Optical Breakdown on Clusters of Gas Nanobubbles in Water; Possible Applications in Laser Ophthalmology
Round 1
Reviewer 1 Report
Respect to the paper manuscript entitled “Optical breakdown on clusters of gas nanobubbles in water; possible
applications in laser ophthalmology” Manuscript ID: applsci-2171874, which was sent to me to review for publication in Applied Sciences. I read the manuscript carefully and patiently. Also, I rebuilt most part of the calculations and I found that they are correct. The topic of this manuscript can be interesting for readers of this valuable Journal. The problem is interesting in this field and the results are important. The manuscript contains new results in laser ophthalmology.
But, the paper needs the following points are noted:
1- Punctuations are used randomly. Insert commas or full stops after each and every equation accordingly.
2- The authors present Equations (1)-(4) without any explanation.
3- think the title needs to be reformulated to become more "friendly".
4- The present form of the abstract is a bit weak not much clear. Hence, I recommend to re-write it with 3/4 stronger sentences about your objectives/ findings that will give a better understanding for the readers.
5- The "Introduction" section should be more concise and some sentences should be rewritten.
6- What are the innovations or advantages of the proposed model compared to the work of other researchers in the introduction?
7- Must be corrected "glitches" of editing.
8- The conclusion must be improved.
9- Suggest the authors cite the related papers in the literature as:
* Laser short-pulse effect on magneto-photo-elasto-thermodiffusion waves of fractional heat equation for non-local excited semiconductor
Optical and Quantum Electronics, 2022, 54(12), 833
* Thermomagnetic effect with two temperature theory for photothermal process under hydrostatic initial stress
Results in Physics, 2017, 7, pp. 3918–3927
*Response of electromagnetic and Thomson effect of semiconductor medium due to laser pulses and thermal memories during photothermal excitation, Results in Physics, 2020, 16, 102877
* Thermomagnetic effect with two temperature theory for photothermal process under hydrostatic initial stress Results in Physics, 2017, 7, pp. 3918–3927
* Thermal-piezoelectric problem of a semiconductor medium during photo-thermal excitation
Waves in Random and Complex Media, 2021, 31(6), pp. 2499–2513
I accept the paper after a minor revision.
Author Response
We are grateful to the referee for a careful reading of the manuscript and comments. The manuscript has been rewritten taking into account the comments made by the reviewer. The reviewer's comments are highlighted in italics. Below are our answers.
Punctuations are used randomly. Insert commas or full stops after each and every equation accordingly.
Thank you for this note. We have placed all the missing punctuation marks throughout the text.
The authors present Equations (1)-(4) without any explanation.
We are well aware that an audience consisting of ophthalmologists (in any case, we would very much like ophthalmologists to read our article) will not be very interested in the theoretical calculations that formed the basis of our experiments. Therefore, we transferred the theoretical part of the manuscript to the appendix, that is, we initially did not strive for mathematical rigor in theoretical conclusions. Equation (1) was taken from the source [5]. In this equation, n_ecr is the critical volume number density of electrons in an electromagnetic wave of frequency omega. Formula (1) is obtained from the equality of the optical frequency omega and the plasma frequency determined by the volume number density of electrons and their mass. Equation (2) is the law of change in the electron density due to the ionization of the liquid walls of a nanobubble. The Theta time is the characteristic time of rising the electron density, which is controlled by the adhesion of electrons to the liquid wall. This time depends on the intensity of the laser radiation, as well as on the adhesion probability, the average electron velocity, and the nanobubble radius. These dependences are clearly seen in formula (3). Actually, the presence of the electron adhesion to liquid wall (that is, the loss of electrons) means that the optical breakdown inside nanobubbles is of a threshold nature, that is, the generation of secondary electrons due to ionization of liquid walls must exceed the loss of electrons due to adhesion. To correctly consider all the features of electron adhesion, we must take into account that electrons are attracted to an ionized (positively charged) liquid wall. In this case, we are dealing with the classical Poisson-Boltzmann problem (equation (4)). The solution to this problem is the known Debye-Hückel approximation, see formulas (5) and (6). We should emphasize once again that we have not described in detail our theoretical model. Otherwise, the volume of text in the Appendix section could substantially exceed the volume of the main text, which contains experimental evidence of the stimulated optical coalescence of nanobubble clusters at low pump intensities. We would like the content of the article to be focused precisely on the experimental results. At the end of the manuscript, we write that we are ready to answer all questions when contacting the corresponding author. In our opinion, this is quite a reasonable practice, we ourselves often contact the authors of articles that appeared to be of our interest.
