Dimension space conversion plasma spectrum analysis system of multi-optical-fiber-bundle imaging mode

Abstract

The invention discloses a multi-optical fiber bundle imaging mode dimension space conversion plasma spectrum analysis system, which is characterized in that a two-dimensional optical fiber array comprising M * N optical fiber micropores is arranged on an optical fiber area array, a one-dimensional optical fiber array comprising M * N optical fiber micropores is arranged on an optical fiber linear array, and an optical fiber surface is connected by adopting M * N optical fibers according to a preset connection relation, the two-dimensional optical fiber array is converted into the one-dimensional optical fiber array, the optical grating disperses light transmitted by the optical fiber linear array, then the light is focused by the imaging lens and then is subjected to optical imaging by the CCD detector, and the spectral data conversion module converts a spectral image into a spectral data graph of each optical fiber channel. According to one-to-one correspondence of optical fibers in the two-dimensional optical fiber area array and the one-dimensional optical fiber linear array, the distribution state of elements in the plasma is reconstructed, and multi-optical-fiber sample element content detection is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of spectrum analysis technology, and more specifically, relates to a dimensional space conversion plasma spectrum analysis system with a multi-fiber bundle imaging mode. Background Art

[0002] Laser-induced breakdown spectroscopy (LIBS) technology uses ultrashort pulse lasers to focus on the sample surface to form a plasma, and then analyzes the plasma emission spectrum to determine the material composition and content of the sample. The ultrashort pulse laser has a high energy density after focusing, and can excite samples in any physical state (solid, liquid, gas) to form plasma. In theory, LIBS technology can analyze samples in any physical state, and is only limited by the power of the laser and the sensitivity and wavelength range of the spectrometer and detector. Furthermore, almost all elements will emit characteristic spectral lines after being excited to form plasma. Therefore, LIBS can analyze most elements. If the composition of the material to be analyzed is known, LIBS can be used to assess the relative abundance of each constituent element or monitor the presence of impurities.

[0003] Traditional commercial LIBS detection instruments have an uneven distribution of target elements in the plasma due to the influence of the sample matrix. The optical fiber can only collect light at a certain position in the plasma due to the influence of the numerical aperture. This leads to poor quantitative analysis accuracy due to the uneven distribution of elements. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a dimensional space conversion plasma spectroscopy analysis system with a multi-fiber bundle imaging mode, which realizes the element content detection of multi-fiber samples by converting the fiber dimension from a two-dimensional array to a one-dimensional linear array.

[0005] To achieve the above-mentioned purpose, the dimensional space conversion plasma spectrum analysis system of the multi-fiber bundle imaging mode of the present invention includes a fiber array, a fiber linear array, a fiber bundle, a grating, an imaging lens, a CCD detector and a spectral data conversion module, wherein:

[0006] A two-dimensional optical fiber array including M×N optical fiber microholes is arranged on the optical fiber array;

[0007] A one-dimensional optical fiber array including M×N optical fiber microholes is arranged on the optical fiber linear array;

[0008] The optical fiber bundle includes M×N optical fibers, which are used to connect the corresponding microholes in the optical fiber array and the optical fiber linear array according to a pre-set connection relationship, thereby converting the two-dimensional optical fiber array into a one-dimensional optical fiber array;

[0009] The grating is used to collimate and disperse the light transmitted by the optical fiber linear array to obtain the dispersed beam light k , k=1,2,…,M×N;

[0010] The imaging lens is used to receive M×N light beams k Focusing

[0011] The CCD detector is used to perform optical imaging on the focused light beam, obtain a spectral image and send it to the spectral data conversion module;

[0012] The spectral data conversion module is used to convert the spectral image into the spectral data graph of each fiber channel. The specific method is as follows: the size of the spectral image is W×H, and the kth beam light is determined according to the optical imaging process of the CCD detector. k The corresponding pixel column number is obtained, and then the grayscale data in the corresponding pixel column is extracted and converted to obtain the spectrum data graph of the k-th optical fiber channel.

[0013] The present invention provides a dimensional space conversion plasma spectral analysis system in a multi-fiber bundle imaging mode. A two-dimensional fiber array including M×N fiber microholes is provided on the fiber surface array, and a one-dimensional fiber array including M×N fiber microholes is provided on the fiber line array. M×N optical fibers are connected to the fiber surface according to a pre-set connection relationship to convert the two-dimensional fiber array into a one-dimensional fiber array. A grating disperses light transmitted by the fiber line array, which is then focused by an imaging lens and then optically imaged by a CCD detector. A spectral data conversion module converts the spectral image into a spectral data graph for each fiber channel.

