Astronomical polarization spectrometer system based on pupil splitting

Abstract

The present invention provides an astronomical polarization spectrometer system based on pupil splitting, comprising a collimator, an aperture stop, a spliced ​​quarter-wave plate, a spliced ​​liquid crystal polarization grating, an imaging mirror and a detector; wherein the quarter-wave plate is spliced ​​by half plates with fast axes forming an angle of 45°, and the liquid crystal polarization grating is spliced ​​by half plates with grating directions forming an angle of 90°. By means of pupil splitting, a polarization spectrum image is obtained, modulation and demodulation of polarization information are realized, and all linear Stokes parameters of a signal can be obtained by taking a picture at one time, thereby realizing fast astronomical spectrum polarization imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of astronomical polarization measurement, and in particular to an astronomical polarization spectrometer system based on a spectral pupil, which is used for astronomical polarization spectrum measurement. Background Art

[0002] The essence of astronomical observation is the observation of electromagnetic waves, which have three basic characteristics: intensity, frequency and polarization. Among optical and near-infrared terminal instruments, photometric and spectroscopic instruments account for the vast majority, and these instruments cannot obtain the polarization information of the target. However, the physical mechanisms of phenomena such as scattering processes, the Zeeman effect around magnetic field sources, and synchrotron radiation are all contained in the polarized light of the observed celestial targets. In terms of scientific applications, polarization spectroscopy measurements have broad application prospects in astronomical observations, and polarization spectroscopy can provide an important scientific basis for the interpretation and prediction of astronomical theoretical model research.

[0003] At present, polarimeter designs all use polarizers or polarization beam splitters at specific angles to measure Stokes parameters. If the full Stokes (I, Q, U) is to be measured, the incident light needs to be decomposed into three or more angles. The commonly used technical method is to rotate the half-wave plate in front of the polarizer. The defect of this technology is that rotating the wave plate will cause the drift of the light beam, resulting in poor measurement accuracy and synchronization; another method is to use polarizers with different polarization angles, such as the polarimeter installed on the Hubble telescope survey camera uses three polarizers, and the rotation angle interval is 60°. The polarizer can be placed on the filter rotating wheel. Since the polarizer only allows 1 / 2 of the light to pass, the light transmission efficiency of this design is low; a polarization beam splitter (such as a Wollaston prism) can also be used instead of a polarizer to split the light beam into two beams to reduce the light loss of the system. Polarization information in two directions can be obtained by taking a picture once, and all linear polarization information can be obtained by rotating once. In actual use, multiple angles are usually rotated to have enough data to eliminate system errors.

[0004] However, whether it is a rotating wave plate or a design with polarizers at different angles, the existence of an electrically controlled mechanical rotating mechanism increases the complexity and instability of the system, and the linear polarization components (Q, U) cannot be obtained simultaneously. There are errors in the results calculated under different exposure timings, and synchronous calculation cannot be achieved. In addition, the beam drift caused by mechanical rotation also leads to a decrease in the accuracy of the calculation results. The polarimeter must be combined with a traditional grating or prism spectrometer, resulting in a large and complex overall size of the polarization spectrometer optical system. Summary of the invention

[0005] The purpose of the present invention is to provide a high-precision polarization measurement system for astronomical polarization spectrum measurement. Through the design of the spectral pupil and the combination of polarization modulation and demodulation of a quarter-wave plate and a liquid crystal polarization grating, all linear Stokes parameters Q and U of different wavelengths can be obtained through a single exposure, thereby realizing the polarization spectrum measurement of celestial targets.

[0006] According to a first aspect of the present invention, an astronomical polarization spectrometer system based on pupil splitting is provided, comprising:

[0007] An entrance slit, a collimator, an aperture stop, a spliced ​​quarter wave plate (QWP), a liquid crystal polarization grating (LCPG), an imaging mirror, and a detector are arranged in sequence along the light incident on the telescope;

[0008] Among them, the collimator is used to collimate the light from the telescope, and the aperture diaphragm is used to limit the diameter of the entrance pupil light beam;

[0009] The spliced ​​quarter wave plate is made up of half plates whose fast axes form a 45° angle;

[0010] The liquid crystal polarization grating is composed of half pieces with a 90° angle between the grating directions, and the modulation and demodulation of polarization information are achieved by pupil splitting;

[0011] After passing through the slit, the light beam is collimated by a collimator onto a spliced ​​quarter-wave plate and a liquid crystal polarization grating, and finally the modulated light is imaged onto a detector through an imaging mirror.

