Atmospheric gravity wave interference imaging observation instrument based on birefringent crystal and imaging method

Abstract

The application relates to an atmospheric gravity wave interference imaging observation instrument based on a birefringent crystal, wherein a main optical axis direction of an incident light line is a z-axis direction, a direction perpendicular to the main optical axis into a room is an x-axis direction, and an xyz coordinate system satisfying a right-hand rule is constructed; the instrument comprises, in sequence along the incident light line, a front telescope, a first collimating mirror, an aperture segmentation and polarization combination structure, a wide-field delay module, a second telescope, a second collimating mirror, a roof prism, a Wollaston prism, an imaging mirror and a detector; the roof prism is arranged at a conjugate image position of an aperture diaphragm behind the second collimating mirror. The application adopts a polarization combination aperture segmentation mode, avoids splitting of an incident wide-field delay module light beam, makes the light beams of upper and lower parts be incident at the same angle, and solves the problems of limited detection field of view and undersampling of interference fringes in a partial field of view region in the prior art. The application greatly improves a usable field of view range of the system and reduces a wind speed inversion error.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of atmospheric gravity wave observation, and in particular to an atmospheric gravity wave interference imaging observation instrument based on a birefringent crystal and an imaging method. BACKGROUND

[0002] Atmospheric wave is a field parameter of the atmosphere, which is a periodic disturbance of a certain atmospheric characteristic parameter such as density and wind speed. Such a wave can be transmitted in the atmosphere, or can exist in the form of a standing wave. Based on the range in which the atmosphere exists, the atmospheric wave has a wide time and space scale, including global disturbance and local wave. The main atmospheric waves include atmospheric planetary wave, atmospheric thermal tide and atmospheric gravity wave. The wave of the atmosphere is an important dynamic process of energy and momentum transmission in the atmosphere, which greatly affects the distribution of temperature, pressure, wind field and composition in the whole middle and high atmosphere.

[0003] The gravity wave process is considered to be one of the most important dynamic processes in the middle and high atmosphere. The gravity wave process can explain the fluctuation of the middle and high atmospheric parameters, and explain the physical reason of some transient processes. At the height of the thermosphere, the gravity wave causes ionospheric disturbance through collision coupling. Therefore, a comprehensive and in-depth understanding of the gravity wave process will provide information for the prediction of space environment disturbance, and provide reliable guarantee for the development of space activities and radio communication. In addition, the turbulence generated by the breaking of gravity waves may have important influence on the transport, photochemical balance and trace components of the middle and high atmosphere.

[0004] In fact, the movement of the atmosphere (wind field) is the most intuitive form of atmospheric gravity wave, and the detection of the atmospheric wind field can directly reflect the dynamic process of the atmosphere, and realize the accurate passive detection of the atmospheric gravity wave. The detection of the atmospheric wind field is mainly realized by observing the Doppler frequency shift of the airglow radiation in the middle and high atmosphere. Aruhliah et al. used a Fabry-Perot etalon system to measure the frequency shift of the airglow spectrum caused by the movement of the atmosphere, Englert et al. developed a DASH based on spatial heterodyne spectroscopy technology for the detection of atmospheric wind field. At present, the most perfect and most promising technology in the world is the wind imaging interferometer based on Michelson core. However, the existing imaging interferometer has the problems of limited detection market and under-sampling of interference fringes in some market areas.

[0005] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present disclosure, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art, and provides a birefringent crystal-based atmospheric gravity wave interference imaging observation instrument and imaging method, which solves the deficiencies of the existing imaging interferometer.

[0007] The present application is achieved by the following technical solutions: a birefringent crystal-based atmospheric gravity wave interference imaging observation instrument, the main optical axis direction of the incident light is the z-axis direction, and the direction perpendicular to the main optical axis into the x-axis direction, and an xyz coordinate system satisfying the right-hand rule is constructed; it comprises a front telescope, a first collimating mirror, an aperture segmentation polarization combination module, a wide-field delay module, a second telescope, a second collimating mirror, a roof prism, a Wollaston prism, an imaging lens and a detector arranged in sequence along the incident optical fiber; the roof prism is arranged at the conjugate image position of the aperture diaphragm after the second collimating mirror;

[0008] The incident light forms a primary image at the field diaphragm through the front telescope, and then becomes a parallel light beam through the first collimating mirror, and is incident on the aperture segmentation polarization combination module, and the light beam is modulated into two parts with different polarization states through the aperture segmentation polarization combination module, but still the same light beam with the same field angle, and the light beam forms an image at the secondary image plane through the second telescope through the wide-field delay module and becomes a parallel light beam through the second collimating mirror, and the light beam is split into two beams along the y-axis through the roof prism, and then the two beams are incident on the Wollaston prism, and each beam is split into two beams with mutually orthogonal polarization directions along the x-axis, and four parallel light beams with different propagation directions are formed, which form an image on the detector after passing through the imaging lens.

