CN105424187A - Refrigeration-type long-wave infrared imaging spectrometer based on Dyson structure - Google Patents

Abstract

A refrigeration-type long-wave infrared imaging spectrometer based on a Dyson structure belongs to the optical technical field and aims to solve the problems in the prior art that refrigeration equipment with a large volume is required, and a lot of energy sources are required to maintain a low temperature. The refrigeration-type long-wave infrared imaging spectrometer based on the Dyson structure provided by the invention comprises an off-axis three-reverse prepositioned telescope objective, a Dyson grating spectrometer and a secondary imaging lens group, wherein the off-axis three-reverse prepositioned telescope objective comprises three reflecting mirrors and a slit, and radiation information of a target scene is imaged by the three reflecting mirrors at the slit; and the Dyson grating spectrometer disperses images formed at the slit according to different wave lengths and images the image containing multiple pieces of spectral information at a first image plane, and a secondary imaging lens group realizes secondary imaging of exit pupils which are remote from the first image plane and far from each other at the different wave lengths at a cold diaphragm of a detector. The refrigeration-type long-wave infrared imaging spectrometer based on the Dyson structure provided by the invention adopts the method of secondary imaging, realizes the second imaging of the system exit pupils which are far from each other at the different wave lengths at the cold diaphragm of the detector, so that a technical requirement for separate refrigeration of the detector can be satisfied.

Description

Cooled long-wave infrared imaging spectrometer based on Dyson structure

technical field

The invention belongs to the field of optical technology, and relates to a cooling type high luminous flux long-wave infrared imaging optical system, in particular to a cooling type long-wave infrared imaging spectrometer based on a Dyson structure.

Background technique

Imaging spectrometer is a new type of space atmospheric optical remote sensing instrument developed on the basis of multispectral remote sensing imaging technology. It can acquire super multispectral bands of targets with high spectral resolution. Imaging spectrometers operating in the long-wave infrared band (8-12 μm) have good confidentiality, can work continuously day and night, are less affected by weather, and have strong anti-interference capabilities. They have obvious advantages in material detection and identification. Since the remote sensing signal in the long-wave infrared band is weak, this requires the optical system of the long-wave infrared imaging spectrometer to have a high luminous flux. At the same time, in order to obtain a high signal-to-noise ratio, the detector needs to be cooled.

The off-axis three-mirror optical system has a simple structure, which can achieve high luminous flux, wide spectral range, no light blocking, reflective structure, avoids chromatic aberration, and has a large degree of structural freedom. stitched like.

The grating spectrometer based on the concentric structure has the advantages of simple and compact structure, small volume, light weight, large numerical aperture, small spectral line bending and band bending, and has received more and more attention in recent years. Among them, Dyson has more prominent advantages in terms of structural volume and luminous flux, which can well meet the requirements of spectrometers in the long-wave infrared band.

The Dyson structure is catadioptric, and the positions of the exit pupils at different wavelengths are far apart due to the difference in refractive index, which makes it difficult to achieve cold diaphragm matching. In the prior art, the cold diaphragm is placed in front of the slit by co-encapsulating the spectrometer and the detector to avoid the mismatching problem of the cold diaphragm, but this method requires a larger volume of refrigeration equipment and more More energy supply needed to maintain low temperature.

Contents of the invention

The purpose of the present invention is to propose a refrigeration-type long-wave infrared imaging spectrometer based on Dyson structure, which solves the problems existing in the prior art that the refrigeration equipment needs to be bulky and the energy needed to maintain low temperature is large.

To achieve the above object, the refrigeration type long-wave infrared imaging spectrometer based on Dyson structure of the present invention comprises:

An off-axis three-mirror front telescopic objective lens, the off-axis three-mirror front telescopic objective lens includes three mirrors and a slit, and the three mirrors image the radiation information of the target scene at the slit;

A Dyson grating spectrometer that disperses the image formed at the slit according to different wavelengths and images the image containing multi-spectral information on the primary image plane. The Dyson grating spectrometer includes a plano-convex thick lens, an aspheric correcting mirror and a concave surface Reflective grating, the light is incident from the slit, after passing through the plano-convex thick lens and the aspheric correcting mirror in turn, it is reflected by the concave reflective grating and splits the light, and then successively passes through the aspheric correcting mirror and plano-convex thick lens to focus on the primary image plane;

And the secondary imaging mirror group, the secondary imaging mirror group will be farther away from the primary image surface and the exit pupil at different wavelengths is farther apart, and the secondary imaging is at the cold diaphragm of the detector; the secondary imaging mirror group It includes a half-moon lens with an aspheric surface, a half-moon lens with both spherical surfaces and a convex lens with an aspheric surface. The half-moon lens diverges, and then converges at the detector through a convex lens with an aspheric surface.