[0012] The astronomical polarization spectrometer system, in which the spliced ​​quarter-wave plate and the liquid crystal polarization grating are designed and combined to form a polarization demodulation combination, can be installed on a filter rotating wheel, and can be rotated out if circularly polarized light needs to be measured. Since the polarization grating divides the pupil into two parts, and the dispersion directions are perpendicular, each part is divided into left-handed circularly polarized light and right-handed circularly polarized light by the polarization grating, so the light is dispersed into four quadrants on the detector target surface, and finally the modulated light is imaged on the detector through an imaging mirror.

[0013] In the example of the present invention, based on the design of the spectral pupil, linear Stokes parameters can be obtained simultaneously in a single exposure, while the traditional polarization spectrometer needs to measure the spectral intensity under different modulation modes for multiple times to obtain the Stokes parameters. This greatly reduces the impact of atmospheric turbulence on the actual observation data and effectively improves the observation efficiency.

[0014] In other examples, when the spliced ​​quarter-wave plate is removed, the astronomical polarization spectrometer system can directly measure the spectrum of the circular polarization component and further measure the full Stokes parameters. Therefore, the astronomical polarization spectrometer system can be configured with two working modes.

[0015] As an optional example, an astronomical polarization spectrometer system based on pupil splitting includes: a slit through which telescope focal plane light passes along the optical axis of the instrument; and a collimator, an aperture stop, a spliced ​​quarter-wave plate, a spliced ​​liquid crystal polarization grating, an imaging mirror and a detector arranged in sequence along the optical axis;

[0016] The collimator is used to collimate the light beam from the telescope; the aperture stop is used to limit the aperture of the entrance pupil light beam; the spliced ​​quarter wave plate is composed of half plates with the fast axis at an angle of 45°; the spliced ​​liquid crystal polarization grating is composed of half plates with the grating direction at an angle of 90°;

[0017] The combination of the spliced ​​quarter-wave plate and the spliced ​​liquid crystal polarization grating realizes modulation and demodulation of polarization information by means of pupil splitting;

[0018] The light beam from the telescope passes through the slit, is collimated by a collimator, and then projected onto a spliced ​​quarter-wave plate and a spliced ​​liquid crystal polarization grating. It is then modulated by an imaging mirror and imaged onto a detector located at the focal plane of the imaging mirror.

[0019] As an optional example, in the spliced ​​quarter wave plate, one fast axis is parallel to the horizontal direction, and the other fast axis is 45° to the horizontal direction. The working band range of the spliced ​​quarter wave plate is 325nm-1100nm.

[0020] As an optional example, the spliced ​​liquid crystal polarization grating is formed by splicing two pieces with mutually perpendicular lines, half of which are at -45° to the horizontal direction, and the other half are at 45° to the horizontal direction. The spliced ​​liquid crystal polarization grating (5) is made of liquid crystal polymer birefringent material.

[0021] As an optional example, a combination of a spliced ​​quarter wave plate and a spliced ​​liquid crystal polarization grating is mounted on an adjustable filter rotating wheel. When circularly polarized light needs to be measured, the spliced ​​quarter wave plate QWP can be rotated out. Since the spliced ​​liquid crystal polarization grating divides the pupil into two parts, and the dispersion directions are perpendicular, each part is divided into left-handed circularly polarized light and right-handed circularly polarized light by the polarization grating, so the light is dispersed into four quadrants on the detector target surface. Finally, the modulated light is imaged on the detector through the imaging mirror.

