A temperature-controlled medium-wave infrared polarized radiation source with adjustable polarization degree and a polarization degree measurement method

Abstract

The present invention discloses a medium-wave infrared polarized radiation source with adjustable polarization degree and a polarization degree measurement method, which belong to the field of photoelectric detection. The present invention places a medium-wave infrared polarizer in a variable temperature transmission bracket, uses liquid inert gas to cool the variable temperature transmission bracket and the medium-wave infrared polarizer inside it, and modulates the proportion of completely polarized radiation components in the total radiation of the polarized radiation source by changing the temperature of the black body source and the variable temperature transmission bracket, thereby realizing adjustable polarization degree of the medium-wave infrared polarized radiation source. At the same time, lowering the temperature of the variable temperature chamber of the variable temperature transmission bracket can effectively reduce the negative interference of the spontaneous radiation of the medium-wave infrared polarizer and the stray light of the variable temperature transmission bracket, and improve the modulation accuracy of the polarization degree of the output light of the radiation source. According to the polarization degree measurement result, the functional relationship between the polarization degree of the output light field of the polarized radiation source and the temperature of the black body source and the temperature of the variable temperature transmission bracket is calibrated; according to the calibrated functional relationship, the polarization degree of the medium-wave infrared polarized radiation source with adjustable polarization degree and temperature control is predicted.

Description

Technical Field

[0001] The invention relates to a design of a temperature-controlled polarization-adjustable medium-wave infrared polarized radiation source and a polarization-degree measurement method, belonging to the technical field of photoelectric detection. Background Art

[0002] Infrared thermal polarization imaging technology is a new infrared imaging technology that has developed rapidly in recent years. It detects and identifies targets through the differences in infrared radiation and polarization characteristics of scenes, and can obtain more scene information than traditional intensity imaging, showing a wide range of application prospects. However, due to the non-ideality of the system itself (non-ideal polarization and nonlinear effects), false polarization information is often generated during polarization thermal imaging, affecting the inversion accuracy of polarization information. Therefore, a controllable infrared polarization radiation source is needed to calibrate the polarization radiation of the infrared polarization imaging system. Polarization radiation sources are usually used to verify the calibration accuracy of polarization optical detectors, detect polarization characteristics of polarization optical detectors, and measure the relative transmittance of polarization optical detectors and their systems.

[0003] The most common method of polarized radiation source is to place linear polarizers at different angles in front of a black body source or an integrating sphere, and the unbiased radiation passes through the polarizer to produce radiation light fields with different linear polarization states. For example, when the American SDL laboratory tested the polarization characteristics of the infrared hyperspectral imaging polarimeter, a wire grid polarizer was placed in front of the black body source, and the polarization angle was changed by rotating the polarizer for calibration; the famous American EOSP polarimeter is provided by an integrating sphere as the light source, and a large disk is covered at the exit, on which eight polarizers capable of achieving different calibration functions are evenly distributed, corresponding to different linear polarization states. Since the polarization degree of polarized light transmitted by the linear polarizer is close to 1, the above-mentioned linear polarizer polarizing radiation source can only change the polarization direction of the radiation, but not the polarization degree, making it difficult to grasp the changes in the response of the calibration instrument to different polarization degrees, and it is difficult to achieve the purpose of polarization calibration in a strict sense. Therefore, the adjustable polarization degree radiation source has become a new calibration light source in the field of polarization calibration in recent years. Its principle is that the unbiased radiation of the black body source or integrating sphere light source passes through the polarizing system to become partially polarized radiation, and the polarization degree and polarization angle of the polarized radiation source are changed by rotating the polarizing glass stack of the polarizing system. Typical examples are the polarization calibration source POLDER designed by the French Space Center (CNES) and the large dynamic range adjustable polarization radiation source VPOLS-II designed by the Institute of Optics and Optics of the Chinese Academy of Sciences

[10] . The polarization system of this type of polarized radiation source is located in the natural environment. In the medium-wave and long-wave infrared bands, the self-radiation of the polarization system will greatly reduce the linear polarization degree of the polarized radiation source. Therefore, this type of polarization method is usually applicable to the visible light to short-wave infrared band (0.4-3.0μm). At the same time, the self-radiation of the polarization system is easily affected by the ambient temperature, air disturbance, etc., and the angle of the glass stack inside the polarization system is difficult to accurately adjust, resulting in uncertainty in the polarization degree of the above-mentioned adjustable polarization radiation source, and the accuracy of polarization calibration is difficult to guarantee. Summary of the invention

[0004] One of the main purposes of the present invention is to provide a medium-wave infrared polarized radiation source with adjustable polarization degree by temperature control, by placing a medium-wave infrared polarizer in a variable temperature transmission bracket, by using liquid inert gas to cool the variable temperature transmission bracket and the medium-wave infrared polarizer inside, by changing the temperature of the black body source and the variable temperature transmission bracket, modulating the proportion of the completely polarized radiation component in the total radiation of the polarized radiation source, and thus realizing the adjustable polarization degree of the medium-wave (3.0-5.2 μm) infrared polarized radiation source. At the same time, lowering the temperature of the variable temperature transmission bracket temperature chamber can effectively reduce the negative interference of the medium-wave infrared polarizer spontaneous radiation and the stray light of the variable temperature transmission bracket, and can effectively improve the modulation accuracy of the polarization degree of the outgoing light of the radiation source.

