CN110081976A - A kind of big visual field grating prism spectrum imaging system - Google Patents

Abstract

The invention discloses a kind of big visual field grating prism spectrum imaging systems, including slit, spherical reflector, plane mirror, grating prism module, microscope group, second level optical filter and detector are focused, is reflected after the light beam of the slit is incident on the spherical reflector；Light beam after reflection is incident on the plane mirror；Light beam after plane mirror reflection is incident on the grating prism module, diffraction occurs at the grating prism module, wherein: the incident focusing microscope group of the first-order diffraction light of different wave length completes imaging process using the detector is reached after the second level optical filter；Aperture diaphragm of the front surface of the grating prism module as whole system, the aperture diaphragm are located at the centre of sphere C of the spherical reflector, and are overlapped with the plane of incidence of the grating prism module.System entirety size is compact, light-weight, structure is simple for this, and the non-run-off the straight of image planes is conducive to the adjustment of system.

Description

A Wide Field of View Grating Prism Spectral Imaging System

technical field

The invention relates to the technical field of spectral imaging, in particular to a large field of view grating prism spectral imaging system.

Background technique

Spectral imaging technology is a new type of multi-dimensional information acquisition technology that combines imaging technology and spectral technology. It can obtain two-dimensional spatial information and one-dimensional spectral information of the detected target to form a data cube. Spectral imaging technology has broad application prospects in military reconnaissance and investigation of agriculture, forestry, water, soil and miner's lamp resources.

The common spectroscopic methods of hyperspectral imaging technology in the prior art mainly include prism and grating splitting, for example, Fery prism type, Offner grating type, Czerny-Turner grating type and Dyson grating type, etc., but these spectrometers are all off-axis. The structure has the defects of complex structure and high development cost, which cannot meet the development requirements of the current hyperspectral instruments with a large field of view and a wide spectral range.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a large field-of-view grating prism spectral imaging system, which is compact in overall size, light in weight, simple in structure, and has no inclination of the image plane, which is beneficial to the installation and adjustment of the system, and can meet the development requirements of current spectral imaging technology. .

The purpose of this invention is to realize through the following technical solutions:

A large field of view grating prism spectral imaging system, the system comprises a slit, a spherical mirror, a plane mirror, a grating prism module, a focusing mirror group, a secondary filter and a detector, wherein:

The light beam passing through the slit is incident on the spherical mirror and is reflected;

The reflected light beam is incident on the plane mirror;

The light beam reflected by the plane mirror is incident on the grating prism module, and diffracted at the grating prism module, wherein: the first-order diffracted light of different wavelengths enters the focusing mirror group, and then passes through the second-stage diffracted light. After the filter reaches the detector, the imaging process is completed;

The front surface of the grating prism module serves as an aperture stop of the entire system, and the aperture stop is located at the spherical center C of the spherical mirror and coincides with the incident surface of the grating prism module.

A rectangular hole is opened in the middle of the flat reflection mirror, and the flat reflection mirror does not block the light beam emitted from the slit by using the rectangular hole.

The grating prism module is formed by gluing a grating substrate, a grating, a protective glass and a prism, wherein:

The grating substrate, protective glass and prism are all made of the same material;

The optical axis of the grating prism module is parallel to the bottom surface of the module, and the central wavelength chief ray enters the grating base plane at an angle of α1, and enters the grating at an angle of incidence _α2 after being refracted _. Reach the prism slope;

_The apex angle of the inclined plane of the prism is β, and finally the light exits at an exit angle of α5.

A long-wave-pass cut-off filter film is plated on the surface of the secondary filter close to the detector, and the short-wave cut-off wavelength is 550 nm, and the secondary filter is placed close to the surface of the detector.

The slit length of the system can reach 29.4 mm, the spectral range is 420-1000 nm, and the F number is 2.4.

The system adopts an on-axis design, which can avoid off-axis aberrations introduced by off-axis systems that are difficult to correct.

It can be seen from the technical solutions provided by the present invention that the overall size of the system is compact, light in weight, simple in structure, and the image plane is not tilted, which is beneficial to the installation and adjustment of the system, and can meet the development requirements of current spectral imaging technology.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a schematic diagram of the overall structure of a large-field grating prism spectral imaging system provided by an embodiment of the present invention;

2 is a schematic structural diagram of a grating prism module provided by an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a spherical mirror provided by an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. FIG. 1 is a schematic diagram of the overall structure of a large-field grating prism spectral imaging system provided by an embodiment of the present invention. The system mainly includes a slit 101, a spherical reflection Mirror 102, plane mirror 103, grating prism module 104, focusing lens group 105, secondary filter 106 and detector 107, wherein:

The light beam passing through the slit 101 is incident on the spherical mirror 102 and then reflected;

The reflected light beam is incident on the plane mirror 103; in the specific implementation, a rectangular hole is opened in the middle of the plane mirror 103, and the plane mirror 103 is not blocked from the slit 101 by the rectangular hole. outgoing beam;

The light beam reflected by the plane mirror 103 is incident on the grating prism module 104, and diffracted at the grating prism module 104, wherein: the first-order diffracted light of different wavelengths is incident on the focusing mirror group 105, and then passes through the grating prism module 104. The secondary filter 106 reaches the detector 107 to complete the imaging process;

The front surface of the grating prism module 104 serves as an aperture stop of the entire system. The aperture stop is located at the spherical center C of the spherical mirror 102 and coincides with the incident surface of the grating prism module 104 .

FIG. 2 is a schematic structural diagram of a grating prism module provided by an embodiment of the present invention. The grating prism module 104 is formed by gluing a grating substrate, a grating, a protective glass and a prism, wherein:

The grating substrate, protective glass and prism are all made of the same material, such as H-K9L;

The optical axis OO' of the grating prism module 104 is parallel to the bottom surface of the module, the central wavelength principal ray is incident on the grating base plane at an angle of α1, and is incident on the grating at an angle of incidence _α2 after refraction, and the light exits at an angle of diffraction α3, and is emitted at an angle of α. ₄ The angle of incidence reaches the slope of the prism;

_The apex angle of the inclined plane of the prism is β, and finally the light exits at an exit angle of α5.

Further, in order to make the central wavelength outgoing ray parallel to the optical axis OO', according to the geometric relationship, it can be known that the

β=α ₅ (1)

When the incident angle of the light incident on the volume holographic grating substrate satisfies the Bragg diffraction angle, the diffraction efficiency is the highest, and the incident angle and the diffraction angle are equal, namely:

where λ _B is the Bragg diffraction wavelength and d is the grating constant. According to Fresnel's law of refraction, the angle at which the central wavelength beam enters the grating is:

where n _C is the refractive index of the center wavelength inside the prism. The light beam is diffracted by the grating, which follows the diffraction law, then the diffraction angle of the central wavelength is:

α _3C =arcsin(λ _C /(d·n _C )-sin(α _2C )) (4)

According to the geometric relationship

β=α _3C +α _4C (5)

According to Fresnel's law of refraction, we have

n _C ·sinα _4C =sinα _5C (6)

The prism vertex angle can be obtained by substituting the above equations (1), (4) and (6) into equation (5)

FIG. 3 is a schematic structural diagram of a spherical reflector provided by an embodiment of the present invention. The system adopts a spherical reflector as a collimating structure, and the slit object point beam enters the spherical reflector, and then is collimated into the grating prism. As shown in Figure 3, point C is the spherical center of the spherical mirror, F' is the focal point of the spherical mirror, which coincides with the position of the slit. According to the principle of reversibility of the optical path, the collimated optical path can be regarded as the imaging of an infinitely distant object, that is, the object distance l=-∞, the primary aberration coefficient of the spherical mirror is:

In the above formula, S _I , S _II , S _III , S _IV and S _V are the primary spherical aberration coefficient, coma coefficient, astigmatism coefficient, field curvature coefficient and distortion coefficient of the spherical mirror, respectively. r is the radius of curvature of the spherical surface, h is the incident height of the paraxial light on the surface, i is the incident angle of the light on the spherical surface, the incident _iz is the incident aperture angle of the main light ray, and J is the Lach invariant. Since it is a mirror, there is no chromatic aberration.

The aperture diaphragm of the above system is located at the spherical center C of the spherical mirror, which is coincident with the incident surface of the grating prism beam splitting element. At this time, i _z =0, then S _Ⅱ =S _Ⅲ =S _Ⅴ =0 in formula (8), for The object point of the focal plane This spherical mirror system has no coma, astigmatism, distortion and chromatic aberration, only spherical aberration and field curvature. Since the system uses a slit of a certain length, the field of view is larger, such introduced field-dependent aberrations can be mutually compensated with the residual aberration of the collimating mirror.

In addition, since the dispersive element of the system is a transmission grating, there will be a second-order spectrum, that is, the second-order diffracted light at 400-500nm will overlap to the spectral region of 800-1000nm on the image plane. In order to avoid spectral aliasing, it is placed in front of the image. A secondary filter, the surface of the secondary filter 106 close to the detector 107 is coated with a long-wave-pass cut-off filter film, and the short-wave cut-off wavelength is 550 nm, and the secondary filter 106 is close to the surface of the detector 107 .

