CN106706131A - Double-incident slit high-resolution imaging spectral system - Google Patents

Abstract

The invention discloses a double-slit incident high-resolution imaging spectroscopic system, which is composed of a double-incidence slit, a photo-splitting subsystem, and a detection subsystem, wherein the photo-splitting subsystem includes a primary reflector, a convex grating, a secondary reflector, and a correction lens. The detection subsystem includes optical filters and area array detectors. The system has high resolution, fast revisit time, low cost and high integration of space system. The double-slit structure enables the system to obtain the spectral information of two target areas at the same time in one observation, shortening the revisit time; through the concentric design method of the primary reflector, convex grating, and secondary reflector, the system aberration can be reduced and the system resolution can be improved .

Description

A double-incident slit high-resolution imaging spectroscopy system

technical field

The present invention relates to a double-slit incident imaging spectroscopic system, in particular to a spectroscopic imager with high resolution, high image quality, long slit, and fast revisit time that can be used in ground telescope systems, spaceborne, and airborne spectral imagers Optical system design.

technical background

The spectral imager was developed on the basis of multispectral remote sensing imaging technology in the 1980s. It can obtain super multispectral images of scenes and targets with high spectral resolution, and has a wide range of applications in atmospheric, ocean and land observations. The spectral imager is an organic combination of imaging technology and spectral technology. Through continuous spectral measurement in the continuous imaging space, the "qualitative, quantitative, timing, and positioning" analysis and dynamic process detection of the target can be achieved, and the spatial information of the object can be obtained. Get the spectral information of the target.

The spectroscopic modes in the spectral imaging system include dispersion type and interference type. The dispersion elements used in the dispersion type mainly include: dispersion prisms, interference filters, planar blazed gratings, etc. The prism spectroscopic imager will form spectral line bending; the mechanical and thermal stability of the interferometric spectroscopic imager has a great influence on the accuracy of the interferometric spectrum, and it is difficult to calibrate the spectrum on orbit. Therefore, grating dispersive imaging spectrometers have significant advantages over other types of imaging spectrometers such as prisms, filters, and interference types. The main limiting factor of the traditional grating dispersion imaging spectrometer is that when the system aperture is large, large optical distortion and stray light with high diffraction order will be generated, which seriously affects the spectral purity and limits the accuracy of the later data processing algorithm. Concave gratings are often used in portable spectrometers due to their small size and compactness. Convex grating spectrometers are often used in aerospace high-resolution hyperspectral imaging systems due to their advantages of symmetry, total reflection, and large image field.

In 1987, D. Kwo first proposed a convex grating imaging spectrometer based on the Offner concentric beam splitting structure. This system uses a convex grating as a dispersion element, and has a simple structure and is easy to achieve a large aperture. This design ensures that all third-order aberrations are zero and only fifth-order astigmatism exists. In 1999, MPChrisp improved the system and significantly improved the imaging quality of the convex grating imaging spectrometer. Compared with the traditional imaging spectrometer, the convex grating imaging spectrometer based on the Offner structure has the characteristics of large aperture, low optical distortion, simple structure, and easy miniaturization, which reduces the design difficulty of the imaging spectrometer and the complexity of back-end data processing, and improves The accuracy of imaging spectrum analysis is improved. PHILIS, a high-efficiency push-broom hyperspectral imager developed by NRL in the United States, uses a spectrometer HyperSpec ^TM VM~15 with a wave band of 400~1000nm, a ground sampling rate of 25m and 130m, and a focal length of 180mm. The Offner structure is adopted, and a 1024×1024 back-illuminated CCD is selected. Only 1024×512 pixels are used for spectral imaging, and each pixel resolves 1.13nm spectrum.

In push-broom imaging spectrometers, in order to achieve high resolution and fast revisit time under the condition of guaranteed signal-to-noise ratio, larger systems are often required, and more expensive. In the fiber optic imaging spectrometer, on the basis of ensuring that various performance indicators remain unchanged, expanding the field of view will inevitably increase the volume and cost of the system.

Therefore, it is difficult for current imaging spectrometers to simultaneously satisfy high spectral resolution, high image quality, fast revisit time, low cost, and high integration of space systems.

Contents of the invention

Aiming at the high resolution, high image quality, long slit, fast revisit time required by the telescope system, and the application background of high integration in the space system, the present invention discloses a double-slit offner imaging spectrum system in order to solve the above-mentioned related problems .

