Method and system for measuring imaging resolution of the outer solar corona region of a coronagraph

Abstract

The present application relates to a kind of outer eclipse coronagraph vignetting area imaging resolution measurement method, including image acquisition step, point division processing calculation step, curve analysis step and coronagraph limit angle resolution calculation step, also provide a kind of outer eclipse coronagraph vignetting area imaging resolution measurement system, including first pre-target object module or second pre-target object module, first coronagraph module or second coronagraph module, detector module and data processing module, to realize with MTF test method to coronagraph outer eclipse body vignetting coverage area imaging quality measurement, then using imaging quality evaluation result to the precise focusing of detector, to improve the quality of coronagraph observation data in this way.

Description

Technical Field

[0001] This invention belongs to the field of imaging resolution measurement technology for coronagraph halo region, and particularly relates to a method and system for measuring imaging resolution of the halo region of an externally shielded coronagraph. Background Technology

[0002] A coronagraph is a telescope used to observe the solar corona surrounding the Sun. It includes external and internal occultation coronagraphs. An external occultation coronagraph uses an outer occultation to block direct sunlight from the Sun, simulating the effect of a total solar eclipse to observe the corona. For wide-field external occultation coronagraphs, the high brightness of the K-coron and F-coronation near the inner field of view can exceed the dynamic range of the CCD detector in certain areas, affecting normal imaging. The edge of the outer occultation in a wide-field external occultation coronagraph produces vignetting in certain areas of the field of view, which can reduce the brightness of the inner field to some extent. However, this single source of vignetting is insufficient to reduce the brightness of the inner field to the required level; a specially designed vignetting stop is also necessary.

[0003] In geometrical optics, a beam of light emanating from an on-axis point, filling the entrance pupil, is imaged by the optical system as a beam filling the exit pupil. Some optical systems, however, cannot image off-axis points with a beam that completely fills the entrance pupil. This results in an off-axis image beam being smaller than the on-axis image beam, leading to a decrease in illuminance at the image plane edges. This phenomenon of partial obstruction of the off-axis beam is called off-axis vignetting. For a specific location, the intensity of vignetting is typically measured by the ratio of pixel brightness with vignetting to pixel brightness without vignetting; a smaller ratio indicates stronger vignetting at that point.

[0004] There are many common evaluation criteria for the decrease in imaging resolution caused by vignetting. To more intuitively reflect the observer's judgment, the Modulation Transfer Function (MTF) curve is chosen as the evaluation criterion. MTF is a contrast-based quantity that reflects the overall imaging quality of an optical system. In optical system performance testing, a set of alternating bright and dark lines of equal width is usually selected as the target object, with the line size gradually decreasing according to a certain rule. During testing, the optical system under test is used to image the target object lines sequentially, and the smallest set of lines that can be clearly distinguished is considered the resolution limit of the optical system. In optics, two lines, one bright and one dark, are generally called a line pair. The number of line pairs per millimeter is the spatial frequency (lp / mm) of the target object. After imaging, the MTF curve of the instrument under test can be plotted with the spatial frequency of each set of lines as the horizontal axis and the corresponding contrast as the vertical axis. For a large field-of-view coronagraph, it is necessary to measure the MTF curves within the vignetting coverage area of ​​the outer shelter at different vignetting intensities, and use this to analyze the impact of vignetting on the coronagraph's imaging resolution. In addition, since the limit resolution shown in the MTF curve is greatly affected by the focusing accuracy of the detector, it can be used as a basis for judgment to help improve focusing accuracy.

[0005] However, the existing MTF testing method is not applicable to large field-of-view externally shielded coronagraphs. First, the external shield is located at a distance from the front of the objective lens, making it impossible to place the target object close to it. In addition, the MTF test is aimed at the effect of vignetting caused by the external shield. Therefore, the test should be made to conform to the actual application scenario of large field-of-view externally shielded coronagraphs. Summary of the Invention

[0006] To address the shortcomings of related technologies, this invention provides a method and system for measuring the imaging resolution of the halo region of an externally shielded coronagraph. This method enables the measurement of the imaging quality of the halo coverage area of ​​the coronagraph's external shield using the MTF test method, and then uses the imaging quality assessment results to accurately focus the detector, thereby improving the quality of coronagraph observation data.

[0007] On one hand, the present invention provides a method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph, comprising:

[0008] The image acquisition steps involve capturing a light source distribution image by the detector module in the direction of the first coronagraph module and the first front target module, capturing a vignetting distribution image by the detector module in the direction of the second coronagraph module and the first front target module, capturing a resolution plate image by the detector module in the direction of the second coronagraph module and the second front target module, and capturing a dark field image by the detector module through occlusion.

[0009] The dot-matrix processing calculation step involves subtracting the dark field image from the light source distribution image, the vignetting distribution image, and the resolution panel image respectively through dot-matrix processing to obtain the normalized distribution of vignetting intensity across the entire field of view and the normalized brightness values ​​of each set of resolution lines. This allows for the extraction of the corresponding position of a vignetting intensity of a specified intensity in the field of view, and the normalized brightness of the resolution line at the specified vignetting intensity position is obtained based on the corresponding position of the vignetting intensity of a specified intensity in the field of view.

