Sun observation-based method for measuring space distribution of flat plate spacing of Fabry-Perot optical filter

Abstract

The invention discloses a method for measuring space distribution of flat plate spacing of a Fabry-Perot optical filter based on sun observation, which relates to the technical field of optics and comprises the following steps of: constructing an observation light path, enabling sunlight to form a telecentric beam through a lens group and then vertically enter the Fabry-Perot optical filter formed by two parallel flat plates, and measuring the space distribution of the flat plate spacing of the Fabry-Perot optical filter; the detector is used for collecting two-dimensional space images of the sun, and pixels of the detector are in one-to-one correspondence with flat plate areas of the light filter; in the measurement process, the solar observation light path is directly utilized, a special measurement light path and equipment do not need to be additionally built, the complexity of the system is greatly reduced, the error risk of equipment installation and debugging is reduced, and the development cost is effectively controlled; the measurement of the space distribution of the flat plate spacing can be synchronously completed in the normal solar observation process, the observation process does not need to be interrupted, the real-time monitoring of the state of the Fabry-Perot optical filter is realized, and the continuity and integrity of observation data are ensured.

Description

Technical Field

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

[0002] Fabry-Perot (FP) filters are widely used for narrowband solar imaging and magnetic field measurements. In actual observations, the filter's transmission wavelength can be altered by adjusting the spacing between parallel plates, thereby acquiring a sequence of narrowband two-dimensional solar images at different wavelengths. However, due to factors such as plate machining accuracy, coating uniformity, installation stress and deformation, and parallelism deviation, the plate spacing of FP filters exhibits spatial non-uniformity. This can distort the filter's spectral response function and, in turn, cause wavelength inconsistencies and non-uniform intensities in the observed images. Furthermore, factors such as changes in ambient temperature and humidity, mechanical vibration, and component aging can cause the spatial distribution of the plate spacing to dynamically change, severely impacting the accuracy of inversion of physical parameters such as the solar brightness field, velocity field, and magnetic field.

[0003] Current methods for measuring the spatial distribution of the spacing between Fabry-Perot (Fabry-Perot) filter plates rely primarily on the addition of a dedicated measurement optical path. These methods typically employ a frequency-stabilized He-Ne laser and a detector, irradiating the Fabry-Perot plate with a beam expander, and using the intensity distribution of the spot collected by the detector to infer the plate spacing characteristics. However, this technology has significant drawbacks. The intensity non-uniformity and speckle effect of the laser itself can introduce measurement errors. Subsequent improved methods optimize accuracy by scanning the plate spacing to obtain the full width at half maximum (FWHM) or peak displacement of the laser profile, but are still affected by the surface roughness of the plate, resulting in a significant decrease in measurement accuracy at the plate edge. Dedicated measurement optical paths require the addition of lasers, reflectors, and detectors, increasing system development costs and the difficulty and risk of error associated with optical path alignment. Furthermore, mechanical switching is required to switch the observation optical path to the measurement optical path during measurement, which inevitably interrupts the solar observation process and prevents real-time monitoring. The wavelength and intensity stability of the laser light source directly affect the measurement results, requiring additional technical investment in light source calibration, further increasing implementation difficulties. Summary of the Invention

[0004] The purpose of the present 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 and high-precision measurement of the plate spacing during solar observation. In order to eliminate the influence of the non-uniform distribution of the plate spacing on the inversion of solar physical parameters, a new method and system for measuring the spatial distribution of the plate spacing of a Fabry-Perot filter based on solar observation is proposed.

[0005] To achieve the above objectives, the present invention adopts the following technology: a method for measuring the spatial distribution of the spacing between the Fabry-Perot filter plates based on solar observation, comprising the following steps: An observation optical path is constructed so that sunlight is formed into a telecentric beam by a lens group and then vertically incident on a Fabry-Perot filter composed of two parallel plates. The beam is then focused by an imaging mirror onto a detector for collecting a two-dimensional image of the sun, with detector pixels corresponding one-to-one to the filter plate areas. The distance between the Fabry-Perot filter plates is adjusted at fixed intervals to scan the solar spectrum. After each adjustment, the detector collects a two-dimensional image of the sun. Calculate the average light intensity of each collected image and generate an average solar spectrum scanning curve; Calculate the light intensity of each detector pixel in each image and generate the solar spectrum scanning curve of the corresponding pixel; The cross-correlation algorithm is used to compare the pixel solar spectrum scanning curve with the average solar spectrum scanning curve to obtain the offset between the two. The deviation between the plate spacing corresponding to each pixel and the average plate spacing is calculated according to the offset, and the spatial distribution of the plate spacing of the Fabry-Perot filter is obtained.