[0022] As an optional example, in a polarization modulation mode composed of a spliced ​​quarter wave plate and a spliced ​​liquid crystal polarization grating, a super achromatic spliced ​​quarter wave plate is arranged before the spliced ​​liquid crystal polarization grating, and when the fast axis direction of the spliced ​​quarter wave plate is placed parallel to the line direction of the spliced ​​liquid crystal polarization grating and at 45°, based on the Jones matrix in polarization optics, after the light beam passes through the spliced ​​quarter wave plate and the spliced ​​liquid crystal polarization grating, the diffraction efficiency of the combination of the spliced ​​quarter wave plate and the spliced ​​liquid crystal polarization grating is calculated based on the magnetic field distribution of the positive and negative first-order parts of the diffraction, thereby obtaining the result of subtracting the positive and negative first-order diffraction efficiencies and adding the positive and negative first-order efficiencies under different angle combinations, and dividing the two to obtain the normalized Q′ and U′ calculation formulas:

[0023]

[0024]

[0025] Among them, η -1 It represents the negative diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate and the spliced ​​liquid crystal polarization grating, η +1 represents the positive diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate and the spliced ​​liquid crystal polarization grating, and Q′ and U′ represent the normalized linear polarization components Q and U, respectively.

[0026] Therefore, based on the polarization demodulation mode of the design combination of the spliced ​​quarter wave plate and the liquid crystal polarization grating proposed in the present invention, when used in an astronomical polarization spectrometer system, all the linear Stokes polarization parameters Q and U of the target can be obtained without delay and optical offset through a single exposure; and when measuring the spectrum of circularly polarized light, the spliced ​​quarter wave plate can be rotated out (i.e., moved out) to directly measure the component V of the circularly polarized light, and then measure the full Stokes parameters, which greatly improves the detection efficiency.

[0027] Compared with the prior art, the astronomical polarization spectrometer system proposed in the present invention is based on the design of a spliced ​​quarter wave plate and a liquid crystal polarization grating (a spliced ​​QWP+LCPG combination), i.e., a snapshot linear Stokes parametric polarization spectrometer, which has high observation efficiency. LCPG replaces the polarizer and the ordinary grating, further reducing the light loss, and the system has no mechanical rotating optical elements, avoiding the decrease in measurement accuracy caused by beam jitter and drifting, and at the same time, all the linear Stokes polarization parameters Q and U of the target can be obtained without delay and optical offset in one exposure, greatly reducing the influence of atmospheric turbulence on the actual observation data, and effectively improving the observation efficiency.

[0028] At the same time, the astronomical polarimeter system of the present invention does not adopt the traditional grating structure design, the instrument has a small physical size, the system is simple, and the research and development cycle and cost are reduced. Therefore, it can be used as an access instrument to dock with a small-aperture telescope for observation, or form a Robot Spectropolarimeter with a small-aperture telescope to perform spectral polarization surveys or long-term polarization monitoring of certain special stars. At the same time, the system is compact and has no mechanical movement, which is very suitable for polarization spectrum measurement of celestial targets by space astronomical instruments.

[0029] It should be understood that all combinations of the aforementioned concepts and the additional concepts described in more detail below can be considered as part of the inventive subject matter of the present disclosure as long as such concepts are not mutually inconsistent. In addition, all combinations of the claimed subject matter are considered as part of the inventive subject matter of the present disclosure.

[0030] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in every figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0032] Figure 1 Schematic diagram of an astronomical polarization spectrometer system according to an exemplary embodiment of the present invention.

[0033] Figure 2 is a schematic diagram of a QWP and a LCPG according to an exemplary embodiment of the present invention.

[0034] Figure 3 is a schematic diagram of a polarization spectrum image obtained by a detector according to an exemplary embodiment of the present invention.

[0035] The meanings of the reference numerals in the accompanying drawings are as follows:

[0036] Slit 1; collimator 2; aperture stop 3; spliced ​​quarter wave plate 4; spliced ​​liquid crystal polarization grating 5; imaging mirror 6; detector 7. DETAILED DESCRIPTION

[0037] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0038] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed by the present invention are not limited to any implementation. In addition, some aspects disclosed by the present invention can be used alone or in any appropriate combination with other aspects disclosed by the present invention.

[0039] The present invention is one of the achievements of the National Natural Science Foundation of China general project "Research on Key Technologies of Snapshot Linear Stokes Parameter Polarization Spectrometer" (12073056).

