Intermediate infrared star light interference fringe generation and aberration suppression evaluation system and method based on 4F spatial filtering

Abstract

The invention discloses an intermediate infrared star light interference fringe generation and aberration suppression evaluation system and method based on 4F system spatial filtering. The system is applied to coherent interference measurement of mid-infrared band fixed star light in astronomical observation. The system comprises a telescope collimation unit, an aberration equivalent unit, a 4F relay light path unit, an adjustable pinhole spatial filtering unit arranged on a 4F middle focal plane, a reference light generation and phase tilt modulation unit and a coherent superposition and interferogram output unit. By arranging the pinhole, the wavefront high-spatial-frequency component of the test arm is cut, so that the influence of atmospheric turbulence or high-order aberration on interference fringes is reduced, and the regularity of the fringes is improved. The system further provides a parameterization strategy for setting the pinhole size with the Airy spot radius as a scale, and interference fringes under different pinhole multiplying power can be subjected to comparative analysis and wavefront diagram PV value calculation. The method is suitable for the scenes of intermediate infrared coherent imaging, wavefront shaping, spatial filtering teaching demonstration and the like.

Description

Technical Field

[0001] This invention relates to the fields of coherent optics and spatial filtering, and in particular to a method for eliminating wavefront distortion of light using spatial filtering technology in the mid- and far-infrared bands to improve astronomical interferometric fringes. Background Technology

[0002] In astronomical observation, the mid-infrared band (commonly used in the N band, 8-13 μm) has advantages such as sensitivity to dust radiation and minimal impact from interstellar extinction, and is widely used in star-forming regions, planetary disks, and high angular resolution astronomical observations. Astronomical interferometry, which can overcome the limitations of a single telescope's aperture on angular resolution and greatly improve angular resolution, is also widely used in astronomical observation. In practical systems, higher-order aberrations and scattering cause high spatial frequency phase fluctuations on the wavefront, leading to phenomena such as fringe bending and breakage, severely affecting the regularity of interference fringes. This is especially true in mid-infrared (e.g., 10 μm band) systems, where laser beam expansion and collimation systems often introduce complex higher-order aberrations due to limitations in the processing precision and refractive index inhomogeneity of infrared materials (e.g., germanium, zinc selenide). Changing the optical path difference or the tilt angle of the light cannot suppress the destructive effects of higher-order aberrations on interference fringes. 4F spatial filtering technology can achieve spatial frequency selective transmission on the Fourier surface, and pinholes can suppress high spatial frequency components, improving the smoothness of the output wavefront. However, existing spatial filters are usually only used as simple "denoising" tools, lacking implementation paths that combine them with stripe generation and parameterized pinholes. Summary of the Invention

[0003] The present invention aims to provide a system and method that combines 4F spatial filtering with coherent superposition, which achieves "gradual improvement" of interference fringes by adjusting the Fourier surface pinholes, and provides indicators such as fringe contrast for quantitative evaluation.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a mid-infrared stellar light interferometric fringe generation and aberration suppression evaluation system based on 4F spatial filtering, comprising:

[0006] The telescope collimating unit is used to couple mid-infrared light from stars into the system and form a collimated beam;

[0007] An aberration introduction unit is placed on the test light path to introduce controllable wavefront aberrations into the test light;

[0008] The 4F relay unit includes a first lens and a second lens. The distance between the first lens and the second lens is the sum of the focal lengths of the two lenses, and the rear focal plane of the first lens corresponds to the front focal plane of the second lens.

[0009] A spatial filtering unit, located at the central focal plane of the 4F relay unit, includes a pinhole aperture with adjustable aperture for selectively transmitting the spatial frequency components of the test light.

[0010] The reference light generation and modulation unit is used to generate a reference light that is coherent with the test light and to apply a controllable linear phase tilt to the reference light to set the period and direction of the interference fringes.

[0011] The coherent superposition and output unit is used to coherently superimpose the test light after 4F spatial filtering with the reference light, output the interference intensity distribution map, and use it to compare and evaluate the interference fringes under different pinhole aperture conditions.

[0012] Furthermore, the aperture of the pinhole aperture is related to the Airy disk radius. The scale is set, where λ is the working wavelength, f is the focal length of the 4F system lens, and D is the entrance pupil diameter; the pinhole radius is... Among them, the pinhole radius multiple Use a value of 0.8 to 2.0.