[0005] The second main purpose of the present invention is to provide a method for measuring the polarization degree of a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control, by placing a medium-wave cooled focal plane thermal imager close to the front of a planar black body source, calibrating the thermal imager in grayscale-radiant illumination, and measuring the transmittance, spontaneous radiation, and reflected radiation of the objective lens. According to the calibration result of the thermal imager, the polarization degree of the medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control is measured using a correction model of a post-polarizer medium-wave cooled polarized thermal imager; according to the polarization degree measurement result of the medium-wave infrared polarized radiation source, the functional relationship between the polarization degree of the outgoing light field of the polarized radiation source and the temperature of the black body source and the temperature of the variable temperature transmission bracket is calibrated; and the polarization degree of the medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control is predicted based on the calibrated functional relationship.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] The invention discloses a medium-wave infrared polarized radiation source with adjustable polarization degree and temperature control, comprising a high-precision surface temperature difference blackbody source, a variable temperature transmission bracket, and a medium-wave infrared polarizer. The optical path is a high-precision surface temperature difference blackbody source emitting unpolarized light L B (T) passes through the left window of the variable temperature transmission bracket, the medium-wave infrared polarizer and the right window to form a partially polarized light, which is regarded as a completely polarized light L p and unpolarized light L N The superposition of the medium-wave infrared polarized radiation source emits the light field S in The linear polarization degree P is the completely polarized light component L pout In the total radiance L out The medium-wave infrared polarizer is placed in a variable temperature transmission bracket, and the temperature of the variable temperature transmission bracket and the medium-wave infrared polarizer inside it is adjusted by liquid inert gas to change the non-polarized light L N ; By adjusting the temperature of the high-precision surface temperature difference blackbody source, L B (T); that is, by changing the temperature of the black body source and the variable temperature transmission bracket, the polarization degree of the light emitted by the radiation source can be accurately adjusted to achieve a temperature-controlled and adjustable medium-wave infrared polarized radiation source.

[0008] The fully polarized light L in the outgoing light field pout Defined as:

[0009]

[0010]

[0011]

[0012] L B (T) = L B (ε B ,T)+(1-α B )·LHt1 (t1) (4)

[0013] L Ht1 (t1) = (1-α a )·L tb (ε t1 ,t1)+(1-α a )·L a (ε a ,t1) (5)

[0014] L c1 (t) = L c1 (ε c ,t)+(1-ρ c -α c )·L Ht (t) (6)

[0015] L Ht (t) = (1-α a )·L tb (ε t ,t)+(1-α a )·L a (ε a ,t) (7)

[0016] L pout =ρ c ·[(L max +L N (t))-(L min +L N (t))]L p =ρ c ·L p (8)

[0017] Where, T is the temperature of the blackbody source; t is the temperature inside the variable temperature transmission bracket cavity; t1 is the indoor ambient temperature; L max , L min is the transmitted radiance of the metal wire grid in the main direction and orthogonal direction of the medium-wave infrared polarizer; τ′1 and τ′2 are the average transmittance of the metal wire grid in the main direction and orthogonal direction in the working band; the blackbody source radiation brightness L B (T) is the black body self-luminous radiance L B (ε B ,T) and the reflected indoor environment radiance L Ht1 (t1) superposition; indoor environment radiance L Ht1 (t1) includes the spontaneous radiance L of indoor objects tb (ε t1 ,t1) and the spontaneous radiance L of the indoor atmosphere a (ε a,t1); the additional radiance L of the left window c1 (t) including the spontaneous radiance L of the window c1 (ε c ,t) and the reflected cavity ambient radiance L Ht (t); radiance of the cavity environment L Ht (t) is the spontaneous radiance L of the variable temperature transmission stent intracavity system tb (ε t ,t) and the atmospheric radiance L in the cavity a (ε a ,t); in the 3.0~5.2μm band, the average absorptivity and emissivity of the atmosphere are α a and ε a ; The average absorptivity and emissivity of a blackbody source are α B and ε B ; The average absorptivity, emissivity and transmittance of the window are α c , ε c and ρ c ; The emissivity of the indoor object and the system in the cavity are ε t1 , ε t .

[0018] The non-polarized light L emitted from the surface of the metal wire grid of the medium-wave infrared polarizer N Mainly includes reflected radiance, self radiance L s (t) and L min , defined as follows:

[0019] L N (t) = [1-(τ′1+τ′2) / 2-α p ]·[L Ht (t)+ρ c ·L Ht1 (t1)]+L s (ε p ,t)+2L min (9)

[0020] In the formula, α p , ε p are the emissivity and absorptivity of the metal wire grid in the working band, that is, the outgoing light field S of the medium-wave infrared polarized radiation source can be calculated. in The linear polarization degree P is:

[0021] L out =ρ c ·[L p +L N (t)]+L c2 (t1) (10)

[0022] L c2(t1) = L c2 (ε c ,t1)+(1-ρ c -α c )·L Ht1 (t1) (11)

[0023] P(T,t)=L pout / L out (12)

[0024] Where, the additional radiance L of the right window is c2 (t1) includes the spontaneous radiance of the window and the reflected indoor environment radiance L Ht1 (t1).

[0025] According to Kirchhoff's law, the radiance of the blackbody source, metal wire grid, environment and window spontaneous radiation in the normal incidence direction is:

[0026] Where c1 is the first radiation constant; c2 is the second radiation constant; ε y Indicates the emissivity of the object being measured; T t Indicates the temperature of the object being measured.

[0027] Liquid nitrogen is preferably used as the liquid inert gas because of its good refrigeration effect (can be reduced to -190°C), low cost and more environmentally friendly.

