System and method for measuring stereo polarization modulation characteristics of converging optical system

Abstract

The present invention belongs to the field of polarization detection technology, and in particular, relates to a system and method for measuring the three-dimensional polarization modulation characteristics of a converging optical system. The method comprises: S1: fixing the converging optical system to be measured on the sample table to be measured; S2: using a light intensity detector to measure the light intensity data of n light beams; S3: using a light intensity detector to receive the light intensity data of h groups of n light beams correspondingly; S4: obtaining the Mueller matrix of the converging optical system to be measured at the current light beam exit position; S5: obtaining the Mueller matrix of the converging optical system to be measured at the i light beam exit positions; S6: obtaining the total Mueller matrix characterizing the polarization modulation characteristics of the converging optical system to be measured; S7: obtaining the three-dimensional vibration characteristics of the convergence point of the converging optical system to be measured. The present invention can measure and calibrate the Mueller matrix of the converging mirror group, eliminating the error caused by the converging mirror group when measuring the polarization modulation characteristics of an ultra-high precision optical system (such as a photolithography machine, etc.).

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization detection, and in particular relates to a system and method for measuring the three-dimensional polarization modulation characteristics of a converging optical system. Background Art

[0002] One of the most important characteristics of light as an electromagnetic transverse wave is that it has polarization characteristics. Polarization, like intensity, spectrum, and phase, is a basic property of light and carries a wealth of information. Optical systems often have polarization modulation characteristics that cannot be ignored. In the fields of ultra-high precision lithography, photon remote sensing, target polarization characteristic measurement, and photon communication, it is necessary to accurately calibrate the polarization modulation characteristics of optical systems. Especially in the field of ultra-high precision lithography, it is of great significance to accurately measure and calibrate the polarization modulation characteristics of converging optical systems.

[0003] When measuring the polarization modulation characteristics of an optical system, a focusing lens group and a collimating lens group are required to ensure the alignment of the optical path, and then the influence of the focusing lens or the collimating lens group on the polarization measurement accuracy is eliminated, that is, their own polarization aberration will cause errors in the measurement results. To compensate for this error, it is necessary to measure the polarization modulation characteristics of the two standard mirrors themselves. At present, how to measure the polarization modulation characteristics of optical systems is being studied in depth. Some scholars use double rotating wave plates to measure the Mueller matrix and can measure the polarization modulation characteristics of optical systems. However, their experimental device still has some shortcomings, such as: the polarization modulation characteristics of the convergence point of the optical system are not taken into account, so it will cause errors when calibrating the polarization modulation characteristics of ultra-high precision optical systems. Summary of the invention

[0004] In view of this, the present invention aims to provide a system and method for measuring the three-dimensional polarization modulation characteristics of a converging optical system, so as to solve the problem that the existing measurement technology mainly measures the polarization modulation characteristics of the target optical system in the collimated light path, and it is difficult to measure the polarization characteristics of the light of the converging optical system, and the polarization aberration of the converging standard mirror itself affects the measurement result. The present invention can measure and calibrate the Mueller matrix of the converging mirror group, eliminating the error caused by the converging mirror group when measuring the polarization modulation characteristics of an ultra-high precision optical system (such as a lithography machine, etc.).

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A system for measuring the stereo polarization modulation characteristics of a converging optical system, comprising:

[0007] A light source unit, the light source unit comprises a light source translation device, a light beam emitting system, a first polarizer and a first wave plate, the light beam emitting system is arranged on the light source translation device, the light source translation device drives the light beam emitting system to translate, the light beam emitting system emits a fine light beam, and the fine light beam is incident on the converging optical system to be measured through the first polarizer and the first wave plate in sequence;

[0008] The sample stage to be tested is used to fix the converging optical system to be tested and make the converging optical system to be tested axially rotate along its own optical axis direction;

[0009] A receiving unit, the receiving unit comprises a second wave plate, a second polarizer and a light intensity detector, and the fine light beam emitted from the converging optical system to be measured is incident on the light intensity detector through the second wave plate and the second polarizer in sequence;

[0010] The rotating unit drives the receiving unit to rotate, so that the receiving unit is placed in different spatial positions and receives the light intensity data of the thin light beam.

[0011] Furthermore, the measurement system also includes a stepper motor, which drives the first wave plate and the second wave plate to rotate at a preset angle ratio; between the first wave plate and the second wave plate, it also includes a plurality of optical elements for changing the propagation direction of light.

