A grating spectrometer

Abstract

The application discloses a compact, high-spectral resolution, wide-waveband coverage and high-throughput grating spectrometer, wherein a first convergent light beam emitted by an incident module is focused on a first focal point of a collimating and imaging mirror, and then becomes a first divergent light beam which is off-axially incident to the collimating and imaging mirror, is reflected by the collimating and imaging mirror into a first collimated light beam which is incident to a middle-step dispersion grating, is dispersed by the middle-step dispersion grating into a first dispersed light beam, and has an included angle with a plane where the first collimated light beam is located; the first dispersed light beam is reflected by the collimating and imaging mirror into a second convergent light beam which is focused on a second focal point of the collimating and imaging mirror, is reflected by a mirror located at the second focal point into a second divergent light beam which is off-axially incident to the collimating and imaging mirror, is reflected by the collimating and imaging mirror into a second collimated light beam which is incident to a cross dispersion module, is separated by cross dispersion of the cross dispersion module into a second dispersed light beam, and is finally focused and imaged by an imaging module.

Description

Technical Field

[0001] This application relates to the field of spectrometer technology, and more particularly to a grating spectrometer. Background Technology

[0002] With the development of fields such as biomedical detection, semiconductor testing, pollutant and atmospheric trace gas monitoring, and astronomical spectroscopic observation, the requirements for the detection sensitivity and spectral resolution of spectrometers are becoming increasingly stringent, gradually increasing from 0.5 nm to below 0.1 nm. The intensity of the detected signal is also gradually increasing from the microwatt (µW) level to below the nW level. Furthermore, higher requirements are being placed on the light transmission efficiency of spectrometers. For example, in astronomical spectroscopic detection, it is necessary to study extremely faint celestial objects in the universe. Similarly, in biomedical fluorescence detection, it is necessary to study faint fluorescence, such as the low-energy fluorescence excited by Raman fluorescence spectroscopy. The aforementioned studies of faint light beams require spectrometers with high light transmission efficiency. High efficiency is also required in atmospheric trace gas monitoring. In addition, many application scenarios require on-site monitoring, such as water quality monitoring and atmospheric trace gas monitoring, which require field testing. Therefore, the spectrometer must also be portable.

[0003] Most existing spectrometers use a CT (Catalyst-Columellar) optical path structure, which presents a contradiction between spectral resolution and spectral coverage. That is, while achieving high spectral resolution, the band coverage is usually only tens of nm, while achieving wide band coverage is difficult to achieve high spectral resolution. Furthermore, due to the optical path arrangement problem, existing CT-structured echelle grating spectrometers cannot have the echelle grating incident at a blaze angle, thus failing to achieve high spectrometer efficiency.

[0004] Therefore, there is an urgent need to provide a compact spectrometer with high spectral resolution, wide band coverage, and high throughput. Summary of the Invention

[0005] To address the aforementioned technical problems, embodiments of this application provide a grating spectrometer that offers advantages such as compact size, high spectral resolution, wide band coverage, and high throughput.

[0006] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0007] A grating spectrometer includes an incident module, a collimating and imaging mirror, a middle-order echelle dispersion grating, a reflecting mirror, a cross dispersion module, and an imaging module arranged along the optical path transmission direction;

[0008] The first converging beam emitted from the incident module is focused at the first focal point of the collimating and imaging mirror, and becomes a first diverging beam after passing through the first focal point. The first diverging beam is incident off-axis onto the collimating and imaging mirror, and is reflected by the collimating and imaging mirror into a first collimated beam that is incident onto the echelle dispersion grating.

[0009] The echelle dispersion grating is located at the pupil plane corresponding to the first focal point of the collimating and imaging lens. The plane containing the first collimated beam has an angle with the blaze plane of the echelle dispersion grating, and the projection beam of the first collimated beam onto the blaze plane is incident at a blaze angle. The blaze plane is a plane that passes through the grating normal of the echelle dispersion grating and is perpendicular to the grating, so that the first collimated beam becomes a first dispersed beam after being dispersed by the echelle dispersion grating, and the plane containing the first dispersed beam has an angle with the plane containing the first collimated beam.

[0010] The first dispersive beam is reflected by the collimating and imaging mirror to become a second converging beam, which is focused at the second focal point of the collimating and imaging mirror. It is then reflected by the reflecting mirror located at the second focal point to become a second diverging beam. The second diverging beam is incident off-axis onto the collimating and imaging mirror, and is reflected by the collimating and imaging mirror to become a second collimated beam, which is then incident onto the cross-dispersion module.

[0011] The cross-dispersion module is located at the pupil plane position corresponding to the second focal point of the collimating and imaging lens, and the dispersion direction of the cross-dispersion module is perpendicular to the dispersion direction of the echelle dispersion grating, so that the second collimated beam becomes a second dispersive beam after being separated by the cross-dispersion of the cross-dispersion module, and the second dispersive beam is focused and imaged by the imaging module.

[0012] Optionally, the first focal point or the second focal point is located on the optical axis of the collimating and imaging mirror.

[0013] Optionally, the angle between the plane containing the first dispersive beam and the plane containing the first collimated beam does not exceed 3°.

