Wide-spectrum multi-channel Thomson scattering diffraction grating spectrometer

Abstract

The wide-spectrum multi-channel Thomson scattering diffraction grating spectrometer comprises an incidence and shaping unit, a light splitting unit, an imaging management unit and a detection unit which are sequentially arranged along a light path, the light splitting unit comprises a diffraction grating and an angle setting and repeated positioning mechanism; the detection unit comprises a multi-element detector array arranged along the spectral dispersion direction; an image surface of the multi-element detector array is provided with a non-detection area aiming at the intrinsic wavelength of the laser, and the angle setting and repeated positioning mechanism is used for adjusting the angle of the diffraction grating so as to position an image point of the intrinsic wavelength of the laser to the non-detection area. Through cooperation of the angle setting mechanism and the image plane non-detection area, image plane-level geometric isolation of the laser intrinsic wavelength is realized, strong intrinsic light interference is avoided fundamentally, and the signal-to-noise ratio is improved. And meanwhile, the detection channel can be reconstructed only by adjusting the grating angle, so that the adaptability and the operation and maintenance efficiency of the equipment to different diagnosis requirements are remarkably enhanced.

Description

Technical Field

[0001] This application relates to the field of plasma diagnostic technology, specifically to a broadband multichannel Thomson scattering diffraction grating spectrometer. Background Technology

[0002] In Thomson scattering diagnostics of tokamak plasmas, traditional multicolor analyzers commonly employ a cascaded interferometric filter approach. This scheme utilizes a "Z-shaped" optical path design, employing a series of interferometric filters to achieve "in-band transmission and out-of-band reflection" at specific wavelengths, thereby completing multi-channel color separation. The center wavelength and bandwidth of each channel are fixedly determined by the inherent passband characteristics of the selected filters. The entire system, including optical color separation, imaging detection, and temperature control circuitry, is typically integrated into a shielded enclosure to form a compact measurement unit.

[0003] Although the technology is relatively mature, its inherent shortcomings become increasingly apparent in experimental scenarios involving high background noise, strong stray light, and long operating periods. A core issue lies in the poor reconfigurability caused by the system's rigid structure. The measurement spectral range of a multicolor meter relies entirely on physical filters. When the scattering angle, device geometry, or target electron temperature range changes, it often requires replacing the entire set of filters or making significant mechanical adjustments, making it difficult to achieve rapid and flexible reconstruction of the spectral range. This inconvenience... Figure 1 This is clearly demonstrated in the data; to adapt to the measurement needs of different temperature ranges, completely different combinations of filters must be configured.

[0004] Existing solutions also have several performance limitations. Their ability to synchronously and efficiently sample a wide spectral range within a single trigger is insufficient; increasing the number of channels significantly reduces the overall system transmittance and increases complexity. The sensitivity of optical components to incident angle and ambient temperature causes drift in optical path geometry and channel relative responsivity, making calibration frequent and complex, difficult to reset after maintenance, and resulting in poor reusability. Suppression of strong background signals near the intrinsic laser wavelength primarily relies on high-optical-density notch filters, lacking a mechanism for physical isolation at the detector image plane level. Therefore, in cases of strong stray light or optical path drift, near-laser line channels still face overload risks and systematic measurement deviations. Furthermore, the non-ideal characteristics of the filter passband edge and parasitic reflections in the optical system together lead to significant spectral overlap and crosstalk between adjacent channels, directly increasing the calculation error and uncertainty of electron temperature inversion.

[0005] The aforementioned shortcomings collectively limit the measurement accuracy, stability, and operational efficiency of traditional interferometric filter polychromators in advanced fusion diagnostics, constituting the technical problem that this application aims to solve. Summary of the Invention

[0006] This application provides a broadband multichannel Thomson scattering diffraction grating spectrometer, which solves the inherent defects of existing interferometric filter cascaded polychromators, such as rigid and fixed channels, insufficient broadband parallel acquisition capability, lengthy calibration chain, near-laser line suppression dependent on filter optical density, and significant spectral crosstalk between channels.

