A long working distance object side telecentric projection optical system

Abstract

The application discloses a long working distance object side telecentric projection optical system, which sequentially comprises an object plane, a vacuum window glass, first to fourth lenses, an aperture diaphragm, fifth to sixth lenses, an interference filter, a beam splitting prism and an image plane along the optical axis direction of the object plane; the rear focal point of the combined system of the vacuum window glass and the first to fourth lenses is located at the center point position of the aperture diaphragm, thereby forming an object side telecentric optical structure; and the axial distance between the vertex of the front surface of the first lens and the object plane is 640 mm, that is, the object side working distance is 640 mm. The application can effectively correct wave aberration, distortion and other aberrations, and realizes good imaging quality. The long working distance object side telecentric projection optical system of the application fully meets the technical requirements of measuring the position, shape, speed and other parameters of liquid drops in a vacuum chamber.

Description

Technical Field

[0001] This invention relates to the field of projection optics system technology, and particularly to a long working distance, telecentric projection optics system. It is used to acquire precise position, shape, velocity, and other key parameters of a measured droplet within a vacuum chamber (or vacuum container, vacuum cavity, etc.) through optical imaging. It is especially suitable for demanding measurement scenarios requiring long working distances, telecentricity, high resolution, and the ability to integrate a vacuum window glass as part of the imaging system. Background Technology

[0002] For measuring objects inside a vacuum chamber (or vacuum container, vacuum cavity, etc.), high-resolution optical imaging is generally used. However, due to the limited volume of the vacuum chamber, a relatively long object-side working distance is usually required, and a telecentric optical path on the object side is also needed to improve measurement accuracy. In addition, for high-vacuum chambers, the window glass is generally quite thick, so this window glass needs to be included as an optical component in the optical system to participate in imaging.

[0003] One application scenario involves a series of droplets traveling at high speed along the rotational symmetry axis of a vacuum chamber. These droplets need to be accurately struck sequentially by a high-frequency carbon dioxide laser pulse sequence to generate plasma, radiating light radiation close to the soft X-ray band. To obtain stable and reliable light radiation pulses, a technique is employed where the pre-pulse and main pulse of the carbon dioxide laser sequentially bombard the same droplet. This requires a measurement system to obtain information such as the droplet's position, shape, and velocity to control the high-speed motion of the droplet and the synchronization of the carbon dioxide laser pulse triggering. This droplet parameter measurement system requires at least one long-working-distance, object-side telecentric projection optics system to obtain image information of the droplet, which can then be transmitted to a high-speed camera to participate in the closed-loop feedback control of the high-speed droplet motion and the synchronized triggering of the carbon dioxide laser pulses.

[0004] Because the vacuum chamber that generates the light radiation pulses is relatively large, typically exceeding 1000 mm in diameter, the object-side working distance of the aforementioned projection optical system must be at least greater than 500 mm. Furthermore, to ensure measurement accuracy, it generally needs to meet the requirements of a telecentric optical path and high resolution. Simultaneously, to detect and measure information from multiple droplets, a relatively large target area is required, necessitating a large object-side field of view for the aforementioned projection optical system.

[0005] Chinese patent CN103257436A discloses a "long working distance microscopic optical system for observation in a vacuum cavity." This patent discloses a technical solution for a microscopic optical system consisting of 10 lenses, including 4 single lenses and 3 sets of cemented doublets. However, it does not disclose its magnification. Furthermore, when the data in its Table 1 is input into optical design software (such as Code V), the disclosed imaging function cannot be obtained. This patent only discloses a schematic diagram of the optical path and does not provide any graphs or data such as aberrations or transfer functions to evaluate its microscopic imaging capabilities. Additionally, its object-side working distance is 98 mm, which is unsuitable for measurement tasks within large vacuum cavities.

[0006] Therefore, there is an urgent need in this technical field for a long working distance object-side telecentric projection optical system specifically optimized for droplet measurement in a vacuum chamber. This optical system should effectively integrate optical characteristics such as long working distance, strict object-side telecentricity, high resolution, and large field of view. It should also properly integrate necessary optical components such as vacuum window glass, filters, and beam-splitting prisms into the optical path, and achieve near-diffraction-limited imaging quality through reasonable aberration correction (especially wave aberration and distortion correction). This would provide a reliable optical foundation for the accurate and stable measurement of droplet parameters. Summary of the Invention

[0007] The purpose of this invention is to provide a long working distance telecentric projection optical system, which is used to measure parameters such as position, shape, and velocity of droplets in a vacuum chamber.

