High-flux laser Thomson scattering multi-grating spectrometer

Abstract

The invention discloses a high-flux laser Thomson scattering multi-grating spectrometer which comprises an entrance slit, a first off-axis parabolic mirror, a first diffraction grating, a second off-axis parabolic mirror, an optical baffle, a third off-axis parabolic mirror, a second diffraction grating, a fourth off-axis parabolic mirror and a middle slit. A fifth off-axis parabolic mirror, a third diffraction grating, a sixth off-axis parabolic mirror and a detector; the off-axis parabolic mirror adopts a short-focus large-aperture design, and is used for collecting laser Thomson scattering photons in a high-flux manner, collimating and focusing laser Thomson scattering light beams without chromatic aberration and spherical aberration and deflecting a folded light path, and the structure realizes collimation and focusing of the Thomson scattering light beams without chromatic aberration and spherical aberration. The imaging quality of the multi-grating spectrometer is improved, spectrum distortion caused by aberration is avoided, the spectral resolution is improved, meanwhile, the luminous flux of the spectrometer is enhanced, and miniaturization and portable development of the spectrometer is achieved.

Description

Technical Field

[0001] The present invention relates to the field of low-temperature plasma laser spectrum diagnosis, and in particular to a high-flux laser Thomson scattering multi-grating spectrometer, which is used to filter out stray light of a central wavelength and strong signals such as Rayleigh scattering, improve the imaging quality of the Thomson scattering spectrum, and simultaneously improve the laser Thomson scattering light flux, thereby enhancing the accuracy of diagnosing the electron density and electron temperature of low-temperature plasma. Background Art

[0002] Free electrons are important energy transfer particles in low-temperature plasmas. They can change the number density and energy distribution of other particles by colliding with other particles (such as molecules, atoms, particles, etc.) (such as dissociation, excitation, ionization, recombination, deexcitation, etc.). The two parameters related to free electrons, electron density and electron temperature, are often functions of other parameters. Therefore, accurate diagnostic research on electron density and electron temperature can lay the foundation for understanding the complex physical mechanisms inside the entire plasma. Among many plasma diagnostic methods, laser Thomson scattering has the advantages of non-invasive measurement, high temporal and spatial resolution, and independence from whether the plasma is in a local thermodynamic equilibrium state. It is recognized as one of the most accurate methods for diagnosing electron density and electron temperature. However, due to the low differential scattering cross section, the laser Thomson scattering signal is relatively weak. In the diagnostic application of low-temperature plasma, the intensity of strong signals such as stray light formed by wall reflection and Rayleigh scattering formed by heavy particle scattering can easily annihilate the weak Thomson scattering signal. Therefore, effective shielding of strong signals such as stray light and Rayleigh scattering is a key factor in obtaining Thomson scattering signals. Multi-grating spectrometers can effectively suppress strong signals such as stray light and Rayleigh scattering through physical shielding, with a suppression ratio of up to 10 -10, has been widely used in laser Thomson scattering diagnostic systems. However, in the currently commonly used multi-grating spectrometers, optical lenses are often used as beam collimation and focusing elements. The lens will inevitably introduce aberrations such as spherical aberration and chromatic aberration, which will affect the imaging quality of the multi-grating spectrometer, causing spectrum distortion and reduced spectral resolution. In addition, for weak laser Thomson scattering signals, the multi-grating spectrometer needs to have a higher light-collecting ability to improve the collection of laser Thomson scattering light flux and enhance signal strength. The large-aperture lens means that its focal length is short, the radius of curvature of the lens surface is small, and the thickness of the lens is thick, which leads to serious off-axis aberrations during off-axis imaging. If these off-axis aberrations are corrected, more optical elements need to be introduced, and these optical elements will inevitably cause the loss of scattered photons and reduce the already weak laser Thomson scattering signal. Therefore, the optical lens also limits the light-collecting ability of the multi-grating spectrometer, resulting in its inability to achieve high-throughput collection of laser Thomson scattering photons. In addition, the focus of the optical lens cannot be separated from the optical path, resulting in a longer optical path, which limits the development of miniaturization and portability of multi-grating spectrometers. Summary of the invention