[0012] Furthermore, the fine light beam is vertically incident on the second wave plate, the second polarizer and the light intensity detector; the diameter of the fine light beam is determined according to the entrance pupil diameter of the converging optical system to be measured and the preset number of measurement positions, and the diameter of the fine light beam is less than the entrance pupil diameter multiplied by the reciprocal of the preset number value.

[0013] Furthermore, the beam output system outputs a coarse beam or a thin beam with known amplitude distribution, and a coarse beam is regarded as a collection of n parallel thin beams;

[0014] The positional relationship between the light source translation device and the light intensity detector is: the light intensity detector vertically receives each thin light beam emitted by the light beam emission system.

[0015] A method for measuring the three-dimensional polarization modulation characteristics of a converging optical system is implemented using a system for measuring the three-dimensional polarization modulation characteristics of a converging optical system, and specifically comprises the following steps:

[0016] S1: Fix the converging optical system to be tested on the sample stage to be tested;

[0017] S2: The light beam emitted by the light beam emission system is incident on the light intensity detector through the first polarizer, the first wave plate, the focusing optical system to be measured, the second wave plate and the second polarizer in sequence. The rotating unit drives the receiving unit to rotate so that the receiving unit is placed in different spatial positions. The light intensity detector measures the light intensity data of n light beams and obtains the amplitude distribution of the n light beams.

[0018] S3: using a stepper motor to drive the first wave plate and the second wave plate to rotate h times at a preset angle ratio, and making the light intensity detector receive light intensity data of h groups of n light beams correspondingly;

[0019] S4: Perform Fourier fitting on all the light intensity data to obtain the Mueller matrix of the converging optical system to be tested at the current light beam exit position;

[0020] S5: using the light source translation device to adjust the light beam exit position of the light beam exit system, replacing the current light beam exit position with the new light beam exit position, and repeating steps S2-S4 until the Mueller matrix of the converging optical system to be tested at the i light beam exit positions is obtained;

[0021] S6: Integrate the Mueller matrices at all the light beam exit positions obtained in step S5 to obtain a total Mueller matrix that represents the polarization modulation characteristics of the converging optical system to be measured;

[0022] S7: Based on the amplitude distribution of all the light beams, the three-dimensional vibration characteristics of the converging point of the converging optical system to be tested are obtained.

[0023] Furthermore, in step S2, if the beam output system outputs a coarse beam with a known amplitude distribution, the coarse beam is regarded as a collection of n fine beams, and the amplitude distribution function of the n fine beams satisfies:

[0024] ;

[0025] Where r is the radius of the coarse beam, is the amplitude value at the center of the coarse beam, F(r) is the proportional coefficient of the light amplitude value at the beam position with a distance r from the center of the coarse beam, is the amplitude of the beamlet.

[0026] Furthermore, in step S3, the light intensity data can be Fourier expanded by the following formula:

[0027] ;

[0028] in, is the light intensity data measured by the light intensity detector, a0-a 12 and b0-b 12 are the Fourier expansion coefficients obtained by fitting the light intensity data. is the rotation angle of the first wave plate.

[0029] Furthermore, in step S6, the total Mueller matrix is ​​expressed as:

[0030] ;

[0031] in, is the Mueller matrix measured at the i-th beamlet exit position, is the total Mueller matrix.

[0032] Furthermore, in step S7, the decomposition formula of the vibration direction of each light beam in the three-dimensional space is:

[0033] ;

[0034] ;

[0035] ;

[0036] in, is the vibration amplitude of the current beamlet in the x direction, is the vibration amplitude of the current thin beam in the y direction, is the vibration amplitude of the current thin beam in the z direction, is the amplitude of the current beamlet, is the amplitude of the beamlet The angle with the Y axis of the spatial rectangular coordinate system.

[0037] will satisfy the amplitude distribution function The distributed coarse beam is regarded as a collection of n thin beams. The decomposition formula of each thin beam in the collection in three-dimensional space is:

[0038] ;

[0039] ;

[0040] .