[0028] The present invention discloses a method for measuring the polarization degree of a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control, which is implemented based on a medium-wave infrared polarized radiation source performance test system. The medium-wave infrared polarized radiation source performance test system includes a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control and a medium-wave cooled focal plane thermal imager. The medium-wave cooled focal plane thermal imager includes an objective lens, a medium-wave analyzer, and an image plane detection unit. The medium-wave cooled focal plane thermal imager is placed in close proximity to the front of a planar blackbody source, the thermal imager is calibrated for grayscale-radiant illumination, and the transmittance ρ of the thermal imager objective lens and the additional radiance L are measured. α ; Establish a correction model for a post-polarizer medium-wave cooled polarization thermal imager based on the Stokes vector and the Mueller matrix, and measure the polarization degree of a temperature-controlled adjustable medium-wave infrared polarized radiation source according to the correction model; calibrate the functional relationship between the polarization degree of the output light field of the polarized radiation source and the blackbody source and the variable temperature transmission bracket according to the measurement results of the polarization degree of the medium-wave infrared polarized radiation source; and predict the polarization degree of the temperature-controlled adjustable medium-wave infrared polarized radiation source according to the calibrated functional relationship.

[0029] The method for measuring the polarization degree of a temperature-controlled adjustable medium-wave infrared polarized radiation source is implemented as follows:

[0030] Step 1: Place the medium-wave cooled polarization thermal imager right in front of the planar blackbody source and perform grayscale-radiance calibrating on the thermal imager.

[0031] Thermal imager output image grayscale signal G and incident radiance L B There is a nonlinear mapping relationship between them as shown in formula (14):

[0032] G=a×L B γ +b (14)

[0033] In the formula, a and b are gain and bias coefficients respectively; γ represents the nonlinear effect between the output signal and the input intensity. The integration time of the cooled medium-wave infrared polarization thermal imager is set, and the black body temperature is gradually adjusted from 10℃ to 75℃ at 1℃ intervals. The polarization thermal imager takes a set of grayscale images G; the grayscale signal of the thermal imager output image and the incident radiation brightness are nonlinearly calibrated according to formula (14) to determine the three fitting parameters a, b and γ.

[0034] Step 2: Measure the transmittance ρ and additional radiance L of the thermal imager objective lens α Place the polarization thermal imager right in front of the black body at T min With T max The temperature of the black body source is modulated within a certain range, and the radiance L of the light field behind the objective lens is measured. t ; Remove the objective lens, repeat the above steps, and measure the radiance L of the light field in front of the objective lens w .

[0035] The radiance L of the light field in front of the objective lens w for:

[0036] L t (T) = ρ(T)·L w (T)+L α (15)

[0037] Where, L w (T) and L t (T) are the radiance of the light field in front of and behind the objective lens of the thermal imager when the temperature of the black body source is T. When T is low, the transmittance ρ of the objective lens is w The attenuation of can be ignored, ρ(T min ) is approximately 1, due to the objective lens L α The impact of L t Slightly larger than L w Assuming L α It has nothing to do with the incident radiance of the objective lens and is a stable value when the environment does not change much. Find the transmittance ρ(L v ):

[0038] L α =Lt (T min )-L w (T min ) (16)

[0039] L v (T) = L t (T)-L α (17)

[0040] ρ(T)=L v (T) / L w (T) (18)

[0041] ρ(L v )=b0+b1L v +b2L v 2 +b3L v 3 +… (19)

[0042] Where, L v (T) is L w (T) radiance through the objective lens; T min is the lowest modulation temperature of the blackbody source; function ρ(L v ) is the objective lens transmittance ρ and L v linear relationship.

[0043] Step 3: Establish a correction model for the post-polarizer medium-wave cooled polarization thermal imager based on the Stokes vector and Mueller matrix. Assume that S in is the Stokes vector of the outgoing radiation field of the medium-wave infrared polarized radiation source; S int is the Stokes vector of the radiation field behind the objective lens; R is the additional radiance generated by the spontaneous radiation and reflected radiation of the polarizer at the image plane; τ1, τ2 and ρ p They represent the average transmittance of the main direction of the analyzer, the orthogonal direction and the substrate in the 3.0-5.2 μm band. The analyzer is regarded as a polarizer with no energy loss and a transmittance of ρ p The combination of glass slides, rotating the 4-aperture polarizer wheel of the medium-wave infrared polarization thermal imager, and performing four measurements at 0°, 60°, 120°, and without polarizer, respectively, obtains the grayscale images G0(T, t), G 60 (T,t),G 120 (T,t) and G NP (T, t). And converted into the corresponding incident radiance image L0(T, t), L 60 (T,t),L 120 (T,t) and L NP(T, t), if the Stokes vector of the radiation field behind the objective lens and the additional noise generated by the analyzer are R, then:

[0044]

[0045] By Stokes Vector S int , and inversely deduce the 0°, 60°, and 120° components of the light field radiated behind the objective lens:

[0046]

[0047] Additional radiation L of thermal imager objective α Approximately unpolarized light, the outgoing light field S of the medium-wave infrared polarized radiation source is in The 0°, 60°, and 120° components are:

[0048]

[0049] In the formula, ρ0, ρ 60 , 120 S in The 0°, 60°, and 120° component objective lens transmittance can be used to calculate the degree of polarization DoLP of the outgoing light field of the medium-wave infrared polarized radiation source. in :

[0050]

[0051] Step 4: Measure the polarization degree of the medium-wave infrared polarized radiation source.

