A three-band cascade spectrometer

Abstract

The application discloses a three-waveband cascade spectrometer and relates to the technical field of spectral diagnosis. Specifically, the three-waveband cascade spectrometer comprises a fiber coupler, a collimating objective, three-stage transmission diffraction gratings arranged in cascade, three exit objectives and three detectors. The first-stage grating diffracts a target short-waveband and outputs the target short-waveband to the first exit objective, and meanwhile, transmits the remaining wavebands in the form of zero-order transmission light to the next-stage grating. The target central wavelengths corresponding to the gratings increase in turn. The signals diffracted by the wavebands are synchronously collected by the detectors after being focused by the exit objectives. The application can solve the problems of low light flux and difficulty in synchronous measurement of multiple wavebands in the prior art, and realizes synchronous measurement of three wavebands with high resolution and high flux.

Description

Technical Field

[0001] This invention relates to the field of spectral diagnostic technology, and in particular to a three-band cascaded spectrometer. Background Technology

[0002] Charge-exchange recombination spectroscopy diagnostics is a key method for diagnosing the distribution parameters of ion temperature, rotational velocity, and density in magnetically confined plasmas. Typical target spectra for diagnostics include the HeII, CVI, and Hα lines. Spectrophotometers analyze the spectral signals to resolve the multiple physical parameters contained within the target plasma.

[0003] Due to the complex experimental environment of nuclear fusion devices, key technical requirements include low-light measurement, real-time dynamic monitoring, and a balance between high resolution and high throughput. Existing single-band spectrometers can only acquire information from a single band per measurement, making it difficult to meet the need for simultaneous measurement of multiple parameters. Multi-band spectrometers mostly achieve multi-band measurements through time-division scanning or optical path switching, making true synchronous measurement difficult and unable to meet the diagnostic needs of transient processes. As the spectral coverage increases, the light throughput is often limited by complex optical designs, leading to a decrease in signal-to-noise ratio and limiting the ability to detect low-light signals. Current technologies struggle to achieve a balance between resolution and throughput.

[0004] Therefore, how to achieve high-throughput, high-resolution three-band synchronous measurement has become an urgent technical problem to be solved. Summary of the Invention

[0005] The main objective of this invention is to provide a three-band cascaded spectrometer, which aims to achieve high-throughput, high-resolution simultaneous measurement across three bands.

[0006] To achieve the above objectives, the present invention proposes a three-band cascaded spectrometer, comprising: an optical fiber coupler, a collimating objective lens, a cascaded three-stage transmission diffraction grating, and a first exit objective lens, a second exit objective lens, a third exit objective lens, a first detector, a second detector, and a third detector, respectively corresponding to each stage of the transmission diffraction grating. The cascaded three-stage transmission diffraction grating includes a first-stage grating, a second-stage grating, and a third-stage grating arranged sequentially along the optical path propagation direction. The target center wavelengths corresponding to the first-stage grating, second-stage grating, and third-stage grating increase sequentially: the target center wavelength corresponding to the first-stage grating is 468.6 nm, the target center wavelength corresponding to the second-stage grating is 529.05 nm, and the target center wavelength corresponding to the third-stage grating is 656.3 nm. The spectral signal to be measured output from the collimating objective lens is incident on the first-stage grating. The first-stage grating diffracts the target's short-wavelength band and outputs it to the corresponding first exit objective lens, while allowing the remaining bands to pass through as zero-order transmission light and be incident on the second-stage grating. The second-stage grating diffracts the target's mid-wavelength band. The light is output to the corresponding second exit objective lens, while the remaining long-wavelength band is transmitted as zero-order transmitted light and incident on the third-order grating. The third-order grating diffracts the target long-wavelength band and outputs it to the corresponding third exit objective lens. The light signals after diffraction of each band are focused by the corresponding exit objective lens and synchronously collected by the corresponding detector. The first-order grating, the second-order grating, and the third-order grating all have the same incident angle and the same diffraction angle, and the incident angle α and the diffraction angle β are both 60°, so that the first-order grating, the second-order grating, and the third-order grating all operate in the Littoral configuration. The line density of the first-order grating is 3700 lines / mm, the line density of the second-order grating is 3300 lines / mm, and the line density of the third-order grating is 2650 lines / mm. The first-level grating, the second-level grating, and the third-level grating are all etched gratings formed on a fused silica substrate, and their duty cycles are all 0.35. The etching depth of the first-level grating is 546 nm, the etching depth of the second-level grating is 625 nm, and the etching depth of the third-level grating is 825 nm. This creates a resonance effect between light of a specific wavelength and the etched line depth, which can enhance the phase modulation of the target wavelength light.

