CN111811650A - C-T structure imaging system based on holographic concave grating - Google Patents

Abstract

The invention proposes a C-T structure imaging system based on a holographic concave grating, which solves the problems of complex structure, large volume, high cost and low energy utilization rate of the existing C-T optical system. The system includes a front optical telephoto unit, a diffraction unit, a detection unit and a data acquisition control unit; the front optical telephoto unit includes a front mirror group, a diaphragm and a collimating mirror; the diffraction unit includes a holographic concave grating; the diaphragm is located in The image-side focal plane of the front mirror group is coincident with the object-side focal plane of the collimating mirror; the collimating mirror is used to collimate and correct the incident light; the holographic concave grating is located on the reflected light path of the collimating mirror and is used for The incident parallel light is split, and the light of the same wavelength in the split beam is focused on the surface of the detection unit; the detection unit includes a detector, and the detector is located on the focal plane of the image side of the holographic concave grating, and is used to receive the target beam in the incident direction after splitting. The optical signal is transmitted to the data acquisition control unit for processing.

Description

C-T structure imaging system based on holographic concave grating

technical field

The invention belongs to the field of imaging, in particular to a C-T structure imaging system based on a holographic concave grating.

Background technique

Imaging spectroscopy is a detection technology that integrates image information and spectral information. It analyzes the detection target by obtaining a "atlas data cube". Camera (can only acquire target contour and grayscale features). Due to the large amount of data obtained by imaging spectroscopy, it is widely used in many fields, such as aerospace, environmental monitoring, and marine environment detection. As the core part of the imaging spectrometer, the optical system determines the spectral range, dispersion rate and resolution of the spectrometer. The traditional cross-type Czerny-Turner (Czerny-Turner, referred to as C-T) optical path and the basic C-T optical path (M-type optical path) have become the optical path of many small spectrometers due to their compact optical path structure, high sensitivity and high resolution. The system's first choice.

At present, in the C-T optical path, the light splitting element is mainly a reflection grating, which can be divided into echelle grating, plane grating and concave grating optical path according to the surface type:

1. C-T optical system with echelle grating as beam splitting element

The echelle grating has high dispersion rate and resolution, which meets the performance requirements of spectrometers for resolution, and has a high diffraction order, which can achieve full-spectrum blaze. However, the free spectral range of the echelle grating is small, the hyperspectral order is seriously overlapped, and the lateral dispersion element is required to perform secondary dispersion of the spectrum, which makes the structure of the C-T optical system complex, the processing technology is complex, and the cost is high;

2. C-T optical system with plane grating as beam splitting element

In the C-T optical system, there are two main types of plane gratings as light splitting elements: blazed gratings and plane diffraction gratings. Taking the blazed grating as an example, the incident light passes through the blazed grating, and the light energy contained in the zero-order without dispersion in the diffraction spectrum at the receiving end always accounts for a large part of the total light energy, and the rest of the light energy is dispersed in the spectrum of each level. The grating often only uses a certain level of it, and its energy utilization rate is low and the volume is large, which cannot meet the needs of miniaturization.

3. Optical system with concave grating as beam splitting element

In the traditional concave grating spectrometer, the concave grating has the function of aberration correction, which greatly simplifies the optical path. Without other forms of optical path optimization, it can automatically obtain a wide spectral range with high resolution and maintain a flat spectral surface. However, the diffraction efficiency of the grating is only 25% to 28% at the highest, and the total energy utilization rate of the system is only 25% to 28%.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problems of relatively complex structure, relatively large volume, relatively high cost and low energy utilization rate in the existing C-T optical system, and proposes a C-T structure imaging system based on holographic concave grating. The invention further simplifies the structure of the existing C-T optical system, reduces the volume, reduces the cost of the small spectrometer, and improves its energy utilization rate.

