CN214667265U - Imaging spectrometer containing free-form surface - Google Patents
Imaging spectrometer containing free-form surface Download PDFInfo
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- CN214667265U CN214667265U CN202121065577.2U CN202121065577U CN214667265U CN 214667265 U CN214667265 U CN 214667265U CN 202121065577 U CN202121065577 U CN 202121065577U CN 214667265 U CN214667265 U CN 214667265U
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Abstract
The utility model relates to an imaging spectrometer who contains free curved surface. The light acquired by the long incident slit is refracted by one side of the optical axis of the meniscus lens in sequence, reflected by the spherical reflector, and then converged and incident on the holographic diffraction grating on the outer surface of the meniscus lens, the divergent light split by the grating is reflected by the free-form surface reflector after geometric aberration compensation, and the converged light after aberration balance is refracted by the other side of the optical axis of the meniscus lens in sequence and imaged on an image plane, so that an image with low astigmatism, wide field of view and high spectral resolution is obtained. The utility model provides an imaging spectrum system has the characteristics of wide field of view, high resolution, low astigmatism, low spectrum bending and low chromatic aberration, has high numerical aperture simultaneously, and light harvesting ability is strong, and better control the full field aberration of full wave band, and spectral resolution is higher to realized extremely low spectrum bending and chromatic aberration, satisfied wide field of view, high resolution, compact volume's remote sensing detection application demand.
Description
Technical Field
The utility model belongs to the technical field of spectral imaging, in particular to wide visual field, high numerical aperture, low astigmatism imaging spectrometer who contains free curved surface.
Background
The wide-view-field and high-resolution imaging spectrum technology has wide application requirements in the fields of fine agriculture, forestry resource investigation, fire early warning, water resource pollution, mineral exploration and the like. The Offner spectroscopic imaging system is a widely used structure, and since the diffraction spectroscopy of the grating destroys the perfect symmetry of the Offner structure, the aberration is not large at short slits and low numerical apertures. However, the wide-field and high-resolution imaging spectroscopy system needs to have both a long slit and a high numerical aperture, and the geometric aberration, especially astigmatism, increases sharply with the increase of the slit and the numerical aperture, so that the conventional imaging spectroscopy system with the Offner structure has difficulty in simultaneously satisfying the application requirements of both the wide field and the high resolution. At present, the main aberration eliminating method is to split the concave spherical mirror of the classical Offner splitting mount into two non-coplanar mirrors, slightly off-axis and tilt, break through the original concentricity, increase the design freedom, and eliminate partial aberration by adjusting the radius ratio and the tilt angle of the two spherical mirrors, but the aberration eliminating effect of the method is not obvious, the system volume is increased, and the design parameters cannot meet the application requirement of wide field and high numerical aperture. The invention applies the free-form surface reflector to the Offner structure spectral imaging system, can correct the aberration introduced by the grating spectral damage system symmetrical structure by using the degree of freedom of the surface type, and simultaneously reduces the volume. In the prior art, a technical scheme for eliminating partial aberration by adjusting the radius ratio and the inclination angle of two spherical mirrors is reported in a Broadband analysis-free imaging spectrometer with high resolution (applied optics, 2020, 59, No.4, lacing Lin, Su Wu, Lei Yu), wherein the numerical aperture is 0.17, the F number is 3, the slit length is 12mm, the spectral resolution is 3nm, the root-mean-square RMS radius is 5 μm at most, and the volume is large.
Before the invention is made, the Chinese patent CN 208902264U issued an imaging spectrometer optical system based on a free-form surface and a curved surface prism, which adopts two free-form surface reflectors, the front outer surface of the curved surface prism is eccentrically arranged by an off-axis, and the structure is complex; the number of spectral channels is 100, limited by the splitting power of the prism. Chinese utility model patent CN 206469982U discloses a convex surface grating Offner-Wynne type beam splitting device, and its slit length has reached 100mm, has satisfied the application demand in wide visual field, and the F number is 6.75, and numerical aperture is only 0.08 promptly.
Disclosure of Invention
The utility model discloses not enough to prior art exists, provide one kind and have that the visual field is big, and numerical aperture is high, and astigmatism is low, and the distortion is low, and simple structure is compact, and spectral resolution is high, has high numerical aperture's formation of image spectrum appearance.
