A spectroscopic imaging method and system for a snapshot imaging spectrometer with a large numerical aperture

Abstract

The present invention relates to a spectroscopic imaging method and system for a large numerical aperture snapshot imaging spectrometer. A spectroscopic imaging system with a coaxial, concentric, and common optical path is adopted. In the incident direction of light, there are, in sequence, a plano-convex lens with a plane front surface, a first meniscus lens bent towards the incident direction of light, a second meniscus lens bent away from the incident direction of light, and a concave grating bent towards the incident direction of light. The aperture stop of the system is arranged on the concave grating. During spectroscopic imaging, the large-aperture polychromatic light emitted from the object surface is first converged by three refractive spherical lenses and then spectrally reflected by the concave grating and focused on the image surface for imaging. The spectroscopic imaging system provided by the present invention has two meniscus lenses in a back-to-back form, with strong aberration correction ability, small spectral line bending and chromatic distortion, can achieve large-aperture and high-spectral-resolution spectroscopic imaging, and has high light energy utilization rate. The light passes through the three spherical refractive lenses twice, and the structure of the system is compact, easy to process and assemble, and has strong stability.

Description

Technical Field

[0001] The present invention relates to a spectral imaging method and system applicable to a snapshot imaging spectrometer with a large numerical aperture. Background Art

[0002] A spectral imaging system can simultaneously obtain two-dimensional spatial information and one-dimensional spectral information of a measured target, and achieve precise identification and analysis of the target object.

[0003] Scanning spectral imaging technology obtains spatial and spectral information of a target scene through scanning, but it cannot simultaneously obtain complete image spectral information in a single exposure, thus limiting the application of scanning imaging spectrometers in monitoring fast-moving or changing targets, etc. At the same time, scanning imaging spectrometers have high requirements for the motion accuracy and stability of their push-broom platforms or their own scanning mechanisms, and are vulnerable to external vibrations, increasing the processing difficulty and cost of moving parts.

[0004] Snapshot spectral imaging technology can obtain two-dimensional spatial information and spectral information of a target object within the integration time of a detector without scanning, and achieve real-time hyperspectral imaging of dynamic targets. It is a novel spectral imaging technology. The spectral element or spectral imaging system, as the core part of the snapshot imaging spectrometer, determines the spectral resolution and imaging performance of the system. Common spectral elements include filter, prism, grating, etc. For a snapshot imaging spectrometer based on filter spectroscopy, the spectral resolution is relatively low, while the prism has poor spectral splitting ability, and the non-linear dispersion seriously affects the spectral resolution. For the snapshot spectral imaging systems reported in the existing literature, their numerical apertures and imaging fields of view are usually small.

[0005] Prior to the present invention, the document “Microlens array snapshot hyperspectralmicroscopy system for the biomedical domain,” (Applied Optics, 60(7), 2021) reported a transmission spectroscopic imaging system based on a grating-prism combination spectroscopic element, which is composed of a collimating lens group, a prism-grating combination spectroscopic element, and a focusing lens group. The spectroscopic imaging optical system obtains a collimating lens group composed of 6 lenses and a focusing lens group composed of 6 lenses by complicating the double Gaussian structure, thereby realizing wide-band and wide-field imaging and achieving the design purpose. However, there are the following deficiencies: First, the system uses a plane grating as the main spectroscopic element, which introduces large aberrations such as spectral line bending and color distortion, seriously affecting the spectral resolution and spatial resolution of the system; second, the collimating objective lens and the focusing objective lens use a relatively complex double Gaussian structure as the initial structure, which is difficult to design and difficult to achieve a larger numerical aperture; third, the system has a large number of lenses and a relatively complex structure, using a total of 12 lenses, a prism, and a grating, which is difficult to process and assemble. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a spectroscopic imaging method and system for a snapshot imaging spectrometer with a large numerical aperture, which can effectively improve spectral resolution and imaging quality, has a simple and compact system structure, and is easy to process and assemble.

[0007] The technical solution adopted by the present invention is to provide a spectroscopic imaging system for a large numerical aperture snapshot imaging spectrometer, which is a coaxial, co-optical path, and approximately concentric structure, including three spherical refractive lenses and a concave grating; according to the incident direction of light, it is: a plano-convex lens with a flat front surface, a first meniscus lens bent in the incident direction of the light, a second meniscus lens bent away from the incident direction of the light, and a concave grating bent in the incident direction of the light; the aperture stop of the system is arranged on the concave grating;

[0008] The optical powers of the plano-convex lens, the first meniscus lens and the second meniscus lens are φ2, φ3 and φ4, respectively, 0.013 mm -1 ≤φ2≤0.0135 mm -1 、-0.0008 mm -1 ≤φ3≤-0.0007 mm -1 and -0.0012 mm -1 ≤φ4≤-0.001 mm -1; their refractive indices of the glass materials are n2, n3, and n4 in sequence, where 1.45 ≤ n2 ≤ 1.51, 1.50 ≤ n3 ≤ 1.55, and 1.50 ≤ n4 ≤ 1.6; their Abbe numbers of the glass materials are v2, v3, and v4 in sequence, where 80 ≤ v2 ≤ 82, 50 ≤ v3 ≤ 55, and 40 ≤ v4 ≤ 42;

[0009] For the concave grating, the grating line density g satisfies 40 lp / mm ≤ g ≤ 60 lp / mm.

[0010] A preferred solution of the spectroscopic imaging system for a large numerical aperture snapshot imaging spectrometer provided by the present invention is that: for the rear surface of the plano-convex lens, the front and rear surfaces of the first meniscus lens, and the front and rear surfaces of the second meniscus lens, the curvature radii of each surface are R 21 , R 31 and R 32 , R 41 and R 42 , satisfying the conditions 35 mm ≤ R 21 ≤ 40 mm, 30 mm ≤ R 31 ≤ 35 mm, and 35 mm ≤ R 32 ≤ 45 mm, 220 mm ≤ R 41 ≤ 240 mm, and 150 mm ≤ R 42 ≤ 170 mm; the curvature radius R5 of the concave grating satisfies 150 mm ≤ R5 ≤ 170 mm.

[0011] The technical solution of the present invention further includes a spectroscopic imaging method for a large numerical aperture snapshot imaging spectrometer, which uses the spectroscopic imaging system as described above and includes the following steps:

[0012] (1) The polychromatic light rays emitted from the object surface are incident on the plano-convex lens. After converging the large-aperture light rays, they are transmitted through the first meniscus lens and the second meniscus lens in sequence and further converged, and then the polychromatic divergent light rays with reduced divergence angles are propagated to the concave grating;

[0013] (2) The concave grating disperses the polychromatic divergent light obtained in step (1) to obtain monochromatic convergent light rays of different wavelengths and reflects and emits them;

[0014] (3) The monochromatic convergent light rays of different wavelengths emitted in step (2) are transmitted through the second meniscus lens, the first meniscus lens, and the plano-convex lens in sequence, focused, and then imaged on the image surface.

[0015] The spectroscopic imaging system provided by the present invention adopts a coaxial and concentric design, and two meniscus lenses are designed in a back-to-back structure form, which increases the numerical aperture of the system and effectively improves the light-gathering ability and resolution of the system. At the same time, a common optical path structure is adopted, making the system simpler and more compact, and expanding the application range of the spectroscopic imaging system.

[0016] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0017] 1. The spectroscopic imaging method provided by the present invention adopts a coaxial, concentric and common optical path spectroscopic imaging system. The large-aperture polychromatic light emitted from the object surface is first converged by three refractive spherical lenses, then spectroscopically reflected by a concave grating, and focused on the image surface for imaging. The spectroscopic imaging system has the characteristics of being structurally compact, smaller in volume, easy to process and assemble, and strong in stability, which is beneficial to the miniaturization and portability of the snapshot imaging spectrometer.

[0018] 2. The spectroscopic imaging system provided by the present invention reasonably selects the glass materials of the three lenses and conducts a complex design. While achieving aberration correction and balance, it increases the numerical aperture of the optical lens, significantly improving the light-gathering ability and resolution of the system.

[0019] 3. The spectroscopic imaging system provided by the present invention designs two meniscus lenses in a back-to-back form, with strong aberration correction ability, small spectral line bending and chromatic distortion, good imaging quality, and can achieve large-aperture spectroscopic imaging.

[0020] 4. The spectroscopic imaging system provided by the present invention has spherical surfaces for the surfaces of the three refractive lenses, and all use domestic glass materials, reducing the processing difficulty and cost of the lens, and having practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of the spectroscopic imaging system provided by an embodiment of the present invention;

[0022] In the figure, 1. Object surface; 2. Plano-convex lens; 3. The first meniscus lens; 4. The second meniscus lens; 5. Concave grating; 6. Image surface; 21. Rear surface of the plano-convex lens; 31. Front surface of the first meniscus lens; 32. Rear surface of the first meniscus lens; 41. Front surface of the second meniscus lens; 42. Rear surface of the second meniscus lens.

[0023] Figure 2 is the spot diagram of ray tracing of the spectroscopic imaging system described in an embodiment of the present invention;

[0024] Figure 3 is the MTF curve graph of the transfer function of the spectroscopic imaging system described in an embodiment of the present invention;

[0025] Figure 4It is the curve graph of the enclosed energy concentration of the spectroscopic imaging system described in the embodiments of the present invention. Specific implementation

[0026] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] Embodiment 1: This embodiment provides a large-aperture compact snapshot spectroscopic imaging system. The optical lens of the system consists of 3 refractive spherical lenses and a concave grating. The object-space numerical aperture NA = 0.33, the object-space field of view φ = 14 mm × 4 mm, and the working wavelength is 400 nm to 700 nm.

[0028] See the attached Figure 1 , which is the structural schematic diagram of the spectroscopic imaging system provided in this embodiment. Among them, the object plane 1 and the image plane 6 are on the same side. In the incident direction of light, the optical elements are, in sequence, a plano-convex lens 2, a first meniscus lens 3, a second meniscus lens 4, and a concave grating 5; among them, the front surface of the plano-convex lens 2 is a plane, the first meniscus lens 3 bends towards the incident direction of light, the second meniscus lens 4 bends away from the incident direction of light, and the concave grating 5 bends towards the incident direction of light.

[0029] For the plano-convex lens, the first meniscus lens, and the second meniscus lens, their optical powers are φ2, φ3, and φ4 in sequence, with the unit of mm -1 , 0.013 ≤ φ2 ≤ 0.0135, -0.0008 ≤ φ3 ≤ -0.0007, and -0.0012 ≤ φ4 ≤ -0.001; their refractive indices of the glass materials are n2, n3, and n4 in sequence, 1.45 ≤ n2 ≤ 1.51, 1.50 ≤ n3 ≤ 1.55, 1.50 ≤ n4 ≤ 1.6; their Abbe numbers of the glass materials are v2, v3, and v4 in sequence, 80 ≤ v2 ≤ 82, 50 ≤ v3 ≤ 55, and 40 ≤ v4 ≤ 42.

[0030] Figure 1 In 21 , R 31 , R 32 , R 41 , and R 42 are the corresponding curvature radii of the rear surface 21 of the plano-convex lens, the front surface 31 and the rear surface 32 of the first meniscus lens, and the front surface 41 and the rear surface 42 of the second meniscus lens, with the unit of mm, satisfying the conditions 35 ≤ R 21 ≤ 40, 30 ≤ R 31 ≤ 35, and 35 ≤ R 32 ≤ 45, 220 ≤ R 41 ≤ 240, and 150 ≤ R 42 ≤ 170; the grating curvature radius is R5, 150 mm ≤ R5 ≤ 170 mm.

[0031] For the grating line density g of the concave grating, 40 lp / mm ≤ g ≤ 60 lp / mm.

[0032] In this embodiment, the parameters of each optical element are shown in Table 1.

[0033] Table 1:

[0034]

[0035] In this embodiment, the grating line density of the concave grating is 42 lines / mm.

[0036] For the spectroscopic imaging system provided in this embodiment, the tube length L = 160 mm.

[0037] Using the spectroscopic imaging system provided in this embodiment, the method of spectroscopic imaging is as follows: The outgoing polychromatic light at the object plane 1 is incident on the plano-convex lens 2. After converging the large-aperture light, it is successively incident on the first meniscus lens 3 and the second meniscus lens 4 to further converge the light, and the polychromatic divergent light with a reduced divergence angle is transmitted to the concave grating 5; the polychromatic divergent light is separated into monochromatic convergent light of different wavelengths by the concave grating and reflected out; the monochromatic convergent light of different wavelengths is then successively incident on the second meniscus lens, the first meniscus lens, and the plano-convex lens, and the light is focused to form an image on the image plane 6, thus completing the imaging process.

[0038] See Appendix Figure 2 , which is the ray tracing spot diagram of the light passing through the spectroscopic imaging system provided in this embodiment. The root mean square radius of the spot diagrams of each field corresponding to the three wavelengths of 400 nm, 550 nm, and 700 nm in the figure is less than 1 μm, and the geometric radius of the spot diagram is less than 3 μm, indicating good imaging quality.

[0039] See Appendix Figure 3 , which is the modulation transfer function (MTF) curve of the spectroscopic imaging system provided in this embodiment corresponding to each field on the image plane. As Figure 3 can be seen, at 166 lp / mm, the MTF values of each field corresponding to the wavelengths of 400 nm, 550 nm, and 700 nm are all greater than 0.55, approaching the diffraction limit, and the curve is relatively smooth, indicating that the lens imaging is clear and uniform, and the system has good imaging quality in the full wavelength range and full field of view.

[0040] See Appendix Figure 4 , which is the encircled energy concentration curve of the spectroscopic imaging system provided in this embodiment at a wavelength of 700 nm. As Figure 4 can be seen, more than 80% of the energy is concentrated within the Airy disk range, and the energy is relatively concentrated.

[0041] The snapshot spectral imaging system provided by the technical solution of the present invention is composed of only three lenses and one concave grating. By reasonably selecting the glass materials of the three lenses and further structural design, the numerical aperture of the lens imaging is effectively improved, the light-gathering ability and the system resolution of the system are increased, and an optical image with uniform illuminance distribution, concentrated energy and high resolution can be obtained.

[0042] The spectral imaging method provided by the technical solution of the present invention has the characteristics of large numerical aperture, good imaging quality, high spectral resolution and high light energy utilization rate after strict aberration correction of the spectral imaging system. Moreover, it has a simple and compact structure, is easy to process and adjust, has strong stability, can be used in the field of spectral imaging, and has broad application prospects.

Claims

1. A spectroscopic imaging system for a large numerical aperture snapshot imaging spectrometer, characterized in that: It has a coaxial, common optical path, and approximately concentric structure, including three spherical refraction lenses and one concave grating; in the light incident direction, they are, in sequence: a plano-convex lens (2) with a plane front surface, a first meniscus lens (3) bent towards the light incident direction, a second meniscus lens (4) bent away from the light incident direction, and a concave grating (5) bent towards the light incident direction; the aperture stop of the system is arranged on the concave grating; The optical powers of the plano-convex lens, the first meniscus lens and the second meniscus lens are φ2, φ3 and φ4, respectively, 0.013 mm -1 ≤φ2≤0.0135 mm -1 、-0.0008 mm -1 ≤φ3≤-0.0007 mm -1 and -0.0012 mm -1 ≤φ4≤-0.001 mm -1 ; The refractive indexes of their glass materials are n2, n3 and n4, 1.45≤n2≤1.51, 1.50≤n3≤1.55, 1.50≤n4≤1.6; The Abbe numbers of their glass materials are v2, v3 and v4, 80≤v2≤82, 50≤v3≤55 and 40≤v4≤42; For the concave grating, the grating line density g satisfies 40 lp / mm ≤ g ≤ 60 lp / mm.

2. The spectroscopic imaging system for a large numerical aperture snapshot imaging spectrometer according to claim 1, wherein: The rear surface (21) of the plano-convex lens, the front surface (31) and rear surface (32) of the first meniscus lens, and the front surface (41) and rear surface (42) of the second meniscus lens have curvature radii of R 21 , R 31 and R 32 , R 41 and R 42 , satisfying the conditions: 35 mm ≤ R 21 ≤ 40 mm, 30 mm ≤ R 31 ≤ 35 mm, and 35 mm ≤ R 32 ≤ 45 mm, 220 mm ≤ R 41 ≤ 240 mm, and 150 mm ≤ R 42 ≤ 170 mm; the curvature radius R5 of the concave grating satisfies: 150 mm ≤ R5 ≤ 170 mm.

3. A spectroscopic imaging method for a large numerical aperture snapshot imaging spectrometer, characterized in that Using the spectroscopic imaging system described in claim 1, it includes the following steps: (1) The polychromatic light emitted from the object surface (1) is incident on the plano-convex lens (2), the large-aperture light is converged and then successively transmitted through the first meniscus lens (3) and the second meniscus lens (4), and after further convergence, the polychromatic divergent light with a reduced divergence angle is propagated to the concave grating (5); (2) The concave grating (5) spectroscopically analyzes the polychromatic divergent light obtained in step 1, and the monochromatic convergent light of different wavelengths is reflected and emitted; (3) The monochromatic convergent light of different wavelengths emitted in step (2) is successively transmitted through the second meniscus lens (4), the first meniscus lens (3), and the plano-convex lens (2), and after being focused by transmission, it is imaged on the image surface (6).

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