For realizing the above purpose of the invention, the technical scheme of the present invention is:

A C-T structure imaging system based on a holographic concave grating, comprising a front optical telephoto unit, a diffraction unit, a detection unit and a data acquisition control unit; the front optical telephoto unit includes a front mirror group arranged in sequence along an optical path , a diaphragm and a collimating mirror; the diffraction unit includes a holographic concave grating; the diaphragm is located on the image-side focal plane of the front mirror group, and coincides with the object-side focal plane of the collimating mirror, and is used to adjust the entrance pupil The light flux in the fiber through the measured medium enters the C-T optical path; the collimating lens is used to collimate and correct the incident light, so that the incident light becomes parallel light, and the parallel light is reflected to the holographic concave grating; The holographic concave grating is located on the reflection light path of the collimating mirror, and is used to split the incident parallel light and focus the light of the same wavelength in the split beam to the surface of the detection unit; the detection unit includes a detector, and the detector It is located on the focal plane of the image side of the holographic concave grating, and is used to receive the optical signal after the target beam splitting in the incident direction, and transmit the optical signal to the data acquisition control unit for processing.

Further, the collimating mirror is an off-axis parabolic mirror, and the off-axis angle does not exceed 5°

Further, the inclination angle of the outgoing light of the holographic concave grating with respect to the incident light does not exceed 5°.

Further, the grating frequency of the holographic concave grating is 0.3 lines/μm.

Further, the detection unit receives diffracted light whose diffracted order is +1.

Further, the glass model selected for the front optical telephoto unit is HERAEUS.AGF series glass.

Further, the detection unit is a CCD image detector.

Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

1. The C-T structure imaging system based on the holographic concave grating of the present invention adopts the holographic concave grating to replace the grating and the focusing spherical mirror in the traditional crossed Cheney-Turner, and combines these two functions to greatly simplify the optical path and further The realization of miniaturization makes the imaging system simple in structure, small in size and low in cost, and can be used in far-ultraviolet and far-infrared spectral regions and miniature spectrometers.

2. The C-T structure imaging system based on the holographic concave grating of the present invention uses the holographic concave grating as the dispersive element, which can reduce the absorption phenomenon. In this optical path, there is only light loss due to the two reflections of the collimating surface and the grating surface, and there is no chromatic aberration. The spectrometer greatly improves energy utilization.

3. In the C-T structure imaging system based on the holographic concave grating of the present invention, since the holographic concave grating itself has the ability to reflect and focus, the crossed Cheney-Turner optical path can be simplified, so that the plane mirror used for reflection and focusing is omitted in the structure, The stability of the optical path of the imaging system is better, so that the spectrometer has very good stability.

4. In the C-T structure imaging system based on the holographic concave grating of the present invention, the holographic concave grating eliminates the influence of ghost lines due to its special processing technology, has aberration correction function, and does not need to perform other forms of optical path optimization. Flat spectral surface with high resolution in the spectral range.

Description of drawings

1 is a schematic diagram of the optical path of a C-T structure imaging system based on a holographic concave grating of the present invention;

Fig. 2 is the light path simulation diagram of the C-T structure imaging system based on the holographic concave grating of the present invention;

3 is an image quality evaluation diagram of the C-T structure imaging system based on the holographic concave grating of the present invention;

FIG. 4 is an image quality evaluation diagram of a conventional cross-type C-T optical path.

Reference signs: 1-front optical telephoto unit, 2-diffraction unit, 3-detection unit, 4-data acquisition control unit, 11-front mirror group, 12-diaphragm, 13-collimating mirror, 21- Holographic concave grating.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, the content of the present invention is described in further detail:

The invention proposes a C-T structure imaging system based on a holographic concave grating. In the system, the holographic concave grating replaces the grating and focusing spherical mirror in the traditional crossed Cheney-Turner. The optical path is greatly simplified, and miniaturization is further realized. While retaining the advantages of the C-T optical path, combined with the advantages of no ghost lines and correction of aberrations of the holographic concave grating, the energy utilization rate of the spectrometer is improved, and it has better correction of aberrations.