[0003] In view of the above-mentioned technical problems existing in a lens-based multi-grating spectrometer, the present invention proposes a high-throughput laser Thomson scattering multi-grating spectrometer based on an off-axis parabolic reflector. The off-axis parabolic reflector has the characteristic of not generating chromatic aberration and spherical aberration when collimating divergent light or focusing collimated light, thereby reducing the spherical aberration and chromatic aberration caused by the lens and improving the imaging quality and spectral resolution. The off-axis parabolic reflector has the characteristic of having a large numerical aperture, thereby enhancing the light-gathering ability of the multi-grating spectrometer and realizing high-throughput collection of laser Thomson scattering signals. The off-axis design of the off-axis parabolic reflector is utilized to separate the focus from the optical path, thereby increasing the structural flexibility of the multi-grating spectrometer and realizing miniaturized and portable development. The specific technical scheme is: a high-throughput laser Thomson scattering multi-grating spectrometer includes: an incident slit, a first off-axis parabolic reflector, a first diffraction grating, a second off-axis parabolic reflector, an optical baffle, a third off-axis parabolic reflector, a second diffraction grating, a fourth off-axis parabolic reflector, an intermediate slit, a fifth off-axis parabolic reflector, a third diffraction grating, a sixth off-axis parabolic reflector and a detector;

[0004] The incident slit is located at the focus of the first off-axis parabolic reflector, and the laser Thomson scattered light enters the multi-grating spectrometer from the incident slit. The first off-axis parabolic reflector is used to collimate the laser Thomson scattered light emitted by the incident slit. The first diffraction grating is used to disperse the laser Thomson scattered light collimated by the first off-axis parabolic reflector, so that scattered light of different wavelengths is located at different spatial positions; the second off-axis parabolic reflector is used to focus the parallel light dispersed by the first diffraction grating, and the scattered light of different wavelengths is focused on the focus of the second off-axis parabolic reflector. The optical baffle is located at the focus of the second off-axis parabolic reflector and is used to filter out the strong signal of the central wavelength; the focus of the third off-axis parabolic reflector coincides with the focus of the second off-axis parabolic reflector and is used to re-collimate the scattered light not blocked by the optical baffle into parallel light. The second diffraction grating is used to reversely disperse the scattered light collimated by the third off-axis parabolic reflector and to compound the scattered light of different wavelengths; the fourth off-axis parabolic reflector is used to filter out the strong signal of the central wavelength; the focus of the third off-axis parabolic reflector coincides with the focus of the second off-axis parabolic reflector and is used to re-collimate the scattered light not blocked by the optical baffle into parallel light. The second diffraction grating is used to reversely disperse the scattered light collimated by the third off-axis parabolic reflector and to compound the scattered light of different wavelengths; The off-axis parabolic reflector is used to focus the parallel scattered light after the reverse dispersion of the second diffraction grating at a focus. The middle slit is located at the focus of the fourth off-axis parabolic reflector and is used to receive the Thomson scattering signal after the notch filtering, that is, the scattered light focused by the fourth off-axis parabolic reflector enters the next stage through the middle slit. The width of the middle slit determines the spectral resolution of the multi-grating spectrometer. The focus of the fifth off-axis parabolic reflector coincides with the focus of the fourth off-axis parabolic reflector and is used to collimate the laser Thomson scattered light emitted by the middle slit. The third diffraction grating is used to disperse the laser Thomson scattered light collimated by the fifth off-axis parabolic reflector so that scattered light of different wavelengths is located at different spatial positions. The sixth off-axis parabolic reflector is used to focus the parallel scattered light after dispersion by the third diffraction grating and focus the parallel scattered light at a focus without generating aberration. The detector is located at the focus of the sixth off-axis parabolic reflector and is used to detect and record the laser Thomson scattering signal.

[0005] The first off-axis parabolic reflector, the second off-axis parabolic reflector, the third off-axis parabolic reflector, the fourth off-axis parabolic reflector, the fifth off-axis parabolic reflector and the sixth off-axis parabolic reflector are designed with a short focus and a large aperture, which increases the light flux of the multi-grating spectrometer without introducing chromatic aberration and spherical aberration.