[0006] Furthermore, the observation optical path is designed so that the main light of each field of view of the light beam enters the Fabry-Perot filter vertically, thereby ensuring the consistency of light incidence.

[0007] Furthermore, when scanning the solar spectrum, the coverage range includes the complete solar spectrum line core and half-maximum full width characteristics, ensuring that the spectral information is complete and without loss.

[0008] Furthermore, when calculating the average solar spectrum scanning curve, the light intensity of the entire image is averaged to eliminate the interference of local light intensity fluctuations on the result.

[0009] 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.

[0010] Furthermore, the measurement process is carried out synchronously with solar observation without switching the optical path, thereby ensuring the continuity and integrity of the observation data.

[0011] Furthermore, by collectively analyzing the spectral curves of multiple detector pixels, high-density sampling measurement of the spatial distribution of the plate spacing within the optical aperture of the Fabry-Perot filter is achieved.

[0012] Furthermore, when Fabry-Perot filters and detectors of different specifications are combined, the plate spacing adjustment interval and the scanning range are adjusted according to the actual observation task.

[0013] In summary, due to the use of the above-mentioned technology, a method for measuring the spatial distribution of the spacing between the Fabry-Perot filter plates based on solar observation has the following beneficial effects: 1. Traditional measurement methods rely on dedicated optical paths and require additional equipment such as lasers, reflectors, and detectors. This not only increases development costs but also increases the difficulty and error risk of optical path installation and adjustment. However, 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. This significantly reduces the complexity of the system, reduces the error risk of equipment installation and commissioning, and effectively controls development costs. 2. The existing technology requires mechanical switching between the observation and measurement optical paths during measurement, which inevitably interrupts the solar observation process and makes real-time monitoring impossible. However, the present invention can simultaneously complete the measurement of the spatial distribution of the plate spacing during normal solar observation without interrupting the observation process, achieving real-time monitoring of the Fabry-Perot filter status. This not only ensures the continuity and integrity of the observation data, but also enables timely acquisition of filter status change information, providing more reliable data support for solar physics research. 3. Traditional laser measurement is affected by factors such as laser intensity non-uniformity, speckle effects, and surface roughness of the flat panel, resulting in limited measurement accuracy, particularly at the edges of the flat panel. This method uses a cross-correlation algorithm to compare spectral curves, leveraging the inherent reference strength of the solar spectrum. This avoids interference from traditional laser measurement, such as uneven light source intensity and speckle effects, achieving extremely high measurement accuracy and meeting the stringent requirements for high-precision inversion of physical parameters such as the solar magnetic field and velocity field. 4. This invention utilizes the correspondence between detector pixels and filter plate areas, and through collective analysis of a large number of pixel spectral curves, achieves high-density sampling of the spatial distribution of plate spacing. This approach comprehensively covers the entire area within the Fabry-Perot filter's clear aperture, accurately quantifying spacing non-uniformities caused by factors such as plate machining accuracy, coating uniformity, and installation stress and deformation. This provides precise data support for the correction of the filter's spectral response function, helping to improve the quality and accuracy of solar observation images. 5. This invention is applicable to Fabry-Perot filters and detector configurations of varying specifications, and allows flexible adjustment of measurement parameters, such as the plate spacing adjustment interval and scanning range, based on actual observation requirements. Whether for different solar spectral line observation tasks or under different observation environments, efficient and accurate measurement of the spatial distribution of plate spacing can be achieved through reasonable parameter adjustment. This device has excellent applicability and versatility, meeting diverse solar observation research needs. 6. Factors such as changes in ambient temperature and humidity, mechanical vibration, and component aging can cause dynamic changes in the spatial distribution of the spacing between the Fabry-Perot filter plates. Traditional measurement methods are greatly affected by the stability of the laser light source and are difficult to accurately reflect these changes. However, the present invention uses the solar spectrum itself as a reference, eliminating the influence of the stability of the external light source on the measurement. Under complex and changing environmental conditions, it can still stably and accurately measure the spatial distribution of the spacing between the plates, effectively reducing the interference of environmental factors on the measurement results, and ensuring the reliability and stability of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a solar observation system based on a Fabry-Perot filter provided by the present invention; Figure 2 Schematic diagram of the corresponding distance between the detector pixel and the Fabry-Perot filter plate provided by the present invention; Figure 3 These are N two-dimensional images of the sun provided by the present invention; Figure 4 is the average solar spectrum curve of the entire solar image provided by the present invention; Figure 5 It is the detector pixel solar spectrum scanning curve provided by the present invention; Figure 6 This is a schematic diagram of the spatial distribution of the spacing between the Fabry-Perot filter plates provided by the present invention. DETAILED DESCRIPTION

