CN216526504U - Large-view-field spectroscopic imaging system based on free-form surface prism - Google Patents
Large-view-field spectroscopic imaging system based on free-form surface prism Download PDFInfo
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- CN216526504U CN216526504U CN202123316394.6U CN202123316394U CN216526504U CN 216526504 U CN216526504 U CN 216526504U CN 202123316394 U CN202123316394 U CN 202123316394U CN 216526504 U CN216526504 U CN 216526504U
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Abstract
The utility model relates to a large-view-field spectroscopic imaging system based on a free-form surface prism. The system has symmetrical light path structure, including entrance slit, free-form surface reflector and curved surface prism spectroscope set in approximate concentric structure; the curved surface prism beam splitter group comprises a curved surface prism and a free-form surface prism, the vertex angles of the two prisms are arranged oppositely, the reflecting surface of the free-form surface prism is plated with a high-reflection film, and the aperture diaphragm of the system is arranged on the reflecting surface of the free-form surface prism. The incident light is reflected by the free-form surface reflector, and the light passes through the curved surface prism group twice to achieve the effect of dispersion and light splitting; the light beams after dispersion and splitting are incident on the free-form surface reflector again, and the incident light with different wavelengths is converged at an image surface after being reflected. The light splitting imaging system provided by the utility model realizes large view field, high resolution and high light energy utilization rate by utilizing the concentric optical structure and the prism dispersion; the system has simple and compact structure, is easy to install and adjust and has wide application prospect.
Description
Technical Field
The utility model relates to the technical field of spectrometers, in particular to a large-field-of-view spectroscopic imaging system based on a free-form surface prism.
Background
The spectral imaging technology combines a spectrum and an imaging technology, so that two-dimensional image information and one-dimensional spectral information of a target scene are acquired simultaneously to form a three-dimensional data cube, and the acquired spectral information is analyzed and processed. From satellite image analysis and even food safety detection, the application of the spectral imaging technology is extremely wide, and with the development of new application backgrounds, new working environments put higher requirements on indexes such as a view field, a signal-to-noise ratio and resolution of a spectral imaging system.
The spectroscopic technology is the core of the spectrometer system and determines the basic performance of the imaging spectrometer, wherein most spectrometer systems designed by taking a grating and a prism as spectroscopic elements are available. The traditional Offner spectrometer uses the convex grating as a light splitting element thereof, has good imaging performance, but the convex grating is difficult to manufacture and expensive, and the grating generally only uses a certain level of spectrum, so that the light energy utilization rate is low, and meanwhile, the defects of stray light, spectrum cascade, ghost image and the like still exist. Before the utility model is made, the chinese invention patent CN110319932A discloses a curved prism dispersion type imaging optical system based on an Offner relay structure, but the system has a small numerical aperture and a small field of view, and the system introduces too many prisms and adopts a mode of separating a main reflection mirror, which increases the difficulty of system adjustment and calibration.
In a concentric optical system, the system symmetry is broken due to the addition of a dispersion element, a large astigmatic aberration system exists, the longer the slit is, the more difficult the aberration correction is, and the prior art often adopts a method of separating a main reflector and a third reflector to increase optimization variables, however, the method increases the complexity of an optical structure, and the adjustment and calibration of the system are difficult.
Disclosure of Invention
Aiming at the defects in the prior art, the utility model provides the prism-type hyperspectral imaging system which has high light energy utilization rate, high spectral resolution, simple and compact structure and easy processing, assembly and adjustment.
