Discharge stability evaluation method and system for laser and laser

Abstract

This application provides a method, system, and laser for evaluating the discharge stability of a laser. The discharge stability evaluation method includes: acquiring a discharge image of the laser; converting the discharge image into a grayscale image; acquiring the grayscale value of each pixel in the grayscale image; calculating the root mean square of the grayscale value gradient fluctuation; calculating the highlight channel value of the grayscale image; and adding the root mean square of the grayscale value gradient fluctuation and the highlight channel value to obtain the discharge instability value. The laser discharge stability evaluation method provided in this embodiment can quantitatively evaluate the discharge stability of the laser, improve the intuitiveness and accuracy of the laser discharge stability evaluation, and enable users to adjust the laser parameters according to the laser discharge instability value to improve the discharge quality of the laser, thereby improving the stability of the laser's output energy.

Description

Technical Field

[0001] This application relates to the field of laser technology, and in particular to a method, system and laser for evaluating the discharge stability of a laser. Background Technology

[0002] An excimer laser is a pulsed laser that uses a mixture of rare and halogen gases discharged in a high-voltage electric field to generate an excimer excited state, which then emits ultraviolet light of a specific wavelength. Excimer lasers are widely used in medical, semiconductor manufacturing, flat panel display manufacturing, and laser projection exposure fields, characterized by high laser output power and high repetition rate. The discharge stability of an excimer laser directly affects the stability of its laser output energy. For example, in laser projection exposure applications, unstable laser energy output can lead to poor exposure uniformity, low projection exposure resolution, and low yield. Therefore, evaluating the discharge stability of excimer lasers is of great significance. Summary of the Invention

[0003] This application provides a method and system for evaluating the discharge stability of a laser, which can quantitatively evaluate the discharge stability of a laser.

[0004] In a first aspect, this application provides a method for evaluating the discharge stability of a laser, comprising:

[0005] Acquire discharge images of the laser;

[0006] Convert the discharge image into a grayscale image;

[0007] Obtain the grayscale value of each pixel in the grayscale image;

[0008] Calculate the root mean square of the grayscale gradient fluctuation;

[0009] Calculate the highlight channel value k of the grayscale image;

[0010] The root mean square of the grayscale gradient fluctuation is added to the high-brightness channel value k to obtain the discharge instability value.

[0011] The laser discharge stability evaluation method provided in this embodiment can quantitatively evaluate the discharge stability of the laser. The quality of the laser's discharge stability can be judged by the magnitude of the discharge instability value. This improves the intuitiveness and accuracy of the laser discharge stability evaluation, allowing users to adjust the laser parameters according to the laser's discharge instability value to improve the laser's discharge quality and thus enhance the stability of the laser's output energy.

[0012] In one possible implementation, the discharge image is a color image, comprising a plurality of RGB pixels, and the grayscale image comprises a plurality of grayscale pixels, wherein the plurality of RGB pixels correspond one-to-one with the plurality of grayscale pixels. The step "converting the discharge image into a grayscale image" includes: converting each of the RGB pixels into a grayscale pixel according to a first calculation formula.

[0013] The first calculation formula is: I = 0.299*R + 0.587*G + 0.114*B, where R is the intensity value of the red light of the pixel, G is the intensity value of the green light of the pixel, B is the intensity value of the blue light of the pixel, and I is the gray value of the corresponding gray pixel.

[0014] In this embodiment, by converting the color discharge image into a grayscale image and then processing it, the image processing and analysis methods can be simplified, and the complexity of calculating the discharge instability value can be reduced.

[0015] In one possible implementation, the step "calculating the root mean square of the grayscale gradient fluctuation" includes:

[0016] The grayscale value distribution I(x) of the grayscale image in the first direction is calculated according to the second calculation formula. i );

[0017] The grayscale gradient fluctuation is calculated using the third calculation formula.

[0018] The root mean square of the grayscale gradient fluctuation is calculated according to the fourth calculation formula.

[0019] In the grayscale image, each pixel is arranged in an array along the first direction and the second direction. The first direction is parallel to the length direction of the discharge electrode in the laser, and the second direction is parallel to the height direction of the discharge electrode in the laser.

[0020] The second calculation formula is: The third calculation formula is: The fourth calculation formula is: x i Let z be the coordinate of the pixel in the first direction. j Let be the coordinates of the pixel in the second direction.

[0021] It should be noted that during laser discharge, the discharge intensity difference along the first direction is more significant, while the difference along the second direction is smaller. In this embodiment, the average grayscale intensity of multiple pixels at different positions in the second direction at the same position in the first direction can be obtained according to the second calculation formula. In this way, the grayscale value distribution can be transformed from two dimensions to one dimension, thereby further simplifying the calculation steps for discharge instability values.

[0022] In the third calculation formula, dI(x) i ) / dx i For the function I(x) i The differential function of dI(x1) / dx1 represents the rate of change of the gray value with respect to the horizontal coordinate x. Furthermore, in this embodiment, the gradient fluctuation of the gray value is obtained by squared dI(x1) / dx1. It can remove the positive and negative differences in the rate of change of grayscale values.

[0023] In this embodiment, the root mean square of the grayscale value gradient fluctuation is calculated using the third calculation formula. This can be understood as the degree of fluctuation in the grayscale value gradient. The root mean square of the grayscale value gradient fluctuation. The larger the value, the greater the variation in grayscale gradient. The greater the fluctuation, that is, the more unstable the grayscale value change along the first direction. The root mean square of the grayscale value gradient fluctuation. The smaller the value, the greater the variation in grayscale gradient. The smaller the fluctuation, that is, the more stable the gray value change along the first direction.