[0010] The curve analysis step involves plotting a curve based on the normalized brightness of the resolution lines at the specified vignetting intensity location. By calculating the contrast of each set of resolution lines in the normalized brightness curve at the specified vignetting intensity location, the MTF curve of the coronagraph at the specified vignetting intensity is obtained. Based on the MTF curve of the coronagraph at the specified vignetting intensity, the imaging quality assessment of the vignetting region of the outer bunker is realized.

[0011] In some embodiments, the method for measuring the imaging resolution of the halo region of an externally shielded coronagraph further includes:

[0012] The steps for calculating the limiting angular resolution of a coronagraph are as follows: Based on a specified set of resolution lines in the MTF curve of the coronagraph at the specified vignetting intensity, the size of the set of resolution lines is obtained, and the limiting angular resolution of the coronagraph is calculated according to the distance between the resolution plate and the objective lens assembly.

[0013] In some embodiments, the image acquisition step further includes:

[0014] The step of acquiring the light source distribution image involves sequentially setting up the first front target module, the first coronagraph module, and the detector module along the optical path, and capturing the light source distribution image in the direction of the first coronagraph module and the first front target module through the detector module.

[0015] The vignetting distribution image acquisition step involves sequentially setting up the first front target module, the second coronagraph module, and the detector module along the optical path direction, and capturing the vignetting distribution image in the direction of the second coronagraph module and the first front target module through the detector module;

[0016] The resolution panel image acquisition step involves sequentially setting the second front target module, the second coronagraph module, and the detector module along the optical path direction, and capturing the resolution panel image by the detector module in the direction of the second coronagraph module and the second front target module.

[0017] The dark field image acquisition step involves capturing the dark field image by blocking the lens of the detector module.

[0018] In some embodiments, the dot division calculation step further includes:

[0019] The steps for calculating the vignetting intensity distribution at the edge of the outer shelter are as follows: subtract the dark field image from the vignetting distribution image, subtract the dark field image from the light source distribution image, and perform dot division to obtain a normalized vignetting intensity distribution across the entire field of view; obtain the vignetting intensity distribution at the edge of the outer shelter by filtering the normalized vignetting intensity distribution across the entire field of view; and extract the corresponding positions of vignetting of a specified intensity in the field of view based on the vignetting intensity distribution at the edge of the outer shelter.

[0020] The resolution line brightness distribution calculation step involves subtracting the dark field image from the resolution panel image and subtracting the dark field image from the vignetting distribution image, and performing dot division to obtain the normalized brightness values ​​of each set of resolution lines. Then, the normalized brightness of the corresponding position of the specified intensity vignetting in the field of view is output pixel by pixel in the resolution panel image in sequence to obtain the normalized brightness of the resolution line at the specified vignetting intensity position.

[0021] In some embodiments, the vignetting intensity is represented by the following calculation model:

[0022]

[0023] Among them, DN V DN represents the brightness of the pixel in the halosed area of ​​the outer bunker in the coronagraph's field of view, while DN represents the brightness of the same pixel when it is not halosed.

[0024] In some embodiments, the resolution line contrast is represented by the following calculation model:

[0025]

[0026] Among them, I max and I min These are the brightness values ​​for the white and black lines of the resolution, respectively.

[0027] In some embodiments, the limiting angular resolution of the coronagraph is represented by the following calculation model:

[0028]

[0029] Where a is the linewidth of the resolution lines; b is the distance between the set of resolution lines and the coronagraph objective.

[0030] On the other hand, the present invention also provides a system for measuring the imaging resolution of the halo region of an externally concealed coronagraph, for implementing the above-mentioned method for measuring the imaging resolution of the halo region of an externally concealed coronagraph, comprising:

[0031] A first front-end target module or a second front-end target module, wherein the first front-end target module is used to provide a simulated light source, and the second front-end target module is used to provide a simulated light source and a resolution board;

[0032] A first coronagraph module or a second coronagraph module, wherein the first coronagraph module is used to provide the coronagraph component under test to block and eliminate part of the light from the simulated light source, and the second coronagraph module is used to provide an outer shelter and the coronagraph component under test to block and eliminate part of the light from the simulated light source;

[0033] The detector module receives light emitted from the first or second coronagraph module and focuses it onto the detector module. The detector module is used to capture light source distribution images, vignetting distribution images, resolution plate images, and dark field images.

[0034] The data processing module is used to perform point-reduction processing on the light source distribution image, the vignetting distribution image, the resolution plate image, and the dark field image, and to draw the MTF curve of the coronagraph at a specified vignetting intensity based on the resolution line normalized brightness at the specified vignetting intensity position obtained by the point-reduction processing. The imaging quality assessment of the vignetting region of the outer bunker is realized through the MTF curve of the coronagraph at the specified vignetting intensity.

[0035] In some embodiments, the first pre-target module or the second pre-target module further includes:

[0036] A collimator is positioned on one side of the simulated light source;

[0037] The first light homogenizer is disposed on the side of the collimator away from the simulated light source;

[0038] The second light homogenizer is disposed on the side of the first light homogenizer away from the collimator;

[0039] In the first front target module, the light from the simulated light source passes sequentially through the collimator, the first homogenizer, and the second homogenizer, and is directed toward the first or second coronagraph module; in the second front target module, the light from the simulated light source passes sequentially through the collimator, the first homogenizer, the second homogenizer, and the resolution plate, and is directed toward the first or second coronagraph module.

