Polarimetric brdf characterization apparatus and method

Abstract

Polarization BRDF characteristic measuring device and method, belong to optical measurement technical field, the present application is to solve the existing BRDF or polarization BRDF measurement slow, low efficiency problem of measurement.The scheme of the present application: the laser light source at the second focal point emits laser light vertically through the circularly polarized light generating system and the polarizing system, the circularly polarized light generating system converts the laser light emitted by the laser light source into circularly polarized light, the polarizing system quantitatively changes the polarization state of the circularly polarized light to form the measuring incident light, the incident light is transmitted through the transmission light of the half mirror, and is reflected by the ellipsoidal mirror to the surface of the sample to be measured at the first focal point, the reflected light wave of the surface of the sample to be measured is reflected again by the inner surface of the ellipsoidal mirror, and is transmitted to the second focal point direction and is reflected by the half mirror, and the reflected light wave is converged to the third focal point of the measuring system through the polarizing system, the polarizing system is adjusted with the polarizing system, and the polarization BRDF characteristic of the sample to be measured is measured.

Description

Technical Field

[0001] This invention relates to rapid measurement technology for BRDF and polarized BRDF, belonging to the field of optical measurement technology. Background Technology

[0002] With the development of aerospace technology, the analysis of the optical characteristics of space targets has become a hot research topic. The optical characteristics of space targets mainly include the infrared radiation characteristics, visible light scattering characteristics, laser scattering characteristics, ultraviolet scattering characteristics and polarization characteristics of the targets, among which visible light scattering characteristics and laser scattering characteristics are the key research contents.

[0003] Analyzing the optical scattering characteristics of space targets involves measuring the Bidirectional Reflectance Distribution Function (BRDF) or polarization BRDF of the satellite surface material. The BRDF is defined as the ratio of reflected radiance to incident radiance. It represents the reflection characteristics of an object's surface at any observation angle under different incident angles, serving as a deterministic function describing the light reflection characteristics of the target surface. Simultaneously, its polarization characteristics (polarization BRDF) can be used to describe the polarization reflection characteristics of the material surface. The Mueller matrix can be used to represent the material's BRDF or polarization BRDF characteristics. BRDF or polarization BRDF measurements are of great significance for studying the optical scattering characteristics of material surfaces.

[0004] Existing BRDF or polarization BRDF measurement technologies generally achieve hemispherical BRDF or polarization BRDF measurements by controlling a detector to traverse the hemispherical reflection space. For example, patents CN201110209229.2 and CN201510738039.8 place the detector on a circular arc track and use a turntable to achieve hemispherical spatial movement. During measurement, the detector's position on the circular arc track and the turntable angle need to be changed one by one, resulting in very slow measurement speed and low efficiency. Therefore, improving the measurement efficiency of BRDF or polarization BRDF measurement systems is a key problem that urgently needs to be solved in this technical field. Summary of the Invention

[0005] To address the problems of slow measurement speed and low measurement efficiency in existing BRDF or polarized BRDF measurements, this invention provides a polarized BRDF characteristic measurement device and method.

[0006] The polarization BRDF characteristic measurement device of the present invention includes an ellipsoidal reflector 1, a laser source 2, a circularly polarized light generation system 3, a polarization system 4, a polarization analysis system 5, a measurement system 6, and a semi-reflective plane mirror 8.

[0007] The sample 7 to be tested is placed at the first focal point F1 of the ellipsoidal reflector 1, and the laser source 2 is placed at the second focal point F2 of the ellipsoidal reflector 1. The laser source 2, the circularly polarized light generation system 3, and the polarization system 4 constitute the incident light forming unit for measurement. The circularly polarized light generation system 3 and the polarization system 4 are arranged sequentially along the optical axis of the laser source 2. The semi-reflective and semi-transparent plane mirror 8 is placed on the light-emitting side of the incident light forming unit for measurement between the first and second focal points. The second focal point of the ellipsoidal reflector 1 is located relative to the virtual image of the semi-reflective and semi-transparent plane mirror 8 as the third focal point F3. The measurement system 6 is placed at the third focal point F3, and the polarization analyzer 5 is placed between the measurement system 6 and the semi-reflective and semi-transparent plane mirror 8.