The three reflectors are all six-time aspheric reflectors, specifically including six-time aspheric reflector A, six-time aspheric reflector B and six-time aspheric reflector C, and the target scene radiation information is passed through six aspheric reflectors in sequence The concave spherical surface of the spherical mirror A, the convex spherical surface of the six-time aspheric mirror B, and the concave spherical surface of the six-time aspheric mirror C are reflected and imaged at the slit.

The six-time aspheric mirror B is the diaphragm of the off-axis three-mirror front telescopic objective lens, and the six-time aspheric mirror B is located near the focal plane of the six-time aspheric mirror C.

The cooling-type long-wave infrared imaging spectrometer also includes a turning mirror A, and the outgoing light at the slit enters the Dyson grating spectrometer through the turning mirror A.

The secondary imaging mirror group also includes a turning mirror B, and the light at the primary image surface is diverged through a half-moon lens with an aspheric surface and a half-moon lens with both spherical surfaces in turn, and then incident on a side with a half-moon lens through the turning mirror B. A convex lens with an aspheric surface converges at the detector through a convex lens with an aspheric surface.

The detector is a cooled HgCdTe detector, and the cold aperture is located 20 mm in front of the focal plane of the detector.

The material of the plano-convex thick lens is ZnSe.

In the secondary imaging lens group, the materials of the half-moon lens with an aspheric surface on one side, the half-moon lens with both spherical surfaces and the convex lens with an aspherical surface on one side are Ge.

The beneficial effects of the present invention are: the front telescopic objective lens in the refrigeration type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention receives the radiation information of the target scene, and images them at the slit, and the Dyson spectrometer images the radiation information at the slit. The image is dispersed according to different wavelengths and the image containing multi-spectral information is formed on the primary image plane, and the exit pupils of different wavelengths located at a farther position and farther apart are secondary imaged on the detector through the secondary imaging mirror group At the cold aperture; using the method of secondary imaging, with 10 μm as the center wavelength, the exit pupils of the system that are far apart at different wavelengths are re-imaged at the position of the cold aperture of the detector to achieve 100% efficiency of the cold aperture, and then meet The technical requirements for cooling the detector alone.

Description of drawings

Fig. 1 is the structure diagram of the off-axis three-mirror telescopic objective lens in the refrigeration type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

Fig. 2 is a spot diagram at the off-axis three-mirror telescopic object mirror surface in the cooling type long-wave infrared imaging spectrometer based on Dyson structure of the present invention;

Fig. 3 is the spectrometer structure schematic diagram of Dyson structure in the refrigeration type long-wave infrared imaging spectrometer based on Dyson structure of the present invention;

Fig. 4 is the schematic diagram of the imaging spectrometer before secondary imaging in the refrigeration type long-wave infrared imaging spectrometer based on Dyson structure of the present invention;

5 is a schematic diagram of the principle of secondary imaging in the refrigeration type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

6 is a schematic diagram of an ideal lens secondary imaging spectrometer in the cooling type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

Fig. 7 is a schematic diagram of the structure of the secondary imaging lens group in the refrigeration type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

Fig. 8 is a schematic diagram of the overall structure of the refrigeration-type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

Fig. 9 is a schematic diagram of the resolution of the refrigeration-type long-wave infrared imaging spectrometer based on the Dyson structure of the present invention;