[0024] In one possible implementation, the highlight channel value k of the grayscale image is calculated using a fifth calculation formula. The fifth calculation formula is: Where, a is the fitting coefficient, and the value of a ranges from 2 to 5; N I(xi)≥240 The grayscale value I(x) of the grayscale image in the first direction. i The number of data points with a grayscale value greater than 240 in N. i The grayscale value I(x) of the grayscale image in the first direction. i The number of all data points.

[0025] It should be noted that the larger the proportion of the bright channel in the discharge image, the worse the discharge instability. In this embodiment, by calculating the value of the bright channel in the discharge image, the accuracy of the discharge instability value can be further improved.

[0026] In one possible implementation, before the step of "calculating the root mean square of the grayscale gradient fluctuation", the discharge stability evaluation method further includes:

[0027] The grayscale image is denoised according to the sixth calculation formula;

[0028] The sixth calculation formula is:

[0029] Where I0 is the grayscale value of the grayscale image before noise reduction, G is the Gaussian function, and I σ The grayscale value is the result of noise reduction processing. In the step "Calculate the root mean square of the grayscale value gradient fluctuation", the root mean square of the grayscale value gradient fluctuation is the root mean square of the gradient fluctuation of the grayscale value after noise reduction processing.

[0030] In this embodiment, by performing noise reduction processing on the grayscale image, the influence of noise on the discharge image on the discharge instability value can be reduced, thereby improving the accuracy of the discharge instability value obtained by the evaluation method of this application. In other words, the evaluation method provided by this application can improve the accuracy of the discharge instability evaluation of the excimer laser.

[0031] In one possible implementation, before the step of "obtaining the grayscale value of each pixel in the grayscale image", the discharge stability evaluation method further includes: selecting a rectangular region in the grayscale image, wherein the rectangular region is located in the middle region of the grayscale image in the second direction.

[0032] Specifically, the rectangular region is located between the cathode and anode, but does not include the cathode and anode. It should be noted that during excimer laser discharge, there will be some bright spots, or hot spots, on the cathode and anode, and the size of these hot spots varies under different discharge conditions. In this embodiment, by selecting the rectangular region between the cathode and anode in the grayscale image for image processing and analysis, the interference of bright hot spots on the electrodes on the image processing and analysis results can be reduced or even avoided, and the location and width of differences in discharge uniformity can be reduced or even avoided, thus improving the accuracy of discharge stability evaluation.

[0033] In one possible implementation, in the step of "acquiring discharge images of the excimer laser," the discharge images are multiple. The discharge stability evaluation method further includes:

[0034] Store multiple of the aforementioned discharge images;

[0035] The discharge instability value for each of the discharge images is calculated sequentially.

[0036] The multiple discharge images can be discharge images under different discharge conditions. The discharge stability evaluation method provided in this embodiment can sequentially calculate the discharge instability value of each discharge image, allowing users to compare the impact of different discharge conditions on discharge stability based on the discharge instability values ​​under different discharge conditions.

[0037] In one possible implementation, before the step of "sequentially calculating the discharge instability value for each of the discharge images", the discharge stability evaluation method further includes:

[0038] Obtain the folder path where the discharge image file is located;

[0039] Read the discharge image and convert it into a grayscale image;

[0040] Determine whether the discharge image is the first discharge image. If the discharge image is the first discharge image, select a rectangular region in the grayscale image corresponding to the first discharge image. If the discharge image is not the first discharge image, select a rectangular region at the same position based on the position information of the rectangular region selected in the grayscale image corresponding to the first discharge image.

[0041] Obtain the grayscale value of each pixel within the rectangular area and store it in a structure array;

[0042] Determine whether the discharge image is the last discharge image. If the discharge image is not the last discharge image, proceed to the step "read the discharge image and convert the discharge image into a grayscale image". If the discharge image is the last discharge image, sequentially obtain the grayscale value of each pixel in the rectangular area corresponding to each discharge image in the structure array, and calculate the discharge instability value.

[0043] In this embodiment, by selecting a rectangular region at the same location in the grayscale images corresponding to multiple discharge images, the influence of different discharge locations on the discharge instability value can be reduced or even avoided, thereby further improving the accuracy of discharge stability evaluation.

[0044] Secondly, this application provides a discharge stability evaluation system for a laser, comprising:

[0045] Image acquisition module, the image acquisition module being used to acquire discharge images of the laser;

[0046] An image processing module is used to convert the discharge image into a grayscale image;

[0047] The data processing module is used to acquire the grayscale value of each pixel in the grayscale image and calculate the root mean square of the grayscale value gradient fluctuation; the data processing module is also used to calculate the highlight channel value of the grayscale image and add the highlight channel value and the root mean square of the grayscale value gradient fluctuation to obtain the discharge instability value.

[0048] The laser discharge stability evaluation system provided in this embodiment can quantitatively evaluate the discharge stability of a laser. The quality of the laser's discharge stability can be determined by the magnitude of the discharge instability value. This improves the intuitiveness and accuracy of the laser discharge stability evaluation, allowing users to adjust the laser parameters based on the laser's discharge instability value to improve the laser's discharge quality and thus enhance the stability of the laser's output energy.

[0049] In one possible implementation, the laser discharge stability evaluation system further includes a storage module. The image acquisition module is used to acquire discharge images of the laser under different discharge conditions. The storage module is used to store the discharge images of the laser under different discharge conditions.

[0050] The discharge stability evaluation system provided in this embodiment can acquire discharge images of the laser under different discharge conditions and calculate the discharge instability value under different discharge conditions, thereby evaluating the discharge instability under different discharge conditions.

[0051] Thirdly, this application provides a laser. The laser includes a discharge cavity and the aforementioned discharge stability evaluation system. An imaging window is provided on the side wall of the discharge cavity, and the image acquisition module acquires discharge images of the laser through the imaging window.

