Stripe correction method for plasma electron density and spectral line measurement

Abstract

The invention discloses a stripe correction method for plasma electron density and spectral line measurement. The method comprises the following steps: reading a stripe to be processed, segmenting a stripe picture into a plurality of narrow strips along a direction vertical to the extending direction of the stripe, identifying the position of each narrow strip, and finding out the position corresponding to each stripe signal in the narrow strips; taking the position of a certain narrow strip as a reference, and solving the position difference of a certain stripe signal of other narrow strips relative to a corresponding stripe in the reference narrow strip; taking the reference narrow strip selected in the step of solving the position difference as a reference, moving a corresponding position along the narrow strip segmentation direction, and taking the moving distance as the position difference solved in the step of solving the position difference; and solving a new position of the stripe in each narrow strip, and finally splicing all the narrow strips together to obtain a corrected image. According to the method, the interference on the stripes caused by other factors can be removed, so that the accuracy of further extracting the physical information from the stripes is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of image processing, and in particular, relates to a fringe correction method for measuring plasma electron density and spectral lines. Background Art

[0002] Stripes produced by interference, diffraction and other methods are widely present in physics research and various scientific practices. In the fields of inertial confinement fusion, magnetic confinement fusion, laboratory astrophysics, etc., accurate diagnosis of plasma state is very important. Accurate diagnosis of plasma state can bring us important information about plasma dynamics evolution and internal related physical processes. Laser probe interferometry is a common method to measure plasma electron density. The electron density is solved by measuring the movement of interference fringes. However, in the construction of the interference light path, some interference will inevitably be introduced. These interferences will be coupled with the density information of the plasma and finally reflected in the movement of the interference fringes. If these fringes are not corrected, the density information of the plasma obtained based on this will be distorted.

[0003] In the Chinese authorized invention patent with application number CN202110655457.6, a detection method for plasma density distribution is disclosed, in which the original laser is split by the first beam splitter to form a first sub-laser and a second sub-laser, and the second sub-laser passes through the plasma area and is combined with the first sub-laser through the second beam splitter to generate a synthetic laser; an interference fringe image is generated based on the synthetic laser; an offset of the interference fringe image is generated based on the interference fringe image; the density of the plasma is calculated based on the offset, and the two-dimensional density distribution of the plasma in multiple directions is repeatedly measured to calculate and construct a three-dimensional spatial distribution image of the plasma density. In the detection method provided by this application, due to the influence of the plasma on the second sub-laser, the shape of the interference fringe will be deformed, and the offsets of multiple interference fringe deformations can be calculated, and then the spatial distribution of the plasma density can be obtained through multiple offsets.

[0004] The defect of the prior art is that, although the above patent realizes the detection of plasma density distribution, it lacks a specific correction method for interference fringes. Summary of the invention

[0005] In view of the problem that the existing plasma density detection method lacks a method for correcting interference fringes, the present invention provides a fringes correction method for measuring plasma electron density and spectral lines.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] A fringe correction method for measuring plasma electron density and spectral lines comprises the steps of:

[0008] Preprocessing: read in the stripes to be processed, divide the stripe image into a number of narrow strips perpendicular to the extension direction of the stripes, and number the narrow strips as 1, 2, 3, ..., i, ..., n;

[0009] Stripe position recognition: Perform position recognition on each narrow stripe and find out the position P corresponding to each stripe signal in the narrow stripe. i (S i );

[0010] Calculate the position difference: Taking the position of a narrow strip as a reference, calculate the position difference of a stripe signal of other narrow stripes relative to the corresponding stripe in the reference narrow strip.

[0011] Shift correction: Taking the reference narrow strip selected in the step of calculating the position difference as the reference, move the corresponding position along the narrow strip segmentation direction, and the moving distance is the position difference calculated in the step of calculating the position difference;

[0012] Get the corrected image: find the new position of the stripes in each narrow strip, and finally piece all the narrow strips together to get the corrected image.

[0013] Furthermore, the stripes are a group of physical signals, which appear as light and dark stripes with a certain regularity on the recording medium due to the coupling of specific physical information.

[0014] Furthermore, fringes include interference fringes, diffraction fringes and spectral lines.