[0009] The aperture segmentation polarization combination module comprises a first polarizer, a second polarizer and a quarter-wave plate arranged along the y-axis direction; the transmission direction of the first polarizer is along the y-axis direction, the transmission direction of the second polarizer is along the x-axis direction, the angle between the optical axis direction of the quarter-wave plate and the positive direction of the x-axis is 45°, and the quarter-wave plate is arranged in the xoy plane and located at the back surface position of the second polarizer.

[0010] The wide-field delay module comprises a first lithium niobate crystal, a half-wave plate and a second lithium niobate crystal arranged in sequence along the z-axis direction; the angle between the optical axis direction of the first lithium niobate crystal and the positive direction of the x-axis is 45°, and the optical axis is in the xoy plane; the optical axis direction of the half-wave plate is along the positive direction of the y-axis; the angle between the optical axis direction of the second lithium niobate crystal and the positive direction of the x-axis is 135°, and the optical axis is in the xoy plane.

[0011] The birefringent crystal-based atmospheric gravity wave interference imaging method comprises:

[0012] The incident light passes through the front telescope of the dome to form a primary image at the field stop, and then passes through the first collimating mirror to become a parallel light beam incident to the aperture division polarization combination module at the position of the aperture stop, the aperture division polarization combination module modulates the light beam into two parts with different polarization states according to the Jones matrix representation, but still the same light beam with the same field angle;

[0013] The light beam passes through the wide-field delay module to be imaged at the secondary image plane by the second telescope, and then passes through the second collimating mirror to become a parallel light beam;

[0014] The light beam passes through the roof prism at the conjugate image of the aperture stop behind the second collimating mirror to be split into two beams along the y-axis, and the two beams are input into the Wollaston prism, and each beam is further split into two beams with mutually orthogonal polarization directions along the x-axis, forming four parallel light beams with different propagation directions;

[0015] The four parallel light beams form four interference patterns with intensities of , , and on the detector after passing through the imaging mirror.

[0016] According to the Jones matrix representation, the Jones matrix of the first polarizer is represented as , the Jones matrix of the second polarizer is represented as , and the Jones matrix of the quarter-wave plate is represented as .

[0017] According to the Jones matrix representation, the Jones matrix of the first lithium niobate crystal and the second lithium niobate crystal of the wide-field delay module is represented as:

[0018]

[0019] wherein, , , ;

[0020] wherein, is the incident angle of the light ray, is the angle from the incident plane to the positive direction of the crystal optical axis in the counterclockwise direction, and are the phase delays introduced by the crystal to the ordinary light and the extraordinary light, respectively. and are the refractive indices of the ordinary light and the extraordinary light, respectively.

[0021] The Jones matrix of the half-wave plate is represented as .

[0022] The application has the following advantages: the atmospheric gravity wave interference imaging observation instrument and imaging method based on a birefringent crystal adopts a polarization combined aperture segmentation mode, avoids splitting of an incident wide field delay module light beam, causes the light beams of upper and lower parts to be incident at the same angle, and solves the problems of limited detection field of view and undersampling of interference fringes in some field of view regions in the prior art. The usable field of view range of the system is greatly improved, and the wind speed inversion error is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the application;

[0024] Figure 2 is a structural schematic diagram of the aperture segmentation polarization combination module in the application;

[0025] Figure 3 is a structural schematic diagram of the wide field delay module in the application;

[0026] Figure 4 is a schematic diagram of simulated interference imaging results of the application;

[0027] In the figure: 1 - a pre-telescope, 2 - a first collimating mirror, 3 - an aperture segmentation polarization combination module, 4 - a wide field delay module, 5 - a second telescope, 6 - a second collimating mirror, 7 - a roof prism, 8 - a Wollaston prism, 9 - an imaging mirror, 10 - a detector, 21 - a first polarizer, 22 - a second polarizer, 23 - a quarter-wave plate, 31 - a first lithium niobate crystal, 32 - a half-wave plate, 33 - a second lithium niobate crystal. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in combination with the drawings of the present application is not intended to limit the protection scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present application. The present application will be further described below in combination with the drawings.

