Hyperspectral imaging optical system

Abstract

The invention provides a hyperspectral imaging optical system, and relates to the technical field of spectral imaging, and the hyperspectral imaging optical system is provided with five lenses with refractive power. The optical system comprises an entrance slit, a first reflecting mirror, a first lens with negative refractive power, a second lens with positive refractive power, a third lens with negative refractive power, a second reflecting mirror, a fourth lens with negative refractive power, a fifth lens with positive refractive power, a plane reflecting grating and a detector in sequence from an object side to an image side along an optical axis, the fourth lens and the fifth lens form a balsaming lens. According to the invention, the imaging quality of the hyperspectral imaging optical system can be improved.

Description

Technical Field

[0001] This invention relates to the field of spectral imaging technology, and more particularly to a hyperspectral imaging optical system. Background Technology

[0002] In numerous fields such as industrial non-destructive testing, agricultural crop growth monitoring, geological and mineral exploration, and environmental pollutant analysis, the demand for precise detection of material composition and state is increasing, making hyperspectral imaging technology a focus of attention. The 900-1700nm wavelength range covers the characteristic absorption and reflection spectral bands of many substances, providing rich material information and offering a powerful tool for accurately analyzing material composition and monitoring material state.

[0003] Chinese Patent Publication No. CN106066307A discloses a compact, high-resolution, wide-field-of-view spectral imaging system, including a front objective lens, an entrance slit, a collimating and focusing lens group, an immersion planar grating, and an area array detector. The entrance slit, collimating and focusing lens group, immersion planar grating, and area array detector constitute a beam-splitting system. The front objective lens has a four-element structure; the immersion planar grating has an isosceles right-angled triangle cross-section; and the collimating and focusing lens group has a four-element structure. However, the above solution lacks synergistic optimization between image plane curvature and field curvature correction. If the image plane tilt angle is too small and not combined with field curvature or astigmatism compensation, it can easily lead to limited edge field imaging quality and focal plane consistency. Therefore, it is essential to provide a hyperspectral imaging optical system that can effectively improve the imaging quality of hyperspectral imaging optical systems. Summary of the Invention

[0004] In view of this, the present invention proposes a hyperspectral imaging optical system.

[0005] This invention provides a hyperspectral imaging optical system, which comprises five lenses with refractive power. Along the optical axis from the object side to the image side, the system includes, in sequence, an entrance slit, a first reflecting mirror, a first lens with negative refractive power, a second lens with positive refractive power, a third lens with negative refractive power, a second reflecting mirror, a fourth lens with negative refractive power, a fifth lens with positive refractive power, a planar reflecting grating, and a detector. The fourth lens and the fifth lens form a cemented lens. The hyperspectral imaging optical system satisfies the following condition: -169.3 < f1 < -168.8; 57.8 < f2 < 58.6; -92.7 < f3 < -92.1; 1.41≤f45 / f3≤1.49; Wherein, f1 represents the focal length of the first lens, f2 represents the focal length of the second lens, f3 represents the focal length of the third lens, and f45 represents the focal length of the cemented lens.

[0006] Based on the above technical solutions, preferably, the object side of the first lens is convex near the optical axis, the image side of the first lens is convex near the optical axis, and the radius of curvature of the object side of the first lens is greater than the radius of curvature of the image side of the first lens.

[0007] Based on the above technical solutions, preferably, the object side of the second lens is concave near the optical axis, the image side of the second lens is concave near the optical axis, and the radius of curvature of the object side of the second lens is smaller than the radius of curvature of the image side of the second lens.

[0008] More preferably, the object-side surface of the third lens is convex near the optical axis, the image-side surface of the third lens is convex near the optical axis, and the radius of curvature of the object-side surface of the third lens is greater than the radius of curvature of the image-side surface of the third lens.

[0009] More preferably, the object-side surface of the fourth lens near the optical axis is concave, the image-side surface of the fourth lens near the optical axis is concave, the object-side surface of the fifth lens near the optical axis is convex, and the image-side surface of the fifth lens near the optical axis is convex.