[0052] In this embodiment, by setting a shooting window on the side wall of the anti-electrocution cavity, the image acquisition module can directly acquire the discharge image of the laser through the shooting window, which can facilitate the acquisition of discharge images and simplify the structure of the discharge cavity and the laser.

[0053] In summary, the laser discharge stability evaluation method provided in this application can quantitatively evaluate the discharge stability of a laser. The magnitude of the discharge instability value can be used to determine the quality of the laser's discharge stability, which improves the intuitiveness and accuracy of the laser discharge stability evaluation. This allows users to adjust the laser parameters based on the laser's discharge instability value to improve the laser's discharge quality and thus enhance the stability of the laser's output energy. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application or the background art, the accompanying drawings used in the embodiments of this application or the background art will be described below.

[0055] Figure 1 This is a simplified diagram of the laser structure, which includes the discharge stability evaluation system for the laser provided in this application.

[0056] Figure 2This is a simplified structural diagram of a laser, including the discharge stability evaluation system for the laser provided in this application, from another angle.

[0057] Figure 3 This is a flowchart of the laser discharge stability evaluation method provided in this application;

[0058] Figure 4 yes Figure 3 The detailed process of step S3 in the discharge stability evaluation method shown;

[0059] Figure 5 In one implementation method Figure 3 The grayscale image obtained in step S2 of the discharge stability evaluation method shown;

[0060] Figure 6 The method shown in step S41 is used to... Figure 5 The grayscale image shown is processed to obtain I(x) i A graph showing how the coordinates change with the first direction;

[0061] Figure 7 The method shown in step S42 is used to... Figure 6 As shown, I(x) i The curve graph is processed to obtain [dI(x)]. i ) / dx i ] 2 With coordinate x i A graph showing the changes;

[0062] Figure 8 This is a flowchart of a laser discharge stability evaluation method provided in another embodiment of this application;

[0063] Figure 9 yes Figure 8 The flowchart of step S9' in the method for evaluating the discharge stability of an excimer laser is shown.

[0064] Figure 10a Is adopted Figure 8 The curve of discharge instability value versus discharge voltage obtained by the discharge stability evaluation method shown is presented.

[0065] Figure 10b Is adopted Figure 8 The graph shows the change of discharge instability value with discharge repetition frequency obtained by the discharge stability evaluation method shown.

[0066] Figure 11 In one implementation, it is the grayscale image corresponding to the discharge image obtained in step S1'.

[0067] Figure 12 Under different discharge voltages, the following methods are used: Figure 8The graph shows a normalized comparison between the discharge instability value obtained by the discharge stability evaluation method and the actual measured energy stability 3σ. Detailed Implementation

[0068] The embodiments of this application are described below with reference to the accompanying drawings.

[0069] This application provides a method, system, and laser for evaluating the discharge stability of a laser. The method and system are used to evaluate the discharge stability of a laser, enabling users to adjust laser parameters, such as electrode design, electrode spacing, gas composition and ratio, based on the laser's discharge quality, thereby improving the discharge quality and thus enhancing the stability of the laser's output energy. Specific embodiments are described in detail below with reference to the accompanying drawings.

[0070] Please see Figure 1 , Figure 1 This is a simplified structural diagram of a laser 100 that includes the discharge stability evaluation system 20 provided in this application.

[0071] The laser 100 includes a discharge stability evaluation system 20. The discharge stability evaluation system 20 is used to acquire discharge image information of the laser 100 and process the discharge image information to obtain the discharge instability value of the laser 100. Users can judge the discharge stability of the laser 100 based on the discharge instability value. It should be noted that the discharge instability value reflects the stability of the discharge process of the laser 100. The larger the value of the discharge instability value, the more unstable the discharge of the laser 100; the smaller the value of the discharge instability value, the more stable the discharge of the laser 100.

[0072] In this embodiment, laser 100 is an excimer laser. An excimer laser is a pulsed laser that uses a mixture of rare and halogen gases discharged in a high-voltage electric field to generate an excimer excited state, thereby emitting ultraviolet light of a specific wavelength. Laser 100 can be a single-cavity excimer laser or a dual-cavity excimer laser. A single-cavity excimer laser has a discharge cavity, which is both the laser generation region and part of the resonant cavity. When laser 100 is a single-cavity excimer laser, the discharge stability evaluation system 20 is used to acquire discharge images of the discharge cavity and process these images to obtain discharge instability values.

[0073] A dual-cavity excimer laser generates amplified laser light through the coordinated operation of a master oscillation cavity and a power amplification cavity. The laser produced by a dual-cavity excimer laser has the advantages of high power and narrow linewidth. When the laser 100 is a dual-cavity excimer laser, the discharge stability evaluation system 20 can be used to acquire discharge images of the power amplification cavity, the master oscillation cavity, or both simultaneously.

[0074] The following description is based solely on the scenario of a single-cavity excimer laser, but this does not constitute any limitation on the scope of protection of this invention.

[0075] Please combine Figure 2 , Figure 2 This is a simplified structural diagram of the laser 100, which includes the discharge stability evaluation system 20 provided in this application, from another angle.

[0076] The laser 10 in this embodiment is a single-cavity excimer laser. The laser 100 includes a discharge cavity 11, a control module 12, and a high-voltage discharge module 13. The discharge cavity 11 includes discharge electrodes 112. The discharge electrodes 112 include a cathode 113 and an anode 114. The cathode 113 and anode 114 are spaced apart and parallel to each other within the discharge cavity 11 and are electrically connected to the high-voltage discharge module 13. The discharge cavity 11 is also filled with a working gas. The working gas is a mixture of halogen elements (such as fluorine, chlorine, etc.) and inert gases (such as argon, krypton, xenon, etc.). The high-voltage discharge module 13 is used to receive external trigger signals, generate pulse voltages according to a set discharge voltage value, and transmit the pulse voltages to the cathode 113 and anode 114. Under the action of the pulse voltages, the cathode 113 and anode 114 excite the working gas located between them to discharge and generate laser light. Specifically, the working gas forms excimers (such as argon fluoride, krypton fluoride, xenon chloride, etc.) under the action of pulse voltage. These excimers will rapidly dissociate in the excited state and release ultraviolet light of a specific wavelength, that is, generate laser.