The technical scheme adopted by the utility model is that the optical path of the large-view-field spectroscopic imaging system based on the free-form surface prism is of a symmetrical structure and comprises an incident slit, a reflector and a curved surface prism spectroscope group which are of an approximate concentric structure; the reflector is a free-form surface reflector, the curved surface of the reflector is bent to the light incidence direction, and the reflector comprises an incident light reflection area and a light splitting reflection area; the curved surface prism beam splitter group comprises a curved surface prism and a free-form surface prism, the vertex angles of the two prisms are arranged oppositely, and the curved surfaces of the two prisms bend to the incident direction of light; the reflecting surface of the free-form surface prism is plated with a high-reflection film, and an aperture diaphragm of the system is arranged on the reflecting surface of the free-form surface prism;
the reflecting surface of the free-form surface reflector is an XY polynomial free-form surface, the coordinate system of the free-form surface reflector is a Cartesian space rectangular coordinate system constructed by taking the vertex of the free-form surface reflector as an original point O, the light incidence direction is the positive direction of a Z axis, the positive direction of a Y axis is upward, the positive direction of an X axis is outward, and the equation of the XY polynomial free-form surface in the coordinate system is as follows:
wherein the content of the first and second substances,
is the radius; c is curvature, c = -4.63 × 10-3(ii) a k is the conic coefficient, k = 0.243;
～
are coefficients of the monomials respectively, and the value range is not less than 0.197
≤0.199， -1.725≤
≤-1.723，-1.688≤
≤-1.686，0.061≤
≤0.063，0.018≤
≤0.021，0.077≤
≤0.079，0.173≤
≤0.175，-0.160≤
≤-0.158，-3.07×10-3≤
≤-3.04×10-3，0.010≤
≤0.014，0.125≤
≤0.128；
The reflecting surface of the free-form surface prism is an XY polynomial free-form surface, the coordinate system of the free-form surface prism is a Cartesian space rectangular coordinate system constructed by taking the vertex of the free-form surface prism as an original point O, the light incidence direction is the positive direction of a Z axis, the positive direction of a Y axis is upward, the positive direction of an X axis is outward, and the equation of the XY polynomial free-form surface in the coordinate system is as follows:
wherein c is curvature, c = -0.011; k is a conic coefficient, k =2.36 × 10-3；
Is the radius;
～
the coefficients of the monomials are respectively, and the value range is not less than 0.010
≤0.012， -5.31×10-5≤
≤-4.91×10-5，-1.2×10-4≤
≤-1.0×10-4，-4.51×10-3≤
≤-4.48×10-3，3.42×10-3≤
≤3.44×10-3，7.635×10-4≤
≤7.640×10-4，2.11×10-3≤
≤2.13×10-3，-3.3×10-3≤
≤-3.1×10-3，3.95×10-3≤
≤3.97×10-3，-2.93×10-4≤
≤-2.88×10-4，8.85×10-4≤
≤8.89×10-4。
The value range of the working F number of the spectroscopic imaging system provided by the utility model is more than or equal to 4 and less than or equal to 5; the total length S of the entrance slit is more than or equal to 70 and less than or equal to 80 mm; the total length L of the system is more than or equal to 210 and less than or equal to 220 mm.
The principle of the utility model is as follows: the light reaches the free-form surface reflector through the entrance slit to be reflected; the reflected light rays are reflected by the rear surface of the free-form surface prism after passing through the curved surface prism and the free-form surface prism, and then pass through the free-form surface prism and the curved surface prism respectively again, so that the light splitting and aberration balancing effects of the curved surface prism are achieved; the light beams after dispersion and splitting are incident on the free-form surface reflector again, aberration compensation and correction are carried out on the light with different wavelengths and different fields of view, and meanwhile, the light beams are converged at the image surface, so that an image with a large field of view, high resolution and high light energy utilization rate is obtained. The curved prism group has both functions of dispersion and focusing, but loses symmetry in the meridional direction, resulting in astigmatism as its inherent aberration, and the introduced light splitting element also breaks the symmetry of the Offner type structure and has large astigmatism, so that free curved surfaces are introduced at two positions of the system to balance and correct aberrations for light rays of various wavelengths and fields.
The utility model combines the free-form surface and the curved surface prism, inhibits the dispersion nonlinearity, well compensates and corrects the aberration, and can meet the application requirements of large field of view, high light energy utilization rate and high spectral resolution.
Compared with the prior art, the utility model has the beneficial effects that:
1. the utility model introduces the free-form surface prism, only uses two curved surface prisms made of different materials to form a light splitting part of the system, and enables the light beam to pass through the curved surface prism group twice, thereby ensuring high light energy utilization rate and effectively inhibiting dispersion nonlinearity; and a reflecting film is plated on the rear surface of the free-form surface prism, so that the volume and the mass of the system are reduced.
2. The free-form surface reflector mirror adopted by the utility model reflects and reflects the incident light and the split light in different areas of the same reflector, thereby being convenient for installation and adjustment.
3. The utility model adopts a combined structure of the free-form surface and the curved surface prism, effectively balances astigmatism introduced by losing symmetry in the meridian direction of the curved surface prism, obviously improves distortion, controls the bending of a spectral line within 6 microns and the bending of a spectral band within 0.5 micron, and is beneficial to spectral calibration and later-stage image processing.
3. The utility model utilizes the advantages of concentric optical system and prism dispersion, has large numerical aperture, high incident light flux and few introduced optical elements, only consists of two curved prisms and a reflector, has simple and compact structure, is easy to assemble and adjust, and has practical application value.
Drawings
FIG. 1 is a schematic structural diagram of a spectroscopic imaging system provided by an embodiment of the present invention;
FIG. 2 is a graph of the RMS radius of a focused light spot at the full-field full-operating band of a spectroscopic imaging system provided by an embodiment of the utility model;
FIG. 3 is a graph of a transfer function curve MTF of a spectroscopic imaging system provided by an embodiment of the present invention;
in the figure, 1. an entrance slit; 2. a free-form surface mirror; 3. a curved prism; 4. a free-form surface prism; 41. a free-form surface prism rear surface (reflective surface); 5. and (4) an image plane.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings and examples.