[0014] Optionally, the incident module includes a multimode fiber and a fiber focal ratio conversion element group, wherein the optical axis of the fiber focal ratio conversion element group and the optical axis of the collimating and imaging mirror have an angle, and the beam emitted from the multimode fiber becomes the first converging beam after passing through the fiber focal ratio conversion element group.

[0015] Optionally, the fiber focal ratio conversion element group includes a fiber collimating lens, a fiber aperture stop, and a fiber imaging lens arranged along the optical path transmission direction, wherein the multimode fiber is located at the front focal point of the fiber collimating lens, and the first focal point is the rear focal point of the fiber imaging lens;

[0016] The beam emitted from the multimode fiber becomes a third collimated beam after passing through the fiber collimating lens. The third collimated beam is then incident on the fiber imaging lens after being selected by the aperture of the fiber aperture stop, and forms the first converging beam through the fiber imaging lens.

[0017] Optionally, the cross-dispersion module includes at least one of a transmissive grating, a reflective grating, and a dispersive prism.

[0018] Optionally, the imaging module includes an imaging element group and a detector, wherein the second dispersive beam is focused and imaged onto the detector by the imaging element group.

[0019] Optionally, the imaging element group is a transmissive element group.

[0020] Optionally, the transmissive element group includes a first lens, a second lens, and a third lens arranged along the optical path transmission direction;

[0021] Wherein, the first lens and the third lens are positive lenses, the second lens is a negative lens, and the detector is located at the rear focal point of the third lens.

[0022] Optionally, the second lens is a cemented triplet lens.

[0023] Compared with existing technologies, the above technical solution has the following advantages:

[0024] The grating spectrometer provided in this application includes an incident module, a collimating and imaging mirror, an echelle dispersion grating, a reflecting mirror, a cross dispersion module, and an imaging module arranged along the optical path transmission direction. The echelle dispersion grating is located at the pupil plane corresponding to the first focal point of the collimating and imaging mirror, and the cross dispersion module is located at the pupil plane corresponding to the second focal point of the collimating and imaging mirror. The dispersion direction of the cross dispersion module is perpendicular to the dispersion direction of the echelle dispersion grating. During operation, the first converging beam emitted from the incident module is focused at the first focal point of the collimating and imaging mirror, and then becomes a first diverging beam that is incident off-axis onto the collimating and imaging mirror. The collimated beam, reflected by the collimating and imaging mirror, is incident on the echelle dispersion grating. After being dispersed by the echelle dispersion grating, it becomes a first dispersive beam. The plane containing the first dispersive beam forms an angle with the plane containing the first collimated beam. The first dispersive beam is then reflected by the collimating and imaging mirror as a second converging beam, which is focused at the second focal point of the collimating and imaging mirror. It is then reflected off-axis by a mirror located at the second focal point as a second diverging beam, which is incident on the collimating and imaging mirror. After being reflected by the collimating and imaging mirror as a second collimated beam, it is then incident on the cross-dispersion module. After being separated by the cross-dispersion of the cross-dispersion module, it becomes a second dispersive beam, which is finally focused and imaged by the imaging module.

[0025] In summary, the grating spectrometer provided in this application has the following advantages:

[0026] 1. This grating spectrometer uses a mid-echelon dispersion grating. The plane containing the incident beam (i.e., the first collimated beam) of the mid-echelon dispersion grating has an angle with the blaze plane of the mid-echelon dispersion grating. The projection beam of the incident beam (i.e., the first collimated beam) of the mid-echelon dispersion grating onto its blaze plane is incident at a blaze angle, so that the mid-echelon dispersion grating operates in a quasi-Littrow incident state, diffracting a beam of high diffraction order. This allows high spectral resolution to be achieved at a very low grating line density. Furthermore, the high diffraction order beam is cross-dispersed and separated by a cross-dispersion module, so that a single exposure can cover an ultra-wide band coverage range from ultraviolet to near-infrared. Thus, this grating spectrometer combines the advantages of high resolution and wide band coverage.

[0027] 2. The echelle dispersion grating operates in a quasi-Littrow incident state, which also maximizes the diffraction efficiency of the echelle dispersion grating. Furthermore, the optical path matching design of the incident module, the first focal point, the collimating and imaging mirror, the echelle dispersion grating, the reflecting mirror, the cross dispersion module, and the imaging module avoids beam energy loss and ensures the overall light transmission efficiency of the spectrometer, thus giving the spectrometer the advantage of high throughput.

[0028] 3. The plane containing the incident beam (i.e., the first collimated beam) of the echelle dispersion grating and the plane containing its diffracted beam (i.e., the first dispersive beam) are at an angle to avoid spatial interference between the incident beam and the diffracted beam. This allows for the placement of a reflector, so that the diffracted beam of the echelle dispersion grating, after being reflected by the collimating and imaging mirror, can be reflected again by the reflector to the collimating and imaging mirror, and then reflected again by the collimating and imaging mirror before being incident on the cross-dispersion module. This optical path design greatly folds the optical path, reducing the spatial size of the spectrometer and giving it the advantage of being compact.