[0008] The laser emitted by the laser source 2 passes perpendicularly through the circularly polarized light generation system 3 and the polarization system 4. The circularly polarized light generation system 3 converts the laser emitted by the laser source 2 into circularly polarized light output. The polarization system 4 quantitatively changes the polarization state of the circularly polarized light to form the incident light for measurement. The incident light is transmitted through the semi-reflective plane mirror 8 and reflected for the first time by the ellipsoidal mirror 1 to the surface of the sample 7 under test. The reflected light wave from the surface of the sample 7 under test is reflected again by the inner surface of the ellipsoidal mirror 1. The reflected light wave is transmitted towards the second focal point F2 and reflected by the semi-reflective plane mirror 8. The reflected light wave is converged to the measurement system 6 by the polarization analysis system 5. The polarization analysis system 5 and the polarization system 4 synchronously adjust the degree of polarization. The measurement system 6 measures the polarization BRDF characteristics of the sample 7 under test.

[0009] Preferably, the incident light forming unit for measurement rotates around the second focal point F2 of the ellipsoidal reflector 1, thereby realizing polarization BRDF measurement under different incident zenith angles.

[0010] Preferably, the circularly polarized light generating system 3 includes a polarizer P1 and a quarter-wave plate Q1 placed in parallel. The transmission direction of the polarizer P1 is fixed in the horizontal direction and defined as the x-axis. The fast axis of the quarter-wave plate Q1 is at 45° to the transmission direction of the polarizer P1. The operating wavelength of the quarter-wave plate Q1 is consistent with the wavelength of the laser source 2.

[0011] Preferably, the polarization system 4 includes a polarizer P2 and a quarter-wave plate Q2 placed in parallel. The polarization degree of the transmitted light is changed by changing the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2. The operating wavelength of the quarter-wave plate Q2 is consistent with the wavelength of the laser source 2.

[0012] Preferably, the laser emitted by the laser source 2 is a polarized source.

[0013] Preferably, the measurement system 6 is a polarization camera or a conventional optical camera.

[0014] Preferably, when the measurement system 6 is a polarization camera, the polarization detection system 5 uses a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6. The polarization degree of the light received by the measurement system 6 is changed by changing the angle between the quarter-wave plate Q3 and the x-axis. The working wavelength of the quarter-wave plate Q3 is consistent with the wavelength of the laser source 2.

[0015] Preferably, when the measurement system 6 is a common optical camera, the polarization analysis system 5 uses a polarizer P3 and a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6. The polarizer P3 and the quarter-wave plate Q3 are parallel. The polarization degree of the transmitted light is changed by changing the angle between the fast axis of the quarter-wave plate Q3 and the transmission direction of the polarizer P3. The working wavelength of the quarter-wave plate Q3 is consistent with the wavelength of the laser source 2.

[0016] This invention provides a first method for measuring polarization BRDF characteristics. This method is based on a polarization analyzer 5 using a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6. The method includes the following steps:

[0017] S1. Initialize the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 in the polarization system 4, and the angle between the quarter-wave plate Q3 and the x-axis to θ0.

[0018] S2. Start the laser source 2 and measurement system 6. The Stokes vector of the circularly polarized light output by the circularly polarized light generation system 3 is S. h The Stokes vector of the light wave received by measurement system 6 is S. r Then, the Mueller matrix M of the sample 7 to be tested is obtained by the following formula. S :

[0019] S r =M Q3 M L2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 1

[0020] In the formula:

[0021] M P2 The Mueller matrix of polarizer P2 is obtained by the following formula:

[0022]

[0023] In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis;

[0024] M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula:

[0025]

[0026] In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2;

[0027] M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula:

[0028]

[0029] In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3;

[0030] M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror.

