Spatial solar spectral magnetic field telescope based on multi-wave plate polarization modulation

Abstract

The application belongs to the field of polarization measurement, and particularly relates to a space solar spectrum magnetic field telescope based on multi-wave plate polarization modulation, which comprises a telescopic system, a relay system and a spectral imaging system; the telescopic system comprises a first 1 / 2 wave plate, a 1 / 4 wave plate and a second 1 / 2 wave plate; when neither the first 1 / 2 wave plate nor the second 1 / 2 wave plate fails, the second wave plate is kept static, the first wave plate and the third wave plate are rotated in the same direction according to a preset different-speed non-synchronous motion time sequence, and measurement of full Stokes components of solar polarization spectrum is realized; when any one of the first 1 / 2 wave plate or the second 1 / 2 wave plate fails, the 1 / 4 wave plate is started, and is rotated in the same direction with the other normal 1 / 2 wave plate according to a re-planned different-speed non-synchronous motion time sequence, so as to maintain the measurement of full Stokes components of solar polarization spectrum. The application can realize full Stokes measurement, and fills the gap of the space solar vector magnetic field detection capability in China.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polarization measurement, and particularly relates to a spatial solar spectrum magnetic field telescope based on multi-wave plate polarization modulation. BACKGROUND

[0002] The sun is a huge plasma body full of magnetic fields, which is in a magnetized state from the internal convection zone to the outer atmosphere. The structure and evolution of the solar magnetic field is the fundamental physical mechanism driving various solar activity phenomena. For example, solar sunspots, flares, filaments, and coronal mass ejections are directly derived from the accumulation and sudden release of magnetic field energy. Therefore, high-precision and high-resolution observation of the solar magnetic field is the core of solving a series of major frontier scientific problems in solar physics, such as the origin of the solar magnetic field generator, the heating mechanism of the million-degree coronal temperature, and the triggering physical process of solar eruptions.

[0003] In the application layer, the warning and prediction of space weather urgently rely on real-time and high-precision monitoring of the global magnetic field activity of the sun. Obtaining full-disk vector magnetic field data is indispensable for the driving data of the current solar activity prediction model based on artificial intelligence. At the same time, the prediction of the propagation and influence of solar eruption events in the geospace is also based on the global magnetosphere magnetic field structure extrapolated from the full-disk vector magnetic field. The assimilation of spatial solar magnetic field observation data into the first generation of “full-link” space weather numerical prediction model in China will significantly improve the prediction ability and accuracy of the near-Earth space environment disturbance.

[0004] At present, the international solar space magnetic field detection technology has made significant progress, and there are several mature special payloads. Typical representatives include the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) of the United States, the Polarimetric and Helioseismic Imager (PHI) on the Solar Orbiter of Europe, and the Solar Optical Telescope (SOT) of the Hinode satellite of Japan. These devices can all achieve full-Stokes parameter measurement of the solar vector magnetic field, providing key data support for global space weather prediction and frontier scientific research.

[0005] However, compared with this, the space solar magnetic field detection technology in China still has deficiencies, especially in the aspect of measurement stability. When the wave plate fails, the space solar spectrum magnetic field telescope cannot complete the measurement of the full Stokes component, and this technical shortcoming restricts the further development of China in the field of solar physics and the ability of independent space weather forecasting.

[0006] Therefore, it is urgent to develop a space solar spectrum magnetic field telescope capable of stable operation in orbit, achieving high-precision and full-Stokes measurement. SUMMARY

[0007] Therefore, the present application aims to provide a space solar spectrum magnetic field telescope based on multi-wave plate polarization modulation to solve the technical problem that the full-Stokes component measurement cannot be realized by the satellite in orbit in China at present.

[0008] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0009] A space solar spectrum magnetic field telescope based on multi-wave plate polarization modulation, comprising a telescope system for collecting a solar beam and performing polarization modulation thereon, a relay system for performing aberration correction on the polarization-modulated solar beam, and a spectral imaging system for performing spectral splitting and imaging on the polarization-modulated solar beam.

[0010] The telescope system comprises a spherical lens and a polarization modulation unit, the spherical lens being used for angle compression of the collected solar beam, and the polarization modulation unit being used for polarization modulation of the angle-compressed solar beam.