[0007] Preferably, the first-level grating, the second-level grating, and the third-level grating are all the same size, and each size is 160mm×300mm.

[0008] Preferably, the collimating objective, the first exit objective, the second exit objective, and the third exit objective all adopt a four-element lens group structure with a telecentric optical path design, and their lens F number is 3 and focal length is 390mm.

[0009] Preferably, the fiber coupler adopts a double-row vertical fiber arrangement structure, with a fiber numerical aperture of 0.22 and a single fiber core diameter of 400μm.

[0010] Preferably, the number of vertical single-row optical fibers in the optical fiber coupler is 50 to 100, and the total number of channels is 100 to 200.

[0011] Preferably, it also includes an adjustment base slide rail, which has a double dovetail groove structure. A rotation adjustment bracket and a height adjustment bracket with a ±5° rotation adjustment range are installed below the collimating objective lens. The rotation adjustment bracket and the height adjustment bracket are disposed on the adjustment base slide rail.

[0012] Preferably, the first, second, and third detectors are all EMCCD detectors with parallel readout mode, with a pixel count of 1024×1024 and a pixel size of 13μm×13μm, and the three detectors acquire data through a synchronous triggering mechanism.

[0013] The above technical solution has the following advantages: This invention employs a cascaded grating layout to achieve synchronous acquisition of multi-band spectra. The zero-order transmission characteristic of the transmission diffraction grating reduces energy loss caused by optical path switching. The system's overall structure is compact and improves space utilization. The deeply etched grating enhances optical efficiency at the target diffraction order, achieving an energy utilization rate of 53.7%, an order of magnitude improvement over traditional spectrometers. The three independent detector design enables synchronous acquisition of different band spectra within the same timeframe. The synchronous triggering mechanism eliminates time deviations during measurement. This scheme meets the high temporal resolution requirements for plasma instability analysis in dynamic experiments. The application of a large-size grating ensures a larger aperture and a higher signal-to-noise ratio. Attached Figure Description

[0014] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a schematic diagram of the structure of a three-band cascaded spectrometer system provided in an embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram of the collimating objective lens group provided in an embodiment of the present invention.

[0016] Figure 3 This is a schematic diagram of the local optical path of the first-stage grating provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] This invention provides a three-band cascaded spectrometer, which will be described below in conjunction with... Figures 1 to 3 The technical solution of this embodiment will be described in detail.

[0019] Example 1 This embodiment provides a three-band cascaded spectrometer, primarily applied to charge-exchange recombination spectroscopy (CXRS) diagnostic systems in controlled nuclear fusion devices. CXRS diagnostics are used to diagnose key distribution parameters of ion temperature, rotational velocity, and density in magnetically confined plasmas. The target spectra include the HeII line (468.6 nm), CVI line (529.05 nm), and Hα line (656.3 nm). Using this spectrometer, the behavior of helium impurities can be observed, obtaining helium concentration distribution and expulsion efficiency; ion temperature can be obtained through Doppler broadening, and rotational velocity through frequency shifting; and hydrogen isotope behavior can be analyzed to obtain physical parameters such as the temperature and density of the main ion, enabling simultaneous monitoring of multiple parameters.

[0020] like Figure 1 As shown, the spectrometer is mounted on a modular vibration-isolation optical experimental platform 14 with a length of 2m; the system housing 13 is used to isolate the internal optical path to ensure the stable performance of optical components such as lenses and diffraction gratings, and to facilitate maintenance and debugging during the experiment.

[0021] The structure of this three-band cascaded spectrometer includes, sequentially arranged along the optical path, an fiber coupler 1, an adjustment base slide rail 2, a collimating objective lens 3, a cascaded three-stage transmission diffraction grating, and exit objectives and detectors corresponding to each stage of the transmission diffraction grating. The cascaded three-stage transmission diffraction grating includes a first-stage grating 4, a second-stage grating 5, and a third-stage grating 6. The corresponding exit objectives include a first exit objective lens 7, a second exit objective lens 8, and a third exit objective lens 9. The corresponding detectors include a first detector 10, a second detector 11, and a third detector 12.

