Transmission type imaging spectrometer

Abstract

The utility model provides a transmission-type imaging spectrometer. The transmission-type imaging spectrometer comprises a slit, a collimating lens group, a light splitting module, an imaging group and a detector which are arranged in sequence, the light splitting module comprises a grating and a prism; polychromatic light enters the collimating lens group through the slit, is collimated into parallel light, is projected to the grating for diffraction light splitting, then enters the prism for refraction light splitting, and is converged on the detector through the imaging group after light splitting. According to the utility model, the light transmission efficiency can be improved, aberration can be corrected, and large-area image correction can be realized.

Description

Technical Field

[0001] The utility model relates to the technical field of spectrometers, and in particular to a transmission-type imaging spectrometer. Background Art

[0002] For Raman applications, the most common spectrometer design on the market is the CT reflective optical path structure, which is relatively easy to manufacture. The optical element is usually a spherical reflector, and the grating is a flat ruled grating, which is easy to process and has low cost. Whether it is scientific research-level Raman or portable Raman application, the only difference is the focal length of the spectrometer, and the optical path principle is basically the same. Figure 1 This is a schematic diagram of the optical path of a CT spectrometer in the prior art. Figure 1 As shown, a beam of polychromatic light is diverged through the incident slit 100 and projected to the collimator 200 , converged into parallel light by the collimator 200 and projected to the grating 300 , and then diffracted and split by the grating 300 and projected to the imaging mirror 400 , and the imaging mirror 400 converges light of different wavelengths to the detector 500 .

[0003] The advantages of this design are easy design and low cost, but the disadvantage is low light transmission efficiency. Usually the focal length to incident pupil diameter ratio F / # can be as small as F / 4. Figure 1 Collimators and imaging mirrors usually use spherical or aspherical reflectors. The incident light and the outgoing light are off-axis optical paths relative to the collimator or imaging mirror, which inevitably introduces off-axis aberrations such as spherical aberration. The smaller the F / # value, the higher the light transmission efficiency, which means that at the same focal length, the larger the aperture of the collimator or imaging mirror, and at the same time, the off-axis aberration increases sharply, seriously affecting the image quality and spectral resolution of the slit. According to the experience of optical path design, F / 4 is a relatively reasonable value, which can not only meet the use requirements of light transmission, but also control off-axis aberrations such as spherical aberration within a reasonable range.

[0004] And the shorter the focal length, the stronger the stray light. Figure 1 Since there are multiple diffraction spectra after the grating diffraction spectrum, it is inevitable that light of other orders except the main light path will hit the collimator or imaging mirror. These lights are reflected to the grating again through the collimator or imaging mirror. The grating diffracts again and finally reflects into the exit slit through the imaging mirror, thus forming stray light. The shorter the focal length, the shorter the distance between the grating and the collimator or imaging mirror, the more serious the phenomenon of multiple reflections and diffractions, and the stronger the stray light formed. Therefore, the CT-type reflective optical path structure has low light transmission efficiency and poor imaging quality. Especially for fiber Raman, the signal is severely lost and the system signal-to-noise ratio is reduced.

[0005] At present, imaging spectrometers are widely used in hyperspectral applications. Imaging spectrometers combine optical imaging and spectral splitting technologies, and can simultaneously obtain spatial and spectral information of objects, with the advantage of unified image and spectrum. Imaging spectrometers based on prism-grating-prism modules (hereinafter referred to as PGP modules) do not have the disadvantages of large off-axis systems, difficult installation and adjustment, and instability. They combine the advantages of prism and grating dispersion and have been applied to aerospace spectral imaging remote sensing, high-speed integrated real-time spectral detection, etc.

[0006] However, hyperspectral imaging spectrometers usually have a wide band, such as 400-1000nm. The design of the collimator and imaging mirror not only needs to eliminate aberrations such as astigmatism, field curvature, and distortion, but also needs to correct chromatic aberration, which is difficult to design and expensive. The PGP module uses a transmission grating and two prisms, which increases the difficulty and cost of debugging. Utility Model Content

[0007] The main purpose of the embodiment of the utility model is to provide a transmission imaging spectrometer to improve light transmission efficiency, correct aberrations, and achieve large-area image correction.

[0008] In order to achieve the above-mentioned object, the embodiment of the utility model provides a transmission imaging spectrometer, comprising:

[0009] A slit, a collimating lens group, a light splitting module, an imaging group and a detector are arranged in sequence;

[0010] The light splitting module includes a grating and a prism;

[0011] The complex light is incident on the collimating lens group through the slit, and is projected onto the grating for diffraction and spectral splitting after being collimated into parallel light, and then enters the prism for refraction and spectral splitting, and after spectral splitting, it is converged onto the detector by the imaging group.