[0011] The polarization modulation unit comprises a first 1 / 2 wave plate, a 1 / 4 wave plate and a second 1 / 2 wave plate arranged in sequence along the propagation direction of the solar beam.

[0012] When neither the first 1 / 2 wave plate nor the second 1 / 2 wave plate fails, the second wave plate is kept stationary, and the first wave plate and the third wave plate are rotated in the same direction according to a preset asynchronous motion time sequence of different speeds to perform polarization modulation on the angle-compressed solar beam, thereby realizing the measurement of the full-Stokes component of the solar polarization spectrum.

[0013] When either the first 1 / 2 wave plate or the second 1 / 2 wave plate fails, the 1 / 4 wave plate is started, and rotates in the same direction with the other normal 1 / 2 wave plate according to a re-planned asynchronous motion time sequence of different speeds to maintain the measurement of the full-Stokes component of the solar polarization spectrum.

[0014] Further, the motion time sequence of the first 1 / 2 wave plate follows the following angle planning:

[0015] θ1= (k-1) π / 8;

[0016] Wherein, θ1 represents the rotation angle of the first 1 / 2 wave plate, k represents the polarization modulation state sequence number, and is a non-negative integer;

[0017] The motion timing of the second 1 / 2 wave plate follows the angle planning as follows:

[0018] θ2=kπ / 8;

[0019] Wherein, θ2 represents the rotation angle of the second 1 / 2 wave plate.

[0020] Further, when the first 1 / 2 wave plate fails, the starting angle of the 1 / 4 wave plate is adjusted to the failure angle of the first 1 / 2 wave plate, denoted as θ3, and the motion timing of the 1 / 4 wave plate follows the angle planning as follows:

[0021] θ4=θ3+kπ / 8;

[0022] Wherein, θ4 represents the rotation angle of the 1 / 4 wave plate after replacing the first 1 / 2 wave plate;

[0023] When the second 1 / 2 wave plate fails, the starting angle of the 1 / 4 wave plate is adjusted to the failure angle of the second 1 / 2 wave plate, denoted as θ5, and the motion timing of the 1 / 4 wave plate follows the angle planning as follows:

[0024] θ6=θ5+(k-1)π / 8;

[0025] Wherein, θ6 represents the rotation angle of the 1 / 4 wave plate after replacing the second 1 / 2 wave plate.

[0026] Further, the telescope system further comprises an aspheric primary mirror and an aspheric secondary mirror, and the sunlight beam is first incident to the aspheric primary mirror for reflection, reflected to the aspheric secondary mirror through the aspheric primary mirror, and then reflected to the spherical lens through the aspheric secondary mirror.

[0027] Further, the relay system comprises a polarization beam splitter, a reimaging lens group and a scanning mechanism arranged in sequence along the optical path, the polarization beam splitter is used for splitting the polarized light, the reimaging lens group is used for imaging the split polarized light, and the scanning mechanism is used for scanning the sunlight beam in the spatial dimension.

[0028] Further, the reimaging lens group comprises a first lens, a second lens and a third lens arranged in sequence; wherein,

[0029] The first lens has an optical aperture of 50mm, an Abbe number of 27.53, and a positive optical power;

[0030] The second lens has an optical aperture of 50mm, an Abbe number of 64.17, and a negative optical power;

[0031] The third lens has an optical aperture of 65mm, an Abbe number of 64.17, and a positive optical power;

[0032] The interval between the first lens and the second lens is 4.9mm;

[0033] The interval between the second lens and the third lens is 42.6mm.

[0034] Further, the extinction ratio of the polarization beam splitter is greater than 5000.

[0035] Further, the relay system further comprises a plane mirror arranged in the incident light path of the polarization beam splitter, and the polarized light is reflected to the polarization beam splitter through the plane mirror.

[0036] Further, the spectral imaging system comprises a slit, a spectrometer and a photoelectric detector, and the polarized light transmitted by the relay system is converged at the slit, dispersed by the spectrometer and then imaged on the photoelectric detector.