[0029] 4. The collimating and imaging mirror combines the collimating and imaging mirrors into one unit and is used multiple times. Specifically, the collimated beam incident on the echelle dispersion grating and the collimated beam incident on the cross dispersion module are both collimated by the collimating and imaging mirror before being emitted. The diffracted beam emitted from the echelle dispersion grating is then focused by the collimating and imaging mirror to form an image at the second focal point. In this way, the collimating and imaging mirror performs multiple collimation and imaging functions simultaneously, thereby reducing the installation difficulty of the collimating and imaging mirror. Furthermore, the collimating and imaging mirror can serve as the assembly and adjustment reference for the entire spectrometer, facilitating optical path design. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the optical path structure of a grating spectrometer provided in an embodiment of this application;

[0032] Figure 2 This is a schematic diagram of the incident beam and diffracted beam in the blaze plane of a mid-echelon dispersion grating.

[0033] Figure 3 A schematic diagram showing the positional relationship between the incident surface, diffraction surface, and blaze plane of the grating spectrometer provided in the embodiments of this application;

[0034] Figure 4 This is a schematic diagram of the spectrum obtained by the grating spectrometer provided in the embodiments of this application;

[0035] Figure 5 This is a schematic diagram of the optical path structure of another grating spectrometer provided in an embodiment of this application;

[0036] Figure 6 This is a schematic diagram of the optical path structure of another grating spectrometer provided in the embodiments of this application. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0039] As described in the background section, there is an urgent need for a compact spectrometer with high spectral resolution, wide band coverage, and high throughput.

[0040] To better understand this application, the spectrometer’s “compact,” “high spectral resolution,” “wide band coverage,” and “high throughput” characteristics will be briefly described first.

[0041] The term "compact" specifically refers to a spectrometer with a compact optical path structure, small size, and easy portability.

[0042] For "high spectral resolution", the spectral resolution of traditional fiber optic spectrometers is about 0.5 nm. In order to achieve atomic spectrum detection, higher spectral resolution is required. "High spectral resolution" mainly refers to the spectral resolution of the spectrometer ≤ 0.1 nm or lower.

[0043] "Wide-band coverage" specifically refers to the ability of a single exposure of the spectrometer to cover the short-wave infrared band from 200nm to 1100nm in the ultraviolet region, and even down to 1.7μm or 2.5μm.

[0044] "High throughput" specifically refers to the spectrometer having high diffraction efficiency and low beam energy loss.

[0045] In view of this, embodiments of this application provide a grating spectrometer. Figure 1 This application provides a schematic diagram of the optical path structure of a grating spectrometer, as shown in the embodiment. Figure 1 As shown, the grating spectrometer includes an incident module 100, a collimating and imaging mirror 6, an echelle dispersion grating 7, a reflecting mirror 8, a cross dispersion module 9, and an imaging module 200 arranged along the optical path transmission direction.

[0046] like Figure 1 As shown, the incident module 100 emits a first converging beam 16, which is focused onto the first focal point 5 of the collimating and imaging mirror 6. After passing through the first focal point 5, the first converging beam 16 becomes a first diverging beam 17. The first diverging beam 17 is incident off-axis onto the collimating and imaging mirror 6, and after being reflected by the collimating and imaging mirror 6, it becomes a parallel first collimated beam 18, which is then incident onto the echelle dispersion grating 7. Specifically, the first diverging beam 17 is incident off-axis onto the collimating and imaging mirror 6, meaning that the principal ray direction of the first diverging beam 17 and the optical axis 25 direction of the collimating and imaging mirror 6 form an angle.

[0047] like Figure 1 As shown, the echelle dispersion grating 7 is located at the pupil plane position corresponding to the first focal point 5 of the collimating and imaging mirror 6. Thus, the first diverging beam 17, which is reflected by the collimating and imaging mirror 6, forms the first collimated beam 18, which can be incident on the echelle dispersion grating 7.

[0048] Figure 2A schematic diagram of the incident and diffracted beams in the blaze plane of a echelle dispersion grating is shown. The groove section of the echelle dispersion grating is a wide and deep right angle, with the two sides of the right angle extending along the Y and Z directions, respectively. The small inclined plane with a larger angle in the groove (i.e., the inclined plane parallel to the Y direction) is the working surface. The normal of the echelle dispersion grating is perpendicular to the plane in which the echelle dispersion grating is located (also called the grating plane). The blaze plane YOZ of the echelle dispersion grating is a plane that passes through the grating normal and is perpendicular to the grating.

[0049] from Figure 2 As can be seen, within the blazed plane YOZ, the incident beam diffracts into multiple wavelengths after hitting the working surface, where N is the diffraction order and λ is the wavelength. N1 The starting wavelength for the Nth order, λ Nm For the Nth order cutoff wavelength, the angle α between the incident beam and the grating normal is the angle of incidence, and the angle β between the diffracted beam and the grating normal is the angle of diffraction. For a beam of a specific wavelength, the angle of incidence α and the angle of diffraction β are equal in the blaze plane YOZ. In this case, both the angle of incidence α and the angle of diffraction β are equal to the blaze angle.

[0050] It can be imagined that within the blaze plane YOZ, when the incident beam is incident along the Z direction, the incident angle α is equal to the diffraction angle β, that is, the blaze angle is... Figure 2 Middle Θ B As shown, it is equal to the angle between the Z direction and the grating normal. Figure 2 In this context, θ represents the incident angle α and the blaze angle Θ of the incident beam. B The angle difference can be understood as follows: when θ is zero, the incident beam is incident at a blaze angle, the echelle dispersion grating is working in a blaze state, and the diffraction efficiency of the grating is the highest at this time, and the incident beam and the diffracted beam coincide in space.