[0006] The first off-axis parabolic reflector, the second off-axis parabolic reflector, the third off-axis parabolic reflector, the fourth off-axis parabolic reflector, the fifth off-axis parabolic reflector and the sixth off-axis parabolic reflector can separate the focus from the optical path according to the off-axis angle, deflect and fold the light beam, and make the multi-grating spectrometer more compact and portable.

[0007] Due to the adoption of the above technical solution, the present invention provides a high-throughput laser Thomson scattering multi-grating spectrometer based on an off-axis parabolic reflector. The structure adopts a short-focus large-aperture off-axis parabolic reflector as the beam collimation and focusing element of the multi-grating spectrometer, which does not produce chromatic aberration and spherical aberration when collimating divergent light or focusing collimated light. At the same time, the short-focus large-aperture off-axis parabolic reflector can achieve high-throughput collection of laser Thomson scattered photons. In addition, the off-axis design of the off-axis parabolic reflector can separate the focus from the optical path, so that the light beam can be deflected and folded, making the multi-grating spectrometer more compact in structure, and realizing a miniaturized portable multi-grating spectrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0009] Figure 1 It is a schematic diagram of the structure of the high-throughput laser Thomson scattering multi-grating spectrometer of the present invention. DETAILED DESCRIPTION

[0010] In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0011] like Figure 1 A high-throughput laser Thomson scattering multi-grating spectrometer based on an off-axis parabolic reflector is shown, which specifically includes an incident slit 1, a first off-axis parabolic reflector 2, a first diffraction grating 3, a second off-axis parabolic reflector 4, an optical baffle 5, a third off-axis parabolic reflector 6, a second diffraction grating 7, a fourth off-axis parabolic reflector 8, an intermediate slit 9, a fifth off-axis parabolic reflector 10, a third diffraction grating 11, a sixth off-axis parabolic reflector 12 and a detector 13.

[0012] The incident slit 1 is located at the focus of the first off-axis parabolic reflector 2, and the laser Thomson scattered light enters the multi-grating spectrometer from the incident slit 1. The first off-axis parabolic reflector 2 is used to collimate the laser Thomson scattered light emitted by the incident slit 1. The first diffraction grating 3 is used to disperse the laser Thomson scattered light collimated by the first off-axis parabolic reflector 2, so that scattered light of different wavelengths is located at different spatial positions; the second off-axis parabolic reflector 4 is used to focus the parallel light dispersed by the first diffraction grating 3, and the scattered light of different wavelengths is focused on the focus of the second off-axis parabolic reflector 4. The optical baffle 5 is located at the focus of the second off-axis parabolic reflector 4 and is used to filter out the strong signal of the central wavelength; the focus of the third off-axis parabolic reflector 6 coincides with the focus of the second off-axis parabolic reflector 4, and is used to re-collimate the scattered light not blocked by the optical baffle into parallel light, and the second diffraction grating 7 is used to inversely disperse the scattered light after collimation by the third off-axis parabolic reflector 6. The fourth off-axis parabolic reflector 8 is used to focus the parallel scattered light after the reverse dispersion of the second diffraction grating 7 at the focus. The middle slit 9 is located at the focus of the fourth off-axis parabolic reflector 8. The scattered light focused by the fourth off-axis parabolic reflector 8 enters the next stage of the light beam through the middle slit 9. The focus of the fifth off-axis parabolic reflector 10 coincides with the focus of the fourth off-axis parabolic reflector 8 and is used to collimate the laser Thomson scattered light emitted by the middle slit. The third diffraction grating 11 is used to disperse the laser Thomson scattered light collimated by the fifth off-axis parabolic reflector 10, so that the scattered light of different wavelengths is located at different spatial positions. The sixth off-axis parabolic reflector 12 is used to focus the parallel scattered light after dispersion by the third diffraction grating 11, and focus the parallel scattered light at the focus without generating aberration. The detector 13 is located at the focus of the sixth off-axis parabolic reflector 12 and is used to detect and record the laser Thomson scattered signal.