[0008] The objective of this invention is achieved as follows:

[0009] A long working distance telecentric projection optical system, comprising, along the optical axis from the object side to the image side: an object plane, a vacuum window glass, a first lens to a fourth lens, an aperture stop, a fifth lens to a sixth lens, an interference filter, a beam splitter prism, and an image plane;

[0010] Wherein, the first lens is a biconvex lens, the second lens is a meniscus positive lens bent toward the aperture stop, the third lens is a meniscus negative lens bent toward the object plane, the fourth lens is a biconcave lens, the fifth lens is a biconcave lens, the sixth lens is a biconvex lens, and all optical surfaces of the first to sixth lenses are spherical.

[0011] The vacuum window glass and the first to fourth lenses together form the front objective lens group, which has a positive combined optical power, and the image-side focal point of the front objective lens group is located at the center of the aperture stop, thus forming a telecentric optical path structure.

[0012] The axial distance from the object plane to the vertex of the object side surface of the first lens is 640 mm ± 60 mm, constituting the object-side working distance of the optical system.

[0013] Furthermore, the focal length f1 of the first lens, the focal length f2 of the second lens, the focal length f3 of the third lens, the focal length f4 of the fourth lens, the focal length f5 of the fifth lens, and the focal length f6 of the sixth lens satisfy the following relationships: 165 mm < f1 < 181 mm, 339 mm < f2 < 375 mm, -1313 mm < f3 < -1188 mm, -421 mm < f4 < -381 mm, -86 mm < f5 < -78 mm, 193 mm < f6 < 213 mm.

[0014] Furthermore, the radius of curvature R1 of the object side surface of the first lens, the radius of curvature R2 of the image side surface, and the central thickness d1 satisfy: 160 mm < R1 < 176 mm, -310 mm < R2 < -280 mm, 14.5 mm < d1 < 15.5 mm, and the material of the first lens is NSK16 optical glass.

[0015] Furthermore, the radius of curvature R3 of the object side surface of the second lens, the radius of curvature R4 of the image side surface, and the central thickness d2 satisfy: 174 mm < R3 < 192 mm, 963 mm < R4 < 1063 mm, 7.3 mm < d2 < 8.3 mm, and the material of the second lens (L2) is NSK16 optical glass.

[0016] Furthermore, the radius of curvature R5 of the object side surface of the third lens, the radius of curvature R6 of the image side surface, and the central thickness d3 satisfy: -712 mm < R5 < -644 mm, -2465 mm < R6 < -2231 mm, 4.7 mm < d3 < 5.3 mm, and the material of the third lens is SF4 optical glass.

[0017] Furthermore, the radius of curvature R7 of the object side surface of the fourth lens, the radius of curvature R8 of the image side surface, and the central thickness d4 satisfy: -393 mm < R7 < -355 mm, 1626 mm < R8 < 1798 mm, 4.7 mm < d4 < 5.3 mm, and the material of the fourth lens (L4) is SF4 optical glass.

[0018] Furthermore, the radius of curvature R9 of the object side surface of the fifth lens, the radius of curvature R 10 and the central thickness d5 satisfy: -507 mm < R9 < -459 mm, 69 mm < R 10 < 76 mm, 2.7 mm < d5 < 3.3 mm, and the material of the fifth lens is SF4 optical glass.

[0019] Furthermore, the radius of curvature R of the side surface of the sixth lens 11 The radius of curvature R of the side surface 12 And the center thickness d6 satisfies: 127mm < R 11 < 140mm, -6587mm < R 12 < -5959mm, 3.3mm < d6<3.7mm, the material of the sixth lens (L6) is NSK18 optical glass.

[0020] Furthermore, the front and rear surfaces of the interference filter are both flat, the center thickness is 2mm, the material is fused silica glass, and the axial distance between it and the beam splitter prism is 20mm.

[0021] Furthermore, both the front and rear surfaces of the beam splitter are flat, with a center thickness of 25 mm. The material is Schott NBK7 optical glass, and the distance from the rear surface of the beam splitter to the image plane is 97.149 mm.

[0022] Furthermore, the vacuum window glass is made of fused silica glass, with both the front and rear surfaces being flat, and a center thickness of 14.5 mm. The distance between the front surface of the vacuum window glass and the object plane is 605.5 mm, and the distance between the rear surface and the front surface of the first lens is 20 mm. Therefore, the distance between the vertex of the front surface of the first lens and the object plane is 640 mm, which means the object-side working distance is 640 mm.

