Laser damage detection method and detection system based on light spot online monitoring system

Abstract

The application provides a kind of laser damage detection method and detection system based on light spot online monitoring system, utilizes existing light spot online monitoring system to collect laser light spot image in real time, extracts laser light spot profile and diffraction ring features in light spot by low-pass filtering and high-pass filtering technology, calculates the motion relationship of light spot centroid and diffraction ring centroid, and judges damage risk in combination with correlation coefficient.The method can efficiently detect early laser damage, avoid the great loss caused by the traditional way when obvious damage is found.Because the original light spot online monitoring system of the system is used, no additional detection equipment is added, so it has the advantages of low cost, real-time response and good effect, and is suitable for laser damage detection of large ultrafast ultrashort laser device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser damage detection, in particular to a laser damage detection method and system based on a light spot online monitoring system, which is suitable for optical element damage detection in large ultrafast ultrashort laser devices. BACKGROUND

[0002] In large ultrafast ultrashort laser devices, the light spot online monitoring system has become a standard configuration, and the number of its detection equipment often exceeds 50% of the total number of device equipment. However, the existing light spot monitoring system is mostly used for light spot quality detection, and does not utilize existing resources for laser damage judgment to achieve efficient integration of resources.

[0003] In existing large ultrafast ultrashort laser devices, the laser damage judgment method used usually has the following problems:

[0004] 1. Early damage detection capability is insufficient. The light spot of the optical element of the laser in the early damage stage often changes very weakly and is not obvious, and the existing detection method may not be able to accurately capture these subtle changes, so that early damage is difficult to be discovered in time.

[0005] 2. Lack of real-time monitoring capability. Some existing laser damage judgment methods rely on offline analysis and cannot provide real-time monitoring. This may cause the early warning window of early damage to be missed at critical moments, resulting in irreversible damage to the equipment, increasing maintenance costs and the risk of experiment interruption.

[0006] 3. High detection cost. Some high-sensitivity detection methods require the use of high-precision, expensive detection equipment or complex operations, which increases the construction and operation cost of the laser device, and is not conducive to wide application in large ultrafast ultrashort laser devices.

[0007] These problems show that the existing method is difficult to meet the needs of large ultrafast ultrashort laser devices for laser damage judgment, and an real-time, low-cost and high-sensitivity detection method is urgently needed to ensure the safety and stability of the equipment.

[0008] After searching, no similar scheme using light spot-diffraction ring double centroid motion analysis has been found, and no similar domestic and foreign data has been collected. SUMMARY

[0009] The present application is directed to the deficiencies in the prior art, and provides a kind of laser damage detection method and system based on light spot online monitoring system, when laser passes through damaged optical element, annular structure, i.e. diffraction ring, is generated by diffraction phenomenon, and diffraction ring is located in laser spot and its centroid moves synchronously with spot centroid.By monitoring and analyzing this relationship, it is judged whether optical element is damaged, with the advantages of low cost, real-time response and good effect, suitable for laser damage detection of large ultrafast ultrashort laser device.

[0010] The technical solution of the present application is as follows:

[0011] A kind of laser damage detection method based on light spot online monitoring system, characterized in that, comprising the following steps:

[0012] S1. utilize light spot online monitoring system to collect continuous laser spot image sequence in real time;

[0013] S2. low-pass filter processing and high-pass filter processing are carried out to the same frame laser spot image respectively;The low-pass filter processing is used to filter out high-frequency noise and background light interference, and extracts main spot profile base;The high-pass filter processing is used to enhance the high-frequency component in image, and highlight the diffraction ring structure generated by optical element damage;

[0014] S3. based on the image after low-pass filter processing in step (2), the centroid coordinates of main spot are calculated using gray weighted average algorithm;

[0015] S4. based on the image after high-pass filter processing in step (2), whether diffraction ring exists inside light spot is identified using contour detection algorithm: if exists, the centroid coordinates of the diffraction ring are calculated using gray weighted average algorithm;If not, return to step (1) and continue to collect monitoring;

[0016] S5. when diffraction ring exists in continuous multiple images, the motion trajectory data of main spot centroid and diffraction ring centroid in preset time window are extracted;

[0017] S6. the correlation coefficient between the motion trajectory of main spot centroid and diffraction ring centroid is calculated;

[0018] S7. the correlation coefficient calculated is compared with preset threshold value: when the correlation coefficient continuously exceeds preset threshold value, it is judged that optical element exists damage risk, and warning or control instruction is triggered.

[0019] Further, the low-pass filter includes image binarization, Gaussian filter, mean filter, Butterworth low-pass filter and bilateral filter.

