CN113639864A - Space full-area ultrahigh contrast imaging method and coronagraph system - Google Patents
Space full-area ultrahigh contrast imaging method and coronagraph system Download PDFInfo
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Abstract
The invention discloses a spatial full-area ultrahigh contrast imaging method and a coronagraph system. According to the method, a ring belt pupil transmittance modulation technology is adopted, transmittance gradient modulation is carried out along the pupil radial direction, the suppression of strong diffraction light of fixed stars is achieved, and the ring belt pupil transmittance modulation adopts a finite band and bilateral symmetry type transmittance modulation band to change the energy distribution of fixed stars at the system pupil position so as to meet the requirement of optimal high-contrast imaging. The transmittance modulation band with finite band and bilateral symmetry consists of finite transmittance modulation annular bands, and the annular bands are modulated to gradually change the transmittance of the central band and symmetrically distribute the transmittance of the central band from left to right. The invention provides and completes a coronagraph system suitable for observing a 360-degree working area aiming at the technical problem of limited ultrahigh contrast imaging area, solves the problem of detection efficiency of a space coronagraph, improves the future planet discovery rate and the observation time utilization rate, and prolongs the effective service life of an extraterrestrial planet space detection satellite.
Description
Technical Field
The invention relates to a spatial full-region ultrahigh contrast imaging method and a coronagraph system. The system and the method relate to the technical fields of solar system outer planet detection, system outer cold planet direct imaging, system outer planet and life signal detection, space astronomical instruments, aerospace, astronomical terminal instruments and adaptive optics, in particular to a space coronagraph system and a method which are suitable for 360-degree full-field working area, large working area and ultrahigh contrast imaging, and particularly relates to a high-contrast coronagraph, a symmetric and annular pupil modulation technology and a realization method which are applied to space full-working area system outer planet direct imaging detection.
Background
Extravehicular planets refer to planets outside the solar system, i.e., planetary systems around other stars or independent planets outside the solar system. The extraterrestrial planet detection is closely related to the search of extraterrestrial civilization, so that the understanding of human beings on the existing life can be broken through, and the living space of human beings can be expanded finally.
To date, most of the outer planets found have been detected indirectly by the method of Rabdosia or Doppler. Direct imaging technology, which can physically separate the light from stars and planets, is the key to identifying extrasystem vital signature signals. The coronagraph is an important instrument for realizing the high-contrast direct imaging detection of extrasystem planets, and can effectively inhibit strong diffraction light from stars so that planets submerged in strong background light can be directly imaged.
At present, limited by the ground atmospheric environment and the observation wave band and the detection capability of a new generation of super self-adaptive optical technology, the ground-based planetary imaging coronagraph can only carry out planetary imaging detection in an infrared wave band, and the contrast can only reach 10-6. The search for cold planets around the sun-like fixed star, especially the earth-like planets in the livable zone, is a breakthrough for detecting and confirming the existence of the life planets in the future, which needs to break through the limitations of the existing ground observation wave band and imaging contrast and needs to develop the ultrahigh contrast imaging technology of the space coronarism instrument.
Space satellite platforms have relatively limited resources or lifetimes, and therefore, it is desirable to fully utilize and maximize the observation efficiency of the coronagraph system. For example, a single exposure can cover a 360 observation region, so that the imaging can be detected no matter which region the planet falls on. This requires new modulation schemes for the coronagraph.
At present, most of the coronagraph systems can only obtain ultrahigh contrast imaging in a specific area of a scientific focal plane of the system, and cannot perform imaging detection on planets in the whole detection area. For example, focal plane modulated coronagraphs developed by the atmospheric push laboratory team of NASA, usa, can only obtain high contrast imaging in a small area on one side; the coronagraph developed by the university of princeton group of america is also capable of acquiring high contrast imaging only in a very small area of a specific quadrant region of the coronagraph.
