Solar imaging spectrometer based on multiple filter settings

Abstract

The application belongs to the field of spectrometers, and particularly relates to a solar imaging spectrometer based on a multiple filter setting. Two pieces of filter window glass with ultraviolet cutoff and bandpass filtering functions are sequentially arranged at the front end of the solar imaging spectrometer, and a narrow-band filter is arranged at the focal point of a spectral imaging light path, so that the imaging spectral bandwidth of a solar Halpha spectrum is accurately controlled within a range of 1 nm through three-stage filtering. The application solves the problems of high requirement of a single filter film system, difficulty in heat control and poor stray light suppression, and realizes super-narrow-band spectral observation with accurate central wavelength and high imaging quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of spectrometer, and particularly relates to a solar imaging spectrometer based on a multiple filter setting. BACKGROUND

[0002] As the only star that can be observed in high spatial resolution, the Sun is an important window for studying the origin and evolution of astrophysical magnetic fields, the acceleration and propagation of high-energy particles, and other key physical processes. Monitoring solar activity, especially studying events such as “strong flares” and “coronal mass ejections”, not only has great value in astrophysics, but also has urgent practical significance in ensuring space weather safety, maintaining communication and navigation, protecting astronaut health, and ensuring the safety of spacecraft in orbit.

[0003] In solar exploration, obtaining narrow-band spectral imaging data is a core means to reveal the dynamics of solar activity. Among them, the hydrogen alpha (Hα) spectral line (center wavelength 656.28 nm, spectral width about 1 nm) is one of the most important spectral lines for observing flares, filaments, and chromospheric dynamics. To achieve high-precision imaging of this spectral line, the instrument must have the ability to stably control the imaging spectral bandwidth within 1 nm and accurately lock the center wavelength at 656.28 nm.

[0004] The existing technology faces the following technical problems: a single filter scheme requires extremely high performance from optical films, resulting in low yield; the intense solar radiation can cause severe temperature changes in the filter elements, affecting imaging 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 a complex spatial radiation environment is a key bottleneck problem in the development of current solar imaging spectrometers. SUMMARY

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

[0006] To achieve the above-mentioned purposes, the technical solution of the present application is as follows:

[0007] A solar imaging spectrometer based on a multiple filter setting, comprising a front filter window assembly arranged at the front end of the solar imaging spectrometer and a narrow-band filter arranged inside the solar imaging spectrometer; the front filter window assembly comprises a first filter window glass and a second filter window glass; wherein,

[0008] The first light filtering window glass adopts a radiation-proof glass, an incident surface of which is coated with an ultraviolet cutoff film, the transmittance of the ultraviolet cutoff film in a 200nm-500nm wave band is less than 0.1%, and the transmittance in a 656.28nm±10nm wave band is not less than 97.5%; and an exit surface of which is coated with a first band-pass filtering film, the transmittance of the first band-pass filtering film in the 656.28nm±10nm wave band is not less than 97.5%, and the transmittance in a 200nm-750nm wave band is less than 0.1%;

[0009] The second light filtering window glass adopts a sapphire or fused quartz glass, an incident surface of which is coated with a second band-pass filtering film, the transmittance of the second band-pass filtering film in a 656.28nm±5nm wave band is not less than 97.5%, and the transmittance in a 400nm-1200nm wave band is less than 1%; and an exit surface of which is coated with an infrared reflection film, the transmittance of the infrared reflection film in the 656.28nm±5nm wave band is not less than 97.5%, and the transmittance in an 800nm-2000nm wave band is less than 0.1%;

[0010] The incident surface of the narrow-band light filter is coated with a third band-pass filtering film, and the exit surface is coated with a fourth band-pass filtering film, the transmittance of the third band-pass filtering film and the fourth band-pass filtering film in the 656.28nm±0.5nm wave band are both not less than 97.5%.