[0037] Compared with the prior art, the application can achieve the following beneficial effects:

[0038] 1. Realize high-reliability on-orbit full-Stokes parameter measurement

[0039] The application first proposes and realizes a three-wave-plate allometric cooperative cold backup polarization modulation scheme suitable for space environment. Through the redundant design of three wave plates (two 1 / 2 wave plates and one 1 / 4 wave plate), when any 1 / 2 wave plate fails, the 1 / 4 wave plate as a cold backup can be immediately started, and the motion timing is re-planned to ensure that the space solar spectrum magnetic field telescope can still complete the measurement of full-Stokes components, providing indispensable measured data driving for China's space weather accurate prediction.

[0040] 2. Obtain high-precision and high-stability polarization modulation effect

[0041] The application compresses the maximum sun beam angle incident to the polarization modulation unit by integrating a spherical lens in the telescope system, significantly reduces the sensitivity of the wave plate phase delay to the incident angle. Combined with the excellent imaging quality brought by the aspheric primary / secondary mirror, it provides nearly ideal beam conditions for the rear-end polarization measurement, thereby greatly improving the precision and consistency of the polarization modulation in the entire field of view, and ensuring the accuracy of the solar magnetic field measurement.

[0042] 3. Prolong the on-orbit life of the rotating motor

[0043] Through the carefully designed allometric asynchronous motion timing, the number of rotating motor movements is optimized under the premise of ensuring the completeness of the modulation matrix, effectively prolonging the on-orbit working life of the rotating motor.

[0044] 4. Consider high time resolution and high signal-to-noise ratio

[0045] The allometric non-synchronous motion timing designed by the application can obtain a sufficient number of linearly independent modulation states in a limited measurement period. This makes the system meet the needs of high time resolution observation of rapidly evolving solar activities (such as flares), and effectively suppresses noise through redundant measurement to improve the signal-to-noise ratio and reliability of data inversion. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application and are incorporated herein for reference. The detailed description of the application and its illustrations provide an explanation of the application, but are not meant to limit the application. In the drawings:

[0047] Figure 1 Structure diagram of the multi-wave plate polarization modulation based spatial solar spectrum magnetic field telescope according to the embodiments of the application;

[0048] Figure 2 Rotation angle diagram of the three wave plates according to the embodiments of the application.

[0049] Legend: telescope system 1, aspheric primary mirror 11, aspheric secondary mirror 12, spherical lens 13, polarization modulation unit 14, first 1 / 2 wave plate 141, 1 / 4 wave plate 142, second 1 / 2 wave plate 143, relay system 2, polarization beam splitter 21, reimaging lens group 22, scanning mechanism 23, plane mirror 24, spectral imaging system 3, slit 31, spectrometer 32 and photodetector 33. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the application clearer, the 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 application, and do not limit the application.

[0051] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0052] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "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 do not indicate or imply 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 of 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 defined with "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0053] 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 fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected 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.

[0054] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0055] As Figure 1 shown, the embodiment of the present application provides a spatial solar spectrum magnetic field telescope based on multi-wave plate polarization modulation, which comprises a telescope system 1, a relay system 2 and a spectral imaging system 3 arranged in sequence along the light path.

[0056] The telescope system 1 comprises an aspheric primary mirror 11, an aspheric secondary mirror 12, a spherical lens 13 and a polarization modulation unit 14. The aspheric primary mirror 11 and the aspheric secondary mirror 12 are used to collect a solar beam, and the aspheric primary mirror 11 is used to perform angle compression on the collected solar beam. The polarization modulation unit 14 is used to perform polarization modulation on the angle-compressed solar beam to form polarized light. The aspheric primary mirror 11 performs angle compression on the maximum solar beam about to be incident on the polarization modulation unit 14, greatly improving the polarization modulation precision of the polarization modulation unit 14 on the solar beam.

[0057] The sunlight beam is firstly reflected by the aspheric primary mirror 11, then reflected by the aspheric secondary mirror 12, and then reflected by the spherical lens 13 for angle compression. The primary mirror and the secondary mirror of the present application are designed as aspheric mirrors, which can be designed into more complex curved surfaces, so as to accurately correct several aberrations in the optical system that most affect the imaging quality, such as spherical aberration, coma, astigmatism, field curvature and the like. The imaging quality close to the diffraction limit is obtained in the full field of view, and the uniformity of the subsequent slit spectral imaging is ensured. At the same time, the aspheric design can significantly reduce the number of lenses, avoid the complex correction of aberration by a multi-piece spherical mirror group, greatly shorten the distance between the primary mirror and the secondary mirror, realize a compact and lightweight telescope, and meet the strict volume and weight limitations of space loads.