[0010] More preferably, the grating direction of the planar reflective grating is parallel to the slit direction of the incident slit, and the grating direction of the planar reflective grating is perpendicular to the optical axis of the incident light.

[0011] More preferably, the first lens and the second lens satisfy the following conditions: 0.78≤(R11+R12) / (R11-R12)≤0.85; -0.11≤(R21+R22) / (R21-R22)≤-0.06; Wherein, R11 represents the radius of curvature of the object side of the first lens, R12 represents the radius of curvature of the image side of the first lens, R21 represents the radius of curvature of the object side of the second lens, and R22 represents the radius of curvature of the image side of the second lens.

[0012] More preferably, the cemented lens satisfies the following conditions: 1.22≤(R31+R32) / (R31-R32)≤1.31; Wherein, R31 represents the radius of curvature of the object side of the cemented lens, and R32 represents the radius of curvature of the image side of the cemented lens.

[0013] More preferably, the refractive indices of the first lens and the fourth lens are both greater than 1.9, the Abbe coefficients of the first lens and the fourth lens are both less than 20, the refractive indices of the second lens and the fifth lens are both less than 1.7, and the Abbe coefficients of the second lens and the fifth lens are both greater than 50.

[0014] More preferably, the first lens and the second lens are both aspherical lenses, and the third lens, the fourth lens and the fifth lens are all spherical lenses.

[0015] The hyperspectral imaging optical system provided by this invention has the following advantages over existing technologies: (1) By configuring the refractive power of the negative-positive-negative three-lens group and setting a cemented lens that matches the plane reflection grating at the rear end, spherical aberration, coma, field curvature and distortion can be synergistically corrected in a wide spectral range, reducing the wave aberration on the axis and at the edge of the image plane. The focal length ratio within the condition range effectively suppresses the secondary chromatic aberration introduced by chromatic aberration superposition and grating dispersion, so that the spectral and image directions can obtain high point spread function compactness and modulation transfer function level at the same time. At the same time, the focal length range of the first lens, the second lens and the third lens is strictly limited, which is conducive to maintaining the flatness of the image plane under large or medium field of view, reducing off-axis aberration, improving edge spatial resolution and radiometric calibration stability, thereby effectively improving the imaging quality of the hyperspectral imaging optical system. The folded optical path of two mirrors and the plane reflection grating is set so that the system can significantly shorten the structural length while ensuring the effective focal length and light transmission aperture, improving the overall compactness. The number of lenses is controlled to five, which reduces the number of surfaces and coatings while ensuring aberration correction, reducing interface reflection and scattering loss, and improving the overall transmittance of the hyperspectral imaging optical system.

[0016] (2) When 0.78≤(R11+R12) / (R11-R12)≤0.85 and -0.11≤(R21+R22) / (R21-R22)≤-0.06 are satisfied, the incidence angle distribution of the principal rays in the meridional and sagittal directions of the first lens is more balanced, thereby reducing the first and higher order spherical aberrations in a wide spectral range and weakening off-axis coma in a large field of view. This makes the curvature direction of the second lens complementary to that of the first lens, facilitating the cancellation of the superposition effect of coma and astigmatism through the pairing of positive and negative curvatures, and improving the imaging quality at the field edge. The above interval ensures that the convergence and image-side numerical aperture of the beam remain within the design window before entering the cemented lens and the reflection grating, reducing spectral line broadening and aberration amplification caused by the offset of grating incidence conditions, improving the actual spectral resolution, and thus helping to improve the imaging quality of the hyperspectral imaging optical system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a hyperspectral imaging optical system provided by the present invention; Figure 2 A schematic diagram of the transfer function curve at a wavelength of 900nm provided by the present invention; Figure 3 A schematic diagram of the transfer function curve at a wavelength of 1700 nm provided by the present invention; Figure 4 The spectral resolution diagram of the entire system at a wavelength of 900 nm provided by this invention; Figure 5 The spectral resolution diagram of the entire system at a wavelength of 1700nm provided by this invention.