[0031] M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time.

[0032] M E1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration.

[0033] M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration.

[0034] S3. Using a fixed step size, repeatedly and synchronously change the angle between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angle between quarter-wave plate Q3 and the x-axis in polarization system 4. Repeat measurement step S2 once for each angle change, with the number of measurements m ≥ 6. Construct a system of equations from m sets of formula 1 to finally obtain the Mueller matrix M of the sample 7 under test. S .

[0035] This invention provides a second method for measuring polarization BRDF characteristics. This method is based on a polarizer P3 and a quarter-wave plate Q3 positioned perpendicular to the optical axis of the measurement system 6 in the polarization analyzer system 5. The method includes the following steps:

[0036] S1. Initialize the angle between the fast axis of quarter-wave plate Q2 and the transmission direction of polarizer P2 in polarization system 4, and the angle between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 to θ0 at the same time.

[0037] S2. Start the laser source 2 and measurement system 6. The Stokes vector of the circularly polarized light output by the circularly polarized light generation system 3 is S. h The Stokes vector of the light wave received by measurement system 6 is S. r Then, the Mueller matrix M of the sample 7 to be tested is obtained by the following formula.S :

[0038] S r =M P3 M Q3 M L2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 2

[0039] In the formula:

[0040] M P2 The Mueller matrix of polarizer P2 is obtained by the following formula:

[0041]

[0042] In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis;

[0043] M P3 The Mueller matrix of polarizer P3 is obtained by the following formula:

[0044]

[0045] In the matrix, θ p3 The angle between the transmission direction of polarizer P3 and the x-axis;

[0046] M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula:

[0047]

[0048] In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2;

[0049] M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula:

[0050]

[0051] In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3;

[0052] M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror.

[0053] M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time.

[0054] M E1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration.

[0055] M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration.

[0056] S3. Using a fixed step size, repeatedly and synchronously change the angles between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angles between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 in polarization system 4. Repeat measurement step S2 once for each angle change, with the number of measurements m ≥ 16. Construct a system of equations from m sets of formulas 2, and finally obtain the Mueller matrix M of the sample 7 to be tested. S .

[0057] The beneficial effects of this invention are as follows: This invention improves upon traditional BRDF or polarized BRDF measurement methods, enabling rapid and efficient measurement of BRDF or polarized BRDF in a fully hemispherical space. By introducing an ellipsoidal reflector, this invention eliminates the need for the measurement system to traverse the hemispherical space, thereby reducing measurement time and significantly improving the measurement speed of BRDF or polarized BRDF. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the polarization BRDF characteristic measurement device of the present invention. The polarization analysis system uses a quarter-wave plate Q3, and the measurement system is a polarization camera.

[0059] Figure 2 This is a schematic diagram of the structure of the polarization BRDF characteristic measurement device of the present invention. The polarization analysis system uses polarizer P3 and quarter-wave plate Q3, and the measurement system is a common optical camera.

[0060] Figure 3 This is a schematic diagram of an ellipsoidal reflector. Detailed Implementation

[0061] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0063] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0064] Specific Implementation Method 1: The following is combined with... Figures 1 to 3 This embodiment describes a polarization BRDF characteristic measurement device, which includes an ellipsoidal reflector 1, a laser source 2, a circularly polarized light generation system 3, a polarization system 4, a polarization analysis system 5, a measurement system 6, and a semi-reflective plane mirror 8.

