Study of Ion-Assisted E-Beam Evaporation Coating Process on Chirped Mirrors
Round 1
Reviewer 1 Report
The authors present the Study of an Ion-Assisted E-beam Evaporation Coating Process on Chirped Mirrors that corresponds to a mirror design with -60fs2 of group delay dispersion and reflectance of about 97.5%.
The article looks well written. However, it is highly technical and merely descriptive. The authors use previously reported tools and apply them to an experimental case, of which they need to give more details to be contrasted or verified. Therefore, the authors are invited to show more experimental details and expand the physical explanation of the results and deviations obtained. For this reason, the article should not be accepted in its present form, but it can be reconsidered once the review comments are addressed.
1) For as-deposited samples, the grain growth mechanism can produce surface roughness with the increase of grain size and thickness of the films because of the accumulation of staking defects. Therefore, the author should estimate surface roughness because it can produce incoherency of light in the thick structure.
2) Authors avoid important details about experimental procedures and used conditions in the ion-assisted electron beam evaporation apparatus. So in order to verify and reproduce this result from other research groups, I invite the authors to describe the experimental procedures and conditions to obtain the mentioned chirped mirror in detail.
3) Figure 12 has a meager resolution. Therefore, I could not review its content well due to low resolution.
4) There are currently a variety of optimization techniques for designing and fabricating mirrors of multilayer dielectric structures. The authors should also contrast some experimental results with other multilayer systems of chirped and modulated structures. For example, genetic algorithm techniques or bio-inspired systems were used for similar purposes. I mention this so you can complement the introduction because the way it is written looks light.
5) The cited articles need to be more recent and are few. In addition, they should extend the referencing by contrasting it with other published articles.
6) The refraction index (n and k) can vary from zero to some thickness, such as microns for different materials. This behavior will differ from material to material and deposition process to deposition process. It is so particular and case-dependent. In that way, the authors remove the design with layers smaller than 50 nm.
Can the author justify this? Is there any physical reason to do that?
Variation of refractive index as a function of the thickness, local absorption due to quantum confinement? Or is the model used in section 2.2 (thin film theory) not valid for ultra-thin films? Please discuss all that I mentioned.
Author Response
- For as-deposited samples, the grain growth mechanism can produce surface roughness with the increase of grain size and thickness of the films because of the accumulation of staking defects. Therefore, the author should estimate surface roughness because it can produce incoherency of light in the thick structure.
Response:
The authors used various approaches, such as E-gun power and vapor shade, to assist the growth of film to be as consistent and flat before the official runs of experiments. Many SEM and VASE measurements were checked for making the IAD coaters to run at the most stable and steady coating conditions. Hence, the coatings of a sample would require at least 24 hours to complete the process.
- Authors avoid important details about experimental procedures and used conditions in the ion-assisted electron beam evaporation apparatus. So in order to verify and reproduce this result from other research groups, I invite the authors to describe the experimental procedures and conditions to obtain the mentioned chirped mirror in detail.
Response:
The experimental parts of the study are added to the paper to give comprehensive and pertinent information to follow the steps of experimental study.
- Figure 12 has a meager resolution. Therefore, I could not review its content well due to low resolution.
Response:
Figures are re-organized to give comprehensive descriptions and higher resolution to show the results.
- There are currently a variety of optimization techniques for designing and fabricating mirrors of multilayer dielectric structures. The authors should also contrast some experimental results with other multilayer systems of chirped and modulated structures. For example, genetic algorithm techniques or bio-inspired systems were used for similar purposes. I mention this so you can complement the introduction because the way it is written looks light.
Response:
The authors have reviewed many books and papers concerning the design of optical film; and, we acknowledge many algorithms can be applied to this problem. In the meantime, the method we chose seems to give you one selection quickly without getting into the trouble of multiple choices. Local minima are the most troublesome issue if the so-called optimization schemes are adopted. The main goal in the paper is to compare the best optimization method that can be used in this study. Rather, a open-source program with reliable scheme is the main purpose in this study. A couple of sentences are added to the contents to explain the issues I mentioned above.
5) The cited articles need to be more recent and are few. In addition, they should extend the referencing by contrasting it with other published articles.
Response:
References are added for including more recent papers.
6) The refraction index (n and k) can vary from zero to some thickness, such as microns for different materials. This behavior will differ from material to material and deposition process to deposition process. It is so particular and case-dependent. In that way, the authors remove the design with layers smaller than 50 nm. Can the author justify this? Is there any physical reason to do that? Variation of refractive index as a function of the thickness, local absorption due to quantum confinement? Or is the model used in section 2.2 (thin film theory) not valid for ultra-thin films? Please discuss all that I mentioned.
Response:
Yes, the refractive index can vary and will show large distributions of measurement values for the samples coated under the same process conditions. That is why the IAD coater manufacture require all materials used for coating must be calibrated with the process conditions and minimum film thickness for specific applications. Since the theory of chirped mirrors rely heavily of alternative layers of high and low index materials, the region of most table layer thickness should be determined so that the boundary of maximum and minimum thickness can be set on the optimization program, In this study, the experimental data shows layer thickness larger than 50 nm is the minimum thickness based on the analysis of experimental data.
Reviewer 2 Report
Manuscript ID: coatings-2142053
Authors have studied the ion-assisted E-beam evaporation coating process on chirped mirrors. However, I suggest the below correction and revision for this paper to be considered in the Coatings journal (MDPI).
