CN112945565B - Aperture-division ultraviolet multiband imaging system and method - Google Patents
Aperture-division ultraviolet multiband imaging system and method Download PDFInfo
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Abstract
The invention relates to a system and a method for aperture-dividing ultraviolet multiband imaging, wherein the system comprises an ultraviolet multiband prepositive aperture-dividing optical system and a postpositive image-combining optical system, the ultraviolet multiband prepositive aperture-dividing optical system comprises a solar-blind ultraviolet band optical filter, a visible-blind ultraviolet band optical filter, an OH free radical radiation characteristic band optical filter and a CN free radical radiation characteristic band optical filter, and the light path image surfaces are the same; the rear image combination optical system comprises a plurality of spherical lenses and at least one even-order aspheric lens, wherein partial lenses of the image combination optical path are tightly attached, and the ultraviolet multiband primary images obtained by the aperture division optical system are imaged on different areas on the detector at the same time. The invention solves the problem of processing cost and the problem of pupil connection between the front aperture dividing system and the rear image combining system; the problem that the existing optical cement strongly absorbs short-wave ultraviolet is solved, and the aberration is corrected by adopting an even-order aspheric lens. The system is suitable for processing and assembling and has practical value.
Description
Technical Field
The invention relates to the field of ultraviolet imaging, in particular to a system and a method for aperture-dividing ultraviolet multiband imaging.
Background
The radiation emitted by the flame during combustion mainly includes two main types, black body radiation and free radical radiation. Blackbody radiation covers the ultraviolet to infrared bands, while free radical radiation is radiation of a specific wavelength emitted after the transition of a free radical unsteady electron in a flame, has a narrow bandwidth, and is generally located in the ultraviolet and visible regions. A common free radical is OH * Radical (characteristic wavelength 308nm), CH * Radical (characteristic wavelengths 314nm and 431nm), CN * Radical (characteristic wavelength 390nm), C 2 * A basal (characteristic wavelength of 514nm), etc. Meanwhile, the radiation intensity of a plurality of free radicals is obtained, so that the proportion of the free radicals can be calculated, the stage of combustion reaction is judged, the components of the fuel are further analyzed, and the combustion process is controlled, which is one of the research hotspots of the current engine combustion diagnosis.
The multiband split-aperture imaging is a technical route for realizing multiband imaging, is characterized in that multiband images are obtained on one detector at the same time, and has the advantages of small volume, low cost, high real-time performance and the like compared with multi-detector imaging and time-sharing filtering imaging. The split-aperture imaging optical system generally consists of a split-aperture optical path and an image combining optical path, and sometimes a front telescopic optical path is added for increasing the field of view, and the design difficulty depends on the number and size of the split apertures, the spectral range and the transmissivity requirement. Generally, to facilitate uniform arrangement of the apertures on the detector, the number of apertures is selected to be 4 or 9. Due to the limitation of aperture size, the sub-aperture systems are generally small field of view. Increasing the field angle and improving the spatial resolution of the system are the difficulties of the sub-aperture imaging system.
At present, aperture-divided imaging optical systems of visible light and infrared bands are common, Guillem Carle and the like realize 9-aperture long-wave infrared imaging in a mode of tilting lenses, and included angles between the lenses and a main optical axis are different. Liyun and the like obtain 9-aperture spectral images through convergent single-time imaging, the edge image surface illumination is improved by using a 9-aperture diaphragm with larger edge aperture, and the system is compact in structure. The Hukefeng designs 9 paths of medium wave infrared sub-aperture light paths in a single imaging mode, achieves 100% cold aperture efficiency, and is combined with a super-resolution reconstruction algorithm, so that the system has a larger field angle and resolution compared with other sub-aperture light paths.