[0022] At the signal input end, fiber optic coupler 1 adopts a double-row vertical fiber arrangement structure, with a single fiber core diameter of 400μm and a numerical aperture of 0.22. The height of fiber optic coupler 1 is set according to the number of fibers. This double-row dense arrangement design allows a single row to accommodate 50 to 100 fibers with a core diameter of 400μm, and the total number of channels of the entire spectrometer can be 100 to 200. This high-density vertical arrangement not only makes efficient use of space resources and achieves high-density sampling, but also effectively reduces gaps between fibers, significantly improves optical coupling efficiency, and meets the needs of simultaneous acquisition of multiple channels. Fiber optic coupler 1 is mounted on the adjustment base slide rail 2, which is 100mm wide and adopts a double dovetail groove structure, providing precise horizontal adjustment capability for the front-end coupling components and ensuring stable beam transmission.

[0023] The collimating objective lens 3 is mounted on the adjustment base slide rail 2 above the height adjustment bracket and the rotation adjustment bracket. To ensure structural stability, the brackets are preferably made of stainless steel. The height adjustment bracket allows the collimating objective lens 3 to move vertically, adjusting it to be coaxial with the center of the fiber coupler to ensure optical path consistency. The rotation adjustment bracket has a range of [range missing]. The collimating objective 3 is used to precisely adjust the direction of the incident light to optimize collimation. It employs a four-element lens group structure with a telecentric optical path design. This design minimizes the number of lenses while ensuring image quality, thereby reducing coating loss and glare contamination. The collimating objective 3 has an F-number of 3, a focal length of 390mm, and an exit pupil diameter of 130mm. This exit pupil diameter is close to the limit of grating manufacturing capabilities, resulting in a theoretically calculated energy efficiency of 53.7%. Compared to the approximately 5% energy efficiency of traditional spectrometers, this embodiment achieves an order-of-magnitude improvement in light throughput.

[0024] The spectral signal to be measured output from the collimating objective lens 3 is incident on the first-stage grating 4. In this embodiment, the three-stage cascaded gratings employ a specific arrangement logic based on dispersion characteristics, system compactness, diffraction efficiency, and experimental requirements. The target center wavelength corresponding to the first-stage grating 4 is 468.6 nm, the target center wavelength corresponding to the second-stage grating 5 is 529.05 nm, and the target center wavelength corresponding to the third-stage grating 6 is 656.3 nm. This cascading method, placing the short-wavelength band in the first stage, is because blue light at 468.6 nm has a higher dispersion rate and stronger wavelength separation capability. Placing it in the first stage allows for more precise spectrum separation, reducing the complexity of subsequent optical path design. Simultaneously, this effectively avoids interference from long-wavelength scattered or transmitted light on the short-wavelength signal, reducing signal loss and background noise.

[0025] The first-stage grating 4 diffracts the short-wavelength band (468.6 nm) of the target and outputs it to the corresponding first exit objective 7. Simultaneously, the first-stage grating 4 allows the remaining wavelength band to pass through as zero-order transmitted light and be incident on the second-stage grating 5. The second-stage grating 5 diffracts the mid-wavelength band (529.05 nm) of the target and outputs it to the corresponding second exit objective 8, while allowing the remaining long-wavelength band to pass through as zero-order transmitted light and be incident on the third-stage grating 6. The third-stage grating 6 then diffracts the long-wavelength band (656.3 nm) of the target and outputs it to the corresponding third exit objective 9. This cascaded arrangement helps maintain a basically consistent optical axis direction for beams of different wavelengths in the subsequent optical system, reducing system size and optical aberrations.

[0026] To maximize diffraction efficiency, the first-order grating 4, the second-order grating 5, and the third-order grating 6 are all the same size, 160 mm. 300mm. The incident angle and diffraction angle of the third-order grating remain consistent in space, and the incident angle... With diffraction angle All This allows all three levels of gratings to operate in a Littrow configuration, where the incident and diffracted light satisfy a symmetrical relationship with respect to the grating normal, which is beneficial for improving the diffraction efficiency of the target diffraction order.