[0040] In some embodiments, the coronagraph assembly to be tested includes: an objective lens diaphragm assembly, an objective lens assembly, an inner shield, an extinction groove assembly, a field lens assembly, a stray light removal diaphragm assembly, a Lyot diaphragm assembly, a relay lens assembly, and a filter arranged sequentially along the optical path.

[0041] In summary, this invention provides a method and system for measuring the imaging resolution of the halos region of an externally shielded coronagraph. It measures the light source distribution image, halos distribution image, resolution plate image, and dark field image. After point division processing, it obtains the resolution line normalized brightness at a specified halos intensity location. Based on the resolution line normalized brightness at the specified halos intensity location, it plots the MTF curve of the coronagraph at the specified halos intensity. Finally, based on the MTF curve of the coronagraph at the specified halos intensity, it achieves the imaging quality assessment of the halos region of the external shield.

[0042] Other features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims, and drawings. Attached Figure Description

[0043] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0044] Figure 1 This is the first flowchart of the method for measuring the imaging resolution of the halo region of the externally shielded coronagraph according to the present invention;

[0045] Figure 2 This is the second flowchart of the method for measuring the imaging resolution of the halo region of the externally shielded coronagraph according to the present invention;

[0046] Figure 3 This is a schematic diagram of the structure of the externally shielded coronagraph halo region imaging resolution measurement system of the present invention;

[0047] Figure 4 This is a schematic diagram of the internal structure of the second front target module of the externally shielded coronagraph halo region imaging resolution measurement system of the present invention.

[0048] In the picture:

[0049] 1. Second front target module; 2. Outer shelter; 3. Objective lens diaphragm assembly; 4. Objective lens assembly; 5. Inner shelter; 6. Extinction groove assembly; 7. Field lens assembly; 8. Stray light removal diaphragm assembly; 9. Lyot diaphragm assembly; 10. Relay lens assembly; 11. Filter; 12. Detector module; 13. Simulated light source; 14. Collimator; 15. First homogenizer; 16. Second homogenizer; 17. Resolution board. Detailed Implementation

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0051] In the description of this invention, it should be understood that the terms "center", "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0052] The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature.

[0053] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Specific Implementation Example 1

[0055] In the accompanying drawings of this invention, Figure 1 This is the first flowchart of the method for measuring the imaging resolution of the halo region of the externally shielded coronagraph according to the present invention; Figure 2 This is the second flowchart of the method for measuring the imaging resolution of the halo region of the externally shielded coronagraph according to the present invention; Figure 3 This is a schematic diagram of the structure of the externally shielded coronagraph halo region imaging resolution measurement system of the present invention; Figure 4 This is a schematic diagram of the internal structure of the second front target module of the externally shielded coronagraph halo region imaging resolution measurement system of the present invention.

[0056] Reference Appendix Figure 1 As shown, this invention provides a method for measuring the imaging resolution of the halo region of an externally shielded coronagraph, including an image acquisition step S1, a point division processing calculation step S2, a curve analysis step S3, and a coronagraph limiting angular resolution calculation step S4, wherein:

[0057] Image acquisition step S1: A light source distribution image is obtained by taking a picture of the first coronagraph module and the first front target module through the detector module 12; a vignetting distribution image is obtained by taking a picture of the second coronagraph module and the first front target module through the detector module 12; a resolution plate image is obtained by taking a picture of the second coronagraph module and the second front target module 1 through the detector module 12; and a dark field image is obtained by taking a picture of the detector module 12 through occlusion.

[0058] In step S2, the data after subtracting the dark field image from the light source distribution image, vignetting distribution image, and resolution plate image are processed by point division to obtain the normalized distribution of vignetting intensity across the entire field of view and the normalized brightness value of each set of resolution lines. This allows the extraction of the corresponding position of vignetting of a specified intensity in the field of view, and the normalized brightness of the resolution line at the specified vignetting intensity position is obtained based on the corresponding position of vignetting of a specified intensity in the field of view.

[0059] In curve analysis step S3, a curve is drawn based on the normalized brightness of the resolution line at the specified vignetting intensity position. By calculating the contrast of each set of resolution lines in the normalized brightness curve of the resolution line at the specified vignetting intensity position, the MTF curve of the coronagraph at the specified vignetting intensity is obtained. Based on the MTF curve of the coronagraph at the specified vignetting intensity, the imaging quality assessment of the vignetting area of ​​the outer bunker 2 is realized.

[0060] Step S4 for calculating the limiting angular resolution of the coronagraph involves obtaining the dimensions of a set of resolution lines from the MTF curve of the coronagraph under a specified vignetting intensity, and calculating the limiting angular resolution of the coronagraph based on the distance between the resolution plate 17 and the objective lens assembly 4.

[0061] It should be noted that in the curve analysis step S3, based on the normalized brightness of the resolution lines at the specified vignetting intensity position obtained in the point division processing calculation step S2, the normalized brightness curve of the resolution lines at the specified vignetting intensity position is plotted. In the normalized brightness curve of the resolution lines at the specified vignetting intensity position, several maximum and minimum brightness values ​​of each set of resolution lines can be obtained. The contrast ratio of each set of resolution lines is calculated using the MTF calculation formula MTF = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness). The results are plotted to obtain the MTF curve of the coronagraph at the specified vignetting intensity.

