Solar blind ultraviolet optical system with large relative aperture and large field of view

Abstract

The invention discloses a large-relative-aperture large-view-field solar blind ultraviolet optical system, which comprises a lens group and an optical filter group, and is characterized in that the lens group sequentially comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens, the optical filter group, the first lens, the second lens and the fourth lens are meniscus negative lenses, the third lens is a biconvex positive lens, the fifth lens is a biconvex positive lens, and the sixth lens is a biconvex positive lens. The fifth lens is a biconvex 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 angle FOV is greater than or equal to 110 degrees; the optical filter group comprises at least one deep out-of-band cut-off optical 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 110-degree large field of view, working wave band coverage of 250-275nm, 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 and is low in design and manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic imaging detection, and particularly to a solar-blind ultraviolet optical system with a large relative aperture and a large field of view. Background Art

[0002] In the optical band, the ultraviolet optical band is relatively special. Specifically, its single-photon energy is relatively high. When it interacts with matter, most of the photon energy will be absorbed by the matter. Therefore, for the ultraviolet band, especially for the solar-blind ultraviolet band of 240 - 280 nm, the generally common design method is to use a reflective system, that is, using fused silica or glass-ceramics as the substrate, processing a special surface shape with optical power, and coating a high-reflection film layer on this basis to achieve the control of light. However, the reflective system has disadvantages such as a small field of view and difficult alignment. For a transmissive system, due to the small number of materials suitable for the ultraviolet band (almost only calcium fluoride and fused silica) and low refractive index, it is very difficult to balance a large field of view and a large relative aperture. In order to balance a large field of view and a large relative aperture, the lens generally needs to be complicated (increasing the number of lenses or introducing special surface shapes such as aspherical surfaces and diffractive surfaces), which will significantly increase the design and manufacturing costs of the lens.

[0003] For example, the existing off-the-shelf solar-blind ultraviolet cameras used for high-voltage line leakage detection, fire flame detection, or other ultraviolet detection systems on the market can perform solar-blind ultraviolet detection, but it is difficult to have the characteristics of a large relative aperture, a large field of view, and high image plane 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, aiming to solve at least one problem existing in the prior art.

[0005] The technical solution provided by the present invention is as follows: A solar-blind ultraviolet optical system with a large relative aperture and a large field of view, comprising a lens group and a filter group arranged at intervals in sequence from the object side to the image side along the optical axis; The lens group successively includes 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; The F number of the solar-blind ultraviolet optical system ≤ 2.0, and the full field of view angle FOV ≥ 110°; The filter group includes at least one deep band-out cutoff filter, and the deep band-out cutoff filter has a high transmittance at 250 nm - 270 nm.

[0006] Further, the air gap between the first lens and the second lens is 10 mm to 13 mm; the air gap between the second lens and the third lens is 19 mm to 21 mm; the air gap between the third lens and the fourth lens is 17 mm to 18 mm; the air gap between the fourth lens and the fifth lens is 1.5 to 2.2 mm; the air gap between the fifth lens and the sixth lens is 0.1 mm to 0.5 mm.

[0007] Further, the first lens to the third lens together form a front lens group with a negative optical power; the fourth lens to the sixth lens together form a rear lens group with a positive optical power.

[0008] Further, in the front lens group, the focal lengths of the first lens, the second lens, and the third lens at 260 nm are f1, f2, and f3 respectively, and f1, f2, f3 satisfy: f1 ∈ (-60, -48), f2 ∈ (-42, -35), f3 ∈ (47, 52).

[0009] Further, in the rear lens group, the focal lengths of the fourth lens, the fifth lens, and the sixth lens at 260 nm are f4, f5, and f6 respectively, and f4, f5, f6 satisfy: f4 ∈ (-227, -150), f5 ∈ (32, 35), f6 ∈ (47, 66).

[0010] Further, the deep band - out cut - off filter is based on fused silica, and multiple layers of optical interference films are deposited on the fused silica substrate. The single - sheet cut - off rate of the deep band - out cut - off filter is better than OD3. According to the application scenario requirements, the out - of - band cut - off rate of the entire system can be greatly improved by stacking multiple sheets.