[0052] The measurement steps are as follows:

[0053] (1) Turn on the relevant experimental equipment, place the medium-wave infrared polarizer in the sample holder, evacuate the vacuum chamber for 30 minutes, and then pour liquid nitrogen into the cooling chamber of the variable temperature transmission holder to cool the polarizer ambient temperature t to -120°C;

[0054] (2) Turn on the surface standard blackbody source, set the blackbody temperature T to 100°C, and use a thermal imager to take four sets of grayscale images. The grayscale image is calibrated with grayscale-radiance to obtain Will Substituting into equation (20) to remove the additional influence of the analyzer, we can obtain the Stokes vector S of the radiation field behind the objective lens of the medium-wave infrared polarization thermal imager: int (100,-120) ;

[0055] (3) S int (100,-120)Substituting into equations (21) and (22), eliminating the influence of the transmittance of the thermal imager objective lens, spontaneous radiation and reflected radiation, we can obtain the 0°, 60°, and 120° components of the outgoing light field of the medium-wave infrared polarized radiation source: and

[0056] (4) Substituting into equation (23), we can calculate the polarization degree of the outgoing light field of the medium-wave infrared polarized radiation source:

[0057] (5) Lower the blackbody temperature T, repeat experimental steps (2), (3) and (4), and measure every 5°C until the blackbody source temperature reaches 20°C. Calculate the polarization degree of the outgoing light field of the medium-wave infrared polarized radiation source.

[0058] (6) Raise the temperature t of the variable temperature transmission bracket vacuum chamber, repeat steps (2), (3), (4) and (5), measure every 10°C until the temperature reaches 30°C, and record the measurement data.

[0059] Step 5: According to the polarization degree measurement results of the medium-wave infrared polarized radiation source, the functional relationship between the linear polarization degree of the outgoing light field of the polarized radiation source and the blackbody source and the variable temperature transmission bracket is fitted, and the polarization degree of the measured temperature-controlled adjustable medium-wave infrared polarized radiation source is predicted according to the calibrated functional relationship.

[0060] DOLP for discrete points in (T,t) Perform a 4th order polynomial fit:

[0061]

[0062] In the formula, a ij is the fitting coefficient matrix. Define the measured value DoLP in The standard deviation E between (T, t) and the simulated value P(T, t) is:

[0063]

[0064] Beneficial effects:

[0065] 1. The present invention discloses a medium-wave infrared polarized radiation source with adjustable polarization degree and a polarization degree measurement method. The medium-wave infrared polarized radiation source with adjustable polarization degree is characterized in that a medium-wave infrared polarizer is placed in a variable temperature transmission bracket, and the variable temperature transmission bracket and the medium-wave infrared polarizer inside thereof are cooled by liquid inert gas to reduce the temperature of the variable temperature transmission bracket variable temperature chamber, effectively reducing the influence of the medium-wave infrared polarizer's spontaneous radiation and the negative interference of the stray light of the variable temperature transmission bracket. The present invention can accurately adjust the polarization degree of the emitted light of the radiation source within the medium wave band (3.0-5.2 μm) by changing the temperature of the black body source and the variable temperature transmission bracket.

[0066] 2. The present invention discloses a method for measuring the polarization degree of a temperature-controlled adjustable medium-wave infrared polarized radiation source. The medium-wave cooled focal plane thermal imager is placed in close proximity to the front of a planar blackbody source, the thermal imager is calibrated for grayscale-radiant illumination, and the transmittance ρ and additional radiance L of the thermal imager objective lens are measured. α ; Establish a correction model for a post-polarizer medium-wave cooled polarization thermal imager based on the Stokes vector and the Mueller matrix, and measure the polarization degree of a temperature-controlled adjustable medium-wave infrared polarized radiation source according to the correction model; calibrate the functional relationship between the polarization degree of the output light field of the polarized radiation source and the blackbody source and the variable temperature transmission bracket according to the measurement results of the polarization degree of the medium-wave infrared polarized radiation source; and predict the polarization degree of the temperature-controlled adjustable medium-wave infrared polarized radiation source according to the calibrated functional relationship.

[0067] 3. The present invention discloses a temperature-controlled and adjustable medium-wave infrared polarized radiation source and a method for measuring polarization degree. A medium-wave cooled focal plane detector whose objective lens spontaneous radiation, transmittance and analyzer stray radiation have been measured is used to calibrate the functional relationship between the linear polarization degree of the outgoing light field of the polarized radiation source and a blackbody source and a variable temperature transmission bracket, so as to more realistically obtain the performance parameters of the polarized radiation source, and improve the prediction accuracy of the polarization degree of the temperature-controlled and adjustable medium-wave infrared polarized radiation source according to the calibrated functional relationship.

[0068] 4. The temperature-controlled and adjustable medium-wave infrared polarized radiation source disclosed in the present invention can be used for performance calibration and detection of medium-wave infrared polarization imaging systems, can effectively improve the quantitative accuracy of medium-wave infrared polarization imaging systems, and provide new theoretical and experimental conditions to support the polarization calibration of thermal polarization imaging systems and their polarization performance evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 A flow chart of a medium-wave infrared polarized radiation source with adjustable polarization degree and a method for measuring polarization degree.

[0070] FIG2 is a diagram of a temperature-controlled adjustable medium-wave infrared polarized radiation source and its polarization degree measurement system of the present invention, wherein: FIG2(a) is a system block diagram, and FIG2(b) is a physical diagram.

[0071] Figure 3 It is a liquid nitrogen electrically controlled variable temperature transmission support structure, sample holder and window transmission spectrum, wherein: Figure 3 (a) is the sample rack, Figure 3 (b) is a variable temperature transmission bracket, Figure 3 (c) is the transmission spectrum of the CaF2 window.

[0072] Figure 4 This is a mathematical model of a medium-wave infrared polarized radiation source with adjustable polarization degree and temperature control.

[0073] Figure 5 This is the simulation result of the linear polarization degree of the light emitted by the medium-wave infrared polarized radiation source.

[0074] Figure 6 It is the fitting curve of the thermal imager output image grayscale G and the irradiance L of the response band.