[0062] In some embodiments, in the step S4 of calculating the limiting angular resolution of the coronagraph, a set of resolution lines is specified, which are the resolution lines corresponding to the position of the human eye's resolution limit. In engineering optics, it is generally considered that the human eye's resolution limit is MTF = 0.03. Therefore, when it is necessary to calculate the limiting angular resolution of the coronagraph for human eye resolution, the corresponding resolution line is found at the position of the human eye's resolution limit in the MTF curve. Based on the size of the set of resolution lines and the distance between the resolution plate 17 and the coronagraph objective lens, the limiting angular resolution of the coronagraph for human eye resolution can be calculated.

[0063] In some embodiments, the image acquisition step S1 further includes:

[0064] In the dark field image acquisition step S11, a dark field image is obtained by placing an obstruction in front of the detector module 12 to ensure that no ambient stray light enters. The dark field image mainly includes the background noise of the detector module 12 itself, which is used to reduce measurement error. In some embodiments, the dark field image can be obtained by covering the lens with a lens cap.

[0065] In step S12, the light source distribution image acquisition step involves sequentially setting up the first front target module, the first coronagraph module, and the detector module 12 along the optical path. The first front target module and the first coronagraph module are adjusted so that the light beam formed by the light emitted from the simulated light source 13 after passing through the collimator 14 shares the same optical axis as the first coronagraph module. The focal length of the collimator 14 is adjusted so that the beam size is sufficient to cover the entire first homogenizer 15. The light passing through the first homogenizer 15 illuminates the second homogenizer 16, which serves as the background of the resolution board 17, for secondary homogenization. The inner cover 5 is moved out of the field of view by adjusting the slider using the built-in support rod. The detector module 12 is used to take a picture to obtain the light source distribution image.

[0066] In step S13 of acquiring the vignetting distribution image, the first front target module, the second coronagraph module, and the detector module 12 are set sequentially along the optical path so that the outer cover 2 coincides with the optical axis. The target object is placed in the blank position of the field of view to visually coarsely focus the detector. At this time, a uniform vignetting can be observed around the outer cover 2 in the field of view. The target object used for focusing is removed, and the vignetting distribution image is obtained by taking a picture through the detector module 12.

[0067] In the resolution board image acquisition step S14, the second front target module 1, the second coronagraph module, and the detector module 12 are set sequentially along the optical path. The target support platform is adjusted to be tilted 45° to the upper right and at a suitable height. The specially made resolution board 17 is installed. At this time, the resolution board 17 is illuminated relatively evenly by the light emitted from the second light homogenizer 16, and all the resolution lines are in the vignetting coverage area and perpendicular to the edge of the shelter. The resolution board image is obtained by the detector module 12.

[0068] It should be noted that when capturing images of the light source distribution, vignetting distribution, resolution plate, and dark field, the images should be captured continuously in the same environment to ensure that the influence of stray light remains consistent. The order of the image acquisition steps is not restricted. The dark field image acquisition step S11, the light source distribution image acquisition step S12, the vignetting distribution image acquisition step S13, and the resolution plate image acquisition step S14 can be performed in a different order within a measurement system.

[0069] Compared to the first coronagraph module, the second coronagraph module has an additional outer shield 2 and an inner shield 5. The second forward target module 1 has an additional resolution board 17 compared to the first forward target module. Therefore, when capturing the light source distribution image, the measurement system does not use the outer shield 2; instead, the simulated light source 13 in the first forward target module is aligned with the first coronagraph module, and the detector module 12 captures the image to obtain a light source image containing the light source illuminance distribution. When capturing the vignetting distribution image, the measurement system uses the outer shield 2, and the simulated light source 13 in the first forward target module is aligned with the first coronagraph module. The second coronagraph module and detector module 12 take pictures to obtain a vignetting distribution image. When taking a resolution plate image, an outer shield 2 and a resolution plate 17 are set in the measurement system. The analog light source 13 in the second front target module 1 is aligned with the second coronagraph module. The resolution plate 17 is located between the analog light source 13 and the second coronagraph module, so that the resolution line covers the entire vignetting area and is taken to obtain a resolution plate image. When taking a dark field image, the lens of the camera in detector module 12 needs to be blocked under the same shooting environment to take a picture and obtain a dark field image.

[0070] In some embodiments, the dot division calculation step S2 further includes:

[0071] Step S21 for calculating the vignetting intensity distribution at the edge of outer shelter 2 involves subtracting the dark field image from the vignetting distribution image and the dark field image from the light source distribution image, followed by dot division, to obtain a normalized vignetting intensity distribution across the entire field of view. This normalized distribution is then filtered to obtain the vignetting intensity distribution at the edge of outer shelter 2. Based on this distribution, the contour lines for specific vignetting intensities can be obtained using the contour function, thereby extracting the corresponding positions of vignetting of a specified intensity in the field of view.

[0072] In step S22, the resolution line brightness distribution calculation involves subtracting the dark field image from the resolution panel image and subtracting the dark field image from the vignetting distribution image, followed by dot division, to obtain the normalized brightness values ​​for each set of resolution lines. Referring to the position corresponding to the specified intensity vignetting in the field of view obtained in step S21, the normalized brightness of the position corresponding to the specified intensity vignetting in the field of view is output pixel by pixel in the resolution panel image to obtain the normalized brightness of the resolution line at the specified vignetting intensity position.