[0020] Further, the high-pass filter includes image gradient calculation, Laplace filter and Gaussian high-pass filter.

[0021] Further, the calculation of the spot centroid coordinates (x0, y0) uses a weighted average of pixel intensity, with the formula:

[0022] x0= [∑(x·I(x,y))] / [∑I(x,y)]

[0023] y0= [∑(y·I(x,y))] / [∑I(x,y)]

[0024] where I(x, y) is the filtered pixel intensity value at coordinates (x, y).

[0025] The application also provides a laser damage detection system for implementing the above laser damage judgment method, characterized by comprising:

[0026] an image acquisition module composed of an existing spot online monitoring system;

[0027] an image processing module for performing low-pass filtering and high-pass filtering on the collected images in parallel;

[0028] a feature extraction module for calculating the spot centroid and the diffraction ring centroid;

[0029] a motion analysis module for analyzing the correlation of the double-centroid motion trajectories;

[0030] a decision output module for generating a control instruction according to the analysis result;

[0031] a control interface module for transmitting the control instruction to a laser device control system.

[0032] Compared with the prior art, the application has the following technical effects:

[0033] 1) The existing spot monitoring system in the device is used without additional hardware, and the single-point modification cost is low, which is suitable for deployment of large-scale ultrafast and ultrashort laser devices.

[0034] 2) By using the combination of low-pass and high-pass filtering, the weak diffraction signal caused by damage can be effectively separated and enhanced, the early damage can be captured sensitively, and the problem that the traditional method cannot identify weak changes is solved, so that the damage discovery time is greatly advanced.

[0035] 3) The judgment is based on the physical motion relationship between the spot and the diffraction ring, has strong anti-interference ability and high reliability. At the same time, the core algorithm does not depend on specific optical elements or optical path structures, has good universality, and can be widely applied to health monitoring of optical systems of various large-scale ultrafast and ultrashort laser devices.

[0036] 4) The method is suitable for various optical elements and is widely applicable to detection and tracking of large-scale ultrafast laser devices. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic diagram of the laser damage detection system based on the light spot online monitoring system of the present application.

[0038] Figure 2 is a light spot image contrast schematic diagram, wherein a is a laser light spot original image, b is a low-pass filtered light spot image, and c is a high-pass filtered light spot image.

[0039] Figure 3 is a schematic diagram of the motion trajectory comparison of the laser light spot centroid and the diffraction ring centroid. DETAILED DESCRIPTION

[0040] The implementation of the present application is described in detail as follows: The implementation is carried out on the premise of the technical solution of the present application, and a detailed implementation manner and specific operation process are given. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

[0041] Embodiment:

[0042] This embodiment takes a set of ultrastrong ultrashort pulse laser device with an output power of 10 petawatts (PW) and a repetition frequency of 1 Hz as an application scenario. A standard CCD-based light spot online monitoring system has been equipped on the optical path of the device, and the image acquisition frequency of the system is 1 frame per second (fps), and the resolution is 1280x960 pixels. In this embodiment, the processing algorithm of the present method is deployed on the industrial computer of the monitoring system through software upgrade, without any modification to any optical or hardware components.

[0043] 1. Image acquisition:

[0044] Using the existing light spot monitoring CCD camera in the ultrastrong ultrashort laser device, a frame of laser light spot image is collected after each pulse of the laser (i.e. every 1 second). The image is transmitted in real time to the processing industrial computer through the gigabit Ethernet interface.

[0045] 2. Image processing and feature extraction:

[0046] After the industrial computer receives each frame of original image, two processing threads are started in parallel:

[0047] Thread 1: Perform low-pass filtering on the collected original laser light spot image to remove high-frequency noise and background light interference, extract the basic outline shape of the main light spot, and obtain the smoothed light spot base image, as shown in b of Figure 2 .

[0048] For the smoothed light spot base image, the centroid coordinates (x0, y0) of the light spot are calculated using the gray-weighted method, and the formula is as follows:

[0049] x0= [∑(x·I(x,y))] / [∑I(x,y)]

[0050] y0= [∑(y·I(x,y))] / [∑I(x,y)]

[0051] In the formula, I(x, y) is the filtered pixel intensity value at coordinates (x, y).

[0052] Thread 2: On the same frame of the original laser spot image, high-pass filtering is performed to sharply sharpen the image edges and clearly show the weak diffraction ring that may exist, with the effect shown as c in the figure. Figure 2

[0053] The profile detection algorithm is used to identify whether there is a diffraction ring inside the spot: if a diffraction ring is identified, the profile of the candidate ring is used as a mask on the original image, and the above-mentioned gray-weighted formula is applied again to calculate the centroid coordinates (x1, y1) of all pixels in the diffraction ring region.