[0065] The sample 7 to be tested is placed at the first focal point F1 of the ellipsoidal reflector 1, and the laser source 2 is placed at the second focal point F2 of the ellipsoidal reflector 1. The laser source 2, the circularly polarized light generation system 3, and the polarization system 4 constitute the incident light forming unit for measurement. The circularly polarized light generation system 3 and the polarization system 4 are arranged sequentially along the optical axis of the laser source 2. The semi-reflective and semi-transparent plane mirror 8 is placed on the light-emitting side of the incident light forming unit for measurement between the first and second focal points. The second focal point of the ellipsoidal reflector 1 is located relative to the virtual image of the semi-reflective and semi-transparent plane mirror 8 as the third focal point F3. The measurement system 6 is placed at the third focal point F3, and the polarization analyzer 5 is placed between the measurement system 6 and the semi-reflective and semi-transparent plane mirror 8.

[0066] The laser emitted by the laser source 2 passes perpendicularly through the circularly polarized light generation system 3 and the polarization system 4. The circularly polarized light generation system 3 converts the laser emitted by the laser source 2 into circularly polarized light output. The polarization system 4 quantitatively changes the polarization state of the circularly polarized light to form the incident light for measurement. The incident light is transmitted through the semi-reflective plane mirror 8 and reflected for the first time by the ellipsoidal mirror 1 to the surface of the sample 7 under test. The reflected light wave from the surface of the sample 7 under test is reflected again by the inner surface of the ellipsoidal mirror 1. The reflected light wave is transmitted towards the second focal point F2 and reflected by the semi-reflective plane mirror 8. The reflected light wave is converged to the measurement system 6 by the polarization analysis system 5. The polarization analysis system 5 and the polarization system 4 synchronously adjust the degree of polarization. The measurement system 6 measures the polarization BRDF characteristics of the sample 7 under test.

[0067] The laser emitted by laser source 2 is a polarized light source. The wavelength of laser source 2 can be selected according to measurement requirements, and its function is to provide a polarized light source; the laser emitted by laser source 2 passes perpendicularly through circularly polarized light generation system 3 and polarization system 4.

[0068] The incident light forming unit rotates around the second focal point F2 of the ellipsoidal reflector 1 to achieve polarization BRDF measurement under different incident zenith angles. When measuring polarization BRDF at a certain zenith angle, the incident light forming unit remains stationary, and the polarization degrees of the polarization system 4 and the analyzer system 5 need to be changed.

[0069] The circularly polarized light generation system 3 includes a polarizer P1 and a quarter-wave plate Q1 placed parallel to each other. The transmission direction of polarizer P1 is fixed in the horizontal direction, defined as the x-axis. The fast axis of the quarter-wave plate Q1 forms a 45° angle with the transmission direction of polarizer P1. The operating wavelength of the quarter-wave plate Q1 is the same as the wavelength of the laser source 2. The function of the circularly polarized light generation system 3 is to convert laser light into circularly polarized light.

[0070] The polarization system 4 includes a polarizer P2 and a quarter-wave plate Q2 placed parallel to each other. The degree of polarization of the transmitted light is changed by altering the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2. The operating wavelength of the quarter-wave plate Q2 is the same as the wavelength of the laser source 2. The function of the polarization system 4 is to quantitatively change the polarization state of circularly polarized light; when the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 is changed, the degree of polarization of the circularly polarized light changes.

[0071] Measurement system 6 uses either a polarization camera or a conventional optical camera. The structure of the corresponding polarization analysis system differs depending on the camera type used.

[0072] See Figure 1 When the measurement system 6 is a polarization camera, the polarization analyzer 5 uses a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6. The operating wavelength of the quarter-wave plate Q3 is the same as the wavelength of the laser source 2. The polarization analyzer 5 is adjusted synchronously with the polarization system 4. By changing the angle between the quarter-wave plate Q3 and the x-axis, the polarization degree of the light received by the measurement system 6 is changed. In this scheme, the polarization analyzer 5 only has a quarter-wave plate, and the polarization camera has its own polarizer. Therefore, only changing the angle between the quarter-wave plate Q3 and the x-axis changes the angle between the quarter-wave plate Q3 and the polarizer in the polarization camera, thus quantitatively changing the polarization state of the light wave incident on the polarization analyzer 5. Furthermore, the adjustment angle step size and frequency of the polarization analyzer 5 are synchronized with those of the polarization analyzer 4. The present invention aims to adjust the polarization degree of the light wave entering the measurement system 6 by changing the angle between the fast axis of the quarter-wave plate Q2 in the polarization system 4 and the transmission direction of the polarizer P2, and the direction of the fast axis of the quarter-wave plate Q3 in the polarization analysis system 5. A measurement is performed under each polarization degree, and multiple measurements are used to construct an equation set to obtain the final measurement result.

