Ultra-wide angle free-form catadioptric telecentric camera lens, design method and imaging system thereof

Abstract

The application provides a super-wide-angle free curved surface catadioptric image-side telecentric lens, a design method thereof and an imaging system, and aims at solving the technical problem that the existing super-wide-angle lens is usually a transmission lens and is difficult to observe plasma in an environment with large temperature difference. The super-wide-angle free curved surface catadioptric image-side telecentric lens fully considers the high-temperature environment when observing plasma in a tokamak device, and innovatively adds a reflection light path, so that the lens is divided into three parts, namely, an aperture diaphragm, a reflection light path and a transmission light path. The aperture diaphragm and the reflection light path are made of metal and are arranged in a high-temperature vacuum chamber between a first observation window and a second observation window of the tokamak device. The lenses in the transmission light path are made of traditional lens materials and are arranged in a room-temperature environment outside the lenses, so that the super-wide-angle free curved surface catadioptric image-side telecentric lens can realize stable observation of plasma when the tokamak device works.

Description

Technical Field

[0001] The present invention relates to an ultra-wide-angle lens, and in particular to an ultra-wide-angle free-form surface catadioptric image-space telecentric lens, a design method thereof, and an imaging system. Background Art

[0002] Ultra-wide-angle lenses have the advantages of a short focal length and a wide angle of view. Their depth of field is significantly greater than that of standard and telephoto lenses, allowing them to capture a wide range of scenes at relatively close distances. Ultra-wide-angle visible-light cameras are important diagnostic tools for monitoring the shape and position of plasma within a tokamak. A tokamak is a toroidal container that uses magnetic confinement to achieve controlled nuclear fusion. Its first wall serves as the boundary that confines the internal plasma. Between the first wall and the outer wall of the device is typically a vacuum chamber for locating components facing the plasma. When a tokamak is in operation, large amounts of high-energy particles and high-energy radiation can overflow from the edge of the first wall. The high heat load and radiation dose can cause melting or corrosion of components facing the plasma. To observe the plasma within the tokamak, a first observation window is provided on the first wall, and a second observation window is provided at a corresponding position on the outer wall. Conventional techniques for observing plasma typically use an ultra-wide-angle visible-light camera mounted on the end of a stainless steel tube within the outer shielding wall. This tube then connects to a second observation window on the outer wall of the tokamak, enabling ultra-wide-angle imaging of the plasma within the tokamak. However, this approach is susceptible to strong electromagnetic interference and high radiation doses from high-energy particles and X-rays, leading to malfunction or even damage, especially during periods of plasma discharge interruption.

[0003] Currently, to further protect the imaging chip and other electronic components of an ultra-wide-angle visible-light camera from the radiation environment, a long-distance relay system can be used to transmit the plasma image from the ultra-wide-angle lens to the outside of the tokamak's shielding wall. The camera's electronics are then placed outside the shielding wall, thereby achieving spatial separation of the optical-mechanical-mechanical systems. This long-distance relay system generally requires the front-mounted ultra-wide-angle lens to have telecentric image space to facilitate docking between the long-distance relay system and the ultra-wide-angle lens, and requires a large positional tolerance between the two to facilitate engineering implementation. However, since the temperature between the first observation window on the first wall of the tokamak and the second observation window on the outer wall can typically reach 200°C, existing ultra-wide-angle lenses are typically transmissive lenses. The refractive index of the glass material used in transmissive lenses changes with temperature, and the thermal expansion coefficient differs significantly from that of the structural material, making them difficult to meet the requirements for plasma observation in environments with large temperature differences. Therefore, how to ensure stable plasma observation over a wide temperature range (20°C-200°C) with ultra-wide-angle lenses is an urgent problem that needs to be solved in the industry. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that existing ultra-wide-angle lenses are usually transmissive lenses and are difficult to observe plasma in environments with large temperature differences, and to provide an ultra-wide-angle free-form surface catadioptric image-space telecentric lens and its design method and imaging system.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0006] An ultra-wide-angle free-form surface catadioptric image-space telecentric lens, which is special in that it includes an aperture stop, a reflection light path, and a transmission light path;

[0007] The aperture diaphragm is a solid diaphragm made of metal;

[0008] The reflective optical path includes a primary reflector, a secondary reflector, and a folding mirror; the reflective surfaces of the primary reflector and the secondary reflector are both free-form surfaces, and the refractive surface of the folding mirror is a flat surface;

[0009] The primary reflector, secondary reflector and folding mirror are all made of metal;

