A filament laser atmospheric detection spectrometer

Abstract

The present invention discloses a filament laser atmospheric detection spectrometer, comprising a telescope system, a slit, and a spectrometer system. Fluorescence spectrum information, which carries material composition information and is generated by the interaction between the filament laser and the atmosphere, is collected by the telescope system at the slit and then enters a spectral analysis system to obtain intensity information of different atmospheric spectra. The present invention enables real-time, high-resolution spectral detection of atmospheric composition on board spacecraft.

Description

Technical Field

[0001] The invention belongs to the field of light filament induced fluorescence spectrum measurement technology and optical design technology, and in particular relates to a light filament laser atmospheric detection spectrometer. Background Art

[0002] Ever since Maiman invented the first ruby ​​laser, people have been committed to continuously improving laser technology in terms of laser pulse width and peak power. With the emergence of ultrashort and ultra-intense laser pulses, people have found that when laser pulses act on transparent media, very fine filaments (i.e., "filamentation") will be produced. Femtosecond laser filamentation is a unique optical phenomenon caused by nonlinear optical effects. Its essence is a dynamic balance between the self-focusing effect and the plasma defocusing effect, which can form a stable plasma channel in the medium. In recent decades, with the continuous deepening of people's research on the femtosecond laser filamentation phenomenon, the principles, mechanisms, physical models and various nonlinear effects of filamentation have gradually become clear. Due to the special properties of filamentation, it has a wide range of applications in real life. For example: using the generated plasma in the field of laser lightning induction; using the characteristics of filamentation to form a virtual antenna; artificially controlling rainfall or snowfall; obtaining ultrashort pulses with few cycles by compressing laser pulses; detecting atmospheric pollution components; terahertz radiation and other fields. The present invention belongs to the field of atmospheric pollution component detection using filament lasers.

[0003] Traditional spaceborne atmospheric pollution monitoring devices rely on spectral imaging and lidar technology, which are unable to achieve real-time monitoring of multi-component atmospheric pollutants, identify unidentified pollutants, or detect the chemical composition of various pollutants with complex morphologies. The principle of filament laser atmospheric detection is that the femtosecond laser in the lidar system is emitted into the atmosphere, with sufficient intensity to ionize or dissociate atmospheric molecules, exciting them into an excited state, forming a filament laser. The filament laser interacts with atmospheric matter, stimulating a fluorescence spectrum that carries information about the composition of the substances. By analyzing the plasma fluorescence spectrum, the composition and type of various substances within the filament's area of ​​action, as well as the ambient pressure and temperature, can be determined. In 2003, Kasparian et al. used this method to detect water vapor and carbon dioxide at high altitudes. However, this lidar system is ground-based and performs remote laser atmospheric detection, making it incapable of space-based monitoring. This disadvantage is that the lidar needs to be transmitted from the ground atmosphere to the high-altitude detection area, making it difficult to avoid the influence of the complex ground atmospheric environment and disturbances, which makes spectral detection and spectral information interpretation difficult. Summary of the Invention

[0004] The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a filament laser atmospheric detection spectrometer, which can realize spaceborne real-time high-resolution spectral detection of atmospheric components.

[0005] The objectives of the present invention are achieved through the following technical solutions: A filament laser atmospheric detection spectrometer, comprising: a telescope system, a slit and a spectrometer system; wherein the telescope system collects fluorescence spectrum information carrying material composition information generated by the interaction between the filament laser and the atmosphere at the slit, and then enters the spectrometer system to obtain intensity information of different atmospheric spectra.

[0006] In the above-mentioned filament laser atmospheric sounding spectrometer, the telescope system includes a primary mirror, a secondary mirror and a folding mirror; wherein the fluorescence spectrum information carrying the material composition information passes through the primary mirror, the secondary mirror and the folding mirror in sequence and converges to the slit.

[0007] In the above-mentioned filament laser atmospheric detection spectrometer, the primary mirror and the secondary mirror both adopt secondary aspheric surfaces; the vertex curvature radius of the primary mirror is larger than the vertex curvature radius of the secondary mirror; the distance between the secondary mirror and the folding mirror is larger than the distance between the folding mirror and the slit.