[0015] Furthermore, in the step of identifying the position of the stripes, a corresponding function is selected according to the source of the stripe signal and the physical characteristics behind it, and the stripe position is identified by fitting and peak finding method;

[0016] The center position of the fringe signal is obtained by fitting the intensity distribution of the signal.

[0017] Furthermore, the peak finding method is to treat the narrow strip as a single processing object, regard the narrow strip as a data column, and find out the distribution of stripes in the narrow strip and the position of each stripe in the stripe.

[0018] Furthermore, the peak finding method includes a fitting method and a local extreme value finding method.

[0019] Furthermore, in the preprocessing step, n is the number of narrow strips, and the narrow strips are segmented perpendicular to the extension direction of the stripes, one by one according to the pixels of the image, and across pixels according to actual needs. All narrow strips can be of equal width or unequal width.

[0020] Furthermore, if the fringe signal is an interference fringe, a Gaussian function is used to perform peak fitting to locate the fringe.

[0021] Furthermore, if the fringe signal is a spectral line generated by the transition between different quantum states in the atom, the Voigt function least squares method is used for fitting;

[0022] The Voigt linear function can be given by:

[0023]

[0024] In the formula, Γ is the natural broadening of the transition line,

[0025] w is the energy resolution of the crystal spectrometer and is given by:

[0026]

[0027] Δs is the size of the light source, D is the working distance of the crystal spectrometer, θ B is the Bragg angle corresponding to the spectral line with energy E;

[0028] Since spontaneous radiation and collisions affect the lifetime of energy levels, resulting in natural width of energy levels, the spectral lines generated by transitions between two energy levels also have natural broadening. The line function corresponding to the natural broadening is the Lorentz line function:

[0029]

[0030] The spectral line broadening caused by the instrument and the broadening caused by the Doppler effect due to the movement of the light source are expressed by Gaussian line functions:

[0031]

[0032] The actual measured signal is coupled with the natural broadening of the spectral line and the resolution of the instrument, so the Vogit line function can also be obtained by convolving the Lorentzian line function and the Gaussian line function:

[0033] V(E-E0,Γ,w)=G(E,w)*L(E,Γ)

[0034] According to the fitting results, the center position of the signal is obtained.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention can correct irregular stripe patterns without affecting the physical information carried by the stripes.

[0037] The present invention can remove the interference on the stripes caused by other factors, thereby ensuring the accuracy of further extracting physical information from the stripes.

[0038] The idea of ​​processing stripes is concise, especially for the processing of curved stripes. This method adopts the idea of ​​differential shift in rectangular coordinate system, avoiding the difficulty of solving stripe tracks in polar coordinates under certain physical backgrounds.

[0039] The method first identifies and locates the position of the fringe by fitting peak search or other methods, and then selects a reference according to the actual situation to move the fringe longitudinally, and finally achieves the purpose of correcting the fringe. The method can remove the influence of interference factors on the physical quantity to be measured, so as to ensure the accuracy of the desired physical result. The fringe processing method disclosed in the present invention can be applied to the subsequent fringe correction of various interference fringes (such as Michelson, Mach-Zehnder, Nomarski interferometer, VISAR) and spectral signals measured by crystal spectrometers and other types of spectrometers. The subsequent correction of fringes obtained in other scenes is also applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is an overall flow chart of a fringe correction method for measuring plasma electron density and spectral lines in an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of the stripe correction principle in an embodiment of the present invention;

[0042] Figure 3 Schematic diagram of the interference fringe correction before and after the embodiment of the present invention;

[0043] Figure 4 It is a schematic diagram of the spectral line fringes measured by the crystal spectrometer before and after correction in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0045] like Figure 1 As shown, this embodiment provides a fringe correction method for measuring plasma electron density and spectral lines, comprising the steps of:

[0046] S1. Preprocessing: read in the stripes to be processed, divide the stripe image into a number of narrow stripes along the direction perpendicular to the extension of the stripes, and number the narrow strips as 1, 2, 3, ..., i, ..., n; n is the number of stripe divisions, which depends on the image pixels and processing accuracy.

