Birefringent crystal wind imaging interferometer capable of eliminating temperature difference

Abstract

The invention discloses a birefringent crystal wind imaging interferometer capable of eliminating temperature difference, and relates to the technical field of atmospheric detection instruments. Comprising a first birefringent crystal, a second birefringent crystal, a half-wave plate, a first birefringent crystal and a second birefringent crystal which are arranged in an arrayed mode, the included angle between the optical axis of the first birefringent crystal and the positive direction of the x axis and the included angle between the optical axis of the second birefringent crystal and the positive direction of the x axis are 45 degrees, and the included angle between the optical axis of the second birefringent crystal and the positive direction of the x axis is 135 degrees. Wherein the positive direction of the x axis is a transverse direction perpendicular to the optical axis; the change direction of the thickness and the refractive index of the first birefringent crystal along with the temperature is opposite to the change direction of the thickness and the refractive index of the second birefringent crystal along with the temperature. Through the principle that optical path difference variations generated by the two birefringent crystals are complementary, the temperature difference elimination effect of the birefringent crystal wind imaging interferometer is effectively improved, and the stability of the birefringent interferometer in different temperature environments is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of atmospheric detection instruments, and in particular to a temperature difference eliminating birefringent crystal wind imaging interferometer. Background Art

[0002] The wind field in the upper atmosphere is an important atmospheric dynamics parameter. High-precision and continuous detection of the wind field can provide rich analytical data for the study of local or global atmospheric fluctuations, the coupling process between the various layers of the atmosphere, and the characteristics of material and energy transport on a global scale. The atmospheric motion in the mesosphere and lower thermosphere is dominated by large-scale tides, planetary waves, and large-scale and small-scale gravity waves. Space-based observation data show that these fluctuations have an important driving effect on the large-scale circulation in the middle atmosphere. However, the coupling, energy dissipation and interaction mechanisms are still controversial. Therefore, it is necessary to perform high-temporal and spatial resolution imaging detection of the dynamic processes in the middle and upper atmosphere, and to finely characterize the atmospheric disturbance image in order to improve and develop the theoretical model of atmospheric dynamics. Passive wind imaging interferometry technology uses the naturally generated airglow radiation in the atmosphere as a light source to detect the atmospheric motion state (wind field). Particles that produce airglow radiation (such as O2, O and OH, etc.) will move with the atmosphere, and the airglow radiation spectrum produced by them will produce Doppler frequency shifts due to their relative motion to the observer. By measuring this Doppler frequency shift, we can know the movement speed of the target atmosphere along the line of sight, and thus invert the atmospheric wave characteristics.

[0003] In the prior art, the birefringent crystal module of the birefringent crystal wind field interferometer consists of two birefringent crystals and a half-wave plate. The two birefringent crystals are respectively located before and after the half-wave plate, and the angle between their optical axes and the positive direction of the x-axis differs by 90°, thereby achieving a wide field effect.

[0004] However, since the two birefringent crystals use the same crystal material, when the ambient temperature changes, the two crystals change in the same trend, resulting in a larger change in the reference optical path difference, which reduces the stability of the birefringent wind imaging interferometer. Therefore, it is a problem to be solved to give full play to the advantages of the birefringent wind imaging interferometer and improve its stability. Summary of the invention

[0005] Based on this, it is necessary to provide a birefringent crystal wind imaging interferometer that eliminates temperature differences in order to address the above technical issues.

[0006] The present invention adopts the following technical solutions:

[0007] A birefringent crystal wind imaging interferometer, comprising:

[0008] A first birefringent crystal, a second birefringent crystal, a half-wave plate, a first birefringent crystal and a second birefringent crystal are arranged, wherein the angle between the optical axes of the first birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 45°, and the angle between the optical axes of the second birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 135°; wherein the positive direction of the x-axis is a lateral direction perpendicular to the optical axis;

[0009] The directions in which the thickness and refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and refractive index of the second birefringent crystal change with temperature, so that the changes in the reference optical path difference produced by the first birefringent crystal and the second birefringent crystal are opposite, and the changes in the total optical path difference produced by the first birefringent crystal and the second birefringent crystal with temperature are close to 0.

[0010] A method for eliminating temperature difference of a birefringent crystal wind imaging interferometer, comprising:

[0011] Selecting materials for the first birefringent crystal and the second birefringent crystal so that the directions in which the thickness and the refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and the refractive index of the second birefringent crystal change with temperature;

[0012] According to the material selection results of the first birefringent crystal and the second birefringent crystal, the first birefringent crystal and the second birefringent crystal are paired so that the change of the total optical path difference generated by the first birefringent crystal and the second birefringent crystal with temperature is close to 0, so as to improve the temperature difference elimination effect of the birefringent crystal wind imaging interferometer.