[0008] In the above-mentioned filament laser atmospheric sounding spectrometer, the primary mirror is concave, the vertex curvature radius of the primary mirror is 1000mm~1300mm, the distance between the primary mirror and the secondary mirror is 420mm~530mm, the light aperture of the primary mirror is 400mm~600mm, the primary mirror is provided with a center hole, and the diameter of the center hole is 50mm~75mm; the secondary mirror is convex, the vertex curvature radius of the secondary mirror is 200mm~350mm, and the distance between the secondary mirror and the folding mirror is 600mm~900mm.

[0009] In the above-mentioned light filament laser atmospheric detection spectrometer, the light aperture of the secondary mirror is 91 mm; and the distance between the folding mirror and the slit is 70 mm.

[0010] In the above-mentioned filament laser atmospheric detection spectrometer, the length of the folding mirror is 71 mm, and the width of the folding mirror is 38 mm.

[0011] In the above-mentioned filament laser atmospheric detection spectrometer, the spectrometer system includes a collimator, a plane grating, a first converging mirror, a second converging mirror and a detector; wherein, the slit output light is collimated by the collimator and enters the plane grating, and the grating diffracted light passes through the first converging mirror and the second converging mirror again to reach the detector, obtaining the intensity information of different atmospheric spectra.

[0012] In the above-mentioned light filament laser atmospheric sounding spectrometer, the collimator, the first converging mirror and the second converging mirror all adopt high-order aspheric surfaces; the vertex curvature radius of the collimator is larger than the vertex curvature radius of the first converging mirror; the vertex curvature radius of the second converging mirror is smaller than the vertex curvature radius of the first converging mirror; the spacing between the collimator and the plane grating is larger than the spacing between the plane grating and the first converging mirror; the spacing between the first converging mirror and the second converging mirror is larger than the spacing between the plane grating and the first converging mirror.

[0013] In the above-mentioned filament laser atmospheric sounding spectrometer, the collimator is concave, the vertex curvature radius of the collimator is 350-400 mm, and the spacing between the collimator and the plane grating is 200-250 mm; the spacing between the plane grating and the first converging mirror is 80-120 mm, and the clear aperture of the plane grating is 22 mm; the first converging mirror is convex, the vertex curvature radius of the first converging mirror is 220-270 mm, and the spacing between the first converging mirror and the second converging mirror is 100-150 mm; the second converging mirror is concave, the vertex curvature radius of the second converging mirror is 140-220 mm, and the spacing between the second converging mirror and the detector is 100-160 mm.

[0014] In the above-mentioned filament laser atmospheric sounding spectrometer, the light-transmitting aperture of the collimating mirror is 22.6×20.72 mm; the light-transmitting aperture of the first converging mirror is 38×23 mm; and the light-transmitting aperture of the second converging mirror is 101×50 mm.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention can realize spaceborne real-time high-resolution spectral detection of atmospheric components;

[0017] (2) The system of the present invention has the advantages of compact structure, small size and light weight, and is particularly suitable for use with satellites. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0019] Figure 1 This is a schematic diagram of the optical path of the filament laser atmospheric sounding spectrometer provided by an embodiment of the present invention;

[0020] Figure 2 1 is a diagram showing the optical path structure of a telescopic system provided by an embodiment of the present invention;

[0021] Figure 3 This is a diagram of the optical path structure of the spectrometer provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] Figure 1 Schematic diagram of the optical path of the filament laser atmospheric detection spectrometer provided by the embodiment of the present invention. Figure 1 As shown, the filament laser atmospheric detection spectrometer includes: a telescope system, a slit 4 and a spectrometer system; wherein, the fluorescence spectrum information carrying material composition information generated by the interaction between the filament laser and the atmosphere is collected at the slit 4 through the telescope system, and then enters the spectrometer system, to obtain the intensity information of different atmospheric spectra, and then perform high-resolution spectral analysis of the atmospheric composition.

[0024] The working principle of this invention is that the fluorescence generated by the filament laser enters the system, is first collected by a telescope and focused at a slit, then dispersed and split on a plane grating through beam collimation. The dispersed light spot is then imaged onto a detector through a converging lens assembly, obtaining intensity information for different atmospheric spectra.