[0073] See Figure 2When the measurement system 6 is a conventional optical camera, the polarization analyzer 5 uses a polarizer P3 and a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6. Polarizers P3 and Q3 are parallel. The degree of polarization of the transmitted light is changed by altering the angle between the fast axis of the quarter-wave plate Q3 and the transmission direction of the polarizer P3. The operating wavelength of the quarter-wave plate Q3 is consistent with the wavelength of the laser source 2. The angle adjustment step size and frequency of the polarization analyzer 5 are synchronized with those of the polarization analyzer 4. This invention aims to adjust the degree of polarization of the light wave entering the measurement system 6 by changing the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 in the polarization analyzer 4 and the angle between the quarter-wave plate Q3 and the transmission direction of the polarizer P3 in the polarization analyzer 5. A measurement is performed at each degree of polarization, and multiple measurements are used to construct an equation set to obtain the final measurement result.

[0074] Specific Implementation Method Two: The following is combined with... Figure 1 This embodiment describes a polarization BRDF characteristic measurement method based on the polarization BRDF characteristic measurement device described in Embodiment 1. When the measurement system 6 is a polarization camera, the polarization detection system 5 uses a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6.

[0075] The method includes the following steps:

[0076] S1. Initialize the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 in the polarization system 4, and the angle between the quarter-wave plate Q3 and the x-axis to θ0.

[0077] The polarization state of circularly polarized light after passing through polarization system 4 is related to the included angle θ0, and the polarization state of the light received by measurement system 6 is also related to the included angle θ0.

[0078] S2. Start the laser source 2 and measurement system 6. The Stokes vector of the circularly polarized light output by the circularly polarized light generation system 3 is S. h The Stokes vector of the light wave received by measurement system 6 is S. r Then, the Mueller matrix M of the sample 7 to be tested is obtained by the following formula. S :

[0079] S r =M Q3 M L2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 1

[0080] Formula 1 only contains the Mueller matrix M of the sample to be tested, sample 7. S It is an unknown quantity.

[0081] In the formula:

[0082] M P2 The Mueller matrix of polarizer P2 is obtained by the following formula:

[0083]

[0084] In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis;

[0085] M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula:

[0086]

[0087] In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2;

[0088] M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula:

[0089]

[0090] In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3;

[0091] M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror.

[0092] M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time.

[0093] M E1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration.

[0094] M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration.

[0095] The calibrated Mueller matrix M L1 M L2 M E1 M E2 Each of these is a 4×4 matrix.

[0096] S3. Using a fixed step size, repeatedly and synchronously change the angle between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angle between quarter-wave plate Q3 and the x-axis in polarization system 4. Repeat measurement step S2 once for each angle change, with the number of measurements m ≥ 6. Construct a system of equations from m sets of formula 1 to finally obtain the Mueller matrix M of the sample 7 under test.S .

[0097] In polarization system 4, the initial angle θ0 between the fast axis of quarter-wave plate Q2 and the transmission direction of polarizer P2 is 0 degrees. Similarly, in polarization analysis system 5, the initial angle between the fast axis of quarter-wave plate Q3 and the x-axis is also 0 degrees. A stepping method can be used, gradually increasing these two angles in fixed steps of 5-10 degrees. Each time the angle is changed, M... Q2 and M Q3 This will change, ultimately affecting the Stokes vector S of the light wave in measurement system 6. r This will change accordingly, and a measurement will be taken at this point to obtain a set of formulas 1.