[0029] As Figure 1As shown, the present application particularly relates to an atmospheric gravity wave interference imaging observation instrument based on birefringent crystal, the main optical axis direction of the incident light is z-axis direction, the direction perpendicular to the paper is x-axis direction, and the xyz coordinate system satisfying the right-hand rule is constructed.

[0030] Further, as shown, Figure 2 The aperture segmentation polarization combination module 3 comprises two parts arranged along the y direction, the first part is a first polarizer 21 with the transmission vibration direction along the y-axis direction, and the second part is a combination of a second polarizer 22 with the transmission vibration direction along the x-axis direction and a quarter-wave plate 23 with the optical axis direction at an angle of 45 degrees with the positive direction of the x-axis, wherein the optical axis of the quarter-wave plate 23 is in the xoy plane.

[0031] As shown, Figure 3 The wide-field delay module 4 comprises three parts arranged along the z-axis direction, the first part is a first lithium niobate crystal 31 with the optical axis direction at an angle of 45 degrees with the positive direction of the x-axis, the optical axis of which is in the xoy plane, the second part is a half-wave plate 32 with the optical axis direction along the positive direction of the y-axis, and the third part is a second lithium niobate crystal 33 with the optical axis direction at an angle of 135 degrees with the positive direction of the x-axis, the optical axis of which is in the xoy plane; the wide-field delay module 4 generates different delay amounts for the two incident light rays, and this combination of the module can slow down the change of the optical path difference with the field of view angle, realizing the wide-field effect.

[0032] The interference imaging observation instrument of the present application is placed vertically on the ground to observe the sky, and the target is O 1 D red line with a wavelength of 630.0 nm. The incident light passes through the front telescope 1 of the dome to form an image at the field stop, then becomes a parallel light beam through the first collimating mirror 2, and is incident on the aperture segmentation polarization combination module 3 located at the aperture stop. According to the Jones matrix representation method, the Jones matrix of the first polarizer 21 can be represented as: , and further establishes a theoretical model of the atmospheric gravity wave interference imaging observation instrument based on birefringent crystal;

[0033] The Jones matrix of the second polarizer 22 can be represented as: The Jones matrix of the quarter-wave plate 23 can be represented as: , and i represents the imaginary unit.

[0034] After modulation by the aperture segmentation polarization combination module 3, the light beam becomes two parts with different polarization states, but still the same light beam with the same field of view angle. Next, the light beam passes through the wide-field delay module 4, and the Jones matrices of the first lithium niobate crystal 31 and the second lithium niobate crystal 33 can be represented as:

[0035]

[0036] wherein, , , ;

[0037] wherein, is the incident angle of the light, is the angle from the incident plane to the positive direction of the optical axis of the crystal in the counterclockwise direction, and are the phase delays introduced by the crystal to the ordinary light and the extraordinary light, respectively. and are the refractive indices of the ordinary light and the extraordinary light, respectively. The Jones matrix of the half-wave plate is represented as .

[0038] The light emitted from the wide-field delay module 4 is imaged at the secondary image plane by the second telescope 5, and then becomes a parallel light beam by the second collimating mirror 6. The roof prism 7 is located at the conjugate image of the aperture stop behind the second collimating mirror 6, and the light beam is split into two beams along the y-axis by the roof prism 7. Then the two beams of light are incident on the Wollaston prism 8, and each beam is further split into two beams of light with mutually orthogonal polarization directions along the x-axis, forming a total of four parallel light beams with different propagation directions. The four parallel light beams pass through the imaging mirror 9 and form four interference patterns on the detector 10. By Jones matrix calculation, the four interference pattern intensities are: , , and , and Ф represents the total phase;

[0039] Using the four interference intensities for inversion calculation, the atmospheric gravity wave data can be obtained.