[0011] Further, a diaphragm is provided on the optical path between the third lens and the fourth lens, and the air gap between the diaphragm and the fourth lens is 0.12 mm to 0.18 mm.

[0012] Further, it further 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.

[0013] Further, it further includes a detector window glass, and the detector window glass is arranged in front of the detector's photosensitive surface.

[0014] Further, the materials of the first lens, the third lens, and the fourth lens are fused silica; the materials of the fifth lens and the sixth lens are calcium fluoride; the material of the second lens is calcium fluoride or fused silica.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The solar-blind ultraviolet optical system with a large relative aperture and a large field of view provided by the present invention adopts a retrofocus structure, that is, the front negative lens group compresses the field of view angle, and the rear positive lens group converges the light. This structure has a longer back intercept, which is beneficial to placing structural components such as filter in front of the image plane. The aberrations of the solar-blind ultraviolet optical system are reasonably corrected and balanced. The solar-blind ultraviolet optical system has a large field of view of 110°, the working band covers 250 - 275 nm, and the F number ≤ 2.0. The solar-blind ultraviolet optical system has a large field of view that is not available in the off-the-shelf products of the same type of solar-blind ultraviolet cameras on the market, and through experiments, it can detect weak radiation with a radiation intensity of 1×10 8 photons / s, with high detection sensitivity. Moreover, the solar-blind ultraviolet optical system only includes six spherical mirrors, and the design and manufacturing costs are low. Description of the Drawings

[0016] Figure 1 is a schematic structural diagram of the solar-blind ultraviolet optical system with a large relative aperture and a large field of view in one embodiment of the present invention; Figure 2 is a schematic structural diagram of the solar-blind ultraviolet optical system with a large relative aperture and a large field of view in another embodiment of the present invention; Figure 3 is an image quality evaluation result diagram of the solar-blind ultraviolet optical system with a large relative aperture and a large field of view in an embodiment of the present invention; Figure 4 is a spot energy envelope curve diagram of the solar-blind ultraviolet optical system with a large relative aperture and a large field of view in an embodiment of the present invention.

[0017] The reference numerals are as follows: 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 Embodiments

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the embodiments described below are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations. Accordingly, the detailed description of the embodiments of the present application provided below in conjunction with the accompanying drawings is only intended to represent selected embodiments of the present application and does not limit the scope of protection required by the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0019] It should be understood that in the description of the embodiments of the present invention, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of the said features.

[0020] In the description of the embodiments of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "arranged", "installed", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection, or a connection that can communicate with each other; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0021] In the optical band, the ultraviolet optical band is relatively special, specifically in that its single-photon energy is relatively high. When it interacts with matter, most of the photon energy will be absorbed by the matter. Therefore, for the ultraviolet band, the generally common design method is to adopt a reflective system, that is, using fused silica or glass-ceramics as the substrate, processing a special surface shape with a focal power, and coating a high-reflection film layer thereon to achieve the regulation of light. However, the reflective system has disadvantages such as a small field of view and difficult alignment, so it cannot meet the detection requirements of a 110° field of view angle.

[0022] The function of the ultraviolet lens is to collect light from the target to the greatest extent and perform imaging detection. Therefore, the light collection ability of the optical system is an important indicator. In the imaging system, the image plane illuminance is proportional to the square of the aperture. In addition, there is a fourth-power relationship of cos between the image plane illuminance of the optical system and the field of view angle, that is, the larger the field of view angle, the lower the edge illuminance. The aperture and the field of view of the optical system are a pair of contradictory quantities, and both of these quantities are positively correlated with the system information collection ability. That is to say, when the aperture and the field of view increase simultaneously, the system complexity will inevitably increase.

[0023] Referring to Figure 1 , the present invention provides a solar-blind ultraviolet optical system with a large relative aperture and a large field of view, which includes a lens group and a filter group 7 arranged at intervals in sequence from the object side to the image side along the optical axis.

[0024] The lens group sequentially includes 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.

[0025] The F number of the solar-blind ultraviolet optical system with a large relative aperture and a large field of view is ≤ 2.0, and the full field of view angle FOV ≥ 110°.