[0010] The aperture stop, the primary reflector, the secondary reflector, the folding mirror, and the transmission light path are sequentially arranged on the light path of the light emitted by the plasma to be detected;

[0011] The aperture stop, primary reflector, secondary reflector, folding mirror and their supporting structure are located in a vacuum chamber between the first wall and the outer wall of the tokamak device, the aperture stop faces the first observation window, and the reflected light of the folding mirror faces the second observation window; the transmission light path is located outside the tokamak device, and its incident end faces the second observation window;

[0012] Light from the plasma being detected is incident from the aperture stop through a first observation window on the first wall of the tokamak device. The incident light is reflected by the primary reflector and the secondary reflector in sequence before reaching the surface of the folding mirror. The folding mirror adjusts the direction of the light reflected by the secondary reflector. The light after being adjusted by the folding mirror passes through a second observation window on the outer wall of the tokamak device and reaches the transmission light path. After passing through the transmission light path, it converges on the image plane.

[0013] The aperture stop, the primary reflector, the secondary reflector, the folding mirror and the transmission light path are respectively provided with support structures.

[0014] Furthermore, the aperture stop, primary reflector, secondary reflector, and folding mirror are all made of aluminum alloy, copper, nickel, beryllium, or titanium alloy.

[0015] Furthermore, the transmission light path includes a plurality of lenses and an attenuation filter, and the attenuation filter is located between any two lenses, or in front of the first lens;

[0016] The front and rear surfaces of the plurality of lenses are all spherical, and the front and rear surfaces of the attenuation filter are all planar.

[0017] Furthermore, the lens is made of glass or crystal;

[0018] The attenuation filter is made of fused quartz or K9 glass.

[0019] Furthermore, the aperture stop, the primary reflector, the secondary reflector, the folding mirror, the lenses and the attenuation filter are respectively provided with support structures;

[0020] The material of the supporting structure of the aperture stop, the primary reflector, the secondary reflector and the folding mirror is the same as that of the aperture stop, the primary reflector, the secondary reflector and the folding mirror;

[0021] The supporting structure of each lens and the attenuation filter is made of aluminum alloy, copper, nickel, beryllium, or titanium alloy.

[0022] Furthermore, the number of lenses in the transmission light path is eight;

[0023] The attenuation filter is located between the fourth lens and the fifth lens.

[0024] Furthermore, the free-form surface shapes of the primary reflector and the secondary reflector are expressed by extended polynomials, which only include even-power terms of x and are symmetrical about the YOZ plane.

[0025] In addition, the present invention also provides a design method for an ultra-wide-angle free-form surface catadioptric image-space telecentric lens, which is special in that it includes the following steps:

[0026] Step 1: Set the aperture stop and construct a spherical reflective optical path with the primary and secondary reflectors by trial and error. Adjust the relative positions of the aperture stop, the primary and secondary reflectors, and the curvature radii of the primary and secondary reflectors. When the divergence angle of light within a large field of view angle is significantly reduced to the preset requirement after passing through the constructed reflective optical path, the current reflective optical path structure is used as the initial reflective optical path structure.

[0027] Step 2: Based on the initial structure of the reflective optical path, gradually increase the conic coefficients of the primary and secondary reflectors and the coefficients of the higher-order terms of the free-form surface until the output light of the light within a large field of view angle after passing through the reflective optical path is quasi-parallel light. The preliminary iterative optimization of the primary and secondary reflectors is completed, and the free-form surface off-axis two-reflective optical path is obtained;

[0028] Step 3: construct an initial structure of the transmission light path by a direct construction method, and connect the constructed initial structure of the transmission light path to the rear of the two off-axis reflection light paths of the free-form surface; iteratively optimize the initial structure of the transmission light path to obtain the transmission light path;

[0029] Step 4, jointly optimizing the two off-axis reflection light paths of the free-form surface obtained in step 2 and the transmission light path obtained in step 3;

[0030] Step 5: After the joint optimization is completed, add the folding mirror to complete the design of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens.

[0031] Furthermore, in step 3, each lens in the initial structure of the transmission light path is a biconvex lens with equal curvature, the lens material is a staggered arrangement of crown glass and flint glass, the initial thickness and initial spacing of the lenses are equal, and the initial diameter-thickness ratio is within the range of 3 to 8; during iterative optimization, the focal length, back intercept, image telecentricity, distortion, air gap between the center and edge of the lens, center and edge thickness of the lens, and diameter-thickness ratio of the optical system are controlled, and the material of the lens is optimized using a hammer optimization method, and the transmission light path is obtained after gradual iterative optimization.