Disclosure of Invention
In order to solve the problem that the imaging working area of the existing high-contrast coronagraph is limited, the invention provides an ultrahigh-contrast imaging coronagraph system which is used for a 360-degree working field of space and a full area.
In order to achieve the purpose, the invention provides the following technical scheme:
a spatial full-area ultrahigh-contrast imaging method adopts a ring belt pupil transmittance modulation technology to perform transmittance gradient modulation along the pupil radial direction so as to realize the suppression of strong diffraction light of fixed stars, the ring belt pupil transmittance modulation adopts a finite zone and a bilateral symmetry type transmittance modulation zone to change the energy distribution of the fixed stars at the system pupil position so as to meet the requirement of optimal high-contrast imaging, the finite zone and the bilateral symmetry type transmittance modulation zone are composed of finite transmittance modulation annular zones, and the annular zone modulation gradually changes the transmittance of a central zone and is symmetrically distributed with the transmittance of the central zone.
Furthermore, the light pupil is modulated by the transmittance change with limited band number along the radial direction, and only limited bands are subjected to film coating treatment in the actual development process.
Furthermore, the transmittance values of the modulation bands are symmetrically distributed in the central (N +1) th annular band.
Further, a high-reflection film is plated at the center and the outermost edge, and the high-reflection film is consistent with the film layer outside the light-transmitting caliber.
Further, the central zone of the (N +1) th zone is predetermined as the highest transmittance zone, the initial transmittance value of each transmittance modulation zone is set, and the transmittance value is dynamically adjusted according to the transmittance change range.
Further, the transmittance value is varied by introducing a limited number of modulation bands to the pupil and using a symmetrical distribution with a central band.
Further, the transmittance gradient modulation method comprises the following steps:
firstly, determining the clear aperture, the band number of a pupil modulator, the modulation function trend and an optimized spatial layout strategy of a coronagraph system according to the resource and envelope constraint provided by a satellite platform;
secondly, setting the variation range and the variation trend of the transmittance of each band according to the initially determined light transmission aperture and the number of modulation bands;
setting an initial transmittance value of each transmittance modulation band, and dynamically adjusting the transmittance value according to the transmittance change range, wherein the system is composed of 2 × N +1 bands, the N +1 band is taken as the center, the subsequent transmittance bands are symmetrically distributed along the center, and N +1 transmittance values are summed;
fourthly, the designed initial pupil transmittance value is brought into the whole set of high-contrast imaging calculation simulation system, and the subsequent iterative optimization process is completed by adjusting the transmittance value of the N +1 band;
and fifthly, establishing an optimal contrast function and criterion, dynamically adjusting the transmittance value of each modulation band, calculating the imaging contrast performance in a specific working area in real time, and judging whether the optimal contrast performance is met.
The coronagraph system based on the space whole-region ultrahigh-contrast imaging method comprises a simulated star light source, a collimation system, an aperture diaphragm, an annulus pupil modulation filter, an imaging system and a detector, wherein the collimation system comprises a reflector and a first parabolic mirror, the imaging system comprises a second parabolic mirror and an imaging mirror, the stellar light from infinity is focused to the incident end of the coronagraph system through a telescope, and is converted to the first parabolic mirror through the reflector to expand a point source target into parallel light so as to simulate the stellar light from infinity; the aperture diaphragm is used for blocking out unnecessary stray light from the system, the annulus pupil modulation filter modulates star light energy, and finally the star light energy is converted to a second parabolic mirror through an imaging mirror and imaged on a focal plane detector of the star crown instrument system, and the annulus pupil modulation filter adopts the imaging method to carry out pupil amplitude modulation.
Furthermore, the coronagraph system has a large working area in space or a 360-degree full-field working area, and the contrast ratio is better than 10-7The coronagraph system is used for spatial high-contrast imaging or extraterrestrial planet detection.
