Stability of Ultrafast Laser-Induced Stress in Fused Silica and Ultra-Low Expansion Glass
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis article investigated the stability of ultrafast laser-induced stress in fused silica (FS) and ultra-low expansion glass (ULE) through two isothermal annealing experiments, measured the changes in stress and deformation at different temperatures, and explored the related mechanisms. However, this article lacks completeness in experiment and conclusion sections. In the experimental section, the stability of ULSF within three temperature ranges has been confirmed through sufficient data. However, there are still a few phenomena that lack explanation and more data need to be supplemented to improve the overall experimental process and complete the evidence chain. The following are the specific issues.
Question 1: The material ULE3 mentioned in Experiment 2 ( ), which is mentioned in line 140 of the text, was processed at a repetition frequency of 225 kHz, different from the 200 kHz used for the material mentioned earlier. Why the authors choose to use this repetition frequency? The specific experimental explanations should be supplemented.
Question 2: The article mentioned that within the range of 200℃ to 500℃ (Figure 3), the 45° astigmatism of all formed samples increased. However, no direct explanation was given for this phenomenon in the article. This point was also mentioned in the discussion section but still no more explanation was provided.
Question 3: In Chapter 3.2, for the process of heating up to 1000℃, only the stability verification of 0° astigmatism from the Experiment 1 was completed, and the data from the Experiment 2 was lacking.
Question 4: The discussion and conclusion sections explain the thermal stability of ULSF under different conditions, but do not explore its potential applications and possible application value. It is recommended that the author explore the potential research value and significance of this work, highlighting the advantages of ULSF in stress relief thermal stability and the future value of this research
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Author Response
We greatly appreciate the thoughtful reviews and feedback provided by all reviewers. The suggestions have greatly improved the quality of the manuscript. We have responded to each point in red below. We have updated the manuscript as indicated in red italics.
1) The material ULE3 mentioned in Experiment 2 ( ), which is mentioned in line 140 of the text, was processed at a repetition frequency of 225 kHz, different from the 200 kHz used for the material mentioned earlier. Why the authors choose to use this repetition frequency? The specific experimental explanations should be supplemented.
Thank you for calling our attention to this ambiguity. We have clarified this and questions from other reviewers by modifying the second paragraph of Chapter 2.2:
FS B, ULE B, and ULE C were figured with the same laser parameters as in Experiment 1, except ULE C was figured with a 225 kHz repetition rate as we used a slightly different calibration to generate the ULSF pattern; similar repetition rates do not significantly alter the ULSF result when all other processing parameters are held.
Slightly different repetition rates, segment length, and pitch reflect our ongoing effort to calibrate the ULSF process for each batch of glass we figure and improve precision and repeatability in the resulting measured stress.
2) The article mentioned that within the range of 200℃ to 500℃ (Figure 3), the 45° astigmatism of all formed samples increased. However, no direct explanation was given for this phenomenon in the article. This point was also mentioned in the discussion section but still no more explanation was provided.
At this time, we do not have a definitive explanation for this interesting result, but we offered one hypothesis in the last paragraph of the Discussion section. There is an alternative hypothesis, which we have added to that paragraph:
An alternative explanation may be that the stress in some regions of the laser-written line segments, such as the start or end of each line segment where shear stresses are more prevalent, relax at a lower temperature than other regions. Additional experiments are needed to test these hypotheses.
We agree that the explanation for this behavior remains open, and we plan to continue researching the issue.
3) In Chapter 3.2, for the process of heating up to 1000℃, only the stability verification of 0° astigmatism from the Experiment 1 was completed, and the data from the Experiment 2 was lacking.
Thank you for your comment. In Chapter 2.2, which outlines the parameters for Experiment 2, we state that these wafers were only thermally cycled up to 500 °C, as this was the range of interest for significant changes to the stress field not driven by viscosity changes leading to nanograting erasure. We have added a sentence to remind the reader of this in the first paragraph of Chapter 3.2.
Only samples from Experiment 1 were thermally cycled up to 1000 °C.
4) The discussion and conclusion sections explain the thermal stability of ULSF under different conditions, but do not explore its potential applications and possible application value. It is recommended that the author explore the potential research value and significance of this work, highlighting the advantages of ULSF in stress relief thermal stability and the future value of this research
Thank you for this recommendation. We have added the following text to the conclusion.
