Littrow shortwave imaging spectroscopy system based on back-arm compensation

Abstract

In order to solve the technical problems of poor imaging quality of the existing Littrow imaging spectrum system due to the difficulty of pupil matching and the vignetting phenomenon in the edge field of view, the present invention provides a Littrow short-wave imaging spectrum system based on rear arm compensation, which includes a slit, a Littrow optical module, a plane grating, a rear arm compensation lens group and a detector module arranged in sequence along the optical path. The present invention utilizes the combination of the Littrow optical module and the rear arm compensation lens group to suppress the spectral bending and spectral distortion generated by the plane grating, realizes the large relative aperture design of the system, and further realizes the short-wave infrared hyperspectral imaging of airborne ground objects.

Description

Technical Field

[0001] The invention relates to a high-resolution imaging spectrometer, and in particular to a Littrow short-wave imaging spectrometer system based on rear arm compensation. Background Art

[0002] The grating spectral system is an optical system used to detect the target spectral information. Its imaging principle can be divided into convex reflection grating, concave reflection grating, plane transmission grating and plane reflection grating according to the existing optical model. Among them, the convex reflection grating and concave reflection grating related technologies are widely used abroad, but less involved in the domestic market; the imaging system of the plane transmission grating is slender, and the system stray radiation is very serious; the plane grating system has a strong ability to suppress stray light.

[0003] The commonly used plane reflection grating spectral system is the Littrow spectral system. However, since the slit direction of its plane grating spectrometer is perpendicular to the meridian plane of the system, the light emitted from different object points on the same spectral line on the slit will produce more serious spectral line bending after passing through the plane grating. Severe spectral line bending will cause spectral aliasing in the system.

[0004] To solve this problem, the prior art discloses a spectral imaging system based on a combination of forearm compensation and a plane grating. The advantages of this system are compact structure and large relative aperture, but it also cannot achieve a telecentric design due to the incident light at the slit. As a result, when it is used with a front mirror, it is difficult to match the pupil of the entire system, and there are problems such as vignetting at the edge of the field of view, which leads to poor imaging quality of the system. Summary of the invention

[0005] In order to solve the technical problems of the existing Littrow imaging spectroscopy system, such as the difficulty in pupil matching and the vignetting phenomenon in the edge field of view, which leads to poor imaging quality of the system, the present invention provides a Littrow shortwave imaging spectroscopy system based on rear arm compensation.

[0006] The idea of ​​the present invention is to combine the Littrow optical model with the rear arm compensation off-axis lens group to effectively suppress the spectral bending and spectral distortion produced by the plane grating, and realize the system's large relative aperture, high resolution, high signal-to-noise ratio, and lightweight and miniaturized design.

[0007] In order to achieve the above purpose and complete the above invention concept, the technical solution of the present invention is as follows:

[0008] A Littrow shortwave imaging spectroscopy system based on back-arm compensation, which is special in that:

[0009] It includes a slit, a Littrow optical module, a plane grating, a rear arm compensation lens group and a detector module which are sequentially arranged along the optical axis;

[0010] The slit is used to suppress spectral aliasing of different channels and receive target spectral information;

[0011] The Littrow optical module comprises a first lens group and a second lens group; the first lens group and the second lens group are optical path multiplexing lens groups, which form a collimating lens group along the incident light path and an imaging lens group along the reflected light path;

[0012] The first lens group includes a first positive lens and a second positive lens; the second lens group includes a first negative lens and a third positive lens; the first positive lens, the second positive lens, the first negative lens and the third positive lens are arranged in sequence along the transmission light path of the incident light;

[0013] The plane grating is used to reflect the light beam collimated by the Littrow optical module, so that the light beam passes through the Littrow optical module again and is converged and imaged onto the detector module through the rear arm compensation lens group;

[0014] The rear arm compensation lens group is located on the side of the Littrow optical module close to the slit, and the rear arm compensation lens group is used to correct the high-order astigmatism of the system; the slit and the rear arm compensation lens group are respectively located on both sides of the optical axis, and the vertical distance between the central axis of the slit and the optical axis of the rear arm compensation lens group is 5 to 8 mm; the rear arm compensation lens group includes a second negative lens and a fourth positive lens; the second negative lens and the fourth positive lens are sequentially arranged along the reflected optical path of the incident light;

[0015] The detector module is located on the transmission light path of the rear arm compensation lens group and is used to convert the received light signal into an electrical signal and an image signal.