Compared with the prior art, the invention has the beneficial effects that:
(1) the adoption of a modulation scheme with a limited band can achieve 360-degree full-area ultrahigh-contrast imaging, effectively reduce the development difficulty of the system, ensure the processing precision of the modulator, reduce the development period and cost, fully utilize the space satellite observation time, and ensure the imaging detection of the extracold planets and the discovery of extracold life signals.
(2) The layout scheme of bilateral symmetry of the central band is adopted, the transmittance value of the modulation filter is further reduced, two bands can be directly used as a group for precise transmittance control, the uniformity of the transmittance of the modulation filter is ensured, and the integral imaging contrast of the system is finally improved.
(3) In the modulation zone, the designed transmittance value of the (N +1) th zone (central zone) is the highest, and the modulation film layer treatment can be omitted; the high-reflection film is plated at the most edge and the center (the 1 st strip and 2 x N +1) and is consistent with the film outside the light-transmitting aperture. The operation further reduces the types of the transmittance of the film layer, and is beneficial to realizing the final high-contrast imaging.
(4) The variation range of the transmittance band is restricted, the central girdle band of the (N +1) th band is defined as the highest transmittance band (normalization 1, the transmittance of the corresponding glass substrate coated antireflection film is generally more than 96%), the highest light transmission efficiency of the system is ensured, the closed loop of the system is combined with the actual processing technology and the coating transmittance precision, the optimal transmittance modulation value is obtained, and the optimal imaging contrast in the whole area is ensured.
Drawings
FIG. 1 is a general block diagram of the coronagraph system of the present invention;
FIG. 2 is a schematic diagram of a spatial configuration of a transmission-modulating filter with a circular ring band having a left-right symmetry in a finite band;
FIG. 3 is a typical image after modulation of the system point spread function;
FIG. 4 is a flow chart of the design and optimization of a finite-band symmetric annular pupil modulation filter.
The labels in the figure are: 1. a telescope focal plane; 2. simulating a fixed star light source; 3. a mirror; 4. a first parabolic mirror; 5. an aperture diaphragm; 6. an annular pupil modulating filter; 7. an imaging mirror; 8. a second parabolic mirror; 9. an imaging detector.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention relates to a Chinese space station engineering project 'inspection telescope external planet imaging coronagraph module', a national natural science foundation astronomy combined key support project 'external planet high-contrast imaging key technology research for large-caliber spliced mirror telescope' (U2031210), and a national major scientific research instrument development project 'solar external planet high-contrast imaging detector development around dark and weak stars' (11827804).
The invention adopts a ring belt pupil transmittance modulation technology to carry out transmittance gradient modulation along the radial direction of the system pupil so as to realize the suppression of strong diffraction light of fixed stars. Different from the traditional ground transmittance modulation mode, the invention optimizes the imaging contrast target to 10 aiming at the detection requirement of space system external cooling planets, particularly the geostationary planets-8And the number is more than 2 orders of magnitude higher than that of the foundation circular hole type modulation technical scheme. Different from the existing continuous transmittance modulation mode, the annular transmittance modulation adopts a finite band and bilateral symmetry type transmittance modulation band to change the energy distribution of the fixed star at the system pupil position so as to achieve the aim of restraining strong diffraction light of the fixed star and finally meet the requirement of optimal high-contrast imaging.
The invention modulates the transmittance change of the pupil with limited band number along the radial direction, only carries out film coating treatment on very limited bands in the actual development process, can effectively reduce the development difficulty, period and cost of the modulator, and ensures the actual processing precision and the actual imaging contrast ratio measurement performance of the modulation sheet.
The transmittance values of the modulation bands are symmetrically distributed in the central (N +1) th annular band, so that the types of the transmittance values of the modulation filter are reduced, the actual processes of coating and erasing photoresist are effectively simplified, and the transmittance can be accurately controlled in a mode of combining two bands into a group directly, and the uniformity of the transmittance on the bands is ensured. The design scheme can effectively ensure the high precision of the transmittance of the modulation filter and finally ensure the imaging contrast performance of the coronagraph system.