[0051] In the embodiments of this application, such as Figure 1 As shown, the first collimated beam 18 is dispersed by the echelle dispersion grating 7 to become the first dispersive beam 19, which includes multiple orders of diffracted beams. To avoid interference between the incident beam (i.e., the first collimated beam 18) and the diffracted beam (i.e., the first dispersive beam 19) of the echelle dispersion grating 7, and to facilitate the design of the optical path structure, the plane containing the first collimated beam 18 is set to have an angle with the blaze plane YOZ of the echelle dispersion grating.

[0052] Specifically, the plane containing the first collimated beam 18 is the incident plane, and the plane containing the first dispersive beam 19 is the diffraction plane. The positional relationship between the incident plane, the diffraction plane, and the blaze plane of the echelle dispersion grating 7 is as follows: Figure 3 As shown, combined with Figure 1 and Figure 3As can be seen, the plane containing the first collimated beam 18 (i.e. the incident plane) has an angle γ with the blaze plane YOZ of the echelle dispersion grating, which in turn makes the plane containing the first dispersive beam 19 (i.e. the diffraction plane) also have an angle γ with the blaze plane YOZ of the echelle dispersion grating, and thus makes the plane containing the first dispersive beam 19 (i.e. the diffraction plane) have an angle 2γ with the plane containing the first collimated beam 18 (i.e. the incident plane). The incident plane containing the first collimated beam 18 and the diffraction plane containing the first dispersive beam 19 are symmetrical about the blaze plane YOZ of the echelle dispersion grating.

[0053] Furthermore, the projection beam of the first collimated beam 18 onto the blaze plane YOZ of the echelle dispersion grating 7 is still incident at a blaze angle. Thus, the echelle dispersion grating 7 operates in a quasi-Littrow incident state, which still allows the echelle dispersion grating 7 to achieve the highest diffraction efficiency.

[0054] It is understandable that the first collimated beam 18, after being dispersed by the echelle dispersion grating 7, forms the first dispersive beam 19, which is still a parallel collimated beam.

[0055] Continue as Figure 1 As shown, a parallel first dispersive beam 19 is incident on the collimating and imaging mirror 6, and reflected by the collimating and imaging mirror 6 to become a second converging beam 20. The second converging beam 20 is focused at the second focal point of the collimating and imaging mirror 6, and reflected by the reflecting mirror 8 located at the second focal point to become a second diverging beam 21. The second diverging beam 21 is incident off-axis on the collimating and imaging mirror 6, and reflected by the collimating and imaging mirror 6 to become a parallel second collimated beam 22, which is then incident on the cross-dispersion module 9. Specifically, the second diverging beam 21 is incident off-axis on the collimating and imaging mirror 6, meaning that the principal ray direction of the second diverging beam 21 and the optical axis 25 direction of the collimating and imaging mirror 6 form an angle.

[0056] As can be seen, this application significantly reduces the spatial size of the spectrometer by setting a reflecting mirror 8 at the second focal point of the collimating and imaging mirror 6, thereby folding the optical path using the reflecting mirror 8. In particular, since the plane where the first collimating beam 18 is located (i.e., the incident plane of the echelle dispersion grating 7) is located has an angle with the blaze plane of the echelle dispersion grating 7, the plane where the first dispersive beam 19 after dispersion by the echelle dispersion grating is located (i.e., the diffraction plane of the echelle dispersion grating 7) is located has an angle with the plane where the first collimating beam 18 is located (i.e., the incident plane of the echelle dispersion grating 7), thus avoiding interference between the incident beam (i.e., the first collimating beam 18) and the diffracted beam (i.e., the first dispersive beam 19) of the echelle dispersion grating 7, thereby causing the first diverging beam 17 and the second converging beam 20 to be spatially offset. After being reflected by the reflecting mirror 8, the second converging beam 20 can become the second diverging beam 21 and re-enter the collimating and imaging mirror 6.

[0057] It should be noted that, since the first dispersive beam 19 diffracted by the echelle dispersion grating 7 is collimated and reflected by the imaging mirror 6 to form the second converging beam 20, which converges to the reflecting mirror 8 located at the second focal point, the echelle dispersion grating 7 is actually located at the pupil plane position corresponding to the second focal point of the collimating and imaging mirror 6.

[0058] It is understandable that the first and second focal points of the echelle dispersion grating 7 do not coincide. This is consistent with the optical path design where the plane containing the first dispersive beam 19 and the plane containing the first collimated beam 18 form an angle. In other words, it is precisely because the plane containing the first dispersive beam 19 and the plane containing the first collimated beam 18 form an angle that the first diverging beam 17 before the first collimated beam 18 is formed by reflection from the collimating and imaging mirror 6 does not coincide with the second converging beam 20 formed by reflection from the first dispersive beam 19 after reflection from the collimating and imaging mirror 6. That is, the second converging beam 20 formed by reflection from the first dispersive beam 19 after reflection from the collimating and imaging mirror 6 will not spatially interfere with the first diverging beam 17 before the first collimated beam 18 is formed by reflection from the collimating and imaging mirror 6, which facilitates the design of the optical path structure.