[0027] According to the grating diffraction equation ,in, For diffraction orders, For the target center wavelength, The spacing between the grating lines. It is a sine function. Angle of incidence The diffraction angle is the first diffraction order in this embodiment. The grating density of each stage is optimized for specific wavelengths: the first-stage grating 4 has 3700 lines / mm, the second-stage grating 5 has 3300 lines / mm, and the third-stage grating 6 has 2650 lines / mm. This is achieved by controlling the grating density. ,in, The grating line density is such that each target band can achieve high diffraction efficiency under a diffraction angle of approximately 60°.

[0028] Taking the first-level grating 4 as an example, such as Figure 3 As shown, the spacing between its scribing lines The wavelength is 270.3 nm, and the incident angle is... In the first diffraction order, the wavelength range for diffraction is 234 nm to 504 nm. Blue light with a center wavelength of 468.6 nm satisfies the grating equation and achieves high-efficiency diffraction, while longer wavelengths of 529.05 nm and 656.3 nm light are not targeted for diffraction output under these grating parameters and mainly pass through the grating as zero-order transmitted light.

[0029] In this embodiment, all three levels of gratings are fabricated on a fused silica substrate using a holographic exposure machine and ion beam etching technology. During fabrication, a chromium-photoresist bilayer is used as a mask on the silicon dioxide substrate, and the target duty cycle is achieved by widening the grating ridges. The deep etching process precisely controls the etching depth and duty cycle to create a resonance effect between the light of a specific wavelength and the etching depth. This can be understood as creating a resonance effect that enhances the phase modulation of the target wavelength light. For example, the etching depth of the first-level grating is 546 nm, which highly matches the resonant mode of 468.6 nm light, thereby effectively coupling energy to the target diffraction order. The duty cycles of the first, second, and third-level gratings are all 0.35, and the etching depths are 546 nm, 625 nm, and 825 nm, respectively.

[0030] The diffracted light signals of each wavelength band are focused by their respective exit objectives. The first exit objective 7, the second exit objective 8, and the third exit objective 9 all employ the same four-element lens group structure as the collimating objective 3, with an F-number of 3 and a focal length of 390mm. Based on the linear dispersion relation... ,in, For line dispersion, For differential operators, For wavelength, This represents the line position on the detector's focal plane. The spacing between the grating lines. It is a cosine function. The diffraction angle, For diffraction orders, It is a multiplication sign. The focal length of the exit objective lens; at a focal length of 390mm and At a 60° angle, the linear dispersions in the 468.6 nm, 529.05 nm, and 656.3 nm bands are 0.35 nm / mm, 0.39 nm / mm, and 0.48 nm / mm, respectively. This ensures that the spectrometer has sufficiently high resolution to distinguish impurity lines from background lines at adjacent wavelengths.

[0031] Finally, the focused light signal is synchronously acquired by the corresponding detector. The first detector 10, the second detector 11, and the third detector 12 all employ electron multiplication charge-coupled device (EMCCD) detectors with high gain characteristics, suitable for low-light measurements. The number of pixels in the detectors is... The pixel size is 13μm × 13μm. In one embodiment, since the fiber core diameter is 400μm, it corresponds to approximately 31 pixels in the vertical direction of the detector image. To improve the signal-to-noise ratio and temporal resolution, all three detectors employ a parallel readout mode to collect signals in the vertical direction of each fiber, and a synchronous triggering mechanism is used to achieve precise timing control, ensuring that the data from the three bands are perfectly aligned in time. This design is suitable for observing plasma instabilities and microsecond to millisecond-scale transient physics processes in controlled nuclear fusion.

[0032] Example 2 This embodiment, based on the foregoing embodiments, further discloses an adjustment mechanism and coupling structure in a three-band cascaded spectrometer for optimizing beam quality and improving sampling capability. For example... Figure 1 As shown, the adjustment base slide rail 2 serves as the fundamental support component of the entire optical path system. Its width is designed to be 100mm, and it employs the aforementioned double dovetail groove structure. This structure provides extremely high mechanical stability for the fiber coupler 1 and the subsequent collimating objective lens 3, and allows operators to perform micron-level fine adjustments in the horizontal direction.