[0016] Furthermore, the first positive lens is a biconvex positive lens;

[0017] The second positive lens is a meniscus positive lens with a convex surface facing the object;

[0018] The first negative lens is a meniscus negative lens with a convex surface facing the object side;

[0019] The third positive lens is a biconvex positive lens;

[0020] The second negative lens is a meniscus negative lens with a convex surface facing the image side;

[0021] The fourth positive lens is a meniscus positive lens with a convex surface facing the image side.

[0022] Further, the first positive lens has a front surface curvature radius of 2009.8 mm, a rear surface curvature radius of -57.8 mm, a thickness of 12 mm, and a spacing of 2.1 mm;

[0023] The second positive lens has a front surface curvature radius of 111.9 mm, a rear surface curvature radius of 590.2 mm, a thickness of 8 mm, and a spacing of 61 mm;

[0024] The first negative lens has a front surface curvature radius of 285 mm, a rear surface curvature radius of 59 mm, a thickness of 3 mm, and a spacing of 3.1 mm;

[0025] The third positive lens has a front surface curvature radius of 76.4 mm, a rear surface curvature radius of -193.43 mm, a thickness of 5.6 mm, and a spacing of 5.7 mm;

[0026] The second negative lens has a front surface curvature radius of -18 mm, a rear surface curvature radius of -11.4 mm, a thickness of 4.1 mm, and a spacing of 4.45 mm;

[0027] The fourth positive lens has a front surface curvature radius of -16.4 mm, a rear surface curvature radius of -14.1 mm, a thickness of 4.2 mm, and a spacing of 17.97 mm.

[0028] Furthermore, the refractive index of the first positive lens is nd1=1.677, and the Abbe number is vd1=55.2;

[0029] The refractive index of the second positive lens is nd2=1.65, and the Abbe number is vd2=50.88;

[0030] The refractive index of the first negative lens is nd3=1.92, and the Abbe number is vd3=20.28;

[0031] The refractive index of the third positive lens is nd4=1.65, and the Abbe number is vd4=39.54;

[0032] The refractive index of the second negative lens is nd5=1.51, and the Abbe number is vd5=64.19;

[0033] The refractive index of the fourth positive lens is nd6=2.01, and the Abbe number is vd6=28.31.

[0034] Furthermore, the width of the slit is 30-100 μm.

[0035] Furthermore, the plane grating has a line density of 80-150 lp / mm and a blaze angle of 4.32°.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The Littrow shortwave imaging spectroscopy system of the present invention comprises a slit, a Littrow optical module, a plane grating, a rear arm compensation lens group and a detector module which are sequentially arranged along the optical axis. The Littrow optical module is combined with the rear arm compensation lens group to realize a large relative aperture design of the system, thereby improving pupil matching, effectively eliminating the phenomenon of vignetting in the edge field of view, suppressing the spectral bending and spectral distortion caused by the plane grating, and thus improving the imaging quality of the system.

[0038] 2. The vertical distance between the central axis of the slit of the present invention and the optical axis of the rear arm compensation lens group is 5 to 8 mm, which can effectively compensate for the residual spectral curvature and astigmatism of the system, thereby improving the imaging quality of the system.

[0039] 3. The Littrow short-wave imaging spectroscopy system of the present invention has an optical space volume of 121 mm×55 mm×48 mm, a compact overall structure, and a wide range of applications.

[0040] 4. The relative aperture of the Littrow shortwave imaging spectroscopy system of the present invention is 1 / 2, the relative aperture is relatively large, and the system has a strong light-collecting ability, thereby improving the signal-to-noise ratio of the system.

[0041] 5. The Littrow short-wave imaging spectroscopy system of the present invention has a simple overall assembly process and has no special requirements on the spacing and relative positions between the optical elements. It only needs to meet the assembly process. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural schematic diagram of an embodiment of a Littrow short-wave imaging spectroscopy system based on rear arm compensation of the present invention;

[0043] Figure 2 It is a spectrum bending curve diagram of an embodiment of the Littrow short-wave imaging spectroscopy system based on rear arm compensation of the present invention;

[0044] Figure 3 It is a spectrum distortion curve diagram of an embodiment of the Littrow short-wave imaging spectroscopy system based on rear arm compensation of the present invention;

[0045] FIG. 4 is a diagram showing the system spectral resolution of an embodiment of the Littrow shortwave imaging spectroscopy system based on rear arm compensation of the present invention.