[0007] This application is achieved through the following technical solution:

[0008] In a first aspect, this application provides a broadband multichannel Thomson scattering diffraction grating spectrometer, characterized in that it includes an incident and shaping unit, a beam splitting unit, an imaging management unit, and a detection unit arranged sequentially along the optical path;

[0009] The beam-splitting unit includes a diffraction grating and an angle setting and repeating positioning mechanism;

[0010] The detection unit comprises a multi-element detector array arranged along the spectral dispersion direction;

[0011] The image plane of the multi-element detector array has a no-detection zone for the intrinsic wavelength of the laser. The angle setting and repositioning mechanism is used to adjust the angle of the diffraction grating to position the image point of the intrinsic wavelength of the laser in the no-detection zone.

[0012] A further optimization is that the angle setting and repeat positioning mechanism includes an angle encoder and its driving or locking components.

[0013] A further optimization is that the angle encoder is an absolute angle encoder.

[0014] A further optimized solution is that the angle setting and repeat positioning mechanism is a fixed angle assembly structure achieved by positioning pins or limit blocks.

[0015] A further optimization is that the no-detection area is formed by setting a light-shielding plate, an absorption block, or a metal blade inside the package of the multi-element detector array or in the image plane optical path.

[0016] A further optimization scheme is that the effective aperture width of each detection unit in the dispersion direction of the multi-element detector array, together with the focal length of the imaging management unit and the dispersion rate of the diffraction grating, determines the equivalent spectral bandwidth of each channel.

[0017] A further optimization scheme includes a channel isolation structure disposed between each detection unit of the multi-element detector array, wherein the channel isolation structure is a metal compartment or a blade.

[0018] A further optimization involves combining the channel isolation structure with the matte finish layer on the inner wall of the chassis to suppress optical crosstalk.

[0019] A further optimization is that the detection unit also includes a signal processing module, which includes a transimpedance amplifier circuit, a filter circuit, and an analog-to-digital converter circuit electrically connected to the multi-element detector array.

[0020] A further optimization includes a heat dissipation unit, which comprises a heat sink and a fan that are thermally connected to the multi-element detector array.

[0021] Compared with the prior art, this application has the following advantages and beneficial effects:

[0022] Through the synergistic effect of the angle setting and repositioning mechanism with the image plane without a detection area, image plane-level geometric isolation of the intrinsic wavelength of the laser is achieved, excluding strong intrinsic light from the effective photosensitive area of ​​all detection channels. This fundamentally solves the problems of near-line leakage, channel overload, and systematic bias that are still difficult to avoid with traditional solutions that rely on high optical density filters. It significantly improves the dynamic response range and measurement signal-to-noise ratio of the spectrometer in environments with strong background noise. At the same time, it ensures the reconfigurability of the channel layout. Different target spectral bands can be shifted to the effective detection range of the detector array simply by adjusting the grating angle, without replacing the core optical components. This greatly enhances the adaptability and maintenance efficiency of the equipment in response to diagnostic needs for different scattering angles and plasma temperatures. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the exemplary embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0024] Figure 1 This is an illustration illustrating how existing filter solutions require replacement of core components due to different measurement targets.

[0025] Figure 2 A schematic diagram of the overall structure of the broadband multichannel Thomson scattering diffraction grating spectrometer provided in the embodiments of this application;

[0026] Figure 3 A schematic diagram of the optical system configuration of the broadband multichannel Thomson scattering diffraction grating spectrometer provided in this application embodiment;

[0027] Figure 4 The electronic system configuration diagram of the broadband multichannel Thomson scattering diffraction grating spectrometer provided in the embodiments of this application;

[0028] Figure 5 A schematic diagram of the detector array packaging structure provided in this application embodiment;

[0029] Figure 6 The schematic diagram of the signal amplification circuit of the signal processing module provided in the embodiments of this application;

[0030] Figure 7 The multi-channel transmittance simulation effect diagram provided in the embodiments of this application is shown. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this application are only for explaining this application and are not intended to limit this application.

[0032] First, some of the technical terms used in this application will be explained to facilitate understanding.