[0013] Furthermore, the pinhole radius multiplier k includes at least three levels: 1.5, 1.2, and 1.0, used to form multiple contrasting interference patterns.

[0014] Furthermore, the aberration introduction unit is a phase surface, and multiple high-order Zernike coefficients are set in the form of Zernike Fringe Phase to introduce high spatial frequency wavefront errors.

[0015] Furthermore, the linear phase tilt parameter of the reference light is set according to the target fringe number N, so that the number of fringe lines within the aperture range satisfies... ,in The stripe period.

[0016] Furthermore, the coherent superposition and output unit can perform coherent superposition based on the complex amplitude data of the optical field, output the interference intensity distribution, and support unified grid resampling of the interferogram under different pinhole magnification to ensure comparability.

[0017] This invention also provides a method for evaluating the generation and aberration suppression of mid-infrared stellar light interferometric fringes based on 4F spatial filtering. This method is based on the system described above and includes:

[0018] a) Acquire and collimate the infrared light from stars;

[0019] b) Introduce controllable wavefront aberrations into the test light to characterize atmospheric turbulence or lens aberrations;

[0020] c) Input the test light into the 4F relay optical path, and set a pinhole aperture at the 4F central focal plane to perform spatial filtering on the test light;

[0021] d) Generate a reference beam coherent with the test beam and apply a linear phase tilt to the reference beam to produce interference fringes of a predetermined period;

[0022] e) Coherently superimpose the test light and the reference light to obtain the interference intensity distribution;

[0023] f) By changing the pinhole diameter and repeating steps c) to e), interference patterns at different pinhole magnifications are obtained;

[0024] g) Evaluate the fringe regularity of the interferogram and test the PV value of the wavefront image to obtain the correspondence between the aberration suppression effect and the pinhole parameter.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. A pinhole setting method is given based on the Airy disk radius, so that pinhole selection under different system parameters can be reused and transferred;

[0027] 2. When higher-order aberrations are present, the suppression effect of pinholes on high spatial frequency phase fluctuations can be visually presented in the interferogram, and shows an interpretable gradual change with the magnification of the pinhole.

[0028] 3. It can output interference fringes and wavefront PV values, realizing a closed loop from "phenomenon display" to "quantitative evaluation";

[0029] 4. Applicable to imaging and teaching demonstrations under long-wavelength conditions such as infrared band (e.g., 10 μm), especially convenient for demonstrating the division of labor between “fringe density determined by the tilt of the reference light and fringe regularity determined by spatial filtering”. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a telescope system;

[0031] Figure 2 This is the overall system structure; where (a) is a schematic diagram of the test arm and (b) is a schematic diagram of the reference arm.

[0032] Figure 3 This is a schematic diagram of the 4F spatial filtering module.

[0033] Figure 4 This is a schematic diagram of interference fringes without aberrations or pinholes.

[0034] Figure 5 This is a schematic diagram of interference fringes with higher-order aberrations added but without pinholes.

[0035] Figure 6 This is a comparative diagram of interference fringes when higher-order aberrations are added and the pinhole radius is 1.5x, 1.2x, and 1.0x.

[0036] The markings in the diagram are: 1-phase screen; 2-first lens; 3-spatial filter unit; 301-pinhole filter; 4-second lens; 5-test light; 6-reference light; 7-first parabolic mirror; 8-second parabolic mirror; 9-first reflecting mirror; 10-second reflecting mirror. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings.

[0038] This invention discloses an evaluation system for mid-infrared stellar light interferometric fringe generation and aberration suppression based on 4F spatial filtering. Figure 2 As shown. The optical path of (a) the test arm includes: collimating light → phase screen 1 (introducing phase difference) → 4F system (including first lens 2 and second lens 4) → spatial filtering unit 3 (including Fourier surface pinhole) → output image plane; the optical path of (b) the reference arm includes: reference light → phase tilt → output image plane. This system specifically includes:

[0039] Aberration introduction unit: set on the test light path, used to introduce controllable wavefront aberration into the test light 5; the aberration introduction unit is a phase surface, and multiple high-order Zernike coefficients can be set in the form of Zernike Fringe Phase to introduce high spatial frequency wavefront errors.