[0075] Figure 7 is the radiance L of the light field in front of and behind the thermal imager objective lens w (T) and L t (T).

[0076] Figure 8 is the objective lens transmittance ρ and L ν The fifth-order polynomial fitting curve.

[0077] Fig. 9 This is the correction principle diagram of the post-polarizer-type medium-wave cooled polarization thermal imager.

[0078] Fig.10 is the measurement result of the polarization degree of the outgoing light field of the medium-wave infrared polarized radiation source when the black body temperature T is 100°C and the temperature of the variable temperature transmission bracket t is -120°C, where: Fig.10 (a), (b), (c) and (d) are four groups of grayscale images detected by the thermal imager; Fig.10 (e), (f), (g) and (h) are the radiance images corresponding to the grayscale images; Fig.10 (i), (j) and (k) are the 0°, 60° and 120° components of the outgoing light field of the medium-wave infrared polarized radiation source; Fig.10 (l) is the polarization degree of the outgoing light field from the medium-wave infrared polarized radiation source.

[0079] Fig.11 For DOLP in (T,t) Discrete point three-dimensional surface.

[0080] Fig.12 For DoLP in (T,t) discrete points fitting surface.

[0081] Fig.13 Comparison chart of simulation and measurement results of medium-wave infrared polarized radiation source. DETAILED DESCRIPTION

[0082] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. It should be pointed out that the described examples are for facilitating the understanding of the present invention and do not have any limiting effect on it.

[0083] The temperature-controlled adjustable medium-wave infrared polarized radiation source and its polarization degree measurement system provided in this embodiment are shown in the physical picture and system block diagram in FIG2. It includes a standard black body source (EOI CDS 100-04) module, a variable temperature transmission bracket (P / N GS21525) module and a medium-wave cooled polarization thermal imager (JADE MWIR) module, and its detection principle is: the unbiased radiation of the planar black body source is converted into partial polarized light (composed of partial polarized radiation transmitted by the black body, spontaneous radiation of the polarizer, self-radiation of the window, etc., reflected radiation and environmental stray radiation, etc.) through the infrared windows at both ends of the variable temperature transmission bracket and the medium-wave infrared polarizer. By adjusting the temperature of the black body source and the variable temperature transmission bracket, the polarization degree of the outgoing light field of the medium-wave infrared polarized radiation source can be changed. The medium-wave polarization thermal imager consists of a medium-wave cooled thermal imager and a 4-aperture filter wheel installed in the back intercept of the infrared objective. The objective of the thermal imager is adjusted to focus on the medium-wave infrared polarizer. By rotating the wheel, partial polarized radiation intensity images of the infrared polarized radiation source target at 0°, 60°, 120° analyzer directions and without an analyzer are collected respectively. Finally, the polarization degree of the outgoing light field of the medium-wave infrared polarized radiation source at different blackbody sources and variable temperature transmission bracket temperatures can be calibrated, thereby providing a temperature-controlled infrared polarization radiation source with adjustable polarization degree for polarization performance testing of other polarization thermal imagers.

[0084] The temperature stability of the 4-inch high-precision surface temperature difference blackbody source CDS 100-04 of EOI Company of the United States is ±0.01℃; the temperature range in absolute mode is 0℃~100℃; the temperature range in temperature difference mode is -25℃~+75℃; the temperature control accuracy in absolute mode is 0.01℃; the maximum temperature display resolution is 0.0001℃; the emissivity is 0.97±0.02.

[0085] The variable temperature transmission stand P / N GS21525 of SPECAC, UK, is a universal variable temperature transmission stand (such as Figure 3), a sample holder equipped with a medium-wave infrared polarizer is placed in the vacuum chamber, liquid nitrogen is added to the sample holder and digital temperature control is performed, the effective temperature control range is -190℃~250℃, and the rising or falling temperature control rate is about 10℃ / min; the temperature setting resolution is 1℃, and the temperature stability is better than ±2℃; the window material can be selected according to the working wavelength, the CaF2 window transmission spectrum range of the component can be from far ultraviolet (130nm) to far infrared (8μm), and the transmittance in the medium-wave infrared working band of 3.0~5.2μm is greater than 94%; before adding liquid nitrogen to the sample holder, the vacuum chamber must be emptied to above 0.05Torr (6.67Pa) to prevent window crystallization; the ANE diaphragm pump is connected to the vacuum chamber through a pipeline for operation, and the maximum vacuum is 0.5mbar (5Pa), which meets the vacuum requirements.

[0086] The performance indicators of the MCT-based cooled mid-wave infrared focal plane thermal imager JADE MWIR are shown in Table 1. Three 1-inch mid-wave infrared polarizers WP25M-IRA (performance parameters are shown in Table 2) from Thorlabs are installed on the 4-aperture polarizer wheel as infrared analyzers. The polarizer azimuth angles are set to 0°, 60°, and 120°, respectively, and an intensity channel is added to form a mid-wave infrared polarization thermal imager with three polarization direction intensities + total intensity.

[0087] Table 1 Performance indicators of JADE MWIR

[0088]

[0089] Table 2 Performance indicators of WP25M-IRA

[0090]

[0091]

[0092] like Figure 4 As shown, the total radiance L of the emitted light field of a temperature-controlled polarization-adjustable medium-wave infrared polarized radiation source (3.0-5.2 μm) blackbody radiation source disclosed in this embodiment is B (T) mainly includes the spontaneous radiance and reflected radiance of the blackbody source; the transmittance of the Al2O3 substrate of the mid-wave infrared polarizer About 0.9, the center of the substrate is a 5mm×5mm unidirectional metal wire grid, and the surface of the non-wire grid is coated with opaque material; unbiased radiance L B (T) Partially polarized light is formed through the metal wire grid, which can be regarded as completely polarized light L p and unpolarized light L N The superposition of c is the average transmittance of the CaF2 window in the 3.0-5.2μm band; Lc is the spontaneous radiance and reflected radiance of the CaF2 window, which is related to the ambient temperature; L H is the atmospheric radiance.

