Uncertainty quantification method for scattered light intensity measurement based on light spot stability analysis

Abstract

The application discloses a scattering light intensity measurement uncertainty quantification method based on light spot stability analysis, and belongs to the technical field of plasma diagnosis. The method comprises the following steps: collecting a laser light spot image by using a surface array detector; performing adaptive background noise filtering and stray light removal based on connected region analysis on the light spot data to obtain high signal-to-noise ratio light spot intensity distribution data; accurately calculating the light spot centroid position of each pulse by using a weighted centroid method, and statistically analyzing the multi-pulse centroid positions to obtain a beam pointing stability parameter; combining the spatial matching relationship between the scattering volume and the collection system in the Thomson scattering light path to construct a quantitative model between the laser centroid offset and the scattering light collection efficiency, and then calculating the relative uncertainty of the transmission coefficient according to the error transfer principle. The application can effectively quantify the influence of laser pointing instability and light path vibration on the measurement accuracy without changing the original system structure.

Description

Technical Field

[0001] This invention belongs to the field of plasma diagnostic technology, specifically relating to a method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis. Background Technology

[0002] Thomson scattering diagnostics is a crucial method for obtaining core parameters of plasma such as temperature and density, and its measurement accuracy directly depends on the accurate measurement of scattered light intensity. In a Thomson scattering diagnostic system, the laser beam is the primary source of excited scattered light. However, laser beam pointing instability and vibrations of mechanical components in the optical path are the main sources of error in scattered light intensity measurement. When the laser beam deviates from the optical axis of the collecting optical path, part or all of the scattering volume will move out of the field of view of the collecting lens or the receiving range of the optical fiber, resulting in a reduction in the number of scattered photons collected by the system, thus affecting the accuracy of subsequent plasma parameter calculations.

[0003] Currently, the methods for addressing the aforementioned problems have significant shortcomings. First, existing methods for processing laser spot data are relatively simple. The acquired raw spot images typically contain a large amount of background noise and isolated noise introduced by environmental stray light, detector noise, etc. Directly using such data for centroid calculation will introduce significant errors, resulting in low reliability of the evaluation results for laser centroid position and pointing stability parameters, and making it difficult to effectively filter out interference while preserving the true shape of the spot. Second, existing technologies lack in-depth analysis of the quantitative relationship between spot pointing stability and the measurement uncertainty of scattered light intensity. In practice, they often rely on empirical estimation or simple evaluation of the overall system performance. Such methods have poor versatility, lack universal quantitative models, and cannot achieve accurate and objective evaluation of measurement uncertainty.

[0004] In summary, existing technologies struggle to accurately assess and quantify the measurement errors in scattered light intensity introduced by beam pointing instability and optical path vibration. This has become a bottleneck restricting further improvements in the measurement accuracy of Thomson scattering diagnostic systems, making it difficult to meet the demands of high-precision, high-reliability plasma physics experimental research. Therefore, a method capable of accurately quantifying such uncertainties is urgently needed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a quantitative method for measuring the uncertainty of scattered light intensity based on spot stability analysis. By adaptively preprocessing and removing stray light from the laser spot image, high signal-to-noise ratio spot intensity distribution data is obtained. Based on this, a weighted centroid calculation method is used to accurately obtain the centroid position of the laser beam on the detection plane, and the beam pointing stability parameter is obtained through statistical analysis of the centroid displacement of multi-pulse spots. Furthermore, by combining the spatial matching relationship between the scattering volume and the collection system in the Thomson scattering diagnostic optical path, a quantitative relationship model between the laser beam pointing offset and the scattered light collection efficiency is constructed, thereby achieving a quantitative assessment of the uncertainty in scattered light intensity measurement. This invention can achieve accurate quantification of the uncertainty in scattered light intensity measurement without changing the original structure of the Thomson scattering diagnostic system, providing a technical basis for the evaluation and optimization of plasma parameter measurement accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for quantifying the uncertainty in scattered light intensity measurement based on spot stability analysis includes:

[0008] Step 1: Use an area array detector to acquire laser spot images on the focal plane of the focusing element and record the two-dimensional shape of the laser beam in real time.

[0009] Step 2: Filter the background noise from the acquired spot image data;

[0010] Step 3: Perform stray light removal processing on the filtered spot image data based on connected component analysis to obtain spot intensity distribution data with high signal-to-noise ratio;

[0011] Step 4: For the high signal-to-noise ratio spot intensity distribution data, the weighted centroid method is used to calculate the spot centroid position of each laser pulse, and the centroid positions of multiple consecutive pulses are statistically analyzed to obtain the beam pointing stability parameter.