The ultraviolet band aperture-dividing imaging system has not been published at present. Common ultraviolet lens materials are only fused quartz and calcium fluoride, and the ultraviolet optical system is designed by using few materials, so that the refractive index and Abbe number types of the lens are limited, and the chromatic aberration of the system is difficult to correct; the cost of the ultraviolet lens material is relatively high, and the lenses with the same shape are used as much as possible during design, so that the processing cost is reduced; the commonly used optical cement has high absorption of ultraviolet radiation and low transmittance in the ultraviolet band, which requires a design that reduces the use of cemented lens forms that are advantageous for aberration correction.
Generally, the ultraviolet optical system is designed by a plurality of limited factors, and the difficulty of improving the image quality and correcting the aberration is high. In order to meet the requirement of engine combustion diagnosis, the pixel scale of ultraviolet enhanced silicon-based imaging devices such as an ultraviolet CMOS, an ultraviolet CCD and an ultraviolet EMCCD reaches millions or even tens of millions of pixels, and the method for simultaneously obtaining a high-resolution multiband ultraviolet image by adopting aperture division becomes possible.
Disclosure of Invention
In order to solve the problems, the invention provides an aperture-dividing ultraviolet multiband imaging system and method, the invention develops the design of an ultraviolet multiband aperture-dividing optical lens, the invention adopts the same image surface of each aperture-dividing light path to solve the problem of pupil connection between an aperture-dividing system and an image-combining system, the problem of processing cost is solved by using lenses with the same shape for each aperture-dividing light path, the whole system is designed into a refraction structure to improve the problem of smaller field angle of the aperture-dividing light path, the system aberration is corrected in the modes of an aspheric lens, lens close attachment and the like, and only a single lens made of fused quartz and calcium fluoride is used, so that the MTF of the whole system reaches 0.8 at the position of 45lp/mm of the Nyquist frequency, the whole aberration is smaller, and the imaging quality is high.
The technical scheme of the invention is as follows:
an aperture-dividing ultraviolet multiband imaging system comprises an ultraviolet multiband front-mounted aperture-dividing optical system and a rear image-combining optical system, wherein the ultraviolet multiband front-mounted aperture-dividing optical system comprises a solar-blind ultraviolet band optical filter, a visible-blind ultraviolet band optical filter, an OH free radical radiation characteristic band optical filter and a CN free radical radiation characteristic band optical filter, four groups of light path lenses are identical in shape, light rays of different bands are converged by changing the space among the lenses, and light path image surfaces are identical;
the rear image combination optical system comprises a plurality of spherical lenses and at least one even-order aspheric lens, wherein partial lenses of the image combination optical path are tightly attached, and the ultraviolet multiband primary images obtained by the aperture division optical system are imaged on different areas on the detector at the same time.
Furthermore, the wavelength of the solar-blind ultraviolet band filter is 240-280nm, the wavelength of the visible blind ultraviolet band filter is 300-360nm, the wavelength of the OH free radical radiation characteristic band filter is 308nm, and the wavelength of the CN free radical radiation characteristic band filter is 390 nm.
Further, the field angle of the system is 10 °.
Further, the overall length of the system is 278.5 mm.
Further, the entrance pupil diameter of the pre-aperture-splitting optical path is 10mm, the single-channel focal length is 43.88mm, and the modulation transfer function value is close to the diffraction limit.
Further, the modulation transfer function value of the object plane at the edge of the image combination optical path reaches 0.5 at 45 lp/mm.
Further, the MTF value of the system at 45lp/mm is close to the diffraction limit.
The invention also relates to an ultraviolet camera which comprises the aperture-dividing ultraviolet multiband imaging system.
The lens has the advantages that lenses with the same shape are used for all the aperture-dividing light paths to solve the problem of processing cost, and the image surfaces of all the aperture-dividing light paths are the same to solve the problem of pupil connection between the front aperture-dividing system and the rear image-combining system; the rear image combination optical system adopts the lens to cling to replace a cemented lens so as to solve the problem that the existing optical cement strongly absorbs short-wave ultraviolet and adopts an even-order aspheric lens to correct aberration.