The present invention is realized through the following technical solutions:

The system includes a double-incidence slit 1, a concave reflection main mirror 2, a convex reflection grating 3, a concave reflection secondary mirror 4, a correction lens 5, an optical filter 6, and an area array detector 7, and is characterized in that: the double-incidence slit The slit 1 corresponds to two different fields of view, and the material is aluminum alloy 6061; the surface type of the concave reflective primary mirror 2 and the secondary mirror 3 is spherical; the surface type of the convex reflective grating 3 is spherical, and the system aperture On the grating; the correction lens 5 is a meniscus lens, and the material is fused silica; the pixel size of the area array detector 7 is 12um, and the number of pixels is 6K×6K.

The specific design of the system is as follows:

1. Design of the entrance slit element

The incident slit element of the system adopts a side-by-side double slit design, and the double slits have the same size, which meets the system index requirements. The double slit interval considers the detector parameters, system spectral resolution and system size, so that after the light beam passing through the double slit passes through the photo-splitting subsystem, the unfolded spectrum will not overlap.

2. Design of the photo-splitting subsystem

Convex reflective grating is selected as the light splitting element of the system, and the convex grating has better comprehensiveness, and the linear dispersion is conducive to quantitative application; the matching design of blaze wavelength selection, detector response, and solar spectral irradiance can obtain better detection sensitivity consistency; reflective The structure is relatively easy to achieve focal plane stability and radiation spectrum stability, and is suitable for space environment applications. Convex grating spectrometers are widely used in aerospace high-resolution hyperspectral imaging systems due to their advantages of symmetric structure, total reflection and large image field.

The photo-splitting subsystem adopts the Offner structure. The photo-splitting subsystem of the convex grating imaging spectrometer based on the Offner concentric structure consists of 3 optical elements: 2 concave spherical mirrors and 1 convex grating. At the same time, the three optical elements have the same spherical center, and the convex grating is located between the two spherical mirrors. It is the key component of the photo-splitting subsystem and the main factor that limits the efficiency of the convex grating imaging spectrometer. The beam collected by the telescope or fiber optic bundle enters the beam splitting subsystem through the double incident slit, and is reflected by the concave primary mirror to the surface of the convex blazed grating. As a result, the one-dimensional vertical grating lines acquired by the area detector present two sets of spectral information of the two slit incident beams, and the one-dimensional parallel to the grating lines are fine fringes similar in shape to the slits; If a fiber bundle is incident, the dimension parallel to the grating reticle is the position dimension corresponding to different fibers. In addition, in the design optimization, an aspheric meniscus lens is introduced to reduce system aberration, and the diaphragm is located on the convex reflective grating. The design itself has the characteristics of large aperture, low optical distortion, simple structure, and easy miniaturization, which reduces the design difficulty of the imaging spectrometer and the complexity of back-end data processing, and improves the accuracy of imaging spectrum analysis.

The geometric parameters of the spectroscopic device also need to consider the design of the diffraction characteristics, which depends on the index of the spectral imaging system. In this patent, the diffraction order of the convex reflective grating is -1, and the grating size and groove density are determined according to the band and spectral sampling rate.

3. Detection subsystem design

The detection subsystem includes two parts: filters and area detectors. Since the working band of the system is from 200nm to 550nm, it is necessary to install a mosaic filter in front of the detector to eliminate the secondary diffraction spectrum at 200nm to 275nm at 400nm to 550nm. Considering the expanded spectrum and resolution of the double slit, the pixel size of the area array detector is 12um, and the number of pixels is 6K×6K.

As mentioned above, a double-incidence high-resolution spectral imaging system according to the present invention includes a double-incidence slit 1, a concave reflective primary mirror 2, a convex reflective grating 3, a concave reflective secondary mirror 4, a correction lens 5, a filter Sheet 6, area array detector 7. The radiation from the strip-type surface target enters the system through the front telescope, and the spectral radiant energy after passing through the slit is reflected by the primary mirror to the convex reflective grating, and the light of different wavelengths from different slits is separated by the reflective grating. Converge on the area array detector 7 through secondary mirror reflection to realize precise spectral imaging.

The F/5 of the double-slit incident high-resolution spectral imaging system has a spectral resolution of 0.04nm; the working wavelength is 200-550nm, and the volume is less than 70×400×1050mm ³ .

Compared with the prior art, the present invention has the advantages that: under the premise of large field of view, high spectral resolution, and high signal-to-noise ratio, the imaging spectrum system can satisfy fast revisit time, low cost and space The system is highly integrated; the convex grating imaging spectroscopy system based on the Offner structure can achieve large aperture, low optical distortion, simple structure, and easy miniaturization.

