A method for measuring the spatial distribution of the plate separation of a fabry-perot filter based on solar observation

Abstract

This invention discloses a method for measuring the spatial distribution of the Fabry-Perot filter plate spacing based on solar observation, relating to the field of optical technology. The method includes the following steps: constructing an observation optical path so that sunlight, after passing through a lens group to form a telecentric beam, is perpendicularly incident on a Fabry-Perot filter composed of two parallel plates. The beam is then converged to a detector via an imaging mirror. The detector is used to acquire a two-dimensional spatial image of the sun, and the detector pixels correspond one-to-one with the plate areas of the filter. This invention directly utilizes the solar observation optical path during the measurement process, eliminating the need for additional dedicated measurement optical paths and equipment, significantly reducing system complexity, minimizing the risk of errors during equipment installation and debugging, and effectively controlling development costs. The spatial distribution of the plate spacing can be measured synchronously during normal solar observation without interrupting the observation process, enabling real-time monitoring of the Fabry-Perot filter's status and ensuring the continuity and integrity of the observation data.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation. Background Technology

[0002] Fabry-Perot (Fabry-Perot) filters are widely used in solar narrowband imaging and magnetic field measurements. In practical observations, the transmission wavelength of the filter can be changed by adjusting the spacing of the parallel plates, thereby obtaining a sequence of two-dimensional narrowband solar images at different wavelengths. However, due to factors such as plate processing precision, coating uniformity, installation stress deformation, and parallelism deviation, the spacing of the Fabry-Perot filter plates exhibits a spatially non-uniform distribution. This leads to distortion of the filter's spectral response function, resulting in inconsistencies in wavelength and intensity in the observed images. Furthermore, changes in environmental temperature and humidity, mechanical vibration, and component aging can cause dynamic variations in the spatial distribution of the plate spacing, severely affecting the inversion accuracy of physical parameters such as solar brightness, velocity, and magnetic fields.

[0003] Current methods for measuring the spatial distribution of the Fabry-Perot filter plate spacing mainly rely on adding a dedicated measurement optical path. This type of method typically uses a frequency-stabilized helium-neon laser and a detector. The laser beam is expanded to illuminate the Fabry-Perot plate, and the plate spacing characteristics are inferred from the intensity distribution of the light spot collected by the detector. However, this technique has significant drawbacks. The inherent inhomogeneity of laser intensity and speckle effect introduce measurement errors. While subsequent improved methods optimize accuracy by scanning the plate spacing to obtain the laser profile's full width at half maximum (FWHM) or peak displacement, they are still affected by the surface roughness of the plate, resulting in a significant decrease in measurement accuracy at the plate edges. Dedicated measurement optical paths require additional equipment such as lasers, mirrors, and detectors, increasing system development costs and raising the difficulty of optical path assembly and adjustment, as well as the risk of errors. Furthermore, the need for mechanical switching to switch the observation optical path to the measurement optical path during measurement inevitably interrupts the solar observation process, making real-time monitoring impossible. The wavelength and intensity stability of the laser source directly affect the measurement results, requiring additional technical investment in source calibration, further increasing the implementation difficulty. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that existing measurement methods rely on external laser light sources and dedicated optical paths, making it difficult to achieve real-time high-precision measurement of the Fabry-Perot filter spacing during solar observation. To eliminate the influence of non-uniform Fabry-Perot filter spacing on the inversion of solar physical parameters, a new method and system for measuring the spatial distribution of Fabry-Perot filter spacing based on solar observation is proposed.

[0005] To achieve the above objectives, the present invention employs the following technique: a method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation, comprising the following steps:

[0006] An observation optical path is constructed so that sunlight is formed into a telecentric beam by a lens group and then incident perpendicularly onto a Fabry-Perot filter composed of two parallel plates. The beam is then converged to a detector by an imaging mirror. The detector is used to acquire two-dimensional spatial images of the sun, and the detector pixels correspond one-to-one with the plate area of ​​the filter.

[0007] The solar spectral lines are scanned by adjusting the spacing of the Fabry-Perot filter plates at fixed intervals, and the detector acquires a two-dimensional spatial image of the sun after each adjustment.

[0008] Calculate the average light intensity of each acquired image to generate an average solar spectrum scan curve;

[0009] Calculate the light intensity of each detector pixel in each image and generate the solar spectrum scan curve for the corresponding pixel;

[0010] A cross-correlation algorithm is used to compare the pixel solar spectrum scan curve with the average solar spectrum scan curve to obtain the offset between the two.

