CN111811650B - 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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- CN111811650B CN111811650B CN202010745070.5A CN202010745070A CN111811650B CN 111811650 B CN111811650 B CN 111811650B CN 202010745070 A CN202010745070 A CN 202010745070A CN 111811650 B CN111811650 B CN 111811650B
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- 238000003384 imaging method Methods 0.000 title claims abstract description 41
- 230000003287 optical effect Effects 0.000 claims abstract description 48
- 238000001514 detection method Methods 0.000 claims abstract description 19
- 238000012545 processing Methods 0.000 claims abstract description 7
- 210000001747 pupil Anatomy 0.000 claims description 5
- 239000011521 glass Substances 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 18
- 230000004075 alteration Effects 0.000 description 8
- 239000006185 dispersion Substances 0.000 description 7
- 238000012937 correction Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 230000003595 spectral effect Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000002329 infrared spectrum Methods 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000002211 ultraviolet spectrum Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000013441 quality evaluation Methods 0.000 description 1
- 238000004088 simulation Methods 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
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- Diffracting Gratings Or Hologram Optical Elements (AREA)
Abstract
The invention provides a C-T type structural imaging system based on a holographic concave grating, which solves the problems of complex structure, larger volume, higher cost and low energy utilization rate of the traditional 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 space focal plane of the front lens group and coincides with the object space 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 the incident parallel light and focusing the light with the same wavelength in the split light beam to the surface of the detection unit; the detection unit comprises a detector, and the detector is positioned on the focal plane of the holographic concave grating and is used for receiving the optical signal of the incidence direction target after light splitting and transmitting the optical signal 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 a holographic concave grating.
Background
The imaging spectrum technology is a detection technology integrating image information and spectrum information, and is characterized in that a detected target is analyzed by obtaining a map data cube, so that the imaging spectrum technology is known as a leap in the development history of an optical instrument, and the imaging spectrum technology is far superior to a traditional full-color optical camera (only the contour and gray scale characteristics of the target can be obtained). Because of the large data volume acquired by the imaging spectrum technology, the imaging spectrum technology is widely applied to various fields, such as aerospace, environment monitoring, marine environment detection and the like. The optical system is used as a core part of the imaging spectrometer, and determines the spectral range, the dispersion ratio, the resolution and other performances of the spectrometer. The traditional cross-type Cheny-Turner (C-T for short) optical path and the basic C-T optical path (M-type optical path) are the first choice of a plurality of small-sized spectrometer optical systems due to the characteristics of compact optical path structure, higher sensitivity, higher resolution and the like.
Currently, in the C-T optical path, the light splitting element is mainly a reflective grating, and may be divided into an echelle grating, a planar grating, and a concave grating optical path according to a plane type:
1. C-T optical system using echelle grating as light-splitting element
The echelle grating has high dispersion rate and resolution, meets the performance requirement of a spectrometer on the resolution, has high diffraction order and can realize full-spectrum blaze. However, the echelle grating has small free spectrum range and high spectrum orders 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 complex structure, complex processing technology and higher cost;
2. C-T optical system using plane grating as light-splitting element
In the C-T optical system, there are mainly two types of planar gratings as the spectroscopic elements: blazed gratings and planar diffraction gratings. Taking blazed grating as an example, the incident light passes through the blazed grating, the zero-order light energy contained in the diffraction spectrum without dispersion at the receiving end always occupies a large part of the total light energy, and the rest light energy is dispersed in each level of spectrum, and when the grating is actually used, only one level of the grating is often utilized, so that the energy utilization rate is low, the volume is large, and the miniaturization requirement cannot be met.
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 an optical path is greatly simplified, other forms of optical path optimization are not needed, a spectrum surface which has higher resolution and keeps straight in a wide spectrum range can be automatically obtained, but the highest 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 traditional C-T optical system, and provides a C-T structural imaging system based on a holographic concave grating.
In order to achieve the above object, the present invention has the technical scheme that:
A C-T structure imaging system based on a 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 space focal plane of the front lens group and coincides with the object space focal plane of the collimating lens, and is used for adjusting the luminous flux of the entrance pupil so that the light passing through the measured medium in the optical fiber enters the C-T light path; the collimating mirror is used for collimating and correcting incident light, so that the incident light is changed into parallel light, and the parallel light is reflected 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 the incident parallel light and focusing the light with the same wavelength in the split light beam to the surface of the detection unit; the detection unit comprises a detector, and the detector is positioned on the image side focal plane of the holographic concave grating and is used for receiving the optical signal of the incidence direction target after being split and transmitting the optical signal to the data acquisition control unit for processing.
Further, the collimating lens is an off-axis parabolic lens, and the off-axis angle is not more than 5 DEG
Further, the angle of inclination of the emergent light of the holographic concave grating relative to the incident light is not more than 5 °.
Further, the grating frequency of the holographic concave grating is 0.3lines/μm.
Further, the detection unit receives diffracted light having a diffraction order of +1.
Further, the glass model of the front optical telescope unit is 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 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 cross-type Cheny-Tenn, 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 area and miniature spectrometer.
2. The C-T structure imaging system based on the holographic concave grating uses the holographic concave grating as a dispersion element, so that the absorption phenomenon can be reduced, only the light loss of the collimation surface and the grating surface reflected twice exists in the light path, no chromatic aberration exists, and the energy utilization rate is greatly improved when the C-T structure imaging system is applied to a spectrometer.
3. In the C-T type structure imaging system based on the holographic concave grating, the holographic concave grating has the reflection focusing capability, so that a cross type cut-off-nano optical path can be simplified, a plane mirror for reflection focusing is omitted in the structure, the stability of the optical path of the imaging system is better, and the spectrometer has very good stability.
