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

Abstract

The invention provides an ultra-wide-angle free-form surface catadioptric image space telecentric lens, a design method thereof and an imaging system, which are used for solving the technical problem that an existing ultra-wide-angle lens is generally a transmission-type lens and is difficult to observe plasmas in an environment with a relatively large temperature difference. According to the ultra-wide-angle free-form surface catadioptric image space telecentric lens, the high-temperature environment during observation of plasmas in a Tokamak device is fully considered, the reflection light path is innovatively added, the lens is divided into the aperture diaphragm, the reflection light path and the transmission light path, the aperture diaphragm and the reflection light path are made of metal materials, and the transmission light path is made of metal materials. The device is arranged in a high-temperature vacuum chamber between a first observation window and a second observation window of a Tokamak device, and each lens in a transmission light path is made of a traditional lens material and is arranged in an external room-temperature environment. The whole ultra-wide-angle free-form surface catadioptric image space telecentric lens can stably observe plasma when the Tokamak device works.

Description

Technical Field

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

[0002] The ultra-wide-angle lens has the advantages of short focal length and wide viewing angle. Its depth of field is significantly greater than that of standard lenses and telephoto lenses, and it can capture a wide range of scenes at a relatively close distance. The ultra-wide-angle visible light camera is an important diagnostic tool for monitoring the shape and position of the plasma inside the tokamak device. The tokamak device is an annular container that uses magnetic confinement to achieve controlled nuclear fusion. Its first wall serves as the boundary for confining the internal plasma. There is usually a vacuum chamber between the first wall and the outer wall of the device, which is used to set the component materials facing the plasma. When the tokamak device is in operation, a large amount of high-energy particles and high-energy radiation will overflow from the edge area of ​​the first wall. The large heat load and radiation dose may cause the component materials facing the plasma to melt or corrode. In order to observe the plasma in the tokamak device, a first observation window is provided on the first wall of the tokamak device, and a second observation window is provided at a corresponding position on the outer wall. In the prior art, when observing plasma, an ultra-wide-angle visible light camera is usually fixed to the end of a stainless steel tube in the outer shielding wall, and then connected to the second observation window on the outer wall of the tokamak device through the stainless steel tube to perform ultra-wide-angle imaging of the plasma inside the tokamak device. However, the problem with this method is that the ultra-wide-angle visible light camera will be subject to strong electromagnetic interference and high-dose radiation from high-energy particles and X-rays, which may cause malfunction or even damage, especially when the plasma discharge is interrupted.

[0003] At present, in order to further protect the imaging chip and other electronic components of the ultra-wide-angle visible light camera from the influence of the radiation environment, a long-distance relay system can be used to transmit the imaging of the plasma by the ultra-wide-angle lens to the outside of the shielding wall of the tokamak device, and the electronic part of the camera is set outside the shielding wall, so as to achieve "optical-mechanical-electrical" separation in space. This long-distance relay system generally requires the front ultra-wide-angle lens to have the characteristics of image telecentricity, so as to facilitate the docking of the long-distance relay system and the ultra-wide-angle lens, and requires a large adjustment position tolerance between the two to facilitate engineering implementation. However, since the temperature between the first observation window of the first wall of the tokamak device and the second observation window of the outer wall can usually reach 200°C, and the existing ultra-wide-angle lens is usually a transmission lens, the refractive index of the glass material used in the transmission lens will change with the temperature, and the thermal expansion coefficient and the structural material are quite different, which is difficult to meet the needs of observing plasma in an environment with a large temperature difference. Therefore, how to stably observe plasma with an ultra-wide-angle lens in a wide temperature range (20°C-200°C) is an urgent problem to be solved in the industry. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that the existing ultra-wide-angle lens is usually a transmission lens and it is difficult to observe plasma in an environment with a large temperature difference, 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 reflecting optical path comprises a primary reflecting mirror, a secondary reflecting mirror and a folding mirror; the reflecting surfaces of the primary reflecting mirror and the secondary reflecting mirror 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 outgoing light of the detected plasma;

[0011] The aperture diaphragm, the primary reflector, the secondary reflector, the 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 diaphragm 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] The light of the detected plasma enters from the aperture diaphragm through the first observation window on the first wall of the tokamak device, and the incident light is reflected by the primary reflector and the secondary reflector in sequence and reaches the surface of the folding mirror. The folding mirror adjusts the direction of the light reflected by the secondary reflector. The light after the direction adjustment by the folding mirror reaches the transmission light path after passing through the second observation window on the outer wall of the tokamak device, and converges on the image plane after passing through the transmission light path.