[0011] The deviation between the plate spacing of each pixel and the average plate spacing is calculated based on the offset, thus obtaining the spatial distribution of the plate spacing of the Fabry-Perot filter.

[0012] Furthermore, the observation optical path is designed so that the main rays of each field of view of the beam enter the Fabry-Perot filter perpendicularly, ensuring the consistency of light incidence.

[0013] Furthermore, when scanning solar spectral lines, the coverage area includes the complete solar spectral line core and full width at half maximum (FWHM) features, ensuring that the spectral information is complete and without any omissions.

[0014] Furthermore, when calculating the average solar spectrum scan curve, the light intensity of the entire image is averaged to eliminate the interference of local light intensity fluctuations on the results.

[0015] Furthermore, the cross-correlation algorithm achieves sub-sampling interval level precision positioning by calculating the mathematical correlation between the pixel spectral curve and the average spectral curve.

[0016] Furthermore, the measurement process is carried out simultaneously with solar observation, without the need to switch optical paths, thus ensuring the continuity and integrity of the observation data.

[0017] Furthermore, by ensemble analysis of the spectral curves of multiple detector pixels, high-density sampling measurement of the spatial distribution of the interplanar spacing within the aperture of the Fabry-Perot filter is achieved.

[0018] Furthermore, when combining Fabry-Perot filters and detectors of different specifications, the plate spacing and scanning range are adjusted according to the actual observation task.

[0019] In summary, due to the adoption of the above-mentioned technology in the method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation, the beneficial effects of this invention are:

[0020] 1. Traditional measurement methods rely on dedicated optical paths, requiring additional equipment such as lasers, reflectors, and detectors, which not only increases development costs but also raises the difficulty of optical path assembly and adjustment and the risk of errors. In contrast, this invention directly utilizes the solar observation optical path during the measurement process, eliminating the need to build additional dedicated measurement optical paths and equipment, significantly reducing the complexity of the system, reducing the risk of errors in equipment installation and adjustment, and effectively controlling development costs.

[0021] 2. Existing technologies require mechanical switching between the observation and measurement optical paths during measurement, which inevitably interrupts the solar observation process and makes real-time monitoring impossible. In contrast, this invention can simultaneously measure the spatial distribution of the plate spacing during normal solar observation without interrupting the observation process, enabling real-time monitoring of the Fabry-Perot filter's state. This not only ensures the continuity and integrity of the observation data but also allows for timely acquisition of information on filter state changes, providing more reliable data support for solar physics research.

[0022] 3. Traditional laser measurements are limited in accuracy due to factors such as laser intensity inhomogeneity, speckle effect, and surface roughness of the plate, especially with a significant decrease in accuracy at the edge of the plate. This invention uses a cross-correlation algorithm to compare spectral curves, giving full play to the reference advantage of the solar spectrum itself, and avoiding interference from light source intensity inhomogeneity and speckle effect in traditional laser measurements. The measurement accuracy reaches an extremely high level, which can meet the stringent requirements for the inversion of high-precision physical parameters such as solar magnetic field and velocity field.

[0023] 4. This invention utilizes the correspondence between detector pixels and filter plate areas, and through the aggregate analysis of a large number of pixel spectral curves, achieves high-density sampling of the spatial distribution of plate spacing. This method can comprehensively cover all areas within the light-passing aperture of the Fabry-Perot filter, accurately quantify the spacing non-uniformity caused by factors such as plate processing precision, coating uniformity, and installation stress deformation, and provide accurate data support for the correction of the filter's spectral response function, which helps to improve the quality and accuracy of solar observation images.

[0024] 5. This invention is applicable to Fabry-Perot filters and detector configurations of different specifications. Measurement parameters, such as the plate spacing adjustment interval and scanning range, can be flexibly adjusted according to actual observation needs. Whether for different solar spectral line observation tasks or in different observation environments, efficient and accurate spatial distribution measurement of plate spacing can be achieved by reasonably adjusting parameters. It has good applicability and versatility and can meet diverse solar observation research needs.