[0058] The relay system 2 comprises a polarization beam splitter 21, an imaging mirror group 22 and a scanning mechanism 23 arranged in sequence along the light path, the polarization beam splitter 21 is used for splitting the polarized light, and the extinction ratio of the polarization beam splitter 21 is greater than 5000; the imaging mirror group 22 is used for imaging the split polarized light; and the scanning mechanism 23 is used for spatially scanning the sunlight beam. The polarization beam splitter 21 and the scanning mechanism 23 are both prior art, and thus the specific structure is not described herein.

[0059] The imaging mirror group 22 comprises a first lens, a second lens and a third lens arranged in sequence, and the first lens is closer to the polarization modulation unit 14 than the third lens; wherein the first lens has a light aperture of 50mm, an Abbe number of 27.53 and a positive optical power; the second lens has a light aperture of 50mm, an Abbe number of 64.17 and a negative optical power; and the third lens has a light aperture of 65mm, an Abbe number of 64.17 and a positive optical power; the distance between the first lens and the second lens is 4.9mm; and the distance between the second lens and the third lens is 42.6mm.

[0060] The relay system 2 further comprises a plane mirror 24 arranged in the incident light path of the polarization beam splitter 21, and the polarized light modulated by the polarization modulation unit 14 is firstly incident to the plane mirror 24 and then reflected by the plane mirror 24 to the polarization beam splitter 21. The plane mirror 24 plays a role of light path folding and does not participate in imaging, and the plane mirror 24 can reduce the axial length of the spatial solar spectrum magnetic field telescope.

[0061] The spectral imaging system 3 comprises a slit 31, a spectrometer 32 and a photoelectric detector 33, the slit 31 is arranged at the focal plane of the imaging mirror group 22, the polarized light transmitted by the relay system is converged at the slit 31, and then imaged on the photoelectric detector 33 after being dispersed by the spectrometer 32. In this process, the scanning mechanism 23 completes the spatial scanning of the sunlight, so as to obtain the solar full-disk magnetic map.

[0062] The present application integrates the polarization modulation unit 14 in the telescope system 1, and the polarization modulation unit 14 modulates the polarization of the sun beam, so that the continuous measurement of all Stokes components can be realized. Figure 2 As shown in the figure, the polarization modulation unit 14 includes a first 1 / 2 wave plate 141, a 1 / 4 wave plate 142 and a second 1 / 2 wave plate 143 arranged in sequence along the propagation direction of the sun beam, that is, the sun beam passes through the first 1 / 2 wave plate 141, the 1 / 4 wave plate 142 and the second 1 / 2 wave plate 143 in sequence.

[0063] The distance between the first 1 / 2 wave plate 141 and the 1 / 4 wave plate 142 and the distance between the 1 / 4 wave plate 142 and the second 1 / 2 wave plate 143 are both 45mm, and the distance deviation is better than 0.01mm. The first 1 / 2 wave plate 141, the 1 / 4 wave plate 142 and the second 1 / 2 wave plate 143 are respectively driven to rotate by a rotary motor, and the first 1 / 2 wave plate 141, the 1 / 4 wave plate 142 and the second 1 / 2 wave plate 143 require strict central symmetry during rotation, and the deviation is better than 0.01mm.

[0064] The first 1 / 2 wave plate 141, the 1 / 4 wave plate 142 and the second 1 / 2 wave plate 143 constitute a three-wave-plate different-speed cooperative cold backup polarization modulation scheme. The scheme refers to that, in normal operation, the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 rotate in the same direction and at different speeds, and the 1 / 4 wave plate 142 remains stationary as a cold backup element to improve reliability; only when any one of the first 1 / 2 wave plate 141 or the second 1 / 2 wave plate 143 fails, so that the polarization modulation unit 14 cannot work normally, the 1 / 4 wave plate 142 will be started to replace the failed 1 / 2 wave plate and cooperate with the other normal 1 / 2 wave plate, so as to maintain the normal operation of the polarization modulation unit 14.