[0013] The aperture stop, the primary reflector, the secondary reflector, the folding mirror and the transmission light path are respectively provided with supporting 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 surfaces, and the front and rear surfaces of the attenuation filter are all flat surfaces.

[0017] Further, 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, each lens and the attenuation filter are respectively provided with a supporting structure;

[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] Further, 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-order terms of x and are symmetric 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 reflection light path with a primary reflector and a secondary reflector as spherical surfaces by trial and error; adjust the relative positions of the aperture stop, the primary reflector and the secondary reflector, and the curvature radii of the primary reflector and the secondary reflector. When the divergence angle of light within a large field of view angle is significantly reduced to a preset requirement after passing through the constructed reflection light path, use the current reflection light path structure as the initial structure of the reflection light path.

[0027] Step 2: On the basis of the initial structure of the reflected light path, gradually increase the cone coefficients of the primary reflector and the secondary reflector 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 reflected light path is quasi-parallel light. The preliminary iterative optimization of the primary reflector and the secondary reflector is completed, and the free-form surface off-axis two-reflection light path is obtained;

[0028] Step 3, constructing an initial structure of the transmission light path by a direct construction method, and connecting 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 optimizing 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 axis mirror to complete the design of the ultra-wide-angle free-form surface catadioptric image-side telecentric lens.

[0031] Furthermore, in step 3, each lens in the initial structure of the transmission light path is selected as a biconvex lens with equal curvature, the lens material is selected in 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 spacing between the center and edge of the lens, the center and edge thickness of the lens, and the diameter-thickness ratio of the optical system are controlled, and the material of the lens is optimized by 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] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens provided by the present invention 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 a first observation window of the tokamak device and a second observation window on the outer wall. Each lens in the transmission light path is made of traditional lens materials and is arranged in a room temperature environment outside the tokamak device. The ultra-wide-angle free-form surface catadioptric image-space telecentric lens as a whole can achieve stable observation of plasma when the tokamak device is working, which 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 light path of the present invention are designed as free-form surfaces. Compared with traditional spherical or aspherical reflector surfaces, they have more degrees of freedom in optical design optimization, improve the correction capability of 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 and secondary reflector in the present invention and their supporting structure are made of the same metal material, which is easy to achieve athermalization, 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 terms of x, 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 diaphragm, and there is no need to open a hole on the reflective lens to set the diaphragm, 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-side telecentric lens. The initial structure of the reflected light path is constructed and optimized by a trial and error method, and the initial structure of the transmitted light path is constructed and optimized by a direct construction method. Then, a joint optimization is performed to complete the design. The method is simple and 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 It is a side view of an embodiment of the ultra-wide-angle free-form surface catadioptric image-space telecentric lens of the present invention 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 It is a design full-field spot diagram of the embodiment of the present invention in working state;