[0054] 1. Motion consistency analysis:

[0055] A plurality of consecutive images are collected to record the centroid coordinates of the spot and the centroid coordinates of the diffraction ring inside the spot.

[0056] The motion sequence of the main spot centroid in the X direction and the motion sequence of the diffraction ring centroid in the X direction are calculated respectively

[0057] The Pearson correlation coefficient formula is used to calculate the correlation coefficient of the two sequences.

[0058] 2. Hazard coefficient judgment:

[0059] The system sets the threshold for damage judgment as ρ = 0.6:

[0060] If a diffraction ring is not identified in a certain frame of image, or ρ < 0.6, the system determines that the optical element is normal, and no operation is performed, and the monitoring continues.

[0061] If a diffraction ring is identified in 5 consecutive frames of images, and the calculated ρ > 0.6, the system determines that there is damage to the optical element.

[0062] Once the damage is determined, the processing software immediately sends a standard instruction package to the laser device general control system through the EtherCAT interface on the industrial computer to trigger a hierarchical response.

[0063] Through the implementation of the embodiment, the laser device successfully realizes early online diagnosis of damage to the terminal optical element.

[0064] ​The present application realizes a laser damage judgment method by using an existing light spot online monitoring system, can identify and trigger the corresponding automatic maintenance program in the early stage of damage, and effectively prevents serious damage of the optical element. The optimized data transmission path between the modules of the system ensures the efficiency of signal processing and the timeliness of decision making, and is especially suitable for large ultrafast ultrashort laser devices with extremely high stability and safety requirements, and greatly improves the stability and reliability of the device.

Claims

1. A laser damage detection method based on an online spot monitoring system, characterized in that, Includes the following steps: S1. Real-time acquisition of continuous laser spot image sequences using an online laser spot monitoring system; S2. Perform low-pass filtering and high-pass filtering on the same frame of laser spot image respectively; the low-pass filtering is used to filter out high-frequency noise and background light interference, and extract the main spot contour base; the high-pass filtering is used to enhance the high-frequency components in the image and highlight the diffraction ring structure caused by damage to optical elements; S3. Based on the image after low-pass filtering in step (2), the centroid coordinates of the main spot are calculated using the gray-scale weighted average algorithm; S4. Based on the image processed by high-pass filtering in step (2), the contour detection algorithm is used to identify whether there is a diffraction ring inside the spot: if it exists, the gray-scale weighted average algorithm is used to calculate the centroid coordinates of the diffraction ring; if it does not exist, return to step (1) to continue the acquisition and monitoring. S5. When the existence of diffraction rings is identified in multiple consecutive frames of images, extract the motion trajectory data of the centroid of the main spot and the centroid of the diffraction ring within a preset time window; S6. Calculate the correlation coefficient between the trajectories of the centroid of the main spot and the centroid of the diffraction ring; S7. Compare the calculated correlation coefficient with the preset threshold: When the correlation coefficient continues to exceed the preset threshold, it is determined that there is a risk of damage to the optical component, and an early warning or control command is triggered.

2. The laser damage detection method according to claim 1, characterized in that, The low-pass filtering includes image binarization, Gaussian filtering, mean filtering, Butterworth low-pass filtering, and bilateral filtering.

3. The laser damage detection method according to claim 1, characterized in that, The high-pass filtering includes image gradient calculation, Laplacian filtering, and Gaussian high-pass filtering.

4. The laser damage detection method according to claim 1, characterized in that, The centroid coordinates (x0, y0) of the light spot are calculated using a weighted average of pixel intensities, as shown in the formula: x0= [∑(x·I(x,y))] / [∑I(x,y)] y0 = [∑(y·I(x,y))] / [∑I(x,y)] Where I(x,y) is the filtered pixel intensity value at coordinate (x,y).

5. A laser damage detection system for implementing the laser damage detection method according to any one of claims 1-4, characterized in that, include: Image acquisition module: consists of the existing online spot monitoring system; Image processing module: used to perform low-pass and high-pass filtering on the acquired images in parallel; Feature extraction module: used to calculate the centroid of the light spot and the centroid of the diffraction ring; Motion analysis module: used to analyze the correlation of motion trajectories of two centers of mass; Decision output module: Used to generate control commands based on analysis results; Control interface module: Used to transmit control commands to the laser device control system.

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