[0040] In the present application, the light passing surface size of the first lithium niobate crystal 31 and the second lithium niobate crystal 33 is set to 50mm x 50mm, and the length along the z-axis direction is set to 40mm. Modeling is performed using optical design software, and the obtained four-part interference patterns are as shown in Figure 4 The intensities of the four interference patterns change with the four phase steps, and the four-intensity method measurement of atmospheric gravity waves can be realized.

[0041] The foregoing is considered as illustrative only of the principles of the application. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the application to the exact construction and operation described. Accordingly, all such variations are intended to be included within the scope of the present application as defined in the claims below and their equivalents.

Claims

1. An atmospheric gravity wave interferometric imager based on birefringent crystals, characterized in that: The z-axis direction is the main optical axis direction of the incident light, and the x-axis direction is the direction perpendicular to the main optical axis into the room, and the xyz coordinate system satisfying the right-hand rule is constructed; it comprises a front telescope (1), a first collimating mirror (2), an aperture segmentation polarization combined module (3), a wide-field delay module (4), a second telescope (5), a second collimating mirror (6), a roof prism (7), a Wollaston prism (8), an imaging mirror (9) and a detector (10) arranged in sequence along the incident light; the roof prism (7) is arranged at the conjugate image position of the aperture diaphragm after the second collimating mirror (6); The incident light forms a primary image at the field stop through the front telescope (1), and then becomes a parallel light beam through the first collimating mirror (2) and is incident on the aperture segmentation polarization combined module (3), the aperture segmentation polarization combined module (3) modulates the light beam into two parts with different polarization states, but still the same light beam with the same field angle, the light beam passes through the wide-field delay module (4) and is imaged at the second image plane through the second telescope (5), and then becomes a parallel light beam through the second collimating mirror (6), the light beam is split into two beams along the y-axis through the roof prism (7), and then the two beams are incident on the Wollaston prism (8), each beam is split into two beams with mutually orthogonal polarization directions along the x-axis, and four parallel light beams with different propagation directions are formed, which are imaged on the detector (10) after passing through the imaging mirror (9).

2. The birefringent crystal-based atmospheric gravity wave interference imaging observatory of claim 1, wherein: The aperture segmentation polarization combined module (3) comprises a first polarizer (21), a second polarizer (22) and a quarter-wave plate (23) arranged along the y-axis direction; the transmission direction of the first polarizer (21) is along the y-axis direction, the transmission direction of the second polarizer (22) is along the x-axis direction, the angle between the optical axis direction of the quarter-wave plate (23) and the positive direction of the x-axis is 45°, and the quarter-wave plate (23) is arranged in the xoy plane and located at the back surface position of the second polarizer (22).

3. The birefringent crystal-based atmospheric gravity wave interference imaging observatory of claim 1, wherein: The wide-field delay module (4) comprises a first lithium niobate crystal (31), a half-wave plate (32) and a second lithium niobate crystal (33) arranged in sequence along the z-axis direction; the optical axis direction of the first lithium niobate crystal (31) is at an angle of 45° with the positive direction of the x-axis, and the optical axis is in the xoy plane; the optical axis direction of the half-wave plate (32) is along the positive direction of the y-axis; the optical axis direction of the second lithium niobate crystal (32) is at an angle of 135° with the positive direction of the x-axis, and the optical axis is in the xoy plane.

4. Atmospheric gravity wave interferometric imaging method based on birefringent crystals, characterized in that: The imaging method comprises: The incident light forms a primary image at the field stop through the front telescope (1), and then becomes a parallel light beam through the first collimating mirror (2) and is incident on the aperture segmentation polarization combined module (3) located at the aperture diaphragm position, the aperture segmentation polarization combined module (3) modulates the light beam into two parts with different polarization states according to the Jones matrix representation, but still the same light beam with the same field angle; The light beam passes through the wide-field delay module (4) and is imaged at the second image plane through the second telescope (5), and then becomes a parallel light beam through the second collimating mirror (6); The light beam is split into two beams along the y axis by a roof prism (7) located at the conjugate image of the back aperture stop of the second collimating mirror (6), and the two beams are input into a Wollaston prism (8), and each beam is split into two beams with mutually orthogonal polarization directions along the x axis, forming four parallel beams with different propagation directions; Four parallel beams of light, after passing through the imaging lens (9), form four interference patterns on the detector (10) with intensities , , and , respectively. Φ represents the total phase.

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