Solar imaging spectrometer based on multiple filtering settings

Abstract

The invention belongs to the field of spectrometers, and particularly relates to a solar imaging spectrometer based on multiple filtering settings, two pieces of filtering window glass with ultraviolet cut-off and band-pass filtering functions are sequentially arranged at the front end of the solar imaging spectrometer, a narrow-band optical filter is arranged at the focal point of a spectral imaging light path, and through triple step-by-step filtering, the spectral imaging light path of the solar imaging spectrometer is obtained. And the imaging spectrum bandwidth of the solar H alpha spectral line is accurately controlled within the range of 1 nm. According to the invention, the problems of too high requirement, difficult thermal control and poor stray light suppression of a single filter film system are solved, and ultra-narrow band spectrum observation with accurate central wavelength and high imaging quality is realized.

Description

Technical Field

[0001] This invention belongs to the field of spectrometer technology, and particularly relates to a solar imaging spectrometer based on multiple filter settings. Background Technology

[0002] As the only star capable of detailed observation with high spatial resolution, the Sun serves as a crucial window for studying key physical processes such as the origin and evolution of celestial magnetic fields and the acceleration and propagation of high-energy particles. Monitoring solar activity, particularly the study of events like strong solar flares and coronal mass ejections, not only has significant value for astrophysical research but also holds urgent practical importance for ensuring space weather safety, maintaining communication and navigation systems, protecting astronaut health, and ensuring the on-orbit safety of spacecraft.

[0003] In solar exploration, acquiring narrow-band spectral imaging data is a core method for revealing the dynamics of solar activity. Among these, the hydrogen alpha (Hα) spectral line (center wavelength 656.28 nm, spectral width approximately 1 nm) is one of the most important spectral lines for observing flares, dark filaments, and chromospheric dynamics. Achieving high-precision imaging of this spectral line requires the instrument to have the ability to stably control the imaging spectral bandwidth within 1 nm and precisely lock the center wavelength at 656.28 nm.

[0004] Existing technologies face the following challenges: single-filter schemes place extremely high demands on the performance of optical thin films, resulting in low yield rates; intense solar radiation energy easily causes drastic temperature changes in filter elements, affecting image quality; and it is difficult to effectively suppress out-of-band stray light interference. Therefore, how to achieve precise control of ultra-narrow spectral bandwidth in the complex radiation environment of space is a key bottleneck problem in the current development of solar imaging spectrometers. Summary of the Invention

[0005] In view of this, the present invention aims to provide a solar imaging spectrometer based on multiple filter settings to solve the problems of excessively high requirements for a single filter system, difficulty in thermal control, and poor suppression of stray light.

[0006] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A solar imaging spectrometer based on multiple filtering configurations includes a front filter window assembly disposed at the front end of the solar imaging spectrometer and a narrowband filter disposed inside the solar imaging spectrometer; the front filter window assembly includes a first filter window glass and a second filter window glass; wherein, The first filter window glass is made of radiation-proof glass. Its incident surface is coated with an ultraviolet cut-off film, which has a transmittance of less than 0.1% in the 200nm-500nm wavelength range and a transmittance of not less than 97.5% in the 656.28nm±10nm wavelength range. Its exit surface is coated with a first bandpass filter film, which has a transmittance of not less than 97.5% in the 656.28nm±10nm wavelength range and a transmittance of less than 0.1% in the 200nm-750nm wavelength range. The second filter window glass is made of sapphire or fused silica glass. Its incident surface is coated with a second bandpass filter film, which has a transmittance of not less than 97.5% in the 656.28nm±5nm wavelength band and a transmittance of less than 1% in the 400nm-1200nm wavelength band. Its exit surface is coated with an infrared reflective film, which has a transmittance of not less than 97.5% in the 656.28nm±5nm wavelength band and a transmittance of less than 0.1% in the 800nm-2000nm wavelength band. The narrowband filter has a third bandpass filter on its incident surface and a fourth bandpass filter on its exit surface. The transmittance of both the third and fourth bandpass filters in the 656.28nm±0.5nm band is not less than 97.5%.

[0007] Furthermore, both the first and second filter windows are set at the same tilt angle to the optical axis but in opposite directions.

[0008] Furthermore, both the first and second filter windows are tilted at 1° relative to the optical axis.

[0009] Furthermore, the first and second filter windows have the same dimensions, with a light transmission diameter of 210mm and a thickness of 23mm.