[0023] This invention has the following advantages and positive effects:

[0024] 1. The long working distance telecentric projection optical system of the present invention adopts a telecentric optical path structure and the maximum telecentric angle is corrected to less than 3.8 mrad, which can effectively ensure the measurement accuracy of parameters such as position, shape and velocity of the object droplet;

[0025] 2. The long working distance telecentric projection optical system of the present invention adopts a reasonable allocation of positive and negative optical power, which can effectively correct aberrations such as wavelet aberration and distortion to achieve good imaging quality and obtain a limit resolution of 250 lp / mm. For the measurement of droplet parameters with a diameter of 20μm~40μm, it can effectively improve the subpixel resolution capability of CCD camera (or CMOS camera).

[0026] 3. The long working distance telecentric projection optical system of the present invention achieves an object-side working distance of 640mm, which can meet the measurement requirements of droplet parameters in larger vacuum chambers. Attached Figure Description

[0027] Figure 1 This is the optical path diagram of the long working distance, object-side telecentric projection optical system of the present invention;

[0028] Figure 2 This is the diffraction modulation transfer function (MTF) plot of the long working distance, object-side telecentric projection optical system of the present invention;

[0029] Figure 3 This is a distribution diagram of wavefront aberration (root mean square value) RMS of the long working distance object-side telecentric projection optical system of the present invention;

[0030] Figure 4 This is a diagram showing the spherical aberration, astigmatism, field curvature, and distortion of the telecentric projection optical system with a long working distance of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0032] This embodiment provides a long working distance telecentric projection optical system for high-precision measurement of the position, shape, velocity, and other parameters of high-speed moving micro-droplets (e.g., diameter 20μm~40μm) in a vacuum chamber.

[0033] The application scenario of the droplet measurement system within the vacuum chamber is as follows: a series of droplets traveling at high speed along the rotational symmetry axis of the vacuum chamber need to be accurately struck sequentially by a high-frequency carbon dioxide laser pulse sequence to excite plasma and emit light radiation close to the soft X-ray band. To obtain stable and reliable light radiation pulses, a technique is employed where a pre-pulse and a main pulse of the carbon dioxide laser sequentially bombard the same droplet. This necessitates a measurement system to obtain parameters such as the droplet's position, shape, and velocity to control the high-speed motion of the droplet and the synchronization of the carbon dioxide laser pulse triggering. This droplet measurement system requires at least one long-working-distance, object-side telecentric projection optics system to obtain image information of the droplet, which is then transmitted to a high-speed camera to participate in the closed-loop feedback control of the high-speed droplet motion and the synchronized triggering of the carbon dioxide laser pulses.

[0034] Because the vacuum chamber that generates the light pulses is relatively large, typically exceeding 1000 mm in diameter, the object-side working distance of the aforementioned projection optical system must be at least greater than 500 mm. Furthermore, to ensure measurement accuracy, it generally needs to meet the requirements of a telecentric object-side optical path and high resolution. Simultaneously, to detect and measure information from multiple droplets, a relatively large target area is required, necessitating a large object-side field of view for the aforementioned projection optical system.

[0035] Based on the droplet diameter of 20μm~40μm and the emission frequency of 100kHz, the field of view diameter of the measured area on the object side is selected as 16mm. A CMOS high-speed camera with a target surface size of 12.8 mm x 9.6 mm is selected, and its target surface field of view diameter is also 16mm. Thus, the magnification of the projection optical system is determined to be -1.

[0036] Based on the selected illumination source being a 532nm pulsed laser, the operating wavelength of the projection optical system is determined to be 532nm, with a bandwidth of 1nm.

[0037] Based on the droplet diameter of 20μm~40μm, the selected CMOS high-speed camera has a pixel size of 5μm x 5μm. The measurement system needs a measurement algorithm with pixel subdivision capability, which requires the resolution of the projection optical system to be greater than that of the CMOS high-speed camera. The image-side numerical aperture (NA) is determined to be 0.0665. Then, according to the following formula, it can be known that the limit resolution is 250 lp / mm for line pairs with a spatial period of 4μm.

[0038]

[0039] The droplet measurement system inside the vacuum chamber requires an object-side working distance of ≥640mm, and its vacuum window glass has a thickness of 14.5mm and is made of fused silica glass. Additionally, a 2mm thick interference filter (made of fused silica glass) and a 25mm thick beam-splitting prism (made of NBK7) need to be added in front of the CMOS high-speed camera.