[0025] 6. Environmental temperature and humidity changes, mechanical vibrations, and component aging can cause dynamic changes in the spatial distribution of the plate spacing of a Fabry-Perot filter. Traditional measurement methods are greatly affected by the stability of the laser source and cannot accurately reflect these changes. However, this invention uses the solar spectrum itself as a reference, eliminating the influence of the stability of the external light source on the measurement. Even under complex and variable environmental conditions, it can still stably and accurately measure the spatial distribution of the plate spacing, effectively reducing the interference of environmental factors on the measurement results and ensuring the reliability and stability of the measurement results. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the solar observation system based on the Fabry-Perot filter provided by the present invention;

[0027] Figure 2 This is a schematic diagram showing the spacing between the detector pixel and the Fabry-Perot filter plate provided by the present invention;

[0028] Figure 3 These are N two-dimensional spatial images of the sun provided by this invention;

[0029] Figure 4 This is the average solar spectrum curve of the entire solar image provided by the present invention;

[0030] Figure 5 This is the solar spectrum scanning curve of the detector pixel provided by the present invention;

[0031] Figure 6 This is a schematic diagram of the spatial distribution of the plate spacing of the Fabry-Perot filter provided by the present invention. Detailed Implementation

[0032] The following will describe, with reference to the accompanying drawings of the embodiments of the present invention, a method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation. 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.

[0033] This invention provides a method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation. The technical problem it aims to solve is to obtain the average solar spectral curve of the entire solar image and the solar spectral scanning curve of each pixel of the detector by scanning the solar spectral lines during solar observation by adjusting the Fabry-Perot filter plate spacing. By comparing the offset of each pixel's solar spectral scanning curve with the average solar spectral curve, the spatial distribution characteristics of the Fabry-Perot filter plate spacing can be measured in real time.

[0034] A method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observations, wherein the Fabry-Perot filter consists of two parallel plates, and the transmission wavelength of the filter is changed by adjusting the spacing between the plates. The method specifically includes the following steps:

[0035] Step 1: After passing through the lens group, sunlight forms a telecentric beam. The principal rays of each field of view of the beam enter the Fabry-Perot filter perpendicularly, and then converge onto the detector through the imaging mirror. The detector is located at the focal plane and is used to acquire a two-dimensional spatial image of the sun.

[0036] like Figure 1 As shown;

[0037] Each pixel of the detector corresponds one-to-one with a different area of ​​the Fabry-Perot filter plate. The detector has an dimensions of m×n, where m represents the number of rows of pixels and n represents the number of columns of pixels. The spacing between the Fabry-Perot filter plates corresponding to each pixel is... for:

[0038] (1)

[0039] In the formula, The spacing between the Fabry-Perot filter plates corresponds to one pixel. The spacing between the plates corresponding to the first pixel in the first row and first column of the detector. The spacing between the plates corresponding to the pixel in the first row and nth column of the detector. The spacing between the plates corresponding to the m-th row and 1-th column pixel of the detector. The spacing between the flat panels corresponding to the m-th row and n-th column of the detector is where m represents the total number of rows of pixels and n represents the total number of columns of pixels.

[0040] like Figure 2 As shown;

[0041] Average plate spacing of Fabry-Perot filters for:

[0042] (2)

[0043] In the formula, The average plate spacing of the Fabry-Perot filter. The spacing between the plates corresponding to the first pixel in the first row and first column of the detector. The spacing between the flat panels corresponding to the m-th row and n-th column of the detector is where m represents the total number of rows of pixels and n represents the total number of columns of pixels.

[0044] The spatial distribution δ of the Fabry-Perot filter plate spacing is defined as the Fabry-Perot filter plate spacing corresponding to each pixel. Relative to average plate spacing Offset:

[0045] (3)

[0046] In the formula, δ represents the Fabry-Perot filter plate spacing corresponding to each pixel. Relative to average plate spacing The offset, The Fabry-Perot filter plate spacing corresponding to the first pixel in the first row and first column of the detector. Relative to average plate spacing The offset, The spacing between the plates of the Fabry-Perot filter corresponding to the pixel in the first row and nth column of the detector. Relative to average plate spacing The offset, The spacing between the plates of the Fabry-Perot filter corresponding to the m-th row and 1-th column pixel of the detector. Relative to average plate spacing The offset, The spacing between the plates of the Fabry-Perot filter corresponding to the m-th row and n-th column of the detector. Relative to average plate spacing The offset.

[0047] Step 2: At equal intervals The transmission wavelength of the Fabry-Perot filter is changed by sequentially adjusting the plate spacing, and the solar spectrum is scanned, covering a complete solar spectrum. Each adjustment of the plate spacing results in the detector acquiring one two-dimensional image of the sun. The Fabry-Perot filter is adjusted N times, and the detector acquires N two-dimensional images of the sun in total. Let the initial plate spacing be... The spacing after the i-th adjustment for:

[0048] (4)

[0049] In the formula, Let be the spacing after the i-th adjustment. The initial plate spacing, The intervals are equal, and i represents the number of adjustments.