[0093] In the 3.0-5.2μm band, when detecting targets at close range, it is assumed that the surface of the object being measured satisfies the gray body condition and the atmospheric α a =ε a =0; standard blackbody source surface α B =ε B =0.97; CaF2 window α c =0,ε c =0,ρ c =0.94; polarizer metal wire grid τ′1=0.813, τ′2=0.006, α p =0,ε p =0.28; Intraluminal stent (polished stainless steel): ε t =0.2; Indoor environment (smooth cast iron) ε t1 = 0.5. When the indoor experimental environment temperature t1 is 20°C, the relationship between the polarization degree P of the output light field of the medium-wave infrared polarized radiation source and the black body source temperature T and the temperature t in the variable temperature transmission bracket cavity can be obtained from equations (1) to (13), as follows: Figure 5 The results show that the polarization degree of the radiation source output light field increases with the increase of the black body source temperature and decreases with the increase of the variable temperature transmission bracket temperature. That is, by modulating the temperature T and t, the radiation source output light field S can be controlled. in degree of polarization.

[0094] The present embodiment discloses a method for measuring the polarization degree of a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control. The grayscale-radiance calibration of the thermal imager is performed. According to formula (14), the grayscale signal of the thermal imager output image and the incident radiation brightness are nonlinearly calibrated to determine three fitting parameters a=1297.7945, γ=0.9904, b=660.4091, that is, the fitting curve of the grayscale G of the thermal imager output image and the irradiance L of the response band is as follows: Figure 6 shown.

[0095] Measuring the transmittance ρ and additional radiance L of thermal imager objective lens α Place the polarization thermal imager right in front of the black body, adjust the black body source temperature between 10℃ and 75℃, and measure the radiance L of the light field in front of and behind the thermal imager objective lens when the black body source temperature is T. w (T) and L t (T), the measurement results are as follows Figure 7 As shown. The lowest modulation temperature T of the blackbody source min is 10℃, the additional radiance L generated by the spontaneous radiation and reflected radiation of the objective lens can be calculated by formula (16): α=0.0473(W / (sr.m 2 )). Use the least square method to calculate the objective lens transmittance ρ and L ν Perform polynomial fitting, and the fifth-order fitting curve is as follows Figure 8 As shown, the root mean square error RMSE is about 0.00047, which can well reflect the distribution of sample points. The fitting function is as follows:

[0096] ρ(L ν )=C·[L ν 0 L ν 1 L ν 2 L ν 3 L ν 4 L ν 5 ] T (26)

[0097] Coefficient matrix: C = [1.0403 -0.0418 0.0114 -0.0017 1.2226 × 10 -4 -3.5261×10 -6 ]

[0098] The correction model of the post-polarizer medium-wave cooling polarization thermal imager is as follows: Fig. 9 According to the corrected model, the polarization degree of the medium-wave infrared polarized radiation source is measured. The measurement results when the black body temperature T is 100°C and the variable temperature transmission bracket temperature t is -120°C are as follows: Fig.10 As shown. Among them, Fig.10 (a), (b), (c) and (d) are four sets of grayscale images detected by the thermal imager. and Fig.10 (e), (f), (g) and (h) are the radiance images corresponding to the grayscale images. and Fig.10 (i), (j) and (k) are the 0°, 60° and 120° components of the outgoing light field of the medium-wave infrared polarized radiation source. and Fig.10 (l) is the degree of polarization DoLP of the outgoing light field of the medium-wave infrared polarized radiation source in (100,-120) .Depend on Fig.10 It can be seen that when the pixel point [XY] = [180130]:

[0099]

[0100]

[0101]

[0102] Plotting discrete points DOLP in (T,t) (T = 20 ~ 100 ° C, interval 5 ° C; t = -120 ~ 30 ° C, interval 10 ° C) three-dimensional surface such as Fig.11 As shown. Among them, {DOLP in (T,t)} max =DOLP in (100,-120) =0.9072, {DOLP in (T,t)} min =DOLP in (20,30) =0.2683. As shown in formula (24), for discrete point DOLP in (T,t) Perform a 4th-order polynomial (Poynomial) fit, and the fitting coefficient matrix is:

[0103]

[0104] Fitting function DoLP in (T,t) surface such as Fig.12 As shown, the fitting root mean square standard deviation RMSE = 8.909×10 -3 , the coefficient of determination R-square = 0.997, with good fitting results.

[0105] Fig.13 Given DoLP in (T,t) and Figure 4 Comparison of the model simulation polarization degree P shows that as the temperature of the blackbody source increases, the difference between the measured value and the simulated value gradually decreases. The standard deviation E between the measured value and the simulated value is defined as shown in formula (25), T = 20 + 5i, t = -120 + 10j; n is the number of measured discrete points. When i = 0, j < 16, the E value is 0.0566; when i = 10, j < 10, the E value is 0.0160. Increasing T and reducing t can reduce the deviation between the measured value and the simulated value. The main reason for the deviation is C aThe spontaneous radiation and reflected radiation of the F2 window, polarizer and thermal imager objective are often partially polarized light. In summary, based on the above experiments, T and t can be adjusted based on formula (24) to obtain a medium-wave infrared polarized radiation source with a certain degree of polarization, that is, the prediction of the polarization degree of the medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control is realized.