[0040] like Figure 1 As shown, a long working distance telecentric projection optical system is used to image a droplet in the area to be measured (i.e., the object plane) onto the target surface (i.e., the image plane) of a CMOS camera. It includes, in sequence from one side of the object plane along its optical axis, the object plane 1, the vacuum window glass 2, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the aperture stop 3, the fifth lens L5, the sixth lens L6, the interference filter 4, the beam splitter prism 5, and the image plane 6.

[0041] The first lens is a biconvex lens with a preferred focal length of 173.714 mm; the second lens is a meniscus positive lens bent toward the aperture stop with a preferred focal length of 357.780 mm; the third lens is a meniscus negative lens bent toward the object plane with a preferred focal length of -1250.562 mm; the fourth lens is a biconcave lens with a preferred focal length of -401.045 mm; the fifth lens is a biconcave lens with a preferred focal length of -82.553 mm; and the sixth lens is a biconvex lens with a preferred focal length of 203.388 mm. The aperture stop is located between the fourth and fifth lenses, and the optical surface of each lens is spherical.

[0042] The rear focal point (i.e., image-side focal point) of the combined system of the vacuum window glass and the first to fourth lenses (i.e., the front group of the objective lens) is located at the center of the aperture stop, forming a telecentric optical structure on the object side. This telecentric optical path structure ensures that the magnification does not change as the object surface moves along the optical axis because the principal ray in the object space is parallel to the optical axis. Thus, even if the object surface is in a defocused position, the height of its image remains unchanged, i.e., the magnification remains constant, which helps to ensure measurement accuracy.

[0043] The first lens preferably has a front surface radius of 167.877 mm, a rear surface radius of -295.206 mm, a center thickness of 15 mm, and is preferably made of Schott NSK16 optical glass. The axial distance from the vertex of its rear surface to the vertex of the front surface of the second lens is 1 mm.

[0044] The second lens preferably has a front surface radius of 183.435 mm, a rear surface radius of 1013.062 mm, a center thickness of 7.753 mm, and is preferably made of Schott NSK16 optical glass. The axial distance from the vertex of its rear surface to the vertex of the front surface of the third lens is 3.447 mm.

[0045] The third lens preferably has a front surface radius of -678.630 mm, a rear surface radius of -2347.906 mm, a center thickness of 5 mm, and is preferably made of Schott SF4 optical glass. The axial distance from the vertex of its rear surface to the vertex of the front surface of the fourth lens is 3.084 mm.

[0046] The fourth lens preferably has a front surface radius of -373.811 mm, a rear surface radius of 1712.163 mm, and a center thickness of 5 mm. Its material is preferably Schott SF4 optical glass. The axial distance from the vertex of its rear surface to the center of the aperture stop surface is 127.189 mm. The axial distance from the center of the aperture stop surface to the vertex of the front surface of the fifth lens is 1.864 mm.

[0047] The fifth lens preferably has a front surface radius of -483.295 mm, a rear surface radius of 72.761 mm, a center thickness of 3 mm, and is preferably made of Schott SF4 optical glass. The axial distance from the vertex of its rear surface to the vertex of the front surface of the sixth lens is 9.235 mm.

[0048] The sixth lens preferably has a front surface radius of 133.399 mm, a rear surface radius of -6273.457 mm, a center thickness of 3.5 mm, and is preferably made of Schott NSK18 optical glass. The axial distance from the vertex of its rear surface to the front surface of the interference filter is 80.774 mm.

[0049] The front and back surfaces of the interference filter are both flat, the center thickness is 2mm, the material is fused silica glass, and the axial distance between it and the beam splitter prism is 20mm.

[0050] The front and rear surfaces of the beam splitter prism are both flat, with a center thickness of 25 mm. The material is Schott NBK7 optical glass, and the distance from the rear surface of the beam splitter prism to the image plane is 97.149 mm.

[0051] The vacuum window glass is made of fused silica glass, with both front and rear surfaces being flat. The center thickness is 14.5 mm. The distance between the front surface of the vacuum window glass and the object plane is 605.5 mm, and the distance between the rear surface and the front surface of the first lens is 20 mm. Therefore, the distance between the vertex of the front surface of the first lens and the object plane is 640 mm, which means the object-side working distance is 640 mm.

[0052] For ease of optical processing and inspection, and to reduce costs, all components have spherical or planar optical surfaces, with no aspherical optical components.