[0040] 4F relay unit: includes a first lens 2 and a second lens 4, the distance between the first lens 2 and the second lens 4 is the sum of the focal lengths of the two lenses, and the rear focal plane of the first lens 2 corresponds to the front focal plane of the second lens 4; the principle of the 4F spatial filtering module is as follows. Figure 3 As shown;

[0041] Spatial filtering unit: Located at the central focal plane of the 4F relay unit, it includes a pinhole aperture (pinhole filter 301) with adjustable aperture for selective transmission of the spatial frequency components of the test light; the aperture of the pinhole aperture is based on the Airy disk radius. The scale is set, where λ is the working wavelength, f is the focal length of the 4F system lens, and D is the entrance pupil diameter; the pinhole radius is... Among them, the pinhole radius multiple The value is taken as 0.8 to 2.0; the pinhole radius multiplier k includes at least three levels: 1.5, 1.2 and 1.0, used to form multiple contrasting interference patterns;

[0042] Reference light generation and modulation unit: used to generate a reference light 6 coherent with the test light, and to apply a controllable linear phase tilt to the reference light to set the period and direction of the interference fringes; the linear phase tilt parameter of the reference light is set according to the target number of fringes N, so that the number of fringes within the aperture range satisfies ,in The stripe period;

[0043] Coherent superposition and output unit: used to coherently superimpose the test light after 4F spatial filtering with the reference light, output the interference intensity distribution map, and use it to compare and evaluate the interference fringes under different pinhole diameter conditions; the coherent superposition and output unit can perform coherent superposition based on the complex amplitude data of the optical field, output the interference intensity distribution, and support uniform grid resampling of the interference map under different pinhole magnification to ensure comparability.

[0044] Based on the above system, the present invention also provides a method for evaluating the generation and aberration suppression of mid-infrared stellar light interference fringes based on 4F spatial filtering, comprising the following steps:

[0045] Step 1: Introduce controllable wavefront aberrations into the test light;

[0046] Step 2: Input the test light into the 4F relay optical path, and set a pinhole aperture at the 4F central focal plane to perform spatial filtering on the test light;

[0047] Step 3: Generate a reference beam coherent with the test beam, and apply a linear phase tilt to the reference beam to produce interference fringes with a predetermined period;

[0048] Step 4: Coherently superimpose the test light and the reference light to obtain the interference intensity distribution;

[0049] Step 5: By changing the pinhole diameter and repeating steps 2 to 4, obtain interference patterns at different pinhole magnifications;

[0050] Step 6: Evaluate the fringe regularity of the interferogram and test the PV value of the wavefront image to obtain the correspondence between the aberration suppression effect and the pinhole parameters.

[0051] Implementation example: Spatial filtering interferometry evaluation with infrared 10um, 75mm entrance pupil, and 300mm focal length in a 4F system.

[0052] 1. Optical parameters: working wavelength λ=10um, entrance pupil diameter D=75mm, focal length of the two lenses f=300mm, and distance between the two lenses is approximately 2f=600mm.

[0053] 2. In Figure 1 The telescope system shown obtains collimated test light (the telescope system includes a first parabolic mirror 7, a second parabolic mirror 8, a first reflecting mirror 9, and a second reflecting mirror 10), and in Figure 2The test optical path shown is equipped with a Zernike-Fringe Phase surface, and higher-order Zernike coefficients are introduced to make the higher-order wavefront error reach the preset RMS range (Peak tovalley = 2.1758 waves, RMS = 0.6255 waves) to obtain the test light.

[0054] 3. Set a resizable pinhole aperture at the rear focal plane of the first lens and calculate the Airy disk radius:

[0055]

[0056] get The selected pinhole radii are: 1.5x: 0.0732 mm, 1.2x: 0.0586 mm, and 1.0x: 0.0488 mm.

[0057] 4. Generate a reference beam coherent with the test beam, such as... Figure 1 As shown, by applying a linear phase tilt to set the stripe period, the number of stripes within the aperture is set to be in the range of 5 to 10.

[0058] 5. Coherently superimpose the test light and the reference light to obtain an interference intensity map. The interference map obtained without aberrations or pinhole filtering is shown below. Figure 3 As shown; the interferogram obtained without pinhole filtering after introducing aberrations is as follows. Figure 4 As shown; the interferograms obtained after introducing aberrations and performing spatial filtering through three different pinhole diameters are as follows. Figure 5 As shown.

[0059] 6. Observe the interference fringe pattern within the effective spot area and obtain the wavefront PV value, as shown in Table 1. Obtain the correspondence between pinhole magnification and improved wavefront distortion, and achieve a quantitative evaluation of the aberration suppression effect.

