CN111811650A - C-T type structure imaging system based on holographic concave grating - Google Patents
C-T type structure imaging system based on holographic concave grating Download PDFInfo
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- CN111811650A CN111811650A CN202010745070.5A CN202010745070A CN111811650A CN 111811650 A CN111811650 A CN 111811650A CN 202010745070 A CN202010745070 A CN 202010745070A CN 111811650 A CN111811650 A CN 111811650A
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- 238000003384 imaging method Methods 0.000 title claims abstract description 37
- 230000003287 optical effect Effects 0.000 claims abstract description 45
- 238000001514 detection method Methods 0.000 claims abstract description 18
- 238000012545 processing Methods 0.000 claims abstract description 7
- 210000001747 pupil Anatomy 0.000 claims description 4
- 230000004907 flux Effects 0.000 claims description 3
- 239000013307 optical fiber Substances 0.000 claims description 3
- 238000001228 spectrum Methods 0.000 description 11
- 230000003595 spectral effect Effects 0.000 description 9
- 230000004075 alteration Effects 0.000 description 8
- 239000006185 dispersion Substances 0.000 description 7
- 238000012937 correction Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000005457 optimization Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000002329 infrared spectrum Methods 0.000 description 2
- 238000013441 quality evaluation Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 238000002211 ultraviolet spectrum Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/2823—Imaging spectrometer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
Abstract
The invention provides a C-T type structure imaging system based on holographic concave grating, which solves the problems of complex structure, larger volume, higher cost and low energy utilization rate of the existing C-T optical system. The system comprises a front optical telescope unit, a diffraction unit, a detection unit and a data acquisition control unit; the front optical telescope unit comprises a front lens group, a diaphragm and a collimating lens; the diffraction unit comprises a holographic concave grating; the diaphragm is positioned on the image focal plane of the front lens group and is superposed with the object focal plane of the collimating lens; the collimating mirror is used for collimating and correcting incident light; the holographic concave grating is positioned on a reflection light path of the collimating mirror and is used for splitting incident parallel light and focusing light with the same wavelength in a split light beam to the surface of the detection unit; the detection unit comprises a detector, the detector is positioned on an image space focal plane of the holographic concave grating and used for receiving optical signals after incident direction target light splitting and transmitting the optical signals to the data acquisition control unit for processing.
Description
Technical Field
The invention belongs to the field of imaging, and particularly relates to a C-T type structure imaging system based on holographic concave grating.
Background
The imaging spectrum technology is a detection technology integrating image information and spectrum information, analyzes a detected target by obtaining a spectrum data cube, is known as a leap in the development history of optical instruments, and far exceeds the traditional panchromatic optical camera (only can obtain the contour and the gray scale characteristics of the target). Due to the large amount of data acquired by the imaging spectrum technology, the imaging spectrum technology is widely applied to a plurality of fields, such as aerospace, environmental monitoring, marine environmental detection and the like. The optical system is used as a core part of the imaging spectrometer, and determines the performance of the spectrometer such as spectral range, dispersion ratio, resolution ratio and the like. The traditional crossed Czerny-Turner (C-T for short) optical path and the basic C-T optical path (M-type optical path) become the first choice of optical systems of various small spectrometers due to the characteristics of compact optical path structure, higher sensitivity, higher resolution and the like.
At present, in a C-T optical path, a light splitting element is mainly a reflective grating, and can be divided into a echelle grating, a planar grating and a concave grating optical path according to a surface type:
1. C-T optical system using echelle grating as light splitting element
The echelle grating has high dispersion rate and resolution ratio, meets the performance requirement of a spectrometer on the resolution ratio, has high diffraction order and can realize full-spectrum blaze. However, the free spectral range of the echelle grating is small, the high spectral levels are seriously overlapped, and a transverse dispersion element is required to carry out secondary dispersion on the spectrum, so that the C-T optical system has a complex structure, a complex processing technology and high cost;
2. C-T optical system with plane grating as light splitting element
In a C-T optical system, there are two main types of plane gratings as a light splitting element: blazed gratings and planar diffraction gratings. Taking a blazed grating as an example, incident light passes through the blazed grating, light energy contained in a zero-order without dispersion in a diffraction spectrum of a receiving end always accounts for a large part of total light energy, and the rest light energy is dispersed in each level of spectrum.