[0098] In this embodiment, since the measurement system 6 is a polarization camera, it can acquire the Stokes vector S in Formula 1 with each measurement. r The three values ​​in the equations are used to construct the system of equations in Formula 1 by measuring only 6 times, thereby solving for the 4×4 Mueller matrix of the sample 7 to be tested.

[0099] The final obtained Mueller matrix M S Used to characterize the polarization BRDF properties of the surface material of the sample 7 under test.

[0100] Specific Implementation Method Three: The following is combined with... Figure 2 This embodiment describes a polarization BRDF characteristic measurement method based on the polarization BRDF characteristic measurement device described in Embodiment 1. When the measurement system 6 is a common optical camera, the polarization analysis system 5 uses a polarizer P3 and a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system 6.

[0101] The method includes the following steps:

[0102] S1. Initialize the angle between the fast axis of quarter-wave plate Q2 and the transmission direction of polarizer P2 in polarization system 4, and the angle between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 to θ0 at the same time.

[0103] The polarization state of circularly polarized light after passing through polarization system 4 is related to the included angle θ0; the degree of polarization of light after passing through polarization analyzer system 5 is related to the included angle θ0.

[0104] S2. Start the laser source 2 and measurement system 6. The Stokes vector of the circularly polarized light output by the circularly polarized light generation system 3 is S. h The Stokes vector of the light wave received by measurement system 6 is S. r Then, the Mueller matrix M of the sample 7 to be tested is obtained by the following formula. S :

[0105] S r =M P3 M Q3 ML2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 2

[0106] Formula 2 only contains the Mueller matrix M of the sample to be tested, sample 7. S It is an unknown quantity.

[0107] In the formula:

[0108] M P2 The Mueller matrix of polarizer P2 is obtained by the following formula:

[0109]

[0110] In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis;

[0111] M P3 The Mueller matrix of polarizer P3 is obtained by the following formula:

[0112]

[0113] In the matrix, θ p3 The angle between the transmission direction of polarizer P3 and the x-axis;

[0114] M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula:

[0115]

[0116] In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2;

[0117] M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula:

[0118]

[0119] In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3;

[0120] M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror.

[0121] M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time.

[0122] ME1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration.

[0123] M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration.

[0124] The calibrated Mueller matrix M L1 M L2 M E1 M E2 Each of these is a 4×4 matrix.

[0125] S3. Using a fixed step size, repeatedly and synchronously change the angles between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angles between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 in polarization system 4. Repeat measurement step S2 once for each angle change, with the number of measurements m ≥ 16. Construct a system of equations from m sets of formulas 2, and finally obtain the Mueller matrix M of the sample 7 to be tested. S .

[0126] In polarization system 4, the initial angle θ0 between the fast axis of quarter-wave plate Q2 and the transmission direction of polarizer P2 is 0 degrees. Similarly, in polarization analysis system 5, the initial angle between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 is also 0 degrees. A stepping method can be used, gradually increasing these two angles in fixed steps of 5-10 degrees. Each time the angle is changed, M... Q2 and M Q3 This will change, ultimately affecting the Stokes vector S of the light wave in measurement system 6. r This will change accordingly, and a measurement will be taken at this point to obtain a set of formulas 2.

[0127] In this embodiment, since the measurement system 6 is a common optical camera, it can acquire the Stokes vector S in Formula 2 with each measurement. r One of the values, therefore, at least 16 measurements are needed to construct the system of equations for Formula 2, thereby solving for the 4×4 Mueller matrix of the sample to be tested 7.

[0128] The final obtained Mueller matrix M S Used to characterize the polarization BRDF properties of the surface material of the sample 7 under test.