[0106] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A temperature-controlled medium-wave infrared polarized radiation source with adjustable polarization degree, characterized in that: It includes a high-precision surface temperature difference blackbody source, a variable temperature transmission bracket, and a medium-wave infrared polarizer; the optical path is a high-precision surface temperature difference blackbody source emitting unpolarized light L B (T) passes through the left window of the variable temperature transmission bracket, the medium-wave infrared polarizer and the right window to form a partially polarized light, which is regarded as a completely polarized light L p and unpolarized light L N The superposition of the medium-wave infrared polarized radiation source emits the light field S in The linear polarization degree P is the completely polarized light component L pout In the total radiance L out The proportion of the medium-wave infrared polarizer in the variable temperature transmission bracket is placed, and the temperature of the variable temperature transmission bracket and the medium-wave infrared polarizer inside it is adjusted by liquid inert gas to change the non-polarized light L N ; By adjusting the temperature of the high-precision surface temperature difference blackbody source, L B (T); that is, by changing the temperature of the black body source and the variable temperature transmission bracket, the polarization degree of the emitted light from the radiation source is accurately adjusted to realize a temperature-controlled and adjustable medium-wave infrared polarized radiation source; The fully polarized light L in the outgoing light field pout Defined as: 50 B (T)=L B (e B ,T)+(1-α B )·L Ht1 (t1) (4) 50 Ht1 (t1)=(1-α a )·L tb (e t1 ,t1)+(1-α a )·L a (e a ,t1) (5) L c1 (t)=L c1 (e c ,t)+(1-ρ c -a c )·L Ht (t) (6) L Ht (t)=(1-a a )·L tb (e t ,t)+(1-a a )·L a (e a ,t) (7) L pout =ρ c ·[(L max +L N (t))-(L min +L N (t))]L p =ρ c ·L p (8) Where, T is the temperature of the blackbody source; t is the temperature inside the variable temperature transmission bracket cavity; t1 is the indoor ambient temperature; L max , L min is the transmitted radiance of the metal wire grid in the main direction and orthogonal direction of the medium-wave infrared polarizer; τ1′ and τ2′ are the average transmittance of the metal wire grid in the main direction and orthogonal direction in the working band; the blackbody source radiation brightness L B (T) is the black body self-luminous radiance L B (ε B ,T) and the reflected indoor environment radiance L Ht1 (t1) superposition; indoor environment radiance L Ht1 (t1) includes the spontaneous radiance L of indoor objects tb (ε t1 ,t1) and the spontaneous radiance L of the indoor atmosphere a (ε a ,t1); the additional radiance L of the left window c1 (t) includes the spontaneous radiance L of the window c1 (ε c ,t) and the reflected cavity ambient radiance L Ht (t); radiance of the cavity environment L Ht (t) is the spontaneous radiance L of the variable temperature transmission stent intracavity system tb (ε t ,t) and the atmospheric radiance L in the cavity a (ε a ,t); in the 3.0~5.2μm band, the average absorptivity and emissivity of the atmosphere are α a and ε a ; The average absorptivity and emissivity of a blackbody source are α B and ε B ; The average absorptivity, emissivity and transmittance of the window are α c , ε c and ρ c ; The emissivity of the indoor object and the system in the cavity are ε t1 , ε t ; The non-polarized light L of the light field emitted from the surface of the metal wire grid of the medium-wave infrared polarizer N Mainly includes reflected radiance, self radiance L s (t) and L min , defined as follows: 50 N (t)=[1-(τ1′+τ2′) / 2-α p ]·[L Ht (t)+ρ c ·L Ht1 (t1)]+L s (e p ,t)+2L min (9) In the formula, α p , ε p are the emissivity and absorptivity of the metal wire grid in the working band, that is, the outgoing light field S of the medium-wave infrared polarized radiation source can be calculated. in The linear polarization degree P is: 50 out =ρ c ·[L p +L N (t)]+L c2 (t1) (10) 50 c2 (t1)=L c2 (e c ,t1)+(1-ρ c -α c )·L Ht1 (t1) (11) P(T,t)=L pout / L out (12) Where, the additional radiance L of the right window is c2 (t1) includes the window spontaneous radiance and reflected indoor environment radiance L Ht1 (t1); According to Kirchhoff's law, the radiance of the blackbody source, metal wire grid, environment and window spontaneous radiation in the normal incidence direction is: Where c1 is the first radiation constant; c2 is the second radiation constant; ε y Indicates the emissivity of the object being measured; T t Indicates the temperature of the object being measured.

2. A temperature-controlled medium-wave infrared polarized radiation source with adjustable polarization degree as claimed in claim 1, characterized in that: The liquid inert gas is liquid nitrogen.

3. A method for measuring the polarization degree of a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control, which is implemented based on a medium-wave infrared polarized radiation source performance test system, wherein the medium-wave infrared polarized radiation source performance test system comprises a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control and a medium-wave cooled focal plane thermal imager; the medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control is a medium-wave infrared polarized radiation source with adjustable polarization degree under temperature control as claimed in claim 1 or 2, characterized in that: The medium wave cooled focal plane thermal imager comprises an objective lens, a medium wave analyzer and an image plane detection unit; The implementation method is as follows: Step 1: Place the medium-wave cooled polarization thermal imager close to the front of the planar blackbody source and perform grayscale-radiance calibrating on the thermal imager; Step 2: Measure the transmittance ρ and additional radiance L of the thermal imager objective lens α ; Place the polarization thermal imager right in front of the black body, at T min With T max The temperature of the black body source is modulated within a certain range, and the radiance L of the light field behind the objective lens is measured. t ; Remove the objective lens, repeat the above steps, and measure the radiance L of the light field in front of the objective lens w ; Step 3: Establish a correction model for the post-polarizer medium-wave cooled polarization thermal imager based on the Stokes vector and Mueller matrix; Step 4: Measure the polarization degree of the medium-wave infrared polarized radiation source; Step 5: According to the polarization degree measurement results of the medium-wave infrared polarized radiation source, the functional relationship between the linear polarization degree of the outgoing light field of the polarized radiation source and the blackbody source and the variable temperature transmission bracket is fitted, and the polarization degree of the measured temperature-controlled adjustable medium-wave infrared polarized radiation source is predicted according to the calibrated functional relationship.