[0033] To address the need for simultaneous multi-channel acquisition in plasma diagnostics, fiber optic coupler 1 employs a double-row, densely packed vertical fiber arrangement. In this embodiment, the number of vertical single-row fibers is set between 50 and 100, depending on experimental requirements, allowing the total number of system channels to reach approximately 100 to 200. With a numerical aperture of 0.22 and a core diameter of 400 μm, this arrangement maximizes the utilization of the entrance pupil area of ​​the collimating objective lens 3, thereby achieving high-density, high-intensity signal acquisition. Simultaneously, the multi-row arrangement effectively reduces gaps between fibers, improving optical coupling efficiency.

[0034] Between the fiber coupler 1 and the first-stage grating 4, the collimating objective lens 3 is mounted on the adjustment base slide rail 2 via a rotation adjustment bracket and a height adjustment bracket. The rotation adjustment bracket provides ± The adjustment margin ensures that the output collimated light can be approximately angle of incidence The light is projected onto the central region of the first-stage grating 4. The height adjustment bracket is used to compensate for the center deviation of different fiber arrangements in the vertical direction, so that the collimating objective lens is coaxial with the center of the fiber coupler, ensuring the consistency of the optical path.

[0035] Furthermore, the design of the three-band cascaded spectrometer fully considers dispersion control and focal plane matching. The line density distribution of each grating is as follows: first-level grating 4 is 3700 lines / mm, second-level grating 5 is 3300 lines / mm, and third-level grating 6 is 2650 lines / mm. When the focal length... Set to 390mm and operating in Littrow configuration and and All At this time, the dispersion performance of the spectrometer was precisely controlled. This means that the spectral separation of different wavelengths on the focal plane of the detector meets the requirements of high-precision measurement. For example, the linear dispersion achieved in the 468.6 nm band is 0.35 nm / mm, which provides a high-resolution guarantee for measuring the Doppler broadening of ions in plasma.

[0036] Example 3 This embodiment focuses on describing the detection and data processing flow of a three-band cascaded spectrometer, particularly its high-performance acquisition mode in low-light environments. For example... Figure 1 As shown, the first detector 10, the second detector 11, and the third detector 12 all employ electron multiplication charge-coupled device (EMCCD) detectors with back-illuminated thinning technology. This detector achieves a quantum efficiency exceeding 95% in the visible light band and effectively enhances the sensitivity of photon detection through its built-in electronic gain mechanism, significantly improving its ability to capture weak light signals in plasma boundary regions.

[0037] The pixel specifications of the detector are as follows: Each pixel measures 13μm × 13μm. To meet the microsecond to millisecond time resolution requirements of the fusion device, all three detectors in this embodiment employ a parallel readout mode, i.e., a pixel-merging readout mode. Since each fiber is projected vertically onto the detector at a height of 400μm, corresponding to approximately 31 pixels, the parallel readout mode allows for the physical accumulation of the charge across these 31 pixels before readout. This approach not only significantly reduces readout noise but also improves the system's signal-to-noise ratio by more than an order of magnitude, while also significantly increasing the frame rate, thus meeting the real-time monitoring requirements for dynamic processes such as plasma instabilities.

[0038] In terms of synchronization control, the three detectors are centrally managed through an external trigger controller, and the synchronous triggering mechanism ensures that the acquisition of spectral signals in the three bands is time-synchronized. This cascaded arrangement combined with synchronous detection design completely solves the measurement lag problem caused by traditional spectrometers using grating switching or time-division scanning. This results in extremely high spatiotemporal correlation of spectral line data with center wavelengths of 468.6nm, 529.05nm, and 656.3nm, enabling the accurate acquisition of synchronous fusion results of different physical parameter information.

[0039] Furthermore, the manufacturing precision of the first-stage grating 4 to the third-stage grating 6 ensures the efficiency of photoflow. Through holographic exposure and ion beam etching processes, the scribe line spacing of the first-stage grating 4 is precisely controlled. Precisely controlled at 270.3 nm, combined with an etching depth of 546 nm, the diffraction efficiency for 468.6 nm light in the Littrow configuration approaches the theoretical limit, while maximizing the preservation of zero-order transmittance in subsequent long-wavelength bands. This cascading effect accumulates layer by layer, and in one embodiment, the theoretically calculated energy efficiency of the system can reach 53.7%.

[0040] In summary, this invention, through integrated cascaded optical path design, deep-etched large-size grating application, and synchronous acquisition by high-gain detectors, successfully solves the technical bottlenecks of existing spectrometers in multi-band synchronous measurement, weak light detection, and the balance between high throughput and high resolution, providing core hardware support for the accurate diagnosis of high-parameter plasmas.

