Laser Beam Jitter Control Based on a LabVIEW FPGA Control System
Round 1
Reviewer 1 Report
The manuscript titled "Laser Beam Jitter Control Based on LabVIEW FPGA Control System" is a well-written and well-structured contribution to the field of laser beam control, although some revision of English could be of use in the writing of the paper.
The authors have presented a novel method for controlling laser beam jitter using LabVIEW FPGA control system and have demonstrated its efficacy with an experimental realization.
The introduction provides a comprehensive overview of the problem of laser beam jitter and its importance in various applications.
The proposed solution is well explained and supported by simulations and experiments.
The results show that the proposed method is effective in reducing laser beam jitter, which is a significant contribution to the field.
The comparison between the proposed method and other existing methods could be improved by including more methods and discussing their limitations. In particular, it could be nice to compare the results obtained in this study with some state of the art results like for instance LIGO and Virgo control of beam pointing (e.g. B. Canuel, et al. “Sub-nanoradiant beam pointing monitoring and stabilization system for controlling input beam jitter in gravitational wave interferometers”, Appl. Opt. 53 (2014) 2906-2916).
The discussion of the results could be more in-depth, especially in terms of the limitations and future work.
From the provided scheme it seems that the camera used to sense the beam position was saturated, which may reduce the sensitivity to the beam center measurement. This issue should be addressed in the discussion and the results should be interpreted in light of this limitation.
The proposed scheme uses a single sensor and so it cannot monitor at the same time both the tilt and the shift of the beam. The authors should consider if the scheme can be expanded to include both degrees of freedom of the beam pointing.
Overall, the manuscript is well written and the proposed method shows promising results for controlling laser beam jitter. I recommend it for publication after the authors address the minor revisions suggested above.
Author Response
Thank you for taking the time to review our paper and providing valuable feedback. We appreciate your comments and suggestions, which will help us to improve the quality of our work.
Regarding your feedback we have made the following revisions to the paper:
- some revision of English could be of use in the writing of the paper.
Response: We apologize for the poor language of our manuscript. We worked on the manuscript for a long time and the repeated addition and removal of sentences and sections obviously led to poor readability. We have now worked on both language and readability language corrections. We really hope that the flow and language level have been substantially improved.
- The comparison between the proposed method and other existing methods could be improved by including more methods and discussing their limitations. In particular, it could be nice to compare the results obtained in this study with some state of the art results like for instance LIGO and Virgo control of beam pointing (e.g. B. Canuel, et al. “Sub-nanoradiant beam pointing monitoring and stabilization system for controlling input beam jitter in gravitational wave interferometers”, Appl. Opt. 53 (2014) 2906-2916).
Response: Thanks for reviewer’s comments, we describe the results of B. Canuel’s work, providing the experimental protocols and the completed results. Part of the manuscript as:” In 2014,B. Canuel et al. developed a beam-pointing control system for a large-scale gravitational wave interferometer and demonstrated its effectiveness through experiments. The results showed that the system could achieve tilt and shift corrections below 10 Hz, with $10^{-8} rad$ and a shift control accuracy of $10^{-7} m$. The system uses a two-quadrant photodiode for beam tilt and shift detection and employs two piezoelectric actuators to drive the correction of the tilt mirror”. In line [18-23].
- The discussion of the results could be more in-depth, especially in terms of the limitations and future work.
Response: Thanks for reviewer’s comments, we have revised in Conclusions part of the manuscript as:” The loop time of the image processing program is 35 ms, which is determined by the camera's frame rate of 30 fps and the onboard clock of the FPGA operating at 100 MHz. The feasibility of the system was verified through experiments using a camera with a low frame rate, and the theoretical maximum processing capacity is within the nanosecond range. Future efforts should enhance the system's functionality by selecting a high-frame-rate camera and FSM appropriate for specific application scenarios. Additionally, the system's performance can be improved by upgrading the spot extraction algorithm, for instance, by incorporating masking to enhance extraction speed or utilizing correlation calculation to improve accuracy. In this system, a single FSM is used to regulate the beam dithering, resulting in limited control over beam shift. To address this limitation, future development should focus on incorporating a dual FSM control system, thereby increasing the control system's degrees of freedom and maintaining the same FSM control principle as in the single FSM setup.” In line [271-283]
- Camera used to sense the beam position was saturated, which may reduce the sensitivity to the beam center measurement. This issue should be addressed in the discussion and the results should be interpreted in light of this limitation.
Response: Thanks for reviewer’s comments, we have revised in Conclusions part of the manuscript as:” The loop time of the image processing program is 35 ms, which is determined by the camera's frame rate of 30 fps and the onboard clock of the FPGA operating at 100 MHz. The feasibility of the system was verified through experiments using a camera with a low frame rate, and the theoretical maximum processing capacity is within the nanosecond range.” in line[271-275]
- The authors should consider if the scheme can be expanded to include both degrees of freedom of the beam pointing.
Response: Thanks for reviewer’s comments, our system could address the laser beam’s tilt currently. We have revised in conclusion part of the manuscript as:” In this system, a single FSM is used to regulate the beam dithering, resulting in limited control over beam shift. To address this limitation, future development should focus on incorporating a dual FSM control system, thereby increasing the control system's degrees of freedom and maintaining the same FSM control principle as in the single FSM setup.” In line [279-283]
We believe that these revisions address the issues raised by the reviewer and enhance the clarity and significance of our work.
Once again, we thank you for your constructive comments and look forward to your continued support.