[0014] The present invention reconstructs the distribution state of elements in plasma through the one-to-one correspondence between optical fibers in a two-dimensional optical fiber array and a one-dimensional optical fiber linear array, realizes the element content detection of multi-fiber samples, and provides a new idea for solving the matrix effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a structural diagram of a specific embodiment of the dimensional space conversion plasma spectrum analysis system of the multi-fiber bundle imaging mode of the present invention;

[0016] Figure 2 is a schematic diagram of optical fiber array conversion in this embodiment;

[0017] Figure 3 It is a schematic diagram of the positional relationship between the one-dimensional fiber array and the grating;

[0018] Figure 4 is a schematic diagram of beam dispersion and focusing;

[0019] Figure 5 It is an optical analogue of optical imaging;

[0020] Figure 6 is an example diagram of the spectral image before and after correction in this embodiment;

[0021] Figure 7 This is the standard mercury lamp element spectrum obtained by the test of the present invention in this embodiment;

[0022] Figure 8 Graphs 1 and 2 are the spectrum analysis results of two samples in this embodiment. DETAILED DESCRIPTION

[0023] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0024] Example

[0025] Figure 1 This is a structural diagram of a specific embodiment of the multi-fiber bundle imaging mode dimensional space conversion plasma spectrum analysis system of the present invention. Figure 1 As shown, the dimensional space conversion plasma spectroscopy analysis system of the multi-fiber bundle imaging mode of the present invention includes a fiber array 1, a fiber linear array 2, a fiber bundle 3, a grating 4, an imaging lens 5 and a CCD (Charge Coupled Device, image sensor) detector 6. The following describes each component in detail.

[0026] A two-dimensional optical fiber array including M×N optical fiber microholes is provided on the optical fiber array 1.

[0027] A one-dimensional optical fiber array including M×N optical fiber microholes is provided on the optical fiber linear array 2 .

[0028] The fiber bundle 3 comprises M×N optical fibers, which are used to connect the corresponding microholes in the optical fiber array 1 and the optical fiber linear array 2 according to a pre-set connection relationship, thereby converting the two-dimensional optical fiber array into a one-dimensional optical fiber array. In this embodiment, the optical fiber array conversion adopts a row-first method, that is, the coordinates (i, j) of the optical fibers in the fiber bundle 3 in the two-dimensional optical fiber array and their sequence numbers k in the one-dimensional optical fiber array have the following mapping relationship:

[0029] k=(i-1)×N+j

[0030] Among them, i = 1, 2,…, M, j = 1, 2,…, N, k = 1, 2,…, M×N.

[0031] Figure 2 This is a schematic diagram of the optical fiber array conversion in this embodiment. Figure 2As shown, the optical fiber array 1 in this embodiment includes 10×10 optical fiber microholes. After the optical fiber array conversion, a one-dimensional optical fiber array of 100 optical fiber microholes is obtained.

[0032] The grating 4 is used to collimate and disperse the light transmitted by the optical fiber linear array 2 to obtain M×N dispersed light beams. k .

[0033] In this embodiment, the grating 4 is a concave grating, which integrates the functions of a concave reflector and a reflection grating. The concave grating can collimate and disperse the divergent light emitted from the optical fiber, which can help improve the resolution of the spectrometer.

[0034] To capture as many beams from different optical fibers as possible, it is best to ensure that the light emitted by the optical fibers is completely incident on the concave grating. Therefore, the long side of the grating 4 is parallel to the optical fiber array 2, and the optical fiber array 2 is incident on the center line of the grating 4.

[0035] In addition, the distance between the optical fiber array 2 and the grating 4 must ensure that the light emitted by the first optical fiber and the last optical fiber in the optical fiber array 2 can be received by the grating 4. This distance depends on the length of the one-dimensional optical fiber array, the numerical aperture of the optical fiber, and the size of the grating. Figure 3 This is a schematic diagram of the positional relationship between the one-dimensional fiber array and the grating. The calculation formula for the fiber numerical aperture NA can be expressed as:

[0036] NA=n×sinθ

[0037] Where n is the refractive index of the medium, and θ is the half-angle of the fiber's aperture. Assuming the numerical aperture of the selected fiber is 0.5 and the refractive index of the medium in air is n = 1, sinθ can be calculated to be 0.5.