[0065] To completely describe the polarization state of a light beam, four Stokes components are required: I (total light intensity), Q (linearly polarized light in 0° / 90° direction), U (linearly polarized light in 45° / 135° direction), and V (circularly polarized light). Q and U describe linearly polarized light, and V describes circularly polarized light.

[0066] The functions of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 are to rotate the polarization direction of linearly polarized light, and to change the distribution between Q and U. The first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 cannot directly generate or measure circularly polarized light.

[0067] 1 / 4 wave plate 142 is to convert linearly polarized light and circularly polarized light. When linearly polarized light at 45° angle incident to 1 / 4 wave plate, the outgoing light will become circularly polarized light. To measure the circularly polarized component V, the polarization modulation unit 14 must include a 1 / 4 wave plate 142, otherwise three wave plates are all 1 / 2 wave plate, no matter how the wave plate is combined, the polarization modulation unit 14 cannot modulate circularly polarized light, resulting in the lack of ability to measure the circularly polarized component V of the spatial solar spectrum magnetic field telescope, and the full Stokes component cannot be measured.

[0068] The first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 rotate in the same direction at a uniform speed, and the rotation angle of the first 1 / 2 wave plate 141 and the rotation angle of the second 1 / 2 wave plate 143 are different and the time sequence is different, that is, the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 keep the same direction rotation with a fixed angle difference, and the 1 / 4 wave plate 142 keeps static.

[0069] By changing the modulation state of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143, each modulation state corresponds to a Mueller matrix, and measuring the light intensity under n groups (n≥4) different modulation states can establish the relationship between the light intensity and the polarization state:

[0070] ;

[0071] Where the column vector on the left side of the equal sign is the actual measured light intensity data under n groups of modulation states, each row of the n×4 matrix on the right side of the equal sign is the first row of the Mueller matrix under the corresponding modulation state, and the column vector on the right side of the equal sign is the Stokes vector to be solved (i.e. four polarization states).

[0072] The above relationship can be simplified as: , is the light intensity column vector, X is the n×4 matrix composed of Mueller matrix rows, and S is the Stokes vector.

[0073] When the matrix X satisfies the reversible condition (for example, when n=4, X is a 4×4 square matrix and is reversible), the Stokes vector to be measured (i.e. I, Q, U, V four polarization states) can be solved by

[0074] When the polarization modulation unit 14 is working normally, the motion time sequence of the first 1 / 2 wave plate 141 follows the following angle planning:

[0075] θ1=(k-1)π / 8;

[0076] ​wherein θ1 represents the rotation angle of the first 1 / 2 wave plate, k represents the polarization modulation state sequence number, and takes a non-negative integer, k = 0, 1, 2…, k serves as a non-negative integer index for discretely identifying different polarization modulation states.

[0077] The motion timing of the second 1 / 2 wave plate 143 follows the angle planning below:

[0078] θ2 = kπ / 8;

[0079] wherein θ2 represents the rotation angle of the second 1 / 2 wave plate.

[0080] The rotation angle difference between the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 is θ2-θ1 = kπ / 8-(k-1)π / 8 = π / 8. This fixed rotation angle difference can make the polarization modulation effects of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 form a stable combined effect, ensuring that the modulation cooperation relationship of the two on the polarization state of sunlight is stable, without the need for complex synchronization control logic, thereby reducing the control difficulty of motor motion.

[0081] The calculation of the Stokes vector (I, Q, U, V) requires at least 4 groups of linearly independent modulation states (i.e. the corresponding Mueller matrix row vectors are not collinear), otherwise the matrix X is not invertible and the polarization state cannot be calculated.

[0082] π / 8 is selected as the fixed rotation angle difference. When k takes 0, 1, 2…, the angles of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 will cover-π / 8, 0, π / 8, 2π / 8…, etc. in turn, which can generate n groups (n≥4) of different modulation states. The Mueller matrix row vectors corresponding to these modulation states are linearly independent, which can ensure that the matrix X is invertible, so that the Stokes vector can be accurately solved.