[0059] Continue as Figure 1 As shown, the cross-dispersion module 9 is located at the pupil plane position corresponding to the second focal point of the collimating and imaging mirror 6. Thus, the second diverging beam 21 reflected by the mirror 8 at the second focal point and then reflected by the collimating and imaging mirror 6 to form the second collimated beam 22 can be incident on the cross-dispersion module 9.

[0060] It is understandable that the echelle dispersion grating 7 and the cross dispersion module 9 are both located at the pupil plane position corresponding to the second focal point of the collimating and imaging mirror 6. Thus, the first dispersive beam 19 emitted from the echelle dispersion grating 7 is focused at the second focal point of the collimating and imaging mirror 6 after being reflected by the collimating and imaging mirror 6, and the second divergent beam 21 emitted from the second focal point of the collimating and imaging mirror 6 is reflected by the collimating and imaging mirror 6 to form the second collimated beam 22, which is then incident on the cross dispersion module 9.

[0061] As mentioned above, the first dispersive beam 19 after dispersion by the echelle dispersion grating 7 includes diffracted beams of multiple orders. That is, the echelle dispersion grating 7 diffracts beams of N diffraction orders, but the beams of each diffraction order are still superimposed, meaning that the beams of each diffraction order in the second collimated beam 22 are still superimposed. Subsequently, as... Figure 1 As shown, the second collimated beam 22 becomes the second dispersive beam 23 after cross-dispersion separation by the cross-dispersion module 9. Since the dispersion direction of the cross-dispersion module 9 is perpendicular to the dispersion direction of the echelle dispersion grating 7, the N diffraction order sub-beams in the second collimated beam 22, after cross-dispersion separation by the cross-dispersion module 9, can ultimately obtain the following... Figure 4 The schematic diagram of the spectrum shown is as follows, where N is the diffraction order and λ is the spectral order.N1 The starting wavelength for the Nth order, λ NB For the intermediate wavelength of the Nth order, λ Nm For the Nth order cutoff wavelength, λ m1 λ is the starting wavelength of the m-th order. mB For the intermediate wavelength of the m-th order, λ mm For the m-th order cutoff wavelength, λ n1 λ is the starting wavelength of the nth order. nB For the intermediate wavelength of the nth order, λ nm It is the cutoff wavelength of the nth order.

[0062] Finally, as Figure 1 As shown, the second dispersive beam 23 is focused and imaged by the imaging module 200 to generate a spectrum.

[0063] In summary, the grating spectrometer provided in this application has the following advantages:

[0064] 1. This grating spectrometer uses a mid-echelon dispersion grating. The plane containing the incident beam (i.e., the first collimated beam) of the mid-echelon dispersion grating has an angle with the blaze plane of the mid-echelon dispersion grating. The projection beam of the incident beam (i.e., the first collimated beam) of the mid-echelon dispersion grating onto its blaze plane is incident at a blaze angle, so that the mid-echelon dispersion grating operates in a quasi-Littrow incident state, diffracting a beam of high diffraction order. This allows high spectral resolution to be achieved at a very low grating line density. Furthermore, the high diffraction order beam is cross-dispersed and separated by a cross-dispersion module, so that a single exposure can cover an ultra-wide band coverage range from ultraviolet to near-infrared. Thus, this grating spectrometer combines the advantages of high resolution and wide band coverage.

[0065] 2. The echelle dispersion grating operates in a quasi-Littrow incident state, which also maximizes the diffraction efficiency of the echelle dispersion grating. Furthermore, the optical path matching design of the incident module, the first focal point, the collimating and imaging mirror, the echelle dispersion grating, the reflecting mirror, the cross dispersion module, and the imaging module avoids beam energy loss and ensures the overall light transmission efficiency of the spectrometer, thus giving the spectrometer the advantage of high throughput.

[0066] 3. The plane containing the incident beam (i.e., the first collimated beam) of the echelle dispersion grating and the plane containing its diffracted beam (i.e., the first dispersive beam) are at an angle to avoid spatial interference between the incident beam and the diffracted beam. This allows for the placement of a reflector, so that the diffracted beam of the echelle dispersion grating, after being reflected by the collimating and imaging mirror, can be reflected again by the reflector to the collimating and imaging mirror, and then reflected again by the collimating and imaging mirror before being incident on the cross-dispersion module. This optical path design greatly folds the optical path, reducing the spatial size of the spectrometer and giving it the advantage of being compact.

[0067] 4. The collimating and imaging mirror combines the collimating and imaging mirrors into one unit and is used multiple times. Specifically, the collimated beam incident on the echelle dispersion grating and the collimated beam incident on the cross dispersion module are both collimated by the collimating and imaging mirror before being emitted. The diffracted beam emitted from the echelle dispersion grating is then focused by the collimating and imaging mirror to form an image at the second focal point. In this way, the collimating and imaging mirror performs multiple collimation and imaging functions simultaneously, thereby reducing the installation difficulty of the collimating and imaging mirror. Furthermore, the collimating and imaging mirror can serve as the assembly and adjustment reference for the entire spectrometer, facilitating optical path design.