[0077] For ease of description, in this application, the length direction of the discharge electrode 112 is defined as the first direction X, the height direction as the second direction Z, and the width direction as the third direction Y. The first direction X, the second direction Z, and the third direction Y are all perpendicular to each other.

[0078] In this embodiment, the side wall of the discharge cavity 11 is provided with an imaging window 115. The discharge stability evaluation system 20 can acquire discharge images inside the discharge cavity 11 through the imaging window 115. The imaging window 115 can be a through hole or a transparent window located on the side of the cavity 111.

[0079] The discharge cavity 11 of the laser 100 also includes a fan 14, an electrostatic precipitator, and a water cooling system. The water cooling system uses circulating cooling water to remove heat generated during laser operation, preventing overheating and ensuring stable operation. The electrostatic precipitator is connected to the cavity of the discharge cavity 11. The fan 14 is used to clean metal fluoride particle contamination generated between the cathode 113 and the anode 114, thereby improving the performance of the discharge cavity 11. The electrostatic precipitator is used to remove impurities and dust particles generated during the discharge of the working gas within the discharge cavity 11 of the laser 100, ensuring the purity of the working gas and thus improving the performance and energy efficiency of the laser 100.

[0080] The fan 14, electrostatic precipitator, and water cooling system are electrically connected to the control module 12. The control module 12 controls the operating status of the fan 14, electrostatic precipitator, and water cooling system, and prepares them before the laser 100 is put into operation.

[0081] The laser 100 also includes a linewidth narrowing module 15, an output coupling mirror 16, and a detection module 17. The output coupling mirror 16 is located on one side of the discharge cavity 11, and the detection module 17 is located on the side of the output coupling mirror 16 facing away from the discharge cavity 11. The laser generated by the discharge cavity 11 first enters the output coupling mirror 16 and then the detection module 17, and then is output to the outside of the laser 100 through the laser shutter. The detection module 17 is used to detect the energy and spectrum of the laser output by the laser 100, and to monitor the performance of the system in real time. It also feeds the signal back to the control module 12 so that the control module 12 can control the discharge voltage, etc., based on the detection results of the detection module 17.

[0082] The linewidth narrowing module 15 is connected to the discharge cavity 11. The linewidth narrowing module 15 is used to control the spectral width of the laser to improve its coherence and stability. Specifically, the laser generated by the discharge cavity 11 enters the linewidth narrowing module 15, which selects the spectrum of the excimer laser, and then the selected excimer laser returns to the discharge cavity 11 for further amplification.

[0083] The discharge stability evaluation system 20 is used to evaluate the discharge stability of the laser 100 to obtain the discharge instability value of the laser 100. The discharge stability evaluation system 20 includes an image acquisition module 21, an image processing module 22, and a data processing module 23. The image acquisition module 21 is used to acquire discharge image information of the laser 100. Specifically, the image acquisition module 21 can be a high-speed camera. When acquiring discharge images, the high-speed camera can be placed on the side of the discharge cavity 11, and the lens of the high-speed camera can be aimed at the imaging window 115 located on the side wall of the discharge cavity 11 to capture the discharge image near the discharge electrode 112 inside the discharge cavity 11.

[0084] In this embodiment, by setting an imaging window 115 on the side wall of the discharge cavity 11, the image acquisition module 21 can directly acquire the discharge image of the laser 100 through the imaging window 115, which can facilitate the acquisition of discharge images and simplify the structure of the discharge cavity 11 and the laser 100.

[0085] It should be noted that, in this embodiment, the discharge image acquired by the image acquisition module 21 is a color image, including three color channels: red, green, and blue (R, G, B). Each pixel has a corresponding RGB value.

[0086] The discharge stability evaluation system 20 also includes a storage module (not shown). The storage module is connected to the image acquisition module 21. The storage module is used to acquire and store the discharge image information acquired by the image acquisition module 21.

[0087] Image processing module 22 is used to acquire a discharge image and convert it into a grayscale image. Data processing module 23 is used to acquire the grayscale image obtained by image processing module 22 and obtain discharge instability values ​​based on the grayscale image. Specifically, data processing module 23 is used to acquire the grayscale value of each pixel in the grayscale image and calculate the root mean square of the grayscale value gradient fluctuation. Simultaneously, data processing module 23 is also used to calculate the highlight channel value of the grayscale image and add the highlight channel value and the root mean square of the grayscale value gradient fluctuation to obtain the discharge instability value.

[0088] The discharge stability evaluation system 20 for laser 100 provided in this embodiment can quantitatively evaluate the discharge stability of laser 100. The quality of the discharge stability of laser 100 can be judged by the magnitude of the discharge instability value. This improves the intuitiveness and accuracy of the discharge stability evaluation of laser 100, allowing users to adjust the parameters of laser 100 according to the discharge instability value to improve the discharge quality of laser 100 and thus improve the stability of the output energy of laser 100.

[0089] Please see Figure 3 , Figure 3 This is a flowchart of the laser discharge stability evaluation method provided in this application.

[0090] The method for evaluating the discharge stability of a laser includes the following steps:

[0091] S1: Acquire the discharge image of the laser;

[0092] S2: Convert the discharge image into a grayscale image;

[0093] S3: Obtain the grayscale value of each pixel in the grayscale image;

[0094] S4: Calculate the root mean square of the grayscale gradient fluctuation;

[0095] S5: Calculate the highlight channel value of the grayscale image;

[0096] S6: Add the root mean square of the grayscale gradient fluctuation to the high-brightness channel value to obtain the discharge instability value.