[0015] The following, in conjunction with the accompanying drawings, provides a clear and complete description of the technology in the embodiments of the present invention, a method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0016] The present invention provides a method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation. The technical problem to be solved is that during the solar observation process, the solar spectrum lines are scanned by adjusting the spacing between the Fabry-Perot filter plates to obtain the average solar spectrum curve of the entire solar image and the solar spectrum scanning curve of each pixel of the detector. By comparing the offset of the solar spectrum scanning curve of each pixel with the average solar spectrum curve, the spatial distribution characteristics of the spacing between the Fabry-Perot filter plates are measured in real time.

[0017] A method for measuring the spatial distribution of the plate spacing of a Fabry-Perot filter based on solar observations, wherein the Fabry-Perot filter is composed of two parallel plates and the transmission wavelength of the filter is changed by adjusting the plate spacing, specifically comprising the following steps: Step 1: After passing through the lens group, sunlight forms a telecentric beam. The main rays of each field of view of the beam are vertically incident on the Fabry-Perot filter, and then converged onto the detector through the imaging mirror. The detector is located at the focal plane and is used to collect a two-dimensional spatial image of the sun. like Figure 1 As shown; Each pixel of the detector corresponds to a different area of ​​the Fabry-Perot filter plate. The size of the detector is m×n, where m means that the detector has m rows of pixels and n means that the detector has n columns of pixels. The spacing of the Fabry-Perot filter plate corresponding to each pixel is for: (1) Where, is the distance between the Fabry-Perot filter plates corresponding to each pixel, is the plate spacing corresponding to the pixel in the first row and first column of the detector, is the plate spacing corresponding to the pixel in the 1st row and the nth column of the detector, is the plate spacing corresponding to the pixel in the mth row and the first column of the detector, is the plate spacing corresponding to the pixel in the mth row and nth column of the detector, m means that there are m rows of pixels in the detector, and n means that there are n columns of pixels in the detector; like Figure 2 As shown; Average plate spacing of Fabry-Perot filter for: (2) Where, is the average plate spacing of the Fabry-Perot filter, is the plate spacing corresponding to the pixel in the first row and first column of the detector, is the plate spacing corresponding to the pixel in the mth row and nth column of the detector, m means that there are m rows of pixels in the detector, and n means that there are n columns of pixels in the detector; The spatial distribution of the Fabry-Perot filter plate spacing δ is defined as the Fabry-Perot filter plate spacing corresponding to each pixel Relative to the average plate spacing Offset: (3) Where δ is the spacing between the Fabry-Perot filter plates corresponding to each pixel. Relative to the average plate spacing The offset, The spacing between the Fabry-Perot filter plates corresponding to the first row and first column pixel of the detector Relative to the average plate spacing The offset, The spacing between the Fabry-Perot filter plates corresponding to the pixel in the 1st row and the nth column of the detector Relative to the average plate spacing The offset, is the spacing between the Fabry-Perot filter plates corresponding to the pixel in the mth row and the first column of the detector Relative to the average plate spacing The offset, is the distance between the Fabry-Perot filter plates corresponding to the pixel in the mth row and nth column of the detector Relative to the average plate spacing The offset of .