In order to achieve the above object of the present invention, the present invention adopts a technical solution of providing an imaging spectrometer including a free-form surface, an optical system of which includes a meniscus lens, a holographic diffraction grating, a spherical reflector and a free-form surface reflector; the meniscus lens is bent to the incident direction of light, and the inner surface and the outer surface of the meniscus lens are spherical surfaces; the incident slit and the image plane are positioned on one side of the inner surface of the meniscus lens, and the spherical reflector and the free-form surface reflector are positioned on one side of the outer surface of the meniscus lens; the incident slit and the spherical reflector are positioned on one side of the optical axis of the meniscus lens, and the free-form surface reflector and the image plane are positioned on the other side of the optical axis of the meniscus lens; the spherical reflector and the meniscus lens are coaxial and concentric; the holographic diffraction grating is positioned at the center of the outer surface of the meniscus lens; the surface type Z of the free-form surface reflector is an XY polynomial, and the equation is as follows:
wherein R = -96.852, C1 =-2.947×10-3，C2=-3.000×10-4，C3=-0.055，C4=-0.096，C5=-2.277×10-4，C6=-0.069，C7=-3.002×10-4，C8=-0.033，C9=-6.111×10-3，C10=1.236×10-3，C11=-0.029，C12=1.253×10-5，C13=-0.016，C14=-3.306×10-3，C15=0.030。
The utility model discloses an imaging spectrometer containing a free-form surface, the value range of the F number of an optical system is 1.7 < F < 2.5; the total length L of the optical system is more than or equal to 90mm and less than or equal to 110 mm; the numerical aperture NA of the optical system is more than or equal to 0.2 and less than or equal to 0.3; the imaging surface of the linear array CCD sensor is positioned on the image plane.
The utility model provides an imaging spectrometer's imaging method, the long penetrating slit acquires the telecentric optical line of incident, internal surface through meniscus lens optical axis one side in proper order, the surface, light after the refraction is reflected by spherical reflector, the light beam assembles on the holographic diffraction grating of incidenting the surface center department that is located meniscus lens, divergent light beam after the grating beam split carries out reflection after the geometric aberration compensation through the free-form surface speculum in proper order, the light of assembling after the aberration is balanced passes through meniscus lens optical axis opposite side surface in proper order again, an internal surface, refracted light is imaged in the image plane, obtain the image of low astigmatic wide field high spectral resolution.
The principle of the utility model is that: since the diffraction and beam splitting of the grating destroy the perfect symmetry of the Offner structure, the conventional Offner type spectral imaging system has large astigmatism and distortion, and it is difficult to realize both a long entrance slit and a high numerical aperture. The utility model discloses a based on Wynne-Offner device's reflex formula light path, add a slice meniscus lens under traditional Offner structure, enlarge best imaging region scope, effectively improved the astigmatism of traditional Offner spectrum appearance and increased the phenomenon sharply along with the slit growth, realize the spectral imaging of long slit; and the XY polynomial surface type free-form surface reflector is used for replacing the traditional spherical reflector, the optical freedom balance is utilized to solve the residual aberration caused by the asymmetry of the system structure due to grating light splitting, and the high numerical aperture is realized, so that the light collecting capacity and the spectral resolution of the spectral imaging system are improved, and the application requirements of wide field of view and high spectral resolution are met.
Compared with the prior art, the beneficial effects of the utility model reside in that:
1. the utility model discloses a what speculum surface adopted is the free-form surface of XY polynomial, helps correcting because the aberration that grating beam split asymmetry introduced reduces the great astigmatism that traditional Offner structure introduced when high numerical aperture, long penetrating slit, can obtain higher spectral resolution in the remote sensing field.
2. The utility model provides a spectral imaging system through introducing meniscus lens, enlarges the best imaging region scope of classic Offner dress frame, and convex surface holographic grating uses meniscus lens as the basement, has wide field of view, and compact structure is convenient for a great deal of advantages such as installation is fixed, satisfies wide field of view, high numerical aperture, low aberration's remote sensing detection demand.
3. The utility model provides a spectral imaging system, spectral resolution is higher relatively, is superior to 1nm, and spectral line bending (smile) is less than 0.3 mu m, and chromatic aberration (keystone) is less than 0.4 mu m, and full operating band maximum RMS facula radius is less than 1.2 mu m, and astigmatism is less than 4 mu m, satisfies high-quality remote sensing and surveys the demand.