The high-reflection film is plated at the center and the most edges (the 1 st zone and 2 x N +1) and is consistent with the film layer outside the light-transmitting aperture. The operation further reduces the types of film transmittance values, and is beneficial to the realization of final high-contrast imaging.
The central girdle of the (N +1) th girdle is preset as a highest transmittance band (normalization 1, the transmittance of a corresponding glass substrate plated with an antireflection film is generally more than 96 percent), so that the highest light transmission efficiency of the system is ensured. Setting an initial transmittance value of each transmittance modulation band, and dynamically adjusting the transmittance value according to the transmittance change range.
The traditional transmittance modulation coronagraph adopts a continuous transmittance modulation mode, the imaging contrast theoretical design value is not high, the realization of ultrahigh contrast imaging indexes is limited, and the traditional transmittance modulation coronagraph is difficult to be used for full-area ultrahigh contrast imaging detection of the externally cooling planets. The invention introduces a limited number of modulation bands to the pupil and changes the transmittance value by adopting symmetrical distribution of the central band, thereby effectively reducing the processing difficulty of the modulation filter. The invention adopts a 'finite band, bilateral symmetry type transmittance modulation band' to change the energy distribution of fixed stars at the pupil position of the system so as to achieve the aim of restraining strong diffraction light of the fixed stars and finally meet the requirement of optimal high-contrast imaging. The invention can thoroughly solve the technical problem that the traditional coronagraph is difficult to realize high-contrast imaging because of adopting a continuous and complex modulation function.
The overall optimization layout modulation function is combined with the actual application condition, so that the performance in the actual application can be ensured, and the development of the core modulator can be realized with high precision. For example, the clear aperture, pupil modulator band count, trend, and optimized spatial layout strategy of the coronagraph system are determined to achieve the highest performance and yield ratio, taking into account the resources and envelope constraints provided by the system.
The coronagraph system based on the spatial full-area ultrahigh contrast imaging method can select optical elements according to actual needs. The composition and the working principle of the spatial full-area ultrahigh contrast imaging coronaries system provided by the embodiment are shown in fig. 1. The imaging focal plane 1 of the telescope is the input end of the coronagraph system, a simulated fixed star light source 2 is arranged at the input end, and the imaging focal plane is turned to a first parabolic mirror 4 through a reflector 3 to expand a point source target into parallel light and simulate stellar light at infinite distance; the aperture diaphragm 5 is used for blocking out unnecessary stray light from the system, the annulus pupil modulation filter 6 modulates the star light energy, and finally the star light energy is turned to the second parabolic mirror 8 through the imaging mirror 7 to be imaged on the imaging detector 9 of the coronarism system. The invention mainly aims at a high-contrast imaging coronagraph with a large working area, particularly a 360-degree full-field working area, and aims at the contrast ratio superior to 10-7The coronagraph is used for a space high-contrast imaging coronagraph and for extraterrestrial planet detection.
The system core is a circular ring band transmittance modulation filter which is positioned on a pupil plane and has a finite band in bilateral symmetry. The modulator consists of a finite transmittance modulation ring band, wherein the transmittance of the ring band modulation is gradually changed by a central band, and the transmittance is symmetrically distributed by starting the central band from the left transmittance to the right transmittance. The transmittance modulation band number is 2 × N +1, and only N +1 kinds of transmittance are provided. By combining the existing coating and photoetching processes and coating photoresist and metal alloy films of different film layers on the glass substrate, the precise processing of the finite-band transmittance modulation filter can be conveniently realized. By combining the existing coating and photoetching processes and coating photoresist and metal alloy films of different film layers on the glass substrate, the precise processing of the finite-band transmittance modulation filter can be conveniently realized. The energy distribution of a point spread function image positioned in a focal plane system can be changed by modulating and redistributing the energy of the stellar light at the pupil, so that high-contrast imaging is obtained in a specific working area, and the direct imaging detection of the extrasystole planets is realized.