[0012] Step 5: Based on the characteristics of the Thomson scattering optical path, establish a quantitative relationship model between the centroid shift of the laser beam and the scattered light collection efficiency. Quantify the collection efficiency through the transmission coefficient T, and calculate the relative uncertainty of the transmission coefficient T using the centroid shift data.

[0013] Furthermore, in step 2, the background noise filtering is adaptive background noise filtering, specifically: the background noise threshold is adaptively determined based on the overall intensity of the light spot, and pixel data below the threshold are filtered out to suppress the influence of ambient stray light and detector noise.

[0014] Furthermore, in step 3, the stray light removal process based on connected component analysis specifically includes: performing 4-neighborhood or 8-neighborhood connected component analysis on the filtered spot data, calculating the connected component value of each pixel through a sliding window, identifying the main area of ​​the spot, and determining isolated pixels or small areas that are not connected to the main area of ​​the spot as stray light areas, setting their intensity values ​​to zero, thereby eliminating stray light interference while preserving the true shape of the spot.

[0015] Furthermore, in step 4, the weighted centroid method calculates the centroid coordinates by using the intensity value of each pixel as a weight. The specific calculation formula is as follows: the X coordinate of the centroid is equal to the sum of the products of the column coordinates of all pixels and their intensity values, divided by the sum of the intensity values ​​of all pixels; the Y coordinate of the centroid is equal to the sum of the products of the row coordinates of all pixels and their intensity values, divided by the sum of the intensity values ​​of all pixels.

[0016] Furthermore, in step 4, the statistical analysis of the centroid positions of multiple continuous pulses specifically involves: continuously acquiring the spot intensity distribution data of multiple laser pulses, calculating the centroid coordinates of each pulse, and statistically analyzing these centroid coordinate sequences to calculate the standard deviation of the centroid displacement in the X-axis and Y-axis directions and the azimuth angle, thereby obtaining the beam pointing stability parameters.

[0017] Furthermore, in step 5, the quantitative relationship model is as follows: the transmission coefficient T is defined as the ratio of the effective scattering region to the maximum effective scattering region, wherein the effective scattering region is the region where the optical fiber receiving range overlaps with the laser scatterer, and its size is related to the centroid offset of the laser beam in the X-axis direction.

[0018] Furthermore, the centroid offset of the laser beam in the X-axis direction follows a one-dimensional normal distribution.

[0019] Furthermore, in step 5, when calculating the relative uncertainty of the transmission coefficient T, based on the error propagation principle, the standard deviation of the centroid displacement in the beam pointing stability parameter is used as input, and the relative uncertainty of the transmission coefficient T is calculated through the quantitative relationship model.

[0020] In a second aspect, the present invention provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis.

[0021] Thirdly, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enable the processor to implement the aforementioned method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis.

[0022] The beneficial effects of this invention are as follows:

[0023] Precise quantification of the uncertainty in scattered light intensity measurement has been achieved: by constructing a quantitative relationship model between laser centroid shift and scattered light collection efficiency, and by calculating based on the error propagation principle, the influence of laser pointing instability and optical path vibration on Thomson scattering diagnosis has been transformed into a calculable transmission coefficient uncertainty for the first time, achieving a breakthrough from qualitative empirical judgment to quantitative scientific evaluation.

[0024] The accuracy and reliability of spot data processing and feature extraction have been improved: Adaptive background noise filtering and stray light removal technology based on connected component analysis are adopted. While effectively suppressing environmental noise and isolated noise interference, the true shape and detailed information of the spot are preserved to the maximum extent, providing a high-quality data foundation for subsequent high-precision centroid calculation.

[0025] The accuracy of beam pointing stability analysis has been improved: the weighted centroid method is used to calculate the beam centroid, which strengthens the dominant role of the high-intensity core region in the positioning results and effectively suppresses the influence of edge noise. Statistical analysis of a large number of pulse (N≥1000) centroid data makes the acquisition of pointing stability parameters more objective and accurate.

[0026] It has good versatility and practicality: the method does not require changes to the hardware structure of the existing Thomson scattering diagnostic system, and can be implemented only through the optimization of software algorithms and data processing flow. It provides a direct and effective technical tool for evaluating and optimizing the measurement accuracy of existing systems, and has wide applicability and important engineering application value. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to the present invention.

[0028] Figure 2 This is a schematic diagram of the optical path for laser beam acquisition.

[0029] Figure 3 This is a schematic diagram of the connected regions in the neighborhood.