[0032] In addition, the present invention also provides a base imaging system, which is special in that it includes the above-mentioned ultra-wide-angle free-form surface catadioptric image-space telecentric lens, a relay system and a camera electronics module;

[0033] The relay system is installed at the rear end of the transmission light path in the ultra-wide-angle free-form surface catadioptric image-space telecentric lens, and the object plane of the relay system is the image plane of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens;

[0034] The camera electronics module is located at the rear end of the relay system, and the photosensitive surface of the camera electronics module is the image plane of the relay system.

[0035] The beneficial effects of the present invention compared to the prior art are as follows:

[0036] 1. The present invention provides an ultra-wide-angle free-form surface catadioptric image-space telecentric lens, which fully considers the high-temperature environment during plasma observation inside a tokamak device, innovatively adds a reflective light path, and divides the lens into three parts: an aperture stop, a reflective light path, and a transmission light path. The aperture stop and the reflective light path are made of metal materials and are arranged in a high-temperature vacuum chamber between the first observation window and the second observation window on the outer wall of the tokamak device. The lenses in the transmission light path are made of traditional lens materials and are arranged in a room temperature environment outside the tokamak device. This allows the ultra-wide-angle free-form surface catadioptric image-space telecentric lens as a whole to achieve stable observation of plasma when the tokamak device is working. This has important practical significance for the further development of controlled nuclear fusion technology and accelerates the pace of realizing controlled nuclear fusion energy applications.

[0037] 2. The primary reflector and secondary reflector in the reflective optical path of the present invention are designed as free-form surfaces. Compared with traditional spherical or aspheric reflector surfaces, they have more degrees of freedom in optical design optimization, improve the ability to correct asymmetric aberrations of off-axis optical systems, and enable the system to have the advantages of large field of view, large relative aperture, low distortion, and image telecentricity.

[0038] 3. The aperture stop, primary reflector, secondary reflector and their supporting structure in the present invention are made of the same metal material, which is easy to achieve athermalization and has good temperature adaptability, and is suitable for plasma observation applications in tokamak devices.

[0039] 4. The free-form surface in the present invention is described by an extended polynomial containing only even-power x terms, which is suitable for processing by single-point diamond turning and has strong feasibility.

[0040] 5. The ultra-wide-angle lens of the present invention is provided with an independent aperture stop, and there is no need to open a hole on the reflective lens to set the stop, thereby avoiding the generation of blind spots in the field of view and not affecting the observation effect of the plasma.

[0041] 6. The present invention provides a design method for an ultra-wide-angle free-form surface catadioptric image-space telecentric lens. The method constructs and optimizes the initial structure of the reflected light path through a trial and error method, constructs and optimizes the initial structure of the transmitted light path through a direct construction method, and then performs joint optimization to complete the design. The method is simple, easy to operate, and has high practicality.

[0042] 7. The imaging system of the present invention is based on an ultra-wide-angle free-form surface catadioptric image-space telecentric lens. Since the wide-angle free-form surface catadioptric image-space telecentric lens has the characteristics of image-space telecentricity and low distortion, it is easy to match with the rear relay system to protect the camera electronics from electromagnetic interference and high-dose radiation, and can achieve long-term stable imaging of the plasma in the tokamak device. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 1 is a side view of an embodiment of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens of the present invention, taken in a direction perpendicular to the optical axis of the aperture stop;

[0044] Figure 2 A stereoscopic view of the present invention;

[0045] Figure 3 The designed full-field spot diagram of the embodiment of the present invention at room temperature;

[0046] Figure 4 This is a design full-field spot diagram of an embodiment of the present invention in working condition;

[0047] Figure 5A modulation transfer function curve diagram of an embodiment of the present invention;

[0048] Figure 6 A schematic diagram of grid distortion is designed for an embodiment of the present invention;

[0049] Figure 7 Schematic diagram of the initial structure of the reflective light path in step 1 of the design method of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens of the present invention;

[0050] Figure 8 Schematic diagram of the initial structure of the transmission light path in step 3 of the design method of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens of the present invention.

