CN116295838A - Astronomical Polarization Spectrometer System Based on Split Pupil - Google Patents

Abstract

The invention provides an astronomical polarization spectrometer system based on a split pupil, which comprises a collimating lens, an aperture diaphragm, a spliced quarter wave plate, a spliced liquid crystal polarization grating, an imaging lens and a detector, wherein the aperture diaphragm is arranged on the collimating lens; the quarter wave plate is formed by splicing half pieces with an included angle of 45 degrees on a fast axis, the liquid crystal polarization grating is formed by splicing half pieces with an included angle of 90 degrees on a grating direction, a polarization spectrum image is obtained in a split pupil mode, modulation and demodulation of polarization information are achieved, all linear Stokes parameters of a signal can be obtained through one-time photographing, and therefore fast astronomical spectrum polarization imaging is achieved.

Description

Astronomical Polarization Spectrometer System Based on Split Pupil

technical field

The invention relates to the technical field of astronomical polarization measurement, in particular to an astronomical polarization spectrometer system based on split pupils, which is used for astronomical polarization measurement.

Background technique

The essence of astronomical observation is the observation of electromagnetic waves, which have three basic characteristics: intensity, frequency and polarization. Among the 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 observed celestial objects. In terms of scientific applications, polarization spectroscopy has 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.

At present, polarimeters are designed to measure Stokes parameters by using polarizers or polarizing beam splitters with specific angles. If the full Stokes (I, Q, U) is to be measured, the incident light needs to be decomposed into three or multiple 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 the rotating wave plate will cause the drift of the 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 survey camera of the Hubble Telescope uses three polarizers with a rotation angle interval of 60°. The polarizers can be placed on the filter rotation wheel. Since the polarizers only allow 1/2 of the light to pass through, Therefore, the light transmission efficiency of this design is low; a polarizing beam splitter (such as a Wollaston prism) can also be used instead of a polarizer to split the beam into two beams to reduce the light loss of the system, and one time to take a photo can obtain polarization information in two directions. All the linear polarization information can be obtained by one rotation. In practice, multiple angles are usually rotated in order to have enough data to eliminate systematic errors.

However, regardless of the design of rotating wave plate or polarizing plate with different angles, the existence of the electromechanical rotating mechanism increases the complexity and instability of the system, and the linear polarization components (Q, U) cannot be obtained at the same time. There are errors in the calculation results under the exposure timing, and synchronous calculation cannot be realized, and the accuracy of the calculation results is also reduced due to the beam drift caused by mechanical rotation. The polarimeter must be combined with a traditional grating or prism spectrometer, resulting in a large and complex optical system of the polarimeter.

Contents of the invention

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 split pupil, the combination of the polarization modulation and demodulation of the quarter wave plate and the liquid crystal polarization grating is adopted. All linear Stokes parameters Q and U of different wavelengths can be obtained to realize the polarization spectrum measurement of celestial objects.

According to the first aspect of the object of the present invention, propose a kind of astronomical polarization spectrometer system based on split pupil, comprising:

The incident slit, collimating mirror, aperture stop, spliced quarter wave plate (QWP), liquid crystal polarization grating (LCPG), imaging mirror and detector are arranged in sequence along the light entering the telescope;

Among them, the collimating mirror is used to collimate the light from the telescope, and the aperture stop is used to limit the aperture of the entrance pupil beam;

The spliced quarter-wave plate is spliced by half pieces whose fast axis forms an included angle of 45°;

The liquid crystal polarization grating is spliced by half sheets whose grating direction forms an included angle of 90°, and realizes the modulation and demodulation of polarization information by means of split pupils;

After passing through the slit, the beam is collimated on the spliced quarter-wave plate and liquid crystal polarization grating through the collimating mirror, and finally the modulated light is imaged on the detector through the imaging mirror.

The astronomical polarization spectrometer system, wherein the design combination of the spliced quarter-wave plate and the liquid crystal polarization grating constitutes a polarization demodulation combination, and this set of modulation combinations can be installed on the filter rotating wheel. The light can be rotated out for measurement. Since the polarization grating divides the pupil into two parts, and the dispersion direction is vertical, each part is divided into left-handed circularly polarized light and right-handed circularly polarized light by the polarization grating. The dispersion is divided into four quadrants, and finally the modulated light is imaged on the detector through the imaging mirror.