[0068] As previously known, the first and second focal points of the echelle dispersion grating 7 do not coincide. However, it is understood that the echelle dispersion grating 7 is located at the pupil plane position corresponding to the first focal point 5 of the collimating and imaging mirror 6. At the same time, the echelle dispersion grating 7 is also located at the pupil plane position corresponding to the second focal point (i.e., at the reflecting mirror 8) of the collimating and imaging mirror 6. Therefore, the first focal point 5 and its second focal point (i.e., at the reflecting mirror 8) should be as close as possible, as long as the first diverging beam 17 and the second converging beam 20 can be staggered.

[0069] Optionally, in some embodiments of this application, such as Figure 1 As shown, the first focal point 5 of the collimating and imaging mirror 6 is located on the optical axis 25 of the collimating and imaging mirror 6, while the second focal point (i.e., at the reflecting mirror 8) is not located on the optical axis 25 of the collimating and imaging mirror 6. This arrangement serves two purposes: firstly, the first focal point 5 is close to the center of the entire optical path structure of the grating spectrometer, which facilitates the addition of optical elements at the location of the first focal point 5 to eliminate stray light from the grating spectrometer; secondly, considering that the light spot at the first focal point 5 is the light spot converged by the first converging beam 16, and the light spot on the reflecting mirror 8 at the second focal point is the light spot converged by the second converging beam 20 after the first dispersive beam 19 emitted from the echelle dispersion grating 7 is reflected by the collimating and imaging mirror 6, it is understandable that the light spot on the reflecting mirror 8 is larger than the light spot at the first focal point 5. Therefore, setting the first focal point 5 on the optical axis of the collimating and imaging mirror 6 also facilitates the design of the optical path structure.

[0070] However, this application does not limit whether the first focal point 5 must be located on the optical axis of the collimating and imaging mirror 6. Alternatively, the second focal point (i.e., at the reflecting mirror 8) can be located on the optical axis 25 of the collimating and imaging mirror 6. In this case, the first focal point 5 is not located on the optical axis 25 of the collimating and imaging mirror 6. However, the first focal point 5 and the second focal point (i.e., at the reflecting mirror 8) should not both be located on the optical axis 25 of the collimating and imaging mirror 6, so as to avoid the reflecting mirror 8 blocking the first converging beam 16 and the first diverging beam 17.

[0071] It is understandable that the larger the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the blazing plane of the echelle dispersion grating 7, the larger the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the plane containing its diffracted beam (i.e., the first dispersive beam 19). Correspondingly, the first diverging beam 17 and the second converging beam 20 deviate further, and the first focal point 5 and the second focal point (i.e., at the mirror 8) also deviate further. Conversely, the smaller the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the blazing plane of the echelle dispersion grating 7, the smaller the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the plane containing its diffracted beam (i.e., the first dispersive beam 19). Correspondingly, the smaller the deviation between the first diverging beam 17 and the second converging beam 20, the smaller the deviation between the first focal point 5 and the second focal point (i.e., at the mirror 8).

[0072] Furthermore, since the incident plane of the first collimated beam 18 and the diffraction plane of the first dispersive beam 19 are symmetrical about the blaze plane of the echelle dispersion grating, the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the plane containing its diffracted beam (i.e., the first dispersive beam) is equal to twice the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the blaze plane of the echelle dispersion grating 7. In other words, the size of the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the plane containing its diffracted beam (i.e., the first dispersive beam) can reflect the size of the angle between the plane containing the incident beam (i.e., the first collimated beam 18) of the echelle dispersion grating 7 and the blaze plane of the echelle dispersion grating 7.

[0073] Based on this, optionally, in some embodiments of this application, the angle between the plane where the first dispersive beam 19 is located and the plane where the first collimating beam 18 is located does not exceed 3°, so that the diffraction efficiency of the echelle dispersion grating 7 will not be affected by the excessive deviation between the plane where the first collimating beam 18 is located and the blaze plane of the echelle dispersion grating 7, and the first focal point 5 and the second focal point (i.e., at the mirror 8) can be made relatively close. Figure 1 The example is shown with an angle of 1.62° between the plane containing the first dispersive beam 19 and the plane containing the first collimated beam 18.

[0074] In practical applications, such as Figure 1 As shown, the collimating and imaging mirror 6 can be a rectangular coaxial parabolic mirror with mechanical dimensions of 100mm × 40mm × 12mm. Figure 1The dimension marked along the Z direction of the collimating and imaging lens 6 is the actual optical dimension of 90mm, and the focal length of the first focal point 5 of the collimating and imaging lens 6 can be 180mm.

[0075] The echelle dispersion grating 7 has a line density of 31.6 g / mm, a grating blaze angle of 63.9°, a grating size of 25 mm × 50 mm, and a working order of 104 orders from 57 to 160, covering a spectral range of 0.355 μm to 1 μm. The echelle dispersion grating 7 is located 180 mm from the exit pupil of the collimating and imaging mirror 6.

[0076] The reflector 8 can be a plane reflector with dimensions of 16mm × 4mm. It is conceivable that the reflector 8 needs to be held by a clamping device. Therefore, the first focal point 5 should be set outside the reflector 8 and its clamping device to avoid obstructing the first converging beam 16 and the first diverging beam 17.