[0129] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A polarization BRDF characteristic measuring device, characterized in that, It includes an ellipsoidal reflector (1), a laser source (2), a circularly polarized light generation system (3), a polarization system (4), a polarization analysis system (5), a measurement system (6), and a semi-reflective plane mirror (8). The sample to be tested (7) is set at the first focal point F1 of the ellipsoidal reflector (1), and the laser source (2) is set at the second focal point F2 of the ellipsoidal reflector (1). The laser source (2), the circularly polarized light generation system (3), and the polarization system (4) constitute the incident light forming unit for measurement. The circularly polarized light generation system (3) and the polarization system (4) are arranged sequentially along the optical axis of the laser source (2). The semi-reflective and semi-transparent plane mirror (8) is set on the light-emitting side of the incident light forming unit for measurement between the first and second focal points. The second focal point of the ellipsoidal reflector (1) is used as the third focal point F3 relative to the virtual image of the semi-reflective and semi-transparent plane mirror (8). The measurement system (6) is set at the third focal point F3. The polarization analyzer (5) is set between the measurement system (6) and the semi-reflective and semi-transparent plane mirror (8). The laser emitted by the laser source (2) passes perpendicularly through the circularly polarized light generation system (3) and the polarization system (4). The circularly polarized light generation system (3) converts the laser emitted by the laser source (2) into circularly polarized light output. The polarization system (4) quantitatively changes the polarization state of the circularly polarized light to form the incident light for measurement. The incident light is transmitted through the semi-reflective and semi-transparent plane mirror (8) and reflected for the first time by the ellipsoidal mirror (1) to the surface of the sample to be tested (7). The reflected light wave on the surface of the sample to be tested (7) is reflected again by the inner surface of the ellipsoidal mirror (1). The reflected light wave is transmitted to the direction of the second focal point F2 and reflected by the semi-reflective and semi-transparent plane mirror (8). The reflected light wave is converged to the measurement system (6) by the polarization detection system (5). The polarization detection system (5) and the polarization system (4) adjust the polarization degree synchronously. The measurement system (6) measures the polarization BRDF characteristics of the sample to be tested (7).

2. The polarization BRDF characteristic measuring device according to claim 1, characterized in that, The incident light forming unit is rotated around the second focus F2 of the ellipsoidal reflector (1) to realize polarization BRDF measurement under different incident zenith angles.

3. The polarization BRDF characteristic measuring device according to claim 2, characterized in that, The circularly polarized light generation system (3) includes a polarizer P1 and a quarter-wave plate Q1 placed in parallel. The transmission direction of the polarizer P1 is fixed in the horizontal direction and is defined as the x-axis. The fast axis of the quarter-wave plate Q1 is at 45° with the transmission direction of the polarizer P1. The working wavelength of the quarter-wave plate Q1 is consistent with the wavelength of the laser source (2).

4. The polarization BRDF characteristic measuring device according to claim 3, characterized in that, The polarization system (4) includes a polarizer P2 and a quarter-wave plate Q2 placed in parallel. The polarization degree of the transmitted light is changed by changing the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2. The working wavelength of the quarter-wave plate Q2 is consistent with the wavelength of the laser source (2).

5. The polarization BRDF characteristic measuring device according to claim 4, characterized in that, The measurement system (6) is a polarization camera or a regular optical camera.

6. The polarization BRDF characteristic measuring device according to claim 5, characterized in that, When the measurement system (6) is a polarization camera, the polarization detection system (5) uses a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system (6). The polarization degree of the light received by the measurement system (6) is changed by changing the angle between the quarter-wave plate Q3 and the x-axis. The working wavelength of the quarter-wave plate Q3 is consistent with the wavelength of the laser source (2).

7. The polarization BRDF characteristic measuring device according to claim 5, characterized in that, When the measurement system (6) is a common optical camera, the polarization analysis system (5) uses a polarizer P3 and a quarter-wave plate Q3 perpendicular to the optical axis of the measurement system (6). The polarizer P3 and the quarter-wave plate Q3 are parallel. The polarization degree of the transmitted light is changed by changing the angle between the fast axis of the quarter-wave plate Q3 and the transmission direction of the polarizer P3. The working wavelength of the quarter-wave plate Q3 is consistent with the wavelength of the laser source (2).