[0051] The specific reference numerals are as follows:

[0052] 1. Aperture stop; 2. Primary reflector; 3. Secondary reflector; 4. Refraction mirror; 5. First lens; 6. Second lens; 7. Third lens; 8. Fourth lens; 9. Attenuation filter; 10. Fifth lens; 11. Sixth lens; 12. Seventh lens; 13. Eighth lens. DETAILED DESCRIPTION

[0053] In order to make the advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] The ultra-wide-angle free-form surface catadioptric image-space telecentric lens of the present invention operates in the visible light band and is used to observe plasma within a tokamak. Considering the high-temperature environment of the vacuum chamber between the first observation window on the first wall and the second observation window on the outer wall of the tokamak, the present invention divides the ultra-wide-angle lens into two parts: the front part is located within the high-temperature vacuum chamber, and the rear part is located outside the tokamak. Because the reflector can be made of metal, which is heat-resistant, the front part of the lens, located within the high-temperature vacuum chamber, adopts a catadioptric lens configuration. Since the area outside the tokamak has reached room temperature, the rear part can use multiple transmissive lenses to correct aberrations across a wide field of view and chromatic aberration within the visible light band.

[0055] like Figure 1 、 Figure 2As shown, an ultra-wide-angle free-form surface catadioptric image-space telecentric lens includes an aperture stop 1, a reflective optical path, and a transmissive optical path. The aperture stop 1 is a physical stop located behind the first observation window on the first wall of the tokamak device and at the front of the entire optical lens. The reflective optical path includes three reflectors, namely a primary reflector 2, a secondary reflector 3, and a folding mirror 4, wherein the primary reflector 2 and the secondary reflector 3 constitute an off-axis two-reflective optical system. The transmissive optical path includes multiple lenses and an attenuation filter 9. In this embodiment, there are eight lenses, which are respectively designated as the first lens 5, the second lens 6, the third lens 7, the fourth lens 8, the fifth lens 10, the sixth lens 11, the seventh lens 12, and the eighth lens 13. The attenuation filter 9 is used to attenuate the visible light band to protect the detector target surface from strong light. It can usually be set between any two lenses, or in front of the first lens. In this embodiment, it is set between the fourth lens 8 and the fifth lens 10.

[0056] The aperture stop 1, the primary reflector 2, the secondary reflector 3, the folding mirror 4, the first lens 5, the second lens 6, the third lens 7, the fourth lens 8, the attenuation filter 9, the fifth lens 10, the sixth lens 11, the seventh lens 12 and the eighth lens 13 are sequentially arranged on the optical path of the light emitted by the detected plasma, and are used to observe the plasma inside the tokamak device.

[0057] The aperture stop 1, primary reflector 2, secondary reflector 3, and folding mirror 4 are located within a vacuum chamber between the first and outer walls of the tokamak device, with the aperture stop 1 facing the first observation window and the reflected light from the folding mirror 4 facing the second observation window. These components are configured to allow light from the plasma being detected to pass through the first observation window and be incident on the surface of the primary reflector 2. Because the aperture stop 1 and the reflected light path are located within the high-temperature environment of the vacuum chamber and require stable imaging at temperatures of 200°C, the aperture stop 1, primary reflector 2, secondary reflector 3, and folding mirror 4 in the present invention can be made of aluminum alloy, copper, nickel, beryllium, or titanium alloy. At the same time, the aperture diaphragm 1, the primary reflector 2, the secondary reflector 3, and the folding axis mirror 4 are also respectively provided with supporting structures, and their supporting structures also need to adopt the above-mentioned metal material. In this embodiment, the aperture diaphragm 1, the primary reflector 2, the secondary reflector 3, the folding axis mirror 4 and their corresponding supporting structures are all made of aluminum alloy, which can achieve athermalization within a wide temperature range and is also easy to turn.

[0058] Furthermore, to interface with the relay system, ultra-wide-angle lenses are typically required to have good image-space telecentricity and low distortion. Since metal mirrors can be machined into non-rotationally symmetrical surfaces through lathing, the reflective surfaces of the primary and secondary mirrors 2 and 3 can be machined into freeform surfaces. Their multi-degree-of-freedom properties can be exploited to control light, resulting in an ultra-wide-angle lens with both image-space telecentricity and low distortion. The folding mirror 4 is a flat surface used to adjust the light output direction of the lens optical path according to the spatial layout of the tokamak.