[0026] The filter group 7 includes at least one deep out-of-band cutoff filter, and the deep out-of-band cutoff filter has a high transmittance at 250 nm - 270 nm.

[0027] Optionally, the air gap between the first lens 1 and the second lens 2 is 10 mm to 13 mm, the air gap between the second lens 2 and the third lens 3 is 19 mm to 21 mm, the air gap between the third lens 3 and the fourth lens 4 is 17 mm to 18 mm, the air gap between the fourth lens 4 and the fifth lens 5 is 1.5 to 2.2 mm, and the air gap between the fifth lens 5 and the sixth lens 6 is 0.1 mm to 0.5 mm.

[0028] 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.

[0029] With the object side in the front and the image side in the back, the front curvature radius of the first lens 1 is 220 mm, and the back curvature radius of the first lens 1 is 23.46 mm; the front curvature radius of the second lens 2 is 111.28 mm, and the back curvature radius of the second lens 2 is 15.70 mm; the front curvature radius of the third lens 3 is 41.70 mm, and the back curvature radius of the third lens 3 is 54.08 mm; the front curvature radius of the fourth lens 4 is 22.97 mm, and the back curvature radius of the fourth lens 4 is 16.90 mm; the front curvature radius of the fifth lens 5 is 30.60 mm, and the back curvature radius of the fifth lens 5 is 29.60 mm; the front curvature radius of the sixth lens 6 is 17.30 mm, and the back curvature radius of the sixth lens 6 is 63.23 mm.

[0030] The effective clear aperture of the first lens 1 is 60 mm, and its thickness is 7.00 mm; the effective clear aperture of the second lens 2 is 36 mm, and its thickness is 6.00 mm; the effective clear aperture of the third lens 3 is 25 mm, and its thickness is 7.00 mm; the effective clear aperture of the fourth lens 4 is 15 mm, and its thickness is 3.00 mm; the effective clear aperture of the fifth lens 5 is 18 mm, and its thickness is 6.00 mm; the effective clear aperture of the sixth lens 6 is 20 mm, and its thickness is 5.29 mm.

[0031] Optionally, the first lens 1, the second lens 2, and the third lens 3 together form a front lens group with a negative optical power, and the fourth lens 4, the fifth lens 5, and the sixth lens 6 together form a rear lens group with a positive optical power.

[0032] Optionally, in the front lens group, the focal lengths of the first lens 1, the second lens 2, and the third lens 3 at 260 nm are f1, f2, and f3 respectively, and f1, f2, and f3 satisfy: f1 ∈ (-60, -48), f2 ∈ (-42, -35), f3 ∈ (47, 52).

[0033] Optionally, in the rear lens group, the focal lengths of the fourth lens 4, the fifth lens 5, and the sixth lens 6 at 260 nm are f4, f5, and f6 respectively, and f4, f5, and f6 satisfy: f4 ∈ (-227, -150), f5 ∈ (32, 35), f6 ∈ (47, 66).

[0034] By reasonably distributing the optical power of the optical system formed by the present invention according to the above ratios, each lens forms a certain ratio relative to the system focal length f, so that the aberration of the optical system formed by the present invention is reasonably corrected and balanced.

[0035] Optionally, the filter group 7 includes a deep out-of-band cut-off filter or a combination of multiple deep out-of-band cut-off filters. All deep out-of-band cut-off filters are based on fused silica, and multiple layers of optical interference films (such as multi-layers of HfO2 and SiO2) are deposited on the fused silica substrate. The single-piece cut-off rate of each deep out-of-band cut-off filter is better than OD3. According to the requirements of the application scenario, the out-of-band cut-off rate of the entire system can be greatly improved by stacking multiple pieces.

[0036] Since there is a small amount of radiation in the solar-blind band in the atmospheric background, it is necessary to use a deep cut-off rate filter to filter the background. According to research, when the cut-off depth of the filter is better than OD6, it can better respond to the target intensity. The single-piece cut-off rate of the filter group 7 provided in this application is better than OD6, and the high rejection ratio characteristic is achieved by means of coating interference, and the transmittance in the range of 250 nm - 270 nm exceeds 35%.