[0013] Preferably, the material selection for the first birefringent crystal and the second birefringent crystal specifically includes:

[0014] Constructing a birefringent crystal library and recording the parameters of each birefringent crystal; wherein the birefringent crystal includes a first birefringent crystal and a second birefringent crystal;

[0015] Arbitrarily combining the first birefringent crystal and the second birefringent crystal in the birefringent crystal library in pairs to obtain a birefringent crystal combination and obtain crystal parameters of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination;

[0016] The crystal thicknesses of the first birefringent crystal and the second birefringent crystal in each birefringent crystal combination are obtained according to the preset reference optical path difference and the crystal parameters of the first birefringent crystal and the second birefringent crystal in each birefringent crystal combination.

[0017] Preferably, pairing the first birefringent crystal and the second birefringent crystal specifically includes:

[0018] Calculating the total optical path difference variation between the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination according to the crystal thicknesses of the first birefringent crystal and the second birefringent crystal;

[0019] A birefringent crystal combination whose total optical path difference variation is closest to 0 under different temperatures and different viewing angles is selected as an optimal pairing combination of the first birefringent crystal and the second birefringent crystal.

[0020] Preferably, the birefringent crystal comprises: calcite, lithium niobate, yttrium vanadate, titanium dioxide and tellurium dioxide.

[0021] Preferably, the parameters of each birefringent crystal include: unit thickness d0, change in unit thickness Δd, temperature change ΔT, unit refractive index n0, change in unit refractive index Δn, thermal expansion coefficient α and thermo-optic coefficient β;

[0022] The thermal expansion coefficient is the ratio of the change in unit thickness to the change in temperature of the birefringent crystal when the temperature changes, that is,

[0023] The thermo-optic coefficient is the ratio of the change in unit refractive index to the change in temperature of a birefringent crystal when the temperature changes, that is,

[0024] Preferably, the step of obtaining the crystal thickness of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination specifically includes:

[0025] According to the preset reference optical path difference, the parameters of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination are substituted into the calculation formula to obtain the crystal thickness of the first birefringent crystal and the second birefringent crystal. The calculation formula is as follows:

[0026]

[0027] Wherein, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal, Δ0 is the preset reference optical path difference, and n o1 and n o2 is the ordinary light refractive index of the first birefringent crystal and the second birefringent crystal, n e1 and n e2 is the extraordinary refractive index of the first birefringent crystal and the second birefringent crystal, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal, and β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal.

[0028] Preferably, the calculation formula of the crystal thickness is simplified to x=A -1 B;

[0029] Where x is the thickness matrix of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination. A represents the crystal parameter matrix B represents the optical path difference matrix

[0030] Preferably, the total optical path difference change is close to 0, and the formula is:

[0031]

[0032] In the formula, is the change in optical path difference produced by the first birefringent crystal, is the change in the optical path difference caused by the second birefringent crystal, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal respectively, n1 and n2 are the refractive indices of the first birefringent crystal and the second birefringent crystal respectively, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal respectively, β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal respectively, and Δ is the total optical path difference change.

[0033] At least one of the above technical solutions adopted by the present invention can achieve the following beneficial effects:

[0034] The present invention improves the double crystal module in the existing double refraction crystal wind imaging interferometer, that is, another double refraction crystal is added on the basis of the original double crystal module, so that the crystal thickness and refractive index of the two double refraction crystals change in opposite directions with temperature, and then the directions of the reference optical path difference changes generated by the two double refraction crystals are also opposite, and finally the total optical path difference change generated by the two crystals is close to 0, thereby improving the stability of the birefringence interferometer under different temperature environments.