In the example of the present invention, based on the split pupil design, the linear Stokes parameter can be obtained at the same time in one exposure, while the traditional polarization spectrometer needs to measure the spectral intensity under multiple different modulation modes to obtain the Stokes parameter, which greatly reduces the impact of atmospheric turbulence on The influence of the actual observation data effectively improves the observation efficiency.

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 then measure the full Stokes parameter. Therefore, the astronomical polarization spectrometer system can be configured Two working modes.

As an optional example, the astronomical polarization spectrometer system based on the split pupil includes: the light passing through the slit of the focal plane of the telescope along the direction of the optical axis of the instrument; Quarter-wave plate, spliced liquid crystal polarization grating, imaging mirror and detector;

Wherein, the collimating mirror is used to collimate the light beam from the telescope; the aperture stop is used to limit the aperture of the entrance pupil beam; The spliced liquid crystal polarization grating is formed by splicing half pieces with a 90° angle between the direction of the grating;

The combination of the spliced quarter-wave plate and the spliced liquid crystal polarization grating realizes the modulation and demodulation of polarization information by way of split pupils;

After the beam from the telescope passes through the slit, it is collimated by the collimating mirror and projected on the spliced quarter-wave plate and the spliced liquid crystal polarization grating, and then modulated by the imaging mirror and then imaged to the focal plane of the imaging mirror. detector.

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 wavelength range of the spliced quarter-wave plate is 325nm-1100nm.

As an optional example, the spliced liquid crystal polarization grating is spliced by two pieces whose reticle directions are perpendicular to each other, half of the reticle directions are at -45° to the horizontal direction, and the other half of the reticle directions are at 45° to the horizontal direction. The spliced liquid crystal polarization grating (5) is made of liquid crystal polymer birefringent material.

As an optional example, a combination of a stitched quarter wave plate and a stitched liquid crystal polarization grating is mounted on an adjustable filter wheel. When it is necessary to measure circularly polarized light, 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 direction is vertical, each part is divided into a left-handed circle by the polarization grating Polarized light and right-handed circularly polarized light, thus dispersing the light into four quadrants on the detector target. Finally, the modulated light is imaged on the detector through the imaging mirror.

As an optional example, in the 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. When the fast axis direction of the type quarter-wave plate is placed parallel to and at 45° to the line direction of the spliced liquid crystal polarization grating, based on the Jones matrix in polarization optics, when the light beam passes through the spliced type quarter-wave plate and the spliced type After the liquid crystal polarization grating, based on the magnetic field distribution of the positive and negative first-order parts of the diffraction, the diffraction efficiency of the combination of the spliced quarter-wave plate and the spliced liquid crystal polarization grating is calculated, and it can be concluded that the The results of subtraction of positive and negative first-order diffraction efficiencies and addition of positive and negative first-order efficiencies are obtained by dividing the two to obtain the normalized calculation formulas of Q' and U':

Among them, η _-1 represents the diffraction efficiency of the negative electrode after the beam passes through the spliced quarter wave plate and the spliced liquid crystal polarization grating, and η ₊₁ represents the diffraction efficiency of the beam after passing through the spliced quarter wave plate and the spliced liquid crystal polarization grating Positive diffraction efficiencies, Q' and U' denote the normalized linear polarization components Q and U, respectively.

Therefore, based on the polarization demodulation mode of the design combination of the spliced quarter-wave plate and the liquid crystal polarization grating proposed by the present invention, when used in the astronomical polarization spectrometer system, no delay and no optical shift can be achieved through one exposure Obtain all the linear Stokes polarization parameters Q and U of the target accurately; and, when measuring the spectrum of circularly polarized light, the spliced quarter-wave plate can be rotated out (that is, removed) to directly realize the component V of circularly polarized light The measurement, and then the full Stokes parameters are measured, which greatly improves the detection efficiency.

Compared with the prior art, the astronomical polarization spectrometer system proposed by the present invention is based on the (spliced QWP+LCPG combination) design scheme of a spliced quarter-wave plate and a liquid crystal polarization grating, that is, a snapshot linear Stokes parametric spectrometer, The observation efficiency is high. LCPG replaces polarizers and ordinary gratings, which further reduces light loss, and the system does not mechanically rotate optical components, avoiding the decrease in measurement accuracy caused by beam jitter and drift, and at the same time, a single exposure can be obtained without delay and without optical offset. All the linear Stokes polarization parameters Q and U of the target greatly reduce the influence of atmospheric turbulence on the actual observation data and effectively improve the observation efficiency.