[0040] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0041] Combination Figure 1 As shown, the astronomical polarization spectrometer system according to the embodiment of the present invention is intended to realize the spectral measurement of the observation beam of the astronomical telescope and obtain the linear polarization components Q and U of the spectrum. Therefore, the linear polarization degree information and polarization azimuth information of the observed target can be obtained according to the Q and U components, which has very important scientific value for studying the characteristics of the target.

[0042] Theoretical Analysis of Snapshot Method for Measuring Linear Stokes Parameters at Different Wavelengths While ensuring the compactness of the system and the simplicity of the optical structure, the technical difficulty of the snapshot polarization measurement method is to obtain two linear parameters, Q and U, in one exposure. Another technical difficulty is to obtain Stokes parameters at different wavelengths.

[0043] like Figure 1 The astronomical polarization spectrometer system design of the example shown includes a slit 1 through which the focal plane light of the telescope passes along the optical axis of the instrument; and a collimator 2, an aperture stop 3, a spliced ​​quarter-wave plate 4, a spliced ​​liquid crystal polarization grating 5, an imaging mirror 6 and a detector 7 arranged in sequence along the optical axis.

[0044] The collimator 2 is used to collimate the light beam from the telescope.

[0045] The aperture stop 3 is used to limit the aperture of the entrance pupil light beam.

[0046] The spliced ​​quarter-wave plate 4 (Quarter-wave plate, referred to as QWP) is made by splicing half plates with their fast axes at an angle of 45°.

[0047] The spliced ​​liquid crystal polarization grating 5 (LCPG for short) is formed by splicing half pieces whose grating directions form an angle of 90°.

[0048] The combination of the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5 realizes modulation and demodulation of polarization information by means of pupil splitting.

[0049] Therefore, the light beam from the telescope passes through the slit, is collimated by the collimator 2, and then projected onto the spliced ​​quarter-wave plate 4 and the spliced ​​liquid crystal polarization grating 5, and then is imaged by the imaging mirror 7 to the detector 7 located at the focal plane position of the imaging mirror 7.

[0050] According to an example of the purpose of the present invention, based on the design of obtaining all linear Stokes polarization parameters in a single exposure, the optimal design selection is made, and polarization spectrum measurement is achieved through the pupil splitting scheme combined with a quarter-wave plate and a liquid crystal polarization grating.

[0051] After the light beam from the slit is collimated by a collimator 2, the size of the collimated light beam cannot exceed the aperture of the QWP (50mm). After the collimated light passes through the aperture, it is incident on the quarter wave plate, which is made up of wave plates with fast axes at an angle of 45°, one of which is parallel to the horizontal direction, and the other is 45° to the horizontal direction. At the same time, the working band range of the achromatic quarter wave plate is 325nm-1100nm, the phase delay accuracy is <λ / 100, the transmittance is >90%, and the surface RMS is <λ / 4@633nm.

[0052] After passing through the QWP, the light enters the spliced ​​liquid crystal polarization grating (LCPG) for polarization demodulation and color separation. The liquid crystal polarization grating is composed of two pieces with perpendicular lines.

[0053] like Figure 2 As shown. Half of the lines of the liquid crystal polarization grating are -45° to the horizontal direction, and the other half are 45° to the horizontal direction. Its substrate is N-BK7 glass, which is made of liquid crystal polymer birefringent material. It has an aperture of 50mm, an operating temperature of -20℃~80℃, a phase period of 5μm, 200 lines, and a diffraction efficiency of >98%.

[0054] The light modulated by QWP+LCPG is finally focused on the detector through the imaging mirror. The pupil design makes the light in the lower left corner be divided into linear polarization in the directions of 0° and 90°, while the light in the upper right corner is divided into linear polarization in the directions of 45° and 135°. Since the polarization grating divides the pupil into two parts and the dispersion directions are perpendicular, each part is divided into ±1 levels by the polarization grating, so the light is dispersed into four quadrants on the detector target surface.

[0055] Furthermore, the Q polarization component of the target can be obtained by subtracting the intensity of the first and third quadrants, and the U polarization component can be obtained by subtracting the intensity of the second and fourth quadrants.