The modulator needs to optimize the transmittance of the pupil along the radial direction, and the optimal transmittance modulation scheme is obtained through the closed-loop iterative optimization of the high-contrast imaging of the system. The invention reduces the difficulty of system development, effectively ensures the processing precision of the modulator, and can realize ultrahigh contrast imaging in a 360-degree full-field working area, so that the high-efficiency and ultrahigh contrast imaging detection of the externally-cooling planet system becomes possible.
Fig. 2 depicts the spatial configuration of a finite-band, left-right symmetric, circular-ring band transmittance modulating filter (the nth and nth' bands have the same transmittance). The figure shows the transmission distribution of the radial pupil modulation scheme of the modulation system, which is composed of 2 × N +1 modulation bands and is arranged in a variation trend that the transmission of the N +1 band is the highest and then gradually decreases in bilateral symmetry. The realization is that only the transmittance band needing to be modulated is leaked through the high-precision photoresist and the film coating process, and then the transmittance value of the corresponding modulation band is realized by changing the film coating thickness of the metal film layer. Fig. 3 is a typical image after modulation of a system point spread function, and compared with an international prior art coronagraph system, ultra-high contrast imaging of a 360 ° whole region can be realized.
Figure 4 depicts the design and optimization process of a finite-band symmetric annular pupil modulation filter. The method comprises the following specific steps:
firstly, determining the clear aperture, the band number of a pupil modulator, the modulation function trend and an optimized spatial layout strategy of a coronagraph system according to the resource and envelope constraint provided by a satellite platform;
secondly, setting the variation range and the variation trend of the transmittance of each band according to the initially determined light transmission aperture and the number of modulation bands;
setting an initial transmittance value of each transmittance modulation band, and dynamically adjusting the transmittance value according to the transmittance change range, wherein the system is composed of 2 × N +1 bands, the N +1 band is taken as the center, the subsequent transmittance bands are symmetrically distributed along the center, and the total N +1 final transmittance value is obtained;
fourthly, the designed initial pupil transmittance value is brought into the whole set of high-contrast imaging calculation simulation system, and the subsequent iterative optimization process is completed by adjusting the transmittance value of the N +1 band;
and fifthly, establishing an optimal contrast function and criterion, dynamically adjusting the transmittance value of each modulation band, calculating the imaging contrast performance in a specific working area in real time, and judging whether the optimal contrast performance is met.
The design and optimization process of the modulator transmittance is shown in fig. 4:
firstly, determining the clear aperture, the band number of a pupil modulator, the modulation function trend and an optimized spatial layout strategy of a coronagraph system according to the resource and envelope constraint provided by a satellite platform;
secondly, setting the variation range and the variation trend of the transmittance of each band according to the initially determined light transmission aperture and the number of modulation bands;
setting an initial transmittance value of each transmittance modulation band, and dynamically adjusting the transmittance value according to the transmittance change range, wherein the system is composed of 2 × N +1 bands, the N +1 band is taken as the center, the subsequent transmittance bands are symmetrically distributed along the center, and N +1 transmittance values are summed;
fourthly, the designed initial pupil transmittance value is brought into the whole set of high-contrast imaging calculation simulation system, and the subsequent iterative optimization process is completed by adjusting the transmittance value of the N +1 band;
and fifthly, establishing an optimal contrast function and criterion, dynamically adjusting the transmittance value of each modulation band, calculating the imaging contrast performance in a specific working area in real time, and judging whether the optimal contrast performance is met.
In conclusion, the invention provides and completes a coronagraph system suitable for observing a 360-degree working area aiming at the technical problem of limited ultrahigh contrast imaging area, can solve the problem of detection efficiency of a space coronagraph, effectively improves the future planet discovery rate and the observation time utilization rate, and prolongs the effective service life of an extraterrestrial planet space detection satellite.