[0011] Further, the first light filtering window glass and the second light filtering window glass are both arranged at the same inclination angle with the optical axis and in opposite directions.

[0012] Further, the first light filtering window glass and the second light filtering window glass are both arranged at an inclination angle of 1° with the optical axis.

[0013] Further, the first light filtering window glass and the second light filtering window glass have the same size, the light passing apertures are both 210mm, and the thicknesses are both 23mm.

[0014] Further, the radiation-proof glass is BK7G18 glass.

[0015] Further, the narrow-band light filter is located at the focal point of the spectral imaging light path.

[0016] Compared with the prior art, the present application can achieve the following beneficial effects:

[0017] 1. The present application adopts a three-stage light filtering design, which gradually narrows from a wide wave band (656.28nm±10nm) to a target bandwidth (656.28nm±0.5nm), finally precisely controls the imaging spectral bandwidth within 1nm, and ensures that the center wavelength is stably locked at 656.28nm, meeting the extreme technical requirements of high-precision imaging of the solar Hα spectrum.

[0018] 2、The application decomposes the requirement of ultra-narrow band filtering to multiple optical surfaces, avoids the problem of putting too high requirements on the single layer filter film system in the traditional scheme, such as bandwidth steepness, temperature stability and yield, thereby improving the realizability and reliability of the system, and reducing the manufacturing cost and risk.

[0019] 3、The application reflects or blocks most of the solar radiation energy of non-working waveband (especially strong ultraviolet and infrared) outside the system through the hierarchical filtering and thermal control film system (such as ultraviolet cutoff film and infrared reflection film) of the front filter window assembly, greatly reduces the heat absorbed by the optical element, which significantly reduces the heat load of the narrow band filter of the last stage, avoids the problems of thermal deformation and thermal wavelength drift caused by local temperature change, thereby ensuring the long-term stability and spectral positioning accuracy of the on-orbit imaging.

[0020] 4、The application filters out a large amount of stray light of non-656.28nm±0.5nm waveband at the front end of the solar imaging spectrometer through the combination of ultraviolet cutoff film, bandpass filter film and infrared reflection film; further optimizes the filtering effect and maximally suppresses the stray light generated inside the solar imaging spectrometer through the narrow band filter at the focal point of the spectral imaging light path. This combined effect makes the stray light of non-656.28nm±0.5nm waveband reaching the imaging surface extremely low, significantly improving the signal-to-noise ratio and spectral purity of the image.

[0021] 5、The application ingeniously integrates the first two filtering functions on the existing and necessary filter window, coats the two surfaces of the filter window, fully utilizes the front filter window, and does not need to introduce an independent filter component. This not only simplifies the structure of the solar imaging spectrometer, reduces the weight and volume, but also reduces the potential adjustment error points and failure points, and improves the on-orbit operation reliability of the solar imaging spectrometer. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0023] Figure 1 The structure schematic diagram of the solar imaging spectrometer based on the multiple filtering arrangement described in the embodiments of the present application.

[0024] Explanation of reference signs: front filter window assembly 1, first filter window glass 11, incident surface 111, emergent surface 112, second filter window glass 12, incident surface 121, emergent surface 122, narrow band filter 2, incident surface 21, emergent surface 22. DETAILED DESCRIPTION

[0025] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0026] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0027] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified and limited, the term "assembly", "connection", "connection" should be understood broadly, for example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "assembly", "connection", "connection" should be understood broadly, for example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0029] The present application proposes a solar imaging spectrometer based on multiple filter settings, which implements three-stage filter design on the solar imaging spectrometer, realizes accurate center wavelength positioning of the solar Hα spectrum line, and accurately limits the imaging spectral bandwidth within 1nm, ensuring the on-orbit imaging effect of the solar imaging spectrometer. Among them, the first two-stage filter design is on the front filter window of the solar imaging spectrometer, and the third-stage filter design is inside the solar imaging spectrometer, preferably at the focal point of the spectral imaging light path. This way cleverly uses the film system of the front filter window, and places the final narrowband filter at the focal point of the spectral imaging light path, maximizing the efficiency of stray light control, and indicating the development direction for fine spectral control design of various spectral instruments for space observation such as the sun.