[0060] Table 1

[0061]

[0062] In summary, this invention provides a system and method for evaluating the generation and aberration suppression of mid-infrared stellar interference fringes based on 4F spatial filtering. The system includes: an aberration introduction unit, a 4F relay optical path composed of a first lens and a second lens, an adjustable pinhole spatial filter unit located at the 4F intermediate focal plane, a reference light generation and phase tilt modulation unit, and a coherent superposition and interferogram output unit. By setting a pinhole at the 4F intermediate focal plane, the high spatial frequency components of the test arm wavefront are clipped, thereby reducing the influence of higher-order aberrations on coherent interference fringes and improving fringe regularity. The method further provides a parameterized strategy for setting the pinhole size using the Airy disk radius as a scale, and can perform comparative analysis and wavefront PV value calculation for interference fringes at different pinhole magnifications (e.g., 1.5x, 1.2x, 1.0x Airy disk radius). This invention is applicable to scenarios such as infrared / visible band coherent imaging, structured light quality assessment, wavefront shaping, and spatial filtering teaching demonstrations.

[0063] The above embodiments are merely typical implementations of the present invention and are not intended to limit the present invention. All equivalent substitutions or improvements made within the scope of the claims of the present invention are within the protection scope of the present invention.

Claims

1. A mid-infrared stellar light interferometric fringe generation and aberration suppression evaluation system based on 4F spatial filtering, characterized in that, include: The telescope collimating unit is used to couple mid-infrared light from stars into the system and form a collimated beam; Aberration equivalent units are set on the test light path to introduce controllable wavefront aberrations into the test light to characterize atmospheric turbulence or higher-order aberrations. The 4F relay unit includes a first lens and a second lens. The distance between the first lens and the second lens is the sum of the focal lengths of the two lenses, and the rear focal plane of the first lens corresponds to the front focal plane of the second lens. A spatial filtering unit, located at the central focal plane of the 4F relay unit, includes a pinhole aperture with adjustable aperture for selectively transmitting the spatial frequency components of the test light. The reference light generation and modulation unit is used to generate a reference light that is coherent with the test light and to apply a controllable linear phase tilt to the reference light to set the period and direction of the interference fringes. The coherent superposition and output unit is used to coherently superimpose the test light after 4F spatial filtering with the reference light, output the interference intensity distribution map, and use it to compare and evaluate the interference fringes under different pinhole aperture conditions.

2. The system according to claim 1, characterized in that, The aperture of the pinhole aperture is equal to the radius of the Airy disk. The scale is set, where λ is the working wavelength, f is the focal length of the 4F system lens, and D is the entrance pupil diameter; the pinhole radius is... Among them, the pinhole radius multiple Use a value of 0.8 to 2.

0.

3. The system according to claim 2, characterized in that, The pinhole radius multiplier k includes at least three levels: 1.5, 1.2, and 1.0, used to form multiple contrasting interference patterns.

4. The system according to claim 1, characterized in that, The aberration introduction unit is a phase surface, and multiple high-order Zernike coefficients are set in the Zernike-Fringe Phase form to introduce high spatial frequency wavefront errors.

5. The system according to claim 1, characterized in that, The linear phase tilt parameter of the reference light is set according to the target fringe number N, so that the number of fringe lines within the aperture range satisfies... ,in The stripe period.

6. The system according to claim 1, characterized in that, The coherent superposition and output unit can perform coherent superposition based on the complex amplitude data of the optical field, output the interference intensity distribution, and support unified grid resampling of the interferogram under different pinhole magnification to ensure comparability.

7. A method for evaluating the generation and aberration suppression of mid-infrared stellar light interferometric fringes based on 4F spatial filtering, said method being based on the system described in any one of claims 1 to 6, characterized in that, The method includes: a) Acquire and collimate the infrared light from stars; b) Introduce controllable wavefront aberrations into the test light to characterize atmospheric turbulence or lens aberrations; c) Input the test light into the 4F relay optical path, and set a pinhole aperture at the 4F central focal plane to perform spatial filtering on the test light; d) Generate a reference beam coherent with the test beam and apply a linear phase tilt to the reference beam to produce interference fringes of a predetermined period; e) Coherently superimpose the test light and the reference light to obtain the interference intensity distribution; f) By changing the pinhole diameter and repeating steps c) to e), interference patterns at different pinhole magnifications are obtained; g) Evaluate the fringe regularity of the interferogram and test the PV value of the wavefront image to obtain the correspondence between the aberration suppression effect and the pinhole parameter.

Images