Large relative aperture large field of view solar blind ultraviolet optical system

Abstract

The application discloses a large-relative-aperture large-field-of-view solar-blind ultraviolet optical system, which comprises a lens set and a filter set, and the lens set comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and the filter set in sequence; the first lens, the second lens and the fourth lens are meniscus negative lenses, the third lens is a double-convex positive lens, the fifth lens is a double-convex positive lens, and the sixth lens is a meniscus positive lens; the F number of the solar-blind ultraviolet optical system is less than or equal to 2.0, and the full field of view FOV is greater than or equal to 110 degrees; and the filter set comprises at least one deep out-of-band cut-off filter. The aberration of the solar-blind ultraviolet optical system is reasonably corrected and balanced, the solar-blind ultraviolet optical system has the advantages of a 110-degree large field of view, a working waveband covering 250-275 nm, an F number less than or equal to 2.0, high detection sensitivity and the like, and the solar-blind ultraviolet optical system only comprises six spherical mirrors, so that the design and manufacturing costs are low.

Description

Technical Field

[0001] This invention relates to the field of photoelectric imaging detection, specifically to a solar-blind ultraviolet optical system with a large relative aperture and a large field of view. Background Technology

[0002] In the optical spectrum, the ultraviolet (UV) band is unique, primarily due to its high single-photon energy. When UV photons interact with matter, most of this energy is absorbed. Therefore, for the UV band, especially the solar-blind UV band of 240-280 nm, a common design approach is to use a reflective system. This involves using fused silica or microcrystalline glass as a substrate, fabricating a special surface with optical power, and then coating it with a high-reflectivity film to control the light. However, reflective systems suffer from drawbacks such as a small field of view and difficulty in assembly and adjustment. For transmission systems, the limited availability of suitable materials for the UV band (almost exclusively calcium fluoride and fused silica) and their low refractive index make it difficult to achieve both a large field of view and a large relative aperture. To achieve both, more complex lenses are typically required (increasing the number of lenses or introducing special surface types such as aspherical or diffractive surfaces), which significantly increases the design and manufacturing costs of the lens.

[0003] For example, the solar-blind ultraviolet camera products currently available on the market for high-voltage line leakage detection, fire flame detection, or other ultraviolet detection systems, while capable of solar-blind ultraviolet detection, are difficult to combine the characteristics of large relative aperture, large field of view, and high image uniformity. Summary of the Invention

[0004] The present invention provides a solar-blind ultraviolet optical system with a large relative aperture and a large field of view, with the aim of solving at least one problem existing in the prior art.

[0005] The technical solution provided by this invention is as follows:

[0006] A solar-blind ultraviolet optical system with a large relative aperture and a large field of view consists of a lens group and a filter group arranged sequentially and at intervals along the optical axis from the object side to the image side;

[0007] The lens group includes, in sequence, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens. The first lens is a meniscus negative lens, the second lens is a meniscus negative lens, the third lens is a biconvex positive lens, the fourth lens is a meniscus negative lens, the fifth lens is a biconvex positive lens, and the sixth lens is a meniscus positive lens.

[0008] The solar-blind ultraviolet optical system has an F-number ≤ 2.0 and a field of view (FOV) ≥ 110°.

[0009] The filter group includes at least one deep out-of-band cutoff filter, which has high transmittance in the 250nm-270nm range.

[0010] Furthermore, the air gap between the first lens and the second lens is 10mm~13mm;

[0011] The air gap between the second lens and the third lens is 19mm~21mm;

[0012] The air gap between the third lens and the fourth lens is 17mm~18mm;

[0013] The air gap between the fourth lens and the fifth lens is 1.5~2.2mm;

[0014] The air gap between the fifth lens and the sixth lens is 0.1mm to 0.5mm.

[0015] Furthermore, the first to third lenses together form a front lens group with negative optical power; the fourth to sixth lenses together form a rear lens group with positive optical power.

[0016] Furthermore, in the front lens group, the focal lengths of the first lens, the second lens, and the third lens at 260nm are f1, f2, and f3, respectively, and f1, f2, and f3 satisfy: f1∈(-60,-48), f2∈(-42,-35), f3∈(47,52).

[0017] Furthermore, in the rear lens group, the focal lengths of the fourth lens, the fifth lens, and the sixth lens at 260nm are f4, f5, and f6, respectively, and f4, f5, and f6 satisfy: f4∈(-227,-150), f5∈(32,35), f6∈(47,66).

[0018] Furthermore, the deep-band out-of-band cutoff filter uses fused silica as a substrate and deposits multiple optical interference films on the fused silica substrate. The single-piece cutoff rate of the deep-band out-of-band cutoff filter is better than OD3. According to the application scenario requirements, the out-of-band cutoff rate of the entire system can be greatly improved by stacking multiple filters.