4. A method for measuring the polarization degree of a temperature-controlled medium-wave infrared polarized radiation source with adjustable polarization degree as claimed in claim 3, characterized in that: In step 2, The radiance L of the light field in front of the objective lens w for: L t (T)=ρ(T)·L w (T)+L α (15) Where, L w (T) and L t (T) are the radiance of the light field in front of and behind the objective lens of the thermal imager when the temperature of the black body source is T. When T is low, the transmittance ρ of the objective lens is w The attenuation of can be ignored, ρ(T min ) is approximately 1, due to the objective lens L α The impact of L t Slightly larger than L w Assume L α It has nothing to do with the incident radiance of the objective lens and is a stable value when the environment does not change much. Find the transmittance ρ(L v ): L α =L t (T min )-L w (T min ) (16) L v (T)=L t (T)-L α (17) ρ(T)=L v (T) / L w (T) (18) ρ(L v )=b0+b1L v +b2L v 2 +b3L v 3 +L (19) Where, L v (T) is L w (T) radiance through the objective lens; T min is the lowest modulation temperature of the blackbody source; function ρ(L v ) is the objective lens transmittance ρ and L v linear relationship.

5. A method for measuring the polarization degree of a temperature-controlled medium-wave infrared polarized radiation source with adjustable polarization degree as claimed in claim 4, characterized in that: In step three, S in is the Stokes vector of the outgoing radiation field of the medium-wave infrared polarized radiation source; S int is the Stokes vector of the radiated light field behind the objective lens; R is the additional radiance generated by the spontaneous radiation and reflected radiation of the polarizer at the image plane; τ1, τ2 and ρ p They represent the average transmittance of the main direction of the analyzer, the orthogonal direction and the substrate in the 3.0-5.2 μm band respectively; the analyzer is regarded as a polarizer with no energy loss and a transmittance of ρ p The combination of glass slides, rotating the 4-aperture polarizer wheel of the medium-wave infrared polarization thermal imager, and performing four measurements at 0°, 60°, 120°, and without polarizer, respectively, obtains the grayscale images G0(T, t), G 60 (T,t),G 120 (T,t) and G NP (T, t); and converted into the corresponding incident radiance image L0(T, t), L 60 (T,t),L 120 (T,t) and L NP (T, t), if the Stokes vector of the radiation field behind the objective lens and the additional noise generated by the analyzer are R, then: By Stokes Vector S int , and inversely deduce the 0°, 60°, and 120° components of the light field radiated behind the objective lens: Additional radiation L of thermal imager objective α Approximately unpolarized light, the outgoing light field S of the medium-wave infrared polarized radiation source is in The 0°, 60°, and 120° components are: In the formula, ρ0, ρ 60 , 120 S in The 0°, 60°, and 120° component objective lens transmittance can be used to calculate the degree of polarization DoLP of the outgoing light field of the medium-wave infrared polarized radiation source. in :

6. A method for measuring the polarization degree of a temperature-controlled and adjustable medium-wave infrared polarized radiation source according to claim 5, characterized in that: Step 4 The measurement steps are as follows: (1) Turn on the relevant experimental equipment, place the medium-wave infrared polarizer in the sample holder, evacuate the vacuum chamber for 30 minutes, and then pour liquid nitrogen into the cooling chamber of the variable temperature transmission holder to cool the polarizer ambient temperature t to -120°C; (2) Turn on the surface standard blackbody source, set the blackbody temperature T to 100°C, and use a thermal imager to take four sets of grayscale images. The grayscale image is calibrated with grayscale-radiance to obtain Will Substituting into equation (20) to remove the additional influence of the analyzer, we can obtain the Stokes vector S of the radiation field behind the objective lens of the medium-wave infrared polarization thermal imager: int (100,-120) ; (3) S int (100,-120) Substituting into equations (21) and (22), eliminating the influence of the transmittance of the thermal imager objective lens, spontaneous radiation and reflected radiation, we can obtain the 0°, 60°, and 120° components of the outgoing light field of the medium-wave infrared polarized radiation source: and (4) Substituting into equation (23), we can calculate the polarization degree DoLP of the outgoing light field of the medium-wave infrared polarized radiation source: in (100,-120) ; (5) Lower the blackbody temperature T, repeat experimental steps (2), (3) and (4), and measure every 5°C until the blackbody source temperature reaches 20°C. Calculate the degree of polarization DOLP of the outgoing light field of the medium-wave infrared polarized radiation source. in (T,-120) ; (6) Raise the temperature t of the variable temperature transmission bracket vacuum chamber, repeat steps (2), (3), (4) and (5), measure every 10°C until the temperature reaches 30°C, and record the measurement data.

7. A method for measuring the polarization degree of a temperature-controlled and adjustable medium-wave infrared polarized radiation source according to claim 6, characterized in that: In step five, DOLP for discrete points in (T,t) Perform a 4th order polynomial fit: In the formula, a ij is the fitting coefficient matrix; define the measured value DoLP in The standard deviation E between (T, t) and the simulated value P(T, t) is:

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