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

It should be understood that all combinations of the foregoing concepts, as well as additional concepts described in more detail below, may be considered part of the inventive subject matter of the present disclosure, provided such concepts are not mutually inconsistent. Additionally, all combinations of claimed subject matter are considered a part of the inventive subject matter of this disclosure.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description when taken in conjunction with the accompanying drawings. Other additional aspects of the invention, such as the features and/or advantages of the exemplary embodiments, will be apparent from the description below, or learned by practice of specific embodiments in accordance with the teachings of the invention.

Description of drawings

The figures are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like reference numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of the various aspects of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the principle of an astronomical polarization spectrometer system according to an exemplary embodiment of the present invention.

Figure 2 is a schematic diagram of a QWP and LCPG of an exemplary embodiment of the present invention.

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

The meaning of each reference sign in the accompanying drawings is as follows:

Slit 1; collimating mirror 2; aperture stop 3; spliced quarter-wave plate 4; spliced liquid crystal polarization grating 5; imaging mirror 6; detector 7.

Detailed ways

In order to better understand the technical content of the present invention, specific embodiments are given together with the attached drawings for description as follows.

Aspects of the invention are described in this disclosure with reference to the accompanying drawings, which show a number of illustrated embodiments. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of numerous ways, since the concepts and embodiments disclosed herein are not limited to any implementation. In addition, some aspects of the present disclosure may be used alone or in any suitable combination with other aspects of the present disclosure.

The invention is one of the achievements of the National Natural Science Foundation of China project "Research on Key Technology of Snapshot Linear Stokes Parametric Polarization Spectrometer" (12073056).

In order to better understand the technical content of the present invention, specific embodiments are given together with the attached drawings for description as follows.

As shown in FIG. 1, the astronomical polarization spectrometer system according to the embodiment of the present invention aims 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, so that the observation can be obtained according to the Q and U components. The linear polarization degree information and polarization azimuth angle information of the target have very important scientific value for studying the characteristics of the target.

Theoretical analysis of snapshot-type linear Stokes parameter measurement method at different wavelengths In the case of ensuring a compact system and a simple optical structure, the technical difficulty of the snapshot-type polarization measurement method lies in obtaining two linear parameters of Q and U at the same time in one exposure. Another technical difficulty It is necessary to obtain Stokes parameters of different wavelengths.

The system design of astronomical polarization spectrometer as shown in Figure 1, it comprises the focal plane light of the telescope along the optical axis direction of the instrument through the slit 1; Type quarter-wave plate 4, spliced liquid crystal polarization grating 5, imaging mirror 6 and detector 7.

The collimating mirror 2 is used to collimate the beam from the telescope.

Aperture stop 3 is used to limit the aperture of the entrance pupil beam.

The spliced quarter-wave plate 4 ((Quarter-wave plate, QWP) for short) is spliced by half plates whose fast axis forms an included angle of 45°.

The spliced liquid crystal polarization grating 5 (Liquid crystal polarization grating, LCPG for short) is formed by splicing half sheets whose grating directions form an included angle of 90°.

The combination of the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating 5 realizes the modulation and demodulation of polarization information by means of split pupils.

Thus, after the light beam from the telescope passes through the slit, it is collimated by the collimating mirror 2 and projected on the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating 5, and then imaged by the imaging mirror 7 to the 7 is the focal plane position of the detector 7 .

In the example according to the purpose of the present invention, the design of all linear Stokes polarization parameters is obtained based on one-time exposure, the optimal design selection is carried out, and the polarization is realized through the combination of the quarter-wave plate and the liquid crystal polarization grating through the split pupil scheme. Spectral measurement.

After the beam from the slit is collimated by a collimating mirror 2, the size of the collimated beam cannot exceed the clear aperture (50mm) of the QWP, and the collimated light is incident on the quarter-wave plate after passing through the diaphragm. The wave plate is spliced by wave plates whose fast axis is at an angle of 45°, one of which is parallel to the horizontal direction, and the other fast axis is at 45° to the horizontal direction. At the same time, the working wavelength range of the achromatic quarter-wave plate is 325nm-1100nm, the phase delay accuracy is <λ/100, the transmittance is >90%, and the surface shape RMS<λ/4@633nm.