3. Optical system using concave grating as light splitting element
In the traditional concave grating spectrometer, the concave grating has an aberration correction function, so that the optical path is greatly simplified, and a spectrum surface which has higher resolution and keeps straight in a wide spectrum range can be automatically obtained without carrying out optical path optimization in other forms, however, the maximum diffraction efficiency of the grating is only 25-28%, and the total energy utilization rate of the system is only 25-28%.
Disclosure of Invention
The invention aims to solve the problems of relatively complex structure, relatively large volume, relatively high cost and low energy utilization rate of the existing C-T optical system, and provides a C-T type structure imaging system based on holographic concave grating.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a C-T type structure imaging system based on holographic concave grating comprises a front optical telescope unit, a diffraction unit, a detection unit and a data acquisition control unit; the front optical telescope unit comprises a front lens group, a diaphragm and a collimating lens which are sequentially arranged along a light path; the diffraction unit comprises a holographic concave grating; the diaphragm is positioned on the image focal plane of the front lens group, is superposed with the object focal plane of the collimating lens and is used for adjusting the luminous flux of the entrance pupil so that light passing through a measured medium in the optical fiber enters a C-T light path; the collimating mirror is used for collimating and correcting incident light, converting the incident light into parallel light and reflecting the parallel light to the holographic concave grating; the holographic concave grating is positioned on a reflection light path of the collimating mirror and is used for splitting incident parallel light and focusing light with the same wavelength in a split light beam to the surface of the detection unit; the detection unit comprises a detector, the detector is positioned on the image space focal plane of the holographic concave grating and used for receiving optical signals after incident direction target light splitting and transmitting the optical signals to the data acquisition control unit for processing.
Furthermore, the collimating lens is an off-axis parabolic mirror, and the off-axis angle is not more than 5 DEG
Further, the angle of inclination of the emergent ray of the holographic concave grating relative to the incident ray is not more than 5 degrees.
Further, the grating frequency of the holographic concave grating is 0.3 lines/mum.
Further, the detection unit receives diffracted light with a diffraction order of +1 order.
Furthermore, the front optical telescopic unit is made of HERAEUS.
Further, the detection unit is a CCD image detector.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
1. the C-T type structure imaging system based on the holographic concave grating adopts the holographic concave grating to replace the grating and the focusing spherical reflector in the traditional crossed type Cheney-Telner, combines the two functions, greatly simplifies the light path, further realizes miniaturization, has simple structure, smaller volume and lower cost, and can be used in far ultraviolet spectrum, far infrared spectrum region and micro spectrometer.
2. The C-T type structure imaging system based on the holographic concave grating uses the holographic concave grating as a dispersion element, can reduce the absorption phenomenon, only has the light loss of two reflections of a collimation surface and a grating surface in the light path, has no chromatic aberration, and greatly improves the energy utilization rate when being applied to a spectrometer.
3. In the C-T type structure imaging system based on the holographic concave grating, as the holographic concave grating has the capability of reflection and focusing, the crossed type Cheney-Telner light path can be simplified, a plane mirror for reflection and focusing is omitted in the structure, the stability of the light path of the imaging system is better, and the spectrometer has very good stability.
4. In the C-T type structure imaging system based on the holographic concave grating, the holographic concave grating eliminates the influence of ghost lines due to the special processing technology, has the aberration correction function, does not need to carry out other forms of optical path optimization, and can automatically obtain a straight spectral plane with high resolution in a wide spectral range.
Drawings
FIG. 1 is a schematic diagram of an optical path of a C-T type structure imaging system based on a holographic concave grating;
FIG. 2 is a light path simulation diagram of a C-T type structure imaging system based on holographic concave grating;
FIG. 3 is an image quality evaluation diagram of a C-T type structure imaging system based on holographic concave grating;
FIG. 4 is an image quality evaluation chart of a conventional cross type C-T optical path.
Reference numerals: the system comprises a 1-front optical telescope unit, a 2-diffraction unit, a 3-detection unit, a 4-data acquisition control unit, a 11-front lens group, a 12-diaphragm, a 13-collimating lens and a 21-holographic concave grating.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
the invention provides a C-T type structure imaging system based on holographic concave grating, in the system, the holographic concave grating replaces the grating and the focusing spherical reflector in the traditional crossed type Cheni-Telner, the two functions are combined, the light path is greatly simplified, the miniaturization is further realized, the advantages of the C-T light path are kept, simultaneously, the advantages of no ghost line and aberration correction of the holographic concave grating are combined, the energy utilization rate of a spectrometer is improved, and meanwhile, the aberration correction is better.