Drawings
Fig. 1 is a schematic structural diagram of an optical system of an imaging spectrometer provided in an embodiment of the present invention;
fig. 2 is a graph of field curvature and astigmatism of an imaging spectrometer according to an embodiment of the present invention;
fig. 3 is a graph of a full-band transfer function curve MTF of an imaging spectrometer according to an embodiment of the present invention;
fig. 4 is a graph of RMS spot radius for a full field of view full operating band in different fields of view, according to an embodiment of the present invention.
In the figure, 1. an entrance slit; 2. a meniscus lens; 21. an inner surface of the meniscus lens; 22. an outer surface of the meniscus lens; 3. a spherical reflector; 4. a convex holographic grating; 5. a free-form surface mirror; 6. image plane (line CCD sensor).
Detailed Description
The technical solution of the present invention will be further explained with reference to the accompanying drawings and examples.
Example 1
Referring to fig. 1, it is a schematic structural diagram of an optical system of the imaging spectrometer provided in this embodiment, and elements of the optical system mainly include a meniscus lens 2, a holographic diffraction grating 4, a spherical mirror 3, and a free-form surface mirror 5; the concrete structure is as follows: the meniscus lens 2 is bent to the incident direction of light, and the inner surface 21 and the outer surface 22 are spherical surfaces; the entrance slit 1 and the image plane 6 are positioned on the inner surface 21 side of the meniscus lens, and the spherical reflector 3 and the free-form surface reflector 5 are positioned on the outer surface 22 side of the meniscus lens; the incident slit 1 and the spherical reflector 3 are positioned at one side of the optical axis of the meniscus lens, and the free-form surface reflector 5 and the image plane 6 are positioned at the other side of the optical axis of the meniscus lens; the holographic diffraction grating 4 is positioned at the center of the outer surface of the meniscus lens 2, the holographic diffraction grating 4 is manufactured by taking the outer surface 22 of the meniscus lens 2 as a substrate, the two working surfaces are overlapped and have the same curvature radius, and the grating groove type is an equidistant linear or curved groove type. The imaging surface of the linear array CCD sensor is positioned on the image plane.
The performance parameters of the imaging spectrometer provided by the embodiment meet the conditions in table 1.
TABLE 1
| Spectral range | 0.5μm～1μm |
| Numerical aperture | 0.2 |
| Number of operations F | 2.5 |
| Image plane dispersion width | 4.6mm |
| Length of slit | 20mm |
| Spectral resolution | 1nm |
| Line bending (smile) | 0.3μm |
| Color distortion (keystone) | 0.4μm |
Each optical element (surface) of this example satisfies the conditions of table 2.
Table 2:
in the embodiment, the length S of the incident slit is more than or equal to 20mm and less than or equal to 35mm, and the length direction of the incident slit and the scribing direction of the holographic diffraction grating are both vertical to the paper surface; the spherical reflector is coaxial and concentric with the meniscus lens, and the ratio K of the curvature radiuses of the front surface and the outer surface of the meniscus lens1K is not less than 0.71Not more than 0.9, the ratio K of the curvature radius of the spherical reflector to the curvature radius of the outer surface of the meniscus lens2Is 2 or more than K2Less than or equal to 3; the surface type Z of the free-form surface reflector is an XY polynomial, and the equation is as follows:
wherein R = -96.852, C1 =-2.947×10-3，C2=-3.000×10-4，C3=-0.055，C4=-0.096，C5=-2.277×10-4，C6=-0.069，C7=-3.002×10-4，C8=-0.033，C9=-6.111×10-3，C10=1.236×10-3，C11=-0.029，C12=1.253×10-5，C13=-0.016，C14=-3.306×10-3，C15=0.030。
The spherical reflector and the free-form surface reflector are coated with high-reflectivity films.
The value range of the F number of the optical system of the imaging spectrometer provided by the utility model is less than F < 2.5 in 1.7; the total length L of the optical system is more than or equal to 90mm and less than or equal to 110 mm; the numerical aperture NA of the optical system is more than or equal to 0.2 and less than or equal to 0.3,
the utility model provides an imaging spectrometer's imaging method does: the long entrance slit obtains the incident telecentric light which sequentially passes through the inner surface 21 and the outer surface 22 on one side of the optical axis of the meniscus lens 2, the refracted light is reflected by the spherical reflector 3, the light beam is converged and incident on the holographic diffraction grating 4 positioned at the center of the outer surface of the meniscus lens 2, the divergent light beam split by the grating is reflected after geometric aberration compensation by the free-form surface reflector 5, the converged light after aberration balance sequentially passes through the outer surface 22 and the inner surface 21 on the other side of the optical axis of the meniscus lens 2, and the refracted light is imaged on the image plane 6, so that the image with high spectral resolution of the low astigmatism and wide field is obtained.