[0056] In the astronomical polarization spectrometer system proposed by the present invention, based on the polarization modulation mode of QWP+LCPG, the arrangement direction of the liquid crystal molecules in the LCPG changes linearly with the spatial coordinates, and within one grating period, the azimuth angle of the liquid crystal molecules changes by 180°. Further combined with the Jones matrix analysis, each optical element has a Jones matrix, and the LCPG Jones matrix is ​​expressed as follows:

[0057]

[0058] in is the rotation matrix. In the absence of absorption and scattering energy loss, A=1, B=exp(iΓ), Γ is the birefringence phase retardation πΔnd / λ of the liquid crystal, and λ represents the wavelength.

[0059] According to the transmittance matrix formula of LCPG, the parameters and rotation matrix without absorption and scattering energy loss are substituted and the following is obtained:

[0060]

[0061] When the incident light beam passes through LCPG, it will be divided into three diffraction orders, the zero order and positive and negative first orders. The diffraction efficiency of the zero order and positive and negative first orders can be calculated by formula (1.2), where the polarization states of the positive and negative first order output light are right-handed and left-handed circularly polarized light, and the polarization states of the positive and negative first order output light are right-handed and left-handed circularly polarized light.

[0062] Combination Figure 1 As shown, the basic principles of polarization modulation and demodulation of the QWP+LCPG combination are as follows:

[0063] Assume that the electromagnetic fields of the incident light are E x and E y , the electromagnetic field of the outgoing light after PG can be calculated. According to the definition of Stokes parameters, the diffraction efficiencies of the zeroth order and the positive and negative first order can be obtained as follows:

[0064]

[0065]

[0066] Where V′=V / I 0 , that is, the normalized amount of Stokes circular polarization. According to formula (1.4), it can be concluded that the Stokes circular polarization component can be obtained by subtracting the positive and negative light intensities and adding the upper and lower light intensities. Therefore, in the system design of the present invention, the polarization spectrometer can directly measure the circularly polarized light without adding QWP.

[0067] In an embodiment of the present invention, Figure 1 As shown in FIG. 1 , for the requirement of all measurements of the linear polarization components Q and U in one exposure, in order to realize the unique advantage of obtaining all the linear Stokes components in one exposure, so as to reduce the influence of atmospheric turbulence on the polarization spectrum measurement and improve the observation efficiency, the polarization spectrometer system of the present invention proposes a design scheme based on split pupil, and introduces a super-achromatic QWP in front of the LCPG, that is, two halves of the QWP are spliced ​​(Patterned QWP), and their fast axes form an angle of 45°, and the corresponding two halves of the LCPG are spliced, and their grating directions form an angle of 90°, as shown in FIG. Figure 2 shown.

[0068] In the polarization modulation mode formed by the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5, a super achromatic spliced ​​quarter wave plate 4 is arranged before the spliced ​​liquid crystal polarization grating 5, and when the fast axis direction of the spliced ​​quarter wave plate 4 is placed parallel to the scribed line direction of the spliced ​​liquid crystal polarization grating 5 and the angle is 45 degrees, based on the Jones matrix in polarization optics, after the light beam passes through the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5, the diffraction efficiency of the combination of the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5 is calculated based on the magnetic field distribution of the positive and negative first-order parts of the diffraction, thereby obtaining the result of subtracting the positive and negative first-order diffraction efficiencies and adding the positive and negative first-order efficiencies under different angle combinations, and the normalized Q′ and U′ are obtained by dividing the two:

[0069]

[0070]

[0071] Among them, η -1 represents the negative diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate 4 and the spliced ​​liquid crystal polarization grating 5, η +1 represents the positive diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate 4 and the spliced ​​liquid crystal polarization grating 5, and Q′ and U′ represent the normalized linear polarization components Q and U, respectively.

[0072] Therefore, the linear polarization degree information and polarization azimuth information of the observed target can be obtained based on the obtained Q and U components.