[0030] The present application will be described in detail below with reference to Figure 1 the accompanying drawings and embodiments.

[0031] As Figure 1 shown, the embodiment of the present application provides a solar imaging spectrometer based on multiple filter settings, which comprises a pre-filter window assembly 1 and a narrow-band filter 2. The pre-filter window assembly 1 is arranged at the front end of the solar imaging spectrometer, and the narrow-band filter 2 is arranged inside the solar imaging spectrometer, preferably at the focal point of the spectral imaging light path.

[0032] The solar imaging spectrometer is different from the earth observation instrument and the ground observation solar instrument, which directly images the sun and is affected by many factors such as alternating space solar radiation, earth infrared radiation, earth sunlight reflection, space environmental pollution, etc. during on-orbit operation. Therefore, the pre-filter window assembly 1 is arranged at the front end of the solar imaging spectrometer. The pre-filter window assembly 1 mainly plays a role in heat insulation and cooling, maintains the normal temperature environment of the internal optical system of the solar imaging spectrometer, and reduces the influence of the external space thermal environment on the performance of the optical system. Considering the step-by-step filtering method, two glasses are selected for the design of the pre-filter window assembly 1, i.e. the first filter window glass 11 and the second filter window glass 12. The first filter window glass 11 and the second filter window glass 12 have the same shape and size, and through film system design and layout, the effects of radiation protection, band-pass filtering and cutoff are achieved. The first filter window glass 11 is a radiation-proof glass (such as but not limited to BK7G18 glass) and the second filter window glass 12 is a sapphire or fused quartz glass.

[0033] In one specific example of the present application, the clear aperture of the first filter window glass 11 and the second filter window glass 12 is 210 mm, and the thickness is 23 mm. In order to prevent the influence of ghost images on imaging, the first filter window glass 11 and the second filter window glass 12 are arranged at the same inclination angle with respect to the optical axis and the inclination directions are opposite, so that the first filter window glass 11 and the second filter window glass 12 are arranged in a V shape. The inclination angle is preferably 1°, i.e. the first filter window glass 11 is inclined by 1° to the optical axis away from the direction of the solar imaging spectrometer, and the second filter window glass 12 is inclined by 1° to the optical axis towards the direction of the solar imaging spectrometer.

[0034] The anti-radiation glass has strong absorption rate in the window material of ultraviolet and infrared wave bands, and high transmittance in the window material of visible light wave band. Considering the illumination spectrum distribution, system working wave band, coating process and window 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 in the wave band of 200nm-500nm is less than 0.1%, the transmittance in the wave band of 646.28nm-666.28nm is not less than 97.5%, the ultraviolet cutoff film is mainly used for reflecting the sunlight in the ultraviolet and near-infrared spectrum, ensuring the effective transmission of light in the working wave band of 646.28nm-666.28nm, so as to effectively reduce the energy absorption of the window material; the exit surface 112 of the first filter window glass 11 is coated with a first band-pass filter film, the transmittance of the first band-pass filter film in the wave band of 646.28nm-666.28nm is not less than 97.5%, the transmittance in the wave band of 200nm-750nm is less than 0.1%, the first band-pass filter film is used to ensure the effective transmission of light in the working wave band, and the light on both sides of the working wave band 646.28nm-666.28nm is reflected and filtered out.