[0041] Further, in step S7, when the light beam emitting system directly emits a thin light beam, the three-dimensional polarization characteristics of the convergence point of the converging optical system to be measured are for:

[0042] ;

[0043] in, is the superposition of n thin beams vibrating in the x direction, is the superposition of n thin beams vibrating in the y direction, is the superposition of n light beams vibrating in the z direction, is the vibration of the nth beamlet in the x direction, is the vibration of the nth beamlet in the y direction, is the vibration of the nth beamlet in the Z direction, is the vibration of the nth beamlet, is the angle between the projection of the vibration direction of the nth beamlet and the X-axis of the spatial rectangular coordinate system, is the angle between the vibration direction of the nth beamlet and the Y axis of the spatial rectangular coordinate system, is the integration range in spherical coordinates .

[0044] When the beam emission system directly emits a thick beam, the three-dimensional polarization characteristics of the convergence point of the converging optical system to be measured for:

[0045] .

[0046] Compared with the prior art, the invention can achieve the following beneficial effects:

[0047] The present invention creates a measurement system and method for the three-dimensional polarization modulation characteristics of the converging optical system, which is used to calibrate the polarization modulation characteristics of the light convergence point of the converging optical system. The present invention adjusts the incident position of the thin light beam on the entrance pupil (using the light source translation device to drive the light beam exit system to translate), thereby measuring the polarization modulation characteristics of the optical system under multiple thin light beams, and completes the measurement of the polarization modulation characteristics of the converging optical system; the present invention designs a new measurement optical path, which is used to measure the Mueller matrix corresponding to the thin light beams at different incident positions, and finally uses the integral form to sum to obtain the polarization modulation characteristics of the converging optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0049] Figure 1 A schematic diagram of the structure of a system for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to an embodiment of the present invention;

[0050] Figure 2 A schematic flow chart of a method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of Fourier fitting described in an embodiment of the present invention;

[0052] Figure 4 A vibration decomposition diagram of a thin light beam in three-dimensional space according to an embodiment of the present invention.

[0053] Description of reference numerals:

[0054] 1. Light source unit; 2. Sample stage to be tested; 3. Receiving unit. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0056] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0057] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0058] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0059] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0060] like Figure 1As shown, the present invention proposes a measurement system for the three-dimensional polarization modulation characteristics of a converging optical system, comprising: a light source unit 1, the light source unit 1 comprises a light source translation device, a light beam exit system, a first polarizer (the first polarizer is used to convert the incident light source into linearly polarized light) and a first wave plate, the light beam exit system (using a thin light beam light source) is arranged on the light source translation device (the translation direction is the direction perpendicular to the entrance pupil plane), the light source translation device drives the light beam exit system to translate, the light beam exit system emits a thin light beam, and the thin light beam is incident on the converging optical system to be measured through the first polarizer and the first wave plate in sequence;

[0061] The sample stage 2 to be tested is used to fix the converging optical system to be tested and make the converging optical system to be tested axially rotate along its own optical axis direction;

[0062] Receiving unit 3, receiving unit 3 includes a second wave plate, a second polarizer and a light intensity detector. The fine light beam emitted from the converging optical system to be measured is incident on the light intensity detector (the light intensity detector adopts an industrial-grade CCD camera) through the second wave plate and the second polarizer in sequence; and the fine light beam is vertically incident on the second wave plate, the second polarizer and the light intensity detector.

[0063] The positional relationship between the light source translation device and the light intensity detector is: the light intensity detector vertically receives each thin light beam emitted by the light beam emission system.

[0064] The rotating unit drives the receiving unit 3 to rotate, so that the receiving unit 3 is placed in different spatial positions, and the receiving unit 3 receives the light intensity data of the thin light beam.

[0065] The measurement system also includes a stepper motor, which drives the first wave plate and the second wave plate to rotate at a preset angle ratio. The first wave plate and the second wave plate are both 1 / 4 wave plates. The first wave plate rotates at an angle of 1.25°, and the second wave plate rotates at an angle of 6.25°.

[0066] The first wave plate and the second wave plate are used to modulate the polarization state of linearly polarized light. Between the first wave plate and the second wave plate, there are also several optical elements for changing the propagation direction of light. For example, a beam expander is placed in the light path between the first wave plate and the second wave plate to meet the calibration requirements of different optical systems.