[0097] In step S1, the discharge image is obtained through... Figure 1 The image is acquired by the image acquisition module 21 shown. In this embodiment, the discharge image is a color image, including three color channels: R, G, and B. The discharge image includes multiple pixels. The multiple pixels are arranged in an array along the first direction X and the second direction Z.

[0098] In step S2, the discharge image is converted into a grayscale image using a weighted average method. The RGB value of each pixel in the discharge image is multiplied by the weight of its corresponding color channel, and then the three products are summed to obtain the grayscale value. Specifically, the color discharge image is converted into a grayscale image using the first calculation formula.

[0099] The first calculation formula is: Gray value = 0.299*R + 0.587*G + 0.114*B

[0100] Where R is the intensity value of red light at the pixel, G is the intensity value of green light at the pixel, and B is the intensity value of blue light at the pixel. The values ​​of R, G, and B range from 0 to 255.

[0101] It should be noted that color images have three color channels, while grayscale images have only one color channel. In this embodiment, by converting the color discharge image to a grayscale image and then processing it, the image processing and analysis methods can be simplified, and the complexity of calculating discharge instability can be reduced.

[0102] Please combine Figure 4 , Figure 4 yes Figure 3 The detailed process of step S3 in the discharge stability evaluation method shown is as follows.

[0103] Step S3 includes:

[0104] S31: Perform noise reduction on the grayscale image according to the sixth calculation formula; the sixth calculation formula is: I σ =I0*G σ ;

[0105] Where I0 is the grayscale value, G is the Gaussian function, and I σ This represents the grayscale value after the convolution operation. It can be understood that I... σ This represents the grayscale value after noise reduction. For simplified calculations, I will be used to denote I in the following text.σ This refers to the grayscale value after noise reduction. In this embodiment, by performing noise reduction processing on the grayscale image, the influence of noise on the discharge instability value can be reduced, improving the accuracy of the discharge instability value obtained by the evaluation method of this application, which in turn improves the accuracy of the evaluation method provided by this application for evaluating the discharge instability of the laser 100.

[0106] S32: Select a rectangular region A in the grayscale image.

[0107] Please combine Figure 5 , Figure 5 In one implementation method Figure 3 The grayscale image obtained in step S2 of the discharge stability evaluation method shown is illustrated. Rectangular region A is located in the middle region of the grayscale image along the second direction Z. Specifically, rectangular region A is located between the cathode 113 and the anode 114, but does not include the cathode 113 and anode 114. That is, the cathode 113 and anode 114 are located outside rectangular region A. It should be noted that during laser discharge, there will be some bright spots, i.e., hot spots, on the cathode 113 and anode 114, and the size of these hot spots on the discharge electrode 112 varies under different discharge conditions. In this embodiment, by selecting the rectangular region A located between the cathode 113 and anode 114 in the grayscale image for image processing and analysis, the interference of bright hot spots on the electrodes on the image processing and analysis results can be reduced or even avoided, thus improving the accuracy of the discharge stability evaluation.

[0108] S33: Obtain the grayscale value I(x) of each pixel within the rectangular region A. i , z j ).

[0109] Where, x i Let z be the coordinates of the pixel in the first direction X, and z be the coordinates of the pixel in the first direction X. j Let Z be the coordinates of the pixel in the second direction.

[0110] Please combine Figure 3 Step S4 includes:

[0111] S41: Calculate the grayscale value distribution I(x) of the grayscale image in the first direction X according to the second calculation formula. i The second calculation formula is:

[0112] Please combine Figure 6 , Figure 6 The method shown in step S41 is used to... Figure 5 The grayscale image shown is processed to obtain I(x) i A curve showing how the coordinates change with the first horizontal direction (X).

[0113] Where I(x) i That is, the grayscale value varies with the coordinate x in the first direction X. i The function of change. It should be noted that when the laser 100 discharges, the difference in discharge intensity along the first direction X is more obvious, while the difference in discharge intensity along the second direction Z is smaller. That is, in the grayscale image, when the position of the first direction X is the same, the difference in grayscale value of different pixels along the second direction Z is small; when the position of the second direction Z is the same, the difference in grayscale value of different pixels along the first direction X is large.

[0114] In this embodiment, the average gray intensity of multiple pixels at different positions in the second direction Z at the same position in the first direction X can be obtained according to the second calculation formula. In this way, the gray value distribution can be transformed from two dimensions to one dimension, thereby further simplifying the calculation steps of discharge instability value.

[0115] For example: This represents the average grayscale value of N pixels along the second direction Z when the coordinate of the first direction X is x1.

[0116] S42: Calculate the grayscale gradient fluctuation according to the third calculation formula. The third calculation formula is:

[0117] Please combine Figure 7 , Figure 7 The method shown in step S42 is used to... Figure 6 As shown, I(x) i The curve graph is processed to obtain [dI(x)]. i ) / dx i ] 2 With coordinate x i A graph showing the changes.

[0118] As can be seen from step S42, the function I(x) i dI(x) is a function that describes the change in grayscale value as the coordinate x changes in the first direction X. In this embodiment, dI(x) i ) / dx i For the function I(x) i The differential function of dI(x1) / dx1 represents the rate of change of the gray value with respect to the coordinate x in the first direction X. For example, dI(x1) / dx1 represents the rate of change of the gray value when the coordinate in the first direction X is x1. Furthermore, in this embodiment, the gradient fluctuation of the gray value is obtained by squaring dI(x1) / dx1. It can remove the positive and negative differences in the rate of change of grayscale values. For example, This represents the gradient fluctuation of the grayscale value when the coordinate in the first direction X is x1. That is, it is the function of the rate of change of grayscale value as the coordinate x in the first direction X changes.