After passing through the QWP, the light enters the spliced liquid crystal polarizing grating (LCPG) for polarization demodulation and color separation. The liquid crystal polarizing grating is spliced by two pieces whose lines are perpendicular to each other.

as shown in picture 2. Half of the reticle direction of the liquid crystal polarization grating is placed at -45° to the horizontal direction, and the other half of the reticle direction is placed at 45° to the horizontal direction. The substrate is N-BK7 glass, which is made of liquid crystal polymer birefringent material, and the aperture is 50mm , the working temperature is -20℃～80℃, the phase period is 5μm, the number of reticles is 200, and the diffraction efficiency is >98%.

The light modulated by QWP+LCPG finally converges the light to the detector through the imaging mirror. The split pupil design makes the light in the lower left corner be divided into two linear polarizations of 0° and 90°, while the light in the upper right corner The light is divided into linear polarizations in two directions of 45° and 135°. Since the polarization grating divides the pupil into two parts, and the dispersion direction is vertical, each part is divided into ±1 level by the polarization grating, so the light is divided into two parts on the detector target surface Dispersion into four quadrants.

Further, the Q polarization component of the target can be obtained by subtracting the intensity of one and three quadrants, and the U polarization component can be obtained by subtracting the intensity of two and four quadrants.

In the astronomical polarization spectrometer system proposed by the present invention, based on the polarization modulation mode of QWP+LCPG, the alignment 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 expression of the LCPG Jones matrix is as follows:

为旋转矩阵，在无吸收和散射的能量损失下，A＝1，B＝exp(iΓ)，Г为液晶的双折射相位迟量πΔnd/λ，λ表示波长。in

is a rotation matrix, and without absorption and scattering energy loss, A=1, B=exp(iΓ), Γ is the birefringent phase retardation πΔnd/λ of liquid crystal, and λ represents the wavelength.

According to the transmittance matrix formula of LCPG, substituting the parameters and rotation matrix without absorption and scattering energy loss, after sorting, we can get:

When the incident light beam passes through the LCPG, it will be divided into three diffraction orders, zero order and plus or minus one order, the diffraction efficiency of zero order, plus or minus one order can be calculated from the formula (1.2), and the polarization state of the plus or minus one order of outgoing light It is right-handed and left-handed circularly polarized light, and the polarization states of the positive and negative primary exit lights are right-handed and left-handed circularly polarized light.

As shown in Figure 1, the basic principle of polarization modulation and demodulation of QWP+LCPG combination is as follows:

Assuming that the electromagnetic fields of the incident light are E _x and E _y respectively, the electromagnetic fields of the outgoing light after passing through PG can be calculated. According to the definition of Stokes parameters, the diffraction efficiencies of zero order and positive and negative orders can be obtained respectively:

Among them, V′=V/I ₀ , which is the normalized amount of Stokes’ circular polarization. According to the formula (1.4), it can be obtained that the Stokes’ circular polarization component can be obtained by subtracting the positive and negative light intensities and adding the above light intensities. Therefore, in the system design of the present invention, the polarized spectrometer can also directly measure circularly polarized light without adding a QWP.

In the embodiment of the present invention, as shown in FIG. 1 , all measurement requirements for one exposure of the linear polarization components Q and U are required, in order to achieve the unique advantage of obtaining all the linear Stokes components at the same time in one exposure, so as to reduce atmospheric turbulence Influence on polarization spectrum measurement, improve observation efficiency, polarization spectrometer system of the present invention proposes the design scheme based on split pupil (Split-pupil), introduces super achromatic QWP before LCPG, promptly two halves QWP stitching (Patterned QWP), its The fast axis forms an included angle of 45°, and the corresponding two halves of LCPG are spliced with their grating directions forming an included angle of 90°, as shown in Figure 2.