[0018] Step 2: At equal intervals The plate spacing of the Fabry-Perot filter is adjusted in sequence to change the transmission wavelength of the Fabry-Perot filter, and the solar spectrum is scanned. The scanning range covers a complete solar spectrum. Each time the plate spacing is adjusted, the detector collects a two-dimensional solar image. The Fabry-Perot filter adjusts the plate spacing N times in total, and the detector collects N two-dimensional solar images in total. Assume that the initial plate spacing is , then the spacing after the i-th adjustment is for: (4) Where, is the spacing after the i-th adjustment, is the initial plate spacing, is an equal interval, i is the number of adjustments; like Figure 3 As shown; The entire solar spectrum is scanned at equal intervals of Δd to ensure that the changes in the transmission wavelength of the Fabry-Perot filter can fully capture the spectral line characteristics (such as the line core and full width at half maximum), avoid the loss of spectral information due to insufficient scanning range, and ensure the accuracy of subsequent spectral curve analysis; through N times of plate spacing adjustment and image acquisition, a dense spectral scanning sequence is formed, which increases the data sample size, reduces the impact of random noise on the measurement results, and provides sufficient calculation samples for the cross-correlation algorithm.

[0019] Step 3: Calculate the average light intensity of each image , and obtain an average solar spectrum scanning curve with the average light intensity varying with the distance between the Fabry-Perot filter plates ; like Figure 4 As shown; The average solar spectrum scanning curve averages the light intensity of the entire image, eliminating the interference of local light intensity fluctuations, representing the overall response characteristics of the solar spectrum and providing a unified reference benchmark for the spectral curve of each pixel.

[0020] Step 4: Calculate the light intensity of each detector pixel in each image Each detector pixel obtains a pixel solar spectrum scanning curve in which the light intensity changes with the distance between the Fabry-Perot filter plates. ; like Figure 5 As shown; The detector has a total of m×n pixels, and a total of m×n pixel solar spectrum scanning curves are obtained. ; The solar spectrum scanning curve of each pixel independently reflects the spectral response of the corresponding area of ​​the plate. Through the curve set of m×n pixels, high-density sampling of the spatial distribution of the plate spacing is achieved, covering all areas within the optical aperture of the Fabry-Perot filter.

[0021] Step 5: Calculate the solar spectrum scanning curve of each pixel using formula (5) Average solar spectrum scanning curve The cross-correlation function : (5) Where, is the cross-correlation function between each pixel solar spectrum scanning curve and the average solar spectrum scanning curve, k (k is an integer, k∈[−N / 2, N / 2]) is the pixel solar spectrum scanning curve Average solar spectrum scanning curve The sliding displacement, It is the curve after the pixel solar spectrum scanning curve is horizontally shifted by k displacement. The k corresponding to the maximum value is the offset of the two curves, represented by τ, and the solar spectrum scanning curve collected by each pixel on the detector is Average solar spectrum scanning curve The offset τ is: (5) Where τ is the solar spectrum scanning curve collected by each pixel on the detector Average solar spectrum scanning curve The offset of The solar spectrum scanning curve collected by the first row and first column pixel of the detector Average solar spectrum scanning curve The offset, The solar spectrum scanning curve collected by the pixel in the 1st row and the nth column of the detector Average solar spectrum scanning curve The offset, The solar spectrum scanning curve collected by the pixel pair of the mth row and the first column of the detector is Average solar spectrum scanning curve The offset, The solar spectrum scanning curve collected by the pixel in the mth row and nth column of the detector is Average solar spectrum scanning curve The offset of .

[0022] The cross-correlation algorithm is used to compare the offset between the pixel spectral curve and the average spectral curve, and mathematical correlation calculations are used to achieve sub-sampling interval precision positioning (e.g., sub-nanometer level). Compared with traditional laser measurement methods, this method avoids interference such as uneven laser intensity and speckle effects, significantly improving measurement accuracy. At the same time, the solar spectrum itself is used directly as a reference, without the need to introduce additional auxiliary light sources such as stabilized lasers, eliminating the impact of external light source stability on the measurement, while avoiding observation interruptions caused by optical path switching, and achieving simultaneous observation and measurement.

[0023] Step 6: Calculate the Fabry-Perot filter plate spacing for each pixel relative to the average plate spacing The deviation of δ is used to obtain the spatial distribution of the Fabry-Perot filter plate spacing: (6) like Figure 6 shown.

[0024] The offset τ is converted into the plate spacing deviation δ, and the spatial distribution spectrum of the Fabry-Perot filter plate spacing is directly output. This can intuitively reflect the spacing non-uniformity caused by factors such as processing errors and installation stress, providing an accurate basis for the correction of the filter spectral response function. Based on the sub-nanometer 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 needs of high-precision inversion of physical parameters such as the solar magnetic field and velocity field.