[0033] 1. APD: Avalanche Photodiode;

[0034] 2. VPH Grating: Volume Phase Holographic Grating;

[0035] 3. ADC: Analog-to-Digital Converter;

[0036] 4. FPGA: Field-Programmable Gate Array;

[0037] 5. TTL: Transistor-Transistor Logic;

[0038] 6. PMT: Photomultiplier Tube;

[0039] 7. Si-PIN: Silicon Positive-Intrinsic-Negative, silicon PIN diode;

[0040] 8. InGaAs-APD: Indium Gallium Arsenide Avalanche Photodiode;

[0041] 9. CMOS: Complementary Metal-Oxide-Semiconductor;

[0042] 10. OD, Optical Density;

[0043] 11. NA: Numerical Aperture;

[0044] 12. HVLP: High Volume Low Pressure;

[0045] 13.TS: Thomson Scattering;

[0046] 14. LIBS: Laser-Induced Breakdown Spectroscopy;

[0047] 15. Te: Electron Temperature;

[0048] 16. CWL, Center Wavelength.

[0049] In this application, the non-detection area refers to a physical non-photosensitive area set on the image plane of the detector to isolate specific wavelengths (such as the intrinsic wavelength of laser light);

[0050] In this application, the angle setting and repeat positioning mechanism refers to a mechanical or electromechanical device that can accurately set and reliably reproduce the angle of an optical element.

[0051] In one embodiment, such as Figure 2 As shown, the broadband multichannel Thomson scattering diffraction grating spectrometer provided in this application has an incident and shaping unit 10, a beam splitting unit 20, an imaging management unit 30 and a detection unit 40 arranged sequentially along the light propagation direction.

[0052] This embodiment achieves multi-channel parallel acquisition with wide spectral coverage through the synergistic effect of the aforementioned units. Relying on the diffraction grating dispersion and angle setting repeatable positioning mechanism, the reconfigurability of the channel layout is significantly improved, enabling rapid adaptation to measurement requirements of different scattering angles and plasma temperature ranges. At the same time, the intrinsic wavelength of the laser is precisely excluded from the detection channel through the image plane-level geometric isolation mechanism, and optical crosstalk is effectively suppressed by combining the channel isolation structure and the extinction treatment layer. This ensures high dynamic response and measurement signal-to-noise ratio in a strong background noise environment, simplifies the calibration process, and enhances the stability and maintenance efficiency of the equipment during long-term operation.

[0053] In one embodiment, the incident and shaping unit 10 is used to receive and preprocess the optical signal. Specifically, the scattered light enters the system through an inlet interface, which can be a bundled fiber or a mechanical inlet slit. The optical signal is then shaped by a collimator, for example, a reflective collimator (such as Thorlabs RC12FC-P01) or a combination of a reflector (such as United Optics 260049) and a collimator (such as United Optics 145138). Its function is to shape the diverging beam into approximately parallel light and to constrain the numerical aperture and angular distribution of the incident light within the system design range.

[0054] This embodiment, through the precise design and implementation of the incident and shaping unit 10, effectively achieves stable reception and preliminary shaping of scattered light, laying a solid foundation for subsequent beam splitting and detection. The collimator transforms the diverging beam into approximately parallel light, significantly reducing the geometric uncertainty of the incident light and ensuring that the beam entering the beam splitting unit 20 has a consistent aperture angle and spatial distribution, thereby reducing dispersion errors caused by angle drift. The entrance interface adopts a flexible design of bundled optical fibers or mechanical slits, ensuring efficient coupling of optical signals and adapting to the input requirements of different experimental scenarios. This active constraint and management of the incident light field not only improves the system's adaptability to changes in scattering angle but also optimizes the optical path stability from the source, providing crucial optical front-end guarantees for the entire spectrometer to achieve high-precision wavelength resolution, reconfigurable channel layout, and long-term measurement consistency.