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 present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A spatial full-area ultrahigh-contrast imaging method is characterized in that a ring belt pupil transmittance modulation technology is adopted, transmittance gradient modulation is carried out along the pupil radial direction, suppression on strong diffraction light of fixed stars is achieved, the ring belt pupil transmittance modulation adopts a finite zone and a bilateral symmetry type transmittance modulation zone to change the energy distribution of the fixed stars at the system pupil position so as to meet the requirement of optimal high-contrast imaging, the finite zone and the bilateral symmetry type transmittance modulation zone are composed of finite transmittance modulation zones, and the zone modulation gradually changes in the transmittance of a central zone and is symmetrically distributed in the left and right transmittance starting from the central zone.
2. The spatial full-area ultrahigh contrast imaging method according to claim 1, characterized in that only a limited number of bands are coated during practical development by performing a limited number of bands of transmittance change modulation on the pupil along the radial direction.
3. The spatial full-area ultrahigh contrast imaging method according to claim 1, wherein the transmittance values of the modulation bands are symmetrically arranged around the central N +1 th annular band.
4. The method of claim 1, wherein a high reflective coating is applied to the center and the edge of the image, said high reflective coating being substantially identical to the coating outside the clear aperture.
5. The spatial full-area ultrahigh contrast imaging method according to claim 1, wherein the central zone of the (N +1) th zone is predetermined as a transmittance highest zone, an initial transmittance value of each transmittance modulation zone is set, and the transmittance value is dynamically adjusted according to the transmittance change range.
6. The method of claim 1, wherein a limited number of modulation bands are introduced into the pupil, and the transmittance is varied with a symmetrical distribution of the central band.
7. The spatial full-area ultrahigh contrast imaging method according to any one of claims 1 to 6, characterized in that the transmittance gradient modulation method comprises the following steps:
firstly, determining the clear aperture, the band number of a pupil modulator, the modulation function trend and an optimized spatial layout strategy of a coronagraph system according to the resource and envelope constraint provided by a satellite platform;
secondly, setting the variation range and the variation trend of the transmittance of each band according to the initially determined light transmission aperture and the number of modulation bands;
setting an initial transmittance value of each transmittance modulation band, and dynamically adjusting the transmittance value according to the transmittance change range, wherein the system is composed of 2 × N +1 bands, the N +1 band is taken as the center, the subsequent transmittance bands are symmetrically distributed along the center, and N +1 transmittance values are summed;
fourthly, the designed initial pupil transmittance value is brought into the whole set of high-contrast imaging calculation simulation system, and the subsequent iterative optimization process is completed by adjusting the transmittance value of the N +1 band;
and fifthly, establishing an optimal contrast function and criterion, dynamically adjusting the transmittance value of each modulation band, calculating the imaging contrast performance in a specific working area in real time, and judging whether the optimal contrast performance is met.
8. The coronagraph system based on the space whole-region ultrahigh-contrast imaging method is characterized by comprising a simulated star light source, a collimation system, an aperture diaphragm, an annulus pupil modulation filter, an imaging system and a detector, wherein the collimation system comprises a reflector and a first parabolic mirror, the imaging system comprises a second parabolic mirror and an imaging mirror, and the stellar light from infinity is focused to the incident end of the coronagraph system through a telescope and is converted to the first parabolic mirror through the reflector to expand a point source target into parallel light so as to simulate the stellar light from infinity; the aperture diaphragm is used for blocking out unnecessary stray light from the system, the annular pupil modulation filter is used for modulating star light energy, and finally the star light energy is converted to a second parabolic mirror through an imaging mirror and imaged on a focal plane detector of a star crown instrument system, and the annular pupil modulation filter is used for carrying out pupil amplitude modulation by adopting the imaging method of any one of claims 1 to 7.
9. The coronagraph system based on the spatial full-area ultrahigh-contrast imaging method according to claim 8, wherein the coronagraph system has a spatial large working area or a 360 ° full-field working area, and the contrast is better than 10-7The coronagraph system is used for spatial high-contrast imaging or extraterrestrial planet detection.
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