As shown in FIG. 1, the C-T type structure imaging system based on the holographic concave grating mainly comprises a front optical telescopic unit 1, a diffraction unit 2, a detection unit 3 and a data acquisition control unit 4. The front optical telescope unit 1 comprises a front lens group 11, a diaphragm 12 and a collimating lens 13 which are sequentially arranged along a light path, the diffraction unit 2 comprises a holographic concave grating 21, the detection unit 3 comprises a detector, and the data acquisition control unit 4 is a transmission and user side. The diaphragm 12 is positioned on the image focal plane of the front lens group 11, is superposed with the object focal plane of the collimating lens 13, and is used for adjusting the luminous flux of the entrance pupil so that light passing through a measured medium in the optical fiber enters a C-T light path; the collimating mirror 13 is used for collimating and correcting the incident light, so that the incident light which is incident in concentric circles is changed into parallel light, and the parallel light is incident on the holographic concave grating 21; the holographic concave grating 21 is positioned on a reflection light path of the collimating mirror 13 and has two functions, namely splitting incident light and focusing light with the same wavelength in the split light beam to the surface of a detector; the detector is located on the image focal plane of the holographic concave grating 21 and is used for receiving the optical signal after the incident direction target is split and transmitting the optical signal to the data acquisition control unit 4 for processing.
As shown in FIG. 2, the working principle of the C-T type structure imaging system based on the holographic concave grating is as follows: incident light enters a C-T light path through a diaphragm 12, is reflected by a collimating mirror 13 and is transmitted to a holographic concave grating 21 as planar light waves, the holographic concave grating 21 diffracts and splits polychromatic light striking the grating surface, divergent light beams are reflected, and the holographic concave grating 21 plays a focusing role, so that the monochromatic light with the same wavelength is gathered on a detector positioned on the focal plane of the holographic concave grating 21, and the detector collects spectral data.
In the imaging system of the invention, the collimating lens 13 can specifically adopt an off-axis parabolic mirror to realize aberration-free focusing of off-axis beams, and the off-axis angle is not more than 5 degrees. The holographic concave grating 21 is a total reflection holographic concave grating, and the inclination angle of the emergent ray relative to the incident ray is not more than 5 degrees. The detector adopts a CCD image detector, and can be applied to a low-light environment by utilizing the advantages that the detector has high sensitivity and can detect low-light incident light, so that the energy utilization rate is improved.
In the embodiment of the present invention, the off-axis angle of the holographic concave grating 21 may be 5 degrees, which is used for receiving the parallel light beams reflected by the collimator 13, the grating frequency may be 0.3lines/μm, and the detector receives the diffracted light with the diffraction order of +1, the holographic concave grating 21 determines the entrance pupil diameter, which is calculated to be 21.76 mm. The detector is located on the image-side focal plane of the holographic concave grating 21. The Z axis is defined as the optical axis direction, the Y direction is obtained by rotating 90 degrees anticlockwise along the positive direction of the Z axis, and the X axis is obtained by an axis vertical to the surface ZOY. The surface inclination of the detector relative to the X axis can be 12 degrees, in order to enable the detector to be positioned on an image surface, the detector has certain eccentricity in the positive direction of the Y axis, and through adjusting the angle and the position, image space focuses with different wavelengths are enabled to be positioned on the same surface and fall on the detector.
Based on the structural arrangement, the C-T type structural imaging system based on the holographic concave grating has the following characteristics.
The C-T type structure imaging system based on the holographic concave grating uses the holographic concave grating 21 as a dispersion element, can reduce the absorption phenomenon, only has the light loss of two reflections of a collimation surface and a grating surface in the light path, has no chromatic aberration, and greatly improves the energy utilization rate when being applied to a spectrometer.
In the C-T type structure imaging system based on the holographic concave grating, as the holographic concave grating 21 has the capability of reflection and focusing, the crossed type Cheney-Telner light path can be simplified, a plane mirror for reflection and focusing is omitted in the structure, and the stability of the light path ensures that the spectrometer has very good stability; meanwhile, the system has a more compact structure and can be applied to a micro spectrometer.