[0010] Furthermore, the radiation-shielding glass is BK7G18 glass.

[0011] Furthermore, the narrowband filter is located at the focal point of the spectral imaging optical path.

[0012] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. This invention employs an innovative triple-stage filtering design to gradually narrow the bandwidth from a wide band (656.28nm±10nm) to the target bandwidth (656.28nm±0.5nm), ultimately precisely controlling the imaging spectral bandwidth within 1nm and ensuring that the center wavelength is stably locked at 656.28nm, thus meeting the extreme technical requirements for high-precision imaging of solar Hα spectral lines.

[0013] 2. This invention decomposes the requirements of ultra-narrowband filtering onto multiple optical surfaces, avoiding the problems of excessively high bandwidth steepness, temperature stability and yield requirements for single-layer filter film systems in traditional solutions. This improves the feasibility and reliability of the system and reduces manufacturing costs and risks.

[0014] 3. This invention uses a multi-stage filtering and thermal control film system (such as an ultraviolet cut-off film and an infrared reflective film) in the pre-filter window assembly to reflect or block most of the solar radiation energy (especially strong ultraviolet and infrared) in the non-working wavelength bands outside the system, which greatly reduces the heat absorbed by the optical elements. This significantly reduces the thermal load on the narrowband filter of the last stage of filtering, avoiding problems such as thermal deformation and thermal wavelength drift caused by drastic local temperature changes, thereby ensuring the long-term stability of on-orbit imaging and the accuracy of spectral positioning.

[0015] 4. This invention utilizes a combination of an ultraviolet cutoff film, a bandpass filter, and an infrared reflective film to filter out a large amount of stray light in the non-656.28nm±0.5nm wavelength band at the front end of the solar imaging spectrometer. Furthermore, a narrow-band filter at the focal point of the spectral imaging optical path further optimizes the filtering effect by leveraging its small incident angle characteristic, and maximally suppresses stray light generated inside the solar imaging spectrometer. This combined effect results in extremely low levels of stray light in the non-656.28nm±0.5nm wavelength band reaching the imaging surface, significantly improving the signal-to-noise ratio and spectral purity of the image.

[0016] 5. This invention ingeniously integrates the first two filtering functions into the existing, necessary filter window, and coats both surfaces of the filter window to fully utilize the pre-filter window without the need for additional independent filter components. This not only simplifies the structure of the solar imaging spectrometer, reduces its weight and size, but also reduces potential assembly and adjustment errors and failure points, thereby improving the on-orbit reliability of the solar imaging spectrometer. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of a solar imaging spectrometer based on multiple filtering settings, as described in an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached drawings: front filter window assembly 1, first filter window glass 11, incident surface 111, exit surface 112, second filter window glass 12, incident surface 121, exit surface 122, narrow band filter 2, incident surface 21, exit surface 22. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, 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, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "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 mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] This invention proposes a solar imaging spectrometer based on a multi-filter design. It employs a triple-stage filtering design to achieve precise center wavelength localization of the solar Hα spectral line and accurately limit the imaging spectral bandwidth to within 1 nm, ensuring effective on-orbit imaging. The first two filters are located on the front filter window of the solar imaging spectrometer, while the third filter is located inside the spectrometer, preferably at the focal point of the spectral imaging optical path. This approach cleverly utilizes the film system of the front filter window and places the final narrowband filter at the focal point of the spectral imaging optical path, maximizing stray light control efficiency and pointing the way for the fine spectral control design of various spectroscopic instruments used in space observations such as the sun.

[0024] The following will refer to Figure 1 The invention will be described in detail with reference to the embodiments.

[0025] like Figure 1 As shown, the present invention provides a solar imaging spectrometer based on multiple filtering settings, including a front filter window assembly 1 and a narrowband filter 2. The front filter window assembly 1 is disposed at the front end of the solar imaging spectrometer, and the narrowband filter 2 is disposed inside the solar imaging spectrometer, preferably at the focal point of the spectral imaging optical path.