[0047] S2, stripe position recognition: perform position recognition on each narrow stripe and find out the position P corresponding to each stripe signal in the narrow stripe. i (S i );

[0048] S3. Calculate the position difference: Taking a certain narrow strip position as a reference, calculate the position difference of a stripe signal of other narrow stripes relative to the corresponding stripe in the reference narrow strip. ΔP i (S i )=P i (S i )–Pnorm(S i ),Pnorm(S i ) is the Sth in the selected benchmark narrow strip i The position of the stripes.

[0049] S4, shift correction: take the reference narrow strip selected in step 1 as the reference, move the corresponding position along the narrow strip segmentation direction, and the moving distance is the position difference calculated in step 1; the position after the move is P i (S i )′=P i (S i )–ΔP i (S i ).

[0050] S5, obtain the corrected image: find the new position of the stripes in each narrow strip, and finally combine all the narrow strips together to obtain the corrected image. Figure 2 As shown, the left picture is the original image before correction, and the right picture is the effect picture after correction; Figure 3 As shown, the upper picture is the original image before correction, and the lower picture is the effect picture after correction.

[0051] Stripes are a group of physical signals, which appear as a regular distribution of light and dark stripes on the recording medium due to the coupling of specific physical information.

[0052] In the step of identifying the position of the stripes, a corresponding function is selected according to the source of the stripe signal and the physical characteristics behind it, and the stripe position is identified by fitting and peak finding method;

[0053] The center position of the fringe signal is obtained by fitting the intensity distribution of the signal.

[0054] The peak-finding method is to treat the narrow strip as a single processing object, regard the narrow strip as a data column, and find out the distribution of stripes in the narrow strip and the position of each stripe in the stripe.

[0055] The peak finding methods include fitting and local extreme value finding.

[0056] In the preprocessing step, n is the number of narrow strips. The narrow strips are segmented perpendicular to the extension direction of the stripes, one by one according to the pixels of the image, and across pixels according to actual needs. All narrow strips can be of equal width or unequal width.

[0057] If the fringe signal is a spectral line generated by the transition between different quantum states in the atom, the Voigt function least squares method is used for fitting;

[0058] The Voigt linear function can be given by:

[0059]

[0060] In the formula, Γ is the natural broadening of the transition line,

[0061] w is the energy resolution of the crystal spectrometer and is given by:

[0062]

[0063] Δs is the size of the light source, D is the working distance of the crystal spectrometer, θ B is the Bragg angle corresponding to the spectral line with energy E;

[0064] Since spontaneous radiation and collisions affect the lifetime of energy levels, resulting in natural width of energy levels, the spectral lines generated by transitions between two energy levels also have natural broadening. The line function corresponding to the natural broadening is the Lorentz line function:

[0065]

[0066] The spectral line broadening caused by the instrument and the broadening caused by the Doppler effect due to the movement of the light source are expressed by Gaussian line functions:

[0067]

[0068] The actual measured signal is coupled with the natural broadening of the spectral line and the resolution of the instrument, so the Vogit line function can also be obtained by convolving the Lorentzian line function and the Gaussian line function:

[0069] V(E-E0,Γ,w)=G(E,w)*L(E,Γ)

[0070] According to the fitting results, the center position of the signal is obtained.

[0071] If the fringe signal is an interference fringe, a Gaussian function is used to perform peak fitting to locate the fringe.

[0072] Correction of interference fringes during the measurement of electron density by laser probe interferometry. Figure 4As shown in the figure, the upper part shows the interference fringes obtained in the process of measuring electron density by laser probe interferometry. Due to the inevitable errors in the optical path construction process and other interference factors, the measured interference fringes are somewhat different from the ideal results, which is manifested as the fringes in the right half of the image showing an upward bending shape and a distorted shape in the entire detail. This will cause errors in the subsequent solution of density information and needs to be corrected. The correction steps are basically the same as the previous example. The only difference is:

[0073] (1) The previous example segmented the image horizontally, but in this example the stripes extend horizontally, so the original image must be segmented vertically. The number of narrow stripes obtained by segmentation is also determined by the vertical pixel width of the image.

[0074] (2) Since the spectral line signal tends to be more Gaussian distributed, in order to retain the original physical information to the maximum extent during the correction process, a Gaussian function is used in this example to perform peak fitting and locate the fringes.

[0075] The final image after correction is as follows Figure 4 Shown in the lower part.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] The present invention can correct irregular stripe patterns without affecting the physical information carried by the stripes.