[0055] In one embodiment, the beam-splitting unit 20 is connected after the incident and shaping unit 10, and its core includes a diffraction grating and an angle setting and repeating positioning mechanism. Figure 3 As shown, the diffraction grating can be a volume phase holographic grating, such as a VPH grating with a line density of 600 lines / mm and a center wavelength of 900nm. The angle setting and repeat positioning mechanism is used to precisely adjust and lock the incident angle of the diffraction grating. Specifically, it can be implemented in two forms: In a preferred form, the mechanism includes a high-precision angle encoder and its drive or locking components, wherein the angle encoder is preferably an absolute angle encoder (such as the Renishaw RESOLUTE series with a RESA30 reading head) to achieve precise angle setting and repeatable positioning; In another alternative form, the mechanism can be a fixed angle assembly structure achieved by positioning pins or limit blocks, which ensures one-time angle setting and long-term stability through precision machining.

[0056] This embodiment achieves precise control and flexible reconstruction of the spectral distribution through the precise design of the spectroscopic unit 20 and a dual-mode angle control mechanism. The high line density design of the diffraction grating ensures excellent dispersive resolution, while the angle setting and repeatability mechanism achieves micron-level precision adjustment and long-term stable reproduction of the incident angle α through closed-loop feedback of the absolute angle encoder or mechanical latching of the fixed-angle assembly. This design enables the system to quickly and accurately locate the image point of the intrinsic wavelength λ0 of the laser to the undetectable region according to experimental requirements, while simultaneously shifting the target measurement spectral band to the effective detection range of the detector array, fundamentally solving the channel rigidity problem of traditional filter solutions. The synergistic effect of the angle encoder and the locking component 22 not only improves the repeatability of angle setting but also significantly reduces spectral band shift caused by mechanical drift or temperature fluctuations, ensuring the consistency of measurement results across experimental cycles. In addition, the fixed-angle assembly structure provides a maintenance-free solution for long-term stable operation scenarios. Both forms together expand the applicability of the equipment, providing a core spectroscopic technology support with flexibility, stability, and reconfigurability for high-requirement diagnostic environments such as tokamak.

[0057] In one embodiment, the imaging management unit 30 is located after the beam-splitting unit 20, and typically uses a convex lens as the focusing lens, such as a lens of model number United Optics 145134. Its function is to reduce the wavelength-dependent angular dispersion generated by the beam-splitting unit 20. Converted to linear positional dispersion on the image plane, wavelength is established. A one-to-one correspondence between the image plane and its spatial coordinates. Its imaging principle is based on the grating equation. ,in For diffraction orders, The grating constant is Angle of incidence Let be the diffraction angle. The linear dispersion rate can be expressed as... , where f is the focal length of the imaging management unit 30. The equivalent spectral bandwidth of each detection channel. The effective aperture width Δx of the channel in the dispersion direction is determined by both the linear dispersion rate and the dispersion value. This constitutes the image plane selection mechanism of linear dispersion and multi-channel narrow window. Multiple channels are distributed along the dispersion direction, forming a "narrow window sampling". The effective opening can be the effective photosensitive surface of an APD, a microslit, a fiber optic aperture plate, or an image spot of a microlens array, etc.

[0058] This embodiment, through the precise optical design and linear dispersion mapping mechanism of the imaging management unit 30, successfully achieves accurate wavelength positioning from angular space to image plane space, laying a core foundation for multi-channel parallel detection. The focusing lens efficiently converts the angular dispersion generated by the diffraction grating into linear positional dispersion on the image plane, establishing a stable and predictable correspondence between wavelength λ and spatial coordinate x. This linear mapping characteristic enables the system to quickly calculate the equivalent spectral bandwidth of each channel through simple geometric relationships. .based on The image plane selection mechanism adjusts the effective aperture width of the detection unit. Alternatively, by utilizing the coordinated design of focal length f and grating parameters d, the spectral resolution and bandwidth of each channel can be flexibly configured, enabling various measurement needs from narrowband fine analysis to broadband rapid scanning. The multi-channel "narrow window sampling" layout along the dispersion direction not only significantly improves signal collection efficiency over a wide spectral range but also ensures spectral independence between channels, effectively reducing overlap and crosstalk between adjacent bands. This innovative design, which transforms complex spectral information into a spatial distribution and processes it in parallel, greatly enhances the system's real-time performance and measurement accuracy in applications such as tokamak plasma diagnostics, providing a highly reliable raw data foundation for electron temperature inversion.