[0012] In one embodiment, the grating and the prism are arranged in parallel.

[0013] In one embodiment, the spacing between the grating and the prism is 1 mm to 3 mm.

[0014] In one embodiment, the distance between the grating and the collimating lens group is a first preset distance, and the distance between the prism and the imaging group is a second preset distance.

[0015] In one embodiment, the relative placement angle between the collimating lens group and the grating is a first preset angle, and the relative placement angle between the imaging group and the grating is a second preset angle.

[0016] In one embodiment, the first preset angle is greater than the second preset angle.

[0017] In one embodiment, the collimating lens group includes a first positive focus lens, a first negative focus lens, a second positive focus lens and a third positive focus lens which are arranged in sequence.

[0018] In one embodiment, the imaging group includes a fourth positive focus lens, a fifth positive focus lens, a second negative focus lens and a sixth positive focus lens which are arranged in sequence.

[0019] In one embodiment, the lenses in the collimating lens group and the imaging group are coated with anti-reflection films.

[0020] In one embodiment, the grating is a volume phase transmission grating.

[0021] The transmission imaging spectrometer of the embodiment of the utility model comprises a slit, a collimating lens group, a spectroscopic module, an imaging group and a detector arranged in sequence. The spectroscopic module comprises a grating and a prism, which can improve the light transmission efficiency, correct the aberration and realize large-area image correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is the principle diagram of the optical path of a CT-type spectrometer in the prior art;

[0024] Figure 2 It is a schematic diagram of a transmission imaging spectrometer in an embodiment of the utility model. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0026] The utility model is a spectrometer solution proposed for fiber Raman applications. For fiber Raman, due to the loss of optical fiber transmission, the signal is attenuated. In order to improve the collection of Raman signals, it can only be achieved by improving the collection efficiency of the spectrometer. The Raman application band is relatively narrow, and it is usually not necessary to consider eliminating the chromatic aberration existing in the system. The utility model adopts a transmission optical path design. The lens group used in the system does not need to eliminate chromatic aberration. The focus needs to be on eliminating spherical aberration and distortion. The design difficulty is relatively small compared to high-spectrum applications. Raman applications not only require spectral detection, but also require rapid mapping imaging, which has high requirements on the system's light transmission efficiency and imaging quality. The utility model uses a lens group for collimation and convergence, which improves the light transmission efficiency on the one hand, and corrects the aberration on the other hand. In addition, a combination of gratings and prisms is used to correct distortion, thereby achieving large-area image correction. The utility model is explained below in conjunction with the accompanying drawings.

[0027] Figure 2 Schematic diagram of a transmission imaging spectrometer in an embodiment of the present utility model. Figure 2 As shown, the utility model is mainly designed for 785nm laser excitation Raman application, with a wavelength range of 785-980nm, and adopts a transmission structure, which is different from the traditional CT reflection optical path structure. The transmission imaging spectrometer of the utility model includes:

[0028] The slit 1, the collimating lens group 2, the beam splitting module 3, the imaging group 4 and the detector 5 are arranged in sequence. The collimating lens group 2 and the imaging group 4 both use an aberration correction imaging lens group.

[0029] The light splitting module 3 comprises a grating 31 and a prism 32. The grating is a volume phase transmission grating.

[0030] In a specific implementation, a beam of complex light is incident on the collimating lens group 2 through the slit 1, and after being collimated into parallel light, it is projected onto the grating 31 for diffraction and splitting, and then enters the prism 32 for refraction and splitting. After splitting, it is converged on the detection surface of the detector 5 by the imaging group 4.

[0031] In one embodiment, the grating 31 is a volume phase transmission grating, which has extremely low polarization effect and high diffraction efficiency. The grating outer diameter is 50.8mm, the grating line is 900G, the blaze wavelength is 930nm, and the diffraction efficiency can reach up to 90%, which can effectively improve the light transmission efficiency of the entire spectrometer. At the same time, the stray light introduced by the volume holographic transmission grating is lower than that of the plane ruled grating.

[0032] In one embodiment, the prism 32 is made of high refractive index material H-ZLAF90, and the vertex angle is 28.5°

[0033] In one embodiment, the grating 31 and the prism 32 are arranged in parallel.

[0034] In one embodiment, the distance between the grating 31 and the prism 32 is 1 mm to 3 mm.