[0059] In this embodiment, the surface profiles of both the primary reflector 2 and the secondary reflector 3 are described using a 9th-order extended polynomial, consisting only of even-power terms of x, symmetrical about the YOZ plane, and totaling 29 terms, making them feasible for machining and testing. A single-point diamond lathe can be used to perform ultra-precision machining on aluminum alloy blanks to obtain the surface profile of the extended polynomial. Laser interferometry and CGH can be used to perform high-precision testing of the surface profile of the extended polynomial. The expression of the extended polynomial is as follows:

[0060]

[0061] Where z(x,y) is the surface sag of the free-form surface, (x,y) is the diameter position coordinate of the free-form surface, c is the curvature of the base quadratic surface, k is the conic constant of the base quadratic surface, is the radial coordinate of the free-form surface diameter, R m is the normalized radius (usually 1), C i is the weight coefficient of the i-th expanded polynomial. 1≤m+n≤9. The expanded polynomial coefficients are shown in the following table:

[0062]

[0063]

[0064] The transmission light path is used to focus light emitted from the reflection light path onto the image plane. The transmission light path's first lens 5, second lens 6, third lens 7, fourth lens 8, attenuation filter 9, fifth lens 10, sixth lens 11, seventh lens 12, and eighth lens 13 are located outside the tokamak, with the first lens 5 facing the second observation window. Since the lenses in the transmission light path only need to form images at room temperature, conventional lens materials with stable performance, such as optical glass or crystal, can be selected. The attenuation filter 9 can be made of conventional fused quartz or K9 glass. The structural supports for the lenses and attenuation filter 9 can be made of aluminum alloy to ensure stable support. The front and back surfaces of the eight lenses are spherical, while the front and back surfaces of the attenuation filter 9 are planar. Between the reflection light path and the transmission light path is the second observation window on the outer wall of the tokamak. The front and back surfaces of the second observation window are both planar, allowing light reflected by the folding mirror 4 to pass through the second observation window and be incident on the surface of the first lens 5.

[0065] The light of the detected plasma is incident from the aperture 1 through the first observation window on the first wall of the tokamak device. The incident light is collimated and reflected by the primary reflector 2 and the secondary reflector 3 in sequence and reaches the surface of the folding mirror 4. The folding mirror 4 adjusts the direction of the light reflected by the secondary reflector 3, and then reaches the first lens 5 through the second observation window on the outer wall of the tokamak device. After being transmitted in sequence by the first lens 5, the second lens 6, the third lens 7, the fourth lens 8, the attenuation filter 9, the fifth lens 10, the sixth lens 11, the seventh lens 12 and the eighth lens 13, it converges on the image plane.

[0066] It is worth noting that a certain distance is set between the upper edge of the aperture diaphragm 1 and the reflected light of the secondary reflector 3, so that the upper edge of the aperture diaphragm 1 does not block the light; a certain distance is set between the lower edge of the aperture diaphragm 1 and the reflected light of the secondary reflector 3, so that the lower edge of the aperture diaphragm 1 does not block the light; a certain distance is set between the lower edge of the secondary reflector 3 and the transmitted light of the aperture diaphragm 1, so that the lower edge of the secondary reflector 3 does not block the light; a certain distance is set between the upper edge of the secondary reflector 3 and the transmitted light of the aperture diaphragm 1, so that the upper edge of the secondary reflector 3 does not block the light; a certain distance is set between the lower edge of the main reflector 2 and the reflected light of the secondary reflector 3, so that the lower edge of the main reflector 2 does not block the light; a certain distance is set between the upper edge of the main reflector 2 and the reflected light of the secondary reflector 3, so that the upper edge of the main reflector 2 does not block the light.

[0067] The ultra-wide-angle free-form surface catadioptric image-side telecentric lens in this embodiment has an F-number of 1.9, an entrance pupil diameter of 5mm, a rectangular field of view of 68°×51°, a diagonal full field of view of 85°, an operating band of visible light, and an image-side telecentricity of less than 0.5°. The second sealed window on the outer wall of the tokamak device has a circular aperture of Φ66mm, a flat front and rear surface, a thickness of 10mm, and is made of fused quartz. The distance between the second sealed window and the single lens is 16.628mm. Therefore, the optical parameters of the optical components in the lens of this embodiment are as follows:

[0068] The aperture stop 1 is an aluminum alloy sheet with a diameter of 5 mm. The distance between the aperture stop 1 and the main reflector 2 is 156.995 mm.

[0069] The primary reflector 2 has a rectangular aperture with an aperture of 188 mm × 132 mm, a thickness of 25 mm, a curvature radius of -120.327 mm, a cone coefficient of -0.43, an eccentricity in the Y direction of 44.655 mm, an inclination in the X direction of -20.791°, and a spacing of 120.487 mm between the primary reflector 2 and the secondary reflector 3.