[0119] S43: Calculate the root mean square of the grayscale gradient fluctuation according to the fourth calculation formula. The fourth calculation formula is:

[0120]

[0121] It should be noted that the function obtained in step S42 The function graph has multiple peaks. In this embodiment, the root mean square of the grayscale gradient fluctuation is calculated using the fourth calculation formula. This can be understood as the degree of fluctuation in the grayscale value gradient. The root mean square of the grayscale value gradient fluctuation. The larger the value, the greater the variation in grayscale gradient. The greater the fluctuation, that is, the more unstable the grayscale value change along the first direction X. The root mean square of the grayscale value gradient fluctuation. The smaller the value, the greater the variation in grayscale gradient. The smaller the fluctuation, that is, the more stable the gray value change along the first direction X.

[0122] In step S5, the highlight channel value k in the grayscale image is calculated using the fifth calculation formula. The fifth calculation formula is:

[0123]

[0124] Where 'a' is the fitting coefficient. The value of 'a' ranges from 2 to 5. In this embodiment, 'a' = 5. I(xi)≥240 N refers to the number of data points with a grayscale intensity greater than 240. i This refers to the total number of data points analyzed in the first direction X. The highlight channel value k can be understood as the weight of the highlight channel within the selected rectangular region. Specifically, step S5 can be performed based on step S41. That is, when calculating the highlight channel value of the grayscale image, the grayscale value distribution I(x) of the grayscale image in the first direction X can be calculated first according to the second calculation formula. i Then, the highlight channel value k in the grayscale image is calculated using the fifth calculation formula to simplify the calculation method of the highlight channel value k.

[0125] It should be noted that the larger the proportion of the bright channel in the discharge image, the worse the discharge instability. In this embodiment, by calculating the value of the bright channel in the discharge image, the accuracy of the discharge instability value can be further improved.

[0126] In step S6, the discharge instability value The larger the discharge instability value Ψ, the worse the discharge instability; the smaller the discharge instability value Ψ, the better the discharge instability, that is, the more stable the discharge.

[0127] The discharge stability evaluation method for laser 100 provided in this embodiment can quantitatively evaluate the discharge stability of laser 100. The magnitude of the discharge instability value Ψ can be used to determine the quality of the discharge stability of laser 100, which can improve the intuitiveness and accuracy of the discharge stability evaluation of laser 100. Furthermore, it allows users to adjust the parameters of laser 100 based on the discharge instability value, such as the design of discharge electrode 112, the spacing between cathode 113 and anode 114, and the composition and ratio of working gas, to improve the discharge quality of laser 100 and thus improve the stability of the output energy of laser 100.

[0128] Please combine Figure 8 , Figure 8 This is a flowchart of a method for evaluating the discharge stability of a laser 100 provided in another embodiment of this application.

[0129] This embodiment and Figure 3 The difference in the illustrated embodiment is that the discharge stability evaluation method of the laser 100 provided in this embodiment evaluates the discharge stability of multiple discharge images.

[0130] Methods for evaluating the discharge stability of lasers include:

[0131] S1': Acquire and store multiple discharge images of laser 100;

[0132] S2': Get the folder path where the discharge image file is located;

[0133] S3': Read the discharge image and convert it into a grayscale image;

[0134] S4': Determine whether the discharge image is the first discharge image. If the discharge image is the first discharge image, proceed to step S5'; if the discharge image is not the first discharge image, proceed to step S6'.

[0135] S5': Select a rectangular area in the grayscale image corresponding to the first discharge image;

[0136] S6': Select a rectangular region at the same location based on the position information of the rectangular region selected from the grayscale image corresponding to the first discharge image;

[0137] S7': Obtain the grayscale values ​​of each pixel within the rectangular area of ​​the grayscale image selected in step S5' or step S6', and store them in a structure array;

[0138] S8': Determine whether the discharge image is the last discharge image. If the discharge image is not the last discharge image, proceed to step S3'; if the discharge image is the last discharge image, proceed to step S9'.

[0139] S9': Obtain the grayscale value of each pixel within the rectangular region corresponding to each discharge image in the structure array, and calculate the discharge instability value.

[0140] In step S1', the multiple discharge images are discharge images under different discharge conditions. Different discharge conditions can be different discharge voltages, different discharge frequencies, different electrode spacings, or different compositions and ratios of the working gas.

[0141] Specifically, in step S1', a camera can be used to collect the overall discharge situation along the axial length of the electrode when the laser 100 is working, capture a spatiotemporal integrated discharge image, obtain the discharge situation corresponding to each laser pulse, and thus obtain discharge images under different discharge conditions.

[0142] In step S1', multiple discharge images are stored using a storage module.

[0143] In step S3', refer to Figure 3 The method in step S2 of the illustrated embodiment, which converts the discharge image into a grayscale image, will not be described in detail here.

[0144] In step S5', refer to Figure 4 In step S32, a rectangular region is selected in the grayscale image corresponding to the first discharge image. The selected rectangular region is located in the middle region of the grayscale image along the second direction Z. Specifically, the rectangular region is located between the cathode 113 and the anode 114, but does not include the cathode 113 and the anode 114. This reduces or even eliminates the interference of bright hot spots on the electrodes on the image processing and analysis results, and reduces or even eliminates the location and width of differences in discharge uniformity, thus improving the accuracy of discharge stability evaluation.

[0145] In step S6', the rectangular region selected in the grayscale image corresponding to the Nth discharge image is located at the same position as the rectangular region selected in the grayscale image corresponding to the first discharge image. This reduces or even eliminates the impact of different analysis locations on the discharge instability value, further improving the accuracy of discharge stability evaluation. Here, N is a positive integer greater than 1.