[0078] The present invention can remove the interference on the stripes caused by other factors, thereby ensuring the accuracy of further extracting physical information from the stripes.

[0079] The idea of ​​processing stripes is concise, especially for the processing of curved stripes. This method adopts the idea of ​​differential shift in rectangular coordinate system, avoiding the difficulty of solving stripe tracks in polar coordinates under certain physical backgrounds.

[0080] The method first identifies and locates the fringe position by fitting peak search or other methods, and then selects a reference according to the actual situation to move the fringe longitudinally, and finally achieves the purpose of correcting the fringe. The method can remove the influence of interference factors on the physical quantity to be measured, so as to ensure the accuracy of the desired physical result. The fringe processing method disclosed in the present invention can be applied to the subsequent fringe correction of various interference fringes (such as Michelson, Mach-Zehnder, Nomarski interferometer, VISAR) and spectral signals measured by crystal spectrometers. The subsequent correction of fringes obtained in other scenes is also applicable.

[0081] The above is a detailed introduction to a fringe correction method for plasma electron density and spectral line measurement provided by the present application. The description of the specific embodiment is only used to help understand the method and its core idea of ​​the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A fringe correction method for plasma electron density and spectral line measurement, characterized in that: Includes steps: Preprocessing: read the stripes to be processed, and divide the stripe image into a number of narrow stripes perpendicular to the extending direction of the stripes; Stripe position recognition: perform position recognition on each narrow stripe and find out the position corresponding to each stripe signal in the narrow stripe; Calculate the position difference: Taking the position of a narrow strip as the reference, calculate the position difference of a stripe signal of other narrow stripes relative to the corresponding stripe in the reference narrow strip; Shift correction: Taking the reference narrow strip selected in the step of calculating the position difference as the reference, move the corresponding position along the narrow strip segmentation direction, and the moving distance is the position difference calculated in the step of calculating the position difference; Get the corrected image: find the new position of the stripes in each narrow strip, and finally piece all the narrow strips together to get the corrected image.

2. The fringe correction method for plasma electron density and spectral line measurement according to claim 1, characterized in that: Fringe includes interference fringes, diffraction fringes and spectral lines.

3. The fringe correction method for plasma electron density and spectral line measurement according to claim 2, characterized in that: The peak-finding method is to treat the narrow strip as a single processing object, regard the narrow strip as a data column, and find out the distribution of stripes in the narrow strip and the position of each stripe in the stripe.

4. The fringe correction method for plasma electron density and spectral line measurement according to claim 3, characterized in that: In the preprocessing step, the narrow strips are segmented perpendicular to the extension direction of the stripes, one by one according to the pixels of the image and across pixels according to actual needs. All narrow strips are divided into equal width and unequal width.

5. The fringe correction method for plasma electron density and spectral line measurement according to claim 4, characterized in that: The peak finding methods include fitting and local extreme value finding.

6. The fringe correction method for plasma electron density and spectral line measurement according to claim 5, characterized in that: If the fringe signal is an interference fringe, a Gaussian function is used to perform peak fitting to locate the fringe.

7. The fringe correction method for plasma electron density and spectral line measurement according to claim 5, characterized in that: If the fringe signal is a spectral line generated by the transition between different quantum states in the atom, the Voigt function least squares method is used for fitting; The Voigt linear function can be given by: In the formula, Γ is the natural broadening of the transition line, w is the energy resolution of the crystal spectrometer and is given by: Δs is the size of the light source, D is the working distance of the crystal spectrometer, θ B is the Bragg angle corresponding to the spectral line with energy E; Since spontaneous radiation and collisions affect the lifetime of energy levels, resulting in natural width of energy levels, the spectral lines generated by transitions between two energy levels also have natural broadening. The line function corresponding to the natural broadening is the Lorentz line function: The spectral line broadening caused by the instrument and the broadening caused by the Doppler effect due to the movement of the light source are expressed by Gaussian line functions: The actual measured signal is coupled with the natural broadening of the spectral line and the resolution of the instrument, so the Vogit line function can also be obtained by convolving the Lorentzian line function and the Gaussian line function: V(E-E0,Γ,w)=G(E,w)*L(E,Γ) According to the fitting results, the center position of the signal is obtained.

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