[0041] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary technical means in the art that are not disclosed herein. The specification and embodiments are only used to illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

Claims

1. A three-band cascaded spectrometer, characterized in that, include: Fiber optic coupler (1), collimating objective lens (3), cascaded three-stage transmission diffraction gratings, and first exit objective lens (7), second exit objective lens (8), third exit objective lens (9), first detector (10), second detector (11), and third detector (12) corresponding to each stage of the transmission diffraction gratings. The cascaded three-stage transmission diffraction grating includes a first-stage grating (4), a second-stage grating (5), and a third-stage grating (6) arranged sequentially along the optical path propagation direction. The target center wavelengths corresponding to the first-stage grating (4), the second-stage grating (5), and the third-stage grating (6) increase sequentially. The target center wavelength corresponding to the first-stage grating (4) is 468.6 nm, the target center wavelength corresponding to the second-stage grating (5) is 529.05 nm, and the target center wavelength corresponding to the third-stage grating (6) is 656.3 nm. The spectral signal to be measured output by the collimating objective (3) is incident on the first-stage grating (4). The first-stage grating (4) diffracts the target short-wavelength band and outputs it to the corresponding first exit objective (7), while allowing the remaining band to pass through as zero-order transmission light and be incident on the second-stage grating (5). The second-stage grating (5) diffracts the target mid-wavelength band... The light is diffracted and output to the corresponding second exit objective (8), while the remaining long wavelength band is transmitted as zero-order transmitted light and incident on the third-order grating (6); the third-order grating (6) diffracts the target long wavelength band and outputs it to the corresponding third exit objective (9); the light signals after diffraction of each band are focused by the corresponding exit objective and then synchronously collected by the corresponding detector; the first-order grating (4), the second-order grating (5) and the third-order grating (6) have the same incident angle and the same diffraction angle, and the incident angle α and the diffraction angle β are both 60°, so that the first-order grating (4), the second-order grating (5) and the third-order grating (6) all work in the Littoral configuration; the line density of the first-order grating (4) is 3700 lines / mm, the line density of the second-order grating (5) is 3300 lines / mm, and the line density of the third-order grating (6) is 2650 lines / mm; The first-level grating (4), the second-level grating (5), and the third-level grating (6) are all etched gratings formed on a fused silica substrate, and their duty cycles are all 0.

35. The etching depth of the first-level grating (4) is 546 nm, the etching depth of the second-level grating (5) is 625 nm, and the etching depth of the third-level grating (6) is 825 nm, so that a resonance effect is formed between the light of a specific wavelength and the etched line depth, which can enhance the phase modulation of the target wavelength light.

2. The three-band cascaded spectrometer according to claim 1, characterized in that, The first-level grating (4), the second-level grating (5) and the third-level grating (6) are all the same size, and each size is 160mm×300mm.

3. The three-band cascaded spectrometer according to claim 1, characterized in that, The collimating objective (3), the first exit objective (7), the second exit objective (8) and the third exit objective (9) all adopt a four-element lens group structure with a telecentric optical path design, and their lens F number is 3 and focal length is 390mm.

4. The three-band cascaded spectrometer according to claim 1, characterized in that, The fiber coupler (1) adopts a double-row vertical fiber arrangement structure, with a fiber numerical aperture of 0.22 and a single fiber core diameter of 400μm.

5. The three-band cascaded spectrometer according to claim 4, characterized in that, The fiber coupler (1) has 50 to 100 vertical single-row optical fibers and a total number of 100 to 200 channels.

6. The three-band cascaded spectrometer according to claim 1, characterized in that, It also includes an adjustment base slide rail (2), which has a double dovetail groove structure. A rotation adjustment bracket and a height adjustment bracket with a ±5° rotation adjustment range are installed below the collimating objective lens (3). The rotation adjustment bracket and the height adjustment bracket are set on the adjustment base slide rail (2).

7. The three-band cascaded spectrometer according to claim 1, characterized in that, The first detector (10), the second detector (11) and the third detector (12) are all EMCCD detectors with parallel readout mode, with a pixel count of 1024×1024 and a pixel size of 13μm×13μm. The three detectors acquire data through a synchronous triggering mechanism.

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