The invention also relates to an ultraviolet multiband aperture-dividing imaging method, which is carried out as follows:
the radiation from the target is divided into 4 light paths with wave bands of 240-280nm, 308nm, 300-360nm and 390nm after passing through the aperture-dividing light path and the built-in ultraviolet filter, images of the 4 wave bands are imaged on a photosensitive surface of the ultraviolet detector through the image-combining light path, and the image obtained by the aperture-dividing light path is imaged on the ultraviolet detector through the post-arranged image-combining light path.
The invention also relates to a design method of the ultraviolet multiband aperture-dividing imaging system, which is carried out as follows:
for a sub-aperture system, designing a sub-optical path with a transmission waveband of 240-390 nm, keeping the shape of a lens unchanged, optimizing the central wavelength of each sub-optical path again by only changing the interval of the lens, controlling the image surfaces of each optical path to be consistent by using operands, and enabling the shape of the corresponding lens of each sub-aperture sub-optical path to be the same after optimization and the image surfaces of the sub-aperture system to be consistent;
for the imaging system, an object plane is overlapped with an image plane of the aperture dividing system, pupil connection is guaranteed, and then proper magnification is selected according to the size of the object plane and the size of a detector to realize complete imaging;
the system is provided with an even-order aspheric surface, and a cemented lens is replaced by an assembling mode of clinging the lens;
and combining and optimizing the optimized aperture dividing system and the image combining system to realize pupil connection and control image height.
Compared with the prior art, the invention has the following beneficial effects:
the ultraviolet multi-band aperture-splitting imaging optical lens for detecting the flame free radicals is designed for spectral analysis of the flame combustion free radicals, and ultraviolet images of four bands of 240-280nm, 308nm, 300-360nm and 390nm can be simultaneously obtained by a single ultraviolet detector. The design difficulty of the system is reduced by respectively designing the aperture system and the image combination system and then integrating and optimizing the aperture system and the image combination system. The field angle of the optical system is 10 degrees, the MTF value of each channel at the position of 45lp/mm reaches more than 0.8, the MTF value is close to the diffraction limit, and the overall image quality is high. The lens only adopts two materials of ultraviolet fused quartz and calcium fluoride, and simultaneously, the shape of the aperture-dividing light path lens is the same, so that the production cost is reduced. Monte Carlo analysis is carried out on all tolerance of the system, the result shows that the yield is more than 50%, and the system is suitable for processing and assembling and has practical value.
The ultraviolet multiband aperture-dividing imaging optical lens for detecting the free radicals of the combustion flame can simultaneously obtain 308nm OH by using only one detector * And 390nm CN * The radiation intensity of free radicals and the distribution condition of the free radicals in flame are researched, the solar blind ultraviolet imaging effect of 240-280nm and the visible blind ultraviolet imaging effect of 300-360nm are explored, and the free radicals can be used for controlling the temperature and the combustion of flameQuantitative analysis of material components provides an optical detection means for flame spectrum analysis and combustion diagnosis of ultraviolet bands.
Drawings
FIG. 1 is a schematic diagram of the ultraviolet multi-band split aperture imaging principle;
FIG. 2 is a quantum efficiency curve of an ultraviolet enhanced CMOS of the ultraviolet camera of an embodiment;
fig. 3 is a spectral transmission curve of 4 uv filters used, wherein:
(a)240～280nm(b)310nm(c)300～360nm(d)390nm；
FIG. 4 is a dimensional planning diagram of a subaperture system;
FIG. 5 is a schematic diagram of an aperture-splitting optical path structure;
fig. 6 is an MTF graph of each sub-aperture optical path of the present embodiment, where:
(a)240～280nm(b)308nm(c)300～360nm(d)390nm；
FIG. 7 is a 300nm to 360nm subaperture optical path aberration, wherein: (a) the field curvature and distortion of the speckles (b) are dispersed;
FIG. 8 is a diagram of an image combining optical path;
fig. 9 shows the resultant optical path aberration curve (a) MTF curve (b) the diffuse spot (c) field curvature and distortion;
FIG. 10 is a schematic diagram of the overall system;
FIG. 11 is the MTF for each channel, where: (a) 240-280nm, (b)308nm, (c) 300-360nm, (d)390 nm;
FIG. 12 is a diagram of systematic aberrator (a) diffuse spot (b) field curvature and distortion;
fig. 13 is a schematic structural view of the ultraviolet camera of the present embodiment;
FIG. 14 shows the results of a principle experiment in this example, in which:
(a)240～280nm(b)308nm(c)300～360nm(d)390nm。
Detailed Description
The technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the examples without making any creative effort, shall fall within the protection scope of the present invention.