[0037] Optionally, a diaphragm is disposed on the optical path between the third lens 3 and the fourth lens 4, and the air gap between the diaphragm and the fourth lens 4 is 0.12 mm to 0.18 mm. In this embodiment, the air gap between the diaphragm and the fourth lens 4 can be set to 0.15 mm. The diameter of the diaphragm can be set to 13 mm.

[0038] Optionally, the solar-blind ultraviolet optical system with a large relative aperture and a large field of view further includes a high-sensitivity detector 9, such as an image detector, such as 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, a back-illuminated thinned CMOS, a resistive anode detector, a capacitive anode detector, an image intensifier, an electron-bombarded active pixel sensor (EBAPS), etc.

[0039] As Figure 2 shown, the solar-blind ultraviolet optical system with a large relative aperture and a large field of view further includes a detector window glass 8, and the detector window glass 8 is disposed in front of the photosensitive surface of the high-sensitivity detector 9.

[0040] Optionally, the materials of the first lens 1, the third lens 3, and the fourth lens 4 are fused silica; the materials of the fifth lens 5 and the sixth lens 6 are calcium fluoride; the material of the second lens 2 is calcium fluoride or fused quartz.

[0041] Figure 3 、 Figure 4 is a schematic diagram of the image quality evaluation result of the system. Through Figure 3 、 Figure 4 it can be seen that the system has good image plane uniformity and high detection sensitivity.

[0042] In summary, the solar-blind ultraviolet optical system with a large relative aperture and a large field of view provided by the present invention adopts a retrofocus structure, that is, a front group of negative lenses compress the field of view angle, and a rear group of positive lenses converge light rays. This structure has a longer back intercept, which is beneficial to placing structural components such as filter films in front of the image plane. Through aberration theory analysis and damped least squares optimization design, a solar-blind ultraviolet optical system composed of six lenses as shown in Figure 1 is finally obtained. The aberrations of the solar-blind ultraviolet optical system are reasonably corrected and balanced. The solar-blind ultraviolet optical system has a large field of view of 110°, the working band covers 250 - 275 nm, and the F number ≤ 2.0. The solar-blind ultraviolet optical system has a large field of view that is not available in the same type of solar-blind ultraviolet camera off-the-shelf products on the market, and through experiments, it can detect weak radiation with a radiation intensity of 1×10 8 photons / s, with high detection sensitivity, and the solar-blind ultraviolet optical system only includes six spherical mirrors, with low design and manufacturing costs.

[0043] As described above, it is only the optimal specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims described above.

Claims

1. A solar-blind ultraviolet optical system with large relative aperture and large field of view, characterized in that: A lens group and a filter group are sequentially arranged from the object side to the image side along the optical axis; The lens group includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens in sequence, wherein the first lens is a negative meniscus lens, the second lens is a negative meniscus lens, the third lens is a biconvex positive lens, the fourth lens is a negative meniscus lens, the fifth lens is a biconvex positive lens, and the sixth lens is a positive meniscus lens; The solar-blind ultraviolet optical system has an F number of ≤2.0 and a full field of view FOV of ≥110°; The filter set includes at least one deep out-of-band cutoff filter, and the deep out-of-band cutoff filter has a high transmittance in the range of 250nm-270nm.

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

3. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 1 or 2, characterized in that: The first to third lenses constitute a front lens group with negative optical power; the fourth to sixth lenses constitute a rear lens group with positive optical power.

4. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 3, characterized in that: 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), and f3∈(47,52).

5. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 3, characterized in that: In the rear mirror 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).

6. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 1, characterized in that: The deep out-of-band cutoff filter is based on fused quartz, and a multilayer optical interference film is plated on the fused quartz substrate. The single-piece cutoff rate of the deep 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 pieces.

7. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 2, characterized in that: An aperture is arranged on the optical path between the third lens and the fourth lens, and an air gap between the aperture and the fourth lens is 0.12 mm to 0.18 mm.

8. The solar-blind ultraviolet optical system with large relative aperture and large field of view 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.

9. The solar-blind ultraviolet optical system with large relative aperture and large field of view according to claim 8, characterized in that: It also includes a detector window glass, which is arranged on the photosensitive surface of the high-sensitivity detector.

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

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