[0073] In some embodiments, the vignetting intensity is represented by the following calculation model:

[0074]

[0075] Among them, DN V DN represents the brightness of the pixel in the vignetting area of ​​the outer shelter 2 in the field of view of the coronagraph, while DN represents the brightness of the same pixel when it is not vignetted. The pixel brightness value is directly read from the image captured by the detector module 12.

[0076] In some embodiments, the resolution line contrast is represented by the following calculation model:

[0077]

[0078] Among them, I max and I min These represent the brightness values ​​of the white and black lines, respectively, I. max and I min The value is read directly from the image captured by detector module 12.

[0079] In some embodiments, the limiting angular resolution of a coronagraph is represented by the following calculation model:

[0080]

[0081] Where 'a' represents the linewidth of the resolution lines; and 'b' represents the distance between the resolution lines and the coronagraph objective lens, both of which are directly measured. The value of 'b' is a preset value specified by the surveyor, who selects different distances based on the measurement conditions.

[0082] Specifically, find the intersection of the human eye's visual resolution limit MTF = 0.03 with the MTF curves of each vignetting intensity in the MTF curve. The spatial frequency corresponding to this intersection point corresponds to the angular resolution limit of the large field-of-view coronagraph. This angular resolution is expressed as θ = arctan(l / L), where l is the resolution linewidth at which the resolution limit is reached, and L is the distance between the resolution line and the coronagraph objective lens.

[0083] Specifically, the entrance pupil diameter of the large field-of-view white light extended coronagraph is 12 mm, the distance between the outer shield 2 and the objective lens is 469.3 mm, and the resolution plate 17 is placed 4500 mm in front of the objective lens. The maximum resolution linewidth is 5000 μm, and the minimum is 1403.1 μm. According to the measurement method provided by this invention, the MTF at the 40% vignetting position decreases from 0.722 to 0.053 as the spatial frequency of the resolution line increases, and at the 5% vignetting position it decreases from 0.376 to 0.034. The MTF values ​​and decreasing trends corresponding to each resolution line are roughly consistent with the simulation results. Under the 5% vignetting condition, the large field-of-view coronagraph reaches the limiting angular resolution at 1574.9 μm, which is 1.2 according to the limiting angular resolution calculation formula. Based on the influence of defocus on MTF in engineering optics, the MTF measurement system described in this invention can be used to assist detector focusing. The data processing module realizes real-time measurement of MTF, and after judging the defocus amount of the optical system, the result is fed back to the electric focusing displacement stage to realize optical system detection. Specific Implementation Example 2

[0085] As attached Figure 3 As shown, the present invention also provides an imaging resolution measurement system for the halo region of an externally concealed coronagraph, used to implement the imaging resolution measurement method for the halo region of an externally concealed coronagraph in Specific Embodiment 1. The system includes a first or second front target module 1, a first or second coronagraph module, a detector module 12, and a data processing module, wherein:

[0086] The first front target module or the second front target module 1, the first front target module is used to provide the simulated light source 13, and the second front target module 1 is used to provide the simulated light source 13 and the resolution board 17.

[0087] In some embodiments, the first front target module is provided with an analog light source 13, a collimator 14, a first light homogenizer 15, and a second light homogenizer 16 in sequence along the optical path direction. The light from the analog light source 13 passes through the collimator 14, the first light homogenizer 15, and the second light homogenizer 16 in sequence and is directed toward the first or second coronagraph module.

[0088] As attached Figure 4 As shown, in some embodiments, the second front target module 1 is provided with an analog light source 13, a collimator 14, a first light homogenizer 15, a second light homogenizer 16 and a resolution plate 17 in sequence along the optical path direction. The light from the analog light source 13 passes through the collimator 14, the first light homogenizer 15, the second light homogenizer 16 and the resolution plate 17 in sequence and is directed toward the first coronagraph module or the second coronagraph module.

[0089] It should be noted that, compared with the first front target module, the second front target module 1 is equipped with a resolution plate 17, which is used in the resolution plate image acquisition step S14 to make the resolution line cover the entire vignetting area and take a picture to obtain the resolution plate image; the resolution plate 17 can be modified according to the shape of the outer cover 2 of the outer cover coronagraph, so as to realize the imaging of resolution lines of different spatial frequencies under the same vignetting intensity, and obtain the imaging limit angular resolution and MTF curve under the vignetting condition. In this embodiment, an outer cover coronagraph with a square outer cover 2 is used for measurement, so the resolution line is selected as a straight line; in a measurement system, the testing personnel can choose to use the first front target module or the second front target module 1.

[0090] In some embodiments, the first front target module or the second front target module 1 uses a xenon lamp as a simulated light source 13. The simulated light source 13 is used to simulate sunlight. The collimator 14 is used to collimate the light. The first light homogenizer 15 is a circular opaline glass, and the second light homogenizer 16 is a square opaline glass. The first light homogenizer 15 is used to reduce the bright spot at the center of the light source, and the second light homogenizer 16 is used to homogenize the light source and act as a background.