[0035] In addition, the angle between the optical axes of the first birefringent crystal and the second birefringent crystal in front of the half-wave plate and the positive direction of the x-axis is set to 45°, and the angle between the optical axes of the first birefringent crystal and the second birefringent crystal in the back of the half-wave plate and the positive direction of the x-axis is set to 135°, so that the interferometer maintains a good wide-field effect under different temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0037] Figure 1 A schematic diagram of the structure of a birefringent crystal module of a birefringent crystal wind imaging interferometer for eliminating temperature differences provided by the present invention;

[0038] Figure 2A schematic flow chart of a method for selecting a newly added birefringent crystal material and an original birefringent crystal material for a birefringent crystal wind imaging interferometer for eliminating temperature differences provided by the present invention;

[0039] Figure 3 This is a diagram showing the field-of-view widening effect of a birefringent crystal wind imaging interferometer for eliminating temperature differences provided by the present invention;

[0040] Figure 4 A comparison diagram of the temperature difference elimination effect of a birefringent crystal wind imaging interferometer for eliminating temperature difference provided by the present invention;

[0041] Figure 5 A comparison diagram of the temperature difference elimination effects of a birefringent crystal wind imaging interferometer for temperature difference elimination provided by the present invention using a pairing of CaCO3 and TiO2 and other pairing combinations.

[0042] Figure 6 A comparison diagram of the temperature difference elimination method of a birefringent crystal wind imaging interferometer provided by the present invention and the temperature difference elimination effect without compensation;

[0043] Figure 7 A comparison diagram of the temperature difference elimination method and the uncompensated field of view widening effect of a birefringent crystal wind imaging interferometer provided by the present invention.

[0044] Reference numerals:

[0045] 1-first birefringent crystal; 2-second birefringent crystal; 3-half-wave plate; 4-first birefringent crystal; 5-second birefringent crystal. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0048] like Figure 1 As shown, a birefringent crystal wind imaging interferometer comprises: a first birefringent crystal, a second birefringent crystal, a half-wave plate, a first birefringent crystal and a second birefringent crystal arranged in an arranged manner, wherein the angle between the optical axes of the first birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 45°, and the angle between the optical axes of the second birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 135°; wherein the positive direction of the x-axis is a lateral direction perpendicular to the optical axis;

[0049] The directions in which the thickness and refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and refractive index of the second birefringent crystal change with temperature, so that the changes in the reference optical path difference produced by the first birefringent crystal and the second birefringent crystal are opposite, and the changes in the total optical path difference produced by the first birefringent crystal and the second birefringent crystal with temperature are close to 0.

[0050] A method for eliminating temperature difference of a birefringent crystal wind imaging interferometer, comprising:

[0051] Selecting materials for the first birefringent crystal and the second birefringent crystal so that the directions in which the thickness and the refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and the refractive index of the second birefringent crystal change with temperature;

[0052] According to the material selection results of the first birefringent crystal and the second birefringent crystal, the first birefringent crystal and the second birefringent crystal are paired so that the change of the total optical path difference generated by the first birefringent crystal and the second birefringent crystal with temperature is close to 0, so as to improve the temperature difference elimination effect of the birefringent crystal wind imaging interferometer.

[0053] In addition, the total optical path difference change is close to 0 ， The formula is:

[0054]

[0055] In the formula, is the change in optical path difference produced by the first birefringent crystal, is the change in the optical path difference caused by the second birefringent crystal, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal respectively, n1 and n2 are the refractive indices of the first birefringent crystal and the second birefringent crystal respectively, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal respectively, β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal respectively, and Δ is the total optical path difference change.

[0056] In addition, the material selection is performed for the first birefringent crystal and the second birefringent crystal, and the flow chart thereof is as follows: Figure 2 As shown, the following steps are included:

[0057] S101: construct a birefringent crystal library and enter the parameters of each birefringent crystal.

[0058] Among them, the birefringent crystal library includes: calcite, lithium niobate, yttrium vanadate, titanium dioxide, and tellurium dioxide.

[0059] The parameters of each birefringent crystal include: unit thickness d0, change in unit thickness Δd, temperature change ΔT, unit refractive index n0, change in unit refractive index Δn, thermal expansion coefficient α and thermo-optic coefficient β.

[0060] The thermal expansion coefficient is the ratio of the change in unit thickness to the change in temperature of a birefringent crystal when the temperature changes, that is,

[0061] The thermo-optic coefficient is the ratio of the change in unit refractive index to the change in temperature when the temperature of a birefringent crystal changes, that is,

[0062] S102: Obtain a birefringent crystal combination by arbitrarily combining any two of the birefringent crystals in the birefringent crystal library and obtaining crystal parameters of a first birefringent crystal and a second birefringent crystal in the birefringent crystal combination.

[0063] S103: Acquire the crystal thicknesses of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination according to the preset reference optical path difference and the parameters of each group of birefringent crystal combinations.