Among them: 1. Six-time aspheric mirror A, 2. Six-time aspheric mirror B, 3. Six-time aspheric mirror C, 4. Slit, 5. Plano-convex thick lens, 51. Plano-convex thick lens Incident surface, 52. Plano-convex thick lens exit surface, 6. Aspheric correction mirror, 61. Aspheric correction mirror incident surface, 62. Aspheric correction mirror exit surface, 7. Concave reflective grating, 8. Primary image surface, 9 , an ideal lens group, 901, a half-moon lens with an aspheric surface on one side, 9011, an incident surface of a half-moon lens with an aspheric surface on one side, 9012, an exit surface of a half-moon lens with an aspheric surface on one side, 902, both sides are Spherical half-moon lens, 9021, the incident surface of a half-moon lens with both spherical surfaces, 9022, the exit surface of a half-moon lens with both spherical surfaces, 903, a convex lens with an aspheric surface on one side, 9031, an aspherical lens on one side Convex lens incident surface, 9032, convex lens exit surface with aspheric surface on one side, 10, cold stop, 11, secondary image surface, 12, turning mirror surface A, 13, turning mirror surface B.

detailed description

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

Referring to accompanying drawing 8, the refrigerated long-wave infrared imaging spectrometer based on the Dyson structure of the present invention includes an off-axis three-reverse front telescopic objective lens, a Dyson grating spectrometer, a secondary imaging mirror group and a detector;

Referring to accompanying drawing 1, described off-axis three anti-front telescopic objective lens comprises three reflecting mirrors and slit 4, and three reflecting mirrors image target scene radiation information at slit 4; Described three reflecting mirrors are six The secondary aspheric mirrors specifically include the six-time aspheric mirror A1, the six-time aspheric mirror B2 and the six-time aspheric mirror C3. The radiation information of the target scene passes through the concave spherical surface of the six-time aspheric mirror A1, The convex spherical surface of the sub-aspherical mirror B2 and the concave spherical surface of the six-time aspheric mirror C3 are reflected and imaged at the slit 4; the six-time aspheric mirror B2 is the diaphragm of the off-axis three-mirror front telescopic objective lens , the six-time aspheric mirror B2 is located near the focal plane of the six-time aspheric mirror C3; first design a coaxial three-mirror structure that meets the requirements, and then perform reasonable off-axis and deflection on the mirror surfaces of each mirror, so as to Ensure that the light does not block each other. At the same time, by controlling the distance between the six-time aspheric mirror A1 mirror and the six-time aspheric mirror B2 mirror and the distance between the six-time aspheric mirror B2 mirror and the six-time aspheric mirror C3 mirror range, to ensure better symmetry of the structure and to make the chief ray vertically incident on the spectrometer, it is necessary to ensure the vertical slit 4 of the chief ray in the off-axis triple mirror telescopic objective lens. Finally, the optimal structure of the off-axis triple mirror telescopic objective lens is obtained through Zemax optimization, and the exit pupil is located at -404mm far away.

See Figure 2, the spot diagram of the off-axis triple-mirror telescopic objective lens, in which the circles represent Airy disks, and it can be seen that the scenes in each field of view can achieve ideal imaging.

Referring to accompanying drawing 3, described Dyson grating spectrometer disperses the image formed at the slit 4 according to different wavelengths and forms an image containing multispectral information on the primary image plane 8, and the Dyson grating spectrometer includes plano-convex thickness Lens 5, aspheric correcting mirror 6 and concave reflective grating 7, the light is incident from the slit 4, after being diverged by plano-convex thick lens 5 and aspheric correcting mirror 6, it is reflected and split by the concave reflective grating 7, and then passes through the non-spherical reflective grating 7 in turn. Spherical correction mirror 6 and plano-convex thick lens 5 focus on primary image plane 8; the introduction of aspheric correction mirror 6 is to correct the spherical aberration caused by the separation of slit 4 and detector from the rear surface of plano-convex thick lens 5.

Referring to Figure 4, the structural diagram of the imaging spectrometer before secondary imaging, the exit pupil distance l _exp1 of the system at this time is 234 mm at 8 μm, 152 mm at 10 μm, and 101 mm at 12 μm. Obviously, the exit pupils at different wavelengths are not in the same position. In order to meet the pupil matching of the entire system, the system is imaged twice.