[0091] It should be noted that in the second front target module 1, the incident beam emitted by the simulated light source 13 is collimated and homogenized by the collimator 14, the first homogenizer 15 and the second homogenizer 16 before illuminating the resolution plate 17. The uniformity and spot size of the final emitted beam have been pre-measured and meet the illumination requirements of the measurement system of the present invention. Since the stability of the xenon lamp light source changes periodically, the entire shooting process is controlled to be completed within a change cycle.

[0092] The first coronagraph module is used to provide the coronagraph component under test to block and eliminate part of the light from the simulated light source 13, and the second coronagraph module is used to provide the outer shelter 2 and the coronagraph component under test to block and eliminate part of the light from the simulated light source 13.

[0093] It should be noted that the second coronagraph module has an additional outer shield 2 compared to the first coronagraph module. The outer shield 2 is used to block the direct light from the simulated light source 13. In a measurement system, the testing personnel can choose to use either the first or second coronagraph module.

[0094] As attached Figure 3 As shown, in some embodiments, both the first coronagraph module and the second coronagraph module are equipped with a coronagraph component to be tested. The coronagraph component to be tested includes a heat-resistant mirror (not shown in the figure), an objective aperture assembly 3, an objective lens assembly 4, an inner shield 5, an extinction groove assembly 6, a field lens assembly 7, a stray light elimination aperture assembly 8, a Lyot aperture assembly 9, a relay mirror assembly 10, and a filter 11 arranged sequentially along the optical path direction.

[0095] Among them, the heat-resistant mirror is used to reflect the direct light of the simulated light source 13 that exceeds the shielding area of ​​the outer shelter 2 into the external space; the objective aperture assembly 3 is used to shield the direct light beam of the simulated light source 13 that exceeds the objective aperture of the objective lens assembly 4 and passes through the direct light beam of the simulated light source 13 that is smaller than the objective aperture; the stray light elimination aperture assembly 8 is used to shield the diffracted light generated by the direct light of the simulated light source 13 and the reflected light from the coronagraph tube wall generated by the objective aperture assembly 3, so that it cannot enter the detector module 12; the inner shelter 5 is used to shield the imaging of the objective lens assembly 4; the field lens assembly 7 and the relay lens assembly 10 are used to image the beam to the detector module 12; by using the outer shelter 2, the objective aperture assembly 3, the stray light elimination aperture assembly 8, the inner shelter 5 and the Lyot aperture assembly 9, all the direct light, diffracted light and other light other than the scattered light generated by the objective lens itself in the optical path are shielded and eliminated, and stray light is eliminated to the greatest extent.

[0096] It should be noted that the imaging performance of each mirror in the first or second coronagraph module has been tested separately. The outer shield 2 has been precision-machined to ensure the sharpness of its edges, and its position has been precisely calibrated during installation. Under these conditions, it can be assumed that the vignetting produced by the edge of the outer shield 2 decreases uniformly outward along the direction perpendicular to the edge and exhibits a good symmetrical distribution.

[0097] The detector module 12 receives light emitted from the first or second coronagraph module and focuses it onto the detector module 12. The detector module 12 is used to capture light source distribution images, vignetting distribution images, resolution plate images, and dark field images.

[0098] The data processing module is used to perform point-reduction processing on the light source distribution image, vignetting distribution image, resolution plate image, and dark field image. Based on the resolution line normalized brightness obtained from the point-reduction processing at the specified vignetting intensity position, the module plots the MTF curve of the coronagraph at the specified vignetting intensity. The imaging quality assessment of the vignetting region of the outer bunker 2 is achieved through the MTF curve of the coronagraph at the specified vignetting intensity.

[0099] It should be noted that the vignetting of the outer shelter 2 in this invention is determined by its own shape and optomechanical design. The imaging resolution within the vignetting area of ​​the shelter can be obtained by software simulation calculation or laboratory measurement, and the two methods have been mutually verified, resulting in high accuracy of the resolution results.

[0100] The specific software simulation calculation method involves first establishing a model of the halosing region imaging resolution measurement system of the coronagraph of this invention in the software, obtaining a ray-tracing point map excluding the outer cover 2. Then, referring to the design drawings of the outer cover 2, the outer cover 2 model is added at the corresponding positions to partially block the light rays, resulting in a ray-tracing point map including the outer cover 2. By performing relevant calculations on the two point map data, the software simulation results of the impact of the halosing of the coronagraph's outer cover 2 on the imaging resolution are obtained.

[0101] In the software, the first coronagraph module and detector module 12 are modeled. The first coronagraph module includes a heat-resistant mirror, objective aperture assembly 3, objective lens assembly 4, inner shelter 5, extinction groove assembly 6, field lens assembly 7, stray light removal aperture assembly 8, Lyot aperture assembly 9, and relay mirror assembly 10. The model parameters are matched with the actual parameters of each component. Based on the vignetting characteristics of the coronagraph outer shelter 2, the vignetting model can be represented as:

[0102]

[0103] A0=∫∫ D A1(x,y)dxdy

[0104] A program was written to draw a simulated image of vignetting distribution and to determine the field of view angles corresponding to different vignetting intensities. In the optical simulation software, the required light rays were sequentially set according to each field of view angle to obtain a ray tracing point map, and the point radius r of the light rays at each field of view angle was recorded. Then, a 2-component model of the outer shelter was built. The shelter's parameters and position coordinates were pre-measured and determined. The shelter model was set to a center-occlusion mode to ensure complete light blocking. Ray tracing was performed again to obtain a point map, and the point radius r corresponding to each field of view was recorded. d The quantitative results of the impact of vignetting on the imaging resolution of the coronagraph were obtained by comparing the speckle radii before and after the addition of the shelter component.

