The Densification Characteristics of Polished Fused Silica Glass and Its Scattering Characteristics

Round 1

Reviewer 1 Report

The paper qualitatively shows the effects of the super polishing process on fused silica samples. The approach is interesting, but the experimental and simulation parts are, in my opinion, only qualitatively related.

It should be very useful to have a BSDF measurement or simply an experimental estimation of the refractive index of the processed samples or a way that allows to correlate the optical performances of the samples with the COMSOL simulations. 

Concerning the experimental part, I have the doubt that the experimental error does not allow to assert the differences in hardness and module values on figure 3.

Other comments:

1.      Line 115 “It is worth noting that the AFM probe could not indent into the fused silica surface sufficiently because of the large hardness and modulus, so the absolute values of hardness and modulus could not be obtained in this case.”

What is the uncertainty of those measurements?

 

2.     Line 121 “As shown in Figure 2a, the surface of the roughly polished sample still has scratch defects in the transverse size of tens of nanometers, and the surface fluctuation can be several nanometers.”

Please, add a profile for figure 2a (maybe crossing one of the scratches) e figure 2c.

 

3.     Line 128 “It means that the mechanical properties of the sample surface become uniform.”

What does exactly mean? Uniform in what?

 

4.     Line 152 How did you estimate the errors associated to the measurements? Could I ask to plot in the same graph hardness values of roughly polished and super-polished and in other graph modulus values of roughly polished and super-polished sample?

 

5.     Line 156 For reader convenience, could you specify what is the correlation coefficient?

 

6.     Line 205 How did you assess the values of 1.6, 1.5 and 1.457 of refractive index?

Author Response

We greatly appreciate the reviewer for his positive evaluation of our work. 

Below is our point-by-point response by addressing the comments.

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

    The study on the optical properties of fused silica glass after polishing has certain significance. The following needs to be revised.

1.     Polishing was used in this paper, it refers to mechanical polishing? Or chemical mechanical polishing? It should be very clear.

2.     The polishing equipment is usually called polisher, polishing device is rarely used.

3.     For such study, you can try chemical mechanical polishing method by using certain slurry, both polishing time and efficiency will be improved. The polishing time referred in the paper is too long.

4.     Surface roughness should be shown in Figure 2, not in Figure 1b, and the value should be shown from Figure, not from the microscopic topography. Line 110-111. Also, Surface roughness and modulus cannot be expressed using the same acronym, such as Rq and Ra.

5.     Surface’s roughness should be surface roughness. The English lever should be improved.

6.     Line 148, not Figure 1d.

7.     Line 156, The correlation coefficient was calculated on the date of height and modulus in Figure 2. How to calculate? Please give the formula and the data about height and modulus.

8.     Line 167, the height value is minimum? It should be maximum?

Author Response

We greatly appreciate the reviewer for the positive evaluation of our work.

Below is our point-by-point response by addressing the comments.

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

The problem of ultrafine sirface smoothing is very hot nowdays. But reading the manuscript, a number of questions arises.

1. What is “modulus” used in the text? Is it Young’s modulus or some other elastic quantity?

2. What cantilevers were used in PeakForce measuremnts?

3. line 94: “The transverse distribution of surface modulus … has been researched in detail by AFM.” – it is incorrect, the modulus could not be measured by AFM in the work. As the Authors state further, “the AFM probe could not indent into the fused silica surface sufficiently because of the large hardness and modulus, so the absolute values of hardness and modulus could not be obtained in this case.” I could not understand though, how could the relative change of the modulus (shown in Fig. 1 b,c) be evaluated than. This procedure should be described in details.

4. It is natural to expect that the scratches clearly seen in Fig. 2a as depressions should be as well clearly seen in Fig. 2b as protrusions. But there almost are no scratches in Fig. 2b. Why is it so?

5. line 130: The words “Figures should be placed in the main text near to the first time they are cited” are unnecessary.

6.  Fig. 3. It is hard to catch the difference in the curves for the two samples. I suggest to put two Hardness curves in one plot, and two Modulus curves in another.

7.  Fig. 5 has an incorrect caption.

8. line 202: “the refractive index of fused silica at the same height level in this model is the same and gradually decreases” But experimentally it was found that the height is negatively correlated to the modulus. It means that the index is higher in the depressions than in the protrusions, and it means that it is NOT the same at the same height level. Thus, the model fails to match the experiment.

The features of the BRDА are poorly discussed. Why is the reflection maximum at 40 degrees, not at 30 (specular reflection)? How its width is connected to the topography numerical characteristics?

8. line 211: “brand peak values” – did you mean “broad peak values"?

Overall, the scientific novelty of the paper is not cleat for me. Considering the experimental part, surface local densification under polishing is a well known fenomenom, see, for example, [doi.org/10.1364/AO.53.002487]. Consedering the model, its problems are indicated in the Comment 8, and the reflection by a media with an altered refraction layer itself can be easily described analytycally.  

Author Response

We greatly appreciate the reviewer for the positive evaluation of the significance of our work;

Below is our point-by-point response by addressing the comments;

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be published in the present form. The authors provided adequate explanation on the queries. 

Author Response

We greatly appreciate the Referee for the recommendation and kind support to our work.

Reviewer 3 Report

The technical problems have been fixed improving the quality of the manuscript; 

the Responces 3 and 4 in the cover letter explained the situation to me, but why not to add the same explanation to the text?

What about Responce 8, I still did not understand why the reslection was not specular. Further, the angular distribution of the scatered light is always connected to the surface roughness (more precisely, with the PSD fiuction of the surafce roughness). But the autors stated that "the width of the scattering peak is related to the size of the physical field", i.e. it does not reflect the surface properties, only the simulation conditions. If so, what was the aim of the simulations? The influence of a depth-dependent refractive index can be easily calculated without simulations.

Thus, I recommend

(1) to add the explanations from Responces 3 and 4 to the text, 

 (2) to discuss the BRDA functions in much more depth, othervise its simulation has no sence.

Author Response

We greatly appreciate the reviewer for the valuable suggestion of our work.

Below is our point-by-point response by addressing the comments.

Please see the attachment.

Author Response File: Author Response.docx