1. Abstract and Conclusion Parts: The writing style looks similar in both parts. However, both parts should be thoroughly revised. For example, in the Abstract part, why “in conclusion” (Line 15) appears, which is weird. In addition, the Conclusion part also, the style is not acceptable. Hence, your revision is expected.
2. Authors did not follow a general abbreviation rule. Note that “Abstract” is an independent part. Hence, this part should be considered separately.
Line 9: GDD => group delay dispersion
Line 11: an ion-assisted deposition (IAD) => an ion-assisted deposition
Line 14: PG-FROG => polarization gating frequency-resolved optical gating
Line 9: “-60” (Note: delete “-“ symbol)
3. In many parts, figure quality is not acceptable.
Figure 11: “Scale bar” needed. Otherwise, it is not science.
Figure 12: Figure’s resolution is not acceptable. I cannot read it, e.g., each axis’ title.
Figure 9: You need to define FWOT in the figure caption. (e.g., the full wavelength optical thickness)
Figures 1, 4, and 9: Keep aspect ratio. Now all these figures are partially elongated in the y-axis direction. You need to increase proportionally in each direction.
Figure 10: axis’s title is not much readable. (please improve it also)
4. Equation typing: Physical parameter should be italic. (Check all the parts)
Line 117: square symbol should be superscript (not ^) for consistency.
5. Other comments
Lines 27 and 28: metals, polymers, and semiconductors => metals, polymers, and ceramics (e.g., semiconductors).
Line 41: group delay dispersion (abbreviated as GDD) => group delay dispersion (GDD)
Line 185: BK7 glass (Note: here, you may introduce the chemical composition of BK7 glass for writing a reader-friendly manuscript).
Check your abbreviation all the parts. Note that (1) you need to introduce its full name before using an abbreviation, and (2) once you introduced an abbreviation, you should use it from then on.
Finally, “equation styles” are somewhat different in each case, i.e., there is no consistency. Check size, style, and ratio (each component in a symbol). Eq. (13), physical parameter should be italic. Check all the other parts also.
Author Response
Thank you for your kind comments and suggestions. The authors have revised the manuscript accordingly and the detailed explanations are delivered as follows.
- Abstract and Conclusion Parts: The writing style looks similar in both parts. However, both parts should be thoroughly revised. For example, in the Abstract part, why “in conclusion” (Line 15) appears, which is weird. In addition, the Conclusion part also, the style is not acceptable. Hence, your revision is expected.
Response:
The abstract and conclusion have been revised with different style for better descriptions of the contribution of this paper.
- Authors did not followa general abbreviation rule. Note that “Abstract” is an independent part. Hence, this part should be considered separately.
Line 9: GDD => group delay dispersion
Line 11: an ion-assisted deposition (IAD) => an ion-assisted deposition
Line 14: PG-FROG => polarization gating frequency-resolved optical gating
Line 9: “-60” (Note: delete “-“ symbol)
Response:
Revised as indicated in the revision.
- In many parts, figure quality is not acceptable.
Figure 11: “Scale bar” needed. Otherwise, it is not science.
Figure 12: Figure’s resolution is not acceptable. I cannot read it, e.g., each axis’ title.
Figure 9: You need to define FWOT in the figure caption. (e.g., the full wavelength optical thickness)
Figures 1, 4, and 9: Keep aspect ratio. Now all these figures are partially elongated in the y-axis direction. You need to increase proportionally in each direction.
Figure 10: axis’s title is not much readable. (please improve it also)
Response:
Revised as indicated in the revision.
- Equation typing: Physical parameter should be italic.(Check all the parts)
Line 117: square symbol should be superscript (not ^) for consistency.
Response:
Revised as indicated in the revision.
- Other comments
Lines 27 and 28: metals, polymers, and semiconductors => metals, polymers, and ceramics (e.g., semiconductors).
Line 41: group delay dispersion (abbreviated as GDD) => group delay dispersion (GDD)
Line 185: BK7 glass (Note: here, you may introduce the chemical composition of BK7 glass for writing a reader-friendly manuscript).
Check your abbreviation all the parts. Note that (1) you need to introduce its full name before using an abbreviation, and (2) once you introduced an abbreviation, you should use it from then on.
Finally, “equation styles” are somewhat different in each case, i.e., there is no consistency. Check size, style, and ratio (each component in a symbol). Eq. (13), physical parameter should be italic. Check all the other parts also.
Response:
Revised as indicated in the revision.
Round 2
Reviewer 1 Report
The authors have responded satisfactorily to my comments and have improved the manuscript. Some minor issues must be addressed. Therefore, it may be considered for publication in Coatings.
Issues: page 2 Lines 66. The cited number is missing. page 11 line 256. in the figure caption of figure 16 the word scattering is bad spelling.
Add more recent references. Here are some related works that you can mention and contrast
https://doi.org/10.1016/j.ijleo.2022.169002
https://doi.org/10.1063/1.4738765
https://doi.org/10.1016/j.tsf.2015.12.069
https://doi.org/10.1364/AO.477072
Author Response
The authors thank the reviewer for the careful review of the revision. Minor errors in the text contents have all been corrected. More recent references are added for comprehensive literatures review purpose.
A final revision of the paper has been submitted again.
Author Response File: 
Author Response.pdf