[0050] like Figure 3 As shown;

[0051] Equally spaced Δd scans cover the entire solar spectrum, ensuring that the transmission wavelength changes of the Fabry-Perot filter can fully capture spectral features (such as line core and full width at half maximum), avoiding the loss of spectral information due to insufficient scanning range, and ensuring the accuracy of subsequent spectral curve analysis. Through N plate spacing adjustments and image acquisitions, a dense spectral scanning sequence is formed, increasing the data sample size, reducing the impact of random noise on the measurement results, and providing sufficient calculation samples for the cross-correlation algorithm.

[0052] Step 3: Calculate the average light intensity of each image. An average solar spectrum scan curve was obtained showing the variation of average light intensity with the spacing between the plates of the Fabry-Perot filter. ;

[0053] like Figure 4 As shown;

[0054] The average solar spectrum scan curve represents the overall response characteristics of the solar spectrum by averaging the light intensity of the entire image, eliminating interference from local light intensity fluctuations, and providing a unified reference standard for the spectral curves of each pixel.

[0055] Step 4: Calculate the light intensity of each detector pixel in each image. Each detector pixel obtains a pixel solar spectrum scan curve showing the change in light intensity as a function of the spacing between the Fabry-Perot filter plates. ;

[0056] like Figure 5 As shown;

[0057] The detector has a total of m×n pixels and obtained a total of m×n pixel solar spectrum scan curves. ;

[0058] The solar spectrum scan curve of each pixel independently reflects the spectral response of the corresponding region of the flat plate. By using the curve set of m×n pixels, high-density sampling of the spatial distribution of the flat plate spacing is achieved, covering all areas within the aperture of the Fabry-Perot filter.

[0059] Step 5: Calculate the solar spectrum scanning curve for each pixel using formula (5). With average solar spectrum scan curve cross-correlation function :

[0060] (5)

[0061] In the formula, Let k be the cross-correlation function between the solar spectral scan curve of each pixel and the average solar spectral scan curve, where k (k is an integer, k∈[−N / 2, N / 2]) is the pixel solar spectral scan curve. With average solar spectrum scan curve The amount of sliding displacement, The curve is the result of horizontally shifting the pixel solar spectrum scan curve by a displacement of k. The maximum value corresponds to the offset between the two curves, denoted by τ, which represents the solar spectral scan curve acquired by each pixel on the detector. With average solar spectrum scan curve The offset τ is:

[0062] (5)

[0063] In the formula, τ is the solar spectrum scan curve collected by each pixel on the detector. With average solar spectrum scan curve The offset; Solar spectral scan curve acquired for the first pixel in the first row and first column of the detector With average solar spectrum scan curve The offset, Solar spectral scan curve acquired for the first row and nth column of the detector With average solar spectrum scan curve The offset, The solar spectral scan curve acquired by the m-th row and 1-th column pixel pair of the detector. With average solar spectrum scan curve The offset, Solar spectral scan curve acquired for the m-th row and n-th column pixel of the detector With average solar spectrum scan curve The offset.

[0064] By using a cross-correlation algorithm to compare the offset between the pixel spectral curve and the average spectral curve, and by calculating the mathematical correlation, the accuracy of sub-sampling interval positioning (such as sub-nanometer level) is achieved. Compared with traditional laser measurement methods, this method avoids interference such as uneven laser intensity and speckle effect, and significantly improves measurement accuracy.

[0065] At the same time, by directly using the solar spectrum itself as a reference, there is no need to introduce additional auxiliary light sources such as frequency-stabilized lasers, which eliminates the influence of the stability of external light sources on the measurement and avoids the interruption of observation caused by optical path switching, thus realizing the synchronous execution of observation and measurement.

[0066] Step 6: Calculate the Fabry-Perot filter plate spacing relative to the average plate spacing for each pixel. The deviation is used to obtain the spatial distribution δ of the plate spacing of the Fabry-Perot filter:

[0067] (6)

[0068] like Figure 6As shown.

[0069] The offset τ is converted into the plate spacing deviation δ, and the spatial distribution map of the plate spacing of the Fabry-Perot filter is directly output. This directly reflects the non-uniformity of the spacing caused by factors such as processing errors and installation stress, and provides an accurate basis for the correction of the filter's spectral response function.

[0070] Based on the sub-nanometer-scale plate spacing scanning interval Δd, combined with the sub-pixel positioning capability of the cross-correlation algorithm, the final measurement accuracy reaches the sub-nanometer level, meeting the requirements for high-precision physical parameter inversion such as solar magnetic field and velocity field.