[0053] Table 1 provides the specific structural parameter values ​​for each lens in this embodiment. The "Surface" column indicates the number of each optical surface from the object plane to the image plane, where STOP represents the aperture stop. The "Radius" column gives the spherical radius corresponding to each surface. The "Thickness / Spacing" column gives the axial distance between two adjacent surfaces. If the two surfaces belong to the same lens, the value of "Thickness / Spacing" represents the thickness of the lens; otherwise, it represents the distance from the object / image plane to the lens or the axial spacing between adjacent lenses. The "Optical Material" column specifies the material of the corresponding lens. The "Half-Aperture" column indicates the half-aperture value of the corresponding surface, i.e., half-height. The "Belonging Object" column indicates the lens corresponding to each surface from the object plane to the image plane.

[0054] Taking the first lens and the second lens as examples, the spherical radius of the front surface 3 of the second lens is 167.877 mm (the sign indicates the direction of curvature of the surface), the distance from the front surface 1 of the first lens to the object surface is 640 mm, and its optical material is Schott NSK16 optical glass. The semi-aperture of the front surface 1 of the first lens is 48.38 mm. The spherical radius of the rear surface 2 of the first lens is -295.206 mm. The thickness from the front surface 1 to the rear surface 2 of the first lens, i.e., the center thickness of the first lens, is 15 mm. The semi-aperture of the rear surface 2 of the first lens is 48.08 mm. That is, the first lens is a biconvex lens.

[0055] The spherical radius and half-aperture of the front surface 3 of the second lens are 183.435 mm and 45.55 mm, respectively. The distance between the front surface 3 of the second lens and the rear surface 2 of the first lens is 1 mm. The optical material of the second lens is Schott NSK16 optical glass. The spherical radius and half-aperture of the rear surface 4 of the second lens are 1013.062 mm and 44.81 mm, respectively. The thickness of the second lens is 7.753 mm. That is, the second lens is a meniscus positive lens bent towards the aperture stop. Except for the half-aperture of the image plane, which represents the half-height of the image-side field of view, the meanings of the parameter values ​​of the other surfaces are inferred from the descriptions of the first and second lenses.

[0056] In addition to the six lenses from the first to the sixth lens, there is also an aperture stop (STOP) between the fourth and fifth lenses. Changes in the aperture size of STOP will affect the imaging effect of the projection optical system.

[0057] Table 1. Structural parameters of the long working distance, object-side telecentric projection optical system of the present invention.

[0058]

[0059] According to the data disclosed in Table 1 of the preferred embodiment of the present invention, the sum of the first three data points in the "Thickness / Gap" column, 605.5, 14.500, and 20.000, yields 640 mm, which is the object-side working distance. Based on the analysis and calculations using professional optical design software (e.g., CODE V), Figure 2 The diffraction modulation transfer function (MTF) of this embodiment indicates that the imaging quality is close to the diffraction limit; it can also be seen that the maximum value of the object-side telecentric angle is 0.22°, and the other aberration corrections are shown in Table 2 below.

[0060] Table 2 Imaging quality of the long working distance, object-side telecentric projection optical system of the present invention

[0061]

[0062] Figure 3 The distribution of wavefront aberration (root mean square value) WFE RMS in this embodiment is shown, with a maximum value of 26.6 mλ, which reflects that the imaging quality of the long working distance object-side telecentric projection optical system of the present invention is close to perfect imaging.

[0063] Figure 4 The diagram shows the spherical aberration, astigmatism, field curvature, and distortion of the long working distance, telecentric projection optical system of the present invention. It can be seen that the maximum value of the distortion is 0.06266%.

[0064] The long working distance object-side telecentric projection optical system provided in this invention integrates optical characteristics such as ultra-long working distance (640mm), strict object-side telecentricity, high resolution (250 lp / mm), and small distortion (<0.063%). It also properly integrates engineering-related optical components such as vacuum window glass, interference filter, and beam splitter prism, providing an efficient, reliable, and cost-controllable optical technology solution for the precision measurement of high-speed micro-targets in a vacuum environment.

Claims

1. A long working distance, object-side telecentric projection optical system, characterized in that, It successively includes, from the object side to the image side along the optical axis: an object plane, a vacuum window glass, the first lens to the fourth lens, an aperture stop, the fifth lens to the sixth lens, an interference filter, a beam splitting prism, and an image plane; Among them, the first lens is a biconvex lens, the second lens is a meniscus positive lens bent towards the aperture stop direction, the third lens is a meniscus negative lens bent towards the object plane direction, the fourth lens is a biconcave lens, the fifth lens is a biconcave lens, and the sixth lens is a biconvex lens, and all the optical surfaces of the first lens to the sixth lens are spherical surfaces; The vacuum window glass and the front group of the objective lens composed of the first lens to the fourth lens together have a positive combined focal power, and the image-side focus of the front group of the objective lens is located at the center position of the aperture stop, thus forming an object-side telecentric optical path structure; The axial distance from the object plane to the vertex of the object side surface of the first lens is 640 mm ± 60 mm, constituting the object-side working distance of the optical system.

