersive objective lens is obtained using equation (7). : (7) In equation (7), For the first wavelength The image distance fitting value.

5. A dispersive objective lens with a numerical aperture of 0.75 according to claim 1, characterized in that, Each lens in the dispersive objective satisfies the constraint shown in equation (8): (8) In equation (8), This represents the total optical power of the dispersive objective lens.

6. A dispersive objective lens with a numerical aperture of 0.75 according to claim 1, characterized in that, The lateral resolution of the dispersive objective lens under the Rayleigh criterion is obtained using equation (9). : (9) In equation (9), For image-side numerical aperture, The wavelength incident on the dispersive objective lens, The aperture number of the dispersive objective lens is given.

7. A dispersive objective lens with a numerical aperture of 0.75 according to claim 6, characterized in that, The working distance between the last refractive surface of the twelfth lens in the dispersive objective and the object being measured is greater than 9 mm.

8. A dispersive objective lens with a numerical aperture of 0.75 according to claim 7, characterized in that, The dispersive objective lens operates in the wavelength range of 450-700 nm.

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