[0046] The reference numerals are as follows:

[0047] 1- slit, 2- Littrow optical module, 3- plane grating, 4- rear arm compensation lens group, 41- second negative lens, 42- fourth positive lens, 5- first lens group, 51- first positive lens, 52- second positive lens, 6- second lens group, 61- first negative lens, 62- third positive lens, 7- detector module. DETAILED DESCRIPTION

[0048] The principle of the present invention is: the Littrow optical model has the advantages of miniaturization and large relative aperture, but the current Littrow optical model is only suitable for spectrometers, not for spectral imaging instruments. The present invention combines the Littrow optical model with the rear arm compensation off-axis lens group, and uses the advantage of the rear arm compensation lens group to correct the spectral bending, so as to expand the Littrow spectrometer into a new type of Littrow imaging spectrometer, break through the traditional Littrow optical model, and establish the Littrow short-wave imaging spectrum system model based on the rear arm compensation and simulate the principle.

[0049] The present invention is described in detail below in conjunction with the accompanying drawings. The accompanying drawings are in simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. It should be noted that the terms "first", "second", "third", "fourth", etc. used in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0050] See also Figure 1 The present invention provides a Littrow short-wave imaging spectroscopy system based on rear arm compensation, which comprises a slit 1, a Littrow optical module 2, a plane grating 3, a rear arm compensation lens group 4 and a detector module 7 arranged in sequence along the optical axis. The optical space volume of the whole system is 121mm×55mm×48mm, the overall structure is compact, and the application range is wide. The relative aperture of the system is 1 / 2, the relative aperture is large, and the light collecting ability is strong, thereby achieving a high signal-to-noise ratio of imaging.

[0051] Slit 1 is mainly used to receive the spectral information obtained by the objective lens. Selecting a suitable slit width can suppress the influence of spectral aliasing. The width of slit 1 is generally 30-100 μm. In this embodiment, the width of slit 1 is 30 μm, which can effectively suppress the aliasing degree of the light image. Slit 1 and rear arm compensation lens group 4 are respectively located on both sides of the optical axis. The vertical distance between the central axis of slit 1 and the optical axis of rear arm compensation lens group 4 is 5-8 mm. This distance can help rear arm compensation lens group 4 to correct the high-order astigmatism of the system, and can also correct the residual spectral curvature of the system, thereby improving the imaging quality.

[0052] The Littrow optical module 2 simultaneously performs the two functions of collimation and imaging of the spectrometer. Finally, the plane grating 3 disperses the collimated light beam, which is then converged and imaged onto the detector target surface through the Littrow optical module 2.

[0053] The Littrow optical module 2 includes a first lens group 5 and a second lens group 6; the first lens group 5 and the second lens group 6 are optical path multiplexing lens groups, which form a collimating lens group along the incident light path and an imaging lens group along the reflected light path, thereby realizing optical path multiplexing, making the overall structure of the spectral system more compact. The first lens group 5 includes a first positive lens 51 and a second positive lens 52; the second lens group 6 includes a first negative lens 61 and a third positive lens 62. The first positive lens 51, the second positive lens 52, the first negative lens 61 and the third positive lens 62 are arranged in sequence along the transmission light path of the incident light.

[0054] In this embodiment, the first positive lens 51 is a biconvex positive lens, which is made of glass with a refractive index nd1=1.677 and an Abbe number vd1=55.2; the front surface curvature radius of the first positive lens 51 is 2009.8 mm, the rear surface curvature radius is -57.8 mm, the thickness is 12 mm, and the interval is 2.1 mm.

[0055] The second positive lens 52 is a meniscus positive lens with its convex surface facing the object, and is made of glass with a refractive index nd2=1.65 and an Abbe number vd2=50.88; the front surface curvature radius of the second positive lens 52 is 111.9 mm, the rear surface curvature radius is 590.2 mm, the thickness is 8 mm, and the interval is 61 mm.

[0056] The first negative lens 61 is a meniscus-shaped negative lens with its convex surface facing the object side, and is made of glass with a refractive index nd3=1.92 and an Abbe number vd3=20.28; the first negative lens 61 has a front surface curvature radius of 285 mm, a rear surface curvature radius of 59 mm, a thickness of 3 mm, and a spacing of 3.1 mm.

[0057] The third positive lens 62 is a biconvex positive lens made of glass with a refractive index nd4=1.65 and an Abbe number vd4=39.54; the front surface curvature radius of the third positive lens 62 is 76.4mm, the rear surface curvature radius is -193.43mm, the thickness is 5.6mm, and the interval is 5.7mm.