[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 It is a schematic diagram of the initial structure of the reflection 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. Axis folding 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 works in the visible light band and is used to observe the plasma inside the tokamak device. Considering that the vacuum chamber between the first observation window of the first wall and the second observation window of the outer wall of the tokamak device is a high-temperature environment, the present invention divides the ultra-wide-angle lens into two parts, the front part is arranged in the high-temperature vacuum chamber, and the rear part is arranged outside the tokamak device. Since the reflector can be made of metal material, and the reflector made of metal material has the characteristic of high temperature resistance, the present invention adopts a catadioptric lens configuration for the front part of the lens arranged in the high-temperature vacuum chamber; and since the area outside the tokamak device has reached room temperature, the rear part can use multiple transmissive lenses to correct the aberration of the large field of view and the chromatic aberration in 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 reflection light path, and a transmission light path. The aperture stop 1 is a physical stop, which is located behind the first observation window on the first wall of the tokamak device and at the front of the entire optical lens. The reflection light path includes three reflectors, namely the main reflector 2, the secondary reflector 3, and the folding mirror 4, wherein the main reflector 2 and the secondary reflector 3 constitute an off-axis two-reflection optical system. The transmission light path includes multiple lenses and an attenuation filter 9. In this embodiment, the number of lenses is eight, which are respectively recorded 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 outgoing light of the detected plasma for observing the plasma inside the tokamak device.

[0057] The aperture stop 1, the primary reflector 2, the secondary reflector 3, and the folding mirror 4 are located in a vacuum chamber between the first wall and the outer wall of the tokamak device, wherein the aperture stop 1 faces the first observation window, and the reflected light of the folding mirror 4 faces the second observation window, and is used to make the light of the detected plasma incident on the surface of the primary reflector 2 through the first observation window. Since the aperture stop 1 and the reflected light path are arranged in a high temperature environment of the vacuum chamber, stable imaging is required at a high temperature of 200°C, so the aperture stop 1, the primary reflector 2, the secondary reflector 3, and the 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] In addition, in order to connect with the relay system, the ultra-wide-angle lens is usually required to have good image telecentricity and low distortion. Since the metal reflector can be processed into a non-rotationally symmetrical surface by turning, the reflecting surface of the primary reflector 2 and the secondary reflector 3 can be processed into a free-form surface, and the light can be regulated by using its multi-degree-of-freedom characteristics, so that the entire ultra-wide-angle lens has the characteristics of image telecentricity and low distortion. The folding mirror 4 is a flat surface, which is used to adjust the light output direction of the lens optical path according to the spatial layout of the tokamak device.

[0059] In this embodiment, the surface shapes of the primary reflector 2 and the secondary reflector 3 are described by a 9th-order extended polynomial, which only includes even-order terms of x, is symmetrical about the YOZ plane, and has a total of 29 terms, which is feasible for processing and detection. The single-point diamond lathe can be used to perform ultra-precision processing on the aluminum alloy blank to obtain the surface shape of the extended polynomial, and the laser interferometer and CGH can be used to perform high-precision detection of the surface shape of the extended polynomial. The expression of the extended polynomial is as follows:

[0060]

[0061] In the formula, 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 cone 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 the light emitted from the reflection light path on the image plane. 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 of the transmission light path are located outside the tokamak device, and the first lens 5 is directly opposite the second observation window. Since each lens in the transmission light path only needs to form an image at room temperature, a conventional lens material with stable performance, such as optical glass material or crystal, etc., can be selected, and the attenuation filter 9 can be selected from conventional fused quartz or K9 glass materials. The structural support members of each lens and the attenuation filter 9 can be made of aluminum alloy to achieve stable support. At the same time, the front and rear surfaces of the eight lenses are all spherical surfaces, and the front and rear surfaces of the attenuation filter 9 are all plane surfaces. Between the reflection light path and the transmission light path is the second observation window on the outer wall of the tokamak device, and the front and rear surfaces of the second observation window are all plane surfaces, which are used to allow the light reflected by the folding mirror 4 to be incident on the surface of the first lens 5 through the second observation window.

[0065] The light of the detected plasma is incident from the aperture diaphragm 1 through the first observation window on the first wall of the tokamak device, and 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. After the folding mirror 4 adjusts the direction of the light reflected by the secondary reflector 3, it reaches the first lens 5 through the second observation window on the outer wall of the tokamak device, and is 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, and 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 is a circular aperture with a diameter of Φ66mm, a flat surface on both the front and rear surfaces, a thickness of 10mm, and a material of fused quartz. The distance between the second sealed window and the single lens one is 16.628mm. Therefore, the optical parameters of each optical component 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 radius of curvature of -120.327 mm, a cone coefficient of -0.43, an eccentricity of 44.655 mm in the Y direction, an inclination of -20.791° in the X direction, 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 a diameter of 88mm×60mm, a thickness of 10mm, a curvature radius of -150.881mm, a cone coefficient of -0.908, an eccentricity in the Y direction of 83.857mm, an inclination in the X direction of 10.272°, and a spacing of 125mm between the secondary reflector 3 and the off-axis mirror 4.