Referring to accompanying drawing 5, the process of secondary imaging is that the light at the primary image plane 8 is imaged at the secondary image plane 11 by the ideal lens group 9 and the cold diaphragm 10 in turn, and the secondary image plane 11 is the detector image. The primary image plane 8I ₁ is imaged on the secondary image plane 11I ₂ , and the exit pupil EXP ₁ of the front system is imaged on EXP ₂ at the position of the cold diaphragm 10 of the detector, thereby realizing the pupil matching requirement. According to the exit pupil position of the imaging optical system before the secondary imaging, select 10 μm as the central wavelength, set the focal length of the secondary imaging lens group as f, and obtain the relevant parameters of the secondary imaging lens group according to formula (1) and formula (2):

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; exp</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Where: f is the focal length of the secondary imaging lens group;

S is the object distance in the secondary imaging mirror group;

S' is the image distance in the secondary imaging mirror group;

l _stop is the position of the cold diaphragm 10 from the secondary image plane 11;

l _exp1 is the distance from the exit pupil to the primary image plane 8.

It is calculated that f=17.67mm, S=-S'=-35.34mm. First, the ideal lens is used to represent the lens group, and the system in Figure 4 is added for secondary imaging, and f, S, -S' are used as variables for slight optimization to obtain the secondary imaging lens group.

The object-side numerical aperture of the optimized ideal lens group 9 is 0.24, the focal length f'=19.03mm, and the entrance pupil position is 302.115mm. Taking the above parameters as limiting conditions, Zemax was used to design and optimize the secondary imaging lens group shown in Figure 7. The secondary imaging mirror group will be farther away from the primary image surface 8 and the exit pupils at different wavelengths are farther apart, and the secondary imaging is at the cold diaphragm 10 of the detector; the secondary imaging mirror group includes one side with a non- Spherical half-moon lens 901, both sides are spherical half-moon lens 902 and one side has aspherical convex lens 903, the light at primary image surface 8 passes through one side with aspheric half-moon lens 901 and both sides are spherical The half-moon lens 902 diverges, and then converges at the detector through a convex lens 903 with an aspheric surface;

The incident surface 9011 of a half-moon lens with an aspheric surface and the exit surface 9032 of a convex lens with an aspheric surface are six-degree aspheric surfaces, the exit surface 9012 of a half-moon lens with an aspherical surface, and a half-moon lens with spherical surfaces on both sides The incident surface 9021, the exit surface 9022 of the half-moon lens with both spherical surfaces and the incident surface 9031 of the convex lens with an aspherical surface are all spherical.

The detector is a refrigerated HgCdTe detector, the working band of the refrigerated HgCdTe detector is 8-12 μm, the F number is 2, the pixel size is 40 μm, and the array size is 256×256 (M×N). In order to achieve a higher signal-to-noise ratio, there is usually a cold diaphragm 10 at the entrance of the cooled detector, and the cold diaphragm 10 is located 20 mm (l _stop ) in front of the focal plane of the detector.

In order to avoid light blocking, the cooling type long-wave infrared imaging spectrometer also includes a turning mirror A12. The exit light at the slit 4 enters the Dyson grating spectrometer through the turning mirror A12. The secondary imaging mirror group also includes a turning mirror B13, on the one hand, the light rays in the structure do not block each other, on the other hand, it also reduces the volume of the system and makes the structure more compact. Referring to FIG. 8 , the present invention can achieve 100% efficiency of the cold diaphragm 10 . In order to ensure that the slit 4 is always an ideal image, during the entire optimization process, no parameters in the telephoto objective lens are set as variables. The parameter values for each face of the final structure are listed in the table below:

The material of the plano-convex thick lens 5 is ZnSe.

In the secondary imaging lens group, the materials of the half-moon lens 901 with an aspheric surface on one side, the half-moon lens 902 with both spherical surfaces and the convex lens 903 with an aspherical surface on one side are Ge.

In the multi-body splicing optical system, on the one hand, the image-side numerical aperture of the front optical system must be equal to the object-side numerical aperture of the rear optical system; on the other hand, the exit pupil of the front optical system and the rear optical system must also be satisfied. The entrance pupils are at the same position, the purpose of which is to avoid vignetting and aperture aberration while ensuring full utilization of energy. In the present invention, because the Dyson spectrometer is a catadioptric structure, the entrance pupil positions of different wavelengths must not be at the same position, so it is necessary to make the exit pupil of the front telescopic objective lens and the entrance pupil of the rear spectrometer both at infinity. When , the path of the chief ray changes very little, and the vignetting and aperture aberration caused by the pupil mismatch can be ignored.