I think the title needs to be reformulated to become more "friendly".
We agree in principle with this point of view. Indeed, potential readers may be confused by the abundance of new terms in the title of the manuscript, in particular, nanobubble clusters. However, we wanted to emphasize already in the title that in this work we will talk about new possibilities in laser ophthalmology using the optical breakdown effect. That is why we have left the original title of the manuscript.
The present form of the abstract is a bit weak not much clear. Hence, I recommend to re-write it with 3/4 stronger sentences about your objectives/ findings that will give a better understanding for the readers.
Thank you for this remark. The abstract has been completely rewritten taking into account the comments of the reviewer.
The "Introduction" section should be more concise and some sentences should be rewritten.
This Section was completely rewritten with taking into account the referee’s advices.
What are the innovations or advantages of the proposed model compared to the work of other researchers in the introduction?
In the Introduction, we would like to emphasize that operations in ophthalmology using the optical breakdown effect are usually performed at low energy energies in laser pump pulses, since at high energies the breakdown is accompanied by the generation of a shock wave, which destroys the eye tissue. Optical breakdown is a nonlinear process that occurs at a certain intensity of laser pump pulses. Thus, the problem is to reduce the energy in the pulse, while leaving the pump intensity unchanged. It would seem that the way out is to reduce the pulse duration; in this case, at a fixed pulse energy, the power increases significantly, i.e., it becomes possible to reduce the energy in the pulse, while maintaining the intensity necessary to excite the breakdown. In our work, we provide evidence that breakdown centers in a liquid saturated with a dissolved gas (for example, atmospheric air) and containing an ionic component (the intraocular fluid obviously satisfies this condition) are clusters of gas nanobubbles. Optical breakdown on such clusters occurs in two stages. The first stage is the coalescence (collapse) of the cluster and the formation of a macroscopic bubble. In the Introduction, we say that for intraocular operations it is not necessary to initiate an optical breakdown accompanied by a bright light flash and shock wave generation, since coalescence occurs at intensities significantly lower than the intensity at which a light flash and shock wave occur. These considerations have been made clearer in the Introduction section.
Must be corrected "glitches" of editing.
The manuscript has been subjected to very careful re-editing.
The conclusion must be improved.
The Conclusion section has been rewritten, but the main points of this section have been retained.
Suggest the authors cite the related papers in the literature as: ...
We are grateful to the Reviewer for this remark. We have referred to these works, Refs. [1-4] in the new version.
Reviewer 2 Report
The manuscript "Optical breakdown on clusters of gas nanobubbles in water; possible applications in laser ophtalmology" describe experimental results and their modelling, on the interaction of short laser pulses with water and the evolution of cavitation microbubbles in the presence of ionization. They exhibit a regime where the shockwave is of limited magnitude, with potential application to ophtalmology.
The work is interesting and well-written, therefore deserving publication once following issues have been cleared
- the applicability to ophthalmology is based on a simple estimate at the end of the discussion. The associated statements would be much more convincing if the authors had performed their experiment also in saline solution. I see no technical objection or difficulty in doing this. The authors should at least comment this aspect, and ideally provide experimental results in saline solution.
- the coalescence of the clusters results in a drastic decay of the interface area prone to host electrons. I do not find any discussion of the effect of this process in Annex A; It would be particularly welcome.
Besides, I noted several typos
- line 196: µm thick (missing space)
- line 334: snapshotting
- Fig. 9 is split between pages 11 and 12
- line 736: electrons **are** "stuck"
- line 791: role
Author Response
We are grateful to the referee for a careful reading of the manuscript and comments. The manuscript has been rewritten taking into account the comments made by the reviewer. The reviewer's comments are in italics. Below are our answers.
The applicability to ophthalmology is based on a simple estimate at the end of the discussion. The associated statements would be much more convincing if the authors had performed their experiment also in saline solution. I see no technical objection or difficulty in doing this. The authors should at least comment this aspect, and ideally provide experimental results in saline solution.
We are grateful to the referee for this remark. Unfortunately, the editors gave us too little time to correct the text of the article, so we will not be able to conduct this new experiment within the period of time set by the editors. However, there is no reason to believe that the coalescence of clusters in aqueous solutions of salts and in deionized water will proceed differently. In our previous experiments based on dynamic light scattering and polarization scatterometry, we found that the content of nanobubble clusters in a physiological solution is 2 orders of magnitude higher than in deionized water. Therefore, we can claim that the effects of coalescence of nanobubble clusters should manifest themselves in physiological solution (i.e., in the intraocular fluid) as well.