[0026] Unlike Earth observation instruments and ground-based solar observation instruments, the solar imaging spectrometer directly images the sun. During its operation in orbit, it is subject to numerous influences, including alternating space solar radiation, Earth's infrared radiation, Earth's solar albedo, and space environmental pollution. Therefore, a front-end filter window assembly 1 is installed at the front end of the solar imaging spectrometer. The front-end filter window assembly 1 mainly serves to insulate and cool the instrument, maintaining the normal temperature environment of the internal optical system and reducing the impact of the external space thermal environment on the performance of the optical system. Considering the step-by-step filtering method, two pieces of glass are selected in the design of the front-end filter window assembly 1: a first filter window glass 11 and a second filter window glass 12. The first filter window glass 11 and the second filter window glass 12 have the same shape and size. Through the design and layout of the film system, the functions of radiation protection, bandpass filtering, and cutoff are achieved. The first filter window glass 11 is radiation-resistant glass (e.g., but not limited to BK7G18 glass), and the second filter window glass 12 is sapphire or fused silica glass.

[0027] In a specific example of the present invention, the light-transmitting aperture of the first filter window glass 11 and the second filter window glass 12 are both 210 mm and 23 mm thick. To prevent ghosting from affecting the imaging, both the first filter window glass 11 and the second filter window glass 12 are set at the same tilt angle to the optical axis but in opposite directions, so that the first filter window glass 11 and the second filter window glass 12 are arranged in a V-shape. The tilt angle is preferably 1°, that is, the first filter window glass 11 is tilted 1° away from the direction of the solar imaging spectrometer and towards the optical axis, and the second filter window glass 12 is tilted 1° towards the direction of the solar imaging spectrometer and towards the optical axis.

[0028] The radiation-shielding glass has a strong absorption rate in the ultraviolet and infrared bands and a high transmittance in the visible light band. Considering the illuminance spectral distribution, the system's operating wavelength, the coating process, and the window's absorption rate curve, the incident surface 111 of the first filter window glass 11 is coated with an ultraviolet cutoff film. The transmittance of the ultraviolet cutoff film is less than 0.1% in the 200nm-500nm wavelength range and not less than 97.5% in the 646.28nm-666.28nm wavelength range. The ultraviolet cutoff film is mainly used to reflect sunlight in the ultraviolet and near-infrared spectral ranges, ensuring radiation protection within the operating wavelength range of 646.28nm-666.28nm. Light can pass through effectively, thereby reducing energy absorption by the window material. The emitting surface 112 of the first filter window glass 11 is coated with a first bandpass filter film. The transmittance of the first bandpass filter film is not less than 97.5% in the 646.28nm-666.28nm band and less than 0.1% in the 200nm-750nm band. The first bandpass filter film is used to ensure the effective transmission of light within the working band, while filtering out the light reflection on both sides of the working band 646.28nm-666.28nm.

[0029] The incident surface 121 of the second filter window glass 12 is coated with a second bandpass filter. The second bandpass filter has a transmittance of not less than 97.5% in the 651.28nm-661.28nm wavelength band and a transmittance of less than 1% in the 400nm-1200nm wavelength band. The second bandpass filter is used to further block the energy in the ultraviolet band from the solar imaging spectrometer. The exit surface 122 of the second filter window glass 12 is coated with an infrared reflective film. The infrared reflective film has a transmittance of not less than 97.5% in the 651.28nm-661.28nm wavelength band and a transmittance of less than 0.1% in the 800nm-2000nm wavelength band. The infrared reflective film can ensure the effective passage of light in the operating wavelength band of 651.28nm-661.28nm, while narrowing the wavelength range.

[0030] This invention ingeniously integrates the first two filtering functions into the existing, necessary filter window, namely the front filter window assembly 1. Coatings are applied to both surfaces of the filter window, fully utilizing the front filter window without requiring additional independent filtering components. This not only simplifies the structure of the solar imaging spectrometer, reducing its weight and size, but also reduces potential assembly and adjustment errors and failure points, thereby improving the on-orbit reliability of the solar imaging spectrometer.

[0031] This invention uses a multi-stage filtering and thermal control film system (such as an ultraviolet cut-off film and an infrared reflective film) in the pre-filter window assembly 1 to reflect or block most of the solar radiation energy (especially strong ultraviolet and infrared) in the non-working wavelength bands outside the system, which greatly reduces the heat absorbed by the optical elements. This significantly reduces the thermal load on the narrowband filter 2 of the last stage of filtering, avoiding problems such as thermal deformation and thermal wavelength drift caused by drastic local temperature changes, thereby ensuring the long-term stability and spectral positioning accuracy of on-orbit imaging.

[0032] The front filter window assembly 1 filters out a large amount of stray light from the front end of the solar imaging spectrometer that is not in the 655.78nm-656.78nm band through the combined action of the ultraviolet cut-off film, the bandpass filter film and the infrared reflective film.