[0077] It should be noted that, in Figure 1 In the optical path structure of the grating spectrometer shown, the first diverging beam 17 passing through the first focal point 5 is incident on the upper half of the collimating and imaging mirror 6 along the Z direction, and the echelle dispersion grating 7 is set corresponding to the upper half of the collimating and imaging mirror 6 along the Z direction, so that the first dispersive beam 19 emitted from the echelle dispersion grating 7 is also incident on the upper half of the collimating and imaging mirror 6 along the Z direction. Furthermore, the reflecting mirror 8 is set close to the optical axis 25 of the collimating and imaging mirror 6, and the second diverging beam 21 reflected by the reflecting mirror 8 is incident on the lower half of the collimating and imaging mirror 6 along the Z direction. This arrangement facilitates the design and adjustment of the optical path structure, but this application does not limit it, as long as the beams do not interfere with each other.

[0078] Optional, such as Figure 1 As shown, the incident module 100 includes a multimode fiber 1 and a fiber focal ratio conversion element group 110. The optical axis and collimation of the fiber focal ratio conversion element group 110 have an angle with the optical axis of the imaging mirror 6. The beam 14 emitted from the multimode fiber 1 becomes the first converging beam 16 after passing through the fiber focal ratio conversion element group 110.

[0079] Specifically, continue as follows Figure 1 As shown, the fiber optic focal ratio conversion element group 110 may include a fiber optic collimating lens 2, a fiber optic aperture stop 3, and a fiber optic imaging lens 4 arranged along the optical path transmission direction. The multimode fiber 1 is located at the front focal point of the fiber optic collimating lens 2, and the first focal point 5 is the rear focal point of the fiber optic imaging lens 4. With this arrangement, the beam 14 emitted from the multimode fiber 1 becomes a parallel third collimated beam 15 after passing through the fiber optic collimating lens 2. The third collimated beam 15 is incident on the fiber optic imaging lens 4 after being selected by the aperture of the fiber optic aperture stop 3, and forms a first converging beam 16 after passing through the fiber optic imaging lens 4.

[0080] It is understandable that the optical axis of the fiber optic focal ratio conversion element group 110 coincides with the principal ray of the first converging beam 16 and the principal ray of the first diverging beam 17. By adjusting the fiber optic focal ratio conversion element group 110, the first converging beam 16 can be adjusted to converge at the first focal point 5 of the collimating and imaging mirror 6. After passing through the first focal point 5, the first converging beam 16 becomes the first diverging beam 17 and is incident on the collimating and imaging mirror 6. It is reflected by the collimating and imaging mirror 6 into the first collimated beam 18. Furthermore, the divergence angle of the first converging beam 16 can be adjusted, thereby adjusting the divergence angle of the first diverging beam 17. Finally, the first collimated beam 18 is incident on the echelle dispersion grating 7. This setting can avoid the loss of beam energy and ensure the efficiency of the entire spectrometer.

[0081] Furthermore, in practical applications, the beam 14 emitted from the multimode fiber 1 may change. In the fiber focal ratio conversion element group 110, the beam 14 emitted from the multimode fiber 1 is first converted into a parallel third collimated beam 15 using the fiber collimating lens 2. Then, the fiber aperture stop 3 is used to select the beam with a fixed aperture. Subsequently, the fiber imaging lens 4 converts the third collimated beam 15, after being selected by the fiber aperture stop 3, into a first converging beam 16. With this setup, because the fiber aperture stop 3 selects the aperture of the beam, even if the beam 14 emitted from the multimode fiber 1 changes, it will not affect the first converging beam 16, and thus will not affect the subsequent optical path.

[0082] In practical applications, the focal ratio conversion ratio of the fiber optic focal ratio conversion element group 110 can be 2, the focal length of the fiber optic collimating lens 2 can be 25mm, the focal length of the fiber optic imaging lens 4 can be 50mm, the aperture of the fiber optic aperture stop can be 5mm, and the angle between the optical axis of the fiber optic focal ratio conversion element group 110 and the optical axis of the collimating lens 6 can be 7.091°.

[0083] In this application, the cross-dispersion module 9 is used to perform cross-dispersion separation on the second collimated beam 22. Optionally, such as... Figure 1 As shown, the cross-dispersion module 9 may include a transmission grating, the grating having a line density of 300 g / mm and a blaze angle of 25°; another option is, such as Figure 5 As shown, the cross-dispersion module 9 may include a reflective grating; alternatively, such as Figure 6 As shown, the cross-dispersion module 9 may include a dispersion prism; alternatively, the cross-dispersion module 9 may also be a combination of one or more of the following: a transmission grating, a reflection grating, a dispersion prism, and other dispersion methods.

[0084] Based on any of the above embodiments, optionally, in some embodiments of this application, such as Figure 1 , Figure 4 as well as Figure 5 As shown, the imaging module 200 includes an imaging element group 210 and a detector 13. The second dispersive beam 23 is focused and imaged onto the detector 13 by the imaging element group 210.

[0085] Preferred, such as Figure 1 , Figure 4 as well as Figure 5 As shown, the imaging element group 210 can be a transmissive element group, which facilitates achieving good imaging quality over a wide band coverage area.