The coalescence of the clusters results in a drastic decay of the interface area prone to host electrons. I do not find any discussion of the effect of this process in Annex A; It would be particularly welcome.
Since the walls of the macroscopic bubble formed as a result of coalescence remain positively charged, the free electrons inside the bubble must stick to these walls, that is, the effective charge of such a bubble must be close to zero. However, due to the presence of anions adsorbed on the inner surface of the bubston cluster, the charge of a macroscopic bubble cannot be exactly equal to zero. However, despite the presence of an adsorbed charge, such a macroscopic bubble will not be ion-stabilized, see our work by Bunkin, N.F.; Bunkin, F.V. Bubston structure of water and electrolyte aqueous solutions. Physics-Uspekhi, 2016, 59, 846 – 865, i.e. such a bubble will rapidly collapse according to the kinetics described in the work Ljunggren, S.; Erikson, J.C. The lifetime of a colloid-sized gas bubble in water and the cause of the hydrophobic attraction. Colloids Surfaces A: Physicochem. Eng. asp. 1997, 129-130, 151-155. We have added an appropriate comment to Appendix 1.
Besides, I noted several typos
- line 196: µm thick (missing space)
- line 334: snapshotting
- Fig. 9 is split between pages 11 and 12
- line 736: electrons **are** "stuck"
- line 791: role
These typos were fixed, thanks for this remark.
Reviewer 3 Report
The authors present a series of experiments with pulsed Nd:YAG laser beams in water. They analyse differences depending on pulse duration and therefore on intensity, and also on the gas disolved in water. They study experimentally and discuss theoretically optical breakdown and their relation to nanobubbles and their clustering. Finally, they comment on possible implications for laser ophtalmology.
The paper is well written, it seems correct to me, the topic is interesting and I believe that the authors present many non-trivial results, both experimental and theoretical. Thus, I recommend this paper for publication in Applied Sciences.
I just have a couple of suggestions:
First, I would recommend a thorough reading of the paper to correct small typos. For instance, in line 153 there is a cm2 where the 2 should be an exponent and in Eq. (A23), there is a "max" missing, I think. There are also some problems with the wording, e.g. in line 89 "gas bubble" should be "gas bubbles" and, in the same line "to the moment of formation" should be "at the moment of formation".
Second and more important, I believe that the title is misleading. I understand that laser ophtalmology is a major motivation for this study and it is true that the authors make some interesting comments on possible implications of their results for this kind of surgery. However, concrete applications are not directly discussed and highlighting the issue in the title does not seem befitting to me. Maybe simply "Optical breakdown on clusters of gas nanobubbles in water" would be more appropriate, although I would leave this decision to the authors.
Author Response
We are grateful to the referee for a careful reading of the manuscript and comments. The manuscript has been rewritten taking into account the comments made by the reviewer. The reviewer's comments are highlighted in italics. Below are our answers.
First, I would recommend a thorough reading of the paper to correct small typos. For instance, in line 153 there is a cm2 where the 2 should be an exponent and in Eq. (A23), there is a "max" missing, I think. There are also some problems with the wording, e.g. in line 89 "gas bubble" should be "gas bubbles" and, in the same line "to the moment of formation" should be "at the moment of formation".
Thank you for these remarks, all mistakes were fixed.
Second and more important, I believe that the title is misleading. I understand that laser ophtalmology is a major motivation for this study and it is true that the authors make some interesting comments on possible implications of their results for this kind of surgery. However, concrete applications are not directly discussed and highlighting the issue in the title does not seem befitting to me. Maybe simply "Optical breakdown on clusters of gas nanobubbles in water" would be more appropriate, although I would leave this decision to the authors.
We are grateful to the referee for this remark. Indeed, we do not discuss specific applications of our approach in ophthalmic surgery. However, optical breakdown in water, in our opinion, is not currently a hot research topic. Indeed, after issuing recent comprehensive review, written by Vanraes, P.; Bogaerts, A. Plasma physics of liquids—a focused review. Appl. Phys. Rev. 2018, 5, 031103, the articles on optical breakdown in liquids have practically ceased to appear in the literature. At the same time, articles on optical breakdown in the context of various applications are published very actively. Among these the articles on the applications of optical breakdown in ophthalmology. That is why we decided to leave ophthalmic applications in the title. Indeed, we do not really suggest the use of our technique in specific operations. This is our first article on this topic, and we are interested in the reaction of the medical community to our work.