[0059] In one embodiment, the detection unit 40 is positioned at the image plane of the imaging management unit 30, and its core is a multi-element detector array arranged along the spectral dispersion direction, such as a Hamamatsu C30659 APD (avalanche photodiode) array. Figure 5 As shown, this application, on the image plane of the multi-element detector array, targets the intrinsic wavelength of the laser. A detection-free zone is specifically set at the expected image point location. This detection-free zone can be formed by setting physical structures such as light-shielding plates, absorption blocks, or metal blades inside the detector package or in the image plane optical path. The angle of the diffraction grating is precisely adjusted through the aforementioned angle setting and repeating positioning mechanism. This can ensure The image point accurately falls within this undetected area, thus achieving image-plane-level geometric isolation for all detection channels, fundamentally avoiding signal overload and measurement deviation caused by strong intrinsic light. The effective aperture width of each detection unit in the dispersion direction of the multi-element detector array, together with the focal length f of the imaging management unit 30 and the dispersion rate of the diffraction grating, determines the equivalent spectral bandwidth of each channel. Its typical value ranges from 1 nanometer to 3 nanometers.

[0060] The detection unit 40 provided in this embodiment achieves efficient and parallel acquisition of dispersive spectra through the precise arrangement and collaborative operation of a multi-element detector array, significantly improving the system's measurement efficiency and signal quality. The linear arrangement of the array along the dispersion direction enables it to simultaneously capture scattering signals from multiple bands, overcoming the time delay problem of traditional single-point scanning or filter rotation schemes, and ensuring the timeliness of acquiring complete spectral data in a single trigger. The effective aperture width of each APD detection unit in the dispersion direction, together with the focal length of the imaging management unit 30 and the dispersion rate of the diffraction grating, determines the equivalent spectral bandwidth of the channel. This design allows for flexible adjustment of the channel bandwidth through geometric parameters, enhancing the system's adaptability to different resolution requirements. The high sensitivity and fast response characteristics of the detector array, combined with the transimpedance amplification, filtering, and digitization circuitry of the subsequent signal processing module, effectively ensure the accurate extraction and low-noise transmission of weak scattering signals. Furthermore, to address the strong background environment, the detection unit 40 features a dedicated no-detection zone on the image plane for the intrinsic laser wavelength. It also employs a channel isolation structure and a chassis extinction layer to synergistically suppress optical crosstalk, fundamentally preventing channel overload and measurement deviations caused by near-laser line leakage. This design, integrating parallel detection, flexible bandwidth configuration, strong background suppression, and low-noise signal processing, makes the detection unit 40 a key functional module for achieving wide-spectrum, high dynamic range, and high signal-to-noise ratio Thomson scattering diagnostics.

[0061] In one embodiment, this application specifies the laser intrinsic wavelength on the image plane of the multi-element detector array. A detection-free zone is specifically set at the expected image point location. This detection-free zone can be formed by setting physical structures such as light-shielding plates, absorption blocks, or metal blades inside the detector package or in the image plane optical path. The angle of the diffraction grating is precisely adjusted through the aforementioned angle setting and repeating positioning mechanism. This can ensure The image point accurately falls within this undetected area, thereby achieving image-plane-level geometric isolation for all detection channels, fundamentally avoiding signal overload and measurement deviation caused by strong intrinsic light. The effective aperture width of each detection unit in the dispersion direction of the multi-element detector array, together with the focal length f of the imaging management unit 30 and the dispersion rate of the diffraction grating, determines the equivalent spectral bandwidth Δλ of each channel, with a typical value ranging from 1 nanometer to 3 nanometers.

[0062] This embodiment achieves precise physical isolation of the intrinsic wavelength λ0 of the laser through the synergistic effect of the detectorless region and the angle setting mechanism. When the angle of the diffraction grating... After precise setting by an absolute angle encoder or fixed angle assembly structure, the image point of λ0 is stably constrained within the non-detector zone, ensuring that the strong intrinsic light completely avoids the photosensitive areas of all effective detection channels. This image-plane-level geometric isolation mechanism fundamentally solves the near-line leakage problem that traditional solutions, which rely on high optical density filters, still struggle to avoid, significantly improving the system's dynamic response range and measurement signal-to-noise ratio in environments with strong background noise.