[0035] The utility model adopts a grating plus prism light splitting module, which can not only realize diffraction light splitting, but also correct the distortion off-axis aberration, which is very suitable for large field of view imaging applications. There is a certain distance between the grating 31 and the prism 32, the distance range is 1-3mm, which is convenient for installation and debugging and plays a certain role in aberration correction.

[0036] In one embodiment, the collimating lens group includes a first positive focus lens 21, a first negative focus lens 22, a second positive focus lens 23 and a third positive focus lens 24 which are arranged in sequence.

[0037] In one embodiment, the imaging group includes a fourth positive focus lens 41, a fifth positive focus lens 42, a second negative focus lens 43 and a sixth positive focus lens 44 which are arranged in sequence.

[0038] The lenses in the collimating lens group and the imaging group are coated with 780-980nm anti-reflection film, with a focal length of 100mm, and can achieve high light flux F / 2.3 and a field of view of 14mm. The imaging lens group minimizes various optical aberrations and can obtain higher spectral resolution.

[0039] In one embodiment, the distance between the grating 31 and the third positive focus lens 24 of the collimating lens group 2 is a first preset distance, and the distance between the prism 32 and the fourth positive focus lens 41 of the imaging group 4 is a second preset distance.

[0040] The first preset distance is smaller than the second preset distance, the first preset distance is 15 mm, and the second preset distance is 20 mm.

[0041] In one embodiment, the relative placement angle between the collimating lens group 2 and the grating 31 is a first preset angle, and the relative placement angle between the imaging group 4 and the grating 31 is a second preset angle.

[0042] In one embodiment, the first preset angle is greater than the second preset angle. The first preset angle may be 17.4 degrees, corresponding to a central wavelength of 880 nm; the second preset angle may be 0.03 degrees, that is, the relative angle between the imaging mirror and the collimating mirror is 17.43 degrees.

[0043] In summary, the transmission imaging spectrometer of the utility model is a full-band image correction spectrometer, the imaging area can reach 30mm×14mm, and detectors with a photosensitive surface ≤30mm×14mm can be used. For applications that require simultaneous monitoring or measurement of multiple samples or light sources, this can be achieved through a multi-channel approach to improve test efficiency.

[0044] For Raman applications, the utility model provides a spectrometer solution with high light transmission efficiency and high imaging quality, which effectively corrects the spectral line bending existing in the system by adopting a combination of prisms and gratings. It is not only suitable for spectral detection of small-area photosensitive detectors, but also suitable for imaging detection of large-area photosensitive detectors.

[0045] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only a specific embodiment of the utility model and is not intended to limit the scope of protection of the utility model. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the utility model should be included in the scope of protection of the utility model.

Claims

1. A transmission imaging spectrometer, characterized in that: include: A slit, a collimating lens group, a light splitting module, an imaging group and a detector are arranged in sequence; The light splitting module includes a grating and a prism; The complex light is incident on the collimating lens group through the slit, and is projected onto the grating for diffraction and spectral splitting after being collimated into parallel light, and then enters the prism for refraction and spectral splitting, and after spectral splitting, it is converged onto the detector by the imaging group.

2. The transmission imaging spectrometer according to claim 1, characterized in that: The grating and the prism are arranged in parallel.

3. The transmission imaging spectrometer according to claim 1, characterized in that: The distance between the grating and the prism is 1 mm to 3 mm.

4. The transmission imaging spectrometer according to claim 1, characterized in that: The distance between the grating and the collimating lens group is a first preset distance, and the distance between the prism and the imaging group is a second preset distance.

5. The transmission imaging spectrometer according to claim 1, characterized in that: The relative placement angle between the collimating lens group and the grating is a first preset angle, and the relative placement angle between the imaging group and the grating is a second preset angle.

6. The transmission imaging spectrometer according to claim 5, characterized in that: The first preset angle is greater than the second preset angle.

7. The transmission imaging spectrometer according to claim 1, characterized in that: The collimating lens group comprises a first positive focus lens, a first negative focus lens, a second positive focus lens and a third positive focus lens which are arranged in sequence.

8. The transmission imaging spectrometer according to claim 1, characterized in that: The imaging group includes a fourth positive focus lens, a fifth positive focus lens, a second negative focus lens and a sixth positive focus lens which are arranged in sequence.

9. The transmission imaging spectrometer according to claim 7 or 8, characterized in that: The lenses in the collimating lens group and the imaging group are coated with anti-reflection films.

10. The transmission imaging spectrometer according to claim 1, characterized in that: The grating is a volume phase transmission grating.

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