[0019] Furthermore, an aperture stop is provided in the optical path between the third lens and the fourth lens, and the air gap between the aperture stop and the fourth lens is 0.12mm~0.18mm.

[0020] Furthermore, it also includes a high-sensitivity detector, wherein the lens group, the filter group, and the high-sensitivity detector are coaxially distributed from the object side to the image side.

[0021] Furthermore, it also includes a detector window glass, which is disposed in front of the detector's photosensitive surface.

[0022] Furthermore, the first, third, and fourth lenses are made of fused silica; the fifth and sixth lenses are made of calcium fluoride; and the second lens is made of calcium fluoride or fused silica.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The large relative aperture and wide field of view solar-blind ultraviolet optical system provided by this invention adopts a reverse telephoto structure, namely, a front negative lens that compresses the field of view and a rear positive lens that converges light rays. This structure has a relatively long back intercept, which is beneficial for placing filters and other structural components in front of the image. The aberrations of this solar-blind ultraviolet optical system are reasonably corrected and balanced. This solar-blind ultraviolet optical system has a 110° wide field of view, a working wavelength covering 250-275nm, and an F-number ≤2.0. This solar-blind ultraviolet optical system possesses a wide field of view not found in commercially available similar solar-blind ultraviolet cameras, and experiments have shown that it can detect radiation intensity of 1×10⁻⁶. 8 The system emits weak radiation of photons per second, has high detection sensitivity, and the solar-blind ultraviolet optical system consists of only six spherical mirrors, resulting in low design and manufacturing costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a solar-blind ultraviolet optical system with a large relative aperture and a large field of view in one embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of a solar-blind ultraviolet optical system with a large relative aperture and a large field of view in another embodiment of the present invention;

[0027] Figure 3 This is an image quality evaluation result diagram of a solar-blind ultraviolet optical system with a large relative aperture and large field of view in an embodiment of the present invention;

[0028] Figure 4 This is a light spot energy envelope curve of a solar-blind ultraviolet optical system with a large relative aperture and large field of view in an embodiment of the present invention.

[0029] The attached figures are labeled as follows:

[0030] 1-First lens, 2-Second lens, 3-Third lens, 4-Fourth lens, 5-Fifth lens, 6-Sixth lens, 7-Filter group, 8-Detector window glass, 9-High-sensitivity detector. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Therefore, the detailed description of the embodiments of this application provided below with reference to the accompanying drawings is intended merely to illustrate selected embodiments of this application and is not intended to limit the scope of protection claimed by this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0033] It should be understood that in the description of embodiments of the present invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of the stated features.

[0034] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0035] In the optical spectrum, the ultraviolet (UV) band is unique due to its high single-photon energy. When UV photons interact with matter, most of their energy is absorbed. Therefore, a common design approach for the UV band is to use a reflective system. This involves using fused silica or microcrystalline glass as a substrate, fabricating a special surface with optical power, and then coating it with a highly reflective film to control the light. However, reflective systems suffer from drawbacks such as a small field of view and difficulty in assembly and adjustment, thus preventing the achievement of a 110° field of view detection requirement.

[0036] The function of an ultraviolet lens is to maximize light collection and imaging of a target. Therefore, the light collection capability of the optical system is a crucial indicator. In an imaging system, the image plane illuminance is proportional to the square of the aperture. Furthermore, the image plane illuminance of an optical system has a cosine fourth power relationship with the field of view; that is, the larger the field of view, the lower the edge illuminance. The aperture and field of view of an optical system are a pair of contradictory quantities, both of which are positively correlated with the system's information collection capability. In other words, increasing both the aperture and the field of view simultaneously inevitably increases the system's complexity.

[0037] See Figure 1 The present invention provides a solar-blind ultraviolet optical system with a large relative aperture and a large field of view, consisting of a lens group and a filter group 7 arranged sequentially and at intervals along the optical axis from the object side to the image side.

[0038] The lens group consists of a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, and a sixth lens 6. The first lens 1 is a meniscus negative lens, the second lens 2 is a meniscus negative lens, the third lens 3 is a biconvex positive lens, the fourth lens 4 is a meniscus negative lens, the fifth lens 5 is a biconvex positive lens, and the sixth lens 6 is a meniscus positive lens.

[0039] This large relative aperture, large field of view solar-blind ultraviolet optical system has an F-number ≤ 2.0 and a full field of view FOV ≥ 110°.

[0040] The filter group 7 includes at least one deep-band out-of-band cutoff filter, which has high transmittance in the 250nm-270nm range.

[0041] Optionally, the air gap between the first lens 1 and the second lens 2 is 10mm~13mm, the air gap between the second lens 2 and the third lens 3 is 19mm~21mm, the air gap between the third lens 3 and the fourth lens 4 is 17mm~18mm, the air gap between the fourth lens 4 and the fifth lens 5 is 1.5~2.2mm, and the air gap between the fifth lens 5 and the sixth lens 6 is 0.1mm~0.5mm.