[0064] According to the preset reference optical path difference, the parameters of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination are substituted into the calculation formula to obtain the crystal thickness of the first birefringent crystal and the second birefringent crystal. The calculation formula is as follows:

[0065]

[0066] Wherein, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal, Δ0 is the preset reference optical path difference, and n o1 and n o2 is the ordinary light refractive index of the first birefringent crystal and the second birefringent crystal, n e1 and n e2 is the extraordinary refractive index of the first birefringent crystal and the second birefringent crystal, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal, and β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal.

[0067] In addition, the calculation formula of crystal thickness is simplified to x = A -1 B.

[0068] Where x is the thickness matrix of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination. A represents the crystal parameter matrix B represents the optical path difference matrix

[0069] S104: Calculating a change in a reference optical path difference between the first birefringent crystal and the second birefringent crystal according to the crystal thicknesses of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination.

[0070] S105: selecting a newly added birefringent crystal combination whose reference optical path difference variation amount generated under different temperatures and different viewing angles is closest to 0 as the optimal newly added birefringent crystal pairing combination.

[0071] The acquisition of the optimal pairing combination of the first birefringent crystal and the second birefringent crystal specifically includes: under different temperatures and different viewing angles, the birefringent crystal combination whose optical path difference variation is closest to 0 is the optimal pairing combination of the first birefringent crystal and the second birefringent crystal.

[0072] This embodiment is designed for the 557nm spectrum, and the preset value of the reference optical path difference of the birefringent crystal wind imaging interferometer is 0.67cm. Through the above steps, the optimal birefringent crystal pairing combination is obtained, which specifically includes: the material of the first birefringent crystal is CaCO3, and the material of the second birefringent crystal is TiO2. The thickness of the first birefringent crystal is 70.14mm, and the thickness of the second birefringent crystal is 177.54mm.

[0073] Computer testing and analysis of the performance of the temperature difference elimination method of the two birefringent crystal pairs of the present invention found that it can achieve ideal field of view widening and temperature difference elimination effects. The field of view widening effect is as follows: Figure 3 As shown in the figure, the optical path difference changes slightly with the field of view, and the effect of eliminating temperature difference is as follows: Figure 3 As shown, the requirements of wide field and temperature compensation are well met.

[0074] like Figure 4 As shown, other birefringent crystals in the birefringent crystal library are selected for pairing, and the temperature difference elimination effects of CaCO3 and TiO2 are compared. It can be seen that when CaCO3 and TiO2 are paired, the change of the reference optical path difference with temperature is smaller than that of other crystal pairs, which can better meet the temperature compensation requirements.

[0075] like Figure 5 As shown in the figure, when the ambient temperature changes, the crystal thickness will change accordingly, and the reference optical path difference will change accordingly, requiring additional temperature drift correction. However, the temperature difference elimination method of the present invention reduces the change of the reference optical path difference with temperature by an order of magnitude, and the entire interferometer system is not easily affected by external temperature changes and has lower temperature sensitivity.

[0076] On the other hand, the field of view widening effect of the temperature difference elimination method proposed in the present invention is better. Figure 6 As shown in Figure 2, the absolute value of the rate of change of the optical path difference of the temperature difference elimination method with the field of view angle is only 2.298×10-3 The absolute value of the change rate of the reference optical path difference with the field of view angle of the traditional compensation scheme with air gap is 3.138×10 -2 The difference between the two is an order of magnitude. The temperature difference elimination method of the present invention is less sensitive to temperature than the uncompensated solution, and has a better wide field effect. The use of a new temperature difference elimination solution design will greatly improve the environmental stability of the birefringent crystal wind imaging interferometer.

[0077] In summary, through the verification of this embodiment, it is explained that the present invention improves the dual crystal module in the birefringent crystal wind imaging interferometer, adds another birefringent crystal on the basis of the original dual crystal module, and provides a birefringent crystal wind imaging interferometer that eliminates the temperature difference. By using different birefringent crystal combinations, the temperature difference elimination effect of the birefringent interferometer is improved, and a good wide field effect is maintained, thereby improving the stability of the birefringent interferometer under different temperature environments. Aiming at the problem that the existing birefringent crystal wind imaging interferometer cannot maintain its good temperature difference elimination effect and good stability under different temperature environments, the present invention provides a new birefringent crystal wind imaging interferometer, which effectively solves the problems existing in the existing birefringent wind imaging interferometer.