As shown in FIG. 1 , the C-T structure imaging system based on the holographic concave grating of the present invention is mainly composed of a front optical telephoto unit 1 , a diffraction unit 2 , a detection unit 3 and a data acquisition control unit 4 . The front optical telephoto unit 1 includes a front mirror group 11, a diaphragm 12 and a collimating mirror 13 arranged in sequence along the optical path, the diffraction unit 2 includes a holographic concave grating 21, the detection unit 3 includes a detector, and a data acquisition control unit 4 is the transmission and the client. The diaphragm 12 is located on the image-side focal plane of the front mirror group 11 and coincides with the object-side focal plane of the collimating mirror 13. Its function is to adjust the luminous flux of the entrance pupil, so that the light passing through the measured medium in the optical fiber enters the C-T optical path. The function of the collimating mirror 13 is to collimate and correct the incident light, so that the incident light incident with concentric circles becomes parallel light, and the parallel light is hit on the holographic concave grating 21; the holographic concave grating 21 is located in the collimating mirror 13 There are two functions on the reflected light path, one is to split the incident light, and the other is to focus the light of the same wavelength in the split beam to the surface of the detector; the detector is located on the focal plane of the image side of the holographic concave grating 21, using It receives the optical signal split by the target in the incident direction, and transmits the optical signal to the data acquisition control unit 4 for processing.

As shown in Figure 2, the working principle of the C-T structure imaging system based on the holographic concave grating is as follows: the incident light enters the C-T optical path through the diaphragm 12, is reflected by the collimating mirror 13, and propagates to the holographic concave grating 21 as a plane light wave. The concave grating 21 diffracts and splits the polychromatic light hitting the grating surface, and reflects the diverging beam. Since the holographic concave grating 21 itself plays a focusing role, the monochromatic light of the same wavelength will be concentrated on the focal plane of the holographic concave grating 21. On the detector, the detector conducts spectral data collection.

In the imaging system of the present invention, the collimating mirror 13 can be specifically an off-axis parabolic mirror to realize aberration-free focusing of the off-axis light beam, and the off-axis angle does not exceed 5°. The holographic concave grating 21 is a total reflection holographic concave grating, and the inclination angle of the outgoing light relative to the incident light does not exceed 5°. The detector uses a CCD image detector, which has the advantages of high sensitivity and low-luminosity incident light can also be detected, so that it can be used in low-luminosity environments and improve energy utilization.

In the embodiment of the present invention, the off-axis angle of the holographic concave grating 21 can be specifically 5 degrees, which is used to receive the parallel beam reflected by the collimating mirror 13, the grating frequency can be 0.3lines/μm, and the detector accepts diffraction For the diffracted light of order +1, the holographic concave grating 21 determines the diameter of the entrance pupil, and the diameter of the entrance pupil is calculated to be 21.76mm. The detector is located on the image-side focal plane of the holographic concave grating 21 . The Z axis is defined as the direction of the optical axis, and the Y direction is rotated 90 degrees counterclockwise along the positive direction of the Z axis, and the axis perpendicular to the surface ZOY is the X axis. The inclination of the detector relative to the surface of the X axis can be 12 degrees. In order to make the detector on the image plane, the detector has a certain eccentricity in the positive direction of the Y axis. By adjusting the angle and position, the image focus of different wavelengths is in the same direction. one side and land on the detector.

Based on the above structural settings, the imaging system of the C-T structure based on the holographic concave grating of the present invention has the following characteristics.

The C-T structure imaging system based on the holographic concave grating of the present invention uses the holographic concave grating 21 as the dispersive element, which can reduce the absorption phenomenon. The optical path only has the light loss of the two reflections from the collimating surface and the grating surface, and has no chromatic aberration, and is applied to the spectrometer Greatly improved energy utilization.