The first embodiment is as follows:
the technical scheme of the embodiment is to provide a large-field-of-view spectral imaging system based on a free-form surface prism. The F number of the optical system is F/# = 5; the total length S of the entrance slit is S =70mm, and the working wavelength is 400-800 nm.
Referring to fig. 1, which is a schematic structural diagram of the spectroscopic imaging system provided in this embodiment, the optical path of the system is a symmetric structure, and according to the incident direction of light, the optical elements are: the system comprises an incident slit 1, a free-form surface reflector 2, a curved surface prism beam splitter group consisting of a curved surface prism 3 and a free-form surface prism 4, and an image surface 5; the free-form surface reflector and the curved surface prism spectroscope group are in an approximate concentric structure; the reflecting curved surface of the free-form surface reflector is bent towards the incident direction of light and comprises an incident light reflecting area and a light splitting reflecting area; in the curved surface prism beam splitter group consisting of a curved surface prism and a free-form surface prism, the vertex angles of the two prisms are arranged oppositely, the curved surfaces of the two prisms bend to the light incidence direction, the rear surface 41 of the free-form surface prism is a reflecting surface plated with a high-reflection film, and the aperture diaphragm of the system is arranged on the reflecting surface of the free-form surface prism.
In this embodiment, the reflection surface of the free-form surface reflector is an XY polynomial free-form surface, the coordinate system of the reflection surface is a cartesian space rectangular coordinate system constructed with the vertex of the free-form surface reflector as an origin O, the light incidence direction is a positive Z-axis direction, the positive Y-axis direction is upward, the positive X-axis direction is outward, and the equations of the XY polynomial free-form surface in the coordinate system are:
wherein the content of the first and second substances,
is the radius; c is curvature, c = -4.63 × 10-3(ii) a k is the conic coefficient, k = 0.243;
～
the coefficients of the monomials are respectively:
=0.198，
=-1.724，
=-1.687，
=0.062，
=0.02，
=0.078，
=0.174，
=-0.159，
=-3.05×10-3，
=0.012，
=0.127。
in this embodiment, the reflection surface of the free-form surface prism is an XY polynomial free-form surface, the coordinate system of the reflection surface is a cartesian space rectangular coordinate system constructed with the vertex of the free-form surface prism as the origin O, the light incidence direction is a positive Z-axis direction, the positive Y-axis direction is upward, the positive X-axis direction is outward, and the equations of the XY polynomial free-form surface in the coordinate system are:
wherein c is curvature, c = -0.011; k is a conic coefficient, k =2.36 × 10-3；
Is the radius;
～
the coefficients of the monomials are respectively:
=0.011，
=-5.11×10-5，
=-1.11×10-4，
=-4.49×10-3，
=3.43×10-3，
=7.638×10-4，
=2.12×10-3，
=-3.2×10-3，
=3.958×10-3，
=-2.912×10-4，
=8.872×10-4。
when the spectroscopic imaging system provided by the embodiment performs imaging, light reaches an incident light reflection area of the free-form surface reflector 2 through the incident slit 1 and is reflected; the reflected light sequentially passes through the curved surface prism 3 and the free-form surface prism 4 of the curved surface prism beam splitter group, is reflected by the back surface 41 of the free-form surface prism, and then sequentially passes through the free-form surface prism and the curved surface prism, so that the light energy utilization rate is high, the dispersion linearity is good, and the dispersion beam splitting effect is achieved; the light beams split by the dispersion are incident on the free-form surface reflector again, and the incident light with different wavelengths is converged at the image surface 5 after being reflected by the light splitting reflection area of the free-form surface reflector.
The parameters of each optical element of this example are shown in table 1.
The performance parameters of the spectroscopic imaging system provided in this example are shown in table 2.
Table 2:
| spectral range (nm) | 400～800 |
| Numerical aperture | 0.1 |
| Image plane dispersion width (mm) | 2 |
| Slit length (mm) | 70 |
| Short wavelength spectral resolution (nm) | ＜1 |
| Long wavelength spectral resolution (nm) | ＜8 |
| Number of spectral channels | 200 |
| Line bending (mum) | ＜6 |
| Band bend (mum) | ＜0.5 |
Referring to fig. 2, which is a graph showing RMS radius curves of the focused light spots in the full-field operating band of the spectroscopic imaging system provided in this embodiment, curve (a) is the RMS radius of the full-field operating band, and curve (b) is the RMS radius of the full-field operating band at the diffraction limit. As can be seen from FIG. 2, in the full-field full-working band, the RMS radius of the system is less than 5.2 μm, which is close to the diffraction limit RMS radius, and the energy is concentrated, thereby meeting the use requirement.