[0030] Figure 4 This is a diagram showing the laser spot distribution before preprocessing and stray light processing;

[0031] Figure 5 This is a diagram showing the laser spot distribution after preprocessing and stray light processing;

[0032] Figure 6 The result is the calculation of the laser spot centroid using the weighted centroid method;

[0033] Figure 7This is a schematic diagram showing the change in the position of the centroid of the laser spot. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] like Figure 1 As shown, this invention provides a method for quantifying the uncertainty in scattered light intensity measurement based on spot stability analysis, the method comprising:

[0036] Step 1: Laser Spot Image Acquisition. A planar array detector is used to acquire laser spot images. During testing, measurements must be taken on the focal plane of the focusing element. The two-dimensional beam shape of the laser beam is recorded in real time over a period of time. Overexposure of the detector can be avoided using an energy attenuator.

[0037] Step 2: Spot Data Preprocessing. Given the pixel size, unit, image height, and image width of the data collected by the detector, firstly, to ensure data integrity, the data in areas without laser signals (spatial domain) is set to zero. The color intensity is automatically adjusted based on the overall energy level of the spot, generating a corresponding color map. Furthermore, an adaptive background noise threshold is applied based on the overall spot intensity, filtering out background noise below the threshold to suppress the influence of ambient stray light and detector noise.

[0038] Step 3: Stray Light Removal Based on Connected Component Analysis. Connected component analysis is performed on the preprocessed data. A sliding window is used to calculate the connected component value for each pixel, identifying the main area of ​​the light spot. Isolated pixels or small areas not connected to the main light spot are identified as stray light areas. The sliding window iterates through all pixels to remove stray light, thus eliminating stray light interference while preserving the true shape of the light spot. This yields high signal-to-noise ratio light spot intensity distribution data, providing accurate data for centroid calculation.

[0039] Step 4: Centroid and pointing stability calculation. For the obtained high signal-to-noise ratio spot intensity distribution data, a weighted centroid calculation method is used to determine the centroid position corresponding to each laser pulse, avoiding the influence of edge noise and intensity unevenness on the centroid calculation results; it is required to continuously acquire spot data for N laser pulses (…). The corresponding centroids are calculated for each pulse. By statistically analyzing the centroid positions of multiple consecutive laser pulses, the standard deviation and azimuth angle of the centroid displacement in different directions are calculated. Based on the definition of beam pointing stability, the beam pointing stability parameters can be obtained.

[0040] Step 5: Uncertainty Assessment of Scattered Light Intensity Measurement. Based on the characteristics of the Thomson scattering optical path, a transmission coefficient T is defined to quantify the decrease in scattering collection efficiency caused by laser drift. When the laser beam deviates from the optical axis of the collection path, part or all of the scattering volume will move out of the field of view of the collecting lens or the receiving range of the optical fiber, resulting in a reduction in the number of photons measured by the system. A quantitative relationship model between beam centroid shift and scattered light collection efficiency is established. Based on the change in the effective scattering area overlapping the receiving range of the optical fiber and the scattering volume, and based on the error propagation principle, the relative uncertainty of the transmission coefficient T is calculated using the centroid shift data obtained above. This uncertainty directly characterizes the degree of influence of laser beam pointing instability and vibration of optical path mechanical components on the measurement of Thomson scattered light intensity.

[0041] Example:

[0042] The core of this approach is the quantification of uncertainty in scattered light intensity measurement. The objective is achieved through four key steps: spot processing, centroid calculation, pointing stability analysis, and uncertainty assessment. Specifically:

[0043] Step 1: Acquisition of light spot image;

[0044] Using an area array detector to acquire light spot images, a laser beam acquisition optical path is constructed as follows: Figure 2 As shown, the main optical components include a reflector, a wedge, a focusing lens (focal length f), and a CCD area array detector. The laser beam emitted from the laser is oriented by the reflector, fine-tuned by the wedge, and then focused onto the focal plane by the focusing lens (focal length f). Finally, the CCD detector acquires and records the two-dimensional image of the laser spot. During testing, measurements must be taken on the focal plane of the focusing element, and the two-dimensional beam shape is acquired in real time by the detector. Background noise must be subtracted during acquisition. An energy attenuator can be used to prevent detector overexposure. The beam pointing stability index is obtained by analyzing the standard deviation of the beam angular displacement over a period of time.

[0045] Step 2: Preprocessing of spot data;

[0046] Subsequent processing of the laser spot data utilizes a CSV format data file stored by the detector. Information such as pixel size, unit, image height, and image width can be read from the detector's documentation. To ensure data integrity, data in areas without laser signals is first zeroed out. Simultaneously, the color intensity is automatically adjusted based on the overall energy level of the laser spot, generating a corresponding color map for subsequent visualization of the spot's morphology. Adaptive background noise filtering: Based on the overall spot intensity, an adaptive background noise threshold is applied, filtering out all background data below the threshold to suppress stray light and detector noise.