Unless otherwise defined, technical or scientific terms used in the embodiments of the present application should have the ordinary meaning as understood by those having ordinary skill in the art. The use of "first," "second," and similar terms in the present embodiments does not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. "mounted," "connected," and "coupled" are to be construed broadly and may, for example, be fixedly coupled, detachably coupled, or integrally coupled; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. "Upper," "lower," "left," "right," "lateral," "vertical," and the like are used solely in relation to the orientation of the components in the figures, and these directional terms are relative terms that are used for descriptive and clarity purposes and that can vary accordingly depending on the orientation in which the components in the figures are placed.
The ultraviolet multiband aperture-dividing imaging lens for combustion flame free radical detection in the embodiment is composed of 4 aperture-dividing light paths and 1 image-combining light path. After passing through the aperture-dividing light path and the built-in ultraviolet filter, the radiation from the target (combustion flame) is divided into 4 light paths with wave bands of 240-280nm, 308nm, 300-360nm and 390nm, and then images of the 4 wave bands on the photosensitive surface of the ultraviolet detector through the image-combining light path, and the image obtained by the aperture-dividing light path is imaged on the ultraviolet detector through the post-positioned image-combining light path, as shown in fig. 1.
Wherein, each wave band function is as follows:
240-280 nm: solar blind ultraviolet band, clean background, detecting flame position, existence and heat radiation intensity;
300-360 nm: visible blind ultraviolet wave bands exist, radiation of various free radicals exists, and the integral shape of the flame is observed;
308 nm: OH free radical radiation characteristic wave band for detecting the intensity and position of OH in the flame combustion process;
390 nm: and the CN free radical radiation characteristic wave band is used for detecting the intensity and the position of CN in the flame combustion process.
The model of the ultraviolet camera used in this embodiment is Prime 95B, the detector is a back-illuminated ultraviolet-enhanced CMOS, the pixel scale is 1200 × 1200, the pixel size is 11 μm, and the response band is 200nm to 1100 nm. The quantum efficiency curve is shown in fig. 2.
And calculating to obtain the Nyquist frequency of 45lp/mm according to the size of the pixel. The imaging pixel size of each path of aperture-divided light path image is 600 multiplied by 600. The 4 ultraviolet filters are narrow-band filters of Edmund Optics, the spectral transmission curve is shown in figure 3, the cut-off wavelength is 200 nm-1200 nm, the outer diameter is 12.5mm, and the effective aperture is 8.8 mm.
The design method of the ultraviolet multiband aperture-dividing imaging lens for combustion flame free radical detection in the embodiment is carried out as follows:
the sub-aperture imaging system generally comprises a telescope system, a sub-aperture system and an image combination system, wherein the image combination system can improve the effective pixel area of the detector, and the telescope system can increase the detection distance. Because the system aims at the spectral analysis of flame combustion free radicals, in order to improve the accuracy of detecting the free radicals and reduce background interference, the acting distance is only several meters, so that the system removes a telescopic system and adopts a form of a sub-aperture system and an image-combining system.