[0070] The secondary reflector 3 has a rectangular aperture with an aperture of 88 mm × 60 mm, a thickness of 10 mm, a curvature radius of -150.881 mm, a cone coefficient of -0.908, an eccentricity in the Y direction of 83.857 mm, an inclination in the X direction of 10.272°, and a spacing of 125 mm between the secondary reflector 3 and the off-axis mirror 4.

[0071] The folding mirror 4 has a rectangular aperture with a diameter of 70 mm × 106 mm and a thickness of 10 mm. The eccentricity in the Y direction is -90.36 mm, the tilt in the X direction is 117.74°, and the interval between the folding mirror 4 and the second sealing window is 75 mm.

[0072] The first lens 5 has a circular aperture of Φ62mm, a front surface curvature radius of 168.849mm, a rear surface curvature radius of -289.981mm, a thickness of 8.201mm, and is made of H-ZK8 from Chengdu Guangming. The distance between the first lens 5 and the second lens 6 is 16.66mm.

[0073] The second lens 6 has a circular aperture of Φ52mm, a front surface curvature radius of -19449.208mm, a rear surface curvature radius of -522.107mm, a thickness of 6.461mm, and is made of H-ZF11 from Chengdu Guangming. The distance between the second lens 6 and the third lens 7 is 25.413mm.

[0074] The third lens 7 has a circular aperture of Φ44mm, a front surface curvature radius of 114.778mm, a rear surface curvature radius of -166.709mm, a thickness of 5.898mm, and is made of H-BAK7GT from Chengdu Guangming. The distance between the third lens 7 and the fourth lens 8 is 2.502mm.

[0075] The fourth lens 8 has a circular aperture of Φ42mm, a front surface curvature radius of -77.282mm, a rear surface curvature radius of 1471.071mm, a thickness of 5.2mm, and is made of Chengdu Guangming's H-ZF52A. The distance between the fourth lens 8 and the attenuation filter 9 is 24.049mm.

[0076] The attenuation filter 9 has a circular aperture of Φ40 mm and a thickness of 5 mm. The interval between the attenuation filter 9 and the fifth lens 10 is 14.046 mm.

[0077] The fifth lens 10 has a circular aperture of Φ40 mm, a front surface curvature radius of 132.753 mm, a rear surface curvature radius of -44.367 mm, a thickness of 12.992 mm, and is made of H-ZPK5 from Chengdu Guangming. The interval between the fifth lens 10 and the sixth lens 11 is 3.621 mm.

[0078] The sixth lens 11 has a circular aperture of Φ36 mm, a front surface curvature radius of -34.298 mm, a rear surface curvature radius of -52.38 mm, a thickness of 11.871 mm, and is made of Chengdu Guangming's F4GTI. The interval between the sixth lens 11 and the seventh lens 12 is 2.97 mm.

[0079] The seventh lens 12 has a circular aperture of Φ34 mm, a front surface curvature radius of -26.891 mm, a rear surface curvature radius of -95.366 mm, a thickness of 10.716 mm, and is made of H-ZPK3 from Chengdu Guangming. The distance between the seventh lens 12 and the eighth lens 13 is 1.763 mm.

[0080] The eighth lens 13 has a circular aperture of Φ29 mm, a front surface curvature radius of -90.378 mm, a rear surface curvature radius of 57.052 mm, a thickness of 9.536 mm, and is made of H-TF8 from Chengdu Guangming. The distance between the eighth lens 13 and the image plane is 12.85 mm.

[0081] Therefore, the distance from aperture stop 1 to the image plane along the z-axis of this embodiment of the ultra-wide-angle free-form catadioptric image-space telecentric lens is less than 445 mm, the distance from primary reflector 2 to folding mirror 4 along the y-axis is less than 240 mm, and the system length along the x-axis is less than 190 mm. Furthermore, the overall dimensions of the lens are less than 190 mm (X-axis) × 120 mm (Y-axis) × 105 mm (Z-axis).

[0082] Figure 3 This is the design full-field spot diagram of this embodiment at room temperature. Figure 4 This is the designed full-field point diagram of this embodiment in the working state, that is, when the working temperatures of the reflected light path and the transmitted light path are 200°C and 20°C, respectively. It can be seen that the RMS radius in the designed full-field point diagram at room temperature does not exceed 2.4μm, and the RMS radius in the designed full-field point diagram in the working state does not exceed 2.6μm, and the athermal effect is excellent.

[0083] like Figure 5 As shown in FIG. , the designed modulation transfer function curve of this embodiment is shown. The designed modulation transfer function is higher than 0.63 at 77 line pairs per millimeter, and the imaging quality is excellent.