[0013] Furthermore, an off-axis parabolic reflector is used as a collimating and focusing element for the laser Thomson scattered light beam in the multi-grating spectrometer, which has the advantages of excellent imaging quality and high spectral resolution, and enhances the reliability of measurement data.

[0014] Furthermore, the first off-axis parabolic reflector 2, the second off-axis parabolic reflector 4, the third off-axis parabolic reflector 6, the fourth off-axis parabolic reflector 8, the fifth off-axis parabolic reflector 10 and the sixth off-axis parabolic reflector 12 adopt a short-focus large-aperture design, which increases the light flux of the multi-grating spectrometer without introducing chromatic aberration and spherical aberration.

[0015] The first off-axis parabolic reflector 2, the second off-axis parabolic reflector 4, the third off-axis parabolic reflector 6, the fourth off-axis parabolic reflector 8, the fifth off-axis parabolic reflector 10 and the sixth off-axis parabolic reflector 12 separate the focus from the optical path according to the off-axis angle, deflect and fold the light beam, and make the multi-grating spectrometer compact and portable.

[0016] Furthermore, the optical baffle 5 adopts a modular design, which can be quickly disassembled and assembled to change the baffles of different widths to meet different measurement requirements.

[0017] Example:

[0018] like Figure 1As shown, the incident slit 1 is located at the focal position of the first off-axis parabolic reflector 2 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°), and the Thomson scattered light signal to be measured enters the spectrometer through the incident slit 1 at a certain divergence angle, irradiates the first off-axis parabolic reflector 2, and is collimated into a parallel light beam; after the parallel light beam is turned 90° by the first off-axis parabolic reflector 2, it is projected onto the first diffraction grating 3 (the number of lines is 1800l / mm, the size is 110mm×110mm) at a certain incident angle. The first diffraction grating 3 performs dispersion and spectroscopy on the scattered light; the dispersed scattered light beam leaves the first diffraction grating 3 at a certain diffraction angle, is focused by the second off-axis parabolic reflector 4 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°) and deflected 90° to its focus, and scattered light of different wavelengths is distributed in different spatial positions, among which strong signals such as stray light and Rayleigh scattering of the central wavelength are distributed in the central position; the optical baffle 5 is located at the center of the focus of the second off-axis parabolic reflector 4, and shields the strong signal of the central wavelength (including stray light and Rayleigh scattering); the third off-axis parabolic reflector 6 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°) collimates the unshielded light to form a parallel light beam; the parallel light beam is deflected 90° by the third off-axis parabolic reflector and projected onto the second diffraction light beam. The second diffraction grating 7 recombines the light beam by reverse dispersion; the recombined light beam is focused and deflected by 90° by a fourth off-axis parabolic reflector 8 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°); the middle slit 9 is located at the focal position of the fourth off-axis parabolic reflector 8, and the slit width is continuously adjustable; after passing through the middle slit 9, the light beam is collimated into a parallel light beam by a fifth off-axis parabolic reflector 10 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°) and then deflected by 90° and projected onto the third diffraction grating 11 for dispersion; the dispersed light beam is focused and deflected by a sixth off-axis parabolic reflector 12 (focal length of 100 mm, diameter of 100 mm, F number of about F / 1, off-axis angle of 90°) to a detector 13; the detector 13 detects and records the Thomson scattering signal.

[0019] The present invention is not limited to the high-throughput laser Thomson scattering multi-grating spectrometer described in the above embodiments, wherein changes in parameters of optical elements (including incident slits, intermediate slits, off-axis parabolic reflectors, optical baffles, etc.) (including but not limited to diameter, focal length, F number, off-axis angle, grating constant, incident angle, slit width, etc.) are all within the protection scope of the present invention.