[0019] Explanation of reference numerals in the attached drawings: 1. First reflecting mirror; 2. First lens; 3. Second lens; 4. Third lens; 5. Second reflecting mirror; 6. Fourth lens; 7. Fifth lens; 8. Planar reflecting grating; 9. Detector. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0022] Please see Figure 1 This application discloses a hyperspectral imaging optical system. The hyperspectral imaging optical system has five lenses with refractive power. Along the optical axis from the object side to the image side, it includes an entrance slit, a first reflecting mirror 1, a first lens 2 with negative refractive power, a second lens 3 with positive refractive power, a third lens 4 with negative refractive power, a second reflecting mirror 5, a fourth lens 6 with negative refractive power, a fifth lens 7 with positive refractive power, a planar reflecting grating 8, and a detector 9. The fourth lens 6 and the fifth lens 7 form a cemented lens.

[0023] The entrance slit is positioned on the focal plane of the relevant optical element that collimates or focuses the light. Only in this position can the incident light be ensured to have a stable and appropriate propagation direction and energy distribution during subsequent propagation. At the same time, the center of the entrance slit is located on the optical axis of the optical path system composed of the first reflecting mirror 1, the first lens 2, the second lens 3, the third lens 4, and the second reflecting mirror 5.

[0024] The grating direction of the plane reflection grating 8 is parallel to the slit direction of the incident slit, and the grating direction of the plane reflection grating 8 is perpendicular to the optical axis of the incident light, so as to ensure that light of different wavelengths can be separated according to the designed angle and direction after passing through the grating diffraction, thereby achieving efficient and accurate light splitting effect.

[0025] After being converged by the front lens, the light enters the hyperspectral imaging optical system through the entrance slit. The direction of the light path is changed by the first reflecting mirror 1, and then pre-processed by the first lens 2, second lens 3, third lens 4, and cemented lens, ensuring the light is incident on the plane reflection grating 8 with a suitable angle and energy distribution. The plane reflection grating 8 uses the principle of diffraction to disperse the mixed light according to wavelength. The dispersed light is then focused onto the detector 9, which converts the optical signal into an electrical or digital signal, completing the spectral data acquisition.

[0026] In one example, the front-facing lens has a focal length of 25mm, a target surface size of 2 / 3 inch, and a numerical aperture of F2.5. The focal length of the front-facing lens determines its light-gathering ability; a 25mm focal length ensures a wide field of view while effectively focusing light onto subsequent optical elements. The 2 / 3-inch target surface size ensures the lens can receive sufficient light, providing ample luminous flux for the system. The numerical aperture of F2.5 affects the lens's light-gathering ability and resolution; a larger numerical aperture means the lens can collect more light, improving system sensitivity and contributing to enhanced image clarity and resolution. The entrance slit width is 30µm, the effective slit length is 9.6mm, and the numerical aperture is F2.5. A narrower slit width improves spectral resolution, allowing the system to more accurately distinguish different wavelengths of light. An appropriate slit length ensures sufficient luminous flux, ensuring detector 9 receives enough light signals, thereby improving the system's ability to resolve different spectral signals and meeting the detail resolution requirements of hyperspectral imaging.

[0027] The Shimadzu 010-120 planar reflective grating 8 is used as the beam-splitting element. It has 100 lines / mm and a blaze wavelength of 1200nm. The combination of the 100 lines / mm and the 1200nm blaze wavelength ensures high diffraction efficiency for different wavelengths of light in the 900-1700nm band, clearly decomposing mixed light into monochromatic light of different wavelengths, thus guaranteeing high-resolution spectral imaging. Based on the principle of grating diffraction, efficient beam splitting in the 900-1700nm band is achieved. Compared to traditional beam splitting methods, the planar reflective grating 8 offers advantages such as good dispersion linearity, low cost, and ease of fabrication, while avoiding the difficulties in fabricating curved gratings and the complex non-coaxial structure of reflective gratings. The good dispersion linearity of the planar reflective grating 8 allows for a more uniform spatial distribution of light of different wavelengths, facilitating subsequent spectral analysis and imaging. Its low cost and ease of fabrication enable effective cost control in large-scale production, enhancing the product's market competitiveness.