[0073] In a specific embodiment, by introducing a super-achromatic QWP in front of the LCPG:

[0074] When the fast axis direction of the spliced ​​quarter wave plate 4 is placed parallel to the ruled line direction of the spliced ​​liquid crystal polarization grating 5, its Jones matrix is ​​expressed as:

[0075]

[0076] When the light beam passes through the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5, only the magnetic field distribution of the positive and negative first-order parts is calculated, and the expression is:

[0077]

[0078] According to formula 1.6, the combined diffraction efficiency is obtained as:

[0079]

[0080] When the fast axis direction of the spliced ​​quarter wave plate 4 and the ruled line direction of the spliced ​​liquid crystal polarization grating 5 are 45°, the diffraction efficiency of the combination is:

[0081]

[0082] Among them, E in Indicates the incident light intensity;

[0083] T represents the transmission matrix of the spliced ​​liquid crystal polarization grating 5, which is expressed as:

[0084]

[0085] in, is the rotation matrix. When ignoring the energy loss of absorption and scattering, A=1, B=exp(iΓ), Γ is the birefringence phase retardation πΔnd / λ of the liquid crystal polymer birefringent material, and λ represents the wavelength.

[0086] Based on equations (1.7) and (1.8), it can be concluded that under different angle combinations, the normalized Q′ and U′ can be obtained by subtracting the positive and negative first-order diffraction intensities and then dividing by the sum of the positive and negative first-order diffraction intensities:

[0087]

[0088]

[0089] As mentioned above, η -1 With η +1They respectively represent the negative and positive diffraction efficiencies of the light beam after passing through the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5 .

[0090] According to the obtained Q and U components, the linear polarization degree information (Fraction of linearpolarization) and polarization azimuth information (Polarization angle) of the observed target can be obtained.

[0091] Therefore, all the linear Stokes polarization parameters Q and U of the target can be obtained without delay and optical offset through a single exposure, thereby realizing fast astronomical spectral polarization imaging, effectively eliminating the influence of atmospheric seeing on polarization measurement, and greatly improving measurement accuracy and efficiency. In addition, the measurement system design has no mechanical moving parts, the optical-mechanical system has a simple structure, and the light transmission efficiency is high. It is suitable as a visiting instrument to dock with a telescope for observation, especially docking with a small-aperture telescope for polarization spectral surveys to monitor celestial bodies (such as blazars, etc.) for a long time, that is, Robot Spectropolarimeter. At the same time, this miniaturized instrument is very beneficial for polarization spectral measurement in space astronomy.

[0092] Combination Figure 1 As shown, in an optional embodiment, the combination of the spliced ​​quarter wave plate 4 and the spliced ​​liquid crystal polarization grating 5 is mounted on an adjustable filter rotating wheel. Therefore, if it is necessary to measure circularly polarized light, the spliced ​​quarter wave plate 4 can be rotated out (moved out of the light path), and the parameter V of the circularly polarized light can be measured, and all Stokes parameters can be measured.

[0093] Therefore, the astronomical polarization spectrometer system proposed in the present invention can be configured with two working modes. One is the combined use of QWP+LCPG to achieve the measurement of the linear polarization component QU. In the other working mode, the polarization component V of the circularly polarized light can be measured by removing the QWP.

[0094] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. An astronomical polarization spectrometer system based on pupil splitting, characterized in that: include: The focal light of the telescope along the optical axis of the instrument passes through the slit (1); as well as A collimator (2), an aperture stop (3), a spliced ​​quarter-wave plate (4), a spliced ​​liquid crystal polarization grating (5), an imaging mirror (6) and a detector (7) are sequentially arranged along the optical axis direction; Wherein, the collimator (2) is used to collimate the light beam from the telescope; The aperture stop (3) is used to limit the aperture of the entrance pupil light beam; The spliced ​​quarter-wave plate (4) is formed by splicing half plates whose fast axes form an angle of 45°; The spliced ​​liquid crystal polarization grating (5) is formed by splicing half pieces whose grating directions form an angle of 90°; The combination of the spliced ​​quarter-wave plate (4) and the spliced ​​liquid crystal polarization grating (5) realizes modulation and demodulation of polarization information by means of pupil splitting; After passing through the slit, the light beam from the telescope is collimated by a collimator (2) and then projected onto a spliced ​​quarter-wave plate (4) and a spliced ​​liquid crystal polarization grating (5), and then imaged onto a detector (7) located at a focal plane position of the imaging mirror (6) through an imaging mirror (6); Wherein, in the spliced ​​quarter-wave plate (4), one fast axis is parallel to the horizontal direction, and the other fast axis is at 45° to the horizontal direction; The spliced ​​liquid crystal polarization grating (5) is formed by splicing two pieces whose engraved lines are perpendicular to each other, with the engraved lines of half being at -45 degrees to the horizontal direction and the engraved lines of the other half being at 45 degrees to the horizontal direction.