[0067] After the light source unit 1 emits a thin light beam, it passes through the first polarizer, the first wave plate, the convergence optical system to be measured, the second wave plate, and the second polarizer in sequence before entering the light intensity detector. The first polarizer is used to convert the incident light source into linearly polarized light; the first wave plate and the second wave plate are used to modulate the polarization state of the linearly polarized light. After rotating the angles of the first wave plate and the second wave plate multiple times, multiple groups of corresponding light intensity values ​​are measured, and the Mueller matrix of the convergence optical system to be measured is obtained after fitting; the incident position of the thin light beam (the incident coordinate on the entrance pupil plane) is adjusted multiple times by the light source translation device, so as to measure the Mueller matrix at different incident positions; after obtaining the Mueller matrix, the Mueller matrix is ​​converted into the Jones matrix, and then the Jones matrix is ​​decomposed into the Pauli matrix to achieve the modulation effect on different polarization components; the measurement results of all the thin light beams are integrated to evaluate the polarization modulation effect of the convergence optical system to be measured.

[0068] like Figure 2 As shown, a method for measuring the three-dimensional polarization modulation characteristics of a converging optical system can be used to measure the polarization aberration of a standard mirror itself to compensate for the error of the measurement result, and can also directly measure the polarization modulation characteristics of some converging optical systems, and specifically includes the following steps: S1: fixing the converging optical system to be measured on the sample stage 2 to be measured; S2: the fine light beam emitted by the light beam emission system is incident on the light intensity detector through the first polarizer, the first wave plate, the converging optical system to be measured, the second wave plate and the second polarizer in sequence, the rotating unit drives the receiving unit to rotate, so that the receiving unit is placed in different spatial positions, the light intensity detector correspondingly measures the light intensity data of n fine light beams, and obtains the amplitude distribution of the n fine light beams; S3: using a stepping motor to drive the first wave plate and the second wave plate to rotate at a preset angle ratio (the preset angle ratio is 1:N, N According to the test requirements, different values ​​are selected) and rotated h times, and the light intensity detector receives the light intensity data of h groups of n light beams correspondingly; S4: Fourier fitting is performed on all the light intensity data to obtain the Mueller matrix of the converging optical system to be tested at the current light beam exit position; S5: The light beam exit position of the light beam exit system is adjusted by using the light source translation device, and the current light beam exit position is replaced by the new light beam exit position, and steps S2-S4 are repeated until the Mueller matrix of the converging optical system to be tested at i light beam exit positions is obtained; S6: The Mueller matrices at all light beam exit positions obtained in step S5 are integrated to obtain the total Mueller matrix that characterizes the polarization modulation characteristics of the converging optical system to be tested; S7: Based on the amplitude distribution of all light beams, the three-dimensional vibration characteristics of the converging point of the converging optical system to be tested are obtained.

[0069] In some examples, in step S2, if the beam output system outputs a coarse beam with a known amplitude distribution, the coarse beam is regarded as a collection of n fine beams.

[0070] The amplitude distribution function of n light beams satisfies:

[0071] ;

[0072] Where r is the radius of the coarse beam, is the amplitude value at the center of the coarse beam, F(r) is the proportional coefficient of the light amplitude value at the beam position with a distance r from the center of the coarse beam, is the amplitude of the beamlet.

[0073] It should be noted that, in step S2, if the light beam emitting system emits light beams, no calculation is required, and the amplitude distributions of the n light beams are directly obtained.

[0074] In some examples, in step S3, since the rotation angle ratio between the first wave plate and the second wave plate is fixed, the output light intensity data can be Fourier expanded by the following formula:

[0075] ;

[0076] in, is the light intensity data measured by the light intensity detector, , are the cosine coefficients and sine coefficients of Fourier expansion, is the rotation angle of the first wave plate.

[0077] The relationship between the Mueller matrix and the Fourier coefficients is:

[0078]

[0079] It should be noted that Figure 3 As shown, the horizontal axis is the rotation angle θ of the first wave plate: from 0° to 180°, and the vertical axis is the light intensity value I detected by the light intensity detector at the corresponding angle. After completing Fourier fitting with the collected light intensity and rotation angle data, the Mueller matrix is ​​obtained using the fitted Fourier coefficients.