[0025] The telescope system has an aperture of at least 500 mm to effectively acquire fluorescence spectral signals. The optical structure utilizes either a two-way coaxial design or an off-axis design. The entire system has an operating F# between 2.5 and 4.5, and a focal length between 1250 mm and 2300 mm. The slit width is less than 70 μm.

[0026] The telescope system of this embodiment adopts RC structure design, and the primary and secondary mirrors adopt secondary aspherical surfaces. The light path passes through the primary mirror 1, the secondary mirror 2, the folding mirror 3 in sequence, and finally converges to the slit 4. Figure 2 As shown in the figure, the telescope system has an aperture of 500mm, a focal length of 4500mm, and a field of view of 0.3mrad. The slit dimensions are 1.37mm (spatial direction) × 0.035m (spectral direction). The maximum RMS diameter of the spot in each field of view is 0.035mm, which is smaller than the 65μm spectral slit dimension.

[0027] Spectrometer system such as Figure 3As shown, a Czerny-Turner spectrometer structure is used, with a plane grating as the grating. Light exiting the slit is collimated by a collimator 5 and enters a plane grating 6. The diffracted light from the grating then passes through a first converging lens 7 and a second converging lens 8 before reaching the detector. The first and second converging lenses 7 and 8 form a converging lens assembly. The spectrometer range is 0.32μm to 0.95μm, with a bandwidth of 630nm. The linear dispersion requirement is 0.67nm / pixel, the spectral resolution is 2nm, and the spectral sampling rate is 3 pixels. A plane grating is used for spectrometry, the image plane size is 0.52mm × 12.8mm (spectral direction), and the number of detector pixels is approximately 941 × 39. The collimator 5, the first converging lens 7, and the second converging lens 8 all utilize high-order aspheric surfaces to correct for aberrations.

[0028] Table 1 gives the detailed structural parameters of the telescope system of the embodiment, and Table 2 gives the detailed structural parameters of the spectrometer system of the embodiment.

[0029] Table 1 Main parameters of telescopic optical system

[0030]

[0031] Table 2 Spectrometer system structure parameters

[0032]

[0033] In addition, the aspheric parameters of the primary mirror 1, secondary mirror 2, collimating mirror 5, first converging mirror 7 and second converging mirror 8 are shown in the following table:

[0034]

[0035]

[0036] Among them, the aspheric equations used for each aspheric surface in the above table are shown below:

[0037]

[0038] Where c represents the curvature, which is the inverse of the vertex curvature radius, that is, 1 / R; k represents the quadratic aspheric coefficient, A represents the quartic aspheric coefficient, B represents the sextic aspheric coefficient, C represents the octadeconic aspheric coefficient, and D represents the decadic aspheric coefficient; z represents the sag height, and h represents the distance from the point on the surface to the central symmetry axis.

[0039] Through the above-mentioned aspheric equations, each mirror can meet the parameters very well, so as to better realize the real-time high-resolution spectral detection of atmospheric composition on board.

[0040] Analysis of the spectrometer system sampling linearity shows that the spectral sampling interval of 2 nm at 950 nm is 3.3 pixels; the spectral sampling interval of 2 nm at 635 nm is 2.7 pixels; and the spectral sampling interval of 2 nm at 320 nm is 2.7 pixels. To indicate the degree of curvature and deformation of the spectrometer image, keystone and smile are used. The X direction represents the spatial line field of view, and the Y direction represents the spectral expansion direction. Keystone represents the difference in X coordinates between the centers of the spectral images of the same spectral line in different fields of view, while smile represents the difference in Y coordinates between the centers of the spectral images of different spectral lines in the same field of view. The maximum keystone is better than 2.5 μm, or 0.18 pixel, and the smile is better than 1.6 μm, or 0.11 pixel. The energy concentration within three pixels exceeds 96%, and the optical transfer function (MTF) reaches 0.99 at 3.7 line-to-line.

[0041] This embodiment presents, for the first time, a filament laser atmospheric sounder system capable of real-time, high-resolution spectral detection of atmospheric composition onboard spacecraft, with a spectral resolution of up to 2 nm. This system has the advantages of a compact structure, small size, and light weight, making it particularly suitable for spacecraft-borne deployment.