[0063] To further enhance performance, in one embodiment, a channel isolation structure is also included between the detector units of the multi-element detector array. This channel isolation structure can be a metal compartment or a blade. Combined with the matting layer on the inner wall of the spectrometer chassis (e.g., using NEXTEL 8-21 dedicated blackening material, applied via HVLP process to form a coating approximately 45 to 55 micrometers thick), this effectively suppresses optical crosstalk caused by oblique scattering and reflected light. This design constitutes a scheme for reducing crosstalk and parasitic paths through an image plane channel isolation structure. The isolation structure is not limited to compartments or blades, but can also be a labyrinth, honeycomb, sawtooth, or cone-hole array; the matting treatment is not limited to a coating, but can also be anodizing, texturing, etc.

[0064] This embodiment achieves multi-level suppression of optical crosstalk and parasitic scattering through the synergistic design of channel isolation structures and the extinction treatment layer on the inner wall of the chassis. Physical isolation structures such as metal compartments or knife edges form independent optical channels at the detector image plane, effectively blocking obliquely scattered light paths between adjacent detection units; while the dedicated black coating on the inner wall of the chassis efficiently absorbs diffuse reflection and reflected light. This dual mechanism of "physical barrier + material absorption" significantly reduces spectral crosstalk between channels, improving the spectral purity and independence of each detection channel. Especially for weak signal measurement scenarios, this design effectively suppresses parasitic light paths generated by strong intrinsic light or high-brightness channels, ensuring baseline stability and measurement accuracy for small signal detection. The diverse implementation methods of the channel isolation structure provide flexible choices for different spatial layout requirements, while the substitutability of the extinction treatment process enhances the adaptability of this technical solution in different application environments. This systematic crosstalk suppression design not only improves the calculation accuracy of electron temperature inversion but also provides important assurance for measurement stability during long-term operation.

[0065] In one embodiment, the detection unit 40 further includes a signal processing module, such as... Figure 4 As shown, this module is electrically connected to a multi-element detector array and typically includes a transimpedance amplifier circuit built with operational amplifiers (such as OPA657, AD8065), a low-pass filter for filtering out high-frequency noise (such as SCLF-95+), and an analog-to-digital converter circuit (ADC model such as HMCAD15TR), which ultimately outputs a standard TTL level signal.

[0066] like Figure 6 As shown, the signal processing module provided in this embodiment achieves precise conditioning and high-quality digital conversion of the detector array output signal through the coordinated operation of multiple circuit stages. The transimpedance amplifier circuit, constructed from high-speed operational amplifiers such as OPA657 and AD8065, efficiently converts the weak current signal generated by the APD array into a processable voltage signal, and its low-noise design ensures the complete extraction of weak scattering signals. The SCLF-95+ low-pass filter effectively suppresses high-frequency noise and sampling aliasing, optimizes the signal-to-noise ratio through bandwidth limiting, and ensures the fidelity of time-resolved waveforms. The HMCAD1511TR analog-to-digital converter circuit finally converts the analog voltage signal into a high-precision digital quantity, which, together with the FPGA, completes the parallel acquisition, integration, and event marking of multi-channel data, and outputs a standard TTL level signal to achieve seamless integration with external acquisition systems.

[0067] In one embodiment, to ensure the stability of the detector during long-term operation, the system also includes a heat dissipation unit 50. This unit 50 is thermally connected to the multi-element detector array through a heat dissipation plate and works with a fan to provide forced air cooling in order to maintain a constant operating temperature of the detector.