[0038] The distance between the optical fiber array 2 and the grating 4 is L, and the smaller value between the distance between the upper end of the projection of the optical fiber array 2 on the grating 4 and the upper end of the grating 4 and the distance between the lower end of the projection and the lower end of the grating 4 is X. Figure 3 The following formula exists:

[0039]

[0040] Therefore, according to the above two formulas, it can be deduced that the distance L between the optical fiber array 2 and the grating 4 is preferably satisfied by the following formula:

[0041]

[0042] As for the incident angle, the M×N light beams after the grating 4 dispersion in the present invention are k The imaging lens 5 needs to focus the light onto the CCD detector 6 for imaging. Figure 4is a schematic diagram of beam dispersion and focusing. Figure 4 As shown, let the angle between the incident light and the diffracted light of the central wavelength light beam in all the light beams emitted by the optical fiber bundle 3 on the grating 4 be γ, and the following formula exists:

[0043] γ=α-β

[0044] Wherein, α is the incident angle of the central wavelength light beam on the grating, and β is the diffraction angle of the central wavelength light beam on the grating. In this embodiment, considering factors such as the grating size and the CCD target surface size, the angle γ is set to 38°.

[0045] According to the grating equation, the relationship between the incident angle α and the included angle γ can be expressed as follows:

[0046]

[0047] in, The grating order of grating 4 can be set to ..., -2, -1, 0, 1, 2, .... When working at the 0th order, the grating has no dispersion effect and acts as an upper reflection order. The specific grating order can be set according to actual needs. In this embodiment, the first order is used, then m represents the number of lines per millimeter of the grating 4. In this embodiment, m=1800 lines / mm. λ0 represents the wavelength of the central wavelength light beam. In this embodiment, the wavelength range involved is the visible light band (400-700 nm), so the central wavelength λ0=550 nm.

[0048] In this embodiment, substituting the relevant data into the above formula, it can be obtained that the incident angle α = 50.57° or -12.57° corresponds to the positive and negative first order of the grating respectively. In order to meet the actual design requirements, this embodiment adopts the -1 order spectrum, then the incident angle α = 50.57°, and the diffraction angle β = 12.57°.

[0049] In practical applications, in order to obtain a more accurate angle of incidence, after obtaining the relevant parameters through preliminary calculations, the initial values can be brought into the Zemax software and set as variables, taking into account the aberrations in geometric optics and the chromatic aberrations in the dispersion process, and adjusting the relative positions of the linear array fiber, grating, and CCD. By continuously observing and optimizing the spot diagram, smaller aberrations and higher dispersion resolution can be obtained, thereby obtaining more reliable data.

[0050] Imaging lens 5 is used to receive M×N light beams k Focus.

[0051] The CCD detector 6 is used to perform optical imaging on the focused light beam to obtain a spectral image and transmit it to the spectral data conversion module 7. Since the original spectral image collected by the CCD detector 6 may be curved due to vertical chromatic aberration of the linear array, in order to improve the quality of the spectral image, the moving least squares algorithm (MLS) can be used to correct the spectral image.

[0052] The spectrum data conversion module 7 is used to convert the spectrum image into a spectrum data graph of each optical fiber channel. Figure 5 It is an optical simulation diagram of optical imaging. Figure 5 As shown in the figure, after optical imaging in the present invention, the light beams of the same optical fiber will be projected into the same column in the spectral image. Therefore, the specific method of converting the spectral image into the spectral data graph in the present invention is as follows: the size of the spectral image is W×H, and the kth light beam light is determined according to the optical imaging process of the CCD detector 6. k The corresponding pixel column number is obtained, and then the grayscale data in the corresponding pixel column (the grayscale value represents the spectral intensity) is extracted to obtain the spectral data graph of the kth optical fiber channel.

[0053] In this embodiment, the optical fiber bundle 3 contains 100 optical fibers, so the collected spectral image is obtained after the dispersion of 100 optical fibers, so the spectral image actually contains the spectral information of 100 channels. Assume that the length and width pixel size of the spectral image is 1298*1350. Select any channel, for example the 45th channel, and assume that the pixel column number corresponding to the channel is 635, then the horizontal coordinate is based on the pixel size of the entire original image, so according to the pixel coordinates (0, 635) to (1298, 635), 1298 grayscale data are read in sequence to form the corresponding 45-channel spectral data graph. For any channel, we can take the same method, find the pixel column number corresponding to the channel, and then read the grayscale value in sequence from 0-1298 according to the horizontal coordinate, thereby converting it into a spectral data graph for the channel.

[0054] In this embodiment, the optical fiber bundle 3 contains 100 optical fibers, so 100 spectral data graphs can be obtained, which correspond to 100 one-dimensional linear optical fiber arrays. Subsequently, other software on the host computer can perform spectral analysis on these 100 spectral data graphs according to actual needs to obtain corresponding analysis results. For example, when it is necessary to obtain the distribution characterization of a certain element (such as CaⅠ422.67nm), the position of the target element can be found in the spectral data graph of 100 channels and the intensity of the corresponding channel can be read. Because the one-dimensional linear array and the two-dimensional surface array also have a one-to-one correspondence, the intensity of the target element can be reconstructed in two dimensions on the two-dimensional surface array, thereby characterizing an intensity distribution of the corresponding element. In addition, the present invention can also use multi-fiber channel cumulative quantification, summing up the light of 100 optical fiber channels and then performing quantitative analysis, thereby solving the problem of the limited receiving range of a single optical fiber in traditional single-fiber spectrometers, effectively improving the accuracy of quantitative analysis, and having a better quantitative analysis effect.