Referring to fig. 2, which is a graph of field curvature astigmatism of the imaging spectrometer provided in this embodiment, in the graph, the abscissa represents the field curvature astigmatism value, the ordinate represents the normalized field of view, and the two curves in the graph, the dashed curve and the solid curve in the graph represent the field curvatures in the sagittal plane and the meridional plane, respectively, as can be seen from the results of fig. 2, the imaging system effectively corrects the astigmatism and the field curvature so that the difference value between the two curves, i.e., the astigmatism value, is within the aberration tolerance range.
Referring to fig. 3, it is a graph of the full-band transfer function curve MTF of the imaging spectrometer provided in this embodiment; in the figure, (a), (b) and (c) are respectively the MTF curves of all the field transfer functions of the spectroscopic imaging system provided by the present embodiment at the image plane corresponding to the wavelengths of 0.5 μm, 0.75 μm and 1 μm, respectively. As can be seen from FIG. 3, the optical transfer functions of the full field of view of the working waveband from 0.5 μm to 1 μm under 120lp/mm are all greater than 0.5, close to the diffraction limit, and the curve is smooth and compact, which indicates that the system has clear and uniform imaging and has good imaging quality in the full waveband and the full field of view.
Referring to fig. 4, it is a graph of RMS spot radius in the full field of view full operating band of the imaging spectrometer provided in this embodiment. As can be seen from FIG. 4, in the full-field full-operating band, the RMS root-mean-square spot radius of the system is less than 1.2 μm, the energy is concentrated, and the use requirement is met.
The result proves, the utility model provides a low astigmatism imaging spectrometer of wide visual field height numerical aperture who contains free-form surface is guaranteeing under compact structure's the prerequisite, and its numerical aperture is about 0.2, and slit length can reach 20mm, is 120lp/mm at the sampling frequency, and the optical transfer function of full operating band, full visual field all is greater than 0.5, and astigmatism, spectrum bending, colour distortion are extremely low, satisfy the wide visual field of spectral imaging system, miniaturization and high resolution requirement.
Claims (5)
1. An imaging spectrometer comprising a free-form surface, characterized by: the optical system comprises a meniscus lens (2), a holographic diffraction grating (4), a spherical reflector (3) and a free-form surface reflector (5); the meniscus lens (2) is bent to the incident direction of light, and the inner surface (21) and the outer surface (22) of the meniscus lens are spherical surfaces; the entrance slit (1) and the image plane (6) are positioned on one side of the inner surface (21) of the meniscus lens, and the spherical reflector (3) and the free-form surface reflector (5) are positioned on one side of the outer surface (22) of the meniscus lens; the incident slit (1) and the spherical reflector (3) are positioned on one side of the optical axis of the meniscus lens, and the free-form surface reflector (5) and the image plane (6) are positioned on the other side of the optical axis of the meniscus lens; the spherical reflector (3) and the meniscus lens (2) are coaxial and concentric; the holographic diffraction grating (4) is positioned at the center of the outer surface of the meniscus lens (2); the surface type Z of the free-form surface reflector (5) is an XY polynomial, and the equation is as follows:
wherein R = -96.852, C1 =-2.947×10-3，C2=-3.000×10-4，C3=-0.055，C4=-0.096，C5=-2.277×10-4，C6=-0.069，C7=-3.002×10-4，C8=-0.033，C9=-6.111×10-3，C10=1.236×10-3，C11=-0.029，C12=1.253×10-5，C13=-0.016，C14=-3.306×10-3，C15=0.030。
2. An imaging spectrometer including a free-form surface as claimed in claim 1, wherein: the value range of the F number of the optical system is less than 1.7 and less than 2.5.
3. An imaging spectrometer including a free-form surface as claimed in claim 1, wherein: the total length L of the optical system is more than or equal to 90mm and less than or equal to 110 mm.
4. An imaging spectrometer including a free-form surface as claimed in claim 1, wherein: the numerical aperture NA of the optical system is more than or equal to 0.2 and less than or equal to 0.3.
5. An imaging spectrometer including a free-form surface as claimed in claim 1, wherein: the imaging surface of the linear array CCD sensor is positioned on the image plane.
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