[0146] In step S9', refer to Figure 3 and Figure 4The method of the embodiment shown performs discharge instability value processing on a rectangular region of a selected grayscale image.

[0147] For specific details, please refer to... Figure 9 , Figure 9 yes Figure 8 The flowchart of step S9' in the discharge stability evaluation method of the laser 100 shown.

[0148] Step S9' includes:

[0149] S91': Obtain the grayscale value I(x) of each pixel within the rectangular area. i , z j );

[0150] S92': Calculate the grayscale value distribution I(x) of the grayscale image in the first direction X according to the second calculation formula. i The second calculation formula is:

[0151] S93': Calculate the grayscale value gradient fluctuation according to the third calculation formula. The third calculation formula is:

[0152] S94': Calculate the root mean square of the grayscale gradient fluctuation according to the fourth calculation formula. The fourth calculation formula is:

[0153]

[0154] S95': Based on step S91', calculate the highlight channel value k in the grayscale image according to the fifth calculation formula. The fifth calculation formula is:

[0155]

[0156] S96': Root mean square of grayscale value gradient fluctuations Adding this to the high-brightness channel value k yields the discharge instability value Ψ.

[0157] When there are N discharge images obtained in step S1', there are N discharge instability values ​​Ψ obtained in step S96', with one discharge image corresponding to one discharge instability value Ψ.

[0158] The discharge stability evaluation method for laser 100 provided in this embodiment can quantitatively evaluate the discharge stability of laser 100. The magnitude of the discharge instability value Ψ can be used to determine the quality of the discharge stability of laser 100, which can improve the intuitiveness and accuracy of the discharge stability evaluation of laser 100. Furthermore, it allows users to adjust the parameters of laser 100 based on the discharge instability value, such as the design of discharge electrode 112, the spacing between cathode 113 and anode 114, and the composition and ratio of working gas, to improve the discharge quality of laser 100 and thus improve the stability of the output energy of laser 100.

[0159] Furthermore, the discharge stability evaluation method for the laser 100 provided in this embodiment can sequentially calculate the discharge instability value under different discharge conditions, thereby enabling quantitative analysis of the discharge stability under different discharge conditions, allowing users to more conveniently and intuitively compare the discharge stability under different discharge conditions.

[0160] Please see Figure 10a and Figure 10b , Figure 10a Is adopted Figure 8 The graph shown illustrates the variation of discharge instability values ​​with discharge voltage obtained using the discharge stability evaluation method. Figure 10b Is adopted Figure 8 The graph shows the change of discharge instability value with discharge repetition frequency obtained by the discharge stability evaluation method shown.

[0161] Depend on Figure 10a It can be seen that as the discharge voltage increases, the discharge instability value increases. That is, the higher the discharge voltage, the more unstable the discharge of laser 100.

[0162] Depend on Figure 10b It can be seen that as the discharge repetition frequency increases, the discharge instability value increases. That is, the higher the discharge repetition frequency, the more unstable the discharge of laser 100.

[0163] Please see Figure 11 , Figure 11 In one implementation, it is the grayscale image corresponding to the discharge image obtained in step S1'.

[0164] In this embodiment, three discharge images are obtained in step S1'. The three discharge images are the grayscale images corresponding to the first discharge image shown in Figure (a), the second discharge image shown in Figure (b), and the third discharge image shown in Figure (c). The discharge instability value Ψ1 of the first discharge image is 0.32, the discharge instability value Ψ2 of the second discharge image is 0.32, and the discharge instability value Ψ3 of the third discharge image is 3.13.

[0165] It should be noted that the more pronounced the evolution of the waterfall-like conical discharge between discharge electrodes 112 into a columnar, high-brightness channel, the worse the discharge stability. Combined with... Figure 11 As can be seen from Figure (a) to Figure (c), the evolution of the waterfall-like conical discharge between the discharge electrodes 112 into a columnar high-brightness channel becomes increasingly obvious, and the discharge stability becomes increasingly worse. Simultaneously, from Figure (a) to Figure (c), the discharge instability values ​​obtained through this embodiment become increasingly larger. Therefore, the discharge instability values ​​obtained by the discharge stability evaluation method of the laser 100 provided in this application correspond well to the phenomenon that the discharge contraction stability deteriorates when the waterfall-like conical discharge between the electrodes evolves into a columnar high-brightness channel.

[0166] Please see Figure 12 , Figure 12 Under different discharge voltages, the following methods are used: Figure 8 The graph shows a normalized comparison between the discharge instability value obtained by the discharge stability evaluation method and the actual measured energy stability 3σ.

[0167] Curve I is a graph showing the change of discharge instability value with voltage, and curve II is a graph showing the change of energy stability 3σ with voltage.

[0168] As shown in curve I, the discharge instability increases with increasing discharge voltage. That is, the higher the discharge voltage, the more unstable the discharge of laser 100. As shown in curve II, the energy stability 3σ increases with increasing discharge voltage.

[0169] It should be noted that the discharge instability of the discharge electrode 112 directly affects the pumping process of the laser 100, leading to a decrease in the stability of the laser energy output by the laser 100. The discharge instability value is strongly correlated with the stability of the laser energy output by the laser 100.

[0170] To further verify the rationality and accuracy of the discharge instability evaluation method provided in this application, this embodiment compares the changes in discharge instability value with voltage and the changes in energy stability 3σ with voltage. To facilitate comparison of the relationship between the changes in discharge instability value and energy stability 3σ with voltage, this embodiment normalizes the discharge instability values ​​at different discharge voltages with the actually measured energy stability 3σ to obtain curve I and curve II.

[0171] Comparing curves I and II, it can be seen that the trends of discharge instability value with voltage and energy stability 3σ with voltage are consistent and quite close. Therefore, the discharge instability value and energy stability 3σ are significantly correlated, further proving the rationality of the discharge instability evaluation method provided in this application. Moreover, the discharge instability value obtained by the discharge instability evaluation method provided in this application has high accuracy and can be used to quantitatively analyze the discharge stability of laser 100.