Description of drawings

1 is a schematic diagram of the optical path of a double-slit hyperspectral imaging system provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of components of a double-slit hyperspectral imaging system provided by an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of a slit element of a double-slit hyperspectral imaging system provided by an embodiment of the present invention;

in:

1. Double incident slit;

2. Concave reflector;

3. Convex reflective grating;

4. Concave reflective secondary mirror;

5. Correction lens;

6. Optical filter;

7. Area array detector.

detailed description

Provide a preferred embodiment of the present invention below in conjunction with figure, mainly be used as further specifying the characteristics of the present invention in detail, rather than being used for limiting the scope of the present invention:

Fig. 1 is a schematic diagram of an optical path of a double-slit hyperspectral imaging system according to a specific embodiment of the present invention. Referring to Figure 1, the double-strip radiation signal from the target is imaged on the double slit 1 of the field diaphragm after passing through the front-end telescope system, and the radiation energy passing through the double slit 1 is reflected to the convex surface by the concave mirror 2 On the reflective grating 3, the light of different wavelengths is separated. After the light of different wavelengths is reflected by the convex reflective grating 3, it is reflected to the concave reflective secondary mirror 4 along different angles, and is reflected by the concave reflective secondary mirror 4 to enter the calibration. The lens 5 finally converges to different positions of the area array detector 7 through the optical filter 6 to realize spectral line separation. The image displayed on the area array detector 7 is a fine fringe image, in which the expanded spectrum of slit 1 is located in the lower half of the detector, and the expanded spectrum of slit 2 is located in the upper half of the detector. Due to the Offner structure, the system realizes imaging with a magnification ratio of 1:1.

Fig. 2 is a schematic diagram of components of the spectral imaging system described above. Referring to accompanying drawing 2, wherein the light-splitting subsystem is composed of a concave reflective primary mirror 2, a convex reflective grating 3, a concave reflective secondary mirror 4, and a correction lens 5; the detection subsystem is composed of an optical filter 6 and an area array detector 7. The grating constant of the convex reflective grating 3 is 190 line pairs per millimeter.

Fig. 3 is a schematic structural diagram of a dual-incidence slit element in a spectral imaging system provided by a specific embodiment of the present invention. Referring to accompanying drawing 3, the size of each slit is 50mm×125um, and the interval between the slits is 35mm. The material of the slit element used in this patent is aluminum alloy 6061.

The working wavelength of the system is 200nm～550nm, the spectral range is 350nm, the numerical aperture NA is 0.1, the slit size is 50mm×125um, the interval between slits is 35mm, the spectral resolution reaches 0.04nm, the detector pixel size is 12um, and the number of pixels It is 6K×6K, and the system magnification ratio is 1:1. The mirror surface of the whole system is designed as a spherical surface, the material is zero-expansion glass-ceramic, and the material of the correction lens is fused silica. The RMS radius of the system diffuse spot in the full field of view is within 5um, which is less than 1/2 the pixel size of the detector, and the system volume is 70×400×1050mm ³ .

Main optical parameters of the system:

Optical element Radius of curvature (mm) diameter (mm) concave reflective primary mirror 1006.5 232 Convex Reflective Grating 510.6 106 concave mirror 987.9 288.6 correction lens 497.1/547.7 160

The system ensures fast revisit time, low cost and highly integrated design of the space system under the premise of high spectral resolution and high image quality in the working band.

Claims (2)

1. A double-slit incident high-resolution imaging spectroscopy system, comprising a double-incidence slit (1), a concave reflective primary mirror (2), a convex reflective grating (3), a concave reflective secondary mirror (4), and a correction lens (5 ), optical filter (6), area array detector (7), in which the concave reflective primary mirror (2), the convex reflective grating (3), the concave reflective secondary mirror (4), and the correction lens (5) constitute the photo-splitting subsystem ; Optical filter (6), area array detector (7) constitute detection subsystem, it is characterized in that: The system aperture is located on the convex reflective grating (3), and the double-strip radiation signals from the target are respectively imaged on the double slits (1) of the field diaphragm after passing through the front-end telescope system, and the radiation energy passing through the double slits passes through the The concave reflector (2) is reflected on the convex reflective grating (3) to separate the light of different wavelengths. After being reflected by the convex reflective grating (3), the light of different wavelengths is reflected to the concave reflective secondary mirror along different angles (4), it is reflected by the concave reflection secondary mirror, enters the correction lens (5), and finally converges to different positions of the area array detector (7) through the optical filter (6); The double incident slit (1) corresponds to two different fields of view; The surfaces of the concave reflective primary mirror (2) and the secondary mirror (4) are spherical; The surface type of the convex reflective grating (3) is spherical; The correction lens (5) is a meniscus lens, and the material is fused silica. 2. A double-slit incident high-resolution imaging spectroscopy system according to claim 1, characterized in that: in the detection subsystem, the filter (6) is a piece to eliminate the 200nm～275nm at 400nm～550nm The mosaic filter of the secondary diffraction spectrum; the pixel size of the area array detector (7) is 12um, and the number of pixels is 6K×6K.