[0020] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high-throughput laser Thomson scattering multi-grating spectrometer, characterized in that include: An incident slit (1), a first off-axis parabolic reflector (2), a first diffraction grating (3), a second off-axis parabolic reflector (4), an optical baffle (5), a third off-axis parabolic reflector (6), a second diffraction grating (7), a fourth off-axis parabolic reflector (8), an intermediate slit (9), a fifth off-axis parabolic reflector (10), a third diffraction grating (11), a sixth off-axis parabolic reflector (12) and a detector (13); The incident slit (1) is located at the focus of the first off-axis parabolic reflector (2), and the laser Thomson scattered light enters the multi-grating spectrometer from the incident slit (1). The first off-axis parabolic reflector (2) is used to collimate the laser Thomson scattered light emitted by the incident slit (1). The first diffraction grating (3) is used to disperse the laser Thomson scattered light collimated by the first off-axis parabolic reflector (2), so that scattered light of different wavelengths is located at different spatial positions. The second off-axis parabolic reflector (4) is used to focus The scattered light of different wavelengths is focused on the focal point of the second off-axis parabolic reflector (4) by using the parallel light dispersed by the first diffraction grating (3); the optical baffle (5) is located at the focal point of the second off-axis parabolic reflector (4) and is used to filter out the strong signal of the central wavelength; the focal point of the third off-axis parabolic reflector (6) coincides with the focal point of the second off-axis parabolic reflector (4) and is used to re-collimate the scattered light not blocked by the optical baffle into parallel light; the second diffraction grating (7) is used to reversely disperse the third off-axis parabolic reflector (6) and to filter out the strong signal of the central wavelength; the focal point of the third off-axis parabolic reflector (6) coincides with the focal point of the second off-axis parabolic reflector (4) and is used to re-collimate the scattered light not blocked by the optical baffle into parallel light; the second diffraction grating (7) is used to reversely disperse the third off-axis parabolic reflector (6) and to filter out the strong signal of the central wavelength; the third off-axis parabolic reflector (6) has a focal point coincident ... third off-axis parabolic reflector (6) has a focal point coincident with the focal point of the second off-axis parabolic reflector (4) and is used to re-collimate the scattered light not blocked by the optical The reflector (6) collimates the scattered light and recombines scattered light of different wavelengths; the fourth off-axis parabolic reflector (8) is used to focus the parallel scattered light after reverse dispersion of the second diffraction grating (7) at a focal point; the middle slit (9) is located at the focal point of the fourth off-axis parabolic reflector (8) and is used to receive the Thomson scattered signal after notch filtering; the focus of the fifth off-axis parabolic reflector (10) coincides with the focus of the fourth off-axis parabolic reflector (8) and is used to collimate the laser Thomson scattered light emitted by the middle slit. The third diffraction grating (11) is used to disperse the laser Thomson scattered light after being collimated by the fifth off-axis parabolic reflector (10), so that scattered light of different wavelengths is located at different spatial positions; the sixth off-axis parabolic reflector (12) is used to focus the parallel scattered light after being dispersed by the third diffraction grating (11), and focus the parallel scattered light at a focal point without generating aberration; the detector (13) is located at the focal point of the sixth off-axis parabolic reflector (12), and is used to detect and record the laser Thomson scattered signal.

2. A high-throughput laser Thomson scattering multi-grating spectrometer according to claim 1, characterized in that The first off-axis parabolic reflector (2), the second off-axis parabolic reflector (4), the third off-axis parabolic reflector (6), the fourth off-axis parabolic reflector (8), the fifth off-axis parabolic reflector (10) and the sixth off-axis parabolic reflector (12) are designed with a short focal length and a large aperture, thereby increasing the light flux of the multi-grating spectrometer without introducing chromatic aberration and spherical aberration.

3. A high-throughput laser Thomson scattering multi-grating spectrometer according to claim 1, characterized in that: The first off-axis parabolic reflector (2), the second off-axis parabolic reflector (4), the third off-axis parabolic reflector (6), the fourth off-axis parabolic reflector (8), the fifth off-axis parabolic reflector (10) and the sixth off-axis parabolic reflector (12) separate the focus from the optical path according to the off-axis angle, so that the light beam is deflected and folded, making the multi-grating spectrometer compact and portable.

4. A high-throughput laser Thomson scattering multi-grating spectrometer according to claim 1, characterized in that: The scattered light focused by the fourth off-axis parabolic reflector (8) enters the next stage through the middle slit (9), wherein the width of the middle slit (9) determines the spectral resolution of the multi-grating spectrometer.

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