Referring to fig. 3, it is a graph of transfer function MTF on the image plane corresponding to each field of view of the spectroscopic imaging system provided in this embodiment; in the figure, (a), (b) and (c) correspond to all field transfer function MTF curves of the imaging spectrometer provided by the embodiment on the image plane at the wavelengths of 0.4 μm, 0.6 μm and 0.8 μm respectively. From fig. 3, the optical transfer functions of the full field of view of the working waveband from 0.4 μm to 0.8 μm under 70lp/mm are all larger than 0.3, close to the diffraction limit, and the curve is smooth and compact, which shows that the system has clear and uniform imaging and good imaging quality in the full waveband and the full field of view.
The large-field-of-view spectral imaging system adopting the free-form surface prism, which is provided by the technical scheme of the utility model, only comprises three optical elements, and the aberration of the system is balanced and corrected by introducing the free-form surface prism and the curved surface prism, so that the light energy utilization rate and the spectral resolution are improved. The system has the advantages of large field of view, high light energy utilization rate, high spectral resolution and the like, and has the characteristics of simple and compact structure, easiness in adjustment and wide application prospect.
Claims (4)
1. The utility model provides a big visual field beam split imaging system based on free-form surface prism which characterized in that: the light path of the system is in a symmetrical structure and comprises an incident slit (1), a reflecting mirror and a curved prism spectroscope group which are in an approximate concentric structure; the reflector is a free-form surface reflector (2), the curved surface of the reflector is bent to the incident direction of light, and the reflector comprises an incident light reflecting area and a light splitting reflecting area; the curved surface prism beam splitter group comprises a curved surface prism (3) and a free-form surface prism (4), the vertex angles of the two prisms are arranged oppositely, and the curved surfaces of the two prisms bend to the incident direction of light; a reflecting surface (41) of the free-form surface prism is plated with a high-reflection film, and an aperture diaphragm of the system is arranged on the reflecting surface of the free-form surface prism;
the reflecting surface of the free-form surface reflector is an XY polynomial free-form surface, the coordinate system of the free-form surface reflector is a Cartesian space rectangular coordinate system constructed by taking the vertex of the free-form surface reflector as an original point O, the light incidence direction is the positive direction of a Z axis, the positive direction of a Y axis is upward, the positive direction of an X axis is outward, and the equation of the XY polynomial free-form surface in the coordinate system is as follows:
wherein the content of the first and second substances,
is the radius; c is curvature, c = -4.63 × 10-3(ii) a k is the conic coefficient, k = 0.243;
～
are coefficients of the monomials respectively, and the value range is not less than 0.197
≤0.199， -1.725≤
≤-1.723，-1.688≤
≤-1.686，0.061≤
≤0.063，0.018≤
≤0.021，0.077≤
≤0.079，0.173≤
≤0.175，-0.160≤
≤-0.158，-3.07×10-3≤
≤-3.04×10-3，0.010≤
≤0.014，0.125≤
≤0.128；
The reflecting surface of the free-form surface prism is an XY polynomial free-form surface, the coordinate system of the free-form surface prism is a Cartesian space rectangular coordinate system constructed by taking the vertex of the free-form surface prism as an original point O, the light incidence direction is the positive direction of a Z axis, the positive direction of a Y axis is upward, the positive direction of an X axis is outward, and the equation of the XY polynomial free-form surface in the coordinate system is as follows:
wherein c is curvature, c = -0.011; k is a conic coefficient, k =2.36 × 10-3；
Is the radius;
～
the coefficients of the monomials are respectively, and the value range is not less than 0.010
≤0.012， -5.31×10-5≤
≤-4.91×10-5，-1.2×10-4≤
≤-1.0×10-4，-4.51×10-3≤
≤-4.48×10-3，3.42×10-3≤
≤3.44×10-3，7.635×10-4≤
≤7.640×10-4，2.11×10-3≤
≤2.13×10-3，-3.3×10-3≤
≤-3.1×10-3，3.95×10-3≤
≤3.97×10-3，-2.93×10-4≤
≤-2.88×10-4，8.85×10-4≤
≤8.89×10-4。
2. The large-field-of-view spectroscopic imaging system based on the free-form surface prism as claimed in claim 1, wherein: the working F number of the system has a value range of 4-5F/#.
3. The large-field-of-view spectroscopic imaging system based on the free-form surface prism as claimed in claim 1, wherein: the total length S of the entrance slit of the system is more than or equal to 70 and less than or equal to 80 mm.
4. The large-field-of-view spectroscopic imaging system based on the free-form surface prism as claimed in claim 1, wherein: the total length L of the system is more than or equal to 210 and less than or equal to 220 mm.
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