In the C-T type structure imaging system based on the holographic concave grating, the holographic concave grating 21 eliminates the influence of ghost lines due to the special processing technology, has the aberration correction function, does not need to carry out optical path optimization in other forms, and can automatically obtain a straight spectral plane with high resolution in a wide spectral range.
The C-T type structure imaging system based on the holographic concave grating can be used in far ultraviolet spectrum and far infrared spectrum regions. The grating constant of the holographic concave grating 21 can be 3.3 mu m, so that fine light splitting is realized, the glass type selected by the front optical telescopic unit 1 is the glass under HERAEUS.AGF series, the light-passing wavelength range can span from extreme vacuum ultraviolet to far infrared bands, and the aberration of the holographic concave grating can meet the evaluation standard through simulation. Taking a dot-sequence diagram as an example, as shown in FIG. 4, it can be found that the diffuse spot radius of the conventional cross C-T optical path is 6299.15-6299.61 μm. As shown in FIG. 3, the diffuse spot radius of the C-T type structure imaging system based on the holographic concave grating is 3234.96-3235.34 μm, so that the spectral resolution of the C-T type structure imaging system based on the holographic concave grating is higher.
Claims (7)
1. A C-T type structure imaging system based on holographic concave grating is characterized in that: comprises a front optical telescope unit (1), a diffraction unit (2), a detection unit (3) and a data acquisition control unit (4);
the front optical telescope unit (1) comprises a front lens group (11), a diaphragm (12) and a collimating lens (13) which are sequentially arranged along a light path; the diffraction unit (2) comprises a holographic concave grating (21);
the diaphragm (12) is positioned on the image focal plane of the front lens group (11), is superposed with the object focal plane of the collimating lens (13), and is used for adjusting the luminous flux of the entrance pupil so that light passing through a measured medium in the optical fiber enters a C-T light path;
the collimating mirror (13) is used for collimating and correcting incident light, converting the incident light into parallel light and reflecting the parallel light to the holographic concave grating (21);
the holographic concave grating (21) is positioned on a reflection light path of the collimating mirror (13) and is used for splitting incident parallel light and focusing light with the same wavelength in a split light beam to the surface of the detection unit (3);
the detection unit (3) comprises a detector, and the detector is positioned on an image space focal plane of the holographic concave grating (21) and used for receiving optical signals after incident direction target light splitting and transmitting the optical signals to the data acquisition control unit (4) for processing.
2. The holographic concave grating-based C-T structure imaging system of claim 1, wherein: the collimating lens (13) is an off-axis parabolic mirror, and the off-axis angle is not more than 5 degrees.
3. The holographic concave grating based C-T structure imaging system of claim 1 or 2, wherein: the angle of inclination of the emergent ray of the holographic concave grating (21) relative to the incident ray is not more than 5 degrees.
4. The holographic concave grating-based C-T structure imaging system of claim 3, wherein: the grating frequency of the holographic concave grating (21) is 0.3 lines/mu m.
5. The holographic concave grating-based C-T structure imaging system of claim 4, wherein: the detection unit (3) receives diffracted light with a diffraction order of + 1.
6. The holographic concave grating-based C-T structure imaging system of claim 5, wherein: the front optical telescopic unit (1) is made of HERAEUS.
7. The holographic concave grating-based C-T structure imaging system of claim 6, wherein: the detection unit (3) is a CCD image detector.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113899451A (en) * | 2021-09-30 | 2022-01-07 | 深圳迈塔兰斯科技有限公司 | Spectrometer and super-surface light splitting device |
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| CN212567670U (en) * | 2020-07-29 | 2021-02-19 | 中国科学院西安光学精密机械研究所 | C-T type structure imaging system based on holographic concave grating |
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- 2020-07-29 CN CN202010745070.5A patent/CN111811650A/en active Pending
Patent Citations (5)
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| JP2001050811A (en) * | 1999-08-09 | 2001-02-23 | Jasco Corp | Optical system and spectrophotometer using the same |
| US20060082772A1 (en) * | 2004-10-20 | 2006-04-20 | Resonon Inc. | Scalable imaging spectrometer |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113899451A (en) * | 2021-09-30 | 2022-01-07 | 深圳迈塔兰斯科技有限公司 | Spectrometer and super-surface light splitting device |
| CN113899451B (en) * | 2021-09-30 | 2024-01-30 | 深圳迈塔兰斯科技有限公司 | Spectrometer and super-surface light-splitting device |
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