[0025] In another embodiment, the Fabry-Perot filter to be measured has a plate spacing of 430 μm, a central wavelength of 6562.8 Å, and a clear aperture of Φ100 mm; The detector specifications are 2048×2048, the pixel size is 6.5μm, the detector target surface is 13.312mm×13.312mm, and the Fabry-Perot filter plate area corresponding to each detector pixel is 0.035mm×0.035mm; Observe the solar quiet zone by adjusting the plate spacing of the Fabry-Perot filter in equal intervals of 0.425 nm to change the transmission wavelength of the filter. Scan the solar Hα spectrum. The core of the Hα spectrum is 6562.8Å, the full width at half maximum is 1Å, and the scanning range of the plate spacing is 430μm±0.045μm. Each time the plate spacing is adjusted, the detector collects a two-dimensional image of the sun. The Fabry-Perot filter adjusts the plate spacing 217 times, and the detector collects a total of 217 two-dimensional images of the sun. Calculate the average light intensity of each image and obtain an average solar spectrum scanning curve in which the average light intensity changes with the plate spacing; Calculate the light intensity of each detector pixel in each image. Each detector pixel obtains a pixel solar spectrum scanning curve in which the light intensity changes with the plate spacing. There are 4,194,304 detector pixels in total, and a total of 4,194,304 pixel solar spectrum scanning curves are obtained. The cross-correlation function between each pixel solar spectrum scanning curve and the average solar spectrum scanning curve is calculated using formula (5), and the offset τ between the solar spectrum scanning curve collected by each pixel and the average solar spectrum scanning curve is obtained as ; The scanning interval of the Fabry-Perot filter plate spacing is 0.425 nm. The deviation of the Fabry-Perot filter plate spacing corresponding to each pixel relative to the average plate spacing is calculated using formula (6), and the spatial distribution δ of the Fabry-Perot filter plate spacing is obtained as follows: .

[0026] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the present technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes to the method for measuring the spatial distribution of the spacing between the Fabry-Perot filter plates based on solar observation and the inventive concept thereof according to the technology of the present invention, and these changes should be covered by the scope of protection of the present invention.

Claims

1. A method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation, characterized in that: The following steps are involved: An observation optical path is constructed so that sunlight is formed into a telecentric beam by a lens group and then vertically incident on a Fabry-Perot filter composed of two parallel plates. The beam is then focused by an imaging mirror onto a detector for collecting a two-dimensional image of the sun, with detector pixels corresponding one-to-one to the filter plate areas. The distance between the Fabry-Perot filter plates is adjusted at fixed intervals to scan the solar spectrum. After each adjustment, the detector collects a two-dimensional image of the sun. Calculate the average light intensity of each collected image and generate an average solar spectrum scanning curve; Calculate the light intensity of each detector pixel in each image and generate the solar spectrum scanning curve of the corresponding pixel; The cross-correlation algorithm is used to compare the pixel solar spectrum scanning curve with the average solar spectrum scanning curve to obtain the offset between the two. The deviation between the plate spacing corresponding to each pixel and the average plate spacing is calculated according to the offset, and the spatial distribution of the plate spacing of the Fabry-Perot filter is obtained.

2. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation according to claim 1, characterized in that: The observation optical path is designed so that the main light of each field of view of the light beam is vertically incident on the Fabry-Perot filter to ensure the consistency of light incidence.

3. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation according to claim 1, characterized in that: When scanning the solar spectrum, the coverage includes the complete solar spectrum line core and half-maximum full width characteristics, ensuring that the spectral information is complete and without loss.

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

5. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates 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.

6. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation according to claim 1, characterized in that: The measurement process is carried out synchronously with solar observation without switching the optical path, thereby ensuring the continuity and integrity of the observation data.

7. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation according to claim 1, characterized in that: By collectively analyzing the spectral curves of multiple detector pixels, high-density sampling measurement of the spatial distribution of the plate spacing within the optical aperture of the Fabry-Perot filter is achieved.

8. The method for measuring the spatial distribution of the spacing between Fabry-Perot filter plates based on solar observation according to claim 1, characterized in that: When combining Fabry-Perot filters and detectors of different specifications, the plate spacing adjustment interval and scanning range are adjusted according to the actual observation task.

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