2. The long working distance, telecentric projection optical system according to claim 1, characterized in that, The focal lengths f1 of the first lens (L1), f2 of the second lens (L2), f3 of the third lens (L3), f4 of the fourth lens (L4), f5 of the fifth lens (L5), and f6 of the sixth lens (L6) satisfy the following relationships: 165 mm < f1 < 181 mm, 339 mm < f2 < 375 mm, -1313 mm < f3 < -1188 mm, -421 mm < f4 < -381 mm, -86 mm < f5 < -78 mm, 193 mm < f6 < 213 mm.

3. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, The curvature radius R1 of the object side surface of the first lens (L1), the curvature radius R2 of the image side surface, and the central thickness d1 satisfy: 160 mm < R1 < 176 mm, -310 mm < R2 < -280 mm, 14.5 mm < d1 < 15.5 mm, and the material of the first lens (L1) is NSK16 optical glass.

4. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, The curvature radius R3 of the object side surface of the second lens (L2), the curvature radius R4 of the image side surface, and the central thickness d2 satisfy: 174 mm < R3 < 192 mm, 963 mm < R4 < 1063 mm, 7.3 mm < d2 < 8.3 mm, and the material of the second lens (L2) is NSK16 optical glass.

5. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, The curvature radius R5 of the object side surface of the third lens (L3), the curvature radius R6 of the image side surface, and the central thickness d3 satisfy: -712 mm < R5 < -644 mm, -2465 mm < R6 < -2231 mm, 4.7 mm < d3 < 5.3 mm, and the material of the third lens (L3) is SF4 optical glass.

6. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, The curvature radius R7 of the object side surface of the fourth lens (L4), the curvature radius R8 of the image side surface, and the central thickness d4 satisfy: -393 mm < R7 < -355 mm, 1626 mm < R8 < 1798 mm, 4.7 mm < d4 < 5.3 mm, and the material of the fourth lens (L4) is SF4 optical glass.

7. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, the curvature radius R9 of the object side surface of the fifth lens (L5), the curvature radius R 10 and the center thickness d5 satisfy: -507mm < R9< -459mm, 69mm < R 10 < 76mm, 2.7mm < d5< 3.3mm, and the material of the fifth lens (L5) is SF4 optical glass.

8. The long working distance, telecentric projection optical system according to claim 1 or 2, characterized in that, the radius of curvature R of the object side surface of the sixth lens (L6) 11 the radius of curvature R of the image side surface 12 and the center thickness d6 satisfy: 127mm < R 11 <140mm, -6587mm < R 12 < -5959mm, 3.3mm < d6<3.7mm, the material of the sixth lens (L6) is NSK18 optical glass.

9. The long working distance, telecentric projection optical system according to claim 1, characterized in that, The interference filter has both front and rear surfaces that are flat, a center thickness of 2mm, is made of fused silica glass, and has an axial distance of 20mm from the beam splitter prism.

10. The long working distance, telecentric projection optical system according to claim 1, characterized in that, The beam splitter prism has flat front and rear surfaces, a center thickness of 25 mm, and is made of Schott NBK7 optical glass. The distance between the rear surface of the beam splitter prism and the image plane is 97.149 mm.

11. The long working distance, telecentric projection optical system according to claim 1, characterized in that, The vacuum window glass is made of fused silica glass, with both front and rear surfaces being flat, and a center thickness of 14.5 mm. The distance between the front surface of the vacuum window glass and the object plane is 605.5 mm, the distance between the rear surface and the front surface of the first lens is 20 mm, and the distance between the vertex of the front surface of the first lens and the object plane is 640 mm, i.e., the object-side working distance is 640 mm.

12. The long working distance, telecentric projection optical system according to claim 1, characterized in that, The field diameter of the measured area is 16 mm, the magnification is -1, the working wavelength is 532 nm, the bandwidth is 1 nm, the image-side numerical aperture (NA) is 0.0665, the limiting resolution is 250 lp / mm, and the maximum telecentric angle is less than 3.8 mrad, i.e., 0.22°.

Images