[0047] Step 3: Stray light removal based on connected component analysis;

[0048] Traditional morphological operations often result in blurred edges of the light spot, failing to guarantee the accuracy of the spot's shape. Connected region analysis, on the other hand, can remove stray light while preserving the main edge shape of the light spot, providing accurate data for centroid calculation.

[0049] Perform 4 / 8 neighborhood connectivity analysis on the preprocessed data, such as... Figure 3 As shown, the algorithm distinguishes between the main light spot and isolated noise. The number of connected components in each pixel is recorded as its connected component value. By sliding the window to calculate the connected component value of each pixel, the region with the largest consecutive connected component value is identified as the main light spot. Then, the number of pixels with a connected component value of 1 is calculated to obtain the size of the noise or background light area. While preserving the main light spot, the sliding window sets the connected component intensity of the noise or background light pixels to zero until all pixels have been traversed. For example... Figures 4-5 The images show the laser spot before and after preprocessing and stray light processing, respectively.

[0050] Step 4: Calculation of centroid and pointing stability;

[0051] The processed spot intensity distribution data was used to calculate the spot centroid using the weighted centroid method, such as... Figure 6 As shown. The weighted centroid method calculates centroid coordinates based on the weighted differences in the intensity distribution of light spot pixels, avoiding the influence of edge noise and uneven intensity on the positioning results. The specific principle and calculation method are as follows:

[0052] The centroid of a laser spot is the center of its energy distribution. The core of the weighted centroid method is to use the intensity value of each pixel as its weight in the centroid calculation. Pixels with higher intensity contribute more to the centroid position, thus highlighting the dominant role of the energy concentration area of ​​the spot, suppressing the interference of low-intensity noise at the edges, and achieving higher accuracy in centroid positioning. Compared to the Gaussian fitting method, the weighted centroid method better reflects the energy distribution characteristics of the laser spot, and is especially suitable for spot data with uneven intensity or residual noise at the edges.

[0053] Let the pixel matrix of the processed spot image be... ,in Here are the row coordinates of the pixels. These are the column coordinates of the pixels, corresponding to the actual X and Y coordinates in space. coordinates The laser intensity value of the pixel, in counts, and Then the centroid coordinates ( , The calculation formula is:

[0054] ,

[0055] ,

[0056] Where M is the total number of rows in the spot image and N is the total number of columns in the spot image; the numerator is the weighted sum of the coordinates and their corresponding intensities, and the denominator is the sum of the intensities of all pixels.

[0057] By using the weighted centroid calculation method described above, the high-intensity region in the beam intensity distribution occupies a higher weight in the centroid calculation, thereby reducing the impact of low-intensity noise at the edge on the centroid positioning result and improving the accuracy of beam pointing stability parameter calculation.

[0058] Pointing stability index calculation: continuously acquire spot data of N laser pulses ( Repeat the above steps to obtain N sets of centroid coordinates. By statistically analyzing the centroid positions of multiple pulses, the standard deviation of the centroid displacement along the X and Y axes and the azimuth angle are calculated. Based on the definition of beam pointing stability, the beam pointing stability can be obtained.

[0059] Step 5: Uncertainty assessment;

[0060] Transmission coefficient definition: Based on the characteristics of the Thomson scattering optical path, the transmission coefficient T is defined to quantify the decrease in scattering collection efficiency caused by laser drift. When the laser beam deviates from the optical axis of the collection path, part or all of the scattering volume will move out of the field of view of the collecting lens or the receiving range of the fiber, resulting in a reduction in the number of photons measured by the system. The laser propagates along the Z-axis, and the laser beam is considered as a cylindrical beam extending along the propagation direction after entering the plasma, with a radius of... The effects of uneven laser beam intensity distribution are temporarily disregarded. A quantitative model is established between beam centroid shift and scattered light collection efficiency, with the fiber receiving range being [missing information]. The effective scattering region of a circle with radius r and the scatterer. Located on the XZ plane. Assume the centroid coordinates of the laser beam are... Defocus caused by Y-axis offset is not considered for now. Therefore:

[0061] ,

[0062] ,

[0063] In the formula, The effective scattering region is the area where the fiber optic receiving range overlaps with the scatterer. The maximum effective scattering region, and It is only related to the X-axis coordinate of the centroid. It follows a one-dimensional normal distribution, where the optical fiber receiving range is a circle with radius R, and dx represents the integration operation with respect to x;