[0068] The heat dissipation unit 50 provided in this embodiment significantly improves the reliability and measurement consistency of the detector system during long-term operation through an active temperature control mechanism. The tight thermal connection between the heat sink and the APD array ensures efficient heat conduction from the heat source to the heat dissipation interface, while the forced convection provided by the LFS0424SS fan continuously dissipates the accumulated heat to the external environment, forming a complete thermal management closed loop. This active heat dissipation design controls the operating temperature fluctuation of the multi-element detector array within an extremely narrow range, effectively suppressing the gain change (ΔM / ΔT) and dark current drift of the avalanche photodiode caused by temperature drift.

[0069] The improved temperature stability directly translates into long-term repeatability of the signal response—the relative responsivity of the detector remains stable across channels, reducing calibration parameter drift caused by temperature fluctuations and eliminating the need for frequent responsivity corrections during continuous operation. Particularly in experimental scenarios requiring long-term continuous data acquisition, such as tokamaks, this heat dissipation design ensures the baseline stability of spectral measurement data throughout the entire process from plasma initiation to continuous discharge. Combined with the aforementioned detectorless and channel-isolated structure, the heat dissipation unit 50 further optimizes the system's performance under high background and high-load conditions, enabling the detector to maintain a high signal-to-noise ratio while avoiding performance degradation due to temperature rise.

[0070] This proactive thermal management of the detector's operating environment not only extends the lifespan of core components but also provides temperature-independent stable measurement conditions for the entire spectrometer system from a physical perspective, enabling it to meet the stringent requirements of fusion diagnostic devices for the long-term operational stability of measurement equipment.

[0071] It should be noted that the technical approach of this application is not limited to tokamak Thomson scattering (TS) diagnostics. Its core inventive points are also applicable to other spectral measurement scenarios requiring near-line suppression and multi-channel sampling, such as observations near narrow lines in Raman / Rayleigh scattering spectroscopy, near-line background suppression in laser-induced breakdown spectroscopy (LIBS), and multi-channel rapid sampling near background spectral lines in various laser diagnostics. Figure 7 As shown in the figure, the multi-channel spectral response simulation effect provided in the embodiment of this application verifies its effective sampling capability over a wide spectral range.

[0072] Regarding the operating wavelength, the scheme described in this application can be adapted to the intrinsic wavelengths of 532nm, 1064nm or other solid-state lasers, and can flexibly cope with spectral changes caused by different scattering angle geometries.

[0073] In terms of detector type, the detection module is not limited to APD array, but can also be replaced by photomultiplier tube (PMT), silicon PIN diode (Si-PIN), indium gallium arsenide APD (InGaAs-APD) or linear CMOS sensor, as long as it follows the core idea of ​​wavelength selection and narrow window sampling on the image plane.

[0074] The working principle of this application is achieved through the collaborative design of optics, mechanics, and electronics, specifically covering three core parts: optical imaging and beam splitting, near-laser line processing and crosstalk control, and photoelectric conversion and signal chain.

[0075] In terms of optical imaging and beam splitting principles, the scattered light first enters the system through the entrance interface (bundled fiber or mechanical slit) of the incident and shaping unit 10, and is shaped into an approximately parallel beam by a collimator (e.g., a reflective collimator or a combination of a reflector and a collimator). This collimation and entrance pupil control step constrains the numerical aperture and angular distribution of the incident light within the design range, providing stable geometric conditions for subsequent beam splitting. The shaped beam then enters the beam splitting unit 20 at an incident angle... When light is incident on a diffraction grating (such as a 600 lines / mm VPH grating), according to the grating equation... Different wavelengths are spatially dispersed due to different diffraction angles β(λ). Precise adjustment is achieved through angle setting and repeatable positioning mechanisms (such as absolute angle encoders or fixed angle assembly structures). This achieves a dual purpose: firstly, to reduce the intrinsic wavelength of the laser. The first step is to precisely locate the image point to the undetected area on the image plane of the multi-element detector array in the detection unit 40; the second step is to shift the entire target measurement spectrum to the effective detection range of the array. The focusing lens of the imaging management unit 30 then converts the angular dispersion into linear positional dispersion on the image plane, and its linear dispersion rate is expressed as... Where f is the focal length. The equivalent spectral bandwidth Δλ of each detection channel is determined by the effective aperture width of that channel in the dispersion direction. Determined together with the linear dispersion rate, i.e. This forms a multi-channel narrow-window sampling mechanism;