In the polarization modulation mode composed of the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating 5, the super-achromatic spliced quarter-wave plate 4 is arranged before the spliced liquid crystal polarization grating 5. When the fast axis direction of the quarter-wave plate 4 is placed parallel to and at 45° to the line direction of the spliced liquid crystal polarization grating 5, based on the Jones matrix in polarization optics, when the light beam passes through the spliced quarter-wave plate 4 and the spliced After the liquid crystal polarization grating 5, based on the magnetic field distribution of the positive and negative first-order parts of the diffraction, the diffraction efficiency of the combination of the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating 5 is obtained through settlement, and thus it can be concluded that at different angles In the combined form, the result of subtraction of the positive and negative first-order diffraction efficiencies and the addition of positive and negative first-order efficiencies can be obtained by dividing the two to obtain 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, and η ₊₁ represents that the light beam passes through the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating The positive diffraction efficiencies behind the grating 5, Q' and U' denote the normalized linear polarization components Q and U, respectively.

Thus, according to the obtained Q, U components, the linear polarization degree information and polarization azimuth information of the observation target can be obtained.

In a specific embodiment, by introducing superachromatic QWP before LCPG:

When the fast axis direction of the spliced quarter-wave plate 4 is placed parallel to the direction of the grooves of the spliced liquid crystal polarization grating 5, its Jones matrix is expressed as:

After 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:

According to formula 1.6, the diffraction efficiency of the combination obtained is:

When the direction of the fast axis of the spliced quarter-wave plate 4 and the line direction of the spliced liquid crystal polarization grating 5 are 45°, the combined diffraction efficiency obtained is:

Among them, E _in represents the incident light intensity;

T represents the transmission matrix of the spliced liquid crystal polarization grating 5, expressed as:

为旋转矩阵，在忽略吸收和散射的能量损失下，A＝1，B＝exp(iΓ)，Г为液晶聚合物双折射材料的双折射相位迟量πΔnd/λ，λ表示波长。in,

is the rotation matrix, under the neglect of the energy loss of absorption and scattering, A=1, B=exp(iΓ), Γ is the birefringent phase retardation πΔnd/λ of the liquid crystal polymer birefringent material, and λ represents the wavelength.

Based on formulas (1.7) and (1.8), the normalized Q′ and U can be obtained by subtracting the positive and negative first-order diffraction intensities under different angle combinations and then dividing by the addition of the positive and negative first-order diffraction intensities. ':

As mentioned above, η ₋₁ and η ₊₁ respectively represent the diffraction efficiencies of the negative electrode and the positive electrode after the light beam passes through the spliced quarter-wave plate 4 and the spliced liquid crystal polarization grating 5 .

According to the obtained Q and U components, the linear polarization information (Fraction of linear polarization) and polarization azimuth information (Polarization angle) of the observation target can be obtained.

Thus, all the linear Stokes polarization parameters Q and U of the target can be obtained without delay and without optical offset through one exposure, so as to realize fast astronomical spectral polarization imaging and effectively eliminate the influence of atmospheric seeing on polarization measurement , greatly improving the measurement accuracy and efficiency. Moreover, the measurement system is designed without mechanical moving parts. The optical-mechanical system has a simple structure and high light transmission efficiency. It is suitable for docking observations with telescopes as a visiting instrument, especially for docking with small-aperture telescopes for long-term monitoring of celestial bodies through polarization spectrum surveys ( Such as blazars, etc.), that is, RobotSpectropolarimeter, and this miniaturized instrument is very beneficial for space astronomy to measure polarization spectra.

As shown in FIG. 1 , 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 rotation 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 optical path), so that the parameter V of circularly polarized light can be measured and all Stokes parameters can be measured.

Therefore, the astronomical polarization spectrometer proposed by the present invention can be configured with two working modes as a system. One is the combined use of QWP+LCPG to realize the measurement of the linear polarization component QU. In another working mode, the QWP can be removed to realize Measurement of the polarization component V of circularly polarized light.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those skilled in the art of the present invention may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the claims.