[0080] The polarization modulation characteristics of the converging optical system to be measured are represented by the Mueller matrix, which is the sum of the Mueller matrices of all the measured light beam exit positions. In actual operation, it is impossible to measure all infinite incident positions. n light rays (light beams) on the entrance pupil plane can be selected for measurement. The polarization modulation characteristics of the converging optical system to be measured can be expressed as:

[0081] ;

[0082] in, is the Mueller matrix measured at the i-th beamlet exit position, is the total Mueller matrix. The total Mueller matrix obtained is It can be normalized according to the first element, and the normalized form is: ; is the first element of the total Mueller matrix.

[0083] like Figure 4 As shown, the decomposition and synthesis of the vibration of each light beam can be performed in the spherical coordinate system. For any vibration direction of any light beam being measured in the three-dimensional space, the decomposition method is:

[0084] ;

[0085] ;

[0086] ;

[0087] in, is the vibration amplitude of the current beamlet in the x direction, is the vibration amplitude of the current thin beam in the y direction, is the vibration amplitude of the current thin beam in the z direction, is the amplitude of the current beamlet, is the amplitude of the beamlet The angle with the Y axis of the spatial rectangular coordinate system.

[0088] The polarization characteristics of the convergence point can be described as the synthesis result of the vibration of each light beam at this point. The polarization state of each light beam can be described by the Jones vector, that is:

[0089] ;

[0090] in, It represents the phase difference between the vibration in the y direction and the vibration in the x direction.

[0091] The Jones vector represents the light propagating along the Z axis, and its vibration is located in the XOY plane. The Jones vector represents the vibration of the photoelectric in two mutually perpendicular directions. However, this is not the case in the converging optical system. All light rays converge at one point, and a new decomposition and synthesis method is needed to describe the polarization characteristics of the convergence point. In three-dimensional space, the vibration of all light rays is decomposed in the spherical coordinate system. The vibration of the decomposed light beam at the convergence point can be vector synthesized in the three directions of decomposition. Under the condition of constructive interference, the vibrations in the three mutually perpendicular directions are superimposed. The three-dimensional polarization characteristics of the convergence point are described as:

[0092] ;

[0093] in, is the superposition of n thin beams vibrating in the x direction, is the superposition of n thin beams vibrating in the y direction, is the superposition of n light beams vibrating in the z direction, is the vibration of the nth beamlet in the x direction, is the vibration of the nth beamlet in the y direction, is the vibration of the nth beamlet in the Z direction, is the vibration of the nth beamlet, is the angle between the projection of the vibration direction of the nth beamlet and the X-axis of the spatial rectangular coordinate system, is the angle between the vibration direction of the nth beamlet and the Y axis of the spatial rectangular coordinate system, is the integration range in spherical coordinates , the specific integration range is determined by the distribution range of all light beams to be integrated.

[0094] For a certain distribution For a real incident beam (coarse beam), the complete polarization characteristics of the convergence point can be obtained by measuring only a few positions in the distribution, such as Figure 4 As shown, if the intensity at the center of the distribution is , then the integral formula of the polarization characteristics at the convergence point is:

[0095] .

[0096] In reality, light is distributed in a three-dimensional space. For symmetrical converging optical systems, the number of measured light rays can be appropriately reduced according to the specific symmetry. For example, in an axisymmetric system, this method only needs to be used to measure a radius of the entrance pupil in one direction (for symmetrical converging optical systems, the results of the symmetrical incident light measurements in each direction are the same, so it is sufficient to measure different positions on the radius in one direction). For off-axis / eccentric systems, the coordinates of the light beam incident on the entrance pupil plane can be adjusted to measure the light beam at any coordinate on the entire entrance pupil plane.

[0097] Before performing step S6, the Mueller matrix needs to be converted into a Jones matrix, and then decomposed into a Pauli spin matrix, so that the physical quantities contained in the Jones matrix are clearer. Each item after decomposition represents a different polarization modulation characteristic. There is a conversion relationship between the Mueller matrix and the Jones matrix, and they can be converted into each other. The formula for decomposing the Jones matrix into the Pauli spin matrix is:

[0098] ;

[0099] It means that the polarization state of the incident light is not changed. Represents the linearity with polarization The relevant weight, represents the component associated with the linear 45 / 135 degree in polarization, Represents the components related to left / right rotation of polarization. A0-A3 are the coefficients of these components, representing the effects of these different operations.