[0028] Furthermore, the object-side surface of the first lens 2 is convex near the optical axis, and the image-side surface of the first lens 2 is also convex near the optical axis. Additionally, the radius of curvature of the object-side surface of the first lens 2 is greater than the radius of curvature of the image-side surface. Because the first lens 2 has negative refractive power, it helps to reduce the angle of incidence of the incident light rays, thereby effectively sharing the large field of view on the object side.

[0029] Furthermore, the object-side surface of the second lens 3 is concave near the optical axis, and the image-side surface of the second lens 3 is also concave near the optical axis. The radius of curvature of the object-side surface of the second lens 3 is smaller than that of the image-side surface. Because the second lens 3 has positive refractive power and its object-side surface is convex, it is beneficial for improving the light-gathering ability of the hyperspectral imaging optical system, while also balancing the aberrations of the hyperspectral imaging optical system and improving its imaging quality.

[0030] Furthermore, the object-side surface of the third lens 4 is convex near the optical axis, and the image-side surface of the third lens 4 is also convex near the optical axis. Moreover, the radius of curvature of the object-side surface of the third lens 4 is greater than the radius of curvature of the image-side surface of the third lens 4. Since the third lens 4 has negative refractive power, it is beneficial to reduce the tilt angle of the incident light rays, thereby effectively sharing the large field of view on the object side.

[0031] Furthermore, the object-side surface of the fourth lens 6 is concave near the optical axis, and the image-side surface of the fourth lens 6 is also concave near the optical axis. The radius of curvature of the object-side surface of the fourth lens 6 is greater than that of the image-side surface. Similarly, the object-side surface of the fifth lens 7 is convex near the optical axis, and the radius of curvature of the object-side surface of the fifth lens 7 is also greater than that of the image-side surface. The fourth lens 6 and the fifth lens 7 form a cemented lens group. This arrangement allows the fourth lens 6, with its negative refractive power, to reduce the angle of incident rays in a large field of view, thereby effectively reducing transverse aberration. The fifth lens 7, which also has positive refractive power, helps to collect light from the edge of the large aperture. Overall, this effectively corrects spherical aberration and some transverse aberrations in the hyperspectral imaging optical system, thus improving the imaging quality of the hyperspectral imaging optical system. Furthermore, forming a cemented lens group with the fourth lens 6 not only appropriately increases the principal ray angle but also effectively reduces system aberrations, further improving the imaging quality of the hyperspectral imaging optical system.

[0032] The cemented lens, together with the first lens 2, the second lens 3, and the third lens 4, forms a lens group that plays a crucial role in pre-processing incident light in the hyperspectral imaging optical system. When light enters the hyperspectral imaging optical system through the entrance slit, it first passes through the first reflecting mirror 1 and the second reflecting mirror 5 to change its propagation direction before entering the lens group. The lens group's function is to precisely adjust the convergence, parallelism, and wavefront shape of the light. The cemented lens effectively reduces reflection and scattering losses between different lens interfaces, improving light transmission efficiency. Meanwhile, the first lens 2, the second lens 3, and the third lens 4, through their different radii of curvature and material properties, work together to adjust the light to a suitable state, ensuring that it is incident on the planar reflective grating 8 in a uniform, parallel, and rationally distributed manner.

[0033] In this embodiment of the invention, the hyperspectral imaging optical system satisfies the following condition: -169.3 < f1 < -168.8; 57.8 < f2 < 58.6; -92.7 < f3 < -92.1; 1.41≤f45 / f3≤1.49; Where f1 represents the focal length of the first lens 2, f2 represents the focal length of the second lens 3, f3 represents the focal length of the third lens 4, and f45 represents the focal length of the cemented lens.

[0034] For the radii of curvature of the first lens 2 and the second lens 3, the hyperspectral imaging optical system satisfies the following equation: 0.78≤(R11+R12) / (R11-R12)≤0.85; -0.11≤(R21+R22) / (R21-R22)≤-0.06; Where R11 represents the radius of curvature of the object-side surface of the first lens 2, R12 represents the radius of curvature of the image-side surface of the first lens 2, R21 represents the radius of curvature of the object-side surface of the second lens 3, and R22 represents the radius of curvature of the image-side surface of the second lens 3. When the above equations are satisfied, the incidence angle distribution of the principal rays in the meridional and sagittal directions of the first lens 2 is more balanced, thereby reducing first-order and higher-order spherical aberrations over a wide spectral range and weakening off-axis coma in a large field of view. This makes the curvature direction of the second lens 3 complementary to that of the first lens 2, facilitating the cancellation of the superposition effect of coma and astigmatism through the pairing of positive and negative curvatures, thus improving the field-edge imaging quality. The above interval ensures that the convergence and image-side numerical aperture of the beam remain within the design window before entering the cemented lens and the reflection grating, reducing spectral line broadening and aberration amplification caused by grating incident condition shifts, improving the actual spectral resolution, and thus contributing to improving the imaging quality of the hyperspectral imaging optical system.

[0035] For the radius of curvature of a cemented lens, the hyperspectral imaging optical system satisfies the following equation: 1.22≤(R31+R32) / (R31-R32)≤1.31; Where R31 represents the radius of curvature of the object side of the cemented lens, and R32 represents the radius of curvature of the image side of the cemented lens. When the above relationship equation is satisfied, the asymmetric curvature enhances the cemented lens's ability to compensate for higher-order aberrations, especially improving the uniformity of PSF and MTF at the edge of a large field of view.

[0036] In this embodiment, the refractive indices of the first lens 2 and the fourth lens 6 are both greater than 1.9, and their Abbe numbers are both less than 20. The refractive indices of the second lens 3 and the fifth lens 7 are both less than 1.7, and their Abbe numbers are both greater than 50. It is understood that the higher the refractive index of the medium, the stronger the dispersion and the smaller the Abbe number; conversely, the lower the refractive index of the medium, the less obvious the dispersion and the larger the Abbe number. By rationally selecting the refractive index and Abbe number of the lenses, the chromatic aberration of the hyperspectral imaging optical system can be further corrected, which is beneficial to improving the imaging quality of the hyperspectral imaging optical system. By pairing strong-dispersion and weak-dispersion materials (the fourth / fifth lenses 7 at the rear end forming a cemented lens), a typical achromatic / apochromatic ratio can be formed, significantly reducing longitudinal and lateral chromatic aberration; at the same time, it has a stronger ability to suppress secondary chromatic aberration caused by grating dispersion coupling, resulting in smaller cross-band focal shift, more stable spectral line shape, and improved effective spectral resolution and cross-band registration consistency.

[0037] Furthermore, the first lens 2 and the second lens 3 are both aspherical lenses, while the third lens 4, the fourth lens 6, and the fifth lens 7 are all spherical lenses. Traditional spherical lenses are prone to aberrations during imaging, leading to blurring and distortion at the edges of the image. However, by using specially designed aspherical lenses, their surface shape can be optimized according to the characteristics of aberrations, effectively compensating for and correcting these aberrations. Simultaneously, by optimizing the installation angle and parameters of the planar reflection grating 8, chromatic aberration and aberrations are balanced, ensuring clear imaging with low distortion throughout the entire field of view, and good consistency between the image edges and center. The precise curved surface design and manufacturing process of the aspherical lens can effectively correct aberrations such as spherical aberration, coma, and field curvature, improving image quality. Optimizing the installation angle and parameters of the planar reflection grating 8 can reduce the impact of chromatic aberration on imaging, further improving image sharpness and accuracy.

[0038] In this embodiment, the specific parameters of each lens are shown in Table 1. Table 1 shows the radius of curvature R, thickness T, material refractive index n, Abbe number V, and focal length F of each lens in the hyperspectral imaging optical system. The units of radius of curvature R, thickness T, and focal length F are all millimeters (mm).

[0039] Table 1

[0040]

[0041] It should be noted that in Table 1, "Surface Number" refers to the serial number of each surface arranged sequentially from the object side to the image side. The radius R value is the lens corresponding to the surface number, which is the radius of curvature of the object side or image side of the lens corresponding to each surface number at the optical axis. In the hyperspectral imaging optical system, "infinite" in the "Radius of Curvature" parameter series means that the object side or image side of the lens is a plane. The first value in the "Thickness" parameter series for each lens is the thickness of the lens on the optical axis.

[0042] The overall parameters of the hyperspectral imaging optical system matched with Table 1 are as follows: f1 = -169.0; f2 = -57.9; f3 = -92.3; f45 / f5 = -1.44; (R11+R12) / (R11-R12)=0.8264; (R21+R22) / (R21-R22)=-0.09; (R31+R32) / (R31-R32)=1.2797; The first reflecting mirror 1 and the second reflecting mirror 5 play a crucial role in the system by altering the direction of light propagation. The quality of their reflective surface materials and coatings directly affects the system's light reflection efficiency in the 900-1700nm wavelength range. To ensure efficient system operation, the reflective surface materials of the mirrors must possess high reflectivity, and the coating process must guarantee that the reflectivity reaches a specific standard within this wavelength range. During mirror installation, high-precision measuring instruments and installation equipment are required to accurately adjust their angles and positions, ensuring that the reflected light propagates precisely to subsequent optical components.

[0043] Detector 9 is a GH-SW640Pro-U3 camera with a pixel size of 15μm, a frame rate of 400Hz, and a signal-to-noise ratio of 62.42dB, meeting the sensitivity, frame rate, and signal-to-noise ratio requirements for hyperspectral imaging in the 900-1700nm band. Its smaller pixel size allows for higher spatial resolution when capturing spectral information, enabling the resolution of more subtle spectral differences. The high frame rate ensures rapid acquisition of spectral data, making it suitable for monitoring and analyzing dynamic targets. The good signal-to-noise ratio ensures that the camera can effectively suppress noise interference and acquire accurate and reliable spectral signals when receiving weak light signals. When installing detector 9, it is necessary to precisely position it to accurately receive the light after it has been dispersed by the planar reflection grating 8 and focused by the subsequent optical structure. Simultaneously, the optical axis consistency between detector 9 and other optical components, as well as the installation stability of detector 9, must be considered to avoid affecting the accuracy of spectral data acquisition.

[0044] The hyperspectral imaging optical system achieves a spectral resolution of 5 nm. By optimizing the grating density, incident angle, and focusing system parameters of the planar reflection grating 8, its spectral subdivision capability is effectively enhanced. It can accurately capture the characteristic spectral differences of substances in the 900-1700 nm wavelength range, providing reliable data support for qualitative and quantitative analysis of material composition. Through precise calculation and optimization of the grating density and incident angle, light of different wavelengths can be more accurately separated after diffraction by the grating. Combined with the optimization of the focusing system parameters, the spectral resolution is further improved, enabling accurate identification of minute components and features in substances.

[0045] Principle Explanation: In the actual operation of the hyperspectral imaging optical system, light first enters the system through an entrance slit. The entrance slit restricts the width and shape of the light, forming a narrow beam with a specific spatial distribution. This beam is then reflected by the first reflecting mirror 1 and the second reflecting mirror 5, changing its propagation direction and allowing it to enter the lens group. After preprocessing by the lens group, the light reaches the planar reflection grating 8 in an ideal state. Based on its unique diffraction principle, the planar reflection grating 8 uses a scribed structure to generate different diffraction angles for different wavelengths of light, thereby precisely dispersing the mixed light of 900-1700nm according to wavelength. The dispersed light is then focused by a carefully designed optical structure and finally accurately projected onto the detector 9. The detector 9 converts the received optical signal into an electrical or digital signal, which is then transmitted to the data processing system for further processing and analysis, thus completing the spectral data acquisition process. During data acquisition, acquisition parameters, such as integration time and gain, need to be set appropriately according to the characteristics of the detector 9 and the system requirements to obtain high-quality spectral data.

[0046] In this embodiment, by configuring the refractive power of a negative-positive-negative three-lens group and setting a cemented lens at the rear end that matches the planar reflection grating 8, spherical aberration, coma, field curvature, and distortion can be synergistically corrected over a wide spectral range, reducing on-axis and wavefront aberrations at the image plane edges. Furthermore, the focal length ratio within the specified range effectively suppresses chromatic aberration superposition and secondary chromatic aberration introduced by grating dispersion, resulting in high point spread function compactness and modulation transfer function levels in both the spectral and image directions. At the same time, the focal length ranges of the first lens 2, the second lens 3, and the third lens 4 are strictly defined. This is beneficial for maintaining image plane flatness under large or medium field of view conditions, reducing off-axis aberrations, improving edge spatial resolution and radiometric calibration stability, thereby effectively improving the imaging quality of the hyperspectral imaging optical system. The folded optical path with two mirrors and a plane reflection grating 8 allows the system to significantly shorten the structural length while ensuring the effective focal length and light transmission aperture, improving the overall compactness. The number of lenses is controlled to five, which reduces the number of surfaces and coatings while ensuring aberration correction, reducing interface reflection and scattering losses, and improving the overall transmittance of the hyperspectral imaging optical system.

[0047] In terms of imaging quality, the hyperspectral imaging optical system employs a design combining spherical and aspherical mirrors. The aspherical mirror is introduced to precisely correct aberrations across a wide wavelength range, such as spherical aberration, coma, and field curvature. Traditional spherical mirrors are prone to aberrations during imaging, leading to blurring and distortion at image edges. However, by using specially designed aspherical mirrors, their surface shape can be optimized according to the characteristics of the aberrations, effectively compensating for and correcting them. Simultaneously, the installation angle and parameters of the planar reflection grating 8 are optimized to further balance the relationship between dispersion and aberrations. Through the synergistic effect of these measures, clear imaging with low distortion is ensured throughout the entire field of view, and the edges and center of the image exhibit high consistency, providing users with high-quality imaging results.

[0048] like Figure 2 and 3 As shown, the hyperspectral imaging optical system also demonstrates excellent performance in terms of transfer function and dot plot. The transfer function measures the system's ability to transmit signals at different spatial frequencies. The hyperspectral imaging optical system has a transfer function value greater than 0.3 at 34 lp / mm, indicating that it can effectively transmit detailed information in the image, ensuring high contrast and sharpness.

[0049] like Figure 4 and 5As shown, the dot plot of the hyperspectral imaging optical system is within two pixel sizes, which means that the hyperspectral imaging optical system can clearly resolve wavelength changes, effectively ensuring the accuracy and reliability of imaging. These performance optimizations greatly enhance the overall imaging performance of the hyperspectral imaging optical system, giving it a significant advantage in the field of hyperspectral imaging.

[0050] The hyperspectral imaging optical system underwent comprehensive and rigorous tolerance analysis, and a reasonable tolerance range was preset. Regarding surface tolerances, the radius of curvature aperture was set to 3, and the tilt angles (X and Y degrees) were both controlled within 0.03. This ensured the shape accuracy of the optical element surfaces and reduced anomalies in light refraction and reflection caused by surface errors. Regarding element tolerances, the refractive index tolerance was set to 0.001, strictly controlling the refractive index deviation of the optical element materials to ensure that the light propagation path within the element met design requirements. Through strict control of these tolerances, the hyperspectral imaging optical system can maintain stable performance under various environmental conditions. For example, when environmental factors such as temperature and humidity change, the hyperspectral imaging optical system can self-adjust within the preset tolerance range, ensuring that light propagation and imaging are unaffected, thereby achieving stable and reliable hyperspectral imaging functionality.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hyperspectral imaging optical system, characterized in that, The hyperspectral imaging optical system comprises five refractive lenses, which, along the optical axis from the object side to the image side, include an entrance slit, a first reflecting mirror (1), a first lens (2) with negative refractive power, a second lens (3) with positive refractive power, a third lens (4) with negative refractive power, a second reflecting mirror (5), a fourth lens (6) with negative refractive power, a fifth lens (7) with positive refractive power, a planar reflection grating (8), and a detector (9). The fourth lens (6) and the fifth lens (7) form a cemented lens. The hyperspectral imaging optical system satisfies the following condition: -169.3＜f1＜-168.8； 57.8＜f2＜58.6； -92.7＜f3＜-92.1； 1.41≤f45 / f3≤1.49; Wherein, f1 represents the focal length of the first lens (2), f2 represents the focal length of the second lens (3), f3 represents the focal length of the third lens (4), and f45 represents the focal length of the cemented lens.

2. The hyperspectral imaging optical system as described in claim 1, characterized in that, The object side of the first lens (2) is convex near the optical axis, and the image side of the first lens (2) is convex near the optical axis. Furthermore, the radius of curvature of the object side of the first lens (2) is greater than the radius of curvature of the image side of the first lens (2).

3. The hyperspectral imaging optical system as described in claim 1, characterized in that, The object side of the second lens (3) is concave near the optical axis, and the image side of the second lens (3) is concave near the optical axis. Furthermore, the radius of curvature of the object side of the second lens (3) is smaller than the radius of curvature of the image side of the second lens (3).

4. The hyperspectral imaging optical system as described in claim 1, characterized in that, The object side of the third lens (4) is convex near the optical axis, and the image side of the third lens (4) is convex near the optical axis. Furthermore, the radius of curvature of the object side of the third lens (4) is greater than the radius of curvature of the image side of the third lens (4).

5. The hyperspectral imaging optical system as described in claim 1, characterized in that, The object side of the fourth lens (6) is concave near the optical axis, and the image side of the fourth lens (6) is concave near the optical axis. The object side of the fifth lens (7) is convex near the optical axis, and the image side of the fifth lens (7) is convex near the optical axis.

6. The hyperspectral imaging optical system as described in claim 1, characterized in that, The grating direction of the planar reflective grating (8) is parallel to the slit direction of the incident slit, and the grating direction of the planar reflective grating (8) is perpendicular to the optical axis of the incident light.

7. The hyperspectral imaging optical system as described in claim 1, characterized in that, The first lens (2) and the second lens (3) satisfy the following conditions: 0.78≤(R11+R12) / (R11-R12)≤0.85; -0.11≤(R21+R22) / (R21-R22)≤-0.06; Wherein, R11 represents the radius of curvature of the object side of the first lens (2), R12 represents the radius of curvature of the image side of the first lens (2), R21 represents the radius of curvature of the object side of the second lens (3), and R22 represents the radius of curvature of the image side of the second lens (3).

8. The hyperspectral imaging optical system as described in claim 1, characterized in that, The cemented lens satisfies the following conditions: 1.22≤(R31+R32) / (R31-R32)≤1.31; Wherein, R31 represents the radius of curvature of the object side of the cemented lens, and R32 represents the radius of curvature of the image side of the cemented lens.

9. A hyperspectral imaging optical system as described in claim 1, characterized in that, The refractive indices of the first lens (2) and the fourth lens (6) are both greater than 1.9, and the Abbe coefficients of the first lens (2) and the fourth lens (6) are both less than 20. The refractive indices of the second lens (3) and the fifth lens (7) are both less than 1.7, and the Abbe coefficients of the second lens (3) and the fifth lens (7) are both greater than 50.

10. A hyperspectral imaging optical system as described in claim 1, characterized in that, The first lens (2) and the second lens (3) are both aspherical lenses, while the third lens (4), the fourth lens (6) and the fifth lens (7) are all spherical lenses.

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