[0064] Uncertainty Calculation: Based on the error propagation formula, assuming the stability of the laser and optical platform remains constant, the relative uncertainty of the transmission coefficient T is calculated using the centroid offset data obtained above. This uncertainty directly characterizes the influence of laser beam pointing instability and vibration of optical path mechanical components on the Thomson scattering intensity measurement. Based on the error propagation principle, the transmission coefficient... The uncertainty can represent the uncertainty in the intensity of the scattered light measured due to the pointing instability of the laser beam and the vibration of mechanical components in the optical path. By constructing a test optical path to continuously collect the position of the centroid of the laser spot for 1000 laser pulses, the change in the position of the centroid of the laser spot on the collection surface is obtained as follows: Figure 7 As shown, the color representation calculates the number of times the centroid falls within the pixel region. Finally, statistical analysis yields the relative uncertainty of the transmission coefficient caused by the laser centroid shift within the effective collection field of view.

[0065] In a second aspect, the present invention provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis.

[0066] Thirdly, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enable the processor to implement the aforementioned method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis.

[0067] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for quantifying the uncertainty in scattered light intensity measurement based on spot stability analysis, characterized in that, include: Step 1: Use an area array detector to acquire laser spot images on the focal plane of the focusing element and record the two-dimensional shape of the laser beam in real time. Step 2: Filter the background noise from the acquired spot image data; Step 3: Perform stray light removal processing on the filtered spot image data based on connected component analysis to obtain spot intensity distribution data with high signal-to-noise ratio; Step 4: For the high signal-to-noise ratio spot intensity distribution data, the weighted centroid method is used to calculate the spot centroid position of each laser pulse, and the centroid positions of multiple consecutive pulses are statistically analyzed to obtain the beam pointing stability parameter. Step 5: Based on the characteristics of the Thomson scattering optical path, establish a quantitative relationship model between the centroid shift of the laser beam and the collection efficiency of the scattered light. Quantify the collection efficiency through the transmission coefficient T, and calculate the relative uncertainty of the transmission coefficient T using the centroid shift data. The transmission coefficient T is defined as the ratio of the effective scattering region to the maximum effective scattering region. The effective scattering region is the region where the fiber receiving range overlaps with the laser scatterer, and its size is related to the centroid shift of the laser beam in the X-axis direction.

2. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, In step 2, the background noise filtering is adaptive background noise filtering, which specifically involves: adaptively determining the background noise threshold based on the overall intensity of the light spot, and filtering out pixel data below the threshold to suppress the influence of ambient stray light and detector noise.

3. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, In step 3, the stray light removal process based on connected component analysis specifically includes: performing 4-neighborhood or 8-neighborhood connected component analysis on the filtered spot image data, calculating the connected component value of each pixel through a sliding window, identifying the main area of ​​the spot, and determining isolated pixels or small areas that are not connected to the main area of ​​the spot as stray light areas, setting their intensity values ​​to zero, thereby eliminating stray light interference while preserving the true shape of the spot.

4. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, In step 4, the weighted centroid method calculates the centroid coordinates by using the intensity value of each pixel as a weight. The specific calculation formula is as follows: the X coordinate of the centroid is equal to the sum of the products of the column coordinates of all pixels and their intensity values, divided by the sum of the intensity values ​​of all pixels; the Y coordinate of the centroid is equal to the sum of the products of the row coordinates of all pixels and their intensity values, divided by the sum of the intensity values ​​of all pixels.

5. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, In step 4, the statistical analysis of the centroid positions of multiple continuous pulses specifically involves: continuously acquiring the spot intensity distribution data of multiple laser pulses, calculating the centroid coordinates of each pulse, and statistically analyzing these centroid coordinate sequences to calculate the standard deviation of the centroid displacement in the X-axis and Y-axis directions and the azimuth angle, thereby obtaining the beam pointing stability parameters.

6. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, The centroid offset of the laser beam in the X-axis direction follows a one-dimensional normal distribution.

7. The method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis according to claim 1, characterized in that, In step 5, when calculating the relative uncertainty of the transmission coefficient T, based on the error propagation principle, the standard deviation of the centroid displacement in the beam pointing stability parameter is used as input, and the relative uncertainty of the transmission coefficient T is calculated through the quantitative relationship model.

8. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When one or more programs are executed by the one or more processors, the one or more processors implement the method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis as described in any one of claims 1-7.

9. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed by a processor, enable the processor to implement the method for quantifying the uncertainty of scattered light intensity measurement based on spot stability analysis as described in any one of claims 1-7.

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