4. In the C-T 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 an aberration correction function, and can automatically obtain a straight spectrum surface with high resolution in a wide spectrum range without optimizing other forms of light paths.
Drawings
FIG. 1 is a schematic diagram of the optical path of a C-T type structured imaging system based on a holographic concave grating of the present invention;
FIG. 2 is a schematic diagram of the optical path of the C-T structured imaging system based on the holographic concave grating;
FIG. 3 is an image quality evaluation chart of the C-T structure imaging system based on the holographic concave grating;
fig. 4 is a diagram showing evaluation of image quality of a conventional cross-type C-T optical path.
Reference numerals: the device 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 attached drawings and specific examples:
The invention provides a C-T type structural imaging system based on a holographic concave grating, in the system, the holographic concave grating replaces a grating and a focusing spherical reflector in the traditional cross-type Cheny-Tenn, the two functions are combined, the light path is greatly simplified, miniaturization is further realized, the advantages of a C-T light path are reserved, meanwhile, the advantages of no ghost lines 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 structural imaging system based on the holographic concave grating mainly comprises a preposed optical telescope unit 1, a diffraction unit 2, a detection unit 3 and a data acquisition control unit 4. The front optical telescopic 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 space focal plane of the front lens group 11 and coincides with the object space focal plane of the collimating lens 13, and has the function of adjusting the luminous flux of the entrance pupil so that the light passing through the measured medium in the optical fiber enters the C-T light path; the collimating mirror 13 performs collimation correction on the incident light, so that the incident light 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 the reflection light path of the collimating mirror 13 and has two functions, namely, the light of the incident light is split, and the light with the same wavelength in the split light beam is focused on the surface of the detector; the detector is located on the focal plane of the holographic concave grating 21, and is configured to receive the optical signal after the object in the incident direction is split, and transmit the optical signal to the data acquisition control unit 4 for processing.
As shown in fig. 2, the working principle of the C-T structure imaging system based on the holographic concave grating is as follows: the incident light enters a C-T light path through the diaphragm 12, is reflected by the collimating mirror 13, propagates to the holographic concave grating 21 as planar light waves, the holographic concave grating 21 diffracts and splits the complex-color light striking the grating surface, and reflects the scattered light, and as the holographic concave grating 21 plays a role in focusing, monochromatic light with the same wavelength is collected on the detector positioned on the focal surface 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 lens to realize aberration-free focusing of off-axis light 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 emergent light rays relative to incident light rays is not more than 5 degrees. The detector adopts a CCD image detector, and the detector has the advantages of high sensitivity and low-luminosity incident light detection, so that the detector can be applied to a low-luminosity environment, and 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 specifically 5 degrees, for receiving the parallel light beam reflected by the collimator lens 13, the grating frequency may be 0.3lines/μm, and the detector receives the diffracted light with the diffraction order of +1, and the holographic concave grating 21 determines the entrance pupil diameter, and the calculated entrance pupil diameter is 21.76mm. The detector is located at 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 the anticlockwise rotation of 90 degrees along the positive direction of the Z axis, and the X axis is the axis perpendicular to the ZOY plane. The detector can be inclined at 12 degrees relative to the surface of the X axis, and in order to enable the detector to be positioned on an image plane, the detector is eccentric to a certain extent in the positive direction of the Y axis, and through adjusting the angle and the position, the image space focuses of different wavelengths are positioned on the same plane 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 structure imaging system based on the holographic concave grating uses the holographic concave grating 21 as a dispersion element, so that the absorption phenomenon can be reduced, only the light loss of the collimation surface and the grating surface reflected twice exists in the light path, no chromatic aberration exists, and the energy utilization rate is greatly improved when the C-T structure imaging system is applied to a spectrometer.
In the C-T type structural imaging system based on the holographic concave grating, as the holographic concave grating 21 has the reflection focusing capability, the cross type Cheny-Tenn optical path can be simplified, a plane mirror for reflection focusing is omitted in the structure, and the stability of the optical path enables the spectrometer to have very good stability; meanwhile, the system is more compact in structure and can be applied to a micro spectrometer.
In the C-T 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 an aberration correction function, and can automatically obtain a straight spectrum surface with high resolution in a wide spectrum range without carrying out other forms of optical path optimization.
The C-T type structure imaging system based on the holographic concave grating can be used for 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, glass with the model of HERAEUS. AGF series is selected as glass for the front optical telescope unit 1, the wavelength range of light can be passed across the extremely far vacuum ultraviolet to far infrared wave band, and the aberration can be obtained through simulation to meet the evaluation standard. Taking the point column diagram as an example, as shown in fig. 4, the diffuse spot radius of the existing cross type C-T light path can be 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 space focal plane of the front lens group (11) and coincides with the object space focal plane of the collimating lens (13) and is used for adjusting the luminous flux of the entrance pupil so that the light passing through the measured medium in the optical fiber enters the C-T light path;
the collimating mirror (13) is used for collimating and correcting incident light, so that the incident light is changed into parallel light, and the parallel light is reflected 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 the incident parallel light and focusing the light with the same wavelength in the split light beam to the surface of the detection unit (3);
the detection unit (3) comprises a detector, and the detector is positioned on the image side focal plane of the holographic concave grating (21) and is used for receiving the optical signal of the incidence direction target after being split and transmitting the optical signal 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 lens, 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 outgoing light rays of the holographic concave grating (21) relative to the incoming light rays is not more than 5 degrees.
4. A holographic concave grating based C-T structure imaging system as claimed in 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 having a diffraction order of +1.
6. The holographic concave grating based C-T structure imaging system of claim 5, wherein: the glass model of the front optical telescope unit (1) is 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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