[0035] The incident surface 121 of the second filter window glass 12 is coated with a second band-pass filter film, the transmittance of the second band-pass filter film in the wave band of 651.28nm-661.28nm is not less than 97.5%, the transmittance in the wave band of 400nm-1200nm is less than 1%, the second band-pass filter film is used to further block the energy in the ultraviolet wave band outside the solar imaging spectrometer. The exit surface 122 of the second filter window glass 12 is coated with an infrared reflection film, the transmittance of the infrared reflection film in the wave band of 651.28nm-661.28nm is not less than 97.5%, the transmittance in the wave band of 800nm-2000nm is less than 0.1%, the infrared reflection film can ensure the effective transmission of light in the working wave band of 651.28nm-661.28nm, and at the same time, the wave band range is narrowed.

[0036] The present application ingeniously integrates the first two filtering functions on the existing and necessary filter window, that is, the front filter window assembly 1, and coats the two surfaces of the filter window, so that the front filter window is fully utilized, and an independent filter component is not additionally introduced. This not only simplifies the structure of the solar imaging spectrometer, reduces the weight and volume, but also reduces the potential adjustment error points and failure points, and improves the on-orbit operation reliability of the solar imaging spectrometer.

[0037] The present application reflects or blocks most of the solar radiation energy (especially strong ultraviolet and infrared) of non-working wave bands outside the system through the hierarchical filtering and heat control film system (such as ultraviolet cutoff film and infrared reflection film) of the pre-filtering window assembly 1, greatly reduces the heat absorbed by the optical element, which significantly reduces the heat load of the narrow-band filter 2 of the last stage of filtering, avoids the problems of thermal deformation and thermal wavelength drift caused by local temperature changes, and thus guarantees the long-term stability and spectral positioning accuracy of the on-orbit imaging.

[0038] The pre-filtering window assembly 1 filters out a large amount of stray light of non-655.78nm-656.78nm wave band at the front end of the solar imaging spectrometer through the combination of ultraviolet cutoff film, band-pass filter film and infrared reflection film.

[0039] The final narrow-band filter 2 can be placed in multiple places inside the solar imaging spectrometer, and the present application selects to be placed at the focal point of the spectral imaging light path, and a smaller size narrow-band filter 2 can achieve the third stage of light, which can reduce the weight and volume of the narrow-band filter 2, and also has the advantage of small incident light angle, which maximally suppresses the stray light generated inside the solar imaging spectrometer.

[0040] The incident surface 21 of the narrow-band filter 2 is coated with a third band-pass filter film, and the exit surface 22 of the narrow-band filter 2 is coated with a fourth band-pass filter film, and the transmittance of the third band-pass filter film and the fourth band-pass filter film to the 655.78nm-656.78nm wave band is not less than 97.5%.

[0041] Through the combined action of the ultraviolet cutoff film, the four band-pass filter films and the infrared reflection film, the stray light of non-655.78nm-656.78nm wave band reaching the imaging surface is extremely low, which significantly improves the signal-to-noise ratio and spectral purity of the image.

[0042] Due to the hierarchical filtering and heat control film system (such as ultraviolet cutoff film and infrared reflection film) of the pre-filtering window assembly 1, most of the solar radiation energy (especially strong ultraviolet and infrared) of non-working wave bands is reflected or blocked outside the system, which greatly reduces the heat absorbed by the optical element, which significantly reduces the heat load of the narrow-band filter 2 of the last stage of filtering, avoids the problems of thermal deformation and thermal wavelength drift caused by local temperature changes, and thus guarantees the long-term stability and spectral positioning accuracy of the on-orbit imaging.

[0043] The present application adopts the innovative design of triple-stage filtering (pre-filter window assembly 1 + narrow-band filter 2), which gradually narrows the wide band (646.28nm-666.28nm) to the target bandwidth (655.78nm-656.78nm), finally precisely controls the imaging spectral bandwidth within 1nm range, and ensures that the center wavelength is stably locked at 656.28nm, meeting the extreme technical requirements of high-precision imaging of solar Hα spectrum.

[0044] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present disclosure can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, which is not limited herein.

[0045] The above detailed description does not constitute a limitation on the scope of protection of the present application. 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 replacements and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

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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