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

[0072] The first lens 5 is a circular aperture with a diameter of Φ62mm, a front surface curvature radius of 168.849mm, a rear surface curvature radius of -289.981mm, a thickness of 8.201mm, and a material of Chengdu Guangming's H-ZK8. The interval between the first lens 5 and the second lens 6 is 16.66mm.

[0073] The second lens 6 is a circular aperture with a diameter 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 interval 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 interval between the third lens 7 and the fourth lens 8 is 2.502mm.

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

[0076] The attenuation filter 9 has a circular aperture with a diameter 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 interval 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 interval between the eighth lens 13 and the image plane is 12.85 mm.

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

[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 the present 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, it is a designed modulation transfer function curve diagram of this embodiment. 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, it is a schematic diagram of grid distortion designed in this embodiment. 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 the reflection light path with the main reflector 2 and the secondary reflector 3 as spherical surfaces through trial and error. During the construction, it is necessary to ensure that the aperture stop 1, the main reflector 2 and the secondary reflector 3 do not block the light within the wide field of view angle range and there is no obstruction between the three. Adjust the relative positions of the aperture stop 1, the main reflector 2 and the secondary reflector 3, as well as the curvature radii of the main 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 reflection light path, the current reflection light path structure is used as the initial structure of the reflection 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 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 having the two off-axis reflection paths of the free-form surface, 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 in the figure, each lens in the initial structure of the transmission light path uses equal curvature biconvex lenses, and the lens material uses crown glass and flint glass in a staggered arrangement. 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. 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 diameter-thickness ratio of the optical system, and optimizing the lens material by hammer optimization, the transmission light path is obtained after gradual iteration.

[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, add the folding mirror 4 according to the monitoring direction of the plasma to complete the design of the ultra-wide-angle free-form surface catadioptric image-side telecentric lens.

[0091] The present invention also provides an imaging system, which includes the above-mentioned 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 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, and the two need to completely overlap in space. 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, and the two also need to completely overlap in space.

[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 the field, the specific technical solution recorded in the above embodiment can be modified, or some of the technical features therein can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solution 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 in that: 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 curved 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 diaphragm (1), the primary reflector (2), the secondary reflector (3), the folding mirror (4), and the transmission light path are arranged in sequence on the light path of the light emitted by the detected plasma; The aperture diaphragm (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 diaphragm (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 diaphragm (1) through a first observation window on a first wall of the tokamak device, the incident light is reflected by a primary reflector (2) and a secondary reflector (3) in sequence, and then reaches 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 is adjusted by the folding mirror (4) passes through a second observation window on an outer wall of the tokamak device, and then 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 surfaces, and the front and rear surfaces of the attenuation filter (9) are all flat surfaces.

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 by extended polynomials, which only include even-order 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), 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), and 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 structure of the reflection light path; Step 2, based on the initial structure of the reflection light path, gradually increase the cone 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, and 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, constructing an initial structure of the transmission light path by a direct construction method, and connecting 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 optimizing 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, add the folding axis mirror (4) to complete the design of the ultra-wide-angle free-form surface catadioptric image-side 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 uses an equal curvature biconvex lens, the lens material uses 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 spacing between the center and edge of the lens, the center and edge thickness of the lens, and the diameter-thickness ratio of the optical system are controlled, and the hammer optimization method is used to optimize the lens material, and the transmission light path is obtained after gradual iterative optimization.

10. An imaging system, characterized in that: It comprises the ultra-wide-angle free-form surface catadioptric image-space telecentric lens, relay system and camera electronics module as described in 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.

Images