Confidence in the lifetime stability of ULSF-induced stress supports its viability as a processing tool to supplement thin optics manufacturing. We demonstrated that changes to the induced surface figure after ULSF are limited to the low tens of nanometers up to 200 °C, indicating that ULSF can survive and continue to perform well in common thermal environments. While there is some directional dependence to the stress stability in small mirrors, this is entirely absent in larger diameter mirrors. Using ULSF for post-coating figure correction has been demonstrated previously [5], and its stability likely depends on the stability of the film, not ULSF. ULSF also represents a critical step toward concurrent figuring and alignment, and offers a contact-free method of optical surface pre-forming to reduce the need for post-alignment wavefront correction. Further areas of interest regarding thermal stability of ULSF include contributions from the beam profile, substrate material, and local nanostructure morphology to directional stress stability.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript presents a rigorous experimental investigation into the thermal stability of ultrafast laser stress figuring (ULSF)-induced stress fields in fused silica (FS) and ultra-low expansion glass (ULE), and provides valuable insights into ULSF stress stability and advances optical fabrication methodologies. Therefore, I recommend acceptance in Photonics after minor revisions. Here are the comments:
- Line 140 on page 5, the authors claimed “except ULE 3 was figured with a 225 kHz repetition rate.” Does the repetition rate affect the results of the ULSF induced stress field, or is the adjustment of repetition rate solely intended to achieve the desired processing patterns?
- Using the same naming method can be confusing; it is advisable to assign new identifiers to the samples in Experiment 2 for clarity.
- Does the sample thickness affect the astigmatism 0° deformation term? During the exploration of trefoil 30° deformation term, the thicknesses of samples are almost consistent.
- Figure. 7 on Page 10, are the subfigures on the left directly generated by Matlab? The background, font, font size are all different from the other figures. Similar formats should be better.
- Ensure all citations are finalized published works, and the formatting adheres to the publication requirements.
Author Response
We greatly appreciate the thoughtful reviews and feedback provided by all reviewers. The suggestions have greatly improved the quality of the manuscript. We have responded to each point in red below. We have updated the manuscript as indicated in red italics.
1) Line 140 on page 5, the authors claimed “except ULE 3 was figured with a 225 kHz repetition rate.” Does the repetition rate affect the results of the ULSF induced stress field, or is the adjustment of repetition rate solely intended to achieve the desired processing patterns?
Thank you for calling our attention to this ambiguity. We have clarified this and questions from other reviewers by modifying the second paragraph of Chapter 2.2:
FS B, ULE B, and ULE C were figured with the same laser parameters as in Experiment 1, except ULE C was figured with a 225 kHz repetition rate as we used a slightly different calibration to generate the ULSF pattern; similar repetition rates do not significantly alter the ULSF result when all other processing parameters are held.
Slightly different repetition rates, segment length, and pitch reflect our ongoing effort to calibrate the ULSF process for each batch of glass we figure and improve precision and repeatability in the resulting measured stress.
2) Using the same naming method can be confusing; it is advisable to assign new identifiers to the samples in Experiment 2 for clarity.
Agreed, this improves readability considerably. The text has been updated to improve clarity regarding Experiment 2 sample identifiers (chapter 2.2, paragraph 2; Table 1; Figure 4; and Table 2).
3) Does the sample thickness affect the astigmatism 0° deformation term? During the exploration of trefoil 30° deformation term, the thicknesses of samples are almost consistent.
Integrated stress is a function of the sample thickness and deformation term, as defined by the modified Stoney’s equation (referenced in line 118, https://doi.org/10.1364/OE.456679). To generate the same amount of stress in samples of equal diameter and material but different thickness, the deformation magnitude will be higher for thinner samples or lower for thicker samples. Table 1 illustrates this for Experiment 1. For our study, maintaining similar stress magnitudes was most important for apples-to-apples comparison.
4) Figure. 7 on Page 10, are the subfigures on the left directly generated by Matlab? The background, font, font size are all different from the other figures. Similar formats should be better.
Thank you, this has now been corrected.
5) Ensure all citations are finalized published works, and the formatting adheres to the publication requirements.
Thank you for identifying this. The citation formatting style has now been corrected.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsIt is OK