[0086] Optional, such as Figure 1 As shown, the transmissive element group 210 may include a first lens 10, a second lens 11 and a third lens 12 arranged along the optical path transmission direction; wherein, the first lens 10 and the third lens 12 are positive lenses, the second lens 11 is a negative lens, and the detector 13 is located at the rear focal point of the third lens 12.

[0087] In practical applications, the focal length of the transmissive element group can be 50mm. In the transmissive element group, the first lens 10 is a positive lens with an effective focal length of 36.8mm, and its material can be apochromatic material S-FPL53; the second lens 11 can be a negative lens, specifically a cemented triplet lens, with an effective focal length of -31mm, and its materials can be H-LAK54, S-FPL53, and H-Lak45, respectively; the third lens 12 can be a positive lens with an effective focal length of 40.3mm, and its material can be heavy lanthanide material H-ZLAF52.

[0088] The second lens 11 is a cemented triplet lens, thus the transmissive element group consists of three groups of lenses, totaling five lenses. This results in a smaller number of lenses included in the imaging element group 210, leading to lower cost and smaller size of the spectrometer.

[0089] The various parts of this manual are described in a combination of parallel and progressive methods. Each part focuses on the differences between the other parts, and the same or similar parts can be referred to each other.

[0090] The features described above regarding the disclosed embodiments can be substituted or combined with each other to enable those skilled in the art to implement or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A grating spectrometer, characterized in that, It includes an incident module, a collimating and imaging mirror, an echelle dispersion grating, a reflecting mirror, a cross dispersion module, and an imaging module arranged along the optical path transmission direction; The first converging beam emitted from the incident module is focused at the first focal point of the collimating and imaging mirror, and becomes a first diverging beam after passing through the first focal point. The first diverging beam is incident off-axis onto the collimating and imaging mirror, and is reflected by the collimating and imaging mirror into a first collimated beam that is incident onto the echelle dispersion grating. The echelle dispersion grating is located at the pupil plane corresponding to the first focal point of the collimating and imaging lens. The plane containing the first collimated beam has an angle with the blaze plane of the echelle dispersion grating, and the projection beam of the first collimated beam onto the blaze plane is incident at a blaze angle. The blaze plane is a plane that passes through the grating normal of the echelle dispersion grating and is perpendicular to the grating, so that the first collimated beam becomes a first dispersed beam after being dispersed by the echelle dispersion grating, and the plane containing the first dispersed beam has an angle with the plane containing the first collimated beam. The first dispersive beam is reflected by the collimating and imaging mirror to become a second converging beam, which is focused at the second focal point of the collimating and imaging mirror. It is then reflected by the reflecting mirror located at the second focal point to become a second diverging beam. The second diverging beam is incident off-axis onto the collimating and imaging mirror, and is reflected by the collimating and imaging mirror to become a second collimated beam, which is then incident onto the cross-dispersion module. The cross-dispersion module is located at the pupil plane position corresponding to the second focal point of the collimating and imaging lens, and the dispersion direction of the cross-dispersion module is perpendicular to the dispersion direction of the echelle dispersion grating, so that the second collimated beam becomes a second dispersive beam after being separated by the cross-dispersion of the cross-dispersion module, and the second dispersive beam is focused and imaged by the imaging module.

2. The grating spectrometer according to claim 1, characterized in that, The first focal point or the second focal point is located on the optical axis of the collimating and imaging mirror.

3. The grating spectrometer according to claim 1, characterized in that, The angle between the plane containing the first dispersive beam and the plane containing the first collimated beam does not exceed 3°.

4. The grating spectrometer according to claim 1, characterized in that, The incident module includes a multimode fiber and a fiber focal ratio conversion element group. The optical axis of the fiber focal ratio conversion element group and the optical axis of the collimating and imaging mirror have an angle. The beam emitted from the multimode fiber becomes the first converging beam after passing through the fiber focal ratio conversion element group.

5. The grating spectrometer according to claim 4, characterized in that, The fiber optic focal ratio conversion element group includes a fiber optic collimating lens, a fiber optic aperture stop, and a fiber optic imaging lens arranged along the optical path transmission direction. The multimode fiber is located at the front focal point of the fiber optic collimating lens, and the first focal point is the rear focal point of the fiber optic imaging lens. The beam emitted from the multimode fiber becomes a third collimated beam after passing through the fiber collimating lens. The third collimated beam is then incident on the fiber imaging lens after being selected by the aperture of the fiber aperture stop, and forms the first converging beam through the fiber imaging lens.

6. The grating spectrometer according to claim 1, characterized in that, The cross-dispersion module includes at least one of a transmission grating, a reflection grating, and a dispersion prism.

7. The grating spectrometer according to claim 1, characterized in that, The imaging module includes an imaging element group and a detector, wherein the second dispersive beam is focused onto the detector by the imaging element group.

8. The grating spectrometer according to claim 7, characterized in that, The imaging element group is a transmissive element group.

9. The grating spectrometer according to claim 8, characterized in that, The transmissive element group includes a first lens, a second lens, and a third lens arranged along the optical path transmission direction; Wherein, the first lens and the third lens are positive lenses, the second lens is a negative lens, and the detector is located at the rear focal point of the third lens.

10. The grating spectrometer according to claim 9, characterized in that, The second lens is a cemented triplet lens.

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