In the C-T structure imaging system based on the holographic concave grating of the present invention, since the holographic concave grating 21 itself has the ability to reflect and focus, the cross-type Cheney-Turner optical path can be simplified, so that the plane mirror for reflective focusing is omitted in the structure, and the optical path The stability of the spectrometer makes the spectrometer very stable; at the same time, the structure of the system is more compact and can be applied to a miniature spectrometer.

In the C-T structure imaging system based on the holographic concave grating of the present invention, the holographic concave grating 21 eliminates the influence of ghost lines due to its special processing technology, has aberration correction function, and does not need to perform other forms of optical path optimization, that is, a wide spectrum is automatically obtained. A flat spectrum with high resolution in the range.

The C-T structure imaging system based on the holographic concave grating of the present invention can be used in the far-ultraviolet spectrum and the far-infrared spectrum region. The grating constant of the holographic concave grating 21 can be 3.3 μm, so as to realize fine light splitting. The glass type selected for the front optical telephoto unit 1 is the glass under the HERAEUS.AGF series, and the wavelength range of light passing spans from extreme vacuum ultraviolet to In the far-infrared band, it can be obtained that the aberration meets the evaluation standard through simulation. Taking the dot diagram as an example, as shown in FIG. 4 , it can be concluded that the radius of the diffused spot of the existing crossed C-T optical path is 6299.15-6299.61 μm. As shown in FIG. 3 , the diffused spot radius of the C-T structure imaging system based on the holographic concave grating of the present invention is 3234.96-3235.34 μm, which shows that the C-T structure imaging system based on the holographic concave grating of the present invention has higher spectral resolution.

Claims (7)

1. a C-T type structure imaging system based on holographic concave grating, is characterized in that: comprise front optical telephoto unit (1), diffraction unit (2), detection unit (3) and data acquisition control unit (4); The front optical telephoto unit (1) comprises a front mirror group (11), a diaphragm (12) and a collimating mirror (13) arranged in sequence along the optical path; the diffraction unit (2) comprises a holographic concave grating ( twenty one); The diaphragm (12) is located on the image-side focal plane of the front lens group (11), and coincides with the object-side focal plane of the collimating mirror (13), and is used to adjust the light flux of the entrance pupil, so that the optical fiber passes through the focal plane. The light of the measuring medium enters the C-T optical path; The collimating mirror (13) is used for collimating and correcting the incident light, so that the incident light becomes parallel light, and the parallel light is reflected to the holographic concave grating (21); The holographic concave grating (21) is located on the reflected light path of the collimating mirror (13), and is used to split the incident parallel light and focus the light of the same wavelength in the split beam to the surface of the detection unit (3); The detection unit (3) includes a detector, the detector is located on the focal plane of the image side of the holographic concave grating (21), and is used for receiving the optical signal after the target beam splitting in the incident direction, and transmitting the optical signal to the data acquisition control Unit (4) performs processing. 2 . The C-T structure imaging system based on a holographic concave grating according to claim 1 , wherein the collimating mirror ( 13 ) is an off-axis parabolic mirror, and the off-axis angle does not exceed 5°. 3 . 3. The holographic concave grating-based C-T structure imaging system according to claim 1 or 2, characterized in that the inclination angle of the emergent light of the holographic concave grating (21) relative to the incident light does not exceed 5°. 4 . The C-T structure imaging system based on holographic concave grating according to claim 3 , wherein the grating frequency of the holographic concave grating ( 21 ) is 0.3 lines/μm. 5 . 5 . The C-T structure imaging system based on holographic concave grating according to claim 4 , wherein the detection unit ( 3 ) receives diffracted light whose diffraction order is +1. 6 . 6 . The C-T structure imaging system based on holographic concave grating according to claim 5 , wherein the glass model selected for the front optical telephoto unit ( 1 ) is HERAEUS.AGF series glass. 7 . 7 . The C-T structure imaging system based on holographic concave grating according to claim 6 , wherein the detection unit ( 3 ) is a CCD image detector. 8 .

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