During actual design, if the aperture dividing system and the image combining system are optimized simultaneously, the number of parameter variables is large, the optimization time is long, and the design complexity is improved. Meanwhile, due to the fact that the number of light paths is large and the light paths are eccentric, the problems that the initial structure of the total system is difficult to find, the primary image surface is difficult to control and the like exist in the mode, lens parameters of the light paths of the aperture dividing system obtained after optimization are generally different, and therefore the production and assembly cost can be improved. The design method comprises the steps of designing a aperture system and an image combining system separately, and then integrating the aperture system and the image combining system for optimization. In this way, the problem of pupil connection between the aperture dividing system and the image combining system is solved, and it is required to ensure that the image planes of the aperture dividing systems are the same, and the image plane of the aperture dividing system is the object plane of the image combining system.
The aperture dividing system adopts a conventional lens structure, the image combining system adopts a similar microscopic structure, and an initial structure is easy to obtain. The primary image surface is an image surface of the aperture dividing system and is positioned between the aperture dividing system and the image combining system, and the size and the position of the image surface are easier to control. For the aperture division system, a sub-optical path with a transmission waveband of 240-390 nm is designed, the shape of a lens is kept unchanged, the central wavelength of each sub-optical path is optimized again only by changing the interval of the lens, and the image planes of each optical path are controlled to be consistent by using operands. After optimization, the shapes of the lenses corresponding to the sub-aperture optical paths are the same, and the processing cost is reduced. The image surfaces of the aperture division systems are consistent, and the requirement of pupil connection is met. For the imaging system, an object plane is overlapped with an image plane of the aperture dividing system, pupil connection is guaranteed, and then proper magnification is selected according to the size of the object plane and the size of the detector to realize complete imaging.
1. Design of sub-aperture system
The sub-aperture system images a target on a primary image surface, and pupil connection needs to be considered during design. The size of the primary image surface is determined to be a circular area with the diameter of 30mm by referring to the size of a conventional lens and considering the design of a subsequent image combination light path. Considering that the lens barrel edge and the lens fixing frame need to be reserved during processing, the image height of each channel is about 4mm, the minimum diameter of the object plane is about 28.9mm, and the size planning diagram is shown in fig. 4.
The diameter of the entrance pupil of the lens can be set to be 10mm by a size chart, in order to realize flame spectrum analysis within a plurality of meters, a standard lens with the effective focal length of 45mm of the lens is preliminarily set, the F number of the system is 4.5, and the corresponding angle of view is calculated by an image height formula
h＝f*tan(FOV/2) (1)
By reverse-pushing to obtain
FOV＝2arctan(h/f) (2)
The field angle FOV is 10 ° by bringing in the image height and focus data.
An initial structure close to the set parameters is searched in the patent lens library, the diameter of the entrance pupil is controlled in Zemax, the effective focal length and the image height of the optical path are controlled by using the operation number, and the optimized structure diagram is shown in FIG. 5.
The MTF effect of the 4-way split aperture optical path is shown in fig. 6. The MTF values of the bands of 308nm and 390nm are close to the diffraction limit, the MTF of the channels of the bands of 240nm to 280nm and 300nm to 360nm can reach 0.3 at the position of 190lp/mm, and the imaging quality of each channel is higher.
The aberration of the aperture-splitting optical path is shown in FIG. 7 (taking 300-360nm channel as an example), the curvature of field is less than 0.12mm, the maximum distortion is about 1.6%, the aberrations are well controlled, and the overall image quality is high.
2. Image synthesis system design
The image combination system is used for imaging a primary image obtained by the aperture division system onto a detector, a target with a limited distance needs to be imaged, and the adopted structure is a microscope-like structure. A Numerical Aperture (NA) is generally adopted for the microscope to replace the field angle, and a larger NA indicates a larger angle of light received by the system and a higher resolution.