According to the transfer function curve of the imaging spectrometer of the present invention, it can be seen that the image quality of the system is close to the diffraction limit. When the system is at the Nyquist frequency of 12.5/mm, the minimum value is 0.55 at the wavelength of 12 μm, which meets the requirements of the optical system.

Referring to FIG. 9 , a schematic diagram of the resolution of the imaging spectrometer system, the resolution of the system at a wavelength of 10 μm is the lowest, which is 25 nm.

Claims (8)

1. The refrigeration type long-wave infrared imaging spectrometer based on Dyson structure, is characterized in that, comprises: The off-axis three-mirror front telescopic objective lens, the off-axis three-mirror front telescopic objective lens includes three mirrors and a slit (4), and the three mirrors image the radiation information of the target scene at the slit (4) ; The image formed at the slit (4) is dispersed according to different wavelengths and the image containing multi-spectral information is imaged on a Dyson grating spectrometer at the primary image plane (8), and the Dyson grating spectrometer includes a plano-convex thick lens ( 5), aspheric correction mirror (6) and concave reflective grating (7), the light is incident from the slit (4), after passing through plano-convex thick lens (5) and aspheric corrective mirror (6) successively, the concave reflective grating (7) Reflect and split the light, and then focus on the primary image plane (8) through the aspheric correction mirror (6) and plano-convex thick lens (5) in turn; And the secondary imaging mirror group, the secondary imaging mirror group will be separated from the primary image surface (8) and the exit pupil that is far away from the position of the different wavelengths, and the secondary imaging is at the cold diaphragm (10) of the detector; The secondary imaging lens group includes a half-moon lens (901) with an aspheric surface on one side, a half-moon lens (902) with spherical surfaces on both sides, and a convex lens (903) with an aspheric surface on one side. The light rays diverge sequentially through a half-moon lens (901) with an aspheric surface and a half-moon lens (902) with both spherical surfaces, and then converge at the detector through a convex lens (903) with an aspheric surface. 2. the refrigeration type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, is characterized in that, described three mirrors are six aspheric mirrors, specifically comprise six aspheric mirrors A (1 ), the six-time aspheric mirror B (2) and the six-time aspheric mirror C (3), the radiation information of the target scene passes through the concave spherical surface of the six-time aspheric mirror A (1) and the six-time aspheric mirror The convex spherical surface of B(2) and the concave spherical surface of the six-time aspheric mirror C(3) are reflected and imaged at the slit (4). 3. the cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 2, is characterized in that, described six times aspherical mirror B (2) is the diaphragm of off-axis three anti-front telescopic objective lens, The six-time aspheric mirror B (2) is located near the focal plane of the six-time aspheric mirror C (3). 4. the cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, is characterized in that, described cooling type long-wave infrared imaging spectrometer also comprises turning mirror A (12), the outgoing light at slit (4) place It enters the Dyson grating spectrometer through the turning mirror A (12). 5. The cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, wherein the secondary imaging mirror group also includes a turning mirror B (13), and the light at the primary image surface (8) is sequentially After diverging through a half-moon lens (901) with an aspheric surface and a half-moon lens (902) with spherical surfaces on both sides, it is incident on a convex lens (903) with an aspheric surface through the turning mirror surface B (13), and then A convex lens (903) with an aspheric surface converges at the detector. 6. the cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, is characterized in that, described detector is cooling type HgCdTe detector, and described cold aperture (10) is positioned at detector focal plane front 20mm place . 7. The cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, characterized in that, the material of the plano-convex thick lens (5) is ZnSe. 8. the cooling type long-wave infrared imaging spectrometer based on Dyson structure according to claim 1, is characterized in that, one side in the secondary imaging lens group has aspheric half-moon lens (901), both sides are all spherical The materials of the half-moon lens (902) and the convex lens (903) with an aspheric surface on one side are Ge.