[0076] In terms of near-laser line processing and crosstalk control, this application suppresses interference through the coordinated use of image-level geometric isolation and channel isolation structures. The detectorless area utilizes physical structures such as light-shielding plates, absorbers, or metal blades to achieve [interference / control]. Absolute isolation ensures that strong intrinsic light does not enter any detection channel, fundamentally avoiding overload and systematic bias. To further improve spectral purity, the detection unit 40 also sets channel isolation structures (such as metal compartments or knife edges) between the channels of the multi-element detector array. This structure, combined with the extinction treatment layer (such as NEXTEL 8-21 black coating) on ​​the inner wall of the spectrometer chassis, effectively suppresses optical crosstalk caused by parasitic paths such as oblique scattering and reflected light, ensuring the baseline stability of small signal measurements.

[0077] In terms of photoelectric conversion and signal chain processing, the multi-element detector array converts the incident photon streams from each channel into current pulses. Since the gain of the avalanche photodiode (APD) is temperature-sensitive, the heat dissipation unit 50 uses a heat sink and fan to force-cool the array, maintaining a constant operating temperature and reducing gain drift. The signal processing module then performs chain processing on the electrical signals: first, a transimpedance amplifier circuit (such as OPA657, AD8065, etc.) converts the picoampere to nanoampere current into a voltage signal; then, a low-pass filter (such as SCLF-95+) filters out high-frequency noise; finally, an analog-to-digital converter circuit (such as HMCAD15TR) performs digital sampling. The FPGA further integrates, marks events, and shapes the multiple signals, ultimately outputting TTL-level synchronous data, completing the entire process from optical signal to standardized digital output.

[0078] The above three working principles are organically combined to form a technical solution based on diffraction grating dispersion, with angle reconfigurability and image plane isolation as the core, and multi-channel parallel acquisition as the feature, which significantly improves the spectrometer's performance in terms of wide spectral coverage, near-line suppression, and long-term stability.

[0079] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above description is only a specific embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A broadband multi-channel Thomson scattering diffraction grating spectrometer, characterized in that, It includes an incident and shaping unit, a beam splitting unit, an imaging management unit, and a detection unit arranged sequentially along the optical path; The beam-splitting unit includes a diffraction grating and an angle setting and repeating positioning mechanism; The detection unit comprises a multi-element detector array arranged along the spectral dispersion direction; The image plane of the multi-element detector array has a no-detection zone for the intrinsic wavelength of the laser. The angle setting and repositioning mechanism is used to adjust the angle of the diffraction grating to position the image point of the intrinsic wavelength of the laser in the no-detection zone.

2. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, The angle setting and repeat positioning mechanism includes an angle encoder and its driving or locking components.

3. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 2, characterized in that, The angle encoder is an absolute angle encoder.

4. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, The angle setting and repeat positioning mechanism is a fixed angle assembly structure achieved by positioning pins or limit blocks.

5. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, The non-detection area is formed by setting a light-shielding plate, an absorption block, or a metal blade inside the package of the multi-element detector array or in the image plane optical path.

6. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, The effective aperture width of each detection unit in the dispersion direction of the multi-element detector array, together with the focal length of the imaging management unit and the dispersion rate of the diffraction grating, determines the equivalent spectral bandwidth of each channel.

7. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, It also includes a channel isolation structure disposed between each detection unit of the multi-element detector array, wherein the channel isolation structure is a metal compartment or a blade.

8. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 7, characterized in that, The channel isolation structure, combined with the matte finish layer on the inner wall of the chassis, is used to suppress optical crosstalk.

9. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, The detection unit also includes a signal processing module, which includes a transimpedance amplifier circuit, a filter circuit, and an analog-to-digital converter circuit electrically connected to the multi-element detector array.

10. The broadband multi-channel Thomson scattering diffraction grating spectrometer according to claim 1, characterized in that, It also includes a heat dissipation unit, which comprises a heat sink and a fan that are thermally connected to the multi-element detector array.

Images