Claims (9)

1. A spectroscopic pupil-based astronomical polarization spectrometer system, comprising:

telescope focal plane light along the instrument optical axis direction passes through the slit (1); and

a collimating mirror (2), an aperture diaphragm (3), a spliced quarter wave plate (4), a spliced liquid crystal polarization grating (5), an imaging mirror (6) and a detector (7) which are sequentially arranged along the optical axis direction;

wherein the collimating mirror (2) is used for collimating the light beam from the telescope;

the aperture diaphragm (3) is used for limiting the caliber of the entrance pupil light beam;

the spliced quarter wave plate (4) is formed by splicing half plates with fast axes forming an included angle of 45 degrees;

the spliced liquid crystal polarization grating (5) is formed by splicing half pieces with 90-degree included angles in the grating direction;

the combination of the spliced quarter wave plate (4) and the spliced liquid crystal polarization grating (5) realizes modulation and demodulation of polarization information in a split pupil mode;

after passing through the slit, the light beam from the telescope is collimated by the collimating lens (2) and then projected on the spliced quarter wave plate (4) and the spliced liquid crystal polarization grating (5), and then imaged by the imaging lens (7) to the detector (7) positioned at the focal plane of the imaging lens (7).

2. The pupil-based astronomical polarization spectrometer system according to claim 1, characterized in that the tiled quarter wave plate (4) has one fast axis oriented parallel to the horizontal and the other fast axis oriented 45 ° to the horizontal.

3. The spectroscopic pupil based astronomical polarization spectrometer system according to claim 1, characterized in that the working band range of the spliced quarter wave plate (4) is 325nm-1100nm.

4. The astronomical polarization spectrometer system based on the split pupil according to claim 1, characterized in that the spliced liquid crystal polarization grating (5) is formed by splicing two pieces with the reticle directions mutually perpendicular, one half of the reticle directions are at-45 ° with respect to the horizontal direction, and the other half of the reticle directions are at 45 ° with respect to the horizontal direction.

5. The spectroscopic pupil based astronomical polarization spectrometer system according to claim 1, characterized in that the tiled liquid crystal polarization grating (5) is made of a liquid crystal polymer birefringent material.

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

7. The spectroscopic pupil-based astronomical polarization spectrometer system according to any one of claims 1-6, characterized in that in a polarization modulation mode formed by a spliced quarter wave plate (4) and a spliced liquid crystal polarization grating (5), an ultra-achromatic spliced quarter wave plate (4) is configured in front of the spliced liquid crystal polarization grating (5), when the fast axis direction of the spliced quarter wave plate (4) is placed in parallel with the line direction of the spliced liquid crystal polarization grating (5) and at 45 °, based on a jones matrix in polarized optics, when a light beam passes through the spliced quarter wave plate (4) and the spliced liquid crystal polarization grating (5), diffraction efficiency of the combination of the spliced quarter wave plate (4) and the spliced liquid crystal polarization grating (5) is obtained through settlement based on magnetic field distribution of positive and negative first order parts of diffraction, and a calculation formula of normalized Q 'and U' is obtained through subtraction of the positive and negative first order diffraction efficiency and addition of the positive and negative first order diffraction efficiency under different angle combination forms is obtained through the calculation formula of the two:

wherein eta _-1 Represents the negative diffraction efficiency, eta, of the light beam after passing through the spliced quarter wave plate (4) and the spliced liquid crystal polarization grating (5) ₊₁ Representing the passage of a light beam through a spliced quarter wavePositive diffraction efficiency after the plate (4) and the spliced liquid crystal polarization grating (5), Q 'and U' represent normalized linear polarization components Q and U, respectively.

8. The spectroscopic pupil based astronomical polarization spectrometer system according to claim 7, wherein the negative diffraction efficiency η _-1 And positive electrode diffraction efficiency eta ₊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 in parallel with the line direction of the spliced liquid crystal polarization grating (5), the jones matrix is expressed as:

after 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 as follows:

according to equation (1.6), the combined diffraction efficiencies are obtained as:

when the fast axis direction of the spliced quarter wave plate (4) and the line direction of the spliced liquid crystal polarization grating (5) are 45 degrees, the diffraction efficiency of the obtained combination is as follows:

wherein E is _in Representing the intensity of incident light;

t represents the transmission matrix of the spliced liquid crystal polarization grating (5), and is expressed as:

wherein,,

for the rotation matrix, a=1, b=exp (iΓ), where Γ is the birefringent phase retardation of the liquid crystal polymer birefringent material, pi Δnd/λ, λ represents the wavelength, ignoring the energy loss of absorption and scattering.

9. The spectroscopic pupil based astronomical polarization spectrometer system according to claim 1, characterized in that all linear Stokes polarization parameters Q and U of the target can be obtained without delay and without optical offset by one exposure.

Images