The numerical aperture of the image combination light path is preliminarily set to be 0.1, the object plane of the image combination light path is a circular plane with the diameter of 30mm, the image plane is a detector, the size of the square area is 13.2mm multiplied by 13.2mm, and the image height is about 9.35 mm. The interface of the detector is a C port, the focal length of the flange is 17.5mm, and enough image distance is reserved during design. In addition, because the transmission capability of the existing optical cement to short-wave ultraviolet is weak, the transmission rate at 300nm is usually lower than 50%, and a close-fitting assembly is adopted to replace the use of a cemented lens during design.
The optical path after optimization is shown in fig. 8 by taking the existing microscope objective as a basic structure. Under the limitation of materials and optical cement, in order to better correct aberration, the surfaces 2 and 24 of the system are even aspheric surfaces, and a close-fitting assembly mode of the lenses is adopted to replace a cemented lens.
The MTF and aberrations of the image combining system are shown in fig. 9. At the position of 45lp/mm of Nyquist frequency, the MTF value of the system is more than 0.45, the MTF value at the position of 20lp/mm is more than 0.65, the maximum diffuse spot radius is about half of the pixel size, and the imaging requirement is met. The curvature of field is less than 0.15mm, the maximum distortion is about 7%, and the aberration is relatively small.
3. Overall system layout
The aperture dividing system and the image combining system are combined together to form the ultraviolet multiband aperture dividing imaging system, and the overall layout of the system is shown in fig. 10.
The combined system is optimized integrally in Zemax, optical path parameters of the optimized system are shown in Table 1 (taking channels of 300-360nm as an example), MTF values of all channels are shown in figure 11, MTF values of channels of 308nm and 390nm are close to diffraction limit, MTF values of channels of 240 nm-280 nm and channels of 300 nm-360 nm reach 0.8 at 45lp/mm, MTF values of all channels at 20lp/mm are larger than 0.95, and the integral image quality is high.
TABLE 1 optical path parameters of the System
Tab.1 System optical parameters
The aberration of the total system is shown in fig. 12, and the diffuse spot radius is half of the pixel, which meets the imaging requirements. The system field curvature is small but 8% distorted and can be corrected by subsequent algorithm processing.
System tolerance analysis
The set optical system tolerances according to the processing ability of the actual optical element and the assembly accuracy of the device are shown in table 2.
TABLE 2 optical System tolerances
Tab.2 Optical system tolerance
Tolerance data are subjected to 100 rounds of sensitivity analysis by adopting a Monte Carlo simulation method, MTF values at 45lp/mm are used as evaluation indexes, and the results are shown in Table 3. The results in the table show that, within the set tolerance range, the MTF value of at least 50% of the lenses at the position of 45lp/mm reaches 0.35, so that the design requirements are met, the yield can be considered to be more than 50%, and the requirements of actual processing and assembly are met.
TABLE 3 results of tolerance analysis
Tab.3 Results of tolerance analysis
| MTF mean nominal value at 45lp/mm | 0.65419953 |
| MTF mean value optimum at 45lp/mm | 0.65713530 |
| MTF mean worst value at 45lp/mm | 0.09059520 |
| 50% results MTF mean at 45lp/mm greater than | 0.35107810 |
| 20% results MTF mean at 45lp/mm greater than | 0.48055448 |
| The MTF mean value at 45lp/mm is larger than that at 10 percent result | 0.54644907 |
Prototype and principle experiment
According to the designed light path structure and lens processing parameters, a physical model is constructed for the whole light path in SolidWorks software, and a three-dimensional diagram of the ultraviolet multiband aperture-division imaging optical lens 1 arranged on an ultraviolet camera 2 is shown in figure 13.
The ultraviolet multiband aperture-dividing imaging optical lens of the embodiment is still processed, a principle test of the system is performed in a mode of replacing the optical filter for time-division imaging, a shooting object is methane flame, and an experimental result is shown in fig. 14. It can be observed from the figure that the flame shape is significantly different after imaging through the system of different transmission bands, which indicates that the temperature and the characteristic free radical are different at different parts of the flame.