[0033] The final narrowband filter 2 can be placed in multiple locations inside the solar imaging spectrometer. In this invention, it is placed at the focal point of the spectral imaging optical path. A smaller narrowband filter 2 can achieve third-order wavelight. The smaller narrowband filter 2 can reduce the weight and volume of the narrowband filter 2, while also having the advantage of a small incident angle, thus suppressing stray light generated inside the solar imaging spectrometer to the greatest extent.

[0034] The incident surface 21 of the narrowband filter 2 is coated with a third bandpass filter film, and the exit surface 22 of the narrowband filter 2 is coated with a fourth bandpass filter film. The transmittance of the third bandpass filter film and the fourth bandpass filter film in the 655.78nm-656.78nm band is not less than 97.5%.

[0035] The combined effect of the ultraviolet cut-off film, four bandpass filters, and infrared reflective film results in extremely low stray light in the non-655.78nm-656.78nm bands reaching the imaging surface, significantly improving the signal-to-noise ratio and spectral purity of the image.

[0036] Because the tiered filtering and thermal control film system (such as ultraviolet cut-off film and infrared reflective film) of the front filter window assembly 1 reflects or blocks most of the solar radiation energy (especially strong ultraviolet and infrared) in the non-working bands outside the system, the heat absorbed by the optical elements is greatly reduced. This significantly reduces the thermal load on the narrowband filter 2 of the last stage of filtering, avoiding problems such as thermal deformation and thermal wavelength drift caused by drastic local temperature changes, thereby ensuring the long-term stability of on-orbit imaging and spectral positioning accuracy.

[0037] This invention employs an innovative design of triple-stage filtering (front filter window component 1 + narrowband filter 2) to gradually narrow the bandwidth from a wide band (646.28nm-666.28nm) to the target bandwidth (655.78nm-656.78nm), ultimately precisely controlling the imaging spectral bandwidth within 1nm and ensuring that the center wavelength is stably locked at 656.28nm, thus meeting the extreme technical requirements for high-precision imaging of solar Hα spectral lines.

[0038] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0039] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A solar imaging spectrometer based on multiple filter settings, characterized in that, It includes a front filter window assembly located at the front end of the solar imaging spectrometer and a narrowband filter located inside the solar imaging spectrometer; the front filter window assembly includes a first filter window glass and a second filter window glass; wherein, The first filter window glass is made of radiation-proof glass. Its incident surface is coated with an ultraviolet cut-off film, which has a transmittance of less than 0.1% in the 200nm-500nm wavelength range and a transmittance of not less than 97.5% in the 656.28nm±10nm wavelength range. Its exit surface is coated with a first bandpass filter film, which has a transmittance of not less than 97.5% in the 656.28nm±10nm wavelength range and a transmittance of less than 0.1% in the 200nm-750nm wavelength range. The second filter window glass is made of sapphire or fused silica glass. Its incident surface is coated with a second bandpass filter film, which has a transmittance of not less than 97.5% in the 656.28nm±5nm wavelength band and a transmittance of less than 1% in the 400nm-1200nm wavelength band. Its exit surface is coated with an infrared reflective film, which has a transmittance of not less than 97.5% in the 656.28nm±5nm wavelength band and a transmittance of less than 0.1% in the 800nm-2000nm wavelength band. The narrowband filter has a third bandpass filter on its incident surface and a fourth bandpass filter on its exit surface. The transmittance of both the third and fourth bandpass filters in the 656.28nm±0.5nm band is not less than 97.5%.

2. The solar imaging spectrometer based on multiple filtering settings according to claim 1, characterized in that, Both the first and second filter windows are set at the same tilt angle to the optical axis, but in opposite directions.

3. The solar imaging spectrometer based on multiple filtering settings according to claim 2, characterized in that, Both the first and second filter windows are tilted at 1° to the optical axis.

4. The solar imaging spectrometer based on multiple filtering settings according to claim 1, characterized in that, The first and second filter windows have the same dimensions, with a light-transmitting aperture of 210mm and a thickness of 23mm.

5. The solar imaging spectrometer based on multiple filtering settings according to claim 1, characterized in that, The radiation-shielding glass is BK7G18 glass.

6. The solar imaging spectrometer based on multiple filtering settings according to claim 1, characterized in that, The narrowband filter is located at the focal point of the spectral imaging optical path.

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