[0105] The specific laboratory measurement method involves setting up a model of the externally shielded coronagraph halo region imaging resolution measurement system of the present invention in a clean laboratory environment. To verify the above software simulation results, a first or second pre-target object module 1 that matches the constructed model is used to simulate sunlight illumination. After the light passes through the resolution plate 17, it illuminates the first or second coronagraph module and is imaged by the detector module 12. The influence of the halo of the external shield 2 on the imaging resolution is calculated based on the obtained image.

[0106] The outer shelter 2 is manufactured with high precision, and its special five-layer structure can suppress the diffraction phenomenon of light at the edge of the outer shelter 2 to the greatest extent. Therefore, the edge diffracted light can be ignored and the vignetting can be assumed to be uniformly and symmetrically distributed around the shelter. The imaging angular resolution of the vignetting area was measured when the outer shelter 2 components were installed and removed, and the corresponding spot radii r and r were calculated respectively. d If the changes in the spot radius caused by installing and removing the outer cover 2 are equivalent in both software simulation and actual measurement, then both methods can be mutually verified as applicable to the imaging resolution measurement of the halo region of the outer cover coronagraph.

[0107] As attached Figure 2As shown, in some embodiments, the MTF curve is calculated and focusing is performed using the externally shielded coronagraph halos region imaging resolution measurement method and system of the present invention. Before starting, the detector is adjusted to at least a small defocus. Three images are acquired sequentially according to different disassembly and assembly states of the external shield 2 of the external coronagraph and the target object 17 of the resolution plate. The data processing module calculates the imaging resolution of the external shield 2 of the coronagraph under different halos intensities based on the obtained images and preset measurement methods and parameters, and plots the corresponding modulation transfer function curves. The data processing module controls the detector focusing motor to move in a certain step size, repeating the above measurement steps until the detector defocuses again. The obtained set of MTF curves is judged, and the MTF curve with the highest limiting resolution is the final measurement result. The corresponding focusing motor position is the precise focal position of the detector. Furthermore, in order to improve the measurement accuracy, the background image and the dark field image should be captured before the focusing motor moves, and the exposure time of each image should be strictly the same.

[0108] In summary, the present invention provides a method and system for measuring the imaging resolution of the halo region of an externally shielded coronagraph, which has at least one or more of the following advantages:

[0109] 1. Based on the traditional method for measuring the resolution of an optical system, by adding a first or second front target module 1 and a data processing module, the resolution of the halos region of the coronagraph outer shelter 2 and the auxiliary calibration of the detector module 12 for focusing are realized. The entire measurement system has a simple structure and low measurement cost. A special resolution plate 17 for the coronagraph in the embodiment is selected to ensure that the spatial frequency of the resolution line shows a regular change at positions with the same halos intensity, so as to more accurately measure the resolution at that position.

[0110] 2. The measurement method of the present invention uses MTF as the imaging quality evaluation standard, and utilizes the relationship between MTF and defocus to assist the detector in precise focusing while testing the imaging resolution of the vignetting area of ​​the outer shelter 2.

[0111] 3. The measurement system of the present invention has a simple structure and is easy to build. It can be mutually verified with theoretical calculations and software simulation results, and the verification results are highly accurate.

[0112] 4. The measurement method and system of the present invention can also provide a basis for the design of the halos aperture of the subsequent externally shielded coronagraph, which helps the observation of the inner field of view and can effectively improve the quality of corona scientific data.

[0113] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0114] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph, characterized in that, include: The image acquisition steps involve: capturing a light source distribution image by the detector module towards the first coronagraph module and the first front target module; capturing a vignetting distribution image by the detector module towards the second coronagraph module and the first front target module; capturing a resolution panel image by the detector module towards the second coronagraph module and the second front target module; and capturing a dark field image by the detector module through occlusion. The first front target module provides a simulated light source, and the second front target module provides both a simulated light source and a resolution panel. The first coronagraph module provides the coronagraph component under test to block and eliminate some of the light from the simulated light source, and the second coronagraph module provides an outer cover and the coronagraph component under test to block and eliminate some of the light from the simulated light source. The dot-matrix processing calculation step involves subtracting the dark field image from the light source distribution image, the vignetting distribution image, and the resolution panel image respectively through dot-matrix processing to obtain the normalized distribution of vignetting intensity across the entire field of view and the normalized brightness values ​​of each set of resolution lines. This allows for the extraction of the corresponding position of a vignetting intensity of a specified intensity in the field of view, and the normalized brightness of the resolution line at the specified vignetting intensity position is obtained based on the corresponding position of the vignetting intensity of a specified intensity in the field of view. The curve analysis step involves plotting a curve based on the normalized brightness of the resolution lines at the specified vignetting intensity location. By calculating the contrast of each set of resolution lines in the normalized brightness curve at the specified vignetting intensity location, the MTF curve of the coronagraph at the specified vignetting intensity is obtained. Based on the MTF curve of the coronagraph at the specified vignetting intensity, the imaging quality assessment of the vignetting region of the outer bunker is realized.

2. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 1, characterized in that, Also includes: The steps for calculating the limiting angular resolution of a coronagraph are as follows: Based on a specified set of resolution lines in the MTF curve of the coronagraph at the specified vignetting intensity, the size of the set of resolution lines is obtained, and the limiting angular resolution of the coronagraph is calculated according to the distance between the resolution plate and the objective lens assembly.

3. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 1, characterized in that, The image acquisition steps further include: The step of acquiring the light source distribution image involves sequentially setting up the first front target module, the first coronagraph module, and the detector module along the optical path, and capturing the light source distribution image in the direction of the first coronagraph module and the first front target module through the detector module. The vignetting distribution image acquisition step involves sequentially setting up the first front target module, the second coronagraph module, and the detector module along the optical path direction, and capturing the vignetting distribution image in the direction of the second coronagraph module and the first front target module through the detector module; The resolution panel image acquisition step involves sequentially setting the second front target module, the second coronagraph module, and the detector module along the optical path direction, and capturing the resolution panel image by the detector module in the direction of the second coronagraph module and the second front target module. The dark field image acquisition step involves capturing the dark field image by blocking the lens of the detector module.

4. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 1, characterized in that, The dot division calculation step further includes: The steps for calculating the vignetting intensity distribution at the edge of the outer shelter are as follows: subtract the dark field image from the vignetting distribution image, subtract the dark field image from the light source distribution image, and perform dot division to obtain a normalized vignetting intensity distribution across the entire field of view; obtain the vignetting intensity distribution at the edge of the outer shelter by filtering the normalized vignetting intensity distribution across the entire field of view; and extract the corresponding positions of vignetting of a specified intensity in the field of view based on the vignetting intensity distribution at the edge of the outer shelter. The resolution line brightness distribution calculation step involves subtracting the dark field image from the resolution panel image and subtracting the dark field image from the vignetting distribution image, and performing dot division to obtain the normalized brightness values ​​of each set of resolution lines. Then, the normalized brightness of the corresponding position of the specified intensity vignetting in the field of view is output pixel by pixel in the resolution panel image in sequence to obtain the normalized brightness of the resolution line at the specified vignetting intensity position.

5. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 4, characterized in that, The intensity of the vignetting is represented by the following calculation model: ， in, DN represents the brightness of the pixel in the halosed area of ​​the outer bunker in the coronagraph's field of view, while DN represents the brightness of the same pixel when it is not halosed.

6. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 1, characterized in that, The resolution line contrast is represented by the following calculation model: ， in, and These are the brightness values ​​for the white and black lines of the resolution, respectively.

7. The method for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 2, characterized in that, The limiting angular resolution of the coronagraph is expressed by the following calculation model: ， Where a is the linewidth of the resolution lines; b is the distance between the set of resolution lines and the coronagraph objective.

8. A system for measuring the imaging resolution of the halo region of an externally occluded coronagraph, used to implement the method for measuring the imaging resolution of the halo region of an externally occluded coronagraph as described in any one of claims 1-7, characterized in that, include: A first front-end target module or a second front-end target module, wherein the first front-end target module is used to provide a simulated light source, and the second front-end target module is used to provide a simulated light source and a resolution board; A first coronagraph module or a second coronagraph module, wherein the first coronagraph module is used to provide the coronagraph component under test to block and eliminate part of the light from the simulated light source, and the second coronagraph module is used to provide an outer shelter and the coronagraph component under test to block and eliminate part of the light from the simulated light source; The detector module receives light emitted from the first or second coronagraph module and focuses it onto the detector module. The detector module is used to capture light source distribution images, vignetting distribution images, resolution plate images, and dark field images. The data processing module is used to perform point-reduction processing on the light source distribution image, the vignetting distribution image, the resolution plate image, and the dark field image, and to draw the MTF curve of the coronagraph at a specified vignetting intensity based on the resolution line normalized brightness at the specified vignetting intensity position obtained by the point-reduction processing. The imaging quality assessment of the vignetting region of the outer bunker is realized through the MTF curve of the coronagraph at the specified vignetting intensity.

9. The imaging resolution measurement system for the halo region of an externally shrouded coronagraph according to claim 8, characterized in that, The first pre-target module or the second pre-target module further includes: A collimator is positioned on one side of the simulated light source; The first light homogenizer is disposed on the side of the collimator away from the simulated light source; The second light homogenizer is disposed on the side of the first light homogenizer away from the collimator; In the first front target module, the light from the simulated light source passes sequentially through the collimator, the first homogenizer, and the second homogenizer, and is directed toward the first or second coronagraph module; in the second front target module, the light from the simulated light source passes sequentially through the collimator, the first homogenizer, the second homogenizer, and the resolution plate, and is directed toward the first or second coronagraph module.

10. The system for measuring the imaging resolution of the halo region of an externally shrouded coronagraph according to claim 8, characterized in that, The coronagraph assembly to be tested includes: an objective lens diaphragm assembly, an objective lens assembly, an inner shield, an extinction groove assembly, a field lens assembly, a stray light removal diaphragm assembly, a Lyot diaphragm assembly, a relay lens assembly, and a filter, arranged sequentially along the optical path.

Images