The embodiment designs the ultraviolet multiband aperture-dividing imaging optical lens for flame combustion free radical detection for spectral analysis of flame combustion free radicals, and realizes that a single ultraviolet detector simultaneously obtains ultraviolet images of 240-280nm, 308nm, 300-360nm and 390nm bands to respectively design an aperture dividing system and an image combining system firstly and then integrate and optimize the aperture dividing system and the image combining system, thereby reducing the design difficulty of the system. The field angle of the optical system is 10 degrees, the MTF value of each channel at the position of 45lp/mm reaches more than 0.8, the MTF value is close to the diffraction limit, and the overall image quality is high. The total length of the system is 278.5mm, each channel is composed of 18 lenses, and the lenses are made of two materials of ultraviolet fused quartz and calcium fluoride only, so that the production cost is reduced. Tolerance analysis results show that the yield of the system is over 50 percent, and the method has practical value in the field of scientific research.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. An aperture-dividing ultraviolet multiband imaging system is characterized in that: the system comprises an ultraviolet multiband front-mounted aperture splitting optical system and a rear-mounted image combining optical system, and consists of 4 aperture splitting optical paths and 1 image combining optical path;
the ultraviolet multiband preposed aperture-dividing optical system comprises a solar-blind ultraviolet band optical filter, a visible-blind ultraviolet band optical filter, an OH free radical radiation characteristic band optical filter and a CN free radical radiation characteristic band optical filter, wherein 4 aperture-dividing optical path lenses have the same shape, light rays of different bands are converged by changing the space between the lenses, and optical path image surfaces are the same;
the rear image combination optical system comprises a plurality of spherical lenses and at least one even-order aspheric lens, wherein partial lenses of the image combination optical path are tightly attached to image the ultraviolet multiband primary images obtained by the aperture division optical system onto different areas on the detector at the same time;
the method comprises the following steps of (1) dividing an aperture optical system, designing a sub-optical path with a transmission waveband of 240-390 nm, keeping the shape of a lens unchanged, optimizing the central wavelength of each sub-optical path again only by changing the interval of the lens, controlling the image surface of each optical path to be consistent by using operands, and controlling the shape of the corresponding lens of each aperture sub-optical path to be the same after optimization, wherein the image surfaces of the aperture sub-optical systems are consistent;
for the rear image combination optical system, an object plane is superposed with an image plane of the aperture division optical system, so that pupil connection is ensured, and then proper magnification is selected according to the size of the object plane and the size of a detector to realize complete imaging.
2. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the wavelength of the solar blind ultraviolet band filter is 240-280nm, the wavelength of the visible blind ultraviolet band filter is 300-360nm, the wavelength of the OH free radical radiation characteristic band filter is 308nm, and the wavelength of the CN free radical radiation characteristic band filter is 390 nm.
3. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the field angle of the system is 10 °.
4. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the overall length of the system is 278.5 mm.
5. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the entrance pupil diameter of the pre-aperture-splitting optical path is 10mm, the single-channel focal length is 43.88mm, and the modulation transfer function value is close to the diffraction limit.
6. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the modulation transfer function value of the object plane at the edge of the image combination optical path reaches 0.5 at the position of 45 lp/mm.
7. The split aperture ultraviolet multiband imaging system of claim 1, wherein: the MTF value of the system at 45lp/mm is close to the diffraction limit.
8. An ultraviolet camera, characterized by: comprising the split-aperture ultraviolet multiband imaging system according to any one of claims 1 to 7.
9. An imaging method based on the split-aperture ultraviolet multiband imaging system of claim 1, characterized in that: the method comprises the following steps:
the radiation from the target is divided into 4 light paths with wave bands of 240-280nm, 308nm, 300-360nm and 390nm after passing through the aperture-dividing light path and the built-in ultraviolet filter, images of the 4 wave bands are imaged on a photosensitive surface of the ultraviolet detector through the image-combining light path, and the image obtained by the aperture-dividing light path is imaged on the ultraviolet detector through the post-arranged image-combining light path.
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