[0042] Specifically, the air gap between the first lens 1 and the second lens 2 can be set to 11.16 mm, the air gap between the second lens 2 and the third lens 3 can be set to 20 mm, the air gap between the third lens 3 and the fourth lens 4 can be set to 17.43 mm, the air gap between the fourth lens 4 and the fifth lens 5 can be set to 1.9 mm, and the air gap between the fifth lens 5 and the sixth lens 6 can be set to 0.3 mm.

[0043] With the object side in front and the image side in back, the front radius of curvature of the first lens 1 is 220 mm, and the rear radius of curvature of the first lens 1 is 23.46 mm; the front radius of curvature of the second lens 2 is 111.28 mm, and the rear radius of curvature of the second lens 2 is 15.70 mm; the front radius of curvature of the third lens 3 is 41.70 mm, and the rear radius of curvature of the third lens 3 is 54.08 mm; the front radius of curvature of the fourth lens 4 is 22.97 mm, and the rear radius of curvature of the fourth lens 4 is 16.90 mm; the front radius of curvature of the fifth lens 5 is 30.60 mm, and the rear radius of curvature of the fifth lens 5 is 29.60 mm; the front radius of curvature of the sixth lens 6 is 17.30 mm, and the rear radius of curvature of the sixth lens 6 is 63.23 mm.

[0044] The first lens 1 has an effective aperture of 60 mm and a thickness of 7.00 mm; the second lens 2 has an effective aperture of 36 mm and a thickness of 6.00 mm; the third lens 3 has an effective aperture of 25 mm and a thickness of 7.00 mm; the fourth lens 4 has an effective aperture of 15 mm and a thickness of 3.00 mm; the fifth lens 5 has an effective aperture of 18 mm and a thickness of 6.00 mm; and the sixth lens 6 has an effective aperture of 20 mm and a thickness of 5.29 mm.

[0045] Optionally, the first lens 1, the second lens 2, and the third lens 3 form a front lens group with negative optical power, and the fourth lens 4, the fifth lens 5, and the sixth lens 6 form a rear lens group with positive optical power.

[0046] Optionally, in the front lens group, the focal lengths of the first lens 1, the second lens 2 and the third lens 3 at 260nm are f1, f2 and f3 respectively, and f1, f2 and f3 satisfy: f1∈(-60,-48), f2∈(-42,-35), f3∈(47,52).

[0047] Optionally, in the rear lens group, the focal lengths of the fourth lens 4, the fifth lens 5, and the sixth lens 6 at 260nm are f4, f5, and f6, respectively, and f4, f5, and f6 satisfy: f4∈(-227,-150), f5∈(32,35), f6∈(47,66).

[0048] By rationally allocating the optical power of the optical system formed by the present invention according to the above proportions, and ensuring that each lens is in a certain proportion relative to the system focal length f, the aberrations of the optical system formed by the present invention are reasonably corrected and balanced.

[0049] Optionally, the filter group 7 includes one deep out-of-band cutoff filter or a combination of multiple deep out-of-band cutoff filters. All deep out-of-band cutoff filters are based on fused silica, and multiple optical interference films (such as multilayer films of HfO2 and SiO2) are deposited on the fused silica substrate. The cutoff rate of each deep out-of-band cutoff filter is better than OD3. Depending on the application scenario requirements, the out-of-band cutoff rate of the entire system can be greatly improved by stacking multiple filters.

[0050] Because a small amount of solar-blind radiation exists in the atmospheric background, a deep cutoff ratio filter is needed to filter the background. Research shows that when the filter cutoff depth is better than OD6, it can respond well to the target intensity. The filter group 7 provided in this application has a single-piece cutoff ratio better than OD6, and uses coated interference to achieve high suppression ratio characteristics, with a transmittance exceeding 35% in the 250nm-270nm range.

[0051] Optionally, an aperture stop is provided in the optical path between the third lens 3 and the fourth lens 4, and the air gap between the aperture stop and the fourth lens 4 is 0.12mm~0.18mm. In this embodiment, the air gap between the aperture stop and the fourth lens 4 can be set to 0.15mm. The diameter of the aperture stop can be set to 13mm.

[0052] Optionally, this large relative aperture, large field-of-view solar-blind ultraviolet optical system also includes a highly sensitive detector 9, such as an image detector, etc. Figure 2 As shown, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the filter group 7, and the high-sensitivity detector 9 are coaxially distributed from the object side to the image side. The high-sensitivity detector 9 includes, but is not limited to, back-illuminated thinned CMOS, resistive anode detector, capacitive anode detector, image intensifier, electron bombardment active pixel sensor (EBAPS), etc.