[0071] In another embodiment, the Fabry-Perot filter to be measured has a plate spacing of 430 μm, a center wavelength of 6562.8 Å, and a light-transmitting aperture of Ф100 mm.

[0072] The detector has dimensions of 2048×2048, a pixel size of 6.5μm, a detector target surface of 13.312mm×13.312mm, and a Fabry-Perot filter plate area of ​​0.035mm×0.035mm corresponding to each detector pixel.

[0073] To observe the quiet region of the Sun, the transmission wavelength of the Fabry-Perot filter was changed by sequentially adjusting the plate spacing of the Fabry-Perot filter at equal intervals of 0.425 nm. The solar Hα spectral line was scanned. The line core of the Hα spectral line is 6562.8 Å, the full width at half maximum (FWHM) is 1 Å, and the scanning range of the plate spacing is 430 μm ± 0.045 μm.

[0074] Each time the plate spacing was adjusted, the detector acquired one two-dimensional image of the sun. The Fabry-Perot filter adjusted the plate spacing 217 times, and the detector acquired a total of 217 two-dimensional images of the sun.

[0075] Calculate the average light intensity of each image to obtain an average solar spectrum scan curve showing the change in average light intensity as a function of the plate spacing;

[0076] The light intensity of each detector pixel in each image is calculated. Each detector pixel obtains a pixel solar spectrum scanning curve of light intensity as a function of the plate spacing. The detector has a total of 4,194,304 pixels, and a total of 4,194,304 pixel solar spectrum scanning curves are obtained.

[0077] The cross-correlation function between the solar spectral scan curve of each pixel and the average solar spectral scan curve is calculated using formula (5), and the offset τ between the solar spectral scan curve acquired for each pixel and the average solar spectral scan curve is obtained. ;

[0078] The scanning interval of the Fabry-Perot filter plate spacing is 0.425 nm. The deviation of the Fabry-Perot filter plate spacing relative to the average plate spacing for each pixel is calculated using formula (6), yielding the spatial distribution δ of the Fabry-Perot filter plate spacing. .

[0079] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the solar observation-based method for measuring the spatial distribution of Fabry-Perot filter plate spacing and its inventive concept, should be covered within the scope of protection of the present invention.

Claims

1. A method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation, characterized in that, Includes the following steps: An observation optical path is constructed so that sunlight is formed into a telecentric beam by a lens group and then incident perpendicularly onto a Fabry-Perot filter composed of two parallel plates. The beam is then converged to a detector by an imaging mirror. The detector is used to acquire two-dimensional spatial images of the sun, and the detector pixels correspond one-to-one with the plate area of ​​the filter. The solar spectral lines are scanned by adjusting the spacing of the Fabry-Perot filter plates at fixed intervals, and the detector acquires a two-dimensional spatial image of the sun after each adjustment. Calculate the average light intensity of each acquired image to generate an average solar spectrum scan curve; Calculate the light intensity of each detector pixel in each image and generate the solar spectrum scan curve for the corresponding pixel; A cross-correlation algorithm is used to compare the pixel solar spectrum scan curve with the average solar spectrum scan curve to obtain the offset between the two. The deviation between the corresponding plate spacing of each pixel and the average plate spacing is calculated based on the offset, and the spatial distribution of the plate spacing of the Fabry-Perot filter is obtained. The observation optical path is designed so that the main rays of each field of view of the beam enter the Fabry-Perot filter perpendicularly, ensuring the consistency of the incident light. When scanning the solar spectral lines, the coverage area includes the complete solar spectral line core and full width at half maximum (FWHM) features.

2. The method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation according to claim 1, characterized in that, When calculating the average solar spectrum scan curve, the light intensity of the entire image is averaged to eliminate the interference of local light intensity fluctuations on the results.

3. The method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation according to claim 1, characterized in that, The cross-correlation algorithm achieves sub-sampling interval level precision positioning by calculating the mathematical correlation between the pixel spectral curve and the average spectral curve.

4. The method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation according to claim 1, characterized in that, The measurement process is carried out simultaneously with solar observation, without the need to switch optical paths.

5. The method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation according to claim 1, characterized in that, By ensemble analysis of the spectral curves of multiple detector pixels, high-density sampling measurement of the spatial distribution of the interplanar spacing within the aperture of the Fabry-Perot filter can be achieved.

6. The method for measuring the spatial distribution of Fabry-Perot filter plate spacing based on solar observation according to claim 1, characterized in that, When combining Fabry-Perot filters and detectors of different specifications, adjust the plate spacing and scanning range according to the actual observation task.

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