[0042] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A filament laser atmospheric detection spectrometer, characterized in that include: A telescope system, a slit (4) and a spectrometer system; wherein, The telescope system collects the fluorescence spectrum information carrying the material composition information generated by the interaction between the filament laser and the atmosphere to the slit (4), and then enters the spectrometer system to obtain the intensity information of different atmospheric spectra; The telescopic system comprises a primary mirror (1), a secondary mirror (2) and a folding mirror (3); wherein, The fluorescence spectrum information carrying the material composition information is sequentially passed through the primary mirror (1), the secondary mirror (2) and the folding mirror (3) and converged to the slit (4); The primary mirror (1) and the secondary mirror (2) both adopt secondary aspheric surfaces; The vertex curvature radius of the primary mirror (1) is greater than the vertex curvature radius of the secondary mirror (2); the distance between the secondary mirror (2) and the folding mirror (3) is greater than the distance between the folding mirror (3) and the slit (4); The primary mirror (1) is a concave surface, the vertex curvature radius of the primary mirror (1) is 1000 mm to 1300 mm, the distance between the primary mirror (1) and the secondary mirror (2) is 420 mm to 530 mm, the light aperture of the primary mirror (1) is 400 mm to 600 mm, and the primary mirror (1) is provided with a central hole, the diameter of the central hole is 50 mm to 75 mm; The secondary mirror (2) is a convex surface, the vertex curvature radius of the secondary mirror (2) is 200 mm to 350 mm, and the distance between the secondary mirror (2) and the folding mirror (3) is 600 mm to 900 mm; The spectrometer system comprises a collimating mirror (5), a plane grating (6), a first converging mirror (7), a second converging mirror (8) and a detector (9); wherein, The slit-emitted light is collimated by a collimating lens (5) and enters a plane grating (6). The grating-diffracted light passes through a first converging lens (7) and a second converging lens (8) again and reaches a detector (9), thereby obtaining intensity information of different atmospheric spectra. The collimating mirror (5), the first converging mirror (7) and the second converging mirror (8) all adopt high-order aspheric surfaces; The vertex curvature radius of the collimating mirror (5) is greater than the vertex curvature radius of the first converging mirror (7); The vertex curvature radius of the second converging mirror (8) is smaller than the vertex curvature radius of the first converging mirror (7); The distance between the collimating mirror (5) and the plane grating (6) is greater than the distance between the plane grating (6) and the first converging mirror (7); The distance between the first converging mirror (7) and the second converging mirror (8) is greater than the distance between the plane grating (6) and the first converging mirror (7); The collimator (5) is a concave surface, the vertex curvature radius of the collimator (5) is 350-400 mm, and the distance between the collimator (5) and the plane grating (6) is 200-250 mm; The distance between the plane grating (6) and the first converging lens (7) is 80 to 120 mm, and the aperture of the plane grating (6) is 22 mm; The first converging mirror (7) is a convex surface, the vertex curvature radius of the first converging mirror (7) is 220 to 270 mm, and the distance between the first converging mirror (7) and the second converging mirror (8) is 100 to 150 mm; The second converging mirror (8) is a concave surface, the vertex curvature radius of the second converging mirror (8) is 140 to 220 mm, and the distance between the second converging mirror (8) and the detector is 100 to 160 mm; The light-through aperture of the collimating mirror (5) is 22.6×20.72 mm; the light-through aperture of the first converging mirror (7) is 38×23 mm; and the light-through aperture of the second converging mirror (8) is 101×50 mm. The aspheric equation used for aspheric surfaces is shown below: Where c represents the curvature, which is the inverse of the vertex curvature radius, that is, 1 / R; k represents the quadratic aspheric coefficient, A represents the quartic aspheric coefficient, B represents the sextic aspheric coefficient, C represents the octadeconic aspheric coefficient, and D represents the decadic aspheric coefficient; z represents the sag height, and h represents the distance from the point on the surface to the central symmetry axis.

2. The filament laser atmospheric detection spectrometer according to claim 1, characterized in that: The secondary mirror (2) has a light aperture of 91 mm; The distance between the folding mirror (3) and the slit (4) is 70 mm.

3. The filament laser atmospheric detection spectrometer according to claim 1, characterized in that: The length of the folding mirror (3) is 71 mm, and the width of the folding mirror (3) is 38 mm.

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