[0053] like Figure 2 As shown, the large relative aperture and large field of view solar-blind ultraviolet optical system also includes a detector window glass 8, which is disposed in front of the photosensitive area of ​​the high-sensitivity detector 9.

[0054] Optionally, the first lens 1, the third lens 3, and the fourth lens 4 are made of fused silica; the fifth lens 5 and the sixth lens 6 are made of calcium fluoride; and the second lens 2 is made of calcium fluoride or fused silica.

[0055] Figure 3 , Figure 4 A schematic diagram illustrating the image quality evaluation results of this system, through Figure 3 , Figure 4 It can be seen that the system has good image plane uniformity and high detection sensitivity.

[0056] In summary, the large relative aperture, large field of view solar-blind ultraviolet optical system provided by this invention adopts a reverse telephoto structure, namely, a front negative lens that compresses the field of view and a rear positive lens that converges light rays. This structure has a relatively long back intercept, which is beneficial for placing filters and other structural components in front of the image. Through aberration theory analysis and damped least squares optimization design, the final result is as follows: Figure 1 The image shows a solar-blind ultraviolet optical system composed of six lenses. This system features well-corrected and balanced aberrations, a wide field of view of 110°, an operating wavelength range of 250-275nm, and an F-number ≤2.0. This wide field of view is unmatched by other commercially available solar-blind ultraviolet cameras of its type, and experiments have shown that it can detect radiation intensities of 1×10⁻⁶. 8 The system emits weak radiation of photons per second, has high detection sensitivity, and the solar-blind ultraviolet optical system consists of only six spherical mirrors, resulting in low design and manufacturing costs.

[0057] The above description is merely the preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A solar-blind ultraviolet optical system with a large relative aperture and a large field of view, characterized in that, It consists of a lens group and a filter group arranged at intervals along the optical axis from the object side to the image side; The lens group comprises, in sequence, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, with a total of six lenses. The first lens is a meniscus negative lens, the second lens is a meniscus negative lens, the third lens is a biconvex positive lens, the fourth lens is a meniscus negative lens, the fifth lens is a biconvex positive lens, and the sixth lens is a meniscus positive lens. The first lens has a convex object-side surface and a concave image-side surface; the second lens has a convex object-side surface and a concave image-side surface; the fourth lens has a convex object-side surface and a concave image-side surface; and the sixth lens has a convex object-side surface and a concave image-side surface. The first to third lenses constitute a front lens group with negative optical power, and the fourth to sixth lenses constitute a rear lens group with positive optical power. In the front lens group, the focal lengths of the first, second, and third lenses at 260nm are f1, f2, and f3, respectively, and f1, f2, and f3 satisfy the following: f1∈(-60mm,-48mm), f2∈(-42mm,-35mm), f3∈(47mm,52mm); In the rear lens group, the focal lengths of the fourth lens, the fifth lens, and the sixth lens at 260nm are f4, f5, and f6, respectively, and f4, f5, and f6 satisfy: f4∈(-227mm,-150mm), f5∈(32mm,35mm), f6∈(47mm,66mm); The solar-blind ultraviolet optical system has an F-number ≤ 2.0 and a field of view (FOV) ≥ 110°. The filter group includes at least one deep out-of-band cutoff filter, which has high transmittance in the 250nm-270nm range.

2. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 1, characterized in that, The air gap between the first lens and the second lens is 10mm~13mm; The air gap between the second lens and the third lens is 19mm~21mm; The air gap between the third lens and the fourth lens is 17mm~18mm; The air gap between the fourth lens and the fifth lens is 1.5~2.2mm; The air gap between the fifth lens and the sixth lens is 0.1mm to 0.5mm.

3. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 1, characterized in that, The deep-band out-of-band cutoff filter uses fused silica as a substrate and deposits multiple optical interference films on the fused silica substrate. The cutoff rate of a single deep-band out-of-band cutoff filter is better than OD3. Depending on the application scenario requirements, the out-of-band cutoff rate of the entire system can be significantly improved by stacking multiple filters.

4. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 2, characterized in that, An aperture stop is provided in the optical path between the third lens and the fourth lens, and the air gap between the aperture stop and the fourth lens is 0.12mm~0.18mm.

5. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 1, characterized in that, It also includes a high-sensitivity detector, and the lens group, the filter group and the high-sensitivity detector are coaxially distributed from the object side to the image side.

6. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 5, characterized in that, It also includes a detector window glass, which is disposed in front of the light-sensitive area of ​​the high-sensitivity detector.

7. The large relative aperture, large field of view solar-blind ultraviolet optical system according to claim 1, characterized in that, The first, third, and fourth lenses are made of fused silica; the fifth and sixth lenses are made of calcium fluoride; and the second lens is made of calcium fluoride or fused silica.

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