Finally, the slit length of the above system can reach 29.4mm, the spectral range is 420-1000nm, can cover the visible light to the near-infrared band, the F number is 2.4, and the spectral resolution can reach 1.2nm, which meets the current development needs of spectral imaging technology.

In addition, the system uses an on-axis design to avoid off-axis aberrations introduced by off-axis systems that are difficult to correct.

The working process of the above-mentioned system is simulated with a specific example below. In this example, the first-order parameters of the system are: the spectral range reaches 420-1000 nm, covering the visible light to near-infrared band, the slit length is 29.4 mm, and the F number is 2.4 , the pixel size is 11 μm, and the raster line logarithm is 170 lines/mm.

Based on the MTF results of the system at 420nm, 550nm, 700nm and 1000nm, when the cut-off frequency is 46lines/mm, the transfer functions of all fields of view of the imaging spectrometer are reduced in the entire wavelength range, although they are affected by the system occlusion. But the MTF is greater than 0.6 at the Nyquist frequency.

In addition, the spot diagram gives the root mean square radius value of the spot diagram of the system at different wavelengths through the ray trace diagram. From the point diagram obtained from the simulation, it can be known that the spot image on the detector is better. falls within one pixel.

The data information finally obtained by the system includes two-dimensional image information and one-dimensional spectral information. The standard for spectral-dimensional imaging quality evaluation generally uses spectral line bending (Smile) and color distortion. These distortions will cause errors in spectral restoration and cause The error of target feature component recognition. Both bending will bring a lot of trouble to subsequent data processing, and it needs to be effectively controlled in the optical system design. (0,0), (0,0.3), (0,0.5), (0,0.7) and (0,1) field of view chief rays were traced and the results showed the maximum spectral line bending and chromaticity in all bands The distortion is less than 3μm (0.32pixel), which meets the technical requirements of the spectral imaging system and ensures the accuracy of spectral restoration.

It should be noted that the content not described in detail in the embodiments of the present invention belongs to the prior art known to those skilled in the art.

To sum up, the overall size of the system provided by the embodiment of the present invention is compact, light in weight, simple in structure, and the image plane is not tilted, which is conducive to the installation and adjustment of the system; and the final slit length can reach 29.4 mm, and the spectral range is 420- 1000nm, can cover visible light to near-infrared band, F number 2.4, spectral resolution of 1.2nm, to meet the current development needs of spectral imaging technology.

The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of changes or Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (6)

1. a large field of view grating prism spectral imaging system, characterized in that the system comprises a slit, a spherical mirror, a plane mirror, a grating prism module, a focusing mirror group, a secondary filter and a detector, wherein : The light beam passing through the slit is incident on the spherical mirror and is reflected; The reflected light beam is incident on the plane mirror; The light beam reflected by the plane mirror is incident on the grating prism module, and diffracted at the grating prism module, wherein: the first-order diffracted light of different wavelengths enters the focusing mirror group, and then passes through the second-stage diffracted light. After the filter reaches the detector, the imaging process is completed; The front surface of the grating prism module serves as an aperture stop of the entire system, and the aperture stop is located at the spherical center C of the spherical mirror and coincides with the incident surface of the grating prism module. 2. The large field of view grating prism spectral imaging system according to claim 1, wherein, A rectangular hole is opened in the middle of the flat reflection mirror, and the flat reflection mirror does not block the light beam emitted from the slit by using the rectangular hole. 3. The large field-of-view grating prism spectral imaging system according to claim 1, wherein the grating prism module is formed by gluing a grating substrate, a grating, a protective glass and a prism, wherein: The grating substrate, protective glass and prism are all made of the same material; The optical axis of the grating prism module is parallel to the bottom surface of the module, and the central wavelength chief ray enters the grating base plane at an angle of α1, and enters the grating at an angle of incidence _α2 after being refracted _. Reach the prism slope; _The apex angle of the inclined plane of the prism is β, and finally the light exits at an exit angle of α5. 4. The large field of view grating prism spectral imaging system according to claim 1, wherein, A long-wave-pass cut-off filter film is plated on the surface of the secondary filter close to the detector, and the short-wave cut-off wavelength is 550 nm, and the secondary filter is placed close to the surface of the detector. 5. The large field of view grating prism spectral imaging system according to claim 1, wherein, The slit length of the system can reach 29.4 mm, the spectral range is 420-1000 nm, and the F number is 2.4. 6. The large field of view grating prism spectral imaging system according to claim 1, wherein, The system adopts an on-axis design, which can avoid off-axis aberrations introduced by off-axis systems that are difficult to correct.