[0055] In order to better illustrate the technical effect of the present invention, a specific example is used to experimentally verify the present invention. In this example, a standard mercury lamp is used to test the spectrometer of the present invention, and a moving least squares (MLS) algorithm is used to correct the spectral image. Figure 6 : is an example of the spectral image before and after correction in this embodiment. Figure 6 As shown in Figure 3, the correction can effectively improve the curvature of the original spectral image.

[0056] Convert the rectified spectral image to 2 16 The relative intensity of the elements can be obtained by reading the grayscale value of a certain fiber channel and converting it into a spectrum. Figure 7 This is the standard mercury lamp elemental spectrum obtained by the present invention in this embodiment. By using the one-to-one correspondence between the fiber channels in the fiber array and the fiber linear array, the elemental intensity of each fiber channel in the spectrum image can be read and normalized to reconstruct the elemental distribution within the plasma. Figure 8 Figure 2 is the spectrum analysis result of two samples in this embodiment. Figure 8 As shown in the figure, boxes 1 and 2 represent the positions of the spectral images of CaⅠ422.67nm and MgⅠ589.59nm, respectively. Then, the element intensities are normalized to achieve elemental quantitative analysis.

[0057] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. A dimensional space conversion plasma spectroscopy analysis system with a multi-fiber bundle imaging mode, characterized in that: The system comprises an optical fiber array (1), an optical fiber linear array (2), an optical fiber bundle (3), a grating (4), an imaging lens (5), a CCD detector (6) and a spectral data conversion module (7), wherein: A two-dimensional optical fiber array including M×N optical fiber microholes is arranged on the optical fiber array (1); A one-dimensional optical fiber array including M×N optical fiber microholes is arranged on the optical fiber linear array (2); The optical fiber bundle (3) comprises M×N optical fibers, and is used to connect the corresponding microholes in the optical fiber array (1) and the optical fiber linear array (2) according to a pre-set connection relationship, thereby converting the two-dimensional optical fiber array into a one-dimensional optical fiber array; The grating (4) is used to collimate and disperse the light transmitted by the optical fiber linear array (2) to obtain a dispersed light beam light k , k=1,2,…,M×N; The imaging lens (5) is used to receive M×N light beams k Focusing The CCD detector (6) is used to perform optical imaging on the focused light beam, obtain a spectral image and send it to the spectral data conversion module (7); The spectrum data conversion module (7) is used to convert the spectrum image into the spectrum data graph of each optical fiber channel. The specific method is as follows: the size of the spectrum image is W×H, and the kth beam light is determined according to the optical imaging process of the CCD detector. k The corresponding pixel column number is obtained, and then the grayscale data in the corresponding pixel column is extracted and converted to obtain the spectrum data graph of the k-th optical fiber channel.

2. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The coordinates (i, j) of the optical fibers in the optical fiber bundle (3) in the two-dimensional optical fiber array and their serial numbers k in the one-dimensional optical fiber array have the following mapping relationship: k=(i-1)×N+j Among them, i = 1, 2,…, M, j = 1, 2,…, N, k = 1, 2,…, M×N.

3. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The grating (4) is a concave grating.

4. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The long side of the grating (4) and the optical fiber linear array (2) remain parallel, and the optical fiber linear array (2) is incident on the center line of the grating (4).

5. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The distance L between the optical fiber linear array (2) and the grating (4) satisfies the following formula: Wherein, NA represents the numerical aperture of the optical fiber, n represents the refractive index of the medium, and X represents the smaller value of the distance between the upper end of the projection of the optical fiber linear array (2) on the grating (4) and the upper end of the grating (4) and the distance between the lower end of the projection and the lower end of the grating (4).

6. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The incident angle α of the central wavelength light beam in all the light beams emitted by the optical fiber bundle (3) satisfies the following formula: Wherein, γ represents the angle between the incident light and the diffracted light of the central wavelength light beam on the grating (4), α represents the incident angle of the central wavelength light beam on the grating (4), represents the grating order of the grating (4), m represents the number of lines per millimeter of the grating (4), and λ0 represents the wavelength of the central wavelength light beam.

7. The multi-fiber dimension conversion spectrometer according to claim 1, characterized in that: The spectral image collected by the CCD detector (6) is corrected using a moving least squares algorithm.

Images