[0078] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A birefringent crystal wind imaging interferometer, characterized in that: include: A first birefringent crystal, a second birefringent crystal, a half-wave plate, a first birefringent crystal and a second birefringent crystal are arranged, wherein the angle between the optical axes of the first birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 45°, and the angle between the optical axes of the second birefringent crystal and the second birefringent crystal and the positive direction of the x-axis is 135°; wherein the positive direction of the x-axis is a lateral direction perpendicular to the optical axis; The directions in which the thickness and refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and refractive index of the second birefringent crystal change with temperature, so that the changes in the reference optical path difference produced by the first birefringent crystal and the second birefringent crystal are opposite, and the changes in the total optical path difference produced by the first birefringent crystal and the second birefringent crystal with temperature are close to 0.

2. A method for eliminating temperature difference of a birefringent crystal wind imaging interferometer according to claim 1, characterized in that: include: Selecting materials for the first birefringent crystal and the second birefringent crystal so that the directions in which the thickness and the refractive index of the first birefringent crystal change with temperature are opposite to those in which the thickness and the refractive index of the second birefringent crystal change with temperature; According to the material selection results of the first birefringent crystal and the second birefringent crystal, the first birefringent crystal and the second birefringent crystal are paired so that the change of the total optical path difference generated by the first birefringent crystal and the second birefringent crystal with temperature is close to 0, so as to improve the temperature difference elimination effect of the birefringent crystal wind imaging interferometer.

3. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 2, characterized in that: The selecting of materials for the first birefringent crystal and the second birefringent crystal specifically includes: Constructing a birefringent crystal library and recording the parameters of each birefringent crystal; wherein the birefringent crystal includes a first birefringent crystal and a second birefringent crystal; Arbitrarily combining the first birefringent crystal and the second birefringent crystal in the birefringent crystal library in pairs to obtain a birefringent crystal combination and obtain crystal parameters of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination; The crystal thicknesses of the first birefringent crystal and the second birefringent crystal in each birefringent crystal combination are obtained according to the preset reference optical path difference and the crystal parameters of the first birefringent crystal and the second birefringent crystal in each birefringent crystal combination.

4. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 2, characterized in that: The pairing of the first birefringent crystal and the second birefringent crystal specifically includes: Calculating the total optical path difference variation between the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination according to the crystal thicknesses of the first birefringent crystal and the second birefringent crystal; A birefringent crystal combination whose total optical path difference variation is closest to 0 under different temperatures and different viewing angles is selected as an optimal pairing combination of the first birefringent crystal and the second birefringent crystal.

5. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 3, characterized in that: The birefringent crystal includes calcite, lithium niobate, yttrium vanadate, titanium dioxide and tellurium dioxide.

6. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 3, characterized in that: The parameters of each birefringent crystal include: unit thickness d0, unit thickness variation Δd, temperature variation ΔT, unit refractive index n0, unit refractive index variation Δn, thermal expansion coefficient α and thermo-optic coefficient β; The thermal expansion coefficient is the ratio of the change in unit thickness to the change in temperature of the birefringent crystal when the temperature changes, that is, The thermo-optic coefficient is the ratio of the change in unit refractive index to the change in temperature of a birefringent crystal when the temperature changes, that is, 7. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 3, characterized in that: The step of obtaining the crystal thickness of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination specifically includes: According to the preset reference optical path difference, the parameters of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination are substituted into the calculation formula to obtain the crystal thickness of the first birefringent crystal and the second birefringent crystal. The calculation formula is as follows: Wherein, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal, Δ0 is the preset reference optical path difference, and n o1 and n o2 is the ordinary light refractive index of the first birefringent crystal and the second birefringent crystal, n e1 and n e2 is the extraordinary refractive index of the first birefringent crystal and the second birefringent crystal, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal, and β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal.

8. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 7, characterized in that: The calculation formula of the crystal thickness is simplified to x = A -1 B; Where x is the thickness matrix of the first birefringent crystal and the second birefringent crystal in the birefringent crystal combination. A represents the crystal parameter matrix B represents the optical path difference matrix 9. The method for eliminating temperature difference of a birefringent crystal wind imaging interferometer as claimed in claim 4, characterized in that: The total optical path difference change is close to 0, and the formula is: In the formula, is the change in optical path difference produced by the first birefringent crystal, is the change in the optical path difference caused by the second birefringent crystal, d1 and d2 are the thicknesses of the first birefringent crystal and the second birefringent crystal respectively, n1 and n2 are the refractive indices of the first birefringent crystal and the second birefringent crystal respectively, α1 and α2 are the thermal expansion coefficients of the first birefringent crystal and the second birefringent crystal respectively, β1 and β2 are the thermo-optic coefficients of the first birefringent crystal and the second birefringent crystal respectively, and Δ is the total optical path difference change.

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