Reviewer 2 Report
The authors are providing a solution to measure the laser beam jitter by using CMOS camera and Flex RIO systems along with LabVIEW and Matlab programming. The idea looks impressive, however the manuscript needs some improvements in terms of defining the problem clearly, quality of pictures, and conclusions. Please see my comment below.
1. What is FSM in the abstract? Please define it.
2. What is your system's accuracy, i.e., the minimum beam deviation it can measure? It is not clear in the manuscript.
3. What are the advantages of using a CMOS camera instead of a CCD in your system? Please discuss it in the manuscript
4. The authors conclusions "Based on the above design, beam control experiments are conducted, and the results show that the system has good robustness, and high integration, and can achieve fast and stable control of the beam to develop a new solution for beam stability control research", but it is not clear in the manuscript in terms of what deviation you achieved, at what distance and at what angle of FSM finally what percent of laser power loss you achieved.
Comments for author File: 
Comments.pdf
Author Response
Thank you for taking the time to review our paper and providing valuable feedback. We appreciate your comments and suggestions, which will help us to improve the quality of our work.
Regarding your feedback we have made the following revisions to the paper:
- What is FSM in the abstract? Please define it.
Response: Thanks for the reviewer’s abstract suggestion. The fast steering mirror (FSM) is defined in the abstract (Line 5, page 1)
- What is your system's accuracy, i.e., the minimum beam deviation it can measure? It is not clear in the manuscript.
Response: Thanks for the reviewer’s comments, The system measures the beam deviation as the deviation of the coordinates between the artificially set spot center of mass and the current spot center of mass. We have revised in Experiment Results and Discussion part of the manuscript:” The system determines the deviation of the beam by comparing the difference in coordinates between the artificially designated laser centroid and the current laser centroid. Figure 8 shows the control system's user interface in LabVIEW. The accuracy error of the X-axis are 0.08 pixels, Y-axis is 0.11 pixels, and the corresponding angle error is 1.047 mrad for X-axis and 8.68 mrad for Y-axis.” (Line 254,page10)
- What are the advantages of using a CMOS camera instead of a CCD in your system? Please discuss it in the manuscript
Response: Thanks for the reviewer’s comments, we have discussed the difference between the two elements in the Introduction part of the manuscript:” We use an image-processing-based laser spot acquisition scheme, where both CMOS and CCD cameras can be used as detection elements to acquire spot images and thus calculate the spot position information. The image generation method in CMOS and CCD cameras differ as CMOS enlarges each pixel individually, while CCD enlarges the raw data of all pixels at a common endpoint. The difference results in higher image quality in CCD cameras and better definition in CMOS cameras. However, CMOS cameras are more cost-effective and have lower power consumption than CCD cameras. Therefore, we prefer CMOS cameras for industrial applications with high real-time processing requirements.” (Line50-59, page2)
- it is not clear in the manuscript in terms of what deviation you achieved, at what distance and at what angle of FSM finally what percent of laser power loss you achieved.
Response: Thanks for the reviewer’s comments, we have included Figure 8 in the manuscript to provide additional information on the control performance of the system. We have revised in Experiment Results and Discussion part of the manuscript:” The system determines the deviation of the beam by comparing the difference in coordinates between the artificially designated laser centroid and the current laser centroid. Figure 8 shows the control system's user interface in LabVIEW. The accuracy error of the X-axis are 0.08 pixels, Y-axis is 0.11 pixels, and the corresponding angle error is 1.047 mrad for X-axis and 8.68 mrad for Y-axis.”.(Line 254-258, page 10)While the experiments do not focus on the loss of laser energy, they consider only the position information of the laser. Further research can be conducted to examine the laser energy detection in the future.
We believe that these revisions address the issues raised by the reviewer and enhance the clarity and significance of our work.
Once again, we thank you for your constructive comments and look forward to your continued support
Round 2
Reviewer 2 Report
The draft has improved significantly with the addition of all relevant information about the experiments and a thorough description of the results. I have a few suggestions for your consideration:
- Please change the caption of Figure 7 to read "Number of samples" and make similar adjustments to the captions of the other figures as well.
- If possible, please include images with higher contrast or with good quality.
- I would like to confirm if the units for the y-axis in Figure 4a are in millivolts (mV) or volts (V), please check it.
Author Response
We would like to express our gratitude for your time and effort in reviewing our work. We have taken your feedback into consideration and made the necessary revisions to the manuscript.
Regarding your feedback we have made the following revisions to the paper:
1 Please change the caption of Figure 7 to read "Number of samples" and make similar adjustments to the captions of the other figures as well.
Response: Thanks for reviewer’s comments, we have revised in Figure captions:”①Fig.7:Number of samples.(page 10 ) ②.Fig.6 (a) Initial laser spot image (d)Filter by the Gaussian kernel (f) Grayscale distribution of the image after processing.(page 9) And all Figure‘s caption is Initial capitalization. ”
2 If possible, please include images with higher contrast or with good quality.
Response: Thanks for reviewer’s comments, we have revised in Figure captions:”①Fig3(a),(b) Enlarged the image.(page 6)②Fig.4(a),(b): Enlarged axis scale font.(page 8) ③Fig.5 Enlarged the front in the Image. (page 8)”
3 I would like to confirm if the units for the y-axis in Figure 4a are in millivolts (mV) or volts (V), please check it.
Response: Thanks for reviewer’s comments, we apologize for the units of figure 4(a). We have revised y-axis’s title in Figure 4(a) is:” Voltage (v)”.(page 8)
We believe that these modifications have significantly strengthened the overall quality of the manuscript and addressed your concerns.Thank you again for your time and effort in reviewing our manuscript. We look forward to the opportunity to receive your positive assessment of the revised version.
Sincerely
ZHANG Delin