[0058] The plane grating 3 is used to emit the light beam collimated by the Littrow optical module 2, so that the light beam passes through the Littrow optical module 2 again, and is converged and imaged onto the detector module 7 through the rear arm compensation lens group 4. The plane grating 3 is a plane mirror, which mainly disperses the complex light, and the line density of the grating is 80-150lp / mm. In this embodiment, the line density of the plane grating 3 is 120lp / mm, and the blaze angle is 4.32°.

[0059] The rear arm compensation lens group 4 is located on a side of the Littrow optical module 2 close to the slit 1, and includes a second negative lens 41 and a fourth positive lens 42; the second negative lens 41 and the fourth positive lens 42 are sequentially arranged along the reflected optical path of the incident light.

[0060] In this embodiment, the second negative lens 41 is a meniscus negative lens with the convex surface facing the image side, which is made of glass with a refractive index nd5=1.51 and an Abbe number vd5=64.19; the front surface curvature radius of the second negative lens 41 is -18 mm, the rear surface curvature radius is -11.4 mm, the thickness is 4.1 mm, and the interval is 4.45 mm.

[0061] The fourth positive lens 42 is a meniscus positive lens with the convex surface facing the image side, which is made of glass with a refractive index nd6=2.01 and an Abbe number vd6=28.31; the front surface curvature radius of the fourth positive lens 42 is -16.4mm, the rear surface curvature radius is -14.1mm, the thickness is 4.2mm, and the interval is 17.97mm.

[0062] The working process of the Littrow shortwave imaging spectroscopy system based on rear arm compensation of the present invention is as follows:

[0063] The incident light enters the Littrow optical module 2 through the slit 1, and passes through the first positive lens 51, the second positive lens 52, the first negative lens 61 and the third positive lens 62 in sequence to reach the plane grating 3. After being reflected by the plane grating 3, it passes through the third positive lens 62, the first negative lens 61, the second positive lens 52 and the first positive lens 51 again to reach the rear arm compensation lens group 4. After the rear arm compensation lens group 4 corrects the received light beam, it is finally converged and imaged onto the detector module 7 to complete imaging.

[0064] In order to reduce the spectral bending of the system, the present invention performs correction through the rear arm compensation lens group 4, which effectively reduces the spectral bending of the system. The design method combining the Littrow optical model with the rear arm compensation off-axis lens group not only effectively suppresses the spectral bending and spectral distortion generated by the plane grating, but also realizes the large relative aperture and high signal-to-noise ratio spectral imaging of the system.

[0065] Figure 2This is a spectral bending curve diagram of the present embodiment. The horizontal axis in the diagram is the image plane height, and the vertical axis is the spectral bending amount at different image plane heights. It can be seen from the diagram that the maximum spectral bending of the system is 3μm, which is about 1 / 10 of the slit width, and its ratio is far smaller than the spacecraft's requirement for spectral instruments (generally required to be 1 / 5).

[0066] Figure 3 This is a spectral distortion curve diagram of this embodiment. The horizontal axis in the figure is wavelength, and the vertical axis is the spectral distortion corresponding to different wavelengths. It can be seen from the figure that the maximum spectral distortion of the system is less than 0.5μm, which is about 1 / 60 of the slit width. Its ratio is far smaller than the requirement of spacecraft for spectral instruments (generally required to be 1 / 5).

[0067] FIG4 is a diagram of the system spectral resolution of this embodiment. It can be seen from the diagram that two light spots separated by 5 nm can be completely separated, that is, the use requirement of a spectral resolution of 5 nm is met.

[0068] Through initial simulation, the numerical aperture of the spectral system of this embodiment is 0.25, and the ambient temperature of the system is -40℃~60℃. In the wavelength range of 0.9~1.7μm, its spectral resolution is better than 5nm, spectral distortion is less than 0.5μm, spectral bending is less than 3μm, and the pixel size is 15μm, which meets the international high-resolution requirements, thus verifying the effectiveness of the design of the rear arm compensating the off-axis lens to eliminate spectral line bending and spectral distortion.

[0069] The Littrow shortwave imaging spectroscopy system based on rear arm compensation provided by the present invention involves a spectral range that includes characteristic absorption spectra and reflection spectra of various ground objects, and can be widely used in remote sensing, medical detection and diagnosis, mineral resource detection, environmental monitoring and other fields.

[0070] Although the embodiments of the present invention have been shown and described above, it will be apparent to those skilled in the art that any changes or modifications to the above embodiments should be deemed to fall within the protection scope of the present invention as long as they are within the spirit of the present invention.