[0100] The specific derivation steps are as follows: First, the Stokes vector is used to define the polarization state of light, and the Mueller matrix is ​​used to describe the change in polarization characteristics when light passes through a converging optical system. The Stokes vector expression is as follows: , represents the sum of the horizontal polarization component and the vertical polarization component, represents the difference between the horizontal polarization component and the vertical polarization component, represents the difference between the 45° polarization component and the 135° polarization component, Represents the difference between the right-hand circular polarization component and the left-hand circular polarization component.

[0101] The Mueller matrix of the converging optical system can be expressed as:

[0102] ;

[0103] The Stokes vector before and after the converging optical system satisfies the relationship: ,in, represents the Stokes vector of the incident light, represents the Stokes vector of the outgoing light.

[0104] The modulation effect of the converging optical system on the polarization state can be described by the Pauli matrix, which is a set of Hermitian matrices that describe the spin, namely , , .

[0105] It means that the polarization state of the incident light is not changed. Represents the linearity with polarization The relevant weight, represents the component associated with the linear 45 / 135 degree in polarization, Represents the components related to left / right rotation of polarization. A0-A3 are the coefficients of these components, representing the effects of these different operations.

[0106] The measured Mueller matrix can be converted into the Jones matrix, and the conversion relationship is as follows:

[0107] ;

[0108] in, , , , are the four elements that make up the Jones matrix, , , , represents the amplitude, , , , Represents the phase, and there is the following relationship between them and the measured Mueller matrix elements:

[0109] ;

[0110] ;

[0111] ;

[0112] ;

[0113] The four phase terms in the measurement are:

[0114] ;

[0115] ;

[0116] ;

[0117] ;

[0118] in, ~ is the element at the corresponding position in the measured Mueller matrix.

[0119] Therefore, the formula for decomposing the Jones matrix into the Pauli spin matrix is:

[0120] .

[0121] The method to measure the stereo polarization modulation effect of the converging optical system based on the coarse beam is to calculate the sum of the Mueller matrices measured by all the thin beams entering the pupil. The integral formula is:

[0122] ;

[0123] in, is the Mueller matrix measured by the light beam at the position (i, j) on the entrance pupil. All the (i, j) position coordinates constitute the entire entrance pupil surface. This represents the integration of these measured Mueller matrices over the entrance pupil (circular domain).

[0124] Based on the thin beam, in actual operation, n light rays can be appropriately selected for measurement according to the symmetry of the converging optical system. The polarization modulation characteristics of the converging optical system can be expressed as:

[0125] ;

[0126] The three-dimensional polarization characteristics of the convergence point can be described as the synthetic result of the vibration of all the beamlets at this point. After the spherical coordinates of all the measured beamlets are decomposed, they are vector-superimposed in three directions:

[0127] .

[0128] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0129] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the three-dimensional polarization modulation characteristics of a converging optical system, implemented by a system for measuring the three-dimensional polarization modulation characteristics of a converging optical system, characterized in that: A system for measuring the three-dimensional polarization modulation characteristics of a converging optical system comprises a light source unit, the light source unit comprises a light source translation device, a light beam emitting system, a first polarizer and a first wave plate, the light beam emitting system is arranged on the light source translation device, the light source translation device drives the light beam emitting system to translate, the light beam emitting system emits a fine light beam, and the fine light beam is incident on the converging optical system to be measured through the first polarizer and the first wave plate in sequence; A sample stage to be tested, the sample stage to be tested is used to fix the converging optical system to be tested and make the converging optical system to be tested perform axial rotation along its own optical axis direction; A receiving unit, the receiving unit comprising a second wave plate, a second polarizer and a light intensity detector, wherein the light beam emitted from the converging optical system to be measured is incident on the light intensity detector via the second wave plate and the second polarizer in sequence; A rotating unit, wherein the rotating unit drives the receiving unit to rotate, so that the receiving unit is placed in a different spatial position and the receiving unit receives the light intensity data of the thin light beam; The measurement method specifically includes the following steps: S1: fixing the converging optical system to be tested on the sample stage to be tested; S2: The light beam emitted by the light beam emitting system is incident on the light intensity detector through the first polarizer, the first wave plate, the converging optical system to be measured, the second wave plate and the second polarizer in sequence, the rotating unit drives the receiving unit to rotate so that the receiving unit is placed in a different spatial position, and the light intensity detector measures the light intensity data of n light beams accordingly, and obtains the amplitude distribution of the n light beams; S3: using a stepper motor to drive the first wave plate and the second wave plate to rotate h times at a preset angle ratio, and causing the light intensity detector to correspondingly receive light intensity data of h groups of n light beams; S4: Perform Fourier fitting on all the light intensity data to obtain the Mueller matrix of the converging optical system to be tested at the current light beam exit position; S5: adjusting the light beam exit position of the light beam exit system by using the light source translation device, replacing the current light beam exit position with the new light beam exit position, and repeating steps S2-S4 until the Mueller matrix of the converging optical system to be tested at the i light beam exit positions is obtained; S6: Integrate the Mueller matrices at all the light beam exit positions obtained in step S5 to obtain a total Mueller matrix that represents the polarization modulation characteristics of the converging optical system to be measured; S7: Based on the amplitude distribution of all the light beams, the three-dimensional vibration characteristics of the converging point of the converging optical system to be tested are obtained.

2. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 1, characterized in that: The measuring system further comprises a stepping motor, which drives the first wave plate and the second wave plate to rotate at a preset angle ratio; and further comprises a plurality of optical elements for changing the propagation direction of light between the first wave plate and the second wave plate.

3. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 1, characterized in that: The fine light beam is vertically incident on the second wave plate, the second polarizer and the light intensity detector; the diameter of the fine light beam is determined according to the entrance pupil diameter of the converging optical system to be measured and the preset number of measurement positions, and the diameter of the fine light beam is less than the entrance pupil diameter multiplied by the reciprocal of the preset number value.

4. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 1, characterized in that: The beam output system outputs a coarse beam or a thin beam with known amplitude distribution, and a coarse beam is regarded as a collection of n parallel thin beams; The positional relationship between the light source translation device and the light intensity detector is: the light intensity detector vertically receives each thin light beam emitted by the light beam emission system.

5. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 1, characterized in that: In step S2, if the beam emitting system emits a coarse beam with a known amplitude distribution, the coarse beam is regarded as a collection of n fine beams, and the amplitude distribution function of the n fine beams satisfies: ； Where r is the radius of the coarse beam, is the amplitude value at the center of the coarse beam, F(r) is the proportional coefficient of the light amplitude value at the beam position with a distance r from the center of the coarse beam, is the amplitude of the beamlet.

6. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 5, characterized in that: In step S3, the light intensity data can be Fourier expanded by the following formula: ； in, is the light intensity data measured by the light intensity detector, a0-a 12 and b0-b 12 are the Fourier expansion coefficients obtained by fitting the light intensity data. is the rotation angle of the first wave plate.

7. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 1, characterized in that: In step S6, the total Mueller matrix is ​​expressed as: ； in, is the Mueller matrix measured at the i-th beamlet exit position, is the total Mueller matrix.

8. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 6, characterized in that: In step S7, the vibration direction of each light beam in the three-dimensional space is decomposed as follows: ； ； ； in, is the vibration amplitude of the current beamlet in the x direction, is the vibration amplitude of the current thin beam in the y direction, is the vibration amplitude of the current thin beam in the z direction, is the amplitude of the current beamlet, is the amplitude of the beamlet The angle with the Y axis of the spatial rectangular coordinate system; will satisfy the amplitude distribution function The distributed coarse beam is regarded as a collection of n thin beams. The decomposition formula of each thin beam in the collection in three-dimensional space is: ； ； 。 9. The method for measuring the three-dimensional polarization modulation characteristics of a converging optical system according to claim 8, characterized in that: In step S7, when the light beam emitting system directly emits a thin light beam, the three-dimensional polarization characteristics of the convergence point of the converging optical system to be measured are for: ； in, is the superposition of n thin beams vibrating in the x direction, is the superposition of n thin beams vibrating in the y direction, is the superposition of n light beams vibrating in the z direction, is the vibration of the nth beamlet in the x direction, is the vibration of the nth beamlet in the y direction, is the vibration of the nth beamlet in the Z direction, is the vibration of the nth beamlet, is the angle between the projection of the vibration direction of the nth beamlet and the X-axis of the spatial rectangular coordinate system, is the angle between the vibration direction of the nth beamlet and the Y axis of the spatial rectangular coordinate system, is the integration range in spherical coordinates ; When the beam emission system directly emits a thick beam, the three-dimensional polarization characteristics of the convergence point of the converging optical system to be measured for: 。

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