[0084] like Figure 6 As shown in FIG, a schematic diagram of grid distortion designed in this embodiment is shown. It can be seen that it is in the form of trapezoidal distortion, and the maximum value does not exceed 5%.

[0085] Based on the above-mentioned ultra-wide-angle free-form surface catadioptric image-space telecentric lens, the present invention also provides a design method thereof, and the specific steps are as follows:

[0086] Step 1: Set the aperture stop 1 and construct a spherical reflective light path with the primary reflector 2 and the secondary reflector 3 by trial and error. During construction, it is necessary to ensure that the aperture stop 1, the primary reflector 2, and the secondary reflector 3 do not block the light within the wide field of view angle range and that there is no obstruction between the three. Adjust the relative positions of the aperture stop 1, the primary reflector 2, and the secondary reflector 3, as well as the curvature radii of the primary reflector 2 and the secondary reflector 3. When the divergence angle of the light within the wide field of view angle range is significantly reduced to the preset requirement after passing through the constructed reflective light path, the current reflective light path structure is used as the initial structure of the reflective light path for subsequent optimization, such as Figure 7 shown.

[0087] Step 2: Based on the initial structure of the reflected light path, gradually increase the cone coefficients and free-form surface higher-order term coefficients of the primary reflector 2 and the secondary reflector 3 until the output light of the light within a large field of view angle range after passing through the reflected light path is quasi-parallel light. The preliminary iterative optimization of the primary reflector 2 and the secondary reflector 3 is completed, and the free-form surface off-axis two-reflection light path is obtained.

[0088] Step 3: After the free-form surface off-axis two-way reflection path is obtained, the transmission light path can be designed. In this embodiment, the initial structure of the transmission light path is constructed by direct construction method, such as Figure 8 As shown, each lens in the initial structure of the transmission light path is a biconvex lens with equal curvature, made of a staggered arrangement of crown glass and flint glass. The initial thickness and initial spacing of the lenses are equal, and the initial aspect ratio is within the range of 3 to 8. The constructed initial structure of the transmission light path is connected to the rear of the two off-axis reflection paths of the free-form surface. By controlling the focal length, back intercept, image telecentricity, distortion, air spacing between the center and edge of the lens, center and edge thickness of the lens, and aspect ratio of the lens, and optimizing the lens material using hammer optimization, the transmission light path is obtained through gradual iterations.

[0089] Step 4: Jointly optimize the two off-axis reflection light paths of the free-form surface obtained in step 2 and the transmission light path obtained in step 3.

[0090] Step 5: After the joint optimization is completed, a folding mirror 4 is added according to the monitoring direction of the plasma to complete the design of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens.

[0091] The present invention also provides an imaging system comprising the aforementioned ultra-wide-angle free-form surface catadioptric image-space telecentric lens, a relay system, and a camera electronics module. The relay system is installed at the rear end of the transmission light path of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens, and the object plane of the relay system is the image plane of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens, with the two planes spatially completely overlapping. The camera electronics module is located at the rear end of the relay system, with the photosensitive surface of the camera electronics module being the image plane of the relay system, and the two planes spatially completely overlapping.

[0092] The above description is only used to illustrate the technical solution of the present invention, rather than to limit it. For ordinary professional and technical personnel in this field, the specific technical solutions recorded in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution protected by the present invention.

Claims

1. An ultra-wide-angle free-form surface catadioptric image-space telecentric lens, characterized by: It includes an aperture stop (1), a reflection light path, and a transmission light path; The aperture diaphragm (1) is a solid diaphragm made of metal; The reflecting light path comprises a primary reflecting mirror (2), a secondary reflecting mirror (3) and a folding mirror (4); the reflecting surfaces of the primary reflecting mirror (2) and the secondary reflecting mirror (3) are both free-form surfaces, and the refractive surface of the folding mirror (4) is a flat surface. The primary reflector (2), the secondary reflector (3) and the folding mirror (4) are all made of metal; The aperture stop (1), the primary reflector (2), the secondary reflector (3), the folding mirror (4), and the transmission light path are sequentially arranged on the light path of the light emitted by the detected plasma; The aperture stop (1), the primary reflector (2), the secondary reflector (3), and the folding mirror (4) are located in a vacuum chamber between a first wall and an outer wall of the tokamak device, the aperture stop (1) faces the first observation window, and the reflected light of the folding mirror (4) faces the second observation window; the transmission light path is located outside the tokamak device, and its incident end faces the second observation window; Light from the plasma to be detected is incident from an aperture stop (1) through a first observation window on a first wall of the tokamak device, and the incident light is reflected by a primary reflector (2) and a secondary reflector (3) in sequence before reaching the surface of a folding mirror (4). The folding mirror (4) adjusts the direction of the light reflected by the secondary reflector (3). The light after the direction adjustment by the folding mirror (4) passes through a second observation window on an outer wall of the tokamak device and reaches a transmission light path, and converges on an image plane after passing through the transmission light path. The aperture stop (1), the primary reflector (2), the secondary reflector (3), the folding mirror (4), and the transmission light path are respectively provided with support structures.

2. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 1, characterized in that: The aperture stop (1), the primary reflector (2), the secondary reflector (3), and the folding mirror (4) are all made of aluminum alloy, copper, nickel, beryllium, or titanium alloy.

3. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 2, characterized in that: The transmission light path comprises a plurality of lenses and an attenuation filter (9), wherein the attenuation filter (9) is located between any two lenses or in front of the first lens; The front and rear surfaces of the plurality of lenses are all spherical, and the front and rear surfaces of the attenuation filter (9) are all planar.

4. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 3, characterized in that: The lens is made of glass or crystal; The attenuation filter (9) is made of fused quartz or K9 glass.

5. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 4, characterized in that: The material of the supporting structure of the aperture stop (1), the primary reflector (2), the secondary reflector (3), and the folding mirror (4) is the same as the material of the aperture stop (1), the primary reflector (2), the secondary reflector (3), and the folding mirror (4); The supporting structure of each lens and the attenuation filter (9) is made of aluminum alloy, copper, nickel, beryllium or titanium alloy.

6. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 5, characterized in that: The number of lenses in the transmission light path is eight; The attenuation filter (9) is located between the fourth lens and the fifth lens.

7. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to any one of claims 1 to 6, characterized in that: The free-form surface shapes of the primary reflector (2) and the secondary reflector (3) are expressed using extended polynomials, only including even-power terms of x, and are symmetrical about the YOZ plane.

8. A method for designing the ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1, setting an aperture stop (1), and constructing a reflection light path in which the primary reflector (2) and the secondary reflector (3) are spherical surfaces by a trial and error method; adjusting the relative positions of the aperture stop (1), the primary reflector (2) and the secondary reflector (3), as well as the curvature radii of the primary reflector (2) and the secondary reflector (3); when the divergence angle of light within a large field of view angle range is significantly reduced to a preset requirement after passing through the constructed reflection light path, the current reflection light path structure is used as the initial reflection light path structure; Step 2: On the basis of the initial structure of the reflection light path, gradually increase the conic coefficients of the primary reflector (2) and the secondary reflector (3) and the coefficients of the higher-order terms of the free-form surface until the output light of the light within a large field of view angle after passing through the reflection light path is quasi-parallel light. The preliminary iterative optimization of the primary reflector (2) and the secondary reflector (3) is completed, and the free-form surface off-axis two-reflection light path is obtained; Step 3: construct an initial structure of the transmission light path by a direct construction method, and connect the constructed initial structure of the transmission light path to the rear of the two off-axis reflection light paths of the free-form surface; iteratively optimize the initial structure of the transmission light path to obtain the transmission light path; Step 4, jointly optimizing the two off-axis reflection light paths of the free-form surface obtained in step 2 and the transmission light path obtained in step 3; Step 5: After the joint optimization is completed, the folding mirror (4) is added to complete the design of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens.

9. The design method of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens according to claim 8, characterized in that: In step 3, each lens in the initial structure of the transmission light path is a biconvex lens with equal curvature, and the lens material is a staggered arrangement of crown glass and flint glass. The initial thickness and initial spacing of the lenses are equal, and the initial diameter-thickness ratio is in the range of 3 to 8. During iterative optimization, the focal length, back intercept, image telecentricity, distortion, air gap between the center and edge of the lens, center and edge thickness of the lens, and diameter-thickness ratio of the optical system are controlled, and the lens material is optimized using a hammer optimization method. After gradual iterative optimization, the transmission light path is obtained.

10. An imaging system, characterized in that: The ultra-wide-angle free-form surface catadioptric image-space telecentric lens, the relay system, and the camera electronics module according to any one of claims 1 to 7; The relay system is installed at the rear end of the transmission light path in the ultra-wide-angle free-form surface catadioptric image-space telecentric lens, and the object plane of the relay system is the image plane of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens; The camera electronics module is located at the rear end of the relay system, and the photosensitive surface of the camera electronics module is the image plane of the relay system.

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