Claims

1. A Littrow shortwave imaging spectroscopy system based on back-arm compensation, characterized in that: It comprises a slit (1), a Littrow optical module (2), a plane grating (3), a rear arm compensation lens group (4) and a detector module (7) which are sequentially arranged along the optical path; The slit (1) is used to suppress spectral aliasing of different channels and receive target spectral information; The Littrow optical module (2) comprises a first lens group (5) and a second lens group (6); the first lens group (5) and the second lens group (6) are optical path multiplexing lens groups, which form a collimating lens group along the incident light path and an imaging lens group along the reflected light path; The first lens group (5) comprises a first positive lens (51) and a second positive lens (52); the second lens group (6) comprises a first negative lens (61) and a third positive lens (62); the first positive lens (51), the second positive lens (52), the first negative lens (61) and the third positive lens (62) are arranged in sequence along the incident light path; The plane grating (3) is used to reflect the light beam collimated by the Littrow optical module (2), so that the light beam passes through the Littrow optical module (2) again and converges onto the detector module (7) through the rear arm compensation lens group (4); The rear arm compensation lens group (4) is located on a side of the Littrow optical module (2) close to the slit (1), and the rear arm compensation lens group (4) is used to correct the high-order astigmatism of the system; the slit (1) and the rear arm compensation lens group (4) are respectively located on both sides of the optical axis, and the vertical distance between the central axis of the slit (1) and the optical axis of the rear arm compensation lens group (4) is 5 to 8 mm; the rear arm compensation lens group (4) comprises a second negative lens (41) and a fourth positive lens (42); the second negative lens (41) and the fourth positive lens (42) are arranged in sequence along the reflected optical path of the incident light; The detector module (7) is located on the transmission light path of the rear arm compensation lens group (4) and is used to convert the received light signal into an electrical signal and an image signal.

2. The Littrow shortwave imaging spectroscopy system based on rear arm compensation according to claim 1, characterized in that: The first positive lens (51) is a biconvex positive lens; The second positive lens (52) is a meniscus positive lens with a convex surface facing the object side; The first negative lens (61) is a meniscus negative lens with a convex surface facing the object side; The third positive lens (62) is a biconvex positive lens; The second negative lens (41) is a meniscus negative lens with a concave surface facing the image side; The fourth positive lens (42) is a meniscus positive lens with a concave surface facing the image side.

3. The Littrow shortwave imaging spectroscopy system based on rear arm compensation according to claim 2, characterized in that: The first positive lens (51) has a front surface curvature radius of 2009.8 mm, a rear surface curvature radius of -57.8 mm, a thickness of 12 mm, and a spacing of 2.1 mm; The second positive lens (52) has a front surface curvature radius of 111.9 mm, a rear surface curvature radius of 590.2 mm, a thickness of 8 mm, and a spacing of 61 mm; The first negative lens (61) has a front surface curvature radius of 285 mm, a rear surface curvature radius of 59 mm, a thickness of 3 mm, and a spacing of 3.1 mm; The third positive lens (62) has a front surface curvature radius of 76.4 mm, a rear surface curvature radius of -193.43 mm, a thickness of 5.6 mm, and a spacing of 5.7 mm; The second negative lens (41) has a front surface curvature radius of -18 mm, a rear surface curvature radius of -11.4 mm, a thickness of 4.1 mm, and a spacing of 4.45 mm; The fourth positive lens (42) has a front surface curvature radius of -16.4 mm, a rear surface curvature radius of -14.1 mm, a thickness of 4.2 mm, and a spacing of 17.97 mm.

4. The Littrow shortwave imaging spectroscopy system based on rear arm compensation according to claim 3, characterized in that: The refractive index of the first positive lens (51) is nd1=1.677, and the Abbe number vd1 is 55.2; The refractive index of the second positive lens (52) is nd2=1.65, and the Abbe number is vd2=50.88; The refractive index of the first negative lens (61) is nd3=1.92, and the Abbe number is vd3=20.28; The refractive index of the third positive lens (62) is nd4=1.65, and the Abbe number is vd4=39.54; The refractive index of the second negative lens (41) is nd5=1.51, and the Abbe number is vd5=64.19; The refractive index of the fourth positive lens (42) is nd6=2.01, and the Abbe number vd6 is 28.

31.

5. The Littrow shortwave imaging spectroscopy system based on rear arm compensation according to claim 4, characterized in that: The width of the slit (1) is 30 to 100 μm.

6. The Littrow shortwave imaging spectroscopy system based on rear arm compensation according to claim 5, characterized in that: The plane grating (3) has a line density of 80-150 lp / mm and a blaze angle of 4.32°.

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