2. The astronomical polarization spectrometer system based on pupil splitting according to claim 1, characterized in that: The working wavelength range of the spliced ​​quarter-wave plate (4) is 325nm-1100nm.

3. The astronomical polarization spectrometer system based on pupil splitting according to claim 1, characterized in that: The spliced ​​liquid crystal polarization grating (5) is made of a liquid crystal polymer birefringent material.

4. The astronomical polarization spectrometer system based on pupil splitting according to claim 1, characterized in that: The combination of the spliced ​​quarter wave plate (4) and the spliced ​​liquid crystal polarization grating (5) is mounted on an adjustable filter rotating wheel.

5. The astronomical polarization spectrometer system based on pupil splitting according to any one of claims 1 to 4, characterized in that: In a polarization modulation mode formed by a spliced ​​quarter wave plate (4) and a spliced ​​liquid crystal polarization grating (5), the spliced ​​quarter wave plate (4) is arranged before the spliced ​​liquid crystal polarization grating (5), and when the fast axis direction of the spliced ​​quarter wave plate (4) and the scribed line direction of the spliced ​​liquid crystal polarization grating (5) are placed parallel and at an angle of 45 degrees, based on the Jones matrix in polarization optics, after the light beam passes through the spliced ​​quarter wave plate (4) and the spliced ​​liquid crystal polarization grating (5), the diffraction efficiency of the spliced ​​quarter wave plate (4) and the spliced ​​liquid crystal polarization grating (5) is calculated based on the magnetic field distribution of the positive and negative first-order parts of the diffraction, thereby obtaining the result of subtracting the positive and negative first-order diffraction efficiencies and adding the positive and negative first-order efficiencies under different angle combinations, and dividing the two to obtain the calculation formulas of normalized Q′ and U′: Among them, η -1 represents the negative diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate (4) and the spliced ​​liquid crystal polarization grating (5), η +1 represents the positive diffraction efficiency of the light beam after passing through the spliced ​​quarter-wave plate (4) and the spliced ​​liquid crystal polarization grating (5), and Q′ and U′ represent the normalized linear polarization components Q and U respectively.

6. The astronomical polarization spectrometer system based on pupil splitting according to claim 5, characterized in that: The negative electrode diffraction efficiency η -1 and the positive electrode diffraction efficiency η +1 is configured to be obtained based on the following process: When the fast axis direction of the spliced ​​quarter wave plate (4) is placed parallel to the scribed line direction of the spliced ​​liquid crystal polarization grating (5), the Jones matrix is ​​expressed as: When the light beam passes through the spliced ​​quarter wave plate (4) and the spliced ​​liquid crystal polarization grating (5), only the magnetic field distribution of the positive and negative first-order parts is calculated, and the expression is: The combined diffraction efficiency is further obtained as: When the fast axis direction of the spliced ​​quarter wave plate (4) and the scribed line direction of the spliced ​​liquid crystal polarization grating (5) are 45 degrees, the obtained combined diffraction efficiency is: Among them, E in Indicates the incident light intensity; T represents the transmission matrix of the spliced ​​liquid crystal polarization grating (5), which is expressed as: in, is the rotation matrix. When ignoring the energy loss of absorption and scattering, A=1, B=exp(iΓ), Γ is the birefringence phase retardation πΔnd / λ of the liquid crystal polymer birefringent material, and λ represents the wavelength.

7. The astronomical polarization spectrometer system based on pupil splitting according to claim 1, characterized in that: All linear Stokes polarization parameters Q and U of the target can be obtained through a single exposure without delay and optical offset.

Images