8. The polarization BRDF characteristic measuring device according to claim 1, characterized in that, The laser emitted by the laser source (2) is a polarized source.

9. A method for measuring polarization BRDF characteristics, the method being implemented based on claim 6, characterized in that, The method includes the following steps: S1. Initialize the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 in the polarization system (4), and the angle between the quarter-wave plate Q3 and the x-axis are both θ0. S2. Start the laser source (2) and measurement system (6). The Stokes vector of the circularly polarized light output by the circularly polarized light generation system (3) is S. h The Stokes vector of the light wave received by the measurement system (6) is S. r Then, the Mueller matrix M of the sample to be tested (7) is obtained by the following formula. S : S r = M Q3 M L2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 1 In the formula: M P2 The Mueller matrix of polarizer P2 is obtained by the following formula: In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis; M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula: In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2; M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula: In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3; M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror. M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time. M E1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration. M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration. S3. With a fixed step size, the angle between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angle between quarter-wave plate Q3 and the x-axis in the polarization system (4) are changed synchronously multiple times. The S2 measurement step is repeated once for each change of the angle. The number of measurements m ≥ 6 times. An equation system is constructed from m sets of formula 1 to finally obtain the Mueller matrix M of the sample to be tested (7). S .

10. A method for measuring polarization BRDF characteristics, the method being implemented based on claim 7, characterized in that, The method includes the following steps: S1. Initialize the angle between the fast axis of the quarter-wave plate Q2 and the transmission direction of the polarizer P2 in the polarization system (4), and the angle between the fast axis of the quarter-wave plate Q3 and the transmission direction of the polarizer P3 are both θ0. S2. Start the laser source (2) and measurement system (6). The Stokes vector of the circularly polarized light output by the circularly polarized light generation system (3) is S. h The Stokes vector of the light wave received by the measurement system (6) is S. r Then, the Mueller matrix M of the sample to be tested (7) is obtained by the following formula. S : S r = M P3 M Q3 M L2 M E2 M S M E1 M L1 M Q2 M P2 S h Formula 2 In the formula: M P2 The Mueller matrix of polarizer P2 is obtained by the following formula: In the matrix, θ p2 The angle between the transmission direction of polarizer P2 and the x-axis; M P3 The Mueller matrix of polarizer P3 is obtained by the following formula: In the matrix, θ p3 The angle between the transmission direction of polarizer P3 and the x-axis; M Q2 The Mueller matrix for the quarter-wave plate Q2 is obtained by the following formula: In the matrix, θ λ2 The angle between the fast axis and the x-axis of the quarter-wave plate Q2; M Q3 The Mueller matrix for the quarter-wave plate Q3 is obtained by the following formula: In the matrix, θ λ3 The angle between the fast axis and the x-axis of the quarter-wave plate Q3; M L1 The Mueller matrix, obtained through calibration, represents the first time light passes through the semi-reflective mirror. M L2 The Mueller matrix is ​​obtained through calibration when the light passes through the semi-reflective lens for the second time. M E1 The Mueller matrix for the first reflected light from the ellipsoidal mirror is obtained through calibration. M E2 The Mueller matrix for the second reflected light from the ellipsoidal mirror is obtained through calibration. S3. With a fixed step size, the angle between the transmission direction of polarizer P2 and the fast axis of quarter-wave plate Q2, and the angle between the fast axis of quarter-wave plate Q3 and the transmission direction of polarizer P3 in the polarization system (4) are changed synchronously multiple times. The S2 measurement step is repeated once for each change of the angle. The number of measurements m≥16 times. An equation system is constructed from m sets of formula 2 to finally obtain the Mueller matrix M of the sample to be tested (7). S .

Images