[0172] The above are merely some embodiments and implementation methods of this application. The scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for evaluating the discharge stability of a laser, characterized in that, include: Acquire discharge images of the laser; Convert the discharge image into a grayscale image; Obtain the grayscale value of each pixel in the grayscale image; Calculate the root mean square of the grayscale gradient fluctuation; Calculate the highlight channel value k of the grayscale image; The root mean square of the grayscale gradient fluctuation is added to the high-brightness channel value k to obtain the discharge instability value.

2. The method for evaluating the discharge stability of a laser according to claim 1, characterized in that, The discharge image is a color image, which includes multiple RGB pixels, and the grayscale image includes multiple grayscale pixels, with each of the multiple RGB pixels corresponding to one of the multiple grayscale pixels. The step "converting the discharge image into a grayscale image" includes: converting each RGB pixel into a grayscale pixel according to a first calculation formula; The first calculation formula is: I = 0.299*R + 0.587*G + 0.114*B, where R is the intensity value of the red light of the pixel, G is the intensity value of the green light of the pixel, B is the intensity value of the blue light of the pixel, and I is the gray value of the corresponding gray pixel.

3. The method for evaluating the discharge stability of a laser according to claim 1, characterized in that, The step "Calculate the root mean square of the grayscale gradient fluctuation" includes: The grayscale value distribution I(x) of the grayscale image in the first direction is calculated according to the second calculation formula. i ); The grayscale gradient fluctuation is calculated using the third calculation formula. The root mean square of the grayscale gradient fluctuation is calculated according to the fourth calculation formula. In the grayscale image, each pixel is arranged in an array along the first direction and the second direction. The first direction is parallel to the length direction of the discharge electrode in the laser, and the second direction is parallel to the height direction of the discharge electrode in the laser. The second calculation formula is: The third calculation formula is: The fourth calculation formula is: x i Let z be the coordinate of the pixel in the first direction. j Let be the coordinates of the pixel in the second direction.

4. The method for evaluating the discharge stability of a laser according to claim 1, characterized in that, The highlight channel value k of the grayscale image is calculated using the fifth calculation formula; The fifth calculation formula is: Where, a is the fitting coefficient, and the value of a ranges from 2 to 5; N I(xi)≥240 The grayscale value I(x) of the grayscale image in the first direction. i The number of data points with a grayscale value greater than 240 in N. i The grayscale value I(x) of the grayscale image in the first direction. i The number of all data points.

5. The method for evaluating the discharge stability of a laser according to claim 1, characterized in that, Before the step "calculating the root mean square of the grayscale gradient fluctuation", the discharge stability evaluation method further includes: The grayscale image is denoised according to the sixth calculation formula; The sixth calculation formula is: Where I0 is the grayscale value of the grayscale image before noise reduction, G is the Gaussian function, and I σ The grayscale value after noise reduction processing; In the step "Calculate the root mean square of grayscale gradient fluctuation", the root mean square of grayscale gradient fluctuation is the root mean square of the gradient fluctuation of the grayscale value after noise reduction.

6. The method for evaluating the discharge stability of a laser according to claim 3, characterized in that, Before the step of "obtaining the grayscale value of each pixel in the grayscale image", the discharge stability evaluation method further includes: A rectangular region is selected in the grayscale image, the rectangular region being located in the middle region of the grayscale image in the second direction.

7. The method for evaluating the discharge stability of a laser according to any one of claims 1 to 6, characterized in that, In the step "acquiring discharge images of the laser", the discharge images are multiple; The discharge stability evaluation method further includes: Store multiple of the aforementioned discharge images; The discharge instability value for each of the discharge images is calculated sequentially.

8. The method for evaluating the discharge stability of a laser according to claim 7, characterized in that, Before the step of "sequentially calculating the discharge instability value of each of the discharge images", the discharge stability evaluation method further includes: Obtain the folder path where the discharge image file is located; Read the discharge image and convert it into a grayscale image; Determine whether the discharge image is the first discharge image. If the discharge image is the first discharge image, select a rectangular region in the grayscale image corresponding to the first discharge image. If the discharge image is not the first discharge image, select a rectangular region at the same position based on the position information of the rectangular region selected in the grayscale image corresponding to the first discharge image. Obtain the grayscale value of each pixel within the rectangular area and store it in a structure array; Determine whether the discharge image is the last discharge image. If the discharge image is not the last discharge image, proceed to the step "read the discharge image and convert the discharge image into a grayscale image". If the discharge image is the last discharge image, sequentially obtain the grayscale value of each pixel in the rectangular area corresponding to each discharge image in the structure array, and calculate the discharge instability value.

9. A system for evaluating the discharge stability of a laser, characterized in that, include: An image acquisition module, which is used to acquire discharge images of the laser; An image processing module is used to convert the discharge image into a grayscale image; The data processing module is used to acquire the grayscale value of each pixel in the grayscale image and calculate the root mean square of the grayscale value gradient fluctuation; the data processing module is also used to calculate the highlight channel value of the grayscale image and add the highlight channel value and the root mean square of the grayscale value gradient fluctuation to obtain the discharge instability value.

10. The laser discharge stability evaluation system according to claim 9, characterized in that, It also includes a storage module. The image acquisition module is used to acquire discharge images of the laser under different discharge conditions; The storage module is used to store discharge images of the laser under different discharge conditions.

11. A laser comprising a discharge cavity, characterized in that, It also includes the discharge stability evaluation system for the laser as described in claim 9 or 10; the side wall of the discharge cavity is provided with an imaging window, and the image acquisition module acquires the discharge image of the laser through the imaging window.

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