[0083] If the angle step is too large (such as π / 4), the number of modulation states will be reduced, which may not cover the full-dimensional information of the polarization state; if the step is too small (such as π / 16), more angle switching is required, which will increase the measurement time and reduce the efficiency.

[0084] The fixed rotation angle difference of π / 8 can not only ensure the diversity of the modulation states (sufficient to support high-precision calculation), but also avoid excessive angle switching, achieving a balance between modulation efficiency and data effectiveness.

[0085] Through the carefully designed asynchronous motion timing of different speeds, the number of rotation motor movements is optimized under the premise of ensuring the completeness of the modulation matrix, effectively prolonging the on-orbit working life of the rotation motor.

[0086] The combination of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143 rotating at different speeds and the 1 / 4 wave plate 142 fixed can form a complete full-Stokes polarization modulator. By accurately controlling the rotation angles of the first 1 / 2 wave plate 141 and the second 1 / 2 wave plate 143, the Mueller matrix of the combination can modulate the time sequence light intensity signal containing all information of I, Q, U and V, and further realize the measurement of the full-Stokes components of the solar polarization spectrum.

[0087] When any one of the first 1 / 2 wave plate 141 or the second 1 / 2 wave plate 143 fails, the 1 / 4 wave plate 142 is started to rotate in the same direction with the other normal 1 / 2 wave plate according to the re-planned asynchronous motion time sequence, so as to maintain the measurement of the full-Stokes components of the solar polarization spectrum.

[0088] When the first 1 / 2 wave plate 141 fails, the starting angle of the 1 / 4 wave plate 142 is adjusted to the stop angle of the first 1 / 2 wave plate 141 when it fails, denoted as θ3, and the motion time sequence of the 1 / 4 wave plate 142 follows the angle planning as follows:

[0089] θ4=θ3+kπ / 8;

[0090] Wherein, θ4 represents the rotation angle of the 1 / 4 wave plate 142 after replacing the first 1 / 2 wave plate 141.

[0091] The starting angle of the 1 / 4 wave plate 142 is set to θ3, which is to accept the polarization state when the first 1 / 2 wave plate 141 fails, so that the light path is smoothly switched from the working of the first 1 / 2 wave plate 141 to the replacement working of the 1 / 4 wave plate 142, ensuring data continuity and avoiding measurement errors caused by angle misalignment.

[0092] Similarly, when the second 1 / 2 wave plate 143 fails, the starting angle of the 1 / 4 wave plate 142 is adjusted to the stop angle of the second 1 / 2 wave plate 143 when it fails, denoted as θ5, and the motion time sequence of the 1 / 4 wave plate 142 follows the angle planning as follows:

[0093] θ6=θ5+(k-1)π / 8;

[0094] Wherein, θ6 represents the rotation angle of the 1 / 4 wave plate 142 after replacing the second 1 / 2 wave plate 143.

[0095] As can be seen, the 1 / 4 wave plate is arranged between the two 1 / 2 wave plates, which can ensure that after the failure of any one 1 / 2 wave plate, the 1 / 4 wave plate and the other normally rotating 1 / 2 wave plate can still form a full-Stokes polarization modulator with complete functions, and the measurement of the full-Stokes components of the solar polarization spectrum.

[0096] It should be understood that the various forms of flow shown above can be used to reorder, add, or remove steps. For example, the steps recited in the present disclosure can be performed in parallel, in series, or in a different order, as long as the desired results of the present disclosure are achieved, which is not limited herein.

[0097] The specific implementation described above does not constitute a limitation on the protection scope 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 protection scope of the present application.

Claims

1. A space solar spectral magnetic field telescope based on multi-waveplate polarization modulation, characterized in that, It includes a telescope system, a relay system, and a spectral imaging system arranged sequentially along the optical path; The telescope system includes a spherical lens and a polarization modulation unit. The spherical lens is used to compress the angle of the collected solar beam; the polarization modulation unit is used to polarize the angle-compressed solar beam to form polarized light. The polarization modulation unit includes a first half-wave plate, a quarter-wave plate, and a second half-wave plate arranged sequentially along the direction of solar beam propagation; When neither the first nor the second half-wave plate malfunctions, the quarter-wave plate remains stationary. The first and second half-wave plates rotate in the same direction according to a preset sequence of asynchronous, non-synchronous motions to modulate the polarization of the compressed solar beam, thereby enabling the measurement of the full Stokes component of the solar polarization spectrum. The preset sequence of asynchronous, non-synchronous motions means that the first and second half-wave plates rotate in the same direction while maintaining a rotation angle difference of π / 8. When either the first or second half-wave plate fails, the quarter-wave plate is activated and rotates in the same direction as the other normally functioning half-wave plate according to a reprogrammed sequence of asynchronous motion at different speeds, in order to maintain the measurement of the full Stokes component of the solar polarization spectrum.

2. The space solar spectroscopic magnetic field telescope based on multi-waveplate polarization modulation according to claim 1, characterized in that, The motion sequence of the first half-wave plate follows the following angular planning: θ1 = (k-1)π / 8; Where θ1 represents the rotation angle of the first half-wave plate, and k represents the polarization modulation state number, which is a non-negative integer; The motion sequence of the second half-wave plate follows the following angular planning: θ2 = kπ / 8; Where θ2 represents the rotation angle of the second half-wave plate.

3. The space solar spectral magnetic field telescope based on multi-waveplate polarization modulation according to claim 2, characterized in that, When the first half-wave plate malfunctions, the starting angle of the quarter-wave plate is adjusted to the malfunction angle of the first half-wave plate, denoted as θ3. The motion sequence of the quarter-wave plate follows the following angle planning: θ4 = θ3 + kπ / 8; Wherein, θ4 represents the rotation angle after the quarter wave plate replaces the first half wave plate; When the second half-wave plate malfunctions, the starting angle of the quarter-wave plate is adjusted to the malfunction angle of the second half-wave plate, denoted as θ5. The motion sequence of the quarter-wave plate follows the following angle planning: θ6 = θ5 + (k-1)π / 8; Where θ6 represents the rotation angle after the quarter waveplate replaces the second half waveplate.

4. The space solar spectral magnetic field telescope based on multi-waveplate polarization modulation according to claim 1, characterized in that, The telescope system also includes an aspherical primary mirror and an aspherical secondary mirror. The sunlight beam is first incident on the aspherical primary mirror and reflected, then reflected by the aspherical primary mirror to the aspherical secondary mirror, and finally reflected by the aspherical secondary mirror to the spherical lens.

5. The space solar spectral magnetic field telescope based on multi-waveplate polarization modulation according to claim 1, characterized in that, The relay system includes a polarization beam splitter, a re-imaging lens group, and a scanning mechanism arranged sequentially along the optical path. The polarization beam splitter is used to split polarized light, the re-imaging lens group is used to image the split polarized light, and the scanning mechanism is used to scan the spatial dimensions of the solar beam.

6. The space solar spectroscopic magnetic field telescope based on multi-waveplate polarization modulation according to claim 5, characterized in that, The re-imaging lens group includes a first lens, a second lens, and a third lens arranged sequentially; wherein, The first lens has a light-transmitting aperture of 50mm, an Abbe number of 27.53, and a positive optical power. The second lens has a light-transmitting aperture of 50mm, an Abbe number of 64.17, and a negative optical power. The third lens has a light-transmitting aperture of 65mm, an Abbe number of 64.17, and a positive optical power. The distance between the first lens and the second lens is 4.9 mm; The distance between the second lens and the third lens is 42.6 mm.

7. The space solar spectroscopic magnetic field telescope based on multi-waveplate polarization modulation according to claim 5, characterized in that, The extinction ratio of the polarization beam splitter is greater than 5000.

8. The space solar spectroscopic magnetic field telescope based on multi-waveplate polarization modulation according to claim 5, characterized in that, The relay system also includes a plane mirror placed in the incident optical path of the polarization beam splitter, through which polarized light is reflected to the polarization beam splitter.

9. The space solar spectroscopic magnetic field telescope based on multi-waveplate polarization modulation according to claim 1, characterized in that, The spectral imaging system includes a slit, a spectrometer, and a photodetector. The polarized light transmitted by the relay system converges at the slit, and after being dispersed by the spectrometer, it is imaged onto the photodetector.

Images