CN115824411A - Large-aperture spectroscopic imaging method suitable for snapshot type spectral imaging system - Google Patents
Large-aperture spectroscopic imaging method suitable for snapshot type spectral imaging system Download PDFInfo
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- CN115824411A CN115824411A CN202211573915.2A CN202211573915A CN115824411A CN 115824411 A CN115824411 A CN 115824411A CN 202211573915 A CN202211573915 A CN 202211573915A CN 115824411 A CN115824411 A CN 115824411A
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Abstract
The invention relates to a large-aperture spectroscopic imaging method suitable for a snapshot type spectral imaging system. The large-aperture polychromatic light beam emitted from the object plane is converged by a meniscus lens and then enters a concave spherical reflector, the light beam is further converged and then reflected to a convex spherical reflection grating, the convex spherical reflection grating is glued on the rear surface of the meniscus lens, the polychromatic convergent light beam is divided into monochromatic divergent light beams with different wavelengths, the monochromatic divergent light beams with different wavelengths are emitted to the concave spherical reflector after the spectral distortion is corrected, the aberration correction is further carried out on the monochromatic divergent light beams with different wavelengths, the divergent light beams are converged at the meniscus lens, the light beams are further converged, and after the aberration correction, the convergent light beam is imaged on an image plane. The imaging method of the off-axis three-mirror optical system structure in the coaxial form is adopted, light rays pass through the common light path structure of the meniscus lens and the concave spherical reflector twice, the aberration correction capability of the system is effectively improved, and the imaging method has the characteristics of large numerical aperture, large field of view and high spectral resolution.
Description
Technical Field
The invention relates to a spectroscopic imaging system of an imaging spectrometer, in particular to a snapshot type spectroscopic imaging system.
Background
The imaging spectrum technology integrates a space imaging technology and a spectrum imaging technology, and greatly widens the application range of people in the fields of space remote sensing, agriculture and forestry resource detection, mineral resource and geological exploration, military detection, biomedical treatment and the like. The snapshot-type hyperspectral imager can simultaneously acquire two-dimensional image information and one-dimensional spectral information of an observation target, realizes non-scanning hyperspectral imaging data acquisition, and is widely applied to the field of astronomy and remote sensing at present.
In an imaging spectrometer, a commonly adopted light splitting element is a prism or a plane grating, the prism light splitting has the advantage of high optical efficiency, but the dispersion of the prism is nonlinear, and extra aberration and spectral line bending are introduced; the dispersion of a planar grating is linear, but the diffraction efficiency is low and there is spectral distortion. Compared with a prism and a plane grating light splitting mode, the light splitting element of the offner light splitting system is a convex spherical reflection grating, and the offner light splitting system has the advantages of simple and compact structure, large relative aperture, high spectral resolution, strong aberration correction capability and the like.
In the snapshot type imaging spectrometer reported in the existing literature, the large numerical aperture, the large imaging field of view and the compact structure can not be satisfied at the same time. The document "Optical design of a prism-grating-based lens array integrated field spectrometer" (Optical Express, vol.26, no.15, 2018) reports a spectral imaging system including a collimating system, a dispersing system and a camera system, wherein the collimating system is composed of six spherical lenses, the dispersing system adopts a method of combining a prism and a grating, and the camera system is composed of six spherical lenses. Although the light splitting mode of combining the grating and the prism is favorable for correcting the spectrum distortion, compared with a prism type spectrometer, the system has low utilization rate of light energy and the defects of spectrum cascade, and the spectrum waveband range and the view field of the system are severely restricted; and the optical elements of the system are numerous, which is not favorable for realizing the compact structure of the system.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a spectral imaging method which is suitable for a snapshot type spectral imaging system and has good imaging quality, large numerical aperture, large field of view and high spectral resolution.
The technical scheme adopted by the invention is to provide a large-aperture spectroscopic imaging method suitable for a snapshot type spectral imaging system, which comprises the following steps:
step 1, converging a large-aperture polychromatic light beam emitted from an object plane through a meniscus lens, and then, injecting the polychromatic light beam to a concave spherical reflector, so that the light beam is reflected after being further converged;
step 2, gluing the convex spherical reflection grating on the rear surface of the meniscus lens, wherein the convex spherical reflection grating and the concave spherical reflector are approximately concentric; the light beams converged in the step 1 are reflected to a convex spherical reflection grating, the polychromatic convergent light is divided into monochromatic divergent light beams with different wavelengths, and spectral distortion is corrected;
and 3, the monochromatic divergent light beam obtained in the step 2 is emitted to the concave spherical reflector by the convex spherical reflection grating, the concave spherical reflector further performs aberration correction on the monochromatic divergent light beam with different wavelengths, the divergent light beam is converged at the meniscus lens, the light beam is further converged, and after the aberration correction, the convergent light beam is imaged on an image plane.
The invention provides a large aperture spectroscopic imaging method suitable for a snapshot type spectral imaging system, wherein the front surface of a meniscus lens is an even aspheric surface, and the equation of the even aspheric surface is as follows:
wherein r is the radius of curvature; c is curvature, k is a conic coefficient, k =4.4 × 10 -3 ；a 2 And a 3 Are the coefficients of the monomials respectively, and the value range is-1.45 multiplied by 10 -8 ≤a 2 ≤-1.35×10 -8 ，4.4×10 -12 ≤a 3 ≤4.8×10 -12 。
The rear surface of the meniscus lens and the front and rear surfaces of the concave spherical reflector are spherical surfaces, and the curvature radiuses of the front and rear surfaces are R in sequence 22 、R 3 Taking mm as a length unit, the condition is satisfied: -62. Ltoreq.R 22 ≤-58，-130≤R 3 ≤-127。
The principle of the invention is as follows: by adopting the method of gluing the meniscus lens and the convex spherical reflection grating, the introduction of the meniscus lens compensates the spherical aberration and astigmatism of the system while realizing the light splitting of the system, the spectral distortion is further corrected, and the light splitting imaging with large numerical aperture, large field of view and high spectral resolution is realized; the light passes through the meniscus lens and the concave spherical reflector twice, has the characteristic of a common light path structure, improves the aberration correction capability of the system, and has a simpler and more compact structure.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the meniscus lens is adopted in the light splitting element, so that the spherical aberration and astigmatism of the system can be effectively compensated, the aberration compensation capability of the system is further improved, and the snapshot type light splitting imaging with wide working waveband and large numerical aperture is realized.
2. The invention combines the meniscus lens and the convex spherical reflection grating optical element, has simple and compact structure, is easy to assemble and adjust, strictly corrects the spectral distortion, controls the spectral line bending within 0.8 mu m and the color distortion within 1.5 mu m, and is beneficial to spectral calibration and later-stage image processing.
Drawings
Fig. 1 is a schematic structural and optical path diagram of a spectroscopic imaging system according to an embodiment of the present invention;
FIG. 2 is a flow chart of a large aperture spectroscopic imaging method suitable for use in a snapshot-type spectral imaging system according to an embodiment of the present invention;
FIG. 3 is a ray tracing point diagram of a spectroscopic imaging system provided by an embodiment of the present invention;
FIG. 4 is a graph of a transfer function MTF of a spectroscopic imaging system provided by an embodiment of the present invention;
FIG. 5 is a graph of the ring-in energy concentration of a spectroscopic imaging system provided by an embodiment of the present invention;
in the figure, 1, object plane; 2. a meniscus lens; 3. a concave spherical reflector; 4. a convex spherical surface reflection grating; 5. and (5) an image plane.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the embodiment.
Example 1:
the embodiment provides an optical system of a large-aperture spectroscopic imaging method suitable for a snapshot type spectral imaging system. The optical lens of the spectroscopic imaging system consists of a meniscus lens, a concave spherical reflector and a convex spherical reflection grating, the numerical aperture NA of an object space is =0.22, the field of view of the object space is 14 multiplied by 3mm, and the working wave band is 450-650 nm.
Referring to fig. 1, it is a schematic diagram of a structure and an optical path of the spectroscopic imaging system provided in this embodiment, in which an object plane 1 and an image plane 5 are located on the same side in space, and optical elements of the spectroscopic imaging system are coaxial, co-optical path, and approximately concentric structures, and according to a light incidence direction, sequentially: a meniscus lens 2 bending to the incident direction of light, a concave spherical reflector 3 bending to the incident direction of light, and a convex spherical reflection grating 4 glued with the rear surface of the meniscus lens; the aperture diaphragm of the system is arranged on the concave spherical reflector 3.
The rear surface of the meniscus lens 2 is glued with the convex spherical reflection grating 4; the rear surface of the meniscus lens and the front and rear surfaces of the concave spherical reflector are spherical surfaces, and the curvature radiuses of the front and rear surfaces are R in sequence 22 、R 3 Taking mm as a length unit, the condition is satisfied: -62. Ltoreq.R 22 ≤-58、-130≤R 3 ≤-127。
The front surface of the meniscus lens 2 is an even aspheric surface, and the equation of the even aspheric surface is as follows:
wherein r is the radius of curvature; c is curvature, k is conic coefficient, k =4.4 × 10 -3 ；a 2 And a 3 Are the coefficients of the monomials respectively, and the value range is-1.45 multiplied by 10 -8 ≤a 2 ≤-1.35×10 -8 ，4.4×10 -12 ≤a 3 ≤4.8×10 -12 。
In this embodiment, the even-order aspheric surface monomial coefficient a 2 =-1.4×10 -8 ，a 3 =4.6×10 -12 (ii) a The structural parameters of the convex spherical reflection grating are as follows: the reticle density is 150lines/mm, the diffraction order is-1.
The numerical aperture NA of the object space of the spectroscopic imaging system is more than or equal to 0.20 and less than or equal to 0.23, and the length L of the cylinder is more than or equal to 120mm and less than or equal to 140mm.
The parameters of each optical element of this example are shown in table 1.
Table 1:
referring to fig. 2, a flowchart of a spectroscopic imaging method applicable to the snapshot-type spectral imaging system provided in this embodiment is shown by the structure and optical path of the spectroscopic imaging system in fig. 1, where the spectroscopic imaging method includes the following specific steps:
step 1, converging a large-aperture polychromatic light beam emitted from an object plane 1 through a meniscus lens 2, and then, injecting the polychromatic light beam into a concave spherical reflector 3, so that the light beam is reflected after being further converged;
step 2, gluing the convex spherical reflection grating 4 on the rear surface of the meniscus lens, wherein the convex spherical reflection grating and the concave spherical reflector are approximately concentric; reflecting the light beams converged in the step 1 to a convex spherical reflection grating, dividing the polychromatic converging light into monochromatic divergent light beams with different wavelengths, and correcting spectral distortion;
and 3, the monochromatic divergent light beam obtained in the step 2 is emitted to the concave spherical reflector by the convex spherical reflection grating, the concave spherical reflector further performs aberration correction on the monochromatic divergent light beam with different wavelengths, the divergent light beam is converged at the meniscus lens, the light beam is further converged, and after the aberration correction, the convergent light beam is imaged on an image plane 5.
Referring to fig. 3, which is a light tracing point diagram of the spectroscopic imaging system provided by the embodiment, in the diagram, the root mean square radius of the point diagram of each field of view corresponding to three wavelengths of 450nm, 550nm and 650nm is less than 1.10 μm, the geometric radius of the point diagram is less than 3.50 μm, and the imaging quality is good.
Referring to fig. 4, it is a transfer function MTF curve on the image plane corresponding to each field of view of the spectroscopic imaging system provided in this embodiment. As can be seen from FIG. 4, under 83lp/mm, the MTF values of the fields of view with the wavelengths of 450nm (a diagram), 550nm (b diagram) and 650nm (c diagram) are all greater than 0.8, which is close to the diffraction limit, the curve is smooth, which indicates that the lens is clear and uniform in imaging, and the system has good imaging quality in the full-wave-band full-field.
Referring to fig. 5, which is a circle energy concentration curve of the spectroscopic imaging system provided by this embodiment with a wavelength of 650nm, it can be seen from fig. 5 that more than 80% of the energy is concentrated at a point within the Airy spot range, and the energy is relatively concentrated.
The snapshot type light splitting imaging system provided by the technical scheme of the invention comprises a meniscus lens, a concave spherical reflector and a convex spherical reflection grating, wherein the meniscus lens and the convex spherical reflection grating are glued, so that the system light splitting is realized, meanwhile, the system aberration is strictly corrected, the spectral distortion is effectively improved, the numerical aperture and the light collecting capacity of the lens imaging are improved, and the optical image with uniform illuminance distribution and high spectral resolution can be obtained.
The spectral imaging method provided by the technical scheme of the invention has the characteristics of large numerical aperture, large field of view, good imaging quality, small spectral distortion and high spectral resolution through strict aberration correction; the provided spectral imaging system has the advantages of compact structure, easiness in processing, assembly and adjustment, strong stability and the like, can be used in the field of spectral imaging, and has wide application prospect.
Claims (3)
1. A large-aperture spectroscopic imaging method suitable for a snapshot type spectral imaging system is characterized by comprising the following steps:
step 1, converging a large-aperture polychromatic light beam emitted from an object plane (1) through a meniscus lens (2), and then, injecting the polychromatic light beam into a concave spherical reflector (3), so that the light beam is further converged and then reflected;
step 2, gluing the convex spherical reflection grating (4) on the rear surface of the meniscus lens, wherein the convex spherical reflection grating and the concave spherical reflector are approximately concentric; reflecting the light beams converged in the step 1 to a convex spherical reflection grating, dividing the polychromatic converging light into monochromatic divergent light beams with different wavelengths, and correcting spectral distortion;
and 3, the monochromatic divergent light beam obtained in the step 2 is emitted to the concave spherical reflector by the convex spherical reflection grating, the concave spherical reflector further performs aberration correction on the monochromatic divergent light beam with different wavelengths, the divergent light beam is converged at the meniscus lens, the light beam is further converged, and after the aberration correction, the convergent light beam is imaged on an image plane (5).
2. The method of claim 1, wherein the step of performing the large-aperture spectroscopic imaging comprises: the front surface of the meniscus lens (2) is an even aspheric surface, and the equation of the even aspheric surface is as follows:
wherein r is the radius of curvature; c is curvature, k is conic coefficient, k =4.4 × 10 -3 ；a 2 And a 3 Are the coefficients of the monomials respectively, and the value range is-1.45 multiplied by 10 -8 ≤a 2 ≤-1.35×10 -8 ，4.4×10 -12 ≤a 3 ≤4.8×10 -12 。
3. The method of claim 1, wherein the step of performing the large-aperture spectroscopic imaging comprises: the rear surface of the meniscus lens and the front and rear surfaces of the concave spherical reflector are spherical surfaces, and the curvature radiuses of the front and rear surfaces are R in sequence 22 、R 3 Taking mm as a length unit, the condition